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Snow accumulation and deposition on a west coast midlatitude mountain Fitzharris, B. B. (Brian Blair) 1975

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SNOW ACCUMULATION AND DEPOSITION ON A WEST COAST MIDLATITUDE MOUNTAIN by BRIAN BLAIR PITZHARRIS B.Sc.Hons., U n i v e r s i t y of Otago, 1967 M.A., U n i v e r s i t y of B r i t i s h Columbia, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Geography We accept t h i s t h e s i s as conforming to the r e q u i r e d standard : THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1975 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I ag ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d tha t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i thou t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Co lumbia Vancouver 8, Canada Date _ _ j j j w j %2£_ FRONTISPIECE : Snow c o v e r on Mount Seymour E l e v a t i o n 1150 m, 9 J a n u a r y 1970 i i i ABSTRACT The f i r s t o b j e c t i v e o f t h i s s t u d y i s t o measure, d e s c r i b e , and attempt t o p r e d i c t v a r i a t i o n s o f net snow a c c u m u l a t i o n w i t h e l e v a t i o n over a mesoscale a r e a o f 14 km 2 on a west coast m i d l a t i t u d e mountain. The second o b j e c t i v e i s t o measure and d e s c r i b e s i m i l a r v a r i a t i o n s of snow d e p o s i t i o n a f t e r each storm f o r two c o n s e c u t i v e w i n t e r s , so d e f i n i n g the snow i n p u t system o f t h e h y d r o l o g i c c y c l e . The w i n t e r s sampled (1969-70, 1970-71) r e p r e s e n t a wide range o f p r o b a b l e c o n d i t i o n s . A r e l a t e d g o a l i s t he development o f a c l i m a t o l o g y o f w i n t e r storms. The f i n a l o b j e c t i v e i s t o e s t i m a t e snow d e p o s i t i o n over a west coast m i d l a t i t u d e mountain a f t e r a storm. Input t o the d e t e r m i n i s t i c model which i s e v o l v e d i s r e s t r i c t e d t o p r e c i p i t a t i o n and temp e r a t u r e d a t a measured at the base o f the mountain. A l l measurements are made on Mount Seymour, B r i t i s h C olumbia, w i t h i n a c a r e f u l l y s t r u c t u r e d e x p e r i m e n t a l d e s i g n u s i n g a double s t r a t i f i e d random s a m p l i n g scheme. Measurements are c o n f i n e d t o a p a r t l y f o r e s t e d t e r r a i n segment o f c o n s t a n t aspect and s l o p e . P r e c i p i t a t i o n d a t a are p r e s e n t e d f o r open areas at 12 e l e v a t i o n s from 120 m to 1260 m f o r 138 storms. These i n c l u d e d a t a f o r 82 snow st o r m s , where a d d i t i o n a l measurements are made w i t h i n i v d e f i n e d p o s i t i o n s o f the f o r e s t . Frequent net snow a c c u m u l a t i o n measurements are a l s o made o f the snowpack. Continuous temperature measurements at s i x e l e v a t i o n s and on a TV mast d e f i n e t h e t h e r m a l regime d u r i n g storms. S e v e r a l t y p e s o f s n o w l i n e are r e c o g n i s e d and t h e i r e l e v a t i o n s m o n i t o r e d e v e r y few days. The f i r s t o b j e c t i v e cannot e a s i l y be a c h i e v e d because s i m p l e e m p i r i c a l r e l a t i o n s h i p s between net snow a c c u m u l a t i o n and e l e v a t i o n are not r e l i a b l e on a west coast m i d l a t i t u d e mountain. T h i s i s a consequence o f t h e f o r m a t i o n of a snow wedge on -the mountain, whose shape and s l o p e i s l a r g e l y c o n t r o l l e d by t h e f r e q u e n c y o f w i n t e r storm t y p e s , except at the end o f the season, or at low e l e v a t i o n s , where melt p r o c e s s e s are i m p o r t a n t . Snow a c c u m u l a t i o n i n the f o r e s t can be e s t i m a t e d from t h a t i n the open w i t h good p r e c i s i o n , p r o v i d e d the snowpack i s g r e a t e r t h a n 1 0 0 cm water e q u i v a l e n t . Snow d e p o s i t i o n from each s t o r m i n c r e a s e s w i t h e l e v a t i o n i n wedge l i k e form. The new s n o w l i n e s and shape o f t h i s new snow wedge are m a i n l y determined by the o r o g r a p h i c i n c r e a s e i n p r e c i p i t a t i o n , and by t h e e l e v a t i o n of the f r e e z i n g l e v e l . Large f l u c t u a t i o n s o f the f r e e z i n g l e v e l among and w i t h i n storms are a f e a t u r e o f west c o a s t m i d l a t i t u d e mountains. Summation of snow d e p o s i t i o n from each storm d e f i n e s the t o t a l w i n t e r snow i n p u t t o the snowpack (the second o b j e c t i v e ) . T h i s i n p u t a l s o i n c r e a s e s V w i t h e l e v a t i o n i n wedge l i k e form, hence e x p l a i n i n g , w i t h snow m e l t , t h e s i m i l a r d i s t r i b u t i o n o f net snow a c c u m u l a t i o n . C o n t r a r y t o e a r l i e r f i n d i n g s , t o t a l w i n t e r p r e c i p i t a t i o n i n c r e a s e s l i n e a r l y w i t h e l e v a t i o n , w i t h no ev i d e n c e o f a c o n s i s t e n t storm maximum at i n t e r m e d i a t e e l e v a t i o n s . The i n p u t o f water by rime i s i n d e x e d , and found t o be s u b s t a n t i a l . Ways o f i m p r o v i n g the e f f i c i e n c y o f the s a m p l i n g network o f t h i s s tudy a re proposed. The c l i m a t o l o g y o f w i n t e r storms (the t h i r d o b j e c t i v e ) i s developed from s u r f a c e s y n o p t i c maps and upper a i r d a t a by examining storm t y p e s , t r a c k s , f r e e z i n g l e v e l s and atm o s p h e r i c f l u x e s o f water vapour. The d i f f e r e n t snow regime o f the two s t u d i e d w i n t e r s i s e x p l a i n e d i n terms o f t h i s c l i m a t o l o g y . The r e l a t i v e importance o f storm type i n p r o v i d i n g s n o w f a l l i s a s s e s s e d f o r each e l e v a t i o n on Mount Seymour. Good agreement i s found when the d e t e r m i n i s t i c model, which i s developed t o e s t i m a t e s t o r m snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n as i n the f i n a l o b j e c t i v e , i s t e s t e d by comparing s i m u l a t e d snow d e p o s i t i o n w i t h independent d a t a . C o n f i d e n c e l i m i t s about the p r e d i c t e d e s t i m a t e s are d i f f i c u l t t o a s s e s s , but do not appear t o be s m a l l . T h r o u g h f a l l of snow i n the f o r e s t i s p r e d i c t e d from t h a t i n t h e open w i t h the r e l a t i o n s h i p s changing w i t h e l e v a t i o n and storm c h a r a c t e r i s t i c s . E v i d e n c e i s p r e s e n t e d t h a t management o f the s e a s o n a l snow cover on west coast m i d l a t i t u d e mountains i s l i k e l y t o be most e f f e c t i v e at i n t e r m e d i a t e e l e v a t i o n s . CONTENTS A b s t r a c t Contents L i s t o f T a b l e s L i s t of F i g u r e s L i s t o f Appendices L i s t o f Symbols Acknowledgement s CHAPTER 1 INTRODUCTION 1.1 D e f i n i t i o n s 1.2 Review 1.2.1 P r e v i o u s s t u d i e s o f snow d e p o s i t i o n and a c c u m u l a t i o n on west c o a s t m i d l a t i t u d e mountains• 1.2.2 Some problems i n snow h y d r o l o g y 1.3 O b j e c t i v e s o f t h i s study 1.4 The p r e s e n t a t i o n of t h i s study 1.5 G e n e r a l r e l e v a n c e of t h i s s tudy CHAPTER 2 THE STUDY AREA 2.1 G e n e r a l l o c a t i o n of Mount Seymour 2.2 G e n e r a l s y n o p t i c f e a t u r e s o f w i n t e r weather 2.3 The l o c a l s e t t i n g 2.4 C h a r a c t e r i s t i c s o f the measurement a r e a 2.4.1 Hypsography 2.4.2 Slop e and aspect 2.4.3 V e g e t a t i o n 2.5 A v a i l a b l e d a t a 2.5.1 C l i m a t i c d a t a 2.5.2 Upper a i r d a t a 2.5.3 Net snow a c c u m u l a t i o n and s n o w f a l l d a t a CHAPTER 3 PARAMETERS .MEASURED AND  EXPERIMENTAL DESIGN 3.1 Measurement o f snow d e p o s i t i o n 3.1.1 Method 3.1.2 Measurement e r r o r 3.2 The t e m p o r a l sample 3.2.1 The storm 3.2.2 The p e r i o d of f i e l d o b s e r v a t i o n s 3.2.3 Nature of w i n t e r s sampled 3.3 The s p a t i a l sample o f snow d e p o s i t i o n measurements 3.3-1 The sample p o p u l a t i o n 3.3.2 The s a m p l i n g scheme 3.3.3 Sampling w i t h e l e v a t i o n (the p r i m a r y s t r a t i f i c a t i o n ) 3.3-4 Sampling w i t h i n the f o r e s t (the secondary s t r a t i f i c a t i o n ) 3.3.5 S i z e o f sample i n the secondary s t r a t u r n 3.4 Measurement o f r a i n f a l l 3-5 Measurement of mixed ra i n / s n o w e v e n t s 3.6 Measurement of rime a c c r e t i o n 3-7 Measurement o f snow cover phenology 3.8 Measurement o f net snow a c c u m u l a t i o n 3-9 Measurement o f a i r temperature v i i i CHAPTER 4 NET SNOW ACCUMULATION 4.1 Snowline phenology-4.1.1 Dates o f f i r s t and l a s t snow on the ground 4.1.2 S e a s o n a l v a r i a t i o n of s n o w l i n e 4.1.3 Season and d u r a t i o n of the snow coyer 4.2 S e a s o n a l v a r i a b i l i t y o f the snowpack 4.2.1 V a r i a b i l i t y o f snow course r e c o r d s ' 4.2.2 V a r i a b i l i t y o f f i e l d o b s e r v a t i o n s 4.3 V a r i a t i o n s of net snow a c c u m u l a t i o n w i t h e l e v a t i o n 4.3.1 Snow course o b s e r v a t i o n s 4.3.2 F i e l d o b s e r v a t i o n s 4.4 V a r i a t i o n s o f net snow a c c u m u l a t i o n w i t h i n the f o r e s t 4.4.1 Snow i n c l e a r i n g s 4.4.2 Snow i n the f o r e s t 4.4.3 Snow h o l l o w s 4.4.4 Wind s c o u r 4.5 Snowpack d e n s i t y 4.5-1 S e a s o n a l and y e a r l y v a r i a t i o n s 4.5.2 V a r i a t i o n s o f snow d e n s i t y w i t h e l e v a t i o n 4.5.3 V a r i a t i o n s o f snow d e n i s t y w i t h i n the f o r e s t CHAPTER 5 ESTIMATION OF NEW SNOW ACCUMULATION 5.1 I n t r o d u c t i o n 5.2 E s t i m a t i o n of new snow a c c u m u l a t i o n w i t h • e l e v a t i o n 5.2.1 A n a l y s i s o f d a t a -the snow wedge 5.2.2 Some i m p l i c a t i o n s i x 5.3 F a c t o r s c o n t r o l l i n g th.e shape of. t h e snow wedge 5.4 E s t i m a t i o n of net snow a c c u m u l a t i o n w i t h i n the f o r e s t 5.5 E s t i m a t i o n of snowpack d e n s i t y w i t h e l e v a t i o n 5.6 C o n c l u s i o n s CHAPTER 6 WINTER PRECIPITATION AND SNOW DEPOSITION 6.1 P r e c i p i t a t i o n 6.1.1 V a r i a t i o n of t o t a l w i n t e r p r e c i p i t a t i o n • w i t h e l e v a t i o n 6.1.2 Comparison w i t h o t h e r l o c a l s t u d i e s 6.1.3 W i n t e r p r e c i p i t a t i o n at s t a t i o n s w i t h a l o n g e r p e r i o d of r e c o r d 6.1.4 V a r i a t i o n o f storm p r e c i p i t a t i o n w i t h e l e v a t i o n 6.2 Snow phenology 6.2.1 Dates o f f i r s t and l a s t s n o w f a l l 6.2.2 S e a s o n a l v a r i a t i o n of new s n o w f a l l 6.2.3 Snow l i n e s on t r e e s 6.3 Snow d e p o s i t i o n 6.3.1 V a r i a t i o n of w i n t e r snow d e p o s i t i o n w i t h e l e v a t i o n 6.3.2 Importance of snow d e p o s i t i o n t o w i n t e r p r e c i p i t a t i o n 6.3-3 V a r i a t i o n of storm snow d e p o s i t i o n w i t h e l e v a t i o n 6.3-4 A q u a l i t a t i v e model of snow d e p o s i t i o n from a storm on a west c o a s t mid-l a t i t u d e mountain 6.4 Rime a c c r e t i o n 6.4.1 R e s u l t s 6.4.2 Rime on t r e e s X 6.4.3 Water e q u i v a l e n t o f a c c r e t e d rime 6.5 C o n c l u s i o n s CHAPTER 7 ANALYSIS OF SNOW DEPOSITION DATA 7.1 A n a l y s i s o f v a r i a n c e o f snow d e p o s i t i o n 7.2 T o t a l mass of snow d e p o s i t e d a f t e r each storm 7.2.1 Method o f c a l c u l a t i o n 7.2.2 R e s u l t s 7.3 R e d u c t i o n of the sa m p l i n g network 7.4 C o n c l u s i o n s CHAPTER 8 CLIMATOLOGY OF SNOWSTORMS 8.1 S y n o p t i c f e a t u r e s of w i n t e r storms 8.1.1 W i n t e r storm t r a c k s 8.1.2 Frequency o f stor m t y p e s 8.1.3 Importance o f each storm type f o r w i n t e r s n o w f a l l at each e l e v a t i o n 8.2 F r e e z i n g l e v e l s o f w i n t e r storms 8.3 The f l u x of at m o s p h e r i c w a t e r vapour d u r i n g w i n t e r 8.3.1 Data and method o f c o m p i l a t i o n 8.3-2 R e s u l t s 8.4 C o n c l u s i o n s CHAPTER 9 PREDICTION OF SNOW DEPOSITION 9.1 A proposed model < 9.2 P r e d i c t i o n of storm p r e c i p i t a t i o n w i t h e l e v a t i o n 9-2-1 O r o g r a p h i c component of p r e c i p i t a t i o n 9-2.2 E m p i r i c a l p r e d i c t i o n e q u a t i o n s x i 9.2.3 More t h e o r e t i c a l approaches 9.3 P r e d i c t i o n of new s n o w l i n e s 9.3.1 P r e d i c t i o n e q u a t i o n s 9.3.2 P r e d i c t i o n o f storm f r e e z i n g l e v e l s 9.4 P r e d i c t i o n of the e q u i v a l e n t e l e v a t i o n 9.5 P r e d i c t i o n o f snow d e p o s i t i o n w i t h ' e l e v a t i o n 9.5.1 Simple cases 9.5.2 Complex cases 9.6 P r e d i c t i o n o f snow d e p o s i t i o n i n the f o r e s t 9.6.1 P r e l i m i n a r y p r e d i c t i o n e q u a t i o n s 9.6.2 The e l e v a t i o n - f o r e s t s t r a t a i n t e r a c t i o n 9.6.3 Improvement o f p r e d i c t i o n e q u a t i o n s 9.7 Adequacy o f the model 9.7.1 C o n f i d e n c e l i m i t s about an e s t i m a t e o f the new snow wedge f o r a storm 9-7.2 A t e s t of the model a g a i n s t independent storm d a t a 9.7.3 C o n f i d e n c e l i m i t s about an e s t i m a t e of t o t a l w i n t e r snow d e p o s i t i o n CHAPTER 10 DISCUSSION 10.1 Main achievements o f t h i s study 10.2 Improvements i n p r e c i s i o n o f t h e model 10.3 E x t r a p o l a t i o n of the model t o o t h e r areas 10.4 E x t e n s i o n s t o t h i s study R e f e r e n c e s Appendices XI LIST OF TABLES Slope and asp e c t o f e l e v a t i o n bands of the t e r r a i n segment and o f snow s a m p l i n g s i t e s Frequency d i s t r i b u t i o n o f c l e a r i n g s i n the t e r r a i n segment F r e e z i n g l e v e l s C g e o p o t e n t i a l meters) at two ra d i o s o n d e s t a t i o n s f o r w i n t e r s 1969-70, 1970-71 compared w i t h l o n g e r p e r i o d s o f r e c o r d Sample s i z e r e q u i r e d t o e s t i m a t e p o p u l a t i o n mean snow d e n s i t y Sample s i z e r e q u i r e d t o e s t i m a t e p o p u l a t i o n mean snow depth S t a t i s t i c s • o f l a r g e samples of r a i n f a l l i n s e l e c t e d open areas Mean, s t a n d a r d d e v i a t i o n and c o e f f i c i e n t of v a r i a t i o n s of monthly water e q u i v a l e n t ( c m ) } Mount Seymour snow course 1969-70 Summary s t a t i s t i c s of wa t e r e q u i v a l e n t (cm), on A p r i l 1, f o r p e r i o d 196O-.7O, N o r t h Shore Mountain snow courses Rates o f change of snow accommodation w i t h e l e v a t i o n . Some examples r e p o r t e d i n the l i t e r a t u r e , N o r t h America Mean water e q u i v a l e n t i n open areas compared w i t h mean water e q u i v a l e n t i n f o r e s t s t r a t a - r e s u l t s of " t " t e s t C h a r a c t e r i s t i c s , of west c o a s t m i d l a t i t u d e mountains•chosen as examples XI1 P r e d i c t i o n equations, f o r e s t i m a t i o n of snowpack water e q u i v a l e n t .(.cm),, i n , f o r e s t s t r a t a based on ac c u m u l a t i o n i n open areas V a r i a t i o n o f t o t a l w i n t e r p r e c i p i t a t i o n w i t h e l e v a t i o n Means and s t a n d a r d d e v i a t i o n s o f d e n s i t y of newly f a l l e n snow i n open a r e a s , w i n t e r s 1969-70, 1970-71 F i r s t and l a s t s n o w f a l l , by-month, at two h i g h -e l e v a t i o n c l i m a t o l o g i c a l s t a t i o n s on the N o r t h Shore Mountains Summary o f storm p r e c i p i t a t i o n t y p e , Mount Seymour, w i n t e r s 1969-70, 1970-71 Frequency of storms d e p o s i t i n g snow at each sa m p l i n g s i t e , w i n t e r s 1969-70, 1970-71 P e r c e n t a g e o f monthly p r e c i p i t a t i o n f a l l i n g as snow at each e l e v a t i o n , open a r e a s , w i n t e r s 1969-70, 1970-71 Amount of rime a c c r e t e d on 0.5 cm di a m e t e r s t a k e s above the snow s u r f a c e , 6 December 1970 - 31 May 1971 A n a l y s i s of v a r i a n c e models used t o examine snow d e p o s i t i o n Number o f storms where a d j a c e n t e l e v a t i o n s and f o r e s t s t r a t a had snow d e p o s i t i o n means t h a t were homogeneous, at the 95 p e r c e n t c o n f i d e n c e l e v e l ( r e s u l t s of Duncans New M u l t i p l e Range T e s t ) Examples o f the t o t a l mas.s of snow d e p o s i t e d on the Mount Seymour t e r r a i n segment from a storm (.Storm 30, w i n t e r 1969-70) C o r r e l a t i o n m a t r i c e s f o r p r e c i p i t a t i o n at 12 e l e v a t i o n s , w i n t e r s 1969-70-* 1970-71 I n f l u e n c e of s i m p l i f i c a t i o n of the e x p e r i m e n t a l d e s i g n on e s t i m a t i o n of t o t a l mass of snow d e p o s i t e d on t h e t e r r a i n segment x i v 8.1 Percentage, f r e q u e n c y o f storm t y p e s f o r a l l s t o r m s , and f o r -snow s t o r m s , w i n t e r s -3 969-70, 1970-71 8.2 Percentage f r e q u e n c y o f g e o s t r o p h i c a i r f l o w ahead o f and b e h i n d f r o n t s , f o r a l l s t o r m s , and f o r snow s t o r m s , w i n t e r s 1969-70, 197.0-71 8.3 Percentage of snow d e p o s i t i o n (water e q u i v a l e n t ) at each e l e v a t i o n a s s o c i a t e d w i t h g e o s t r o p h i c a i r f l o w d i r e c t i o n , w i n t e r 1969-70 . 8.4 Percentage of snow d e p o s i t i o n (water e q u i v a l e n t ) at each e l e v a t i o n a s s o c i a t e d w i t h g e o s t r o p h i c a i r f l o w d i r e c t i o n , w i n t e r 1970-71 8.5 Mean snow d e p o s i t i o n (mm wat e r e q u i v a l e n t ) p e r type o f storm at each e l e v a t i o n 8.6 Mean f r e e z i n g l e v e l s d u r i n g s t o r m s , P o r t Hardy ( i n g e o p o t e n t i a l meters) and Mount Seymour ( i n m e t e r s ) , w i n t e r s 1969-70, 1970-71 8.7 V a r i a t i o n of mean f r e e z i n g l e v e l of snow storms w i t h s y n o p t i c storm type 9.1 R e g r e s s i o n e q u a t i o n s f o r p r e d i c t i o n o f storm p r e c i p i t a t i o n w i t h e l e v a t i o n and p r e c i p i t a t i o n •at the base o f the mountain 9.2 Simple c o r r e l a t i o n c o e f f i c i e n t s between the o r o g r a p h i c component of p r e c i p i t a t i o n and v a r i a b l e s from r a d i o s o n d e d a t a 9.3 Simple l i n e a r r e g r e s s i o n e q u a t i o n s r e l a t i n g f r e e z i n g l e v e l s on Mount Seymour (Y) t o .'those of r a d i o s o n d e a s c e n t s at P o r t Hardy (X) 9.4 R e g r e s s i o n r e l a t i o n s h i p s between snow d e p o s i t i o n i n f o r e s t s t r a t a and i n open areas 9.5 D e t a i l s ' o f r e g r e s s i o n r e l a t i o n s between snow d e p o s i t i o n i n open and f o r e s t s t r a t a 9.6 R e g r e s s i o n e q u a t i o n s between snow d e p o s i t i o n i n f o r e s t s t r a t a and i n open areas 9.7 Nature o f c o n f i d e n c e l i m i t s about an e s t i m a t e of the snow d e p o s i t i o n from a storm averaged over t h e t e r r a i n segment LIST OP APPENDICES D e t a i l s o f the f o r e s t cover on Mount Seymour A l Measures o f f o r e s t c h a r a c t e r i s t i c s o f the t e r r a i n , segment A2 Photographs o f the f o r e s t near each o f the snow s a m p l i n g s i t e s R e s u l t s of p i l o t s t u d i e s w i t h l a r g e samples B l S t a t i s t i c s o f p i l o t s t udy w i t h l a r g e samples of new snow d e n s i t y t hroughout the f o r e s t , w i n t e r 1968-69 B2 S t a t i s t i c s o f p i l o t s t udy w i t h l a r g e samples of new snow depth Snow cover phenology Summary s t a t i s t i c s o f t h e snowpacks o f Nor t h Shore Mountain snow courses L i s t o f s t o r m s , w i n t e r s 1969-70, 1970-71 W i n t e r p r e c i p i t a t i o n F l V a r i a t i o n o f w i n t e r p r e c i p i t a t i o n w i t h e l e v a t i o n f o r each s t o r m (mm) F2 Mean w i n t e r p r e c i p i t a t i o n at Vancouver and at h i g h e r c l i m a t o l o g i c a l s t a t i o n s on the N o r t h Shore Mountains V a r i a t i o n of snow d e p o s i t i o n w i t h e l e v a t i o n f o r each storm The d e n s i t y of newly f a l l e n snow Summary of snow c r y s t a l t y pe from storm s n o w f a l l Examples of snow d e p o s i t i o n , the temperature f i e l d , t h e s u r f a c e s y n o p t i c s i t u a t i o n s and o f th e f l u x o f water vapour f o r each of t h e more common snow sto r m t y p e s x v i i LIST OF FIGURES F r o n t i s p i e c e : Snow coyer on Mount Seymour e l e v a t i o n 1150 m, 9 January 1970 F i g . 1.1 Mount Seymour, the west c o a s t m i d l a t i t u d e mountain chosen f o r t h i s study F i g . 1.2 Two systems of the h y d r o l o g i c c y c l e i n mountainous t e r r a i n F i g . 1.3 T o p i c s and methods o f h y d r o l o g i c study F i g . 2.1 G e n e r a l l o c a t i o n of Mount Seymour F i g . 2.2 The l o c a l s e t t i n g F i g . 2.3 The t e r r a i n segment chosen f o r t h i s study F i g . 2.4 Views o f the chosen t e r r a i n segment F i g . 2.5 H y p s o g r a p h i c curves f o r the chosen t e r r a i n segment and f o r two a d j a c e n t r i v e r b a s i n s F i g . 2.6 Slope and aspect o f t h e chosen t e r r a i n segment and o f snow s a m p l i n g s i t e s F i g . 2.7 D i s t r i b u t i o n o f v e g e t a t i o n type w i t h e l e v a t i o n F i g . 2.8 Canopy c l o s u r e of the f o r e s t at each s a m p l i n g s i t e F i g . 3 .1 Percentage measurement e r r o r f o r s p e c i f i c mass of new snow d e p o s i t e d F i g . 3.2 D i f f e r e n c e s from normal (.period 1931-60) o f s e l e c t e d m e t e o r o l o g i c a l parameters a t Van-couver I n t e r n a t i o n a l A i r p o r t f o r w i n t e r s 1969-70, 1970-71 x v i i i F i g . 3 . 3 D e p a r t u r e f r o m normal of the mean 700. mb h e i g h t (decameters) f o r each-month, of w i n t e r 1969-70,. w i n t e r 197.0-71 F i g . 3.4 P r o b a b i l i t y of w i n t e r s n o w f a l l s as t o t a l depth, o f new snow at H o l l y b u r n R i d g e , 920 m, and Vancouver C i t y , near sea l e v e l F i g . 3.5 Monthly water e q u i v a l e n t at Seymour Mountain and Grouse Mountain-snow courses f o r w i n t e r s 1969-70, 1970-71 compared w i t h the l o n g t e r m r e c o r d s F i g . 3.6 P r o b a b i l i t y o f r e c o r d i n g g r e a t e r than g i v e n w ater e q u i v a l e n t on A p r i l 1 at Seymour mountain and Grouse Mountain snow courses F i g . 3.7 Diagrammatic r e p r e s e n t a t i o n o f double s t r a t i f i e d s a m p l i n g scheme used t o e s t i m a t e snow d e p o s i t i o n over the t e r r a i n segment F i g . 3.8 S c a t t e r diagram comparing f r e e a i r temperature d u r i n g storms on CBUT-TV tower at 920 m w i t h t e m p e r a t u r e s i n a s c r e e n i n the f o r e s t at 970 m F i g . 4.1 E l e v a t i o n a l coverage of new snow at end of each s t o r m , w i n t e r 1969-70 F i g . 4.2 S e a s o n a l v a r i a t i o n s , o f s n o w l i n e s w i n t e r 1969- 70 F i g . 4 .3 E l e v a t i o n a l coverage o f new snow at end of each s t o r m , w i n t e r 1970-71 F i g . 4.4 S e a s o n a l v a r i a t i o n of snowlines, w i n t e r 1970- 71 F i g . 4.5 Snow cover phenology, w i n t e r 1969-70 F i g . 4.6 Snow cover phenology., w i n t e r 1970-71 F i g . 4.7 R e l a t i o n s h i p between d u r a t i o n of complete snow cover and w i n t e r maximum of snowpack water e q u i v a l e n t F i g . 4.8 Snowpack water e q u i v a l e n t i n open and i n the f o r e s t s t r a t a f o r v a r i o u s e l e v a t i o n s , w i n t e r 1969-70 x i x F i g . 4 . 9 Snowpack water e q u i v a l e n t i n open and i n . the f o r e s t s t r a t a for. v a r i o u s e l e v a t i o n s j, w i n t e r 197.0-71 F i g . . 4 . 1 0 V a r i a t i o n o f snowpack wa t e r e q u i v a l e n t w i t h e l e v a t i o n on the f i r s t day of each month, open a r e a s , f o r w i n t e r s 1969-70 and 1970-71 F i g . 4 . 1 1 Snow h o l l o w s i n mid-season and l a t e i n season F i g . 4 . 1 2 Wind s c o u r about t r e e s d u r i n g March 1971 at 1260 m F i g . 4 . 1 3 D e n s i t y o f snowpack i n open areas i n w i n t e r 1969-70 and w i n t e r 1970-71 F i g . 4 . 1 4 S e a s o n a l v a r i a t i o n i n average snowpack-d e n s i t y , Mount Seymour snowcourse C1969-70). and f o r o t h e r areas F i g . 5.1 S e a s o n a l v a r i a t i o n i n mean s l o p e of snow wedge F i g . 5-2 Mean s l o p e of snow wedge d u r i n g the a c c u m u l a t i o n p e r i o d as a f u n c t i o n of water e q u i v a l e n t at the upper s a m p l i n g l i m i t on the mountain F i g . 5.3 Slope of s e c t i o n s o f snow wedge d u r i n g the a c c u m u l a t i o n p e r i o d as a f u n c t i o n of w a t e r e q u i v a l e n t at the upper l i m i t of each s e c t i o n F i g . 5-4 Water e q u i v a l e n t at upper s a m p l i n g l i m i t o f snow wedge as a f u n c t i o n of e l e v a t i o n o f the s n o w l i n e F i g . 5-5 H y p o t h e t i c a l example of h y p s o m e t r i c c u r v e , snow wedges and t o t a l w a t e r s t o r e d as snow i n two d i f f e r e n t y e a r s , F i g . 5-6 P r e d i c t i o n of snow a c c u m u l a t i o n i n c l e a r i n g s from t h a t i n open areas F i g . 5-7 P r e d i c t i o n of snow a c c u m u l a t i o n beneath-the canopy from t h a t i n open areas X X F i g . 6.1 V a r i a t i o n o f w i n t e r p r e c i p i t a t i o n w i t h e l e v a t i o n F i g . 6.2 V a r i a t i o n s of p r e c i p i t a t i o n w i t h e l e v a t i o n f o r storms o f s e l e c t e d months F i g . 6.3 E l e v a t i o n a l coverage o f snow on t r e e s , w i n t e r 1969-70 F i g . 6.4 E l e v a t i o n a l coverage o f snow on t r e e s , w i n t e r 1970-71 F i g . 6.5 V a r i a t i o n o f w i n t e r snow d e p o s i t i o n w i t h e l e v a t i o n , w i n t e r s 1969-70, 1970-71 F i g . 6 . 6 . Two examples of d e p o s i t i o n from storms which gave snow at h i g h e r e l e v a t i o n s only-F i g . 6.7 Two examples of d e p o s i t i o n from storms which gave snow at h i g h e r and i n t e r -. mediate e l e v a t i o n s F i g . 6.8 D e p o s i t i o n from a storm w i t h snow t o low e l e v a t i o n s F i g . 6.9 D e p o s i t i o n from a stor m w i t h l a r g e amounts o f -snow F i g . 6.10 The a d d i t i v e e f f e c t o f snow d e p o s i t i o n from each storm F i g . 6.11 Schematic diagram o f snow d e p o s i t i o n from a storm on a west c o a s t m i d l a t i t u d e mountain (a) Storm w i t h r e l a t i v e l y c o n s t a n t f r e e z i n g l e v e l (b) Composite s t o r m w i t h f l u c t u a t i n g f r e e z i n g l e v e l F i g . 6.12 Rime d e p o s i t s a c c r e t e d onto 0.5 cm di a m e t e r r e c e p t o r s t a k e and t o t r e e s F i g . 6.13 H o r i z o n t a l l e n g t h o f rime a c c r e t e d on 0.5 cm di a m e t e r s t a k e s , by e l e v a t i o n and d i r e c t i o n o f growth, 6 December 1970 -31 May 1971 x x i F i g . 7-1 F i g . 7.2 F i g . 8.1 F i g . 8.2 F i g . 8.3 F i g . 8.4 F i g . 8.5 F i g . 8.6 F i g . 8.7 F i g . 9.1 F i g . 9.2 Homogeneity- of means., of storm snow d e p o s i t i o n between a d j a c e n t s a m p l i n g s i t e s , as a f u n c t i o n o f the e l e v a t i o n i n t e r v a l between s a m p l i n g s i t e s T o t a l mass of snow d e p o s i t e d on t h e t e r r a i n segment, w i n t e r s 1969-70,. 1970-71 G e n e r a l i s e d t r a c k s of stor m s , w i n t e r s 1969-70, 1970-71 I n f l u e n c e of storm type i n d e t e r m i n i n g w i n t e r snow d e p o s i t i o n (.water e q u i v a l e n t ) at each, e l e v a t i o n , w i n t e r 1969-70 I n f l u e n c e of storm type i n d e t e r m i n i n g w i n t e r snow d e p o s i t i o n (.water e q u i v a l e n t ) at each, e l e v a t i o n , w i n t e r 1970-71 Comparison of the d i s t r i b u t i o n s of mean f r e e z i n g l e v e l s on Mount Seymour, snow s t o r m s , f o r the w i n t e r s 1969-70, 1970-71 Mean monthly v e r t i c a l l y i n t e g r a t e d w a t e r vapour f l u x v e c t o r s , P o r t Hardy, w i n t e r s 1969-70, 1970-71 Mean monthly z o n a l f l u x e s d u r i n g snowstorms Mean monthly m e r i d i o n a l f l u x e s d u r i n g snow-storms Proposed model o f snow d e p o s i t i o n i n open areas from a storm on west c o a s t mid-l a t i t u d e mountain (a) Storm w i t h r e l a t i v e l y c o n s t a n t f r e e z i n g l e v e l (b) A composite storm w i t h f l u c t u a t i n g f r e e z i n g l e v e l A l l terms d e f i n e d i n t e x t Maximum p r e c i p i t a t i o n r e c o r d e d from a storm on Mount Seymour, as a f u n c t i o n of storm p r e c i p i t a t i o n at the base of the mountain x x i i P i g . 9 .3 R e l a t i o n s h i p s between new s n o w l i n e s and mean storm f r e e z i n g l e v e l F i g . 9.k R e l a t i o n s h i p between the e q u i v a l e n t . . e l e v a t i o n and mean sto r m f r e e z i n g l e v e l F i g . 9.5 R e l a t i o n s h i p between the r a t i o R and the r a t i o I . A l l terms are d e f i n e d i n the t e x t F i g . 9.6 Best f i t r e g r e s s i o n r e l a t i o n s f o r each e l e v a t i o n of snow d e p o s i t i o n i n f o r e s t s t r a t a as a f u n c t i o n of snow d e p o s i t i o n i n open areas F i g . 9.7 An example of the c o n f i d e n c e l i m i t s about an e s t i m a t e of the new snow wedge f o r a stor m F i g . 9.8 Test of the model about an independent d a t a s e t f o r t h e w i n t e r 196:8-69 F i g . 9.9 C o n f i d e n c e l i m i t s about an e s t i m a t e of t o t a l w i n t e r snow d e p o s i t i o n , w i n t e r s 1969-70, 1970-71 x x i i i L I S T O P S Y M B O L S cA = c o n t i n e n t a l A r c t i c a i r C = v a l u e of maximum d u r a t i o n of snow cov e r (days) D = d u r a t i o n of complete snow cover (days) DA = p o s t f r o n t a l wind d i r e c t i o n (degrees) DB = p r e f r o n t a l wind d i r e c t i o n (degrees) e = base of n a t u r a l l o g a r i t h m E = d e s i r e d c o n f i d e n c e l i m i t s F M = m e r i d i o n a l a t m o s p h e r i c water vapour f l u x at a s i n g l e l e v e l (gm/cm/mb/sec) F Z = z o n a l a t m o s p h e r i c water vapour f l u x at a s i n g l e l e v e l (gm/cm/mb/sec) g = a c c e l e r a t i o n due t o g r a v i t y (cm/sec 2) h = number o f s a m p l i n g s i t e H = e l e v a t i o n (m) H c = e l e v a t i o n of complete new s n o w l i n e (m) Hd = e l e v a t i o n c o r r e s p o n d i n g t o the most r a p i d r a t e of change o f snow cov e r d u r a t i o n (m) H e = the e q u i v a l e n t e l e v a t i o n (m), i . e . the l o w e s t e l e v a t i o n on the mountain where sto r m snow d e p o s i t i o n e q u a l s storm p r e c i p i t a t i o n H"FL = mean h e i g h t o f storm f r e e z i n g l e v e l (m) Hj_ = e l e v a t i o n of the i n c o m p l e t e s n o w l i n e (m) H 0 = e l e v a t i o n of the i n c o m p l e t e new s n o w l i n e (m) Hi = e l e v a t i o n of top of mountain (m) i = number of r e p l i c a t i o n s x x i v unit, vector d i r e c t e d to the east number of hours wh.en the f r e e z i n g l e v e l during the storm i s . below 1400. m, d i v i d e d by the length, of the storm i n hours u n i t vector d i r e c t e d to the north constant r e l a t e d to r a t e of increase of snow cover duration w i t h e l e v a t i o n maritime A r c t i c a i r maritime Po l a r a i r maritime T r o p i c a l a i r s p e c i f i c new snow mass (mm water equivalent or kg/m2) s p e c i f i c new snow mass deposited at e l e v a t i o n H, where H > H e. Units are mm water equivalent or kg/m2 s p e c i f i c new snow mass deposited at e l e v a t i o n H, where Hp < H < H e. Units are mm water equivalent or kg/m mean p r e d i c t e d snow d e p o s i t i o n f o r winter (mm water equivalent or kg/m2) storm snow d e p o s i t i o n averaged over the t o t a l area of the t e r r a i n segment (mm water equivalent) s p e c i f i c new snow mass deposited i n open areas (mm water equivalent or kg/m2) s p e c i f i c new snow mass deposited i n a f o r e s t stratum (mm water equivalent or kg/m2) sample s i z e winter p r e c i p i t a t i o n (mm) mean d a i l y p r e c i p i t a t i o n f o r the winter (mm) p r e c i p i t a t i o n (mm) at e l e v a t i o n H maximum p r e c i p i t a t i o n on the mountain from each storm (mm) XXV p o r o = o r o g r a p h i c component o f p r e c i p i t a t i o n (.mm) P s = p r e s s u r e at the surface*! . (jab) P(l20). = p r e c i p i t a t i o n (mm) a t the base of the m o u n t a i n , e l e v a t i o n H - 120 m q = s p e c i f i c h u m i d i t y (gm/kg) Q m = v e r t i c a l l y i n t e g r a t e d m e r i d i o n a l f l u x o f at m o s p h e r i c water vapour (gm/cm/sec) Q z = v e r t i c a l l y i n t e g r a t e d z o n a l f l u x of a t m o s p h e r i c water vapour (gm/cm/sec) R = r a t i o M ( H j ) / P ( H j ) where Hj. i s e l e v a t i o n at the top o f the mountain s = number of secondary s t r a t a SI = s t a b i l i t y i n d e x S z 2 = e s t i m a t e of, p o p u l a t i o n v a r i a n c e of new snow depth S y 2 = e s t i m a t e of p o p u l a t i o n v a r i a n c e of new snow d e n s i t y t = v a l u e of Students t d i s t r i b u t i o n T = time-T(H) = temperature (°C) at e l e v a t i o n H u = z o n a l component of wind v e l o c i t y (cm/sec) v = m e r i d i o n a l component o f wind v e l o c i t y (cm/sec) V = maximum wind v e l o c i t y d u r i n g a storm (cm/sec) w = water e q u i v a l e n t o f snow pack (cm) W = p r e c i p i t a b l e w ater (mm) W = mean w i n t e r p r e c i p i t a b l e water (mm) X = f r e e z i n g l e v e l at P o r t Hardy ( g e o p o t e n t i a l meters) Y = f r e e z i n g l e v e l on Mount Seymour (m) x x v i z = new -snow .depth, measured v e r t i c a l l y (m), a = p r o b a b i l i t y o f c o m m i t t i n g a Type T e r r o r B = v e r t i c a l wind shear (cm/sec/100 m) Y = d e n s i t y of newly f a l l e n snow (kg/m 3) 0 2 = v a r i a n c e o f p o p u l a t i o n 0 = snow a c c u m u l a t i o n i n open areas (cm) x x v i i A C KN.O.WLED.GEMEN T.S A g r e a t number of people have g i v e n me a s s i s t a n c e i n t h i s s t u d y , b o t h a c a d e m i c a l l y and i n the f i e l d . I am most g r a t e f u l t o the f o l l o w i n g p e o p l e who f r e q u e n t l y accompanied me and a s s i s t e d w i t h measurements on Mount Seymour, sometimes i n b e a u t i f u l w eather, but o f t e n i n the c o l d , wet and snow': P e t e r L e w i s , T e r r y Day, Hok Woo, Ian M c Q u i l l a n , Ken T u s t i n , Bob McDonald, John B o t t o m l e y , Steve Evans, L a r r y Minnock, Mike and P a u l i n e Smith and C l i f f Ames. I a l s o acknowledge the a s s i s t a n c e g i v e n by the members or a s s o c i a t e s of my t h e s i s committee: e s p e c i a l l y , Dr. J.R. Mackay f o r h i s i n t e r e s t , and e f f o r t s t o a t t a i n r e s e a r c h f i n a n c e on my b e h a l f , and t o D r s . B. G o o d e l l , W. Mathews, 0. Slaymaker, T. Oke, M. Church and J . Hay, t o g e t h e r w i t h P. S c h a e r e r and the l a t e W.W. J e f f r e y . T h i s study was made p o s s i b l e by the f i n a n c i a l a s s i s -t ance g i v e n me by the Canadian S c h o l a r s h i p and F e l l o w s h i p Committee, w h i c h s u p p o r t e d me d u r i n g my s t a y i n Canada, and by the Department of Geography, U n i v e r s i t y o f B r i t i s h Columbia which purchased most of the i n s t r u m e n t a t i o n . I a p p r e c i a t e the w i l l i n g c o - o p e r a t i o n shown me by the p e r s o n n e l of the Mount Seymour P r o v i n c i a l P a r k , who on o c c a s i o n s a l s o h e l p e d x x v i i i d i g out my- v e h i c l e , from the snow;. R e g u l a r measurements at 1260 m would have been i m p o s s i b l e w i t h o u t the g e n e r o s i t y of the s k i c h a i r l i f t o p e r a t o r s on Mount Seymour; t h e r e were some o c c a s i o n s when they c o n t i n u e d or s t a r t e d t h e c h a i r l i f t f o r me a l o n e . The c o - o p e r a t i o n o f t h e Canadian B r o a d c a s t i n g C o r p o r a t i o n i s a p p r e c i a t e d ; they a l l o w e d use of t h e i r TV t r a n s m i s s i o n tower and garage f o r c o l l e c t i o n of temperature d a t a , and o f t e n warmed me up w i t h hot c o f f e e . The f e a r l e s s e f f o r t s o f s t e e p l e j a c k s Lewis and Church ensured t h a t the t h e r m i s t o r c a b l e was s e c u r e l y p l a c e d on the tower. F i n a l l y I r e c o g n i s e the tremendous c o n t r i b u t i o n o f my w i f e , Joanna, t o many a s p e c t s o f t h i s s t u d y . As a r e l i a b l e f i e l d a s s i s t a n t , o f t e n i n m i s e r a b l y c o l d c o n d i t i o n s , a t y p i s t and e d i t o r , a dogged c h a r t r e a d e r , and an enthu-s i a s t when I needed encouragement, she ensured-, t h a t t h i s study was completed. 1 CHAPTER 1 1. INTRODUCTION Many a s p e c t s o f the h y d r o l o g i c a l c y c l e have been r e p e a t e d l y documented and are w e l l u n d e r s t o o d , but t h e r e s t i l l e x i s t s a s e r i o u s l a c k o f i n f o r m a t i o n about mesoscale v a r i a t i o n s o f snow d e p o s i t i o n and a c c u m u l a t i o n i n moun-t a i n o u s t e r r a i n . V a r i a t i o n s o f s n o w f a l l over a few square k i l o m e t r e s • a r e the key t o many-aspects o f h y d r o l o g y , but t h e s e , a l o n g w i t h r e l a t e d m e t e o r o l o g i c a l v a r i a t i o n s , have' r e c e i v e d l i t t l e a t t e n t i o n . The mesoscale i s the f o c u s o f t h i s s t u d y . Snow d e p o s i t i o n a n d - a c c u m u l a t i o n are measured over an a r e a o f 14.3 km 2 at t w e l v e e l e v a t i o n s from 120 m t o 1260 m i n a f o r e s t e d environment on a west c o a s t m i d l a t i t u d e mountain. A l l f i e l d measurements are made w i t h i n a s t r u c t u r e d e x p e r i -m e ntal d e s i g n . I n t h i s severe f i e l d environment l a r g e r e p l i c a t i o n s of s i m p l e manual measurements are p r e f e r r e d over remote r e c o r d i n g . F o r t h i s r e a s o n , measurements are l o g i s t i c a l l y c o n f i n e d t o a s i n g l e mountain, Mount Seymour ( F i g . 1 . 1 ) , w h i c h i s easy o f a c c e s s by r o a d and c h a i r l i f t i n a l l weather. Snow d e p o s i t i o n and r a i n f a l l measurements are made a f t e r each storm f o r two c o n s e c u t i v e w i n t e r s (1969-70, 1970-71)• 2 View l o o k i n g N.E. a c r o s s B u r r a r d I n l e t View l o o k i n g S.W. towards the F r a s e r R i v e r d e l t a from e l e v a t i o n 1200 m on Mount Seymour F i g , l . l Mount Seymour, the west c o a s t m i d l a t i t u d e mountain chosen f o r t h i s s t u d y 3 The d a t a c o l l e c t e d i s p a r t i c u l a r l y i n t e r e s t i n g i n t h a t t h e s e w i n t e r s produced markedly d i f f e r e n t snow d e p o s i t i o n and a c c u m u l a t i o n regimes. 1.1 D e f i n i t i o n s Mount Seymour i s an example o f a "west c o a s t m i d l a t i t u d e  mountain". T h i s i s d e f i n e d as one ©n which the new snow-l i n e s from most w i n t e r storms o c c u r at some e l e v a t i o n above i t s base. Such mountains are t y p i c a l o f the west c o a s t o f l a n d masses w i t h i n the b e l t o f the d i s t u r b e d w e s t e r l i e s . Those o f w e s t e r n N o r t h A m e r i c a , S c o t l a n d , N o r w a y N e w Z e a l a n d and C h i l e are the most n o t a b l e . " The term "snow d e p o s i t i o n " r e f e r s t o the amount o f new snow p r e s e n t on the ground at the end o f each storm. I t r e p r e s e n t s the amount of new snow e n t e r i n g s t o r a g e as p a r t of the s e a s o n a l snowpack. I t does not i n c l u d e new snow which may have m e l t e d b e f o r e the end of the storm. "Snow a c c u m u l a t i o n " i s used i n the customary s e n s e ; i t r e f e r s t o the water e q u i v a l e n t of the t o t a l snowpack. Snow a c c u m u l a t i o n r e p r e s e n t s the end p r o d u c t f o r any p o i n t • i n time o f the sum of snow d e p o s i t i o n minus snow m e l t . For t h i s r e a s o n i t more s t r i c t l y can be r e f e r r e d t o as "net  snow a c c u m u l a t i o n " . The snow cover o f t h i s s tudy i s s e a s o n a l i n n a t u r e . 4 " w i n t e r " i s used t o d e s i g n a t e t h e . p e r i o d from October 1 t o May 31. T h i s i s much l o n g e r t h a n the customary d e f i n i t i o n , but i s used here because almost a l l ..snow f a l l s between th e s e dates on the N o r t h Shore M o u n t a i n s . " P r e d i c t i o n " i s used i n the s t a t i s t i c a l sense. That i s , no m a t t e r how many tim e s an event i s p r o c e s s e d under a g i v e n s e t of i n v a r i a n t c o n d i t i o n s , the same outcome w i l l always r e s u l t . The term p r e d i c t i o n i s not used i n the m e t e o r o l o g i c a l f o r e c a s t sense i n t h a t the p r e d i c t i o n equa-t i o n s d eveloped f o r snow d e p o s i t i o n i n t h i s study are d e s i g n e d t o " f o r e c a s t " a f t e r a st o r m e v e n t . That' i s , g i v e n p r e c i p i t a t i o n and temperature d a t a a t the base o f a west co a s t m i d l a t i t u d e mountain f o r a s t o r m , the r e s u l t a n t snow d e p o s i t i o n on the mountain i s t o be p r e d i c t e d a f t e r the storm. H i n d s i g h t f o r e c a s t i n g i s more p r a c t i c a l i n snow h y d r o l o g y , t h a n i n some o t h e r branches o f h y d r o l o g y i n t h a t s t o r a g e of water as snow a l l o w s more)'.time .for p r e d i c t i o n o f r u n o f f . 1.2 Review 1.2.1 P r e v i o u s s t u d i e s o f snow d e p o s i t i o n and a c c u m u l a t i o n  on west c o a s t m i d l a t i t u d e mountains Few s t u d i e s have been made of snow d e p o s i t i o n v a r i -a t i o n s w i t h e l e v a t i o n on a west c o a s t m i d l a t i t u d e mountain. The U.S. Army (1956) has c a r r i e d out the most e x t e n s i v e 5 a n a l y s e s o f snow a c c u m u l a t i o n v a r i a t i o n s , but measured s n o w f a l l a t r e l a t i v e l y few p o i n t s . T h i s comprehensive r e p o r t examined s e v e r a l a r e a s , but the W i l l a m e t t e B a s i n Snow L a b o r a t o r y i n the Cascade Range i s the most r e l e v a n t t o Mount Seymour. I t covers 29 km 2, i s h e a v i l y f o r e s t e d and extends from an e l e v a t i o n of 610 m t o 1680 m. The c l i m a t e s of. the two areas are s i m i l a r w i t h heavy p r e c i p i -t a t i o n and w i n t e r t e m p e r a t u r e s c l o s e t o f r e e z i n g . Other s t u d i e s o f s e a s o n a l snowpack v a r i a t i o n s w i t h e l e v a t i o n have been r e p o r t e d from C a l i f o r n i a by Court (1963) and Anderson and West (1965), and from New Z e a l a n d by A r c h e r (1970) and O ' L o u g h l i n (1969). Only t h e l a s t a u t h o r d i s c u s s e s s n o w f a l l over a range o f e l e v a t i o n s . Woo (1972) has produced a n u m e r i c a l s i m u l a t i o n of snow s t o r a g e and melt water r e l e a s e on a s m a l l mountain catchment at the U n i -v e r s i t y of B r i t i s h Columbia Research F o r e s t , a few k i l o -metres t o the e a s t o f Mount Sey-mour. T h i s s t u d y extends the d e t e r m i n i s t i c p a r t o f Woo's model by i n v e s t i g a t i n g a wi d e r range of e l e v a t i o n s and s t o r m s , and by t a k i n g more d e t a i l e d s p a t i a l measurements w i t h i n the f o r e s t . Review o f t h e s e s t u d i e s i n d i c a t e s t h a t l i t t l e d e t a i l i s known o f s e a s o n a l snow a c c u m u l a t i o n v a r i a t i o n s i n the mesoscale on west co a s t m i d l a t i t u d e mountains. Even l e s s i s known of snow d e p o s i t i o n v a r i a t i o n s . M e s o s c a l e s t u d i e s o f snow a c c u m u l a t i o n o r d e p o s i t i o n are few i n h y d r o l o g y , but a c o n s i d e r a b l e number- e x i s t i n g l a c i o l o g y . Some 6 r e l a t e t o west c o a s t m i d l a t i t u d e mountain g a l c i e r s - c l o s e t o Mount Seymour (e . g . the B l u e G l a c i e r , - L a C h a p e l l e 19&5» South Cascade G l a c i e r , M e i e r and Tangborn 1965)• 1.2.2 Some problems i n snow h y d r o l o g y P r e s e n t methods of e s t i m a t i n g snowpack a c c u m u l a t i o n i n mountain areas are l i m i t e d . I n N o r t h A m e r i c a , most e s t i m a t e s are based on d a t a from snow c o u r s e s , but t h e s e g i v e o n l y an i n d e x o f the snowpack f o r an a r e a . A number of d i s a d v a n t a g e s f o l l o w . Snow course d a t a do not r e a d i l y r e v e a l i n t e r a c t i o n e f f e c t s . T h e i r i n d e x v a l u e o f t e n f a i l s f o r extreme e v e n t s , and i s s u b j e c t t o unknown change through, a l t e r a t i o n of the s u r r o u n d i n g environment. Because they are u s u a l l y s i t e d i n c l e a r i n g s , which are a r e a s o f maximum a c c u m u l a t i o n , t h e i r v a l u e s are b i a s e d e s t i m a t e s o f s p a t i a l a v e r a g e s . For example, Court (1963), found snow c o u r s e s i n C a l i f o r n i a r e p r e s e n t a t i v e o f s i t e s 800 m h i g h e r t h a n t h e i r a c t u a l e l e v a t i o n . I n a d d i t i o n , a number of y e a r s of r e c o r d are n e c e s s a r y t o e s t a b l i s h the r e l a t i o n s h i p between snow melt stream f l o w and the b e h a v i o u r o f the snow course i n d e x . Many c o u n t r i e s cannot a f f o r d t h i s time l a g , because e s t i m a t e s o f stream f l o w are o f t e n wanted i m m e d i a t e l y f o r d e s i g n or o p e r a t i o n o f h y d r o - e l e c t r i c power s t a t i o n s or i r r i g a t i o n schemes. 7 Most of thes e d i s a d v a n t a g e s are e l i m i n a t e d i f s t a t i s -t i c a l e s t i m a t e s o f t o t a l w ater s t o r e d as snow are based on more r e p r e s e n t a t i v e s a m p l i n g n e t w o r k s . Such has been the approach i n Japan Ce.g- H i g a s h i 1958), i n the S o v i e t -Union ( e . g . Uryvaev e t a l 1965)* and'more r e c e n t l y i n the U.S.A. by B a r t o s and Rechard (1973), but the enormous, s p a t i a l v a r i a b i l i t y o f . t h e snowpack sometimes makes such s a m p l i n g i m p r a c t i c a l over l a r g e mountain areas.- T h i s s u g g e s t s a need t o dev e l o p r e l a t i o n s h i p s between snow a c c u m u l a t i o n and topography, so t h a t the number o f measure-ment o b s e r v a t i o n s i s r e d u c e d , y e t r e a s o n a b l e e s t i m a t e s of t o t a l w a t e r s t o r a g e are s t i l l p o s s i b l e . A l o g i c a l f i r s t s t e p i n t h i s approach i s the development o f r e l a t i o n -s h i p s between snow a c c u m u l a t i o n and e l e v a t i o n . There i s an a l t e r n a t i v e approach. Good e s t i m a t e s of water s t o r e d i n mountain snowpacks may come w i t h the development of t h e o r e t i c a l models d e s c r i b i n g d e p o s i t i o n , a c c u m u l a t i o n and a b l a t i o n o f the s e a s o n a l snow c o v e r . U n f o r t u n a t e l y t h e r e are few o f th e s e i n snow h y d r o l o g y . J a k h e l l n (1965) i n Norway has r e l a t e d snowpack a c c u m u l a t i o n t o v a r i a t i o n s i n f r e e z i n g l e v e l . Anderson and Rockwood (1970) have- c o n s t r u c t e d a s i m u l a t i o n model (SSARR) t o generate snow a c c u m u l a t i o n and r u n o f f f o r a west c o a s t mid-l a t i t u d e mountain, based on d a t a from the U.S. Army (1956) i n v e s t i g a t i o n s . S e v e r a l R u s s i a n a t t e m p t s t o e s t i m a t e mountain snow cov e r on t h e o r e t i c a l grounds have been 8 p u b l i s h e d (Denisov 1967, B o r o i k o v a 1968). However, s i n c e l i t t l e i n f o r m a t i o n i s a v a i l a b l e about a r e a l v a r i a t i o n s o f s n o w f a l l and m e t e o r o l o g i c a l c h a r a c t e r i s t i c s o f each st o r m , t h e s e models are weakest when e s t i m a t i n g i n p u t t o the snowpack. F o r example, the R u s s i a n s assume a l i n e a r i n c r e a s e o f p e r c i p i t a t i o n w i t h e l e v a t i o n . Anderson and Rockwood use a 2°F/1000 f e e t l a p s e r a t e , and a temperature o f 33°F t o d e l i m i t the ra i n / s n o w boundary, on the s o l e grounds t h e s e v a l u e s g i v e more r e a l i s t i c o u t p u t . Thus w h i l e the snow cov e r a b l a t i o n - r u n o f f system o f the h y d r o l o g i c c y c l e has r e c e i v e d c o n s i d e r a b l e a t t e n t i o n (e.g. U.S. Army 1956, L e a f 1962), l i t t l e r e s e a r c h i n snow h y d r o l o g y has sought t o d e f i n e i n d e t a i l the snow i n p u t system o f the c y c l e ( F i g . 1.2). S t u d i e s which d e s c r i b e and p r e d i c t snow d e p o s i t i o n v a r i a t i o n s w i t h t o p o g r a p h y , e s p e c i a l l y e l e v a t i o n , w i l l a l l o w c o n s t r u c t i o n o f more r e a l i s t i c models of snowpack e v o l u t i o n and hence may improve e s t i m a t e s of w a t e r s t o r e d i n mountain snowpacks. R e a l i s t i c models o f snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n s h o u l d a l s o c o n s i d e r the c l i m a t o l o g y of w i n t e r snow storms. S t u d i e s which r e l a t e the b e h a v i o u r of the snow cov e r t o weather are f a i r l y common i n snow h y d r o l o g y (e.g. Ager 1967, McKay 1964, M i l l e r 1955) and i n g l a c i o l o g y (e.g. Hoinkes 1968, Marcus 1964). However, t h e r e have been o n l y a few s t u d i e s r e l a t i n g mountain snow d e p o s i t i o n and the c l i m a t o l o g y o f snow storms (e.g. You n k i n 1968, 9 Storm C h a r a c t e r i s t i c s r i m i n g p r e c i p i t a t i o n p r o c e s s e s INPUT SYSTEM R a i n f a l l Snow D e p o s i t i o n snow melt p r o c e s s e s t Net Snow A c c u m u l a t i o n =• E v a p o r a t i o n OUTPUT SYSTEM t t snow melt p r o c e s s e s — r u n - o f f -p r o c e s s e s Run-off P i g . 1.2 S i m p l i f i c a t i o n o f two systems of t h e . h y d r o l o g i c c y c l e i n mountainous t e r r a i n . 10 B o s s o l a s c o 1954). Thus the N a t i o n a l Academy of S c i e n c e s , N.R.C. (1967) recommends t h a t : " Areas o f maximum snow a c c u m u l a t i o n and p r o l o n g e d coverage of s e a s o n a l snow s h o u l d be s t u d i e d ... i n c o n n e c t i o n w i t h p r e v a i l i n g c i r c u l a t i o n p a t t e r n s . Average c y c l o n e t r a c k s ... s h o u l d be r e l a t e d t o s p e c i f i c c a s e - h i s t o r i e s o f snow storms ... f o r s e v e r a l c o n s e c u t i v e years". " The mountain snow cov e r i s a major and renewable h y d r o l o g i c a l r e s o u r c e . With i n c r e a s i n g demands f o r w a t e r , t h e r e i s a need f o r assessment o f t h i s r e s o u r c e by d e t a i l i n g the s i g n i f i c a n c e o f s n o w f a l l t o w i n t e r p r e c i p i t a t i o n i n mountain a r e a s . Management o f t h i s snow cov e r r e s o u r c e has been c o n s i d e r e d by Anderson (1963) and M a r t i n e l l i (1964). They suggest the p r i n c i p a l medium f o r a r t i f i c i a l c o n t r o l o f snow s t o r a g e - w i l l be m a n i p u l a t i o n o f the f o r e s t c o v e r . Thus- i t becomes i m p o r t a n t to-know the i n f l u e n c e o f the f o r e s t on snow d e p o s i t i o n . Many s t u d i e s have documented changes i n the snowpack r e s u l t i n g from d e l i b e r a t e mod-i f i c a t i o n o f the f o r e s t , but few (e.g. West 1961, M i l l e r 1966) seek t o i s o l a t e t he p r o c e s s e s i n v o l v e d . On west co a s t m i d l a t i t u d e mountains, t h e changing e f f e c t o f the f o r e s t on snow d e p o s i t i o n a t d i f f e r e n t e l e v a t i o n s i s o f p a r t i c u l a r i n t e r e s t , because o f the changing p o s i t i o n o f the s n o w l i n e w i t h d i f f e r e n t storms. There are o f course many o t h e r problems i n snow h y d r o l o g y . Many of thes e have been h i g h l i g h t e d by M e i e r (1969). B u t , from the f o r e g o i n g r e v i e w of t h e l i t e r a t u r e , the f o l l o w i n g o b s e r v a t i o n s are made : 11 On west co a s t m i d l a t i t u d e mountains the amount of r e s e a r c h on snow.accumulation has been s m a l l , and has been n e g l i g i b l e on snow d e p o s i t i o n . There i s a need t o develop methods t o p r e d i c t snow a c c u m u l a t i o n v a r i a t i o n s w i t h e l e v a t i o n . Few s t u d i e s measure ;and d e s c r i b e the snow i n p u t system o f the h y d r o l o g i c a l c y c l e f o r mountainous t e r r a i n . Such s t u d i e s c o u l d be used t o e x p l a i n the r e s u l t a n t snow a c c u m u l a t i o n p a t t e r n s , and t o a s s e s s the importance o f storm t y p e s and t r a c k s i n p r o d u c i n g snow d e p o s i t i o n and t o model snow d e p o s i t i o n p r o c e s s e s . P r e v i o u s models o f the snow i n p u t system i n 'moun-t a i n o u s t e r r a i n have been based l a r g e l y on- assumption r a t h e r t h a n on measurement o f the r e l e v a n t p r o c e s s e s . More r e a l i s t i c models may improve p r e d i c t i o n o f snow melt r u n o f f . The e f f e c t o f f o r e s t on the snow d e p o s i t i o n p r o c e s s i s an i m p o r t a n t c o n s i d e r a t i o n f o r management of the snow cover r e s o u r c e . 12 1.3 O b j e c t i v e s o f t h i s study This- study has f o u r i n t e r r e l a t e d o b j e c t i v e s . F i r s t , t o d e s c r i b e and attempt t o p r e d i c t v a r i a t i o n s o f snow accumu-l a t i o n w i t h e l e v a t i o n and p o s i t i o n w i t h i n the f o r e s t on a west c o a s t m i d l a t i t u d e mountain. Second, t o measure and d e s c r i b e new snow d e p o s i t i o n w i t h e l e v a t i o n and w i t h i n the f o r e s t a f t e r each storm f o r two c o n s e c u t i v e w i n t e r s . T h i s d a t a w i l l t h e n be a n a l y s e d t o e x p l a i n - the snow a c c u m u l a t i o n p a t t e r n s produced on west co a s t m i d l a t i t u d e mountains, t o a s s e s s the snow i n p u t t o the h y d r o l o g i c a l c y c l e , and t o compute the t o t a l mass o f snow d e p o s i t e d over the mesoscale o f a mountain segment. The snow d e p o s i t i o n d a t a w i l l a l s o be r e l a t e d t o w i n t e r storm t y p e s and t r a c k s . The t h i r d o b j e c t i v e o f t h i s study i s t o examine the c l i m a t o l o g y o f w i n t e r s t o r m s , e s p e c i a l l y t h e i n f l u e n c e of storm type i n p r o d u c i n g s n o w f a l l at each e l e v a t i o n on a west c o a s t m i d l a t i t u d e mountain. T h i s f o l l o w s the p r o p o s a l s o f the N a t i o n a l Academy o f S c i e n c e s N.R.C. (1967). The f i n a l o b j e c t i v e i s t o c o n s t r u c t a model which e s t -i m a t e s , a f t e r a g i v e n storm, the amount o f snow d e p o s i t e d on Mount Seymour. The model i s based on storm c h a r a c t e r -i s t i c s r e c o r d e d a t the base o f t h e mountain, o r a t o f f i c i a l m e t e o r o l o g i c a l s t a t i o n s . T h i s attempts a s o l u t i o n - t o a common h y d r o l o g i c a l problem where mountain- p r e c i p i t a t i o n 13 must be I n f e r r e d knowing o n l y meteorO'logica-l data;.from v a l l e y and'radiosonde s t a t i o n s . 1.4' The p r e s e n t a t i o n o f t h i s study P e r t i n e n t d e t a i l s o f the Mount Seymour study a r e a are g i v e n i n the next c h a p t e r . B e f o r e measurements o f snow d e p o s i t i o n and a c c u m u l a t i o n were t a k e n i t was c o n s i d e r e d i m p o r t a n t t o e s t a b l i s h an e x p e r i m e n t a l d e s i g n . The-d e s i g n chosen, s a m p l i n g • p r o c e d u r e s and methods o f measurement are d i s c u s s e d i n Chapter t h r e e . The next two c h a p t e r s examine the f i r s t o b j e c t i v e o f t h i s study : Chapter f o u r d e s c r i b e s snow a c c u m u l a t i o n v a r i a t i o n s on Mount Seymour over two w i n t e r s ; and Chapter f i v e i n v e s t i g a t e s e m p i r i c a l methods o f e s t i m a t i n g snow a c c u m u l a t i o n . v a r i a t i o n s w i t h e l e v a t i o n and w i t h p o s i t i o n -w i t h i n the f o r e s t . Snow a c c u m u l a t i o n i s t r e a t e d b e f o r e d e p o s i t i o n because i t has been measured i n p r e v i o u s s t u d i e s and. i s hence more f a m i l i a r . F u r t h e r , i f e m p i r i c a l e s t i m a t e s of snow a c c u m u l a t i o n v a r i a t i o n s w i t h topography are s u c c e s s -f u l , t he o t h e r o b j e c t i v e s o f t h i s study become l e s s i m p o r t a n t t o snow h y d r o l o g y . D e s c r i p t i o n and a n a l y s e s o f snow d e p o s i t i o n , , c o v e r i n g the second o b j e c t i v e o f t h i s s t u d y , are p r e s e n t e d i n Chapters s i x and- seven. The c l i m a t o l o g y of snow storms i s the s u b j e c t o f the f o l l o w i n g c h a p t e r . T h i s i n c l u d e s d i s c u s s i o n 14 of the t h i r d o b j e c t i v e . The' f i n a l o b j e c t i v e i s a t t a i n e d i n Chapter n i n e where a model p r e d i c t i n g snow d e p o s i t i o n on Mount Seymour i s d e v e l o p e d . The model dev e l o p e d i n t h i s study i s d e t e r m i n i s t i c , or p a r a m e t r i c , and o f the " p a r t i a l system s y n t h e s i s w i t h l i n e a r a n a l y s i s t y p e " (Amorocho and Hart 1964). T h i s t y p e o f model s t r i v e s t o d e s c r i b e t h e o p e r a t i o n o f t h e w i n t e r snow d e p o s i t i o n system "by l i n k a g e or c o m b i n a t i o n o f components whose presence i s presumed t o e x i s t i n the system and whose f u n c t i o n s are known and p r e d i c t a b l e " . T h i s i s what Amorocho and Hart c a l l . s y s t e m s y n t h e s i s ( F i g . 1. The p r e s e n t s m a l l degree of knowledge and the p r a c -t i c a l i m p o s s i b i l i t y o f e s t a b l i s h i n g a c c u r a t e l i n k a g e s between the component phenomena do not p e r m i t f u l l s y n t h e s i s o f the snow i n p u t system chosen f o r t h i s s t u d y . For example, l i t t l e d e t a i l i s known, or can be e a s i l y o b t a i n e d , of the m i c r o p h y s i c s o f p r e c i p i t a t i o n p r o c e s s e s i n c l o u d s above Mount Seymour, or o f a i r f l o w d u r i n g storms over the mountain r i d g e s o f the a r e a . Thus o n l y p a r t i a l system s y n t h e s i s i s p o s s i b l e . T h e r e f o r e , t h i s study d e v e l o p s a model u s i n g l i n e a r c o r r e l a t i o n a n a l y s i s . Here the r e l a t i o n s h i p between i n p u t ( s t o r m t y p e , p r e c i p i t a t i o n and temperature at base- of mountain) and output (snow d e p o s i t i o n on the mountain) i s e s t a b l i s h e d by s t a t i s t i c a l methods I n v o l v i n g t h e use o f measured i n p u t and output d a t a . However, the approach 15 PHYSICAL HYDROLOGY PARAMETRIC. AND STOCHASTIC • HYDROLOGIES TYPICAL TOPICS OF STUDY PARAMETRIC METHODS Meteo r o l o g y and C l i m a t o l o g y Mass b a l a n c e Energy c o n v e r s i o n and t r a n s f e r B i o s y s t e m s Watershed h y d r a u l i c s and hydromechanics p C o r r e l a t i o n A n a l y s i s p f^' P a r t i a l system s y n t h e s i s ^ w i t h l i n e a r a n a l y s i s ^ ^ G e n e r a l system s y n t h e s i s ^ G e n e r a l non l i n e a r a n a l y s i s STOCHASTIC METHODS Markov Chains Monte C a r l o methods Methods p a r t i c u l a r l y dependent on p h y s i c a l ^ knowledge o f the h y d r o l o g i c system. ^//////////////////y A f t e r Amorocho and Har t (1964). F i g . 1.3 T o p i c s and methods o f h y d r o l o g i c s t u d y . 16 i s not e n t i r e l y e m p i r i c a l i n t h a t the v a r i a b l e s , chosen f o r c o r r e l a t i o n are thos e t h a t e x i s t i n g knowledge i n d i c a t e s are.-'important. Moreover some attempt i s made t o d e s c r i b e the i n t e r n a l mechanics of the system i n e x p l i c i t form and. t o g i v e p h y s i c a l meaning t o the par a m e t e r s . 1.5 G e n e r a l r e l e v a n c e of t h i s study G e n e r a l l y , s t u d i e s such as t h i s p r o v i d e d a t a , and d e f i n e p r o c e s s e s o f use t o h y d r o e l e c t r i c power and water s u p p l y development, f l o o d f o r e c a s t i n g ^ r e c r e a t i o n a l p l a n n i n g , avalanche s t u d i e s , u p l a n d a g r i c u l t u r e , mountain t r a n s p o r t a t i o n and mountain b u i l d i n g codes. T h i s study a l s o has some l o c a l r e l e v a n c e . The b u l k o f the water s u p p l y f o r the g r e a t e r Vancouver p o p u l a t i o n of one m i l l i o n , r e s u l t s from r u n o f f from the N o r t h Shore M o u n t a i n s , where t h i s study a r e a i s l o c a t e d . . S e v e r a l major s k i areas o p e r a t e h e r e , and s i t u a t e d c l o s e t o a l a r g e p o p u l a t i o n , t h e s e mountains have i m p o r t a n t r e c r e a t i o n a l p o t e n t i a l . Suburban homes are s t e a d i l y b e i n g b u i l t at h i g h e r e l e v a t i o n s , so t h a t c o n s i d e r a t i o n o f snow l o a d s and^ snow c l e a r a n c e from roads i s i n c r e a s i n g l y p e r t i n e n t . I n t h i s c o n n e c t i o n , the d a t a p r e s e n t e d here adds t o the d i s -c u s s i o n s o f S c h a e r e r (1970). and S c h a e f e r and N i k l e v a (1973). 17 For the f i r s t time i n the area,, v a r i a t i o n s o f p r e -c i p i t a t i o n and snow a c c u m u l a t i o n are documented f o r a f u l l range o f e l e v a t i o n s from sea l e v e l t o 1250 m. Temperature c o n d i t i o n s f o r the w i n t e r months are a l s o examined. D e n s i t i e s o f newly- f a l l e n snow are measured. These can be used t o o b t a i n r e a l i s t i c f a c t o r s f o r c o n v e r s i o n o f s n o w f a l l depth t o water e q u i v a l e n t . I n a d d i t i o n , assump-t i o n s may be made about many m e c h a n i c a l p r o p e r t i e s - of the l o c a l snow s i n c e t h e s e can be r e l a t e d t o d e n s i t y (Bader 1962). 18 CHAPTER 2 2 . THE- STUDY AREA 2.1 The g e n e r a l l o c a t i o n of Mount Seymour Mount Seymour l i e s i m m e d i a t e l y t o the n o r t h of Van-couver, a t l a t i t u d e 49° 23 N, l o n g i t u d e 122° 57 W ( F i g . 2.1). I t i s s e p a r a t e d from the P a c i f i c Ocean, 160 km t o the west, by Vancouver I s l a n d , w i t h mountains above 2000 m, and by the 40 km wide w a t e r s of the S t r a i t of G e o r g i a . To the sout h w e s t , t h e mountains of the Olympic P e n i n s u l a (up t o 2400 m h i g h ) form an a d d i t i o n a l b a r r i e r t o the u s u a l onshore a i r f l o w . I n s p i t e o f these f a c t s , the c l i m a t e of the Vancouver a r e a i s m a r i t i m e , l a r g e l y dominated by P a c i f i c Ocean weather systems, w i t h i n the b e l t of the d i s t u r b e d w e s t e r l i e s (Kendrew and K e r r 1955)-2.2 G e n e r a l s y n o p t i c f e a t u r e s of w i n t e r weather From October t o mid-May the weather o f the Mount Seymour a r e a i s dominated by the A l e u t i a n Low, a semi-permanent p r e s s u r e system. From the r e g i o n o f t h i s low are f r e q u e n t l y spawned a s e r i e s o f low p r e s s u r e c e l l s and a s s o c i a t e d f r o n t s which move toward the B r i t i s h Columbia c o a s t . Sometimes f o u r o r f i v e c e l l s come as a s e r i e s , or " f a m i l y " , t h a t may dominate the weather f o r two or t h r e e weeks (Kendrew and K e r r 1955) . 19 F i g . 2.1 G e n e r a l l o c a t i o n o f Mt. Seymour F i g . 2.2 The l o c a l s e t t i n g 20 Kendrew and K e r r r e c o g n i s e s e v e r a l a i r m a s s e s which may i n f l u e n c e the B r i t i s h Columbia c o a s t i n w i n t e r . I n many c a s e s , they cannot be c l e a r l y d i s t i n g u i s h e d . M a r i -time T r o p i c a l (mT) a i r i s a deep, warm- s e c t o r o f d e p r e s s i o n s from the southwest. More o f t e n , mT a i r i s r a i s e d a l o f t by o c c l u s i o n o f the warm s e c t o r over the ocean. At the o t h e r extreme, c o n t i n e n t a l A r c t i c a i r (cA) may i n f l u e n c e the a r e a i n w i n t e r . T h i s a i r o r i g i n a t e s from the Mackenzie • V a l l e y and Yukon r e g i o n s . On most o c c a s i o n s i t i s c o n f i n e d e a s t o f the R o c k i e s , but i t can r e a c h the c o a s t i f a p e r s i s t e n t n o r t h e r l y f l o w d e v e l o p s (Baudat and Wright 1969), and i f the airmass i s deep, or i f a d e p r e s s i o n or t r o u g h i n t e n s i f i e s o f f the southwest B r i t i s h Columbia c o a s t . On the a v e r a g e , c o n t i n e n t a l A r c t i c a i r o u t b r e a k s around th e S t r a i t o f G e o r g i a o c c u r once i n two w i n t e r s (Kendrew and K e r r 1955) • C o n t i n e n t a l A r c t i c a i r i s dry and c o l d , so by i t s e l f seldom produces more th a n a few snow f l u r r i e s . However, i t l i e s as a l a y e r or dome c l o s e t o the s u r f a c e and may be o v e r r i d d e n by an onshore f l o w o f m o i s t P a c i f i c a i r . T h i s s i t u a t i o n produces heavy- snow t o low e l e v a t i o n s ( J a c k s o n 1957)• C o l d m a r i t i m e a i r m a s s e s o r i g i n a t e as cA a i r i n the c o l d dry i n t e r i o r of n o r t h e a s t A s i a , A l a s k a and the Yukon. When such a i r - i s moved over the P a c i f i c i t i s r a p i d l y warmed and moistened by the r e l a t i v e l y warm ocean. This-21 i n d u c e s i n s t a b i l i t y and .much c u m l i f o r m c l o u d . The degree of m o d i f i c a t i o n , and hence h e i g h t of the. f r e e z i n g l e v e l , depends on the l e n g t h o f s o j o u r n over the P a c i f i c . Thus the t r a j e c t o r y of- the a i r i s i m p o r t a n t . There r e s u l t a l a r g e number of p o s s i b l e s i t u a t i o n s , but two b road t y p e s of m a r i t i m e a i r are f r e q u e n t l y r e c o g n i s e d (Kendrew and K e r r 1955). The c o l d t y p e , c a l l e d m a r i t i m e A r c t i c a i r - (mA), r eaches the c o a s t a f t e r a s h o r t d i r e c t passage over the P a c i f i c . F r e e z i n g l e v e l s are low, and the a i r . i s g e n e r a l l y u n s t a b l e . The warm t y p e , c a l l e d m a r i t i m e P o l a r a i r (mP), r e a c h e s the c o a s t a f t e r l o n g c o n t a c t w i t h the ocean. I t i s u s u a l l y warm and humid. Such storms g e n e r a t e s t r a t i f o r m c l o u d s , and g i v e r i s e t o l e s s showery p r e c i p i t a t i o n . F r e e z i n g l e v e l s are h i g h e r and the a i r i s g e n e r a l l y s t a b l e . 2 .3 The l o c a l s e t t i n g Mount Seymour i s one o f a s e r i e s o f mountains f o r m i n g a w e l l d e f i n e d f r o n t range r u n n i n g e a s t - w e s t t o the n o r t h o f Vancouver ( F i g . 2.2). C o l l e c t i v e l y , t h e s e are-known as the N o r t h Shore Mountains-. Mount Seymour i s 1451 m h i g h , r e p r e s e n t a t i v e o f o t h e r peaks i n the a r e a . The N o r t h Shore Mountains are d i s s e c t e d by s e v e r a l deep, g l a c i a l l y eroded v a l l e y s e x t e n d i n g n o r t h from B u r r a r d I n l e t . Two o f t h e s e f l a n k Mount Seymour. On the west l i e s the Seymour V a l l e y and on the e a s t a v a l l e y o c c u p i e d by I n d i a n Arm. 22 A l l f i e l d o b s e r v a t i o n s were made on one t e r r a i n segment, a 14.3 km 2 a r e a o f Mount Seymour w i t h r e l a t i v e l y c o n s t a n t aspect and s l o p e (.Figs. 2.3 and 2 . 4 ) . 2.4 C h a r a c t e r i s t i c s o f the measurement a r e a 2-4.1 Hypspgraphy F i g . 2.4 shows h y p s o g r a p h i c curves f o r two r i v e r b a s i n s i n the N o r t h Shore M o u n t a i n s , and f o r the Mount Seymour t e r r a i n segment. I n t h e C a p i l a n o and Seymour Creek b a s i n s , 50 p e r c e n t o f the a r e a i s below 840 m, w h i l e 50 p e r c e n t of the Mount Seymour t e r r a i n segment l i e s below 335 m. The t e r r a i n segment i s c o n s i d e r e d a r e a s o n a b l e sample o f the e l e v a t i o n range i n the N o r t h Shore M o u n t a i n s , s i n c e o n l y 10 p e r c e n t of the b a s i n areas l i e above the h i g h e s t e l e v a t i o n (1260 m) • sampled i n t h i s t h e s i s . 2 . 4 . 2 Slope and as p e c t Slope and a s p e c t o f the t e r r a i n segment were measured from a map (scale. 1 : 1 2 , 0 0 0) at 10 random p o i n t s w i t h i n each o f 12 e l e v a t i o n a l bands c o n t a i n i n g snow a c c u m u l a t i o n and d e p o s i t i o n s a m p l i n g s i t e s ( T a ble 2 . 1 , F i g . 2 . 6 ) . Most v a l u e s o f s l o p e and a s p e c t f o r s a m p l i n g s i t e s f a l l ' w i t h i n one s t a n d a r d d e v i a t i o n o f the mean o f t h e s e parameters f o r each e l e v a t i o n band. The d a t a i n d i c a t e F i g . 2.3 The t e r r a i n , segment chosen f o r t h i s study 24 L o o k i n g toward the top of Mount Seymour from t h e c a r p a r k , lOBO m (March 1971) L o o k i n g toward the T.V. t r a n s m i s s i o n tower (on s k y l i n e at 870 m) from the lower p a r t of t h e road (200 m) F i g - 2.4 Views of the chosen t e r r a i n segment 20001 1 — : — i -1 - i — - l T- 1 i r Copilano batln (oreo 193.1 km*) Seymour basin (area 185.0 km1) I500to Mount Seymour terrain segment (area 14.3 km') 1000 500 _1 L. J I I - — 20 40 60 % Area 80 100 P i g . • 2 . 5 H y p s o g r a p h i c curves f o r the chosen t e r r a i n segment and f o r two a d j a c e n t r i v e r b a s i n s F i g . 2.6 Slope and aspect o f the chosen t e r r a i n segment and of snow sampli n g s i t e s TABLE 2.1 S l o p e and asp e c t of e l e v a t i o n bands of t e r r a i n segment  and o f snow s a m p l i n g s i t e s * E l e v a t i o n (metres) Slope (degrees) Aspect (degrees E of N) E l e v a t i o n bands of Snow Sampling S i t e T e r r a i n segment Snow Sampling S i t e T e r r a i n segment Snow Sampling S i t e t e r r a i n segment me an s t . dev. mean s t . dev. :1080 - 1280 1260 1 4 5 1 4 153 31 155 990 - 1080 1060 15 7 12** 12 167 23 210** 1 4 5 900 - 990 970 12 4 13 1 4 5 10 160 810 - 900 870 16 3 15 151 16 163 720 - 810 790 • 19 3 20 153 7 152 630 - 720 710 19 2 20 153 7 160 5 4 0 - 630 5 9 0 19 3 20 158 9 167 450 - 5 4 0 4 9 0 21 2 20 157 9 164 360 - 450 4 0 0 20 4 17 159 5 160 27G,- 360 330 17 5 19 150 7 156 180 - 270 220 1 4 2 12 150 9 1 4 5 90 - 180 120 12 5 6 151 15 170 Means and s t a n d a r d d e v i a t i o n s o b t a i n e d from a random sample of t e n p o i n t s i n each e l e v a t i o n a l band. Compiled from a map of s c a l e 1:12,000 contour i n t e r v a l 100 f e e t . The f i r s t v a l u e i s f o r the snow samp l i n g s i t e used i n the w i n t e r 1969-70, the second f o r the w i n t e r 1970-71. OA 27 t h a t the t e r r a i n - segment i s r e l a t i v e l y homogeneous w i t h r e s p e c t t o asp e c t and s l o p e , t h a t t he s a m p l i n g s i t e s are r e p r e s e n t a t i v e • o f each e l e v a t i o n a l band and t h a t t o g e t h e r they are r e p r e s e n t a t i v e o f the whole t e r r a i n segment. 2 . 4 . 3 V e g e t a t i o n A study o f snow d e p o s i t i o n w i t h e l e v a t i o n i s comp-l i c a t e d by the f a c t t h a t v e g e t a t i o n a l s o v a r i e s w i t h e l e -v a t i o n . U n f o r t u n a t e l y , the l i t e r a t u r e has not y e t r e s o l v e d which f o r e s t c h a r a c t e r i s t i c s e x e r t the most i m p o r t a n t i n f l u e n c e s on snow d e p o s i t i o n . I t i s p o s s i b l e the same f o r e s t c h a r a c t e r i s t i c s may h a v e ' v a r y i n g importance at d i f f e r e n t e l e v a t i o n s . Based on ,the f o r e s t c l a s s i f i c a t i o n o f B r i t i s h Columbia proposed by K r a j i n a (1965, 1969), the v e g e t a t i o n on Mount Seymour i s d i s c u s s e d i n d e t a i l by P e t e r s o n (1964), O r l o c i (1964) and Brooke (1966). Below an e l e v a t i o n o f 900 m, the mountain l i e s w i t h i n the Western Hemlock Zone. The dominant t r e e s p e c i e s i s w e s t e r n hemlock (Tsuga  h e t e r o p h y l l a ) , w i t h o c c a s i o n a l Douglas f i r (Pseudotsuga  m e n z i e s i i ) , e s p e c i a l l y where d i s t u r b e d by l o g g i n g or f i r e , and w e s t e r n r e d cedar (Thuja p l i c a t a ) . Toward h i g h e r e l e v a t i o n s , mountain hemlock (Tsuga m e r t e n s i a n a ) and a m a b i l i s f i r ( A b i e s a m a b i l i s ) appe- ar.' Of the many shrubs V a c c i n i u m a l a s k a e n s e i s the most common. 28 The s u b a l p i n e Mountain Hemlock Zone begins•above 900 m. Brooke (.196.6) r e c o g n i s e s two subzones-, the F o r e s t Zone up t o 1100. m, and the P a r k l a n d Zone at h i g h e r e l e v a -t i o n s , where the t r e e s t h i n out) c o n s i d e r a b l y . The dominant t r e e s p e c i e s are mountain hemlock, a m a b i l i s f i r , y e l l o w cedar (Chamaecyparis n o o t k a t e n s i s ) , w i t h some w e s t e r n hem-l o c k a t lower l e v e l s . The dominant shrub s p e c i e s are Rhododendron a l b i f l o r u m and V a c c i n i u m membranaceum. Tree s p e c i e s o f the S u b a l p i n e Zones are b e t t e r adapted t o snowy c o n d i t i o n s than those at lower e l e v a t i o n s , i n t h a t t h e i r branches are more f l e x i b l e and bend downward. T h i s - e n a b l e s them t o shed i n t e r c e p t e d snow, and a v o i d damage from e x c e s s -i v e snow l o a d i n g . F i v e v e g e t a t i o n types were r e c o g n i s e d and mapped from 1963 a i r photographs of Mount Seymour ( s c a l e v a r i e d from 1:7542 t o 1:12,800). The a r e a of each type was p l a n i m e t e r e d , and the p e r c e n t a g e a r e a c a l c u l a t e d f o r the t e r r a i n segment. The r e s u l t s h i g h l i g h t the f o r e s t e d n a t u r e o f the mountain (Fig.. 2v7). Areas of young t r e e s , d e s c r i b e d as second growth predominate. Open areas and c l e a r i n g s , t o g e t h e r , . make up l e s s t h a n 20 p e r c e n t o f the t e r r a i n segment. When the r e s u l t s are c o n s i d e r e d f o r each e l e v a t i o n a l band, i t " ' i s c l e a r t h e r e are. wide d i f f e r e n c e s between e l e v a t i o n s . Open areas and c l e a r i n g s are i m p o r t a n t o n l y above 900 m. As c l e a r i n g s may be s i g n i f i c a n t i n the snow- d e p o s i t i o n p r o c e s s '.(Anderson e t a l 1958, Hansen a n d - F f o l l i o t t 1968), 29 a f r e q u e n c y d i s t r i b u t i o n of s i z e , .of/ c l e a r i n g s was- c o m p i l e d from a i r photographs f o r each, e l e v a t i o n band. (Table 2.2). Most c l e a r i n g s are s m a l l e r than 15 m i n d i a m e t e r , except near the top of the mountain, and' at a more r e c e n t l y l o g g e d a r e a near 600 m. The f o r e s t has a l s o been d e s c r i b e d at each s a m p l i n g s i t e by the u s u a l measures of t r u n k d i a m e t e r , and h e i g h t (Appendix A ) . However, as Rothacher (1963) and C u r t i s (1970) s u g g e s t , t h e s e parameters" alone may not be s a t i s -f a c t o r y i n d i c e s of f o r e s t i n f l u e n c e s on snow d e p o s i t i o n , s i n c e they were developed f o r o t h e r purposes and are d e f i c i e n t i n p h y s i c a l i n t e r p r e t a t i o n . M i l l e r (1964) d i s c u s s e s some u s e f u l measures on i n d i v i d u a l t r e e s which b e t t e r r e f l e c t the t h r e e d i m e n s i o n a l n a t u r e o f t h e f o r e s t , and. which may be r e l a t e d t o snow d e p o s i t i o n . Of t h e s e , an i n d e x o f canopy c l o s u r e was o b t a i n e d ( F i g 2.8). T h i s was d e f i n e d as the- percentage' of 25 randomly s e l e c t e d p o i n t s o c c u r r i n g beneath a t r e e canopy at each, s a m p l i n g s i t e . Other measures and p h o t o -graphs of the f o r e s t near each.of the 12 s a m p l i n g s i t e s are g i v e n i n Appendix A. F i g s . 2.7, 2.8 and o t h e r data, i n Appendix A, r e v e a l t h e d i v e r s e n a t u r e o f the f o r e s t at the s a m p l i n g s i t e s , a product; of' s e l e c t i v e l o g g i n g at d i f f e r e n t t imes i n the p a s t . Perhaps the most anomalous s a m p l i n g s i t e i s t h a t at 590 m. 30 100 80 ^ S 6 0 ^ < 2 5 40H 0 , Second Growth (50°/o ) * v . . • • >C Mature %Trees(l9°/o)/ ^ < f i ft X .N K Deciduous Trees ( 1 5 ° / o ) ^ x • ' ' / ^ y^Clearings (6°/o) < £ / " v ^ "~- — 200 4 0 0 600 8 0 0 Elevation (Meters) 1000 1200 F i g . 2.7 D i s t r i b u t i o n o f v e g e t a t i o n • t y p e w i t h e l e v a t i o n 10 0-8 h 0 6 x T> _C V c W o U 0 4 >. o. o § 0-2 U 1 0 = Totally closed canopy 0 0 = Completely open . JL 200 400 600 500 Elevation (Meters) 1000 1200 F i g . 2.8 Canopy c l o s u r e of the f o r e s t at each, s a m p l i n g s i t e 31 TABLE 2.2 Frequency • d i s t r i b u t i o n of. c l e a r i n g s * i n the t e r r a i n segment E l e v a t i o n band (metres) Diameter o f C l e a r i n g < 15 m 15-30 m 30-45 m 45-60 m 1080-1280 68$ 22$ 10$ '990-1080 86$ 12$ 2$ 900- 990 72$ 22$ 6$ 810- 900 90% 10$. 720- -310 89$ 11$ 630- 720 98$ 2$ 540- 630 62% 35$ :3$ 450- 540 84$ 14$ 1$ 1$ 360- 450 81$ 17$ 2$ 270- 360 92$ 7$ 1$ 180- 270 90$ 8$ 2$ 90- 180 84$ 13$ 2$ 1$ Compiled from a i r photographs t a k e n A p r i l 1963 * I n c l u d e s ro'ads, c l e a r i n g s , s k i . r u n s , e t c . 32 However, t h e r e do eocis/t some g e n e r a l t r e n d s w i t h e l e v a t i o n . Both t r e e h e i g h t and s i z e of canopy te n d t o decrease towards the top of the mountain. The p r e v i o u s l y mentioned t h i n n i n g of the f o r e s t above 900 m i s a l s o w e l l i l l u s t r a t e d . 2 .5 A v a i l a b l e d a t a 2.5 .1 C l i m a t i c d a t a S t a n d a r d c l i m a t i c s t a t i o n s r e c o r d i n g p r e c i p i t a t i o n and temperature d a t a d u r i n g the p e r i o d o f t h i s r e s e a r c h were numerous at lower e l e v a t i o n s , but- i n a d e q u a t e i n t h e mountain a r e a s . Only- one mountain s t a t i o n , H o l l y b u r n Ridge (15 km t o the west at an e l e v a t i o n of 920 m), r e c o r d e d d a i l y p r e -c i p i t a t i o n and t e m p e r a t u r e . A f i r s t o r d e r c l i m a t e s t a t i o n w i t h o v e r t h i r t y y e a r s of r e c o r d was l o c a t e d near sea l e v e l at Vancouver I n t e r n a t i o n a l A i r p o r t , 25 km t o the southwest of Mount Seymour ( F i g . 2 . 2 ) . S e v e r a l c l i m a t i c s t a t i o n s have o p e r a t e d at h i g h e r e l e v a t i o n s i n the p a s t . P r e c i p i t a t i o n measurements-began at H o l l y b u r n Ridge i n 1954, and temperature measurements i n i 9 6 0 . Grouse Mountain (1105 m) r e c o r d e d p r e c i p i t a t i o n d a t a f o r the y e a r s 19 34-40. On Mount Seymour, a p a r t i a l 10 y e a r r e c o r d (1958-68) of d a i l y p r e c i p i t a t i o n i s a v a i l a b l e from the CBUT t e l e v i s i o n t r a n s m i t t i n g tower (870 m). Three temporary c l i m a t i c s t a t i o n s above 900 m measured 33 temperature i n a l l s e a s o n s , and p r e c i p i t a t i o n d u r i n g snow-f r e e p e r i o d s , between 1960-1962 (Peterson- 1964, Brooke 1966) . 2 .5 .2 Upper a i r d a t a I n c o n s i d e r i n g any asp e c t o f mountain c l i m a t e , upper a i r d a t a i s • i m p o r t a n t . U n f o r t u n a t e l y , t h e r e i s no r a d i o -sonde s t a t i o n at Vancouver. The n e a r e s t s t a t i o n s are P o r t Hardy at t h e n o r t h e r n t i p of Vancouver I s l a n d , 350 km t o the n o r t h w e s t , and Q u i l l a y u t e ( f o r m e r l y at Tatoosh I s l a n d ) on the Olympic P e n i n s u l a , 165 km t o the southwest ( F i g . 2 . 1 ) . Both s t a t i o n s are w e l l exposed t o a p p r o a c h i n g P a c i f i c a i r -f l o w s . The m o d i f i c a t i o n i n air m a s s - p a r a m e t e r s by sub-sequent passage over Vancouver I s l a n d or the Olympic P e n i n -s u l a , t he S t r a i t o f G e o r g i a , and t h e c i t y o f Vancouver i s not known. However, P e t e r s o n (1964) c l a i m e d t o have found a good c o r r e l a t i o n between the h e i g h t of f r e e z i n g l e v e l s at P o r t Hardy and Mount Seymour. I t was d e c i d e d from t h i s e v i d e n c e , t o g e t h e r w i t h the ease o f ac c e s s and the c o n s i d -e r a b l e r e l a t i v e cheapness o f the Canadian r a d i o s o n d e d a t a , t o use d a t a from o n l y P o r t Hardy i n t h i s s t u d y . At b o t h r a d i o s o n d e s t a t i o n s , o b s e r v a t i o n s are t a k e n every 12 h o u r s . I t i s p o s s i b l e f o r weather- systems t o move c o m p l e t e l y t h r o u g h the ar e a between o b s e r v a t i o n s . D e t a i l e d s t u d i e s ( K r e i t z b e r g 1964, 1970) show t h a t the 34 s p a t i a l and t e m p o r a l s a m p l i n g p a t t e r n of r a d i o s o n d e s t a t i o n s i s o f t e n i n s u f f i c i e n t t o d e f i n e t h e d e t a i l e d s t r u c t u r e o f storms. 2 . 5 . 3 Snow a c c u m u l a t i o n and s n o w f a l l - d a t a There have been a number o f o t h e r s t u d i e s w h i c h d i s c u s s snow on Mount Seymour. Between i 9 6 0 and 1 9 6 2 , P e t e r s o n (1964) and Brooke ( .1966), r e c o r d e d snow depth and snow cover phenology above 1000 m. The p r e s s u r e s i n d u c e d by c r e e p i n g snow a t e l e v a t i o n s o f 1100 m and 1200 m were r e p o r t e d by Mathews and Mackay (1963) and Mackay and Mathews ( 1 9 6 7 ) . S t e i n and Brooke (1964) d e s c r i b e d an o c c u r r e n c e of r e d snow on the mountain. The maximum ground snow l o a d s at v a r i o u s e l e v a t i o n s on a number o f B r i t i s h Columbia mountains are p r e s e n t e d by S c h a e r e r ( 1 9 7 0 ) . These i n c l u d e d o b s e r v a t i o n s t a k e n on Mount Seymour i n 1 9 6 9 . A number o f papers d i s c u s s s n o w f a l l a t lo w e r e l e v a -t i o n s , based on snow depth r e c o r d e d r o u t i n e l y a t s t a n d a r d c l i m a t o l o g i c a l s t a t i o n s ( H a r r y and Wright 1957, Thomas 1 9 5 7 , Wright 1 9 6 6 a , Wright 1 9 6 6 b , Wright and Trenholm 1 9 6 9 , S c h a e f e r and N i k l e v a 1973)- The s y n o p t i c c o n d i t i o n s l e a d i n g t o h e a v i e r f a l l s o f snow i n the- Vancouver a r e a are d e s c r i b e d by J a c k s o n (1957) and Baudat and Wright ( 1 9 6 9 ) . -35 There were seven snow courses o p e r a t i n g i n the N o r t h Shore Mountains d u r i n g t h i s s t u d y . These are l i s t e d i n Appendix D w i t h t h e i r l e n g t h o f r e c o r d and e l e v a t i o n . Grouse Mountain has one o f the l o n g e s t r e c o r d s i n B r i t i s h Columbia. On Mount Seymour, snow cou r s e o b s e r v a t i o n s were t a k e n about 1 km t o the west o f the t e r r a i n segment at t h e b e g i n n i n g o f each month from F e b r u a r y t o June and on May 15. A l l o t h e r snow c o u r s e s were r e a d l e s s f r e q u e n t l y . 36 CHAPTER 3 3. PARAMETERS MEASURED AND EXPERIMENTAL DESIGN 3•1 Measurement o f snow d e p o s i t i o n 3.1 .1 Method Snow d e p o s i t i o n was measured a f t e r each s t o r m as the s p e c i f i c mass o f new snow, p e r u n i t o f ground a r e a . S p e c i f i c new snow mass (M) i s g i v e n by: M = Y Z where Y = d e n s i t y o f n e w l y • f a l l e n snow z = new snow d e p t h , measured v e r t i c a l l y . Snow d e n s i t y and depth o f new snow increment were measured above a ' s t y r o f o a m snowboard ( a r e a - 250 c m 2 ) , p l a c e d on the p r e v i o u s snow s u r f a c e and l o c a t e d by a dowel. The snowboard remained l e v e l w i t h t h e snow s u r f a c e under most weather c o n d i t i o n s , except d u r i n g r a i n on snow events when the s t y r o f o a m d i d not s e t t l e as r a p i d l y as d i d t h e s u r r o u n d i n g snow s u r f a c e . New snow d e n s i t y was measured b y . w e i g h i n g the c o n t e n t s o f - a 500 cm 3 CRREL snow sampler, ( l e n g t h 19.6 cm, d i a m e t e r 5.7 cm). I f new snow depth was g r e a t e r t h a n the l e n g t h o f the s a m p l i n g t u b e , a d d i t i o n a l d e n s i t y measurements were t a k e n w i t h depth. The maximum depth o f new snow r e c o r d e d from any storm was 103 cm. When snow depth was l e s s t h a n t h e l e n g t h o f the t u b e , h o r i z o n t a l r a t h e r t h a n v e r t i c a l samples were t a k e n . 37 3.1 .2 Measurement e r r o r New snow depth, was-measured t o ±0 ..5 cm, or t o w i t h i n ±0.25 cm f o r depths l e s s t h a n 4 cm. The c o n t e n t s of the 500 cm 3 CRREL sampler were emptied i n t o a i r t i g h t j a r s and s u b s e q u e n t l y weighed t o ±0.05 gm on a l a b o r a t o r y b a l a n c e . Volume of the sampler was checked by measuring the amount of water i t c o u l d c o n t a i n . I t was e s t i m a t e d t o be c o r r e c t t o ±1 cm 3. To ensure the c o r r e c t volume i n f i e l d measurements, the ends o f the snow sample were p l a n e d o f f w i t h a s t e e l - e d g e d r u l e . These e r r o r s i n w e i g h i n g and i n the volume o f the sampler r e s u l t i n a p e r -centage- measurement e r r o r o f s p e c i f i c new snow mass which v a r i e s w i t h snow depth ( F i g . 3 . 1 ) . A c t u a l l y , t h e r e e x i s t s a f a m i l y o f curves f o r each snow d e n s i t y , but w i t h i n t he d e n s i t y range 100-400 kg/m 3 t h e s e curves are v e r y c l o s e t o g e t h e r and can be r e p r e s e n t e d by thos e shown. I n a d d i t i o n t o the computed measurement e r r o r , f u r t h e r measurement e r r o r s can r e s u l t from c o l l a p s e -:of t h e snow s t r u c t u r e w i t h i n t he sampler, or from a d h e s i o n of snow t o the sample tube w a l l . I n such c a s e s , t h e volume o f snow weighed may be g r e a t e r o r l e s s than 500 cm 3. T h i s e r r o r was reduced by waxing the sample t u b e , and by r e j e c t i n g those samples where c o l l a p s e or a d h e s i o n was s u s p e c t e d . 50 40 0 4 8 12 16 20 24 28 New Snow Depth (cm) P i g . 3-1 Percentage measurement e r r o r f o r s p e c i f i c mass of new snow d e p o s i t e d 39 Assessment o f the magnitude of t h i s s u b j e c t i v e e r r o r i s d i f f i c u l t . Gary (.1971) s who e s t i m a t e d t h e " w i t h i n p l a c e " sample v a r i a b i l i t y o f new snow d e n s i t y , quoted a c o e f f i c i e n t o f v a r i a t i o n o f 5.0 p e r c e n t . T h i s was l a r g e r t h a n f o r depth hoar (2.5%), o l d dry snow (2.4$) and o l d wet snow (1.7J8)-. Work e t a l (1964) found the 500 cm 3 CRREL sampler tended t o o v e r e s t i m a t e the water e q u i v a l e n t by 7 p e r c e n t . However, t h e i r f i g u r e was based on an e s t i m a t e of water e q u i v a l e n t f o r the t o t a l snowpack by use o f a s e r i e s o f samples. From t h i s , i t seems t h a t t h e measure-ment e r r o r o f s p e c i f i c snow mass may be. l a r g e r , by an unknown amount, t h a n t h a t shown i n F i g . 3 • 1,.depending on the s k i l l o f the o p e r a t o r and on snow c o n d i t i o n s . When new snow depths were l e s s than the di a m e t e r of the s a m p l i n g t u b e , no measurements o f new snow d e n s i t y were made. The s p e c i f i c new snow mass was then computed by u s i n g the d e n s i t y v a l u e from the n e a r e s t s a m p l i n g s i t e where a measurement c o u l d be t a k e n . I n thes e c a s e s , the s p e c i f i c new snow mass, was s m a l l ( l e s s t h a n 15 kg/m 2), hence a b s o l u t e e r r o r s from t h i s p rocedure were not l i k e l y . t o be unduly l a r g e . 3 .2 The t e m p o r a l sample 3 . 2 . 1 The storm • The b a s i c s a m p l i n g i n t e r v a l used i n t h i s study i s 40 the s t o r m , here d e f i n e d as a p e r i o d of p r e c i p i t a t i o n a s s o c i -a t e d w i t h a p a r t i c u l a r s y n o p t i c s i t u a t i o n . Snow d e p o s i t i o n and r a i n f a l l were sampled no l a t e r t h a n w i t h i n 24 hours and i n most cases w i t h i n 12 hours a f t e r each storm. Storms were numbered c o n s e c u t i v e l y , s t a r t i n g w i t h the f i r s t one a f t e r October 1 (see l i s t o f s t o r m s , Appendix E ) . S i n c e the b u l k of the p r e c i p i t a t i o n i n the Vancouver a r e a i s f r o n t a l i n o r i g i n (Walker 1961), t h e r e seldom was any c o n f u s i o n i n d e l i m i t i n g s t o r m s . However, c e r t a i n d i f f i c u l t i e s d i d a r i s e i n n o n - f r o n t a l s i t u a t i o n s : I f an onshore f l o w o f m o i s t a i r b e h i n d a f r o n t was p e r s i s t e n t , two storms - one f r o n t a l , t h e o t h e r n o n - f r o n t a l - were r e c o g n i s e d ; i f p o s t - f r o n t a l showers were b r i e f , a s i n g l e s torm s i t u a t i o n e x i s t e d . Storms o c c a s i o n a l l y o c c u r r e d i n such r a p i d s u c c e s s i o n t h a t i t was i m p o s s i b l e t o sample a f t e r each. I n t h e s e c a s e s , the storms were c l a s s i f i e d s e p a r a t e l y , a l t h o u g h the sample d i d i n c l u d e the combined p r e c i p i t a t i o n . F o r s a m p l i n g p u r p o s e s , the i n i t i a l d e c i s i o n as t o what c o n s t i t u t e d a storm was made a f t e r c o n s u l t i n g 'the l a t e s t a v a i l a b l e s u r f a c e - and mountain weather f o r e c a s t s as w e l l as the s k i r e p o r t f o r l o c a l m o u n t a i n s , and a f t e r v i e w i n g a crude s u r f a c e s y n o p t i c p i c t u r e and weather s a t e l l i t e photograph on a n i g h t l y t e l e v i s i o n f o r e c a s t . 41 S u b s e q u e n t l y , the s y n o p t i c s i t u a t i o n was examined on o f f i c i a l w e a t h e r - o f f i c e s y n o p t i c c h a r t s . A t e m p o r a l s a m p l i n g scheme such as t h i s i s - o n l y as v a l i d as the weather f o r e -c a s t s and the a c c u r a c y w i t h which the a c t u a l weather p a t t e r n s are p o r t r a y e d by the- s y n o p t i c c h a r t s . L i t t l e i n f o r m a t i o n i s r o u t i n e l y a v a i l a b l e on the s t r u c t u r e o f weather systems below the s y n o p t i c s c a l e (100-1000 k m 2 ) . T h i s i s a problem t h a t i s i n h e r e n t i n t h i s s t u d y , w h e r e i n the e f f e c t s o f such systems are examined on a l e s s e r s p a t i a l s c a l e (about 10 km 2). 3.2 .2 The p e r i o d o f f i e l d o b s e r v a t i o n s Samples f o l l o w i n g each storm were t a k e n w i t h i n the " w i n t e r " p e r i o d October 1 t o May 31, 1969-70 and 1970-71. Except f o r these months, f a l l s o f snow are u n u s u a l below 1300 m (Chapter 6 ) . Some samples of d e n s i t y o f newly f a l l e n snow were t a k e n i n the w i n t e r 1968-69. I n the w i n t e r 1969-70, snow d e p o s i t i o n was sampled from a l l storms w i t h snow. I n a d d i t i o n , r a i n f a l l was sampled from a l l s:t'orms except those o c c u r r i n g i n October and the f i r s t week i n November. I n the w i n t e r 1970-71, complete p r e c i p i t a t i o n was sampled from a l l s t o r m s . Thus-p r e c i p i t a t i o n - whether r a i n or snow - was measured by storms f o r one complete w i n t e r and' f o r most o f a n o t h e r (138 s t o r m s ) . Snow d e p o s i t i o n was measured by storms f o r two complete w i n t e r s C82 s t o r m s ) . 42 3 . 2 . 3 Nature of w i n t e r s sampled The two w i n t e r s o f t h i s study were d i f f e r e n t ifrom each o t h e r i n many ways and i t i s f e l t they r e p r e s e n t a wide range o f c o n d i t i o n s about the n o r m a l . A s e l e c t i o n of c l i m a t i c d a t a r e c o r d e d at Vancouver I n t e r n a t i o n a l A i r p o r t (near sea l e v e l ) show the 'Winter o f 1969-70 t o be m i l d e r and d r i e r t h a n n o r m a l , i n sharp c o n t r a s t t o the w e t t e r w i n t e r t h a t f o l l o w e d ( P i g . 3 . 2 ) . On the l a r g e r s c a l e , t h e r e were i m p o r t a n t d i f f e r e n c e s i n t he g e n e r a l c i r c u l a t i o n , here i n d i c a t e d by d e p a r t u r e s from normal o f the mean 700 mb h e i g h t ( F i g . 3 . 3 ) . The w i n t e r of 1969-70 d i s p l a y e d s t r o n g n e g a t i v e a nomalies over and' s o u t h of the A l e u t i a n I s l a n d s , e s p e c i a l l y from December t o March. These anomalies were a s s o c i a t e d w i t h a g r e a t l y expanded and more i n t e n s e A l e u t i a n Low i n the n o r t h e a s t . P a c i f i c , w hich produced p e r s i s t e n t s o u t h e r l y f l o w s o ver the Vancouver r e g i o n and the warmer, d r i e r c o n d i t i o n s i n what i s p o t e n t i a l l y the s n o w i e s t p a r t o f the y e a r . By c o n t r a s t the w i n t e r o f 1970-71 d i s p l a y e d s t r o n g p o s i t i v e 700 mb anomalies i n the n o r t h e a s t P a c i f i c , e s p e c i a l l y from October t o F e b r u a r y . D u r i n g t h i s p e r i o d the A l e u t i a n low was weakened o r e l i m i n a t e d by the development o f an e x t e n s i v e r i d g e i n the e a s t e r n P a c i f i c . A p e r s i s t e n t n o r t h e r l y f l o w d e v e l o p e d , p r o d u c i n g w e t t e r and c o l d e r c o n d i t i o n s w i t h f r e q u e n t o u t b r e a k s o f A r c t i c a i r t o the P a c i f i c c o a s t . F i g . 3-2 D i f f e r e n c e s from normal ( p e r i o d 1931-60). of s e l e c t e d m e t e o r o l o g i c a l parameters at Vancouver I n t e r n a t i o n a l A i r p o r t f o r w i n t e r s 1969-70, 1970-71 F i g . 3.3 D e p a r t u r e from normal of the mean 700. mb h e i g h t (decameters) f o r each-month o f w i n t e r 196-9-70. From Monthly Weather Review F i g . 3-3 (.continued) Departure from normal o f . t h e mean 700 mb height' (decameters) f o r each-month of w i n t e r 1970-71 46 These d i f f e r e n c e s , i n th.e g e n e r a l c i r c u l a t i o n between the two w i n t e r s were s t r o n g l y r e f l e c t e d i n a t m o s p h e r i c f r e e z i n g l e v e l s and s n o w f a l l . The monthly mean f r e e z i n g l e v e l s , as measured at a d j a c e n t r a d i o s o n d e s t a t i o n s f o r these w i n t e r s , a l s o l a y on e i t h e r s i d e of the l o n g t e rm v a l u e s (Table 3.1). S n o w f a l l was l e s s t h a n normal i n t h e w i n t e r 1969-70. By c o n t r a s t , the w i n t e r o f 1970-71 e x p e r i e n c e d the g r e a t e s t snow amounts measured at Vancouver I n t e r n a t i o n a l A i r p o r t s i n c e r e c o r d s began i n 1938, i n c l u d -i n g an a l l - t i m e h i g h f o r January of 122 cm, a l t h o u g h g r e a t e r amounts had been r e c o r d e d at the o l d e r Vancouver C i t y weather s t a t i o n . At t h i s l a t t e r s t a t i o n , t he w i n t e r s o f the stu d y produced s n o w f a l l s which spanned most o f the range r e c o r d e d i n the l a s t 70 y e a r s ( F i g . 3 . 4 ) . From more l i m i t e d d a t a , the s n o w f a l l s at the h i g h e r e l e v a t i o n o f H o l l y b u r n (920 m) a l s o seemed t o i n c l u d e a wide range o f c o n d i t i o n s ( F i g . 3 . 4 ) . Snow water e q u i v a l e n t s measured a t two N o r t h Shore Mountain snow co u r s e s were below normal i n the w i n t e r 1969-70, and above normal i n 1970-71 ( F i g . 3 - 5 ) . Grouse M o u n t a i n , 9 km t o the west o f Mount Seymour, i s i n c l u d e d because o f i t s l o n g e r p e r i o d of r e c o r d . D u r i n g the p e r i o d o f t h i s s t u d y , Seymour Mountain r e c o r d e d i t s l o w e s t March water e q u i v a l e n t (87 cm i n 1970), and i t s h i g h e s t May v a l u e (287 cm-in 1971) s i n c e r e c o r d s began i n I960., From the .36 • 47 TABLE 3.1 F r e e z i n g l e v e l s ( g e o p o t e n t i a l m e t e r s )  at two r a d i o s o n d e s t a t i o n s ; f o r W i n t e r s 1969-70, 1970-71, compared w i t h l o n g e r  p e r i o d s o f r e c o r d Longer p e r i o d o f r e c o r d W i n t e r s of study Tatoosh I s . P o r t Hardy P o r t Hardy P o r t Hardy Month 1946-55 1951-60 1969-70 . 1970-71 Oct 2440 2280 2202 2399 Nov 1730 1560 1782 1347-Dec 1200 1180 . 1292 627 J a n 860 760 865 1130 Feb 1060 870 1775 1103 Mar 1020 840 1163 604 Apr 1420 1380 1035 1215 May 2240 2080. 1638 2007 Oct-May me an 1496 1369 1469 1304 Monthly S. Dev. 587 574 452 623 Notes: ( ±) Longer term d a t a f o r P o r t Hardy i s from T i t u s C1965). That f o r Tatoosh I s l a n d ( n o w - Q u i l l a y u t e ) from R a t n e r (1957) . ( i i ) Data f o r 1969-70 ,. 197.0-71 computed from "Monthly B u l l e t i n o f Canadian•Upper A i r D a t a " . r 4 8 1190 «3<H 650 J t A f Winttr 1970-71 Based on 18years observation .999 99 95 -90 80 70 60 50 40 -30 20 *> 05 01 001 •999 995 99 95 SO 80 70 60 -50 -40 -30 SO -10 05 01 005 001 F i g . 3-4 P r o b a b i l i t y of winter s n o w f a l l s , as t o t a l depth of new snow at Hollyburn Ridge, 920 m, (.top) and Vancouver C i t y , near; sea l e v e l , (bottom). The h o r i z o n t a l a x i s gives the p r o b a b i l i t y of exceeding a given depth of s n o w f a l l 49 SEYMOUR MOUNTAIN Elevation 1113 m. 120 based on period 1960-71 c £ 8 ° Feb Mar Apr May June 120 c J 8 0 o > cr UJ c I 40 0 GROUSE MOUNTAIN Elevation 1158m I I I based on period 193 6-71 / ^ ^ ^ ^ max / • 1971 ' / ^ ^ ^ ^ / / - mean > — — —• " " " ^ ^ 1970 r — » — * min i ' - i rr 240 L160 80 Feb Mar Apr May E o c i) a > c r U (-4; -t-> o June F i g . 3 .5 Monthly water e q u i v a l e n t at Seymour Mountain and Grouse Mountain snow courses f o r w i n t e r s 1969-70 ,. 1 9 7 0 - 7 15 compared w i t h the l o n g t e r m r e c o r d s . Compiled from B.C. Snow Survey B u l l e t i n s • 50 y e a r s t o 1971 o f A p r i l r e a d i n g s at Grouse M o u n t a i n , o n l y f i v e y e a r s (1940, 1941, 1942, 1944 ,. 1963) have r e c o r d e d l e s s snow th a n i n 1970, and o n l y two ye a r s (1946, 1964), have r e c o r d e d more t h a n i n 1971. At t h e Seymour snow course t h e p r o b a b i l i t y o f h a v i n g a lower water e q u i v a l e n t t h a n i n 1969-70, o r a h i g h e r w a t e r e q u i v a l e n t than i n 1970-71, i s about 10$ ( F i g . 3-6). The p r o b a b i l i t y p l o t was c o n s t r u c t e d from a c t u a l Seymour v a l u e s f o r y e a r s a f t e r I960, and back t o 1936 from e s t i m a t e d v a l u e s based on the l i n e a r r e g r e s s i o n r e l a t i o n s h i p , S = 23.98 + 1.07 G w i t h r 2 = O.87 and the s t a n d a r d e r r o r o f the e s t i m a t e = ± 19.3 cm, and where, S = Seymour wa t e r e q u i v a l e n t i n cm G = Grouse water e q u i v a l e n t i n cm From t h i s e v i d e n c e i t i s c o n s i d e r e d t h e two w i n t e r s o f t h i s study are a sample o f a wide range o f l i k e l y snow d e p o s i t i o n and snow a c c u m u l a t i o n c o n d i t i o n s on Mount Seymour. 3.3 The S p a t i a l sample o f snow d e p o s i t i o n measurements T h i s s e c t i o n d i s c u s s e s the s i z e and d i s t r i b u t i o n o f samples used t o o b t a i n e s t i m a t e s o f snow d e p o s i t i o n compat-i b l e w i t h t h e aims o f t h i s t h e s i s . I n the g e n e r a l sense, 51 300 •999 -995-99 -95 •7 -6 -5 -4 -3 Probability 01 -005 •001 F i g . .3.6 P r o b a b i l i t y o f r e c o r d i n g g r e a t e r t h a n g i y e n water e q u i v a l e n t on A p r i l 1 at Seymour Mountain and Grouse Mountain snow c o u r s e s . The p r o b a b i l i t y o f e x c e e d i n g , .a g i v e n water e q u i v a l e n t i s g i v e n a l o n g the h o r i z o n t a l a x i s 52 snow d e p o s i t i o n i s c o n t r o l l e d by m e t e o r o l o g i c a l and top o -g r a p h i c a l f a c t o r s . The i m p o r t a n t m e t e o r o l o g i c a l f a c t o r s are : f r e e z i n g l e v e l , m o i s t u r e s u p p l y , wind speed and d i r e c t i o n , a i r m a s s s t a b i l i t y , and i n some cases antecedent c o n d i t i o n s . The i m p o r t a n t t o g o g r a p h i c a l f e a t u r e s a r e - : e l e v a t i o n , s l o p e , a s p e c t , exposure and v e g e t a t i o n ( Meiman 1968, L e a f 1962, Grant and S c h l e u s n e r 1961). The e f f e c t s o f s l o p e and as p e c t have been reduced by c h o o s i n g a • t e r r a i n segment on Mount Seymour which i s r e l a t i v e l y con-s t a n t w i t h r e s p e c t t o the s e parameters ( P i g s . 2.3, 2.6). 3.3.1 The sample p o p u l a t i o n To o b t a i n . a n e s t i m a t e o f s p e c i f i c snow mass d e p o s i t e d a f t e r each storm, s e p a r a t e e s t i m a t e s o f the means o f the p o p u l a t i o n s o f new snow depth and new snow d e n s i t y were made. These e s t i m a t e s r e f e r s t r i c t l y t o snow d e p o s i t i o n w i t h i n the chosen t e r r a i n segment (the sample p o p u l a t i o n ) . They are p r o b a b l y c l o s e l y r e l a t e d t o snow d e p o s i t i o n s on s i m i l a r t e r r a i n segments elsewhere i n the N o r t h Shore Mountains (a t a r g e t p o p u l a t i o n ) . 3.3-2 The s a m p l i n g scheme R e s u l t s o f p i l o t s t u d i e s , u s i n g l a r g e s i m p l e random samples, i n d i c a t e d t h a t s u b s t a n t i a l v a r i a b i l i t y i n the pop-u l a t i o n s o f new snow depth and d e n s i t y o c c u r r e d w i t h b o t h 53 e l e v a t i o n • a n d p o s i t i o n w i t h i n the f o r e s t . This- suggested t h a t more p r e c i s e e s t i m a t e s o f the two p o p u l a t i o n s were e s s e n t i a l ; t h e y were made w i t h a d o u b l e , s t r a t i f i e d , random s a m p l i n g scheme s i m i l a r , t o t h a t used f o r measurement o f r a i n f a l l by Nkemdirim (1968), and of snow a c c u m u l a t i o n by B a r t o s and Rechard (1973) • The method and advantages o f s t r a t i f i e d random s a m p l i n g are d i s c u s s e d by Cochran (1953) and Preese (1962). E l e v a t i o n was s e l e c t e d as the c r i t e r i o n o f p r i m a r y s t r a t i f i c a t i o n ; the secondary - s t r a t i f i c a t i o n was a c c o r d i n g t o p o s i t i o n w i t h i n the f o r e s t . S i n c e t h i s scheme p r o v i d e s s e p a r a t e e s t i m a t e s f o r each l e v e l o f s t r a t i f i c a t i o n , i t p e r m i t s comparison o f snow d e p o s i t i o n a t - d i f f e r e n t e l e v a t i o n s and a t d i f f e r e n t f o r e s t p o s i t i o n s . I t may a l s o be used t o o b t a i n a r e a l e s t i m a t e s and.hence computation o f the a b s o l u t e mass of snow d e p o s i t e d on the t e r r a i n - s e g m e n t . 3 . 3 . 3 Sampling w i t h e l e v a t i o n ( t h e p r i m a r y s t r a t i f i c a t i o n ) I t was n e c e s s a r y t o d e c i d e at what e l e v a t i o n a l i n t e r v a l samples s h o u l d be t a k e n . Pew papers i n the l i t ^ e r a t u r e d i s c u s s t h i s t o p i c , a l t h o u g h Nkemddrim (1968) s u g g e s t s a 1 0 0-foot i n t e r v a l f o r p r e c i p i t a t i o n gauges i s "adequate". I n Wyoming, B a r t o s and Rechard (1973) found e l e v a t i o n bands of 200 f e e t t o have s i g n i f i c a n t l y d i f f e r e n t snow a c c u m u l a t i o n s . 54 S i n c e f r e e z i n g • l e v e l s g e n e r a l l y i n t e r s e c t the west c o a s t m i d l a t i t u d e mountains;- the t h i c k n e s s o f the at m o s p h e r i c m e l t i n g l a y e r below the f r e e z i n g l e v e l i s l i k e l y t o be an im p o r t a n t f a c t o r i n f l u e n c i n g v a r i a b i l i t y w i t h e l e v a t i o n o f snow d e p o s i t i o n . T h i s i s a consequence o f the r a p i d changes i n snow p r o p e r t i e s which o c c u r i n t h e m e l t i n g l a y e r (Ohtake 1969). P i n d e i s e n (1940) and'Lumb (1963) show t h e depth o f t h i s l a y e r t o be i t s e l f v a r i a b l e , depending on l a p s e r a t e , t ype of snow c r y s t a l and i t s f a l l v e l o c i t y , and i n t e n s i t y o f p r e c i p i t a t i o n . A t l a s e t a l (1967) compute a t h i c k n e s s o f 350 m f o r p r e c i p i t a t i o n i n t e n s i t y 1 mm/hour, and 1900 m f o r i n t e n s i t y 10 mm/hour. Mason (1971) and Wexler (1955) agree t h a t t h i c k n e s s , as measured on weather r a d a r , u s u a l l y ranges between 100 and 200 m. On t h i s e v i d e n c e , 12 s a m p l i n g s i t e s were e s t a b l i s h e d a p p r o x i m a t e l y every 100 m up the mountain t o an e l e v a t i o n o f 1260 m. These are l o c a t e d i n F i g . 2 . 3 , shown diagram-a t i c a l l y i n P i g . 3«7 and l i s t e d i n Table 2 . 1 . The s a m p l i n g s i t e s were not chosen randomly, but- were e s t a b l i s h e d where t h e r e o c c u r r e d a s u i t a b l e open a r e a , and where a c a r c o u l d be c o n v e n i e n t l y p a r k e d o f f the acce s s r o a d . No b i a s i s exp e c t e d from t h i s p r o c e d u r e . The e l e v a t i o n o f each s a m p l i n g s i t e was e x t r a c t e d from a map ( s c a l e 1:12j000) w i t h a 30.5 m (100 f o o t ) c o n t o u r i n t e r v a l , and s u b s e q u e n t l y checked w i t h an a l t i m e t e r . E a c h - i s c o n s i d e r e d p r e c i s e to-±- 6 55. y> THE SAMPLING SITE Secondary stratum - position within forest . I> 3H'- — — ^ \4rJ-3»^ i 1 , Open area Clearing Canopy Beneath T r e e edge canopy T r u n k F i g . 3.7 Diagrammatic r e p r e s e n t a t i o n • o f double s a m p l i n g scheme used, t o e s t i m a t e snow over the t e r r a i n segment s t r a t i f i e d d e p o s i t i o n 56 3.3 .4 Sampling w i t h i n the f o r e s t (the secondary s t r a t i f i c a t i o n ) D u r i n g p r e l i m i n a r y f i e l d work, f e a t u r e s such as snow h o l l o w s beneath t r e e s , d r i f t i n g i n open a r e a s , wind s c o u r , and snow p i l e d a g a i n s t t r u n k s o f t r e e s , were f r e q u e n t l y observed. F u r t h e r , t h e l i t e r a t u r e suggests t h a t c l e a r i n g s r e c e i v e more d e p o s i t e d snow t h a n do open areas (Anderson et a l 1958, C o s t i n e t a l 1961). S l i d i n g o f snow from t r e e s t o the snow s u r f a c e a t t h e canopy edge i s a l s o des-c r i b e d ( M i l l e r 1964, 1966, S a t t e r l u n d and Haupt 1967, Hoover and L e a f 1966). On t h i s e v i d e n c e , f i v e secondary s t r a t a ( o r domains o f s t u d y ) were chosen. These were d e l i n e a t e d at each s a m p l i n g s i t e , and i s o l a t e d i s t i n c t s u b p o p u l a t i o n s where the v a r i a n c e s o f new snow depth and d e n s i t y p o p u l a t i o n s might be homogeneous. The s t r a t a are d e f i n e d below, and are shown d i a g r a m a t i c a l l y i n F i g . 3-7. ( i ) Open areas : c l e a r areas g r e a t e r t h a n t h r e e t r e e h e i g h t s (H) i n d i a m e t e r , w e l l exposed t o p r e v a i l i n g winds. ( i i ) C l e a r i n g s : open areas i n f o r e s t , o n e - q u a r t e r t o t h r e e t r e e h e i g h t s i n d i a m e t e r . ( i i i ) Canopy edge : a r e a i m m e d i a t e l y beneath the edge of the canopy o f i n d i v i d u a l t r e e s . 57 ( i v ) Beneath canopy : a r e a beneath the canopy o f i n d i v i d u a l t r e e s , e x c l u d i n g t h a t i n c l u d e d i n ( v ) . (v) Tree t r u n k s : a r e a w i t h i n one metre o f the t r u n k s o f t r e e s . 3.3-5 S i z e of sample i n the secondary s t r a t u m The s i z e o f sample r e q u i r e d t o e s t i m a t e the means of new snow depth and d e n s i t y must be d e c i d e d b e f o r e e s t i m a t e s o f the mean o f s p e c i f i c snow mass can be o b t a i n e d . The sample s i z e (n) n e c e s s a r y t o e s t i m a t e the.mean of an i n f i n i t e , normal p o p u l a t i o n , t o w i t h i n g i v e n c o n f i d e n c e l i m i t s , u s i n g s i m p l e random s a m p l i n g , i s : n = (a/i) E 2 where c 2 = v a r i a n c e o f p o p u l a t i o n t = v a l u e o f t d i s t r i b u t i o n , p r o b a b i l i t y a E = d e s i r e d c o n f i d e n c e l i m i t s To f i n d n, i t i s n e c e s s a r y t o have e s t i m a t e s S 2 , S 2 o f t h e p o p u l a t i o n v a r i a n c e s o f new snow depth ( a 2 ) and d e n s i t y ( a 2 ) . L i t t l e i s known o f t h e s e v a l u e s , s i n c e they are not r e p o r t e d i n the l i t e r a t u r e . A r e v i e w o f r a i n f a l l measurements does s u g g e s t , however, t h a t a 2 , a 2 might z y v a r y w i t h storm type ( H u f f and Shipp 1969), and w i t h the 58 t e m p o r a l s a m p l i n g I n t e r v a l (Nkemdirim 1968). Based on R u s s i a n measurements o f the t o t a l snowpack, i t seems t h a t a 2 i s c o n s i d e r a b l y g r e a t e r t h a n a 2 (Uryvaev et a l 1965). z y To e s t i m a t e a 2 , a p i l o t s tudy was made i n t h e w i n t e r 1968-69. A f t e r each s t o r m , and at a number o f e l e v a t i o n s , s i x r e p l i c a t i o n s o f new snow d e n s i t y were t a k e n randomly throughout t h e f o r e s t . No secondary s t r a t a were r e c o g n i s e d . S 2 was found t o be unique f o r each s t o r m and f o r each e l e -v a t i o n (Appendix B l ) . I n most c a s e s , s i x d e n s i t y measure-ments t a k e n randomly w i t h i n the f o r e s t would e s t i m a t e t h e mean p o p u l a t i o n d e n s i t y at each e l e v a t i o n t o w i t h i n ±10 kg/m 3 at t h e 90% c o n f i d e n c e l e v e l (Table 3 . 2 ) . I n t h e p i l o t s t u d y , the core from the CRREL snow sampler was weighed w i t h a f i e l d b a l a n c e which had l e s s p r e c i s i o n t h a n the l a b o r a t o r y b a l a n c e used f o r a l l o t h e r d e n s i t y measurements. The r e s u l t i s a l a r g e r measurement e r r o r , which i s i n c o r p o r a t e d i n t o the v a l u e o f S 2. F o r t h i s r e a s o n , and because o f s t r a t -Y i f i c a t i o n o f the samples, i t i s b e l i e v e d t h a t b e t t e r e s t i m a t e s o f p o p u l a t i o n mean d e n s i t y were o b t a i n e d from subsequent d e n s i t y measurements made i n the w i n t e r s 1969-70', 1970-71. I n a n o t h e r e x p e r i m e n t , 12 samples o f new snow d e n s i t y were t a k e n from open areas at one e l e v a t i o n (1260 m). T h i s gave a mean d e n s i t y o f 160 kg/m 3 and s t a n d a r d d e v i a t i o n of ±6 kg/m 3. From t h i s d a t a , o n l y two samples were r e q u i r e d t o e s t i m a t e t h e p o p u l a t i o n mean d e n s i t y t o ±10 kg/m 3 at the 95$ c o n f i d e n c e l e v e l . 59 TABLE 3-2 Sample s i z e r e q u i r e d .to e s t i m a t e p o p u l a t i o n , mean  new snow d e n s i t y throughout the, f o r e s t t o w i t h i n ±10 kg/m 3 at a c o n f i d e n c e l e v e l of 90$. Based on s t a t i s t i c s - o f p i l o t study- (Appendix B l ) Date of Sample E l e v a t i o n (metres) 400 590 790 . 10 6.0'. 1260 11.1.69 3 14.1.69 4 5-.17.1.69 3 21.1.69 4 2 6 3 28.1 .69 6 8 2 5 • 4 .2.69 4 13 5 4 9 .2.69 6 8 8 4 2 11.2.69 9 4 8 . 13 16.2.69 4 4 5 2 .3 .69 4 8 7 7 7-3.69 10 6 4 4 9.3 .69 12 4 5 28.3 .69 2 6.4 .69 4 3 60 I n s e v e r a l i n s t a n c e s , t h e snow s u r f a c e had de v e l o p e d a h a r d c r u s t . T h i s e n a b l e d a l a r g e number of samples o f new snow depth t o be de t e r m i n e d from the- subsequent s n o w f a l l . Such measurements were made i n the secondary s t r a t a - , at s e v e r a l e l e v a t i o n s and a f t e r s e v e r a l storms (Appendix B2) . I t w i l l be noted t h a t S| i s d i f f e r e n t f o r each p o s i t i o n i n the f o r e s t and e l e v a t i o n , a p p e a r i n g t o be more a f u n c t i o n o f storm " c h a r a c t e r i s t i c s . Based on the s t a t i s t i c s o f t h e s e d a t a , the number o f samples r e q u i r e d t o e s t i m a t e the popu-l a t i o n mean new snow depth, i s g i v e n i n T a b l e 3 . 3 . On the whole, e s t i m a t e s t o w i t h i n ±1 cm, at the 95% c o n f i d e n c e l e v e l , c o u l d be made w i t h fewer t h a n s i x samples. The d a t a i n d i c a t e t h a t a l a r g e r sample s i z e s h o u l d be t a k e n at 1260 m. At t h i s e l e v a t i o n , s a m p l i n g s i t e s were exposed, a l l o w i n g f r e q u e n t d r i f t i n g and hence l a r g e v a r i a b i l i t y i n new snow depth. A range o f ±1 cm i n snow depth r e p r e s e n t s a s a m p l i n g e r r o r of ±2 kg/m 2 i n s p e c i f i c snow mass (±2 mm water e q u i v a l e n t ) , as c a l c u l a t e d w i t h new snow d e n s i t i e s u s u a l l y e n c o u n t e r e d on Mount Seymour. Because the v a r i a n c e s of the p o p u l a t i o n s o f new snow depth and d e n s i t y a l t e r w i t h each s t o r m , e l e v a t i o n , and, p o s i t i o n w i t h i n the f o r e s t , i t was d i f f i c u l t t o determine how many samples s h o u l d be t a k e n on a n y - p a r t i c u l a r o c c a s i o n . T h e r e f o r e , i t was d e c i d e d t o t a k e a s e t number of,samples a f t e r each storm. The use o f c o n s t a n t sample s i z e a l l o w s e a s i e r a p p l i c a t i o n o f such t e c h n i q u e s as a n a l y s i s of v a r i a n c e . 61 TABLE 3.3 Sample s i z e r e q u i r e d to. e s t i m a t e p o p u l a t i o n mean  new snow depth' 'to -within ±1 cm, at' a c o n f i d e n c e  l e v e l o f 95% Based on s t a t i s t i c s - of l a r g e samples (Appendix B2) Date o f sample Secondary S t r a t u m • E l e v a t i o n (metres) (Storm no.. ) 790 870 970 10 6,0 1260 19.2 .71 open a r e a 4 (45) canopy edge beneath canopy 9 4 2 .4 .71 open a r e a 3 4 4 5- 5 (61) c l e a r i n g 4 3 4 6 canopy edge 3 4 22 beneath canopy 4 12 7 .4.71 open a r e a 4 6 (62) c l e a r i n g , canopy edge beneath canopy 3 10 . 11 7 12.4.71 open a r e a 4 50 . (64) 62 However, a consequence o f t h i s s t r a t e g y i s t h a t t h e c o n f i -dence l i m i t s , and/or the p r o b a b i l i t y , w i t h w h i c h the sample e s t i m a t e s the p o p u l a t i o n • m e a n , v a r y on each o c c a s i o n . S i x new snow depths and one new snow d e n s i t y measure-ment were made i n each secondary s t r a t u m . An a d d i t i o n a l s e t o f t h e s e measurements was made i n open areas t o a l l o w f o r d r i f t i n g and a l s o because good e s t i m a t e s were impor-t a n t f o r the study of v a r i a t i o n s o f p r e c i p i t a t i o n w i t h e l e v a t i o n . Both t h e p i l o t s t u d i e s and the exp e r i m e n t s w i t h l a r g e samples i n d i c a t e d t h a t the chosen sample s i z e s were r e a s o n a b l e f o r most storms. T h e r e f o r e , f o r each storm w i t h snow t h e r e were d e r i v e d e s t i m a t e s M h s i = Y h s i • z h s i where, i = number o f r e p l i c a t i o n s i n each secondary s t r a t u m . For depth Z, i = 1 , 2 , . . . 6 , except i n open a r e a s , where, i = 1 ,2 , 12. F o r d e n s i t y y, 1 = 1 , except i n open areas where, i = 1 ,2. s = number o f secondary s t r a t a , s = 1 , 2 , . . 5 h = number of s a m p l i n g s i t e s r e c e i v i n g new snow, h = 1,2,...n, where, n < 12. Hence, at each s a m p l i n g s i t e w i t h new snow, 36 new snow "-depth and 6 new snow d e n s i t y measurements were o b t a i n e d , g i v i n g 36 samples o f s p e c i f i c snow mass-for each e l e v a t i o n a l band. 63 The above s a m p l i n g scheme was. used f o r a l l storms i n the w i n t e r 1969-70,. but i t was found i m p r a c t i c a l t o m a i n t a i n t h i s scheme on some o c c a s i o n s i n the w i n t e r 1970-71, when many s u c c e s s i v e • storms d e p o s i t e d snow to-r low :; e l e v a t i o n s . I n the l a t t e r s i t u a t i o n s , complete measure-ments were always made i n open a r e a s , and new snow depths - but not new snow d e n s i t y samples - were n o r m a l l y t a k e n i n the o t h e r f o u r s t r a t a - . Access t o a l l s a m p l i n g s i t e s was by ro.ad, e x c e p t t o the h i g h e s t (1260 m), where access was- by c h a i r l i f t . T h i s d i d not o p e r a t e i n severe weather; i n w h i c h e v e n t , snow measurements at the h i g h e s t s i t e were t a k e n the f o l l o w i n g day. When bad weather was p r o l o n g e d , e s t i m a t e s f o r open areas were made from d a t a b e i n g c o n t i n u o u s l y r e c o r d e d by a snow gauge. 3.4 Measurement o f r a i n f a l l R a i n f a l l was measured i n the open at the 12 s a m p l i n g s i t e s a f t e r each storm. S t a n d a r d f i v e - i n c h d i a m e t e r r a i n , gauges and P l u v i u s gauges were used. I n p l a c e s s u b j e c t t o i n t e r f e r e n c e by the p u b l i c , a s e r i e s o f expendable f i v e -i n c h d i a m e t e r c o f f e e cans was s u b s t i t u t e d . These were c a l i b r a t e d i n d i v i d u a l l y b e f o r e use. F o r p a r t o f the s t u d y , c o n t i n u o u s l y r e c o r d i n g gauges measured- r a i n f a l l i n t e n s i t y at two e l e v a t i o n s . 64 A v a s t l i t e r a t u r e d i s c u s s e s the i n h e r e n t e r r o r s from measuring r a i n f a l l w i t h r a i n gauges. E x h a u s t i v e r e v i e w s are g i v e n by K u r t y k a (.1953) and I s r a e l s e n (.1967). E r r o r s are l a r g e l y o f two typ e s - those caused by i n s t r u -m e n tal s h o r t c o m i n g s and those by poor s i t i n g o f the i n s t r u -ments so as t o l e a d t o u n r e p r e s e n t a t i v e v a l u e s . F u r t h e r , Rodda (1967), and Robinson and Rodda (1969), have shown t h a t the r e l a t i v e c a t c h f o r the same type of gauge may v a r y w i t h l o c a t i o n and season.. I n t h i s s t u d y , r a i n f a l l i n the s t a n d a r d gauges and c o f f e e cans c o u l d be measured t o ±0.13 mm, and t o ±0.5 mm f o r the P l u v i u s gauges. T h i s i s a s m a l l e r measure-ment e r r o r t h a n t h a t f o r s p e c i f i c new snow mass. To as s e s s the sa m p l i n g e r r o r f o r r a i n f a l l , gauges were e s t -a b l i s h e d t h r o u g h o u t open areas at f o u r e l e v a t i o n s . The r e s u l t s from s e v e r a l storms i n d i c a t e a s i n g l e gauge g i v e s a good e s t i m a t e (Table 3 . 4 ) . T h i s s a m p l i n g e r r o r i s a l s o c o n s i d e r a b l y l o w e r t h a n t h a t f o r new snow mass (Appendix B l , , B2) . A l l r a i n gauges were so p o s i t i o n e d t h a t the ' o r i f i c e ' was p a r a l l e l t o the g e n e r a l slope- of the t e r r a i n , as r e c o -mmended by the World M e t e o r o l o g i c a l O r g a n i s a t i o n (1961) . They were not equipped w i t h w i n d s h i e l d s , as recommended f o r mountain are a s by I s r a e l s e n (1967). However, a t low e r e l e v a t i o n s on Mount Seymour open areas are e f f e c t i v e l y 65 TABLE 3.4 S t a t i s t i c s of ..large samples of r a i n f a l l ' i n s e l e c t e d open areas Storm No. Date of E l e v a t i o n Sample Mean S.D. (1970-7D Sample (metres) S i z e (mm) (mm) 10 12.11.70 790 7 68.7 0.7 11 16 .11.70 790 7 34 .1 0.6 66 21. 4.71 490 10 8.0 0.4 67 23. 4 .71 490 10 6.2 0.2 68 30. 4.71 490 10 • 12.4 0.5 68 30. 4.71 220 6 7.3 0.4 70 14. 5.71 330 8 14 . 7 0.5 71 17. 5.71 330 8 9.2 0.6 71 17- 5.71 490 7 11.6 0.4 72 19. 5.71 330 8 18.8 0.5 72 19. 5.71 490 9 21.7 0 .8 73 25. 5.71 330 9 6.6 0.2 73 25. 5-71 490 11 7.3 0.2 66 s h i e l d e d from wind by the s u r r o u n d i n g f o r e s t . . Ab.oye.900. m, exposure t o wind i n c r e a s e s as the f o r e s t t h i n s , so some u n d e r c a t c h would r e s u l t h e r e . Because gauges-were emptied a f t e r each storm, e v a p o r a t i o n l o s s e s were n e g l i g i b l e . 3.5 Measurement of mixed.rain/snow events D u r i n g some s t o r m s , the f r e e z i n g l e v e l and. hence the rain/snow boundary may m i g r a t e up or down the mountain. Thus, b o t h r a i n . a n d snow may o c c u r . D e t e r m i n a t i o n of the amounts o f r a i n - and the amount o f snow a f t e r a mixed r a i n / snow storm remains a major measurement problem o f h y d r o -m e t e o r o l o g y . The s i m p l e p r o c e d u r e s used i n t h i s study have not s o l v e d t h i s problem, but are d e s i g n e d t o m i n i m i s e e r r o r s i n a s s e s s i n g the r e l a t i v e amounts of s n o w f a l l and r a i n f a l l . I f r a i n f e l l a f t e r a p e r i o d o f snow, some, i f not a l l o f it,.-was absorbed by the snow; some c o u l d a l s o p e r c o l a t e t o t h e u n d e r l y i n g o l d snow layers". To ensure t h a t t h i s l a t t e r p o r t i o n was measured, the o r i f i c e o f the r a i n gauge was p l a c e d f l u s h w i t h the o l d snow s u r f a c e . The p o r t i o n o f the r a i n absorbed by the new snow l a y e r r e s u l t e d i n an i n c r e a s e d v a l u e o f new snow d e n s i t y . Thus, t h i s p rocedure a l l o w s the d e t e r m i n a t i o n of t o t a l s t o r m p r e c i p i t a t i o n , but t h e n c r e d i t s excess w a t e r e q u i v a l e n t t o s n o w f a l l a t the expense of r a i n f a l l . 67 I f a storm began with, r a i n , t h e n turned, t o snow, r a i n f a l l was measured i n the r a i n gauge and s n o w f a l l by the p rocedure p r e v i o u s l y d e s c r i b e d . T o t a l p r e c i p i t a t i o n was the sum of the two. I f any s n o w f a l l m e l t e d i t would e n t e r the r a i n gauge and be measured as r a i n f a l l . Thus, t h i s p r o c e d u r e can c r e d i t excess water t o r a i n f a l l at the expense o f s n o w f a l l , However, t h i s e r r o r was l i k e l y t o be s m a l l , s i n c e measurements were made as soon as p o s s i b l e a f t e r the end o f the s t o r m , b e f o r e any a p p r e c i a b l e melt c o u l d b e g i n . 3.6 Measurement o f rime a c c r e t i o n Rime forms on t e r r e s t r i a l o b j e c t s exposed t o wind d r i v e n s u p e r c o o l e d a i r f l o w s . The rime i s a c c r e t e d by f r e e z i n g of s u p e r c o o l e d c l o u d d r o p l e t s as they s t r i k e an exposed s u r f a c e ( L a Ch'apelle 1969). The Mount Seymour w i n t e r environment can p r o v i d e c o n d i t i o n s conducive t o the development of r i m e , but to-a c t u a l l y measure the i n p u t of water i n t h i s form i s d i f f i c u l t , because much i s accumulated on t r e e s or i s mixed w i t h snow-f a l l ' d u r i n g storms. The amount o f rime accumulated on o b j e c t s i s a l s o a f u n c t i o n o f - t h e i r s i z e and shape ( F o w l e r and'Berndt 1971). Here, o n l y an i n d e x o f the i n p u t o f water from rime i s o b t a i n e d by measuring the h o r i z o n t a l l e n g t h of rime a c c r e t e d from storms on s m a l l d i a m e t e r 68 CO .5 cm) s t a k e s p l a c e d v e r t i c a l l y above, the snow s u r f a c e . The d i r e c t i o n of growth. Calways i n t o , the p r e v a i l i n g wind) was a l s o r e c o r d e d f o r each storm. Care was t a k e n t o remove a l l rime from the s t a k e s b e f o r e the next storm. O b s e r v a t i o n s were made at eac h . s a m p l i n g s i t e f o r a l l storms between 6 December 19 70 and 31 May 1971. Few storms w i t h rime o c c u r r e d o u t s i d e o f t h i s p e r i o d , or i n the p r e v i o u s w i n t e r . 3.7 Measurement o f snow co v e r phenology On the t e r r a i n segment, the e l e v a t i o n s o f the snow c o v e r , o f the new snow b l a n k e t a f t e r each storm, and o f snow on t r e e s , were r e c o r d e d by s i x zones d e f i n e d hereunder. O b s e r v a t i o n s were made on each v i s i t t o the mountain. On the average, one v i s i t was made every two or t h r e e days. The e l e v a t i o n s of t h e lower l i m i t s of the s e zones are somewhat s u b j e c t i v e , but c o n s i d e r e d a c c u r a t e t o ±30 m. (a) Complete snow cover.' : the zone i n which the snow c o v e r s more than 90 p e r c e n t of the ground s u r f a c e . The lower l i m i t of t h i s zone i s here c a l l e d the "complete s n o w l i n e " . (b) Incomplete snow co v e r : the zone where some snow i s o b s e r v e d , but g r e a t e r than 10 p e r c e n t of the ground can be seen. I t i n c l u d e s 69 areas where snow h o l l o w s around t r e e s have eocposed the ground s u r f a c e .(cf. Brooke 196.6). The lower l i m i t o f t h i s zone i s here c a l l e d the " i n c o m p l e t e s n o w l i n e " (Hj_) . (c) Complete new snow cover : the zone i n which the new snow from a st o r m covers more than 90 p e r -cent of the s u r f a c e . The lower l i m i t i s the "complete new s n o w l i n e " ( H c ) . (d) Incomplete new snow c o v e r : t h e zone i n which some new snow i s o b s e r v e d , but g r e a t e r t h a n 10 p e r c e n t o f the u n d e r l y i n g s u r f a c e can be seen. The lower l i m i t of t h i s zone, here c a l l e d the " i n c o m p l e t e new s n o w l i n e " and denoted by H Q, i s d e f i n e d as the l o w e s t e l e v a t i o n at which new snow c o u l d be r e c o g n i s e d . '.(A storm, w i t h a ^ f r e e z i n g l e v e l much lower t h a n normal would deposit-new snow below the p r e v i o u s s n o w l i n e s . A f t e r t h i s e v e n t , the e l e v a t i o n s o f the s n o w l i n e s and new s n o w l i n e s would c o i n c i d e ) . (e) Moderate t o heavy snow loads- on t r e e s : the zone i n which a l l p a r t s o f - t h e branches o f t r e e s bore snow. The snow must be s u f f i c i e n t t o n o t i c e a b l y bend the b r a n c h e s . The lower 70 e l e y a t i o n of t h i s zone i s here c a l l e d the "heavy l o a d l i n e " . . U s u a l l y no- . snow would be m e l t i n g from the t r e e s i n t h i s zone. L i g h t snow l o a d s on t r e e s : the zone i n which e i t h e r o n l y p a r t s o f the branches o f t r e e s bore snow, o r the snow l o a d on t r e e s d i d not n o t i c e a b l y bend'the b r a n c h e s . The f i r s t c o n d i t i o n • o f t e n r e s u l t e d from melt d u r i n g a-p e r i o d of sunny weather, o r from a r i s e i n the f r e e z i n g l e v e l d u r i n g a s t o r m , w i t h the subsequent r a i n a l l o w i n g some snow t o melt or s l i d e o f f b r a n c h e s . G e n e r a l l y , t h e snow was borne by the branch stem, not the f o l i a g e . The second c o n d i t i o n r e s u l t e d from a l o w e r i n g o f the f r e e z i n g l e v e l and ra i n / s n o w boundary a f t e r the passage o f a f r o n t . I n th e s e c i r c u m s t a n c e s , s n o w f a l l was o f t e n l i g h t . U s u a l l y , snow r a p i d l y d i s a p p e a r e d from t r e e s i n t h i s zone. The lower l i m i t i s here c a l l e d the " l i g h t l o a d l i n e " . 71 3 .7 Measurement of net snow, a c c u m u l a t i o n Measurement o f snowpack.water e q u i v a l e n t was made w i t h a F e d e r a l snow sampler, which Work et a l (.1964) con-s i d e r t o o v e r e s t i m a t e by an average- 8%. Two or t h r e e samples were t a k e n i n each of the f i v e s t r a t a - d e f i n e d p r e -v i o u s l y , a t each s a m p l i n g s i t e - w h e r e snow was p r e s e n t . Measurements were o b t a i n e d about e v e r y two weeks, but o c c a s i o n a l l y more or l e s s f r e q u e n t l y depending on weather c o n d i t i o n s . A much b e t t e r e s t i m a t e o f snow pack water e q u i v -a l e n t c o u l d have been made by u s i n g a s e r i e s o f snow c o u r s e s ; however, t h i s would have e n t a i l e d a n i m p r a c t i c a l number o f samples. The s u c c e s s i v e measurements of water e q u i v a l e n t were always t a k e n at the same p l a c e , hence they can be compared. These measurements d i f f e r from those of snow d e p o s i t i o n , i n t h a t they are but an i n d e x o f snowpack development, r a t h e r t h a n an e s t i m a t e , o f the p o p u l a t i o n mean wat e r e q u i v a l e n t . Some of the water e q u i v a l e n t measurements at h i g h e l e v a t i o n s i n 1971 were l a t e r found t o be low when compared w i t h t h e i r p r e d e c e s s o r s and w i t h t h o s e at a d j a c e n t e l e -v a t i o n s . I c e l e n s e s produced t h e s e erroneous measurements . because t h e y p r e v e n t e d obtainment o f complete snow c o r e s i n the s a m p l i n g t u b e s . Snowpack d e n s i t i e s computed from t h e s e v a l u e s were a l s o u n d e r e s t i m a t e d . However, snow 72 d e n s i t y i s a more c o n s e r v a t i v e parameter t h a n i s - w a t e r e q u i v a l e n t . . Thus, r e a s o n a b l e e s t i m a t e s of the t r u e d e n s i t y were p o s s i b l e between two dates f o r which snow d e n s i t i e s were c o n s i d e r e d t o be r e l i a b l e . C o n verted v a l u e s o f wat e r e q u i v a l e n t were made w i t h t h e s e e s t i m a t e d d e n s i t i e s and known snowpack d e p t h s . P l o t s o f snow d e n s i t y a g a i n s t time o f season ( e . g . F i g s . 4 . 1 3 , 4.14) were a l s o found u s e f u l i n c h e c k i n g f o r o t h e r erroneous water e q u i v a l e n t measurements. 3.9 Measurement o f a i r temperature To examine the a i r temperature regime on the moun-t a i n , i n c l u d i n g t he e l e v a t i o n of f r e e z i n g l e v e l s , d u r i n g storm p e r i o d s , a network o f s i x temperature r e c o r d i n g s t a t i o n s was e s t a b l i s h e d between 120 m and 1260 m ( F i g . 2 . 3 ) . A i r t e m p e r a t u r e s were r e c o r d e d c o n t i n u o u s l y w i t h C a s e l l a thermohygrographs i n s t a n d a r d Department o f Transport-Stevenson s c r e e n s f o r most o f t h e p e r i o d October t o May f o r two y e a r s , 1969-70 and 1970^71. To c a l i b r a t e the r e c o r d , s t a n d a r d p r e c i s i o n maximum and minimum thermometers were p l a c e d i n each s c r e e n . Temperatures were e x t r a c t e d from the c h a r t s e v e r y two h o u r s , and are c o n s i d e r e d a c c u r a t e t o ±0 .3°C. The s c r e e n s were a t t a c h e d t o w e l l , exposed t r e e t r u n k s , and' c o u l d be r a i s e d or low e r e d t o about one metre above the 73 snowpack surface'. To p r e v e n t the screens, from, f i l l i n g w i t h b l o w i n g snow., t h e y were l i n e d on the i n s i d e w i t h w h i t e n y l o n mesh. D u r i n g most storms i t i s b e l i e v e d t h a t v e n t i l a t i o n was good. E x c e p t i o n s at the h i g h e s t s t a t i o n r e s u l t e d from p e r i o d s of i n t e n s e r i m i n g o r b l i z z a r d con-d i t i o n s . O c c a s i o n a l l y a c l o c k would s t o p , or the f l e x -i b i l i t y o f the b i m e t a l l i c s t r i p would become a l t e r e d , t h r o u g h f o r m a t i o n o f i c e on the thermohygrographs. .These c o n d i t i o n s were e s p e c i a l l y common when the f r e e z i n g l e v e l l owered r a p i d l y a f t e r a p e r i o d o f r a i n . Temperatures d u r i n g storm p e r i o d s o n l y were used f o r a n a l y s i s . At thes e times r a d i a t i o n e r r o r s are l i k e l y t o be n e g l i g i b l e , and v e n t i l a t i o n around t r e e t r u n k s and scr e e n s adequate. Brooke (1966) measured t e m p e r a t u r e s above 1000 m on Mount Seymour w i t h i n a v a r i e t y o f p l a n t communities .and on exposed s i t e s . He r e p o r t s l a r g e d i f f e r e n c e s i n maximum tem p e r a t u r e s d u r i n g sunny weather, but " temperatures are l a r g e l y e q u a l i s e d on o v e r c a s t . d a y s , r e g a r d l e s s of v e g e t a t i o n c o v e r and exposur e " . To examine the f r e e a i r t emperature above the f o r e s t canopy d u r i n g s t o r m s , a c a b l e , w i t h t h e r m i s t o r beads at i n t e r v a l s , was a t t a c h e d t o the CBUT t e l e v i s i o n t ower. The tower i s l o c a t e d on an exposed r i d g e at 870 m and extends more th a n 25 m above the f o r e s t canopy. The h i g h e s t t h e r m i s t o r was at an e l e v a t i o n of about 920 m, 51.3 m above the ground. T h i s t h e r m i s t o r was covered 74 w i t h a l u m i n i s e d .mylar t a p e . The. r e s i s t a n c e .of• the therm-i s t o r was measured on a Wheatstone b r i d g e and R u s t r a k r e c o r d e r , v i a a s w i t c h i n g box, f o r 130 seconds every 2 8 m i n u t e s . D u r i n g each c y c l e , two c o n s t a n t r e s i s t a n c e s ' were s w i t c h e d i n t o the c i r c u i t f o r c a l i b r a t i o n . The v a l u e s o f temperature o b t a i n e d from t h e r e c o r d e r c h a r t s were con-s i d e r e d a c c u r a t e t o ±0.25°C. These measurements were t a k e n throughout most o f the. p e r i o d January t o May, d u r i n g the two w i n t e r s 1969-70 .and 1970-71. There i s good agreement between f r e e a i r temp-e r a t u r e s r e c o r d e d on the t e l e v i s i o n tower at 920 m and tempera t u r e s measured at t h e temperature r e c o r d i n g s t a t i o n at 970 m ( P i g . 3 . 8 ) . The d a t a p r e s e n t e d was drawn at random from 15 d i f f e r e n t s t o r m s . On t h i s e v i d e n c e i t i s assumed t h a t d u r i n g most storms the s c r e e n t e m p e r a t u r e s a c c u r a t e l y r e f l e c t e d t h e f r e e a i r t h e r m a l regime. The 1:1 l i n e i s drawn t o a l l o w f o r a l a p s e r a t e o f 0.7°C/100 m, a mean r a t e f o r Mount Seymour d u r i n g storms (see s e c t i o n 9 . 3 - 2 ) . T h i s l a p s e r a t e a l s o f a l l s w i t h i n the range o f p s e u d o a d i a b a t i c l a p s e r a t e s g i v e n i n t h e S m i t h s o n i a n M e t e o r o l o g i c a l T a b l e s f o r the c o n d i t i o n s o f most storms at about 950 m ( i . e . p r e s s u r e 950 t o 850 mb, tempera t u r e s -10 t o 15°C). 75 15 o CM 01 v L. 3 ** O t_ tl a E <_ 1:1 line allowing for lapse r a te of 0 v 7 ° C / 1 0 0 m 1.5 Air temperature in screen at 970 m F i g . .3.8 S c a t t e r diagram comparing free a i r temperature during storms on CBUT-TV tower at 920-m w i t h -temperatures i n a screen i n the f o r e s t at 970 m, The 1:1 l i n e takes i n t o account.the d i f f e r e n t e l e v a t i o n s of the temperature sensors. Data from 15 storms 76 CHAPTER 4 4. NET SNOW ACCUMULATION Net snow a c c u m u l a t i o n r e p r e s e n t s the end p r o d u c t of d e p o s i t i o n a l and m e l t p r o c e s s e s . Thus any model p r e d i c t i n g snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n and w i t h i n the f o r e s t (when combined w i t h a model of m e l t i n g ) s h o u l d u l t i m a t e l y be a b l e t o e x p l a i n the snowpack v a r i a -t i o n s d i s c u s s e d below. C o n v e r s e l y , a n a l y s i s o f t h e s e snowpack v a r i a t i o n s might suggest p a r t i c u l a r snow-depo-s i t i o n f e a t u r e s t h a t s h o u l d be i n v e s t i g a t e d . T h i s c h a p t e r b e g i n s by documenting t h e b e h a v i o u r o f the s n o w l i n e and the l e n g t h of the snow season on Mount Seymour. Next , •' s p a t i a l and t e m p o r a l v a r i a t i o n s o f net snow a c c u m u l a t i o n are examined, t h r o u g h the f i e l d measurements on the Mount Seymour t e r r a i n segment, and t h r o u g h the l o n g e r p e r i o d o f r e c o r d from N o r t h Shore Mountain snow c o u r s e s . F i n a l l y , b e h a v i o u r of the snowpack d e n s i t y i s d e s c r i b e d . 77 4.1.1 Dates o f f i r s t and l a s t snow on the- ground The dates o f the f i r s t a n d - l a s t s n o w f a l l , and the l e n g t h o f the s n o w f a l l season a t v a r i o u s e l e v a t i o n s , . f o r two w i n t e r s , a r e g i v e n i n Appendix C. Sometimes the date of the f i r s t s n o w f a l l was t h e same at a number o f e l e v a t i o n s . T h i s was a consequence o f a marked l o w e r i n g of the s n o w l i n e by a sto r m a d v e c t i n g much c o o l e r a i r t h a n i t s p r e d e c e s s o r s . At the top o f the mountain-, the f i r s t snow f e l l toward the end o f October i n b o t h 1969 and 1970.. The' dates when snow was l a s t p r e s e n t on the ground, at each s a m p l i n g a r e a are a l s o g i v e n i n Appendix C. These are c o m p a t i b l e w i t h the l o n g term d a t a a v a i l a b l e . D u r i n g 11 y e a r s o f r e c o r d at the Mount Seymour snow course (1113 m), t h e r e was always some snow on the ground on June 1 s t . From 15 y e a r s o f r e c o r d a t t h e H o l l y b u r n Ridge c l i m a t i c s t a t i o n (950 m), snow was always p r e s e n t on the ground at the end o f A p r i l , and d i s a p p e a r e d by the end o f May on 11 o c c a s i o n s . I t p e r s i s t e d i n t o J une, i n the o t h e r 4 y e a r s . Through 9 y e a r s at Mount Seymour (CBUT) the snow m e l t e d c o m p l e t e l y i n A p r i l i n one y e a r , but o t h e r w i s e d i s a p p e a r e d i n May. In an unseasonably c o o l and stormy summer, snow p a t c h e s can s u r v i v e u n t i l the f o l l o w i n g w i n t e r at e l e v a t i o n s above 1200. m (.e.g. as i n 1964, Dr. J.R. Mackay, p e r s o n a l communication). 78 4.1.2 . S e a s o n a l v a r i a t i o n o f s n o w l i n e Large and f r e q u e n t f l u c t u a t i o n s of s n o w l i n e s were a f e a t u r e o f b o t h w i n t e r s s t u d i e d ( P i g s . 4.2, 4.4). F o r the most p a r t , s n o w l i n e p o s i t i o n s were c o n t r o l l e d by the new s n o w l i n e s o f - s u c c e s s i v e storms ( F i g s . 4.1, 4.3). F r e q u e n t l y they were lowered s e v e r a l hundred metres by a storm w i t h a f r e e z i n g l e v e l below t h a t : o f i t s p r e d e c e s s o r s . C o n v e r s e l y , the s n o w l i n e sometimes r o s e r a p i d l y , though l e s s d r a m a t i c a l l y , when melt and r a i n w a s h d u r i n g a warmer th a n u s u a l storm e l i m i n a t e d a t h i n snow c o v e r . F o r t h i s r e a s o n , and because o f v a r i a t i o n s i n snow depth of the e x i s t i n g snowpack w i t h e l e v a t i o n , the complete and incom-p l e t e s n o w l i n e s d i d not always behave s i m i l a r l y . The d i f f e r e n c e s i n the n a t u r e o f the i n p u t t o the snowpack at each e l e v a t i o n i n the two w i n t e r s ( F i g s . 4.1, 4.3), produced marked c o n t r a s t s i n snowcover. I n the w i n t e r 196.9-70, the complete s n o w l i n e was u s u a l l y c l o s e t o 1000 m. T h i s was almost 500 m h i g h e r t h a n the f o l l o w i n g y e a r , when i t descended t o s e a ^ l e v e l on f o u r o c c a s i o n s . However, the s n o w l i n e s seldom p e r s i s t e d at the same e l e v a -t i o n f o r p e r i o d s g r e a t e r than t e n days. From the end o f A p r i l , the s n o w l i n e s began t o r i s e s t e a d i l y i n p a r a l l e l f a s h i o n as melt p r o c e e d e d , and t h e r e were fewer new i n p u t s o f snow. I n the w i n t e r o f 1969-70,. they r o s e at a r a t e of 5.6 m/day. I n 1970-71, the r a t e Occurrence of rain storm 1200 -1000-1 ¥ <u E c o v« o > 4> 800-J 600 ' t I i I I I I I I • 400-200H 1 • 1 1 1 1 1 1 D • . 1 • • 1 1 t I 1 R a i n storm Complete new Snowcover Incomplete new Snowcover et 1 t I • i , I i I • I • i 1 II t i II i» i II* Hi »• I 1 Winter 1969-70 OCT NOV DEC JAN MONTH FEB M A R APR MAY F i g . 4 . 1 E l e v a t i o n a l coverage of new snow at end o f each storm w i n t e r 1969-70 9 F i g . 4.2 S e a s o n a l v a r i a t i o n ' of- s n o w l i n e s w i n t e r 1969-70 co o Occurrence of rain storm 1200 H 1000 800 -A t_ ib •*-* 4) E C g a > US 600 H 400 H 200 H • Rain storm Complete new Snowcover j incomplete new 1 Snowcover I OCT NOV I i i . ! i • ' i i i Winter 1970-71 DEC JAN FEB MAR APR MAY MONTH F i g . 4.3 E l e v a t i o n a l coverage of new snow at end of each storm, w i n t e r 1970-71 - p " : 1 r-' "T* I | I NOV D E C JAN F E B MAR APR MAY J U N M O N T H F i e . 4.4 S e a s o n a l v a r i a t i o n of s n o w l i n e s w i n t e r 1970-71 co 83 of r i s e , beginning from an elevation- 400. m lower., was 6.5 m/day. This compares with, a r i s e of. 21 m/day, f o r the "equivalent snowline" of Court' (.196.3), i n the.King's R i v e r B a s i n , C a l i f o r n i a , and 10 m/day i n the Eastern Alps (Landsberg 1958). Let a melt degree day be defined as a day wi t h maximum temperature 1°C above f r e e z i n g at 1260 m. Then there was an average of 5.1 melt degree days/day i n May 1970, and 6.0 melt degree days/day i n May 1971. C o i n c i d e n t a l l y , from t h i s data, the r a t e ' o f r i s e of the snowlines was found t o be the same f o r both w i n t e r s , 1.1 m/melt degree day. 4.1.3 Season and dur a t i o n of snow cover The snow season (period between f i r s t and l a s t snow on the ground), and d u r a t i o n ( a c t u a l number of days with snow on the ground) at s e v e r a l e l e v a t i o n s f o r two winters are given i n Appendix C, and p l o t t e d i n F i g s . 4.5, 4.6. Both are s u b s t a n t i a l l y greater at a l l e l e v a t i o n s i n the winter 1970-71. Since snowpacks on t h i s we'.st coast mountain are deep, they p e r s i s t f o r 7 months or more at e l e v a t i o n s above 1200 m. In another area f o r which; s i m i l a r data i s a v a i l a b l e , the Eastern European A l p s , t h i s does not occur u n t i l an e l e v a t i o n some 800. m higher (Geiger 1965) . In the years of t h i s study, the d u r a t i o n was u s u a l l y considerably l e s s than the snow season, 8 F i g . 4 . 6 Snow cover phenology, w i n t e r 1970-71 \ 85 because o f m i d - w i n t e r -melt p e r i o d s . At h i g h e r e l e v a t i o n s , t h i s d i f f e r e n c e decreased,, e s p e c i a l l y i n the. c o l d e r w i n t e r o f 1970-71. I n g e n e r a l , t h e snow cover phenology parameters i n F i g s . 4 . 5 , 4.6 behaved i r r e g u l a r l y w i t h e l e v a t i o n , e x cept f o r t h e d u r a t i o n of the complete snow c o v e r . T h i s curve tended t o f l a t t e n at lower- e l e v a t i o n s . Here the d u r a t i o n was c o n s t r a i n e d by the s m a l l number of storms p r o d u c i n g snow. At h i g h e r e l e v a t i o n s , t h e d u r a t i o n was a l s o con-s t r a i n e d i n s p r i n g and e a r l y summer by an .-increase i n the energy a v a i l a b l e f o r m e l t . There are two reas o n s f o r t h i s i n c r e a s e . F i r s t , the amount of in c o m i n g short-wave r a d i a -t i o n grows l a r g e r i n May and June as the days'grow l o n g e r , and as h i g h p r e s s u r e r i d g e s and c l e a r s k i e s b e g i n t o dominate the Vancouver weather (Kendrew and K e r r 1955, Walker 1961). S e c o n d l y , f o r most o f the w i n t e r , t h e r e are f r e q u e n t f a l l s o f new snow ( F i g s . 4 . 1 , 4 . 3 ) , so the snow s u r f a c e u s u a l l y has a h i g h a l b e d o ( v a l u e s o f 0.80 t o 0.90 are g i v e n f o r new snow i n U.S. Army 1956). I n s p r i n g , f a l l s o f new snow become i n f r e q u e n t o r cease and c o n s e q u e n t l y , more o f t h e g r e a t e r i n c o m i n g shortwave r a d i a t i o n w i l l be absorbed. The r e s u l t i s i l l u s t r a t e d i n F i g . 4.7 which shows t h a t the d u r a t i o n o f t h e complete snow c o v e r d i d not exceed 250 days d e s p i t e t h e magnitude o f t h e maximum w i n t e r w ater e q u i v a l e n t . F i g . , 4.7 R e l a t i o n s h i p between d u r a t i o n of complete snow cover and w i n t e r maximum of snowpack water e q u i v a l e n t 87 A system where, c o n s t r a i n t s , a c t ..to.' impose l i m i t s on growth at lower and upper p o i n t s , can be. r e p r e s e n t e d by the s i g m o i d growth f u n c t i o n CLotka 1956). When f i t t e d t o the d u r a t i o n d a t a i t has the form: D = C 1 + ,e- K(H-H d) where D • = d u r a t i o n o f complete snow cover (days) C = v a l u e of maximum d u r a t i o n (days) e = ' base of n a t u r a l l o g a r i t h m K =. co n s t a n t ( t h i s i s r e l a t e d t o r a t e o f i n c r e a s e of d u r a t i o n w i t h e l e v a t i o n ) H = e l e v a t i o n (metres) = e l e v a t i o n c o r r e s p o n d i n g t o the most r a p i d r a t e o f change of d u r a t i o n (metres) For 1969-70s the r e s u l t a n t e q u a t i o n found by i n f o r m a l t r i a l and e r r o r methods was, D , = 230  1 + e-0.010(H-990). and f o r 1970-71 d a t a , D = 210 1 + e-0..00.6 (H-560). 88 These f i t t e d f u n c t i o n s gaye r e a s o n a b l e r e s u l t s ( F i g s . 4.5,-4.6), except above 10 0.0. m i n 1971. • T h i s anomaly r e s u l t e d because June 1971, was one o f t h e ' c o o l e s t , c l o u d i e s t months on r e c o r d . T h i s meant the d u r a t i o n o f t h e r e m a i n i n g h i g h e l e v a t i o n snow co v e r was not under the same, p r e v i o u s l y d e s c r i b e d , c o n s t r a i n t as u s u a l a t t h i s time of y e a r . The a n a l y s i s suggests t h a t the maximum d u r a t i o n of the snow c o v e r . (C) i s n o r m a l l y i n the v i c i n i t y o f 210-230 days f o r Mount Seymour. 4.2 S e a s o n a l v a r i a b i l i t y o f the snowpack 4.2.1 V a r i a b i l i t y of snow course r e c o r d s The snow co u r s e s of t h e N o r t h Shore Mountains n o r m a l l y b u i l d . s t e a d i l y t o a maximum i n May, t h e n r a p i d l y b e g i n t o melt (Appendix D, F i g . 3-5). I f i t i s assumed the snowpack b e g i n s t o b u i l d i n e a r n e s t i n mid December, then the mean r a t e o f i n c r e a s e u n t i l F e b r u a r y at Mount Seymour (1113 m) i s 2.41 cm o f water e q u i v a l e n t / d a y . Between F e b r u a r y and May the average, r a t e o f i n c r e a s e i s 0.87 cm/day. Average r a t e of melt i s 0.93 cm/day i n the f i r s t h a l f of May, i n c r e a s i n g t o 2.18 cm/day i n the second h a l f . However, th e s e r a t e s can a l t e r markedly from month t o month and y e a r t o y e a r . F o r ex;ample, i n 1964, t h e snowpack c o n t i n u e d t o b u i l d u n t i l at l e a s t 89 June 1 s t . I n some o t h e r y e a r s , the maximum has been re a c h e d by A p r i l r a t h e r t h a n May. O c c a s i o n a l l y , the snow-pack may decrease r a t h e r t h a n i n c r e a s e i n the months p r i o r t o A p r i l . The s t a n d a r d d e v i a t i o n s o f water e q u i v a l e n t at Mount Seymour over an 11 y e a r p e r i o d are at l e a s t one q u a r t e r o f the mean, f u r t h e r i l l u s t r a t i n g the s u b s t a n t i a l v a r i a b i l i t y from y e a r t o y e a r (Table 4.1). T h i s v a r i -a b i l i t y i n c r e a s e s w i t h the s e a s o n , because maximum a c c u m u l a t i o n i s r e a c h e d i n d i f f e r e n t months i n d i f f e r e n t y e a r s . On t h e N o r t h Shore Mountains the h i g h e s t water e q u i v a l e n t r e c o r d e d i n A p r i l (snowpack c l o s e t o maximum) was 371 cm at Loch Lomond, and the l o w e s t , 38 cm, at Grouse Mountain (Appendix D). At a l l snow .courses,, the extreme range of A p r i l 1 s t water e q u i v a l e n t s i s g r e a t e r t h a n 140 cm. 4 . 2 . 2 V a r i a b i l i t y o f f i e l d o b s e r v a t i o n s V a r i a t i o n s o f snowpack water e q u i v a l e n t t h r o u g h o u t the two w i n t e r s 1969-70, 1970-71 are p l o t t e d a t a number of e l e v a t i o n s ( o r s a m p l i n g s i t e s ) f o r a l l secondary s t r a t a , i n P i g s . 4 . 8 , 4 . 9 . The . :pl'ots i l l u s t r a t e - - t h a t t h e s t e a d y b u i l d u p o f the snowpack may be i n t e r r u p t e d by m i d w i n t e r melt p e r i o d s Cas f o r example..in w i n t e r 1 9 6 9 - 7 0 ) , and'by the r a p i d m e l t of the pack, toward t h e end o f the season. 90 TABLE 4.1 Mean, s t a n d a r d d e v i a t i o n and c o e f f i c i e n t o f v a r i a t i o n s  o f m o nthly water e q u i v a l e n t (cm), .Seymour  Mountain-snow course,' 1960-1970 C o e f f i c i e n t of v a r i a t i o n o f snow d e n s i t y g i v e n f o r comparison MONTH Water E q u i v a l e n t D e n s i t y me an s t . d e v . C.V. % C.V. % Feb 1 111 32 29 12 Mar 1 141 35 ' 25 18 Apr 1 1-62 54 33 14 May 1 188 59 31 11 May 15 174 -56 32 9 Jun 1 140 68 49 6 TABLE 4.2 Summary s t a t i s t i c s o f water e q u i v a l e n t (cm)  on A p r i l 1 f o r p e r i o d 1960-1970> N o r t h Shore Mountain snow courses Snow course E l e v a t i o n Cm) me an s t .dev. C.V. % Grouse Mountain 1158 133 48 36 Mount Seymour 1113 - 162 54 33 Dog Mountain 10 82 127 45 35 H o l l y b u r n 1022 159 52 33 Loch Lomond 1097 115 47 41 P a l i s a d e . L a k e - 884 153 55 36 Source: Computed from d a t a i n " B . C . Snow Survey B u l l e t i n s " , V i c t o r i a , B r i t i s h Columbia-. 91 180 140 100 5 O C T NOV D E C J A N FEB MAR M O N T H A P R MAY J U N 8 0 3 c r 6 0 -\ 2 0 - \ 1060 m C l e a r i n g s O p e n A r e a s NOV D E C J A N 1 1 " — T -F E B MAR A P R MAY J U N M O N T H E 40 u c V a cr . UJ L. V o 5 0 9 7 0 m /ANn . NOV .DEC ' J A N ' F E B ' MAR A P R ' MAY J U N M O N T H P i g . 4.8 Snowpack water e q u i v a l e n t i n open and s t r a t a f o r v a r i o u s e l e v a t i o n s , w i n t e r i n t he f o r e s t 1969-70 92 260 DEC JAN FEB MAR APR MONTH MAY JUN JUL MONTH F i g . 4.9 Snowpack' water e q u i v a l e n t i n open and i n the- f o r e s t s t r a t a f o r v a r i o u s e l e v a t i o n s , w i n t e r 1970-71 160 93 970 m 120 H 80 40 • c S> 0 t_ 120 v 870 m Estimate based upon known depth and assumed density, -o Open Areas a 5 -» -f C learings + . _ . 1- Canopy Edge S : <i Beneath Canopy 80 A 40 H -A Close to Tree Trunks DEC JAN FEB MAR APR MONTH MAY JUN DEC JAN FEB MAR MONTH F i g . . 4:.9 C o n t i n u e d . . APR MAY JUL 94 The Seymour Mountain- snow course, c o n s i s t e n t l y r e c o r d e d g r e a t e r snow a c c u m u l a t i o n s t h a n measurements of t h i s study made at a s i m i l a r e l e v a t i o n on the t e r r a i n -segment . ...However, the snow course i s s i t e d on a s h e l t e r e d p a r t o f the mountain, and p r o b a b l y r e c o r d s ' water e q u i v a l e n t s g r e a t e r than normal f o r i t s e l e v a t i o n . For example, i t c o n s i s t e n t l y r e c o r d s v a l u e s g r e a t e r t h a n those at Grouse M o u n t a i n , which i s 45 m h i g h e r and o n l y 8.3 km t o the west (Table 4 .2 , Appendix D). 4.3 V a r i a t i o n s of net snow a c c u m u l a t i o n w i t h e l e v a t i o n 4 .3 .1 Snow course o b s e r v a t i o n s Mean wa t e r e q u i v a l e n t s at snow co u r s e s on d i f f e r e n t N o r t h Shore Mountains - show no t r e n d w i t h e l e v a t i o n when t h e i r complete r e c o r d s are c o n s i d e r e d (Appendix D), nor even when a common p e r i o d o f r e c o r d i s examined (Table 4 . 2 ) . T h i s suggests t h a t the e f f e c t o f e l e v a t i o n i s masked by v a r i a t i o n s due t o o t h e r f a c t o r s . D i f f e r e n c e s o f snow a c c u m u l a t i o n o f 2-1.38$ have been r e p o r t e d w i t h aspect a l o n e (Meiman 1968). P a c k e r C1962, Idaho) shows.a l i n e a r i n -c r e a s e o f 1.0 4 cm per 10$. .decrease -in f o r e s t canopy. L u l l and Rushmore C1960,. New York) giye. y a l u e s o f 0.84 cm and K i t t r e d g e (1953, C a l i f o r n i a ) v a l u e s from 1.27 t o 5-59 cm, p e r 10$ change i n crown d e n s i t y f o r v a r i o u s t r e e s p e c i e s . 95 Anderson and Pagenhart .0-957, C a l i f o r n i a ) showed t h a t , aside, from e l e v a t i o n , s o l a r energy r e c e i v e d , and. f o r e s t v a r i a b l e s were a l s o i m p o r t a n t p a r a m e t e r s . I n c o a s t a l i B r i t i s h Columbia d i s t a n c e from the sea a f f e c t s l o c a l • t emperature:and weather m a r k e d l y , so t h a t l a r g e v a r i a t i o n s i n snow a c c u m u l a t i o n can o c c u r over s h o r t d i s t a n c e s . 4.3.2 F i e l d o b s e r v a t i o n s Snowpack. water e q u i v a l e n t f o r open areas t h r o u g h -out the two w i n t e r s was a d j u s t e d t o the f i r s t day o f each month and p l o t t e d as a f u n c t i o n of e l e v a t i o n ( F i g . 4.10).. ( I t s h o u l d be n o t e d t h a t , f o r c l a r i t y , the w ater e q u i v a l e n t s c a l e i n 1969-70 was made t w i c e t h a t i n 1970-71). V a l u e s at 1260 m seem anomalous, because the s a m p l i n g s i t e was on a v e r y exposed knob. However, they are r e t a i n e d because such a s i t e i s t y p i c a l o f l a r g e areas o f the upper p a r t o f the mountain. S i m i l a r p l o t s f o r the W i l l a m e t t e B a s i n , Oregon (U.S. Army, 1956, F i g . 1, P l a t e 3.3), suggest water e q u i v -a l e n t ( y - a x i s ) i n c r e a s e d l i n e a r l y w i t h e l e v a t i o n ( x - a x i s ) from th e s n o w l i n e . The l i n e • r e p r e s e n t i n g t h i s l i n e a r r e l a t i o n s h i p t o g e t h e r w i t h the x-ax;is, formed a "snow-Wedge" . The o r i g i n a l data- p o i n t s were not shown, and no i n d i c a t i o n g i v e n of goodness o f - f i t . The Mount Seymour d a t a a l s o d i s p l a y t h i s snow-wedge form ( F i g . 4.10). a l t h o u g h the 96 100 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1 1 0 0 1 2 0 0 1 3 0 0 E l e v a t i o n ( m e t a r s ) 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1100 12 0 0 13 0 0 Elevation (metars) 4.10 V a r i a t i o n • of • .snowpack water e q u i v a l e n t with.' elevation,--; on t h e f i r s t day of each month, open a r e a s , f o r w i n t e r s 1969-70 ( t o p and-1970-71 (bottom). TABLE 4.3 Rate o f change of snow a c c u m u l a t i o n w i t h e l e v a t i o n Some examples r e p o r t e d i n the l i t e r a t u r e LOCATION E l e v a t i o n Range' (metres) Rate o f Change '- (cm water equiv/100 m) SOURCE C a l i f o r n i a 2500-3420 10 .2 Court (1963) C a l i f o r n i a 1770-2190 18.3 M i x s e l l et a l (1951) A l b e r t a 1520-1680 12 .9 S t a n t o n (1966) C o l o r a d o 2490-3260 22.0 U.S. S o i l C o n s e r v a t i o n S e r v i c e (1965-67) New Mexico 3020-3380 4.5 Gary and C o l t h a r p (1967) Idaho 820-1680 8.9 Packer (1962) Ben Ohau Range, N.Z. 975-1646 18.1 * A r c h e r (1970) Tasman G l a c i e r , N.Z. 1020-2340 73.4 N.Z. Hydrology Annual (1968) W i l l a m e t t e - B a s i n 647-1500 25.0 U .'S. Army (1956) Mount Seymour 0-1260 54.0 T h i s study * Based on depth o f snow, not water e q u i v a l e n t —a 98 wedges are not as s i m p l e as tho s e r e p o r t e d f o r the W i l l a m e t t e B a s i n . j As a r u l e , t h e s l o p e o f • the'-'snow wedge became l a r g e r d u r i n g the a c c u m u l a t i o n s e a s o n , but remained f a i r l y c o n s t a n t d u r i n g the melt p e r i o d . The snow-wedge behaved s i m i l a r l y i n the W i l l a m e t t e B a s i n (U.S. Army 1956, P l a t e 3-3, F i g . 2). The i n c r e a s e s o f snow accumu-l a t i o n w i t h e l e v a t i o n on Mount Seymour were much g r e a t e r t h a n r e p o r t e d f o r o t h e r a r e a s i n N o r t h A m e r i c a (Table 4.3). 4.4 V a r i a t i o n s o f snow a c c u m u l a t i o n w i t h i n the f o r e s t T h i s s e c t i o n d i s c u s s e s f i e l d measurements, comments on some s p e c i a l f e a t u r e s , and t e s t s f o r d i f f e r e n c e s i n snow a c c u m u l a t i o n between t h a t i n the f o r e s t s t r a t a from t h a t i n open a r e a s . 4.4.1 Snow i n c l e a r i n g s The amount of snow i n c l e a r i n g s was not s i g n i f i -c a n t l y g r e a t e r t h a n t h a t i n open a r e a s , at a n y - e l e v a t i o n sampled. The r e s u l t s of " t " - - t e s t s are given, i n Table 4.4.. These r e s u l t s c o n t r a s t w i t h r e p o r t s from o t h e r environments (.Anderson e t a l 1958, C o s t i n e t a l 196l;) . P o s s i b l e reasons f o r t h i s c o n f l i c t are : 99 TABLE 4 . 4 . Mean water, e q u i v a l e n t I n open areas compared  with: mean wa t e r e q u i v a l e n t i n f o r e s t s t r a t a - r e s u l t s o f " t " - t e s t W i n t e r F o r e s t S t r a t a E l e v a t i o n (metres) 1260 10 6.0 970 870". 790 . 710 590 1969-70 c l e a r i n g s ns ns ns — — — — canopy edge * ns- - - - -beneath canopy * * - • - -c l o s e t o t r e e t r u n k s s * * . - - -1970-71' c l e a r i n g s ns ns ns ns ns ns ns canopy edge ns ns ns ns ns ns ns beneath canopy ns * ns ns ns * * c l o s e t o t r e e t r u n k s ns * * * * * i ) The " t " - t e s t examines the n u l l h y p o t h e s i s t h a t ]i open = u f o r e s t s t r a t a where u = p o p u l a t i o n mean water e q u i v a l e n t . i i ) ns = no s i g n i f i c a n t d i f f e r e n c e found between p o p u l a t i o n means. * = s i g n i f i c a n t d i f f e r e n c e found between p o p u l a t i o n means (95% c o n f i d e n c e l e v e l ) . ( i i i ) Number o f p a i r e d o b s e r v a t i o n s v a r i e d between 9 and, 14. ( i v ) The v a r i a n c e between p a i r e d samples were homo-geneous, i n a l l cases except f o r , t h o s e comparisons between open areas and t r e e t r u n k s at t h e lower e l e v a t i o n s . Here t h e method o f " t " - t e s t s w i t h unequal v a r i a n c e s was used. ( S t e e l and T o r r i e I960, p.8l). Notes 100 (a) The d e n s i t y of f r e s h l y f a l l e n snow on Mount Seymour i s h i g h (Chapter 6 ) . T h e r e f o r e , t u r b u l e n c e above c l e a r i n g s i s ' l e s s e f f e c t i v e i n d r i f t i n g snow. (b) I n s e v e r a l of t h e s t u d i e s r e f e r r e d t o above, the snowpack was sampled a t , or a f t e r , maximum a c c u m u l a t i o n . F i g s . 4.8, 4.9 i n d i c a t e t h a t snow a c c u m u l a t i o n becomes g r e a t e r i n c l e a r i n g s o n l y d u r i n g the l a t t e r p a r t o f the season, and i s not marked d u r i n g t h e p e r i o d when the snow-pack i s b u i l d i n g up. T h i s s u g g e s t s t h a t p r o c e s s e s connected w i t h m e l t i n g are more i m p o r t a n t t h a n those o f d e p o s i t i o n ' i n p r o -d u c i n g a g r e a t e r snowpack i n c l e a r i n g s . : These r e s u l t s may have l e s s v a l i d i t y at 970 m, and below 790 m, where the open area s sampled were not s u b s t a n t i a l l y g r e a t e r t h a n f o u r t r e e h e i g h t s i n .diameter, and so may have behaved as l a r g e c l e a r i n g s . Snow always remained l o n g e r i n c l e a r i n g s t h a n i n open areas ( F i g s . 4.8, 4.9). 4.4.2 Snow i n o t h e r f o r e s t s t r a t a I n 1970-71', water e q u i v a l e n t s at t h e canopy edge, and o c c a s i o n a l l y beneath the canopy, were not s i g n i f i c a n t l y I 101 d i f f e r e n t , from t h a t i n t h e open,. (The r e s u l t s , o f t h e " t " - t e s t s are g i v e n i n T a b l e 4.4.) I n the winter. 196.9!-70 t h e r e were s i g n i f i c a n t d i f f e r e n c e s , because w e l l d e f i n e d h o l l o w s i n the snow about the t r u n k s o f t r e e s d e v e l o p e d e a r l y i n the season, and p e r s i s t e d a t a l l e l e v a t i o n s . These h o l l o w s became pronounced o n l y toward the end' o f t h e w i n t e r 1970-71 ( P i g s . 4.8, 4.9). 4.4.3 Snow h o l l o w s The h o l l o w s r e f e r r e d t o above are c a l l e d snow h o l l o w s ( F i g . 4.11) and h a v e - p r e v i o u s l y - b e e n d e s c r i b e d on Mount Seymour by Brooke (1966). They are caused by i n t e r c e p t i o n o f snow by t r e e crowns, wind s c o u r , melt about the t r e e t r u n k i n d u c e d by l o n g wave r a d i a t i o n from the t r e e , and' p r e f e r e n t i a l melt beneath the canopy. P r e f e r e n t i a l melt r e s u l t s because the albedo of the snow s u r f a c e i s de.creased by melt d r i p and n e e d l e s f a l l i n g from the t r e e f o l i a g e . H o l l o w s can be a c c e n t u a t e d when i n t e r c e p t e d snow s l i d e s o f f a t r e e t o form a r a i s e d r i m beneath the p e r i p h e r y o f the canopy. Each p r o c e s s assumes d i f f e r e n t i m portance depending on the n a t u r e and time o f the w i n t e r . Snow h o l l o w s appear t o be a d i s t i n c t i v e f e a t u r e o f a west coas't m i d l a t i t u d e mountain environment., e s p e c i a l l y • i n m i l d e r w i n t e r s such as 1969-70 .. They are' u s u a l l y 102 F i g . 4.11 Snow h o l l o w s i n mid-season ( t u p , e l e v a t i o n 1000 m, January 1969) and l a t e i n season (bottom, e l e v a t i o n 1100 m, A p r i l 1969) 103 p r e s e n t Immediately above the s n o w l i n e , where new snow i s most e f f e c t i v e l y i n t e r c e p t e d by t r e e crowns and melt p r o c e s s e s are dominant. As t h e season p r o g r e s s e s , snow h o l l o w s develop a t p r o g r e s s i v e l y h i g h e r e l e v a t i o n s on the mountain. 4.4.4 Wind s c o u r I n t h e c o l d e r , s n o w i e r w i n t e r of 1970-71, t h e d i s -t r i b u t i o n o f d e p o s i t e d snow was s t r o n g l y a f f e c t e d by the wind at e l e v a t i o n s above 1000 m. Prom F e b r u a r y t o A p r i l , wind s c o u r i n g e x c a v a t e d h o l l o w s , o f t e n g r e a t e r t h a n one metre deep, beneath the t r e e canopy edge ( F i g . 4.12) and snow was p i l e d a g a i n s t the t r u n k s o f t r e e s . C o nsequently snow a c c u m u l a t i o n d i s t r i b u t i o n w i t h i n the f o r e s t d i s -p l a y e d a d i f f e r e n t p a t t e r n t h a n a t lo w e r e l e v a t i o n s , pr th a n i n t h e p r e v i o u s , m i l d e r w i n t e r ( F i g . 4.9). 4.5 Snowpack d e n s i t y I n t h i s s e c t i o n , snow course and f i e l d o b s e r v a t i o n s are examined t o as s e s s the v a r i a b i l i t y o f snow d e n s i t y . I n many s i t u a t i o n s i t i s e a s i e r t o measure depth r a t h e r t h a n t h e water e q u i v a l e n t o f the snowpack. Water e q u i v -a l e n t s may be computed i n such cases i f e s t i m a t e s can be made o f snowpack d e n s i t y . D e n s i t y i s a l s o a u s e f u l 104 F i g . 4.12 Wind s c o u r about t r e e s d u r i n g March 1971 at 1260 m. Bottom photograph i s a c l o s e - u p view o f a wind s c o u r h o l l o w . 105 parameter f o r assessing c e r t a i n mechanical and thermal p r o p e r t i e s of snow OB.ader 196.2).. 4 . 5 . 1 Seasonal and y e a r l y v a r i a t i o n s of snowpack density During the winters of t h i s study, snowpack density tended to increase through the season ( F i g . 4 . 1 3 ) , although temporary decreases i n the density were introduced by sus-t a i n e d periods of heavy sn o w f a l l (e.g. A p r i l 1970, February-1971) . The longer p e r i o d of record from the North Shore Mountain snow courses a l s o shows a steady increase (Appendix D). As i n d i c a t e d by Seymour Mountain data, the v a r i a t i o n s from year to year i n snowpack density i s l e a s t during the melt p e r i o d ( F i g . 4.14). At t h i s time the snowpack tends towards a l i m i t i n g d e n s i t y of about 600 kg/m3. Further increases i n density can only be made by f i r n i f i c a t i o n , a process h a l t e d by melt of the snowpack. The l a r g e r standard d e v i a t i o n s of the accumulation p e r i o d r e f l e c t the v a r i a b i l i t y of input of deposited snow i n t o the snowpack. The density of new snow may range from 100 to 400 kg/m 3, depending on storm c h a r a c t e r i s t i c s (Chapter 6 ) . In a d d i t i o n , r a i n or melt periods may occur at t h i s time of year i n some w i n t e r s . This was the s i t u a t i o n p r i o r to March 1 1970,. when the density at the Mount Seymour snow course was 42.3 kg/m3. By c o n t r a s t , the period p r i o r to March 1971, when the den s i t y was 352 kg/m 3, was 106 600-500 H E ~^400-o a 300-200-- i • ' " — r 1 — f I I i /i i1 X ^ x : ' i ' \ 1 i / i ' & I A i y° 3 ^ * I ' / V* 0 6\ / // / \ x / Z>4\ / 1 &i \ \ n a 1 2 6 0 m i \\\\ 4 \W X 1 1 1 3 m . M o u n t S e y m o u r S n o w C o u r s e -A 1 0 6 0 m • 9 7 0 m DEC JAN FEB MAR APR MAY JUN 600 500 e> 400 Q 300 200 T~~T ,5 ' O ' A + v O A % 9 x Q o • 2 • O X 1113 M o u n t S e y m o u r S n o w C o u r s e • 9 7 0 m • 8 7 0 m O 7 9 0 m A 7 1 0 m + 5 9 0 m DEC ~~1 JAN 1 FEB 1 MAR 1 APR 1 MAY ~~R JUN MONTH P i g . 4.13 -Density of snowpack i n open areas i n w i n t e r 1969-70 ( t o p ) and w i n t e r 197.0-71 Cbottom) 107 c h a r a c t e r i s e d by, few .melt p e r i o d s , and a l a r g e number- o f c o l d show storms d e p o s i t i n g low .density snow. The s e a s o n a l p a t t e r n o f snow d e n s i t y v a r i a b i l i t y i s d i f f e r e n t from t h a t o f snow water e q u i v a l e n t (see T a b l e 4 . 1 f o r c o m p a r i s o n ) . Snow d e n s i t y v a r i e s l e s s as mel t p r o g r e s s e s and i s a l s o t he more c o n s e r v a t i v e parameter. T h i s s m a l l s e a s o n a l v a r i a b i l i t y o f snowpack d e n s i t y has a l s o been n o t e d by F i n d l a y and M cKay (1972). Thus good e s t i m a t e s o f water e q u i v a l e n t at any one e l e v a t i o n can be made thro u g h o u t the season w i t h many snow depth and o n l y o c c a s i o n a l snow d e n s i t y measurements. Snowpack d e n s i t i e s on Mount Seymour, as elsewhere on t h e N o r t h Shore Mountains and o t h e r west c o a s t mid-l a t i t u d e mountains such as i n New Z e a l a n d , are s u b s t a n t i a l l y g r e a t e r t h a n those f o r s e a s o n a l snow c o v e r s o f o t h e r environments ( F i g . 4.14). The p r i n c i p a l r e a s o n s f o r ; t h i s are the h i g h e r d e n s i t y o f newly f a l l e n snow, the f r e q u e n t m i d w i n t e r melt p e r i o d s and r a i n - storms which produce i c y l a y e r s , and compaction by the l a r g e overburden p r e s s u r e s of the.deep snowpack. These h i g h d e n s i t i e s have s e v e r a l p r a c t i c a l i m p l i c a t i o n s . F o r example, v e r t i c a l snow l o a d s on s t r u c t u r e s w i l l be l a r g e f o r any g i v e n depth,.and on s l o p e s , s u b s t a n t i a l snow creep pressures' can develop (Mackay and Mathews 1967), which.-may s e v e r e l y damage b u i l d i n g s o r t r e e s . 108 IOO i r F E B MAR APR MAY MONTH F i g . 4.14 S e a s o n a l v a r i a t i o n i n average snowpack d e n s i t y Mount Seymour .snowcourse • (±9(50-70) and f o r other, a r e a s . 'North American d a t a f o r v a r i o u s y e a r s o f r e c o r d i s from McKay (1968). New Ze a l a n d d a t a from N.Z. Hydrology Annual. (1968) i s ' based on t h r e e y e a r s • o b s e r v a t i o n s } and i s : f r o m t h e Tasman G l a c i e r , e l e v a t i o n 1550 m 109 4 . 5 . 2 V a r i a t i o n s o f snow d e n s i t y w i t h - e l e v a t i o n S i n c e t he F e d e r a l snow tube does not measure snow-pack water e q u i v a l e n t p r e c i s e l y (Work et a l 1964), i t i s d i f f i c u l t t o compare w i t h c o n f i d e n c e snow d e n s i t i e s w h i c h v a r y over s m a l l r anges. F i e l d measurements i n d i c a t e a c o n f u s e d p a t t e r n o f snowpack d e n s i t y w i t h e l e v a t i o n ( F i g . 4 . 1 3 ) . No c l e a r l y d e f i n e d p a t t e r n emerges because o f the d i f f e r i n g i n f l u e n c e s o f new snow amount, new snow d e n s i t y , snow m e l t , overburden p r e s s u r e and o t h e r metamorphism p r o c e s s e s o p e r a t i n g at each e l e v a t i o n . S i m i l a r l y , snowpack d e n s i t i e s c a l c u l a t e d from the N o r t h Shore Mountain snow course r e c o r d s d i s p l a y no c l e a r t r e n d w i t h e l e v a t i o n (Appendix D). 4.5-3 V a r i a t i o n s o f snow d e n s i t y w i t h i n the f o r e s t S i n c e the d i f f e r e n c e s i n snowpack d e n s i t y between f o r e s t s t r a t a appear t o be o f t h e same magnitude as the measurement e r r o r o f the F e d e r a l snow t u b e , l i t t l e can be s a i d about v a r i a t i o n s w i t h i n t h e f o r e s t . However, as a g e n e r a l s t a t e m e n t , d e n s i t i e s a r e h i g h e r near t r e e s because of f r e q u e n t m e l t - d r i p from the f o l i a g e , and more r a p i d metamorphism o f the snow w i t h t he f o r m a t i o n o f snow h o l l o w s . The d i s t r i b u t i o n of snow d e n s i t y i s not s i m p l e because some storms d e p o s i t snow i n open a r e a s , but not beneath t r e e s (Chapter 6 ) , so the v a r i o u s s t r a t a r e c e i v e i n p u t s o f new snow t h a t a r e d i f f e r e n t i n q u a n t i t y and d e n s i t y . 110 At higher- e l e y a t i o n s , snowpack d e n s i t y , c l o s e -to t r e e s may be l e s s t h a n i n open a r e a s , because the f o l i a g e . p r o t e c t s the snow from wind compaction. 4.6 C o n c l u s i o n s T h i s c h a p t e r has d e s c r i b e d t h e snowpack o f the N o r t h Shore M o u n t a i n s . Prom t h i s d i s c u s s i o n may be drawn s e v e r a l f e a t u r e s which are l i k e l y t o be common t o o t h e r west c o a s t m i d l a t i t u d e mountains : 1. They are c h a r a c t e r i s e d by a deep snowpack which e x i s t s f o r g r e a t e r t h a n 7 months at h i g h e r e l e -v a t i o n s Ce.g. above 1200 m on Mount Seymour, above 1600 m on Tasman G l a c i e r , New Z e a l a n d ) . At e l e v a t i o n s below 500 m t h e r e may be l i t t l e o r no snow i n some w i n t e r s . 'At a l l ' e l e v a t i o n s t h e r e i s s u b s t a n t i a l v a r i a b i l i t y i n the w i n t e r e q u i v -a l e n t o f t h e snowpack from y e a r t o y e a r . 2. There are l a r g e and f r e q u e n t f l u c t u a t i o n s o f the s n o w l i n e , c o n t r o l l e d by p o s i t i o n s of new s n o w l i n e s and. the common m i d - w i n t e r melt p e r i o d s . 3. The d u r a t i o n . :of the s e a s o n a l snow co v e r i s con-s t r a i n e d at b o t h upper and lower e l e v a t i o n s . I l l Show water e q u i v a l e n t v a r i e s w i t h e l e v a t i o n - i n the shape of a snow-wedge. The s l o p e o f t h i s wedge changes w i t h season. I f t he mountain i s f o r e s t e d , snow i n c l e a r i n g s may not be s i g n i f i c a n t l y d i f f e r e n t from t h a t i n open a r e a s . I n m i l d e r w i n t e r s snow h o l l o w s w i l l form around t r e e s . Scour w i l l o c c u r about t r e e s exposed t o s t r o n g winds i n c o l d e r s t o r m s , when the d e n s i t y o f s u r f a c e snow i s - low. Such f e a t u r e s mean snow a c c u m u l a t i o n w i t h i n the f o r e s t i s l e s s t h a n i n open a r e a s . Snow d e n s i t y v a r i a t i o n s t h r o u g h o u t the season t e n d t o be more c o n s e r v a t i v e t h a n those o f snow accumu-l a t i o n . Thus r e a s o n a b l e e s t i m a t e s o f snow d e n s i t y at any one e l e v a t i o n may be made from e a r l i e r measurements, a l l o w i n g e s t i m a t e s of wa t e r e q u i v a l e n t i f snowpack depth i s known. T h i s i s e s p e c i a l l y t r u e l a t e i n t h e s e a s o n , when melt-r a t h e r t h a n d e p o s i t i o n a l p r o c e s s e s dominate. D e n s i t y o f the snowpack i s g r e a t e r than f o r many o t h e r e n v i r o n m e n ts. There i s no c l e a r p a t t e r n o f v a r i a t i o n o f d e n s i t y w i t h e l e v a t i o n . 112 CHAPTER 5 5. ESTIMATION OF NET 'SNOW ACCUMULATION 5 .1 I n t r o d u c t i o n The p o s s i b i l i t y o f e s t a b l i s h i n g w o rkable e m p i r i c a l r e l a t i o n s h i p s between net s e a s o n a l snow a c c u m u l a t i o n and e l e v a t i o n on west c o a s t m i d l a t i t u d e mountains•are examined i n t h i s c h a p t e r . These r e l a t i o n s h i p s would be of the form w(H, T) = f ( H , H-j_), where w i s water e q u i v a l e n t o f the snow-pack at some e l e v a t i o n H, and Hj_ i s the e l e v a t i o n of the i n c o m p l e t e s n o w l i n e a t time T. The u t i l i t y of the snow course concept f o r i n d e x i n g snow a c c u m u l a t i o n on such mountains i s r e l a t e d t o t h i s q u e s t i o n , and i s a l s o examined. An attempt i s made t o e s t i m a t e net snow a c c u m u l a t i o n i n the f o r e s t s t r a t a from t h a t i n open a r e a s . F i n a l l y e s t i m a t i o n o f snowpack d e n s i t y w i t h e l e v a t i o n i s d i s c u s s e d . At t h i s s t a g e , none o f t h e s e attempted e s t i m a t i o n s w i l l i n v o l v e snow d e p o s i t i o n . Apart from Mount Seymour, snow a c c u m u l a t i o n i s con-s i d e r e d f o r t h r e e o t h e r examples of west c o a s t m i d l a t i t u d e mountains (Table 5.1). The W i l l a m e t t e B a s i n d a t a are-i n c l u d e d because they r e p r e s e n t e x t e n s i v e e a r l y work on the type of mountain of concern h e r e . The mountains'of .this TABLE 5•1 C h a r a c t e r i s t i c s of west c o a s t m i d l a t i t u d e mountains chosen as examples C h a r a c t e r i s t i c s Mount Seymour W i l l a m e t t e B a s i n Ben Ohau Range Tasman G l a c i e r 'Country B.C. Canada Oregon U.S.A. South I s . N.Z. South I s . N.Z. Slope range (degrees) 8 20 . 15 12 Aspect range (degrees) 25 225 75 75 E l e v a t i o n range (meters) 1260 853 671 1320 Max. e l e v a t i o n sampled (meters) 1260 1500 1646 2340 Max. snow water e q u i v -a l e n t sampled (cm) 236 203 40 596 V e g e t a t i o n hemlock Douglas f i r cedar Douglas f i r hemlock n o b l e f i r snow t u s s o c k a l p i n e scrub none ( i c e ) Years o f o b s e r v a t i o n 1969-71 1949-51 1966 1968-69 R e f e r e n c e a u t h o r ' s o b s e r v a t i o n s U.S. Army (1956) A r c h e r (1970) N.Z. Hydrology Annual (1968) 114 b a s i n are s i m i l a r t o .Mount Seymour i n t h a t the zone of' s e a s o n a l snow cover i s f o r e s t e d . The New Z e a l a n d examples are not f o r e s t e d . The snow, c o v e r on the Tasman G l a c i e r may not be t y p i c a l o f many mountain s l o p e s but the s e d a t a are i n c l u d e d because o f the g r e a t range o f a l t i t u d e , up t o and beyond t h e g l a c i e r e q u i l i b r i u m l i n e . 5.2 E s t i m a t i o n of net snow a c c u m u l a t i o n w i t h e l e v a t i o n 5 . 2 . 1 A n a l y s i s ' o f snow wedge d a t a P l o t s o f the snow wedge f o r the W i l l a m e t t e B a s i n (U.S. Army 1956, P i g . l , p l a t e 3.3) suggested t h a t water e q u i v a l e n t (the o r d i n a t e ) i n c r e a s e d as a s i m p l e l i n e a r f u n c t i o n w i t h e l e v a t i o n (the a b s c i s s a ) from t h e s n o w l i n e . However, the snow wedges produced on Mount Seymour ( F i g . 4.10) and on the Tasman G l a c i e r do not always show c o n s t a n t . i n c r e a s e s of water e q u i v a l e n t w i t h e l e v a t i o n . F o r example, the Mount Seymour d a t a a l l o w a s i m p l e l i n e a r f i t f o r January 1970, and up u n t i l March f o r the w i n t e r 1970-71, but o t h e r w i s e c u r v i l i n e a r r e l a t i o n s h i p s must bemused. Such c u r v i l i n e a r i t y r e s u l t s from melt a t lower- e l e v a t i o n s , when the upper p a r t s o f the wedge are s t i l l r e c e i v i n g 1 f r e s h i n p u t s o f snow. T h i s e f f e c t was most pronounced i n 1969-70 ,. because the w i n t e r was u n u s u a l l y m i l d , w i t h f r e q u e n t m e l t p e r i o d s , and because few storms d e p o s i t e d snow below 900 m. 115 I t i s p o s s i b l e , .to, de.s-cri.be w(H,.. T), f o r t h e s e examples w i t h l i n e a r and c u r v i l i n e a r . f u n c t i o n s . However, such a p r o c e d u r e would be' of l i t t l e v a l u e because' P i g . 4.10 i n d i c a t e s t h a t the shape of the snow wedge does not behave c o n s i s t e n t l y from month t o month, or year t o y e a r . Even the mean s l o p e o f the snow wedge changes, g e n e r a l l y becoming l a r g e r d u r i n g t h e a c c u m u l a t i o n s e a s o n , and r e m a i n i n g c o n s t a n t or d e c r e a s i n g d u r i n g the melt p e r i o d ( F i g . 5.1). Moreover, the Mount Seymour d a t a suggest t h a t the b e h a v i o u r o f t h i s mean s l o p e i s not the same from y e a r t o y e a r . The U.S. Army (1956) b e l i e v e d t h a t d u r i n g t h e accum-l a t i o n season i n the W i l l a m e t t e B a s i n t h e r e e x i s t e d a s i m p l e l i n e a r r e l a t i o n s h i p between the mean s l o p e o f - t h e snow wedge and water e q u i v a l e n t at the. upper sample l i m i t o f t h e mountain ( F i g . 5.2). T h i s i m p l i e d t h a t a s i n g l e monthly measurement of snowpack water e q u i v a l e n t at the top o f the mountain would a l l o w d e f i n i t i o n of the f u n c t i o n w(H, T ) . U n f o r t u n a t e l y , t h i s s i m p l e r e l a t i o n s h i p does not appear t o be v a l i d f o r o t h e r west c o a s t m i d l a t i t u d e mountains. F u r t h e r , f o r the Mount Seymour examples, the r e l a t i o n s h i p i s d i f f e r e n t i n s u c c e s s i v e y e a r s ( F i g . 5.2). The f a i l u r e of t h i s method t o s a t i s f a c t o r i l y e s t i m a t e w(H, T) becomes even more apparent when i t i s remembered t h a t the upper s u r f a c e o f the snow we'dge I s " not always" a s t r a i g h t l i n e , as i m p l i e d by the use of the term "mean s l o p e " ; A 116 SoutharnHamispharaMonth May Jun Jul Aug Sap Oct Nov Dac Jan Fab Mar D«c Jan Fab Mar Apr May Jun Jul Aug Sap Oct Northarn Hamisphara Month F i g . 5.1 S e a s o n a l y a r i a t i o n i n mean s l o p e of snow wedge 117 80 640 W a t e r e q u i v a l e n t a t h i g h e s t s a m p l e p o i n t o t s n o w w e d g e ( c m ) F i g . 5.2 Mean s l o p e o f snow wedge d u r i n g t h e a c c u m u l a t i o n p e r i o d as a f u n c t i o n of water e q u i v a l e n t at the upper s a m p l i n g l i m i t on the mountain 120 100 80 Mount Seymour S n o w w e d g e s e c t i o n 1 9 6 9 - 7 0 1 0 6 0 - 1 2 6 0 m O 9 7 0 - 1 0 6 0 m . • b e l o w 9 7 0 m A 1 9 7 0 - 7 1 60 40 20 ho W i l l o m e t t e B a s i n 1 9 4 9 - 5 1 OB 40 80 120 160 200 240 W a t e r e q u i v a l e n t a t h i g h e s t s a m p l e p o i n t o f s n o w w e d g e s e c t i o n • F i g . 5«3 Slop e of s e c t i o n s of snow wedge d u r i n g . t h e a c c u m u l a t i o n p e r i o d as a f u n c t i o n o f water e q u i v a l e n t at the upper l i m i t o f each s e c t i o n 118 s i m i l a r a n a l y s i s o f the Mount Seymour d a t a , but. f o r .homo-geneous s e c t i o n s of the snow wedge,, d i s p l a y e d some, t r e n d s , but t h e s e were s t i l l not. .consistent, from s e c t i o n t o s e c t i o n or y e a r t o y e a r ( P i g . 5.3)• The're i s a l s o no apparent r e l a t i o n s h i p between: the water e q u i v a l e n t of the snowpack at the upper s a m p l i n g l i m i t o f the snow wedge and the p o s i t i o n o f the s n o w l i n e ( F i g . 5 - 4 ) . However, the p o i n t s on the graph do d e s c r i b e a type of e l l i p t i c a l p a t h t h r o u g h the season ( e . g . Mount Seymour, w i n t e r 1970-71), but t h i s p a t h i s not i d e n t i c a l from y e a r t o y e a r . 5 . 2 . 2 Some i m p l i c a t i o n s The p r e v i o u s d i s c u s s i o n showed t h a t on west coast-m i d l a t i t u d e mountains snow a c c u m u l a t i o n i n c r e a s e s w i t h e l e v a t i o n i n the form o f a snow wedge. However, the shape-, s l o p e and r e l a t i o n s h i p w i t h the s n o w l i n e of t h i s snow wedge are not c o n s i s t e n t from month t o month, y e a r t o year or l o c a l i t y t o l o c a l i t y . I t must th e n be c o n c l u d e d t h a t e m p i r i c a l r e l a t i o n s h i p s o f the form w(H, T) w i l l not produce r e l i a b l e p r e d i c t i v e models on t h i s type o f mountain. The approach f a i l s because the s l o p e and e x t e n t of the snow wedge i s not c o n s i s t e n t l y r e l a t e d t o the magnitude of the snowpack or time of y e a r . 600 o a c» a. E . a ~ •o E m «» » •c cn ID ^ 'JE «• ° * o c c C* 1/1 O H -> o cr » t -a 5 500 400 300 200 100 h Willamette Basin 1949 O 1950 O 1951 A Mount Seymour 1969 -70 • 1970 -71 • Tasman G lac ie r 1968 -69 Ben Ohau Ra. 1966 • 200 400 600 800 1000 1200 1400 1600 1800 E leva t i on of snowline (meters) F i g . 5.4. Water e q u i v a l e n t at upper sampling l i m i t of snow wedge as a - f u n c t i o n of e l e -v a t i o n of the s n o w l i n e r — 1 VO 120 On west c o a s t m i d l a t i t u d e mountains ' i t i s p o s s i b l e f o r w a t e r e q u i v a l e n t s , to-be s i m i l a r i n d i f f e r e n t y e a r s (or months) at one e l e v a t i o n , but the d i s t r i b u t i o n o f water e q u i v a l e n t w i t h e l e v a t i o n may be markedly d i f f e r e n t from y e a r t o y e a r . A h y p o t h e t i c a l example i s shown i n F i g . 5 . 5 . T h i s sharp e l e v a t i o n - t i m e • i n t e r a c t i o n e f f e c t , a l s o d i s -p l a y e d i n e a r l i e r examples, has been r e p o r t e d e l s e w h e r e ( P a c k e r 1962, Anderson and West 1965). The i n t e r a c t i o n i m p l i e s ' t h a t a s i n g l e snow course a t one e l e v a t i o n cannot p r o v i d e a good i n d e x of snow a c c u m u l a t i o n on a west co a s t m i d l a t i t u d e mountain. For the h y p o t h e t i c a l example, a snow course a t e l e v a t i o n 1300 m r e c o r d s the same'water e q u i v a l e n t i n y e a r 1 as i n y e a r 2. Yet the volume o f water s t o r e d as s e a s o n a l snow i n y e a r 1 i s 26 p e r c e n t g r e a t e r t h a n t h a t i n y e a r 2. By r e l a t i n g the shape o f the snow wedge t o t h e - h y p s o m e t r i c curve i t i s apparent t h a t the water e q u i v a l e n t of the'snow-pack at t h e h i g h e s t e l e v a t i o n sampled need not be i n d i c a t i v e o f the t o t a l amount o f water s t o r e d on the mountain. F u r t h e r , samples o f the s h a l l o w snowpack near the s e a s o n a l s n o w l i n e assume g r e a t e r i m p o r t a n c e , because when combined w i t h the r e l a t i v e l y l a r g e a r e a o f any catchment at t h i s e l e v a t i o n , t hey are shown t o produce a s i g n i f i c a n t c o n t r i -b u t i o n t o the t o t a l w ater s t o r e d as snow. 121 Pig. 5.5 H y p o t h e t i c a l example o f h y p s o m e t r i c c u r v e , snow, wedges and t o t a l w a t e r s t o r e d as snow i n two d i f f e r e n t y e a r s 122 5.3 F a c t o r s c o n t r o l l i n g the shape o f the snow wedge There are t h r e e p r i n c i p a l p r o c e s s e s t h a t c o n t r o l the shape o f - t h e snow wedge : (a) The v a r i a t i o n o f p r e c i p i t a t i o n w i t h e l e v a t i o n . On most mountains t h e r e i s ' a s t e a d y - i n c r e a s e of p r e c i p i t a t i o n w i t h e l e v a t i o n . However the r a t e of i n c r e a s e , and the e l e v a t i o n of any maximum of p r e c i p i t a t i o n , w i l l change w i t h the s t a b i l i t y and wind shear of the storm a i r mass (Sawyer 1956). Hence the f r e q u e n c y o f v a r i o u s storm t y p e s w i l l d e termine the v a r i a t i o n w i t h e l e v a t i o n o f the t o t a l w i n t e r p r e c i p i t a t i o n , and s u b s e q u e n t l y of the snowpack. (b) The v a r i a t i o n o f snow me l t w i t h e l e v a t i o n . I t i s c h a r a c t e r i s t i c of west c o a s t m i d l a t i t u d e mountains t h a t d u r i n g a'nd between w i n t e r s t o r m s , melt w i l l o c c u r a t l e a s t at l o w e r - e l e v a t i o n s . However, from y e a r t o y e a r the energy a v a i l a b l e f o r m elt i s u n l i k e l y t o be the same at each e l e v a t i o n . (c) The e l e v a t i o n of the rain/snow boundary d u r i n g s u c c e s s i v e storms. T h i s boundary i s l a r g e l y c o n t r o l l e d by storm' f r e e z i n g l e v e l s . W i n t e r s t o r m f r e e z i n g l e v e l s 123 i n t e r s e c t i n g west, c o a s t m i d l a t i t u d e mountains may move over a wide range o f e l e v a t i o n i n the space of a few days Ce.g. ahead o f and b e h i n d a f a m i l y of east'moving f r o n t s ) . The f r e q u e n c y of w i n t e r storm f r e e z i n g l e v e l s at each e l e v a t i o n , t o g e t h e r w i t h the magnitude o f t h e storm s n o w f a l l s may'be the main f a c t o r c o n t r o l l i n g the shape and s l o p e of t h e snow wedge. T h i s i s i n v e s t i g a t e d i n f o l l o w i n g chapters'. I t i s s i g n i f i c a n t t h a t i n those c o n t i n e n t a l mountain r e g i o n s where the . f r e e z i n g l e v e l i s at- ( o r "below") the base- o f t h e mountain, the e l e v a t i o n - t i m e i n t e r a c t i o n e f f e c t does not appear t o e x i s t . C o n s i s t e n t e m p i r i c a l r e l a t i o n s d e s c r i b i n g w(H, T) might t h e n be p o s s i b l e ( e . g . i n Western C o l o r a d o , U.S. S o i l ; C o n s e r v a t i o n S e r v i c e , 1965-67, and i n Germany:, G r a s n i c k 1967) . 5.4 E s t i m a t i o n o f net snow a c c u m u l a t i o n w i t h i n the f o r e s t I f snowpack.water e q u i v a l e n t i s measured i n open areas a l o n e , i t may be p o s s i b l e t o e s t i m a t e t h a t i n the f o r e s t by r e g r e s s i o n t e c h n i q u e s . The e q u a t i o n s o f Table 5 . 2 , p r o d u c e d by' the s t e p w i s e r e g r e s s i o n p r o c e d u r e , a l l o w such e s t i m a t e s t o be made, f o r any p a r t o f the season. F o r one s t r a t u m -c l o s e t o t r e e t r u n k s - the e q u a t i o n i n c l u d e s a time element. T A B L E 5.2 P r e d i c t i o n e q u a t i o n s f o r e s t i m a t i o n of snowpack water e q u i v a l e n t (em) i n f o r e s t s t r a t a based on a c c u m u l a t i o n i n open areas W i n t e r F o r e s t s t r a t u m R e g r e s s i o n e q u a t i o n S . E . o f est(cm) n R2 1969-70 c l e a r i n g ( C L ) canopy edge ( C E ) beneath canopy ( C ) c l o s e t o t r e e t r u n k s (TR) C L = 4 . O + O . O O O 8 0 H C E = -.0 .7+0 . O O O 6 0 H C= - 1 . 9 + 0 . O O O 5 0 H TR= 0 . 8 - 1 . 0 6 0 + 0 . O O 1 2 0 H 8 . 1 9.4 10 . 2 8.5 45 45 45 45 0.92 0 .86 0 .75 0.67 1 9 7 0 - 7 1 c l e a r i n g ( C L ) canopy edge ( C E ) beneath canopy CC) c l o s e t o t r e e t r u n k s (TR) C L = 5 . . 4 + 0 , 9 40, C E = 1 . 8 + 0 . 7 5 0 c= -1.2+0.650 TR= - 7 . 9 + 0 . 9 0 0 - 0 . O O 2 0 T 9.4 1 1 . 6 . 1 0 . 8 9.7 81. 81 8 1 81 0.96 0.91 0.91 0.90 Data from w i n t e r s 1969-70, 1 9 7 0 - 7 1 combined c l e a r i n g ( C L ) canopy edge ( C E ) beneath canopy ( C ) c l o s e t o t r e e t r u n k s (TR) C L = 4.0+0.940 C E = -1 .0+0.750 • c = -2.6+0.650, TR= -7 .0 + 0 . 8 2 0 - 0 . O O 2 0 T 9.6 10 .4 1 1 . 1 1 1 . 1 126 1 2 6 126 126 0.95 0.90 0.87 ' 0.83 N O T E S : ( i ) ( i i ) ( i i i ) ( i v ) R e g r e s s i o n e q u a t i o n s found u s i n g f o r w a r d s t e p w i s e m u l t i p l e r e g r e s s i o n A l l v a l u e s o f r or R s i g n i f i c a n t at 99$ c o n f i d e n c e l e v e l . 0 -= snow.accumulation i n open areas (cm) at an e l e v a t i o n , H . H = e l e v a t i o n o f measurement (metres) T = time i n d a y s , from December 1 . v a r i a b l e s t e s t e d were : 0 - 0 2 0 H H H 2 0 T T T 2 H T 125 This- I n d i c a t e s t h a t because o f l a t e w i n t e r m e l t around the base of t r e e s , t he r e l a t i o n s h i p s betw.een snow accumu-l a t i o n i n t h i s s t r a t u m and t h a t i n the open changes w i t h season. 95 p e r c e n t c o n f i d e n c e l i m i t s have been computed about an e s t i m a t e o f snow a c c u m u l a t i o n i n b o t h c l e a r i n g s ( F i g . 5 .6) and-beneath the canopy ( F i g . 5-7) f o r a g i v e n v a l u e o f a c c u m u l a t i o n i n the open. The c o n f i d e n c e l i m i t s f o r t h e s e examples span an i n t e r v a l o f 38 cm and 44 cm r e s -p e c t i v e l y , which i s t o o l a r g e t o make the e q u a t i o n s p r a c t i c a l u n l e s s snow a c c u m u l a t i o n i n the open i s g r e a t e r t h a n about 100 cm wat e r e q u i v a l e n t . Those e q u a t i o n s based on the combined d a t a f o r two w i n t e r s are not ve r y d i f f e r e n t from t h o s e f o r w i n t e r 1970-71. However, the combined a n a l y s i s was dominated by d a t a f o r the second w i n t e r , because o f l a r g e r samples and a g r e a t e r range o f v a l u e s . The e q u a t i o n s f o r 1969-70 would be used i n a m i l d e r w i n t e r when i n t e r a c t i o n , o r 0H, terms are i n c l u d e d . The i n t e r a c t i o n means t h a t the r e l a t i o n s h i p between snow a c c u m u l a t i o n i n the open a n d - t h a t i n t he f o r e s t changes w i t h e l e v a t i o n , and i s p r o b a b l y produced by the development o f snow h o l l o w s . ( R e g r e s s i o n l i n e s f o r examples o f e l e v a t i o n s 1260 m and 400.. m are-g i v e n i n F i g s : 5 . 6 , 5 . 7 ) . I f the w i n t e r i s c o l d e r , w i t h heavy snow accumu-l a t i o n , the e q u a t i o n s f o r w i n t e r 1970-71, or f o r a l l ' 126 Snowpack water equivalent in open (cm) F i g . 5.6 P r e d i c t i o n of snow, a c c u m u l a t i o n i n c l e a r i n g s (CL) from t h a t i n open areas ( ( J ) ) . . The two examples of l i n e s f o r a m i l d w i n t e r are based on the e q u a t i o n d e r i v e d from 1969-70 d a t a which i n c l u d e s an i n t e r -a c t i o n w i t h e l e v a t i o n term 127 4 0 8 0 1 2 0 1 6 0 2 0 0 2 4 0 S n o w p a c k w a t e r e q u i v a l e n t i n o p e n ( c m ) F i g . . 5 . 7 P r e d i c t i o n o f snow a c c u m u l a t i o n beneath. the. canopy (_e). from t h a t i n open areas ((J)) . The two examples of l i n e s f o r a m i l d w i n t e r are based on the e q u a t i o n d e r i v e d from 19-69---70 d a t a , w h i c h i n c l u d e s an i n t e r a c t i o n with, e l e v a t i o n term-128 d a t a combined would be a p p r o p r i a t e . The h i g h e x p l a n a t i o n ( i . e . h i g h R 2 v a l u e s ) obtained, f o r the r e g r e s s i o n r e l a t i o n -s h i p f o r the 1970-71 d a t a suggest t h a t i n a c o l d , snowy, w i n t e r , snow courses i n the open may i n d e x a c c u m u l a t i o n i n the f o r e s t a d e q u a t e l y . However, i n a m i l d e r w i n t e r , when the i n t e r a c t i o n w i t h e l e v a t i o n (0H) term becomes i m p o r t a n t , a snow course p r o v i d e s a p o o r e r i n d e x of f o r e s t a c c u m u l a t i o n ( l o w e r R 2 v a l u e s ) . The r e g r e s s i o n e q u a t i o n s r e f l e c t the r e l a t i v e b e h a v i o u r of the snowpack among s t r a t a . There are p r o g r e s s i v e d e c r e a s e s i n r e g r e s s i o n i n t e r c e p t v a l u e s , and i n s l o p e s o f the b e s t f i t l i n e s , t h r o u g h the spectrum of s t r a t a from c l e a r i n g s t o c l o s e t o t r e e t r u n k s . There are a l s o p r o g r e s s i v e decreases i n e x p l a n a t i o n because the p r o c e s s e s of snow a c c u m u l a t i o n down t h i s spectrum become l e s s r e l a t e d t o those i n the open. 5.5 E s t i m a t i o n o f snowpack d e n s i t y w i t h e l e v a t i o n For most of the s e a s o n , the n a t u r e o f new s n o w f a l l s appears t o be t h e dominant f a c t o r a f f e c t i n g v a r i a t i o n s w i t h e l e v a t i o n . T h e r e f o r e , the d i s t r i b u t i o n o f snowpack d e n s i t y w i l l be c l o s e l y c o n t r o l l e d by the p r e v i o u s h i s t o r y o f s t o r m s , t h e i r r ain/snow b o u n d a r i e s , and new snow den-s i t i e s . As l o n g as snow storms w i t h d i v e r s e f r e e z i n g l e v e l s are f r e q u e n t , no p e r s i s t e n t or steady t r e n d w i t h e l e v a t i o n i s t o be e x p e c t e d . I n a d d i t i o n , i n t e r a c t i o n w i t h e l e v a t i o n can be pronounced(e.g. snowpack d e n s i t y a t 590 m behaved d i f f e r e n t l y t han at h i g h e r e l e v a t i o n s 129 from January t o March- 197.1, F i g . 4..13). Thus, as w i t h snow a c c u m u l a t i o n , i t i s . c o n c l u d e d t h a t any e m p i r i c a l r e l a t i o n s h i p s between snow d e n s i t y and e l e v a t i o n are u n l i k e l y t o be c o n s i s t e n t from month t o month, or y e a r t o y e a r . Even when new s n o w f a l l s c e a s e - l a t e r i n the season, the s i t u a t i o n i s c o m p l i c a t e d by d i f f e r e n t p r o c e s s e s o f metamorphism o p e r a t i n g a t d i f f e r e n t e l e v a t i o n s . At lower e l e v a t i o n s , m e l t - f r e e z e , and i n c r e a s i n g g r a i n s i z e , e q u i -t emperature metamorphism (Sommerfield and La C h a p e l l e 1970) dominate, but at h i g h e r e l e v a t i o n s t h e s e p r o c e e d at d i f f e r e n t r a t e s and, because o f the deep snowpack, are augmented by the b e g i n n i n g s o f p r e s s u r e metamorphism. , 5•6 C o n c l u s i o n s Simple e m p i r i c a l r e l a t i o n s h i p s between net snow a c c u m u l a t i o n , or d e n s i t y , and e l e v a t i o n are not l i k e l y t o be r e l i a b l e on west co a s t m i d l a t i t u d e mountains. T h i s i s a consequence o f t h e f o r m a t i o n of a snow wedge whose shape and' s l o p e appears t o be l a r g e l y c o n t r o l l e d by the r e l a t i v e f r e q u e n c y of v a r i o u s w i n t e r storm t y p e s . These f i n d i n g s i n d i c a t e t h a t a s u c c e s s f u l approach t o e s t i m a t i o n o f snowpack v a r i a t i o n s w i t h e l e v a t i o n s h o u l d be more p h y s i c a l l y based by i n c l u d i n g v a r i a b l e s t h a t are d i r e c t l y r e l a t e d t o the p r o c e s s e s o p e r a t i n g . Proposed models 130 s h o u l d s i m u l a t e on a day t o day or storm b a s i s the v a r i a t i o n s i n e l e v a t i o n o f the rain/snow b o u n d a r i e s and t h e amounts of snow d e p o s i t e d . These p r o c e s s e s are examined f u r t h e r i n the f o l l o w i n g c h a p t e r s . Snow melt i s a l s o an i m p o r t a n t c o n s i d e r a t i o n , but not d e a l t w i t h h e r e . S i n c e the shape o f the snow wedge i s p a r t i c u l a r l y s e n s i t i v e t o t h e p o s i t i o n o f the r a i n / s n o w boundary from s u c c e s s i v e s t o r m s , a c l i m a t o l o g i c a l i n v e n t o r y o f sto r m t y p e s , f r e e z i n g l e v e l s , and s n o w l i n e s f o r each w i n t e r are a l s o i n c l u d e d i n t h i s s t u d y . The changing shape o f the snow wedge, and r e s u l t a n t e l e v a t i o n - t i m e i n t e r a c t i o n e f f e c t s , r e n d e r u n s u i t a b l e the t r a d i t i o n a l snow course where measurements are t a k e n at a s i n g l e e l e v a t i o n on t h e mountain. More r e l i a b l e i n d i c e s o f snow a c c u m u l a t i o n w i l l be o b t a i n e d w i t h a s e r i e s o f snow courses at d i f f e r e n t e l e v a t i o n s , and w i t h o b s e r v a t i o n s of the s n o w l i n e . The optimum number of snow samples f o r a s p e c i f i e d e l e v a t i o n range has y e t t o be det e r m i n e d . Reasonable e m p i r i c a l r e l a t i o n s h i p s are produced which e s t i m a t e a c c u m u l a t i o n i n the f o r e s t s t r a t a from t h a t i n the open, p r o v i d e d t h a t w a t e r e q u i v a l e n t i s g r e a t e r than 100 cm. These are thought t o be g e n e r a l l y a p p l i c a b l e t o the t e r r a i n segment, because the w i n t e r s sampled i n c l u d e d a wide range of a c c u m u l a t i o n s r e c o r d e d i n the l a s t 36 y e a r s . Separate r e l a t i o n s s h o u l d be used: one f o r c o l d e r , snowier w i n t e r s ; and the o t h e r f o r warmer w i n t e r s , when the development of snow h o l l o w s i n t r o d u c e s an i n t e r a c t i o n e f f e c t w i t h e l e -v a t i o n between a c c u m u l a t i o n i n the open and i n the f o r e s t . 131 The d a t a I s too. v a r i a b l e to. a l l o w p r e c i s e e s t i m a t e s of snow i n the f o r e s t i f based on open a r e a water e q u i v -a l e n t l e s s than 100. cm. I n the s e c a s e s , e i t h e r b e t t e r measurement methods, or more s o p h i s t i c a t e d models i n c o r p o r a t i n g some p h y s i c a l p r o c e s s e s , w i l l have t o be employed t o improve the e s t i m a t e s . 132 CHAPTER 6 6. WINTER PRECIPITATION; AND SNOW DEPOSITION T h i s c h a p t e r r e p o r t s the r e s u l t s of w i n t e r and storm p r e c i p i t a t i o n measurements, b o t h r a i n and snow. The v a r i a t i o n s w i t h e l e v a t i o n of th e s e elements are des-c r i b e d and compared w i t h o t h e r l o c a l s t u d i e s . A q u a l i -t a t i v e model of storm snow d e p o s i t i o n i s proposed f o r west c o a s t m i d l a t i t u d e mountains. The p r o p o r t i o n of w i n t e r p r e c i p i t a t i o n f a l l i n g as snow i s a s s e s s e d f o r each e l e v a t i o n . F i n a l l y an e s t i m a t e i s made o f the c o n t r i -b u t i o n o f rime t o w i n t e r p r e c i p i t a t i o n . P r e s e n t a t i o n and a n a l y s i s of th e s e measurements p r o v i d e s the b a s i c d a t a f o r the f o l l o w i n g c h a p t e r s where a c l i m a t o l o g y o f snow storms i s developed and a model c o n s t r u c t e d t o p r e d i c t snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n and w i t h i n the f o r e s t . 6 .1 P r e c i p i t a t i o n 6.1 .1 V a r i a t i o n o f t o t a l w i n t e r p r e c i p i t a t i o n w i t h e l e v a t i o n T o t a l w i n t e r p r e c i p i t a t i o n i n c r e a s e d l i n e a r l y w i t h e l e v a t i o n ( F i g . 6 . 1 , T a b l e 6 . 1 ) . The p r i n c i p a l anomalies from t h i s l i n e a r t r e n d o c c u r r e d at 490 m and from 870 t o 133 TABLE 6 . 1 Variation of t o t a l winter p r e c i p i t a t i o n with elevation. A l l data for snow expressed i n water equivalent. Winter 1 9 6 9 - 7 0 + Elevation (meter s) Total Precip. (mm) Snow Dep. (mm) Ra i n f a l l (mm) Mean Precip. /storm (mm) % of precip. f a l l i n g as snow Mean snow/ snow storm (mm) mean r a i n / rain storm (mm) 1260 1854 1300 554 28 70 .1 34.2 ( 3 8 ) * 21 .3 (26) 1060 1857 1243 6l4 29 66 .9 35-5 (35) 21 .2 970 1630 719 911 26 44 1 21 .8 (33) 29 .4 ( 3 D 870 1594 359 1235 25 22 5 16 .3 (22) 29 .4 (42) 790 1715 268 1447 27 15 .6 14.9 (18) 31 • 5 (46) 710 1585 153 1132 25 9 .7 9.0 (17) 30 .5 (47) 590 1368 H5 1323 21 3 3 4 .5 (10) 24 • 5 (54) 190 1366 10 1356 21 0 7 1 .7 ( 6) 23 .4 (58) 400 1379 4 1375 22 0 .3 1 .3 ( 3) 22 .4 (61) 330 1320 1 1319 21 0 1 1.0 ( 1) 20 .9 (63) 220 1238 12 1226 19 0 9 12.0 ( 1) 19 .5 (63) 120 1198 12 1186 19 1 0 12.0 ( 1) 18 .8 (63) Winter 1970-71 Elevation (meters) Total " Precip. (mm) Snow Dep. (mm) Ra i n f a l l (mm) Mean Precip. /storm (mm) % of 'precip. f a l l i n g as snow Mean snow/ snow storm (mm) Mean rain ( m i r r a i n / storm ) 1260 ' 3520 2438 1082 48 6 9 . 3 ' 1 1 .3 (55) 56.4 (19) 1060 3448 2253 1195 47 65.3 43.3 (52) 54 .3 (22) 970 2873 I676 1197 39 58 .3 3 4 . 9 (48) 46.0 (26) 870 2653 1208 1445 36 '15.5 26.5 (46) 51.6 (28) 790 2832 1206 1626 39 42.6 2 9 . 4 (41) 4 9 . 3 (33) 710 2556 930 1626 35 36.4 25-1 (37) 43-9 (37) 590 2349 699 1650 32 29 .8 2 3 . 5 (30) 37.5 (44) 490 2230 466 1764 31 2 1 . 0 2 1 . 2 (22) 3 3 . 9 (52) 400 2252 392 i 8 6 0 31 17.4 19.6 (10) 34.4 ( 5 4 ) 330 2130 254 I876 29 11.9 14 .1 (18) 3 3 . 5 (56) 220 1949 222 1727 27 11.4 14 .8 (15) 2 9 . 3 (59) 120 1837 216 1621 25 11 .8 16.6 (13) 2 6 . 6 (61) * figures in brackets give number of storms of each p r e c i p i t a t i o n type sampled at each elevation. + p r e c i p i t a t i o n for the period 5 November 1969 to 31 May 1970 + p r e c i p i t a t i o n for the period 1 October 1970 to 31 May 1971. CD <! !—1 P CD 4 •< H- ~ 0 1000 H ct o - | — i 1 • 1 1 r- i 1 r 0 200 400 600 ' 600 1000 1200 1400 Elevation (meters) 135 970 jn. The f o l l o w i n g l e a s t square e q u a t i o n s were f i t t e d t o the d a t a : For w i n t e r 1969-70 P= .1104+0 ..62H r 2 = 0.91 S.E.= 65 For w i n t e r 1970-71 P- 1588+1.48H r 2 = 0 ..94 S.E.= 131 where : P = w i n t e r p r e c i p i t a t i o n (mm) H = e l e v a t i o n (m) The s l o p e of the r e g r e s s i o n l i n e (and hence the o r o g r a p h i c component of p r e c i p i t a t i o n ) was much g r e a t e r i n the second w i n t e r . The magnitude o f the s l o p e d i f f -erence suggests y e a r - e l e v a t i o n i n t e r a c t i o n e f f e c t s may be common f o r w i n t e r p r e c i p i t a t i o n . D i f f e r e n c e s i n p r e c i p i t a t i o n between th e two w i n t e r s were not as g r e a t as i n d i c a t e d , because 9 storms ( a l l r a i n storms) were not sampled at the b e g i n n i n g of the w i n t e r 1969-70. N e v e r t h e l e s s i n the w i n t e r 1970-71, mean p r e c i p i t a t i o n p e r storm sampled was 32 p e r c e n t h i g h e r at 120 m, and 71 p e r c e n t h i g h e r at 1260 m. The w i n t e r 1970-71 was a snowier w i n t e r , and hence such r e s u l t s c o u l d be produced i f t h e r e was a b i a s i n the measurement methods f o r snowstorms, a t the expense o f r a i n s t o r m s . However, t h e r e seems a more fundamental p h y s i c a l r e a s o n i s o p e r a t i n g , s i n c e the mean r a i n f a l l p er r a i n storm was a l s o g r e a t e r 136 i n 1970-71 t h a n i n t h e p r e v i o u s w i n t e r . T h i s p o i n t i s e l a b o r a t e d f u r t h e r l a t e r . S u f f i c e t o say h e r e , t h a t the h i g h e r mean storm p r e c i p i t a t i o n o f the w i n t e r 1970-71 was produced by a h i g h e r f r e q u e n c y o f thos e storm t y p e s conducive t o h e a v i e r p r e c i p i t a t i o n (e.g. those c o n t a i n i n g more v i g o r o u s f r o n t a l systems o r more u n s t a b l e a i r masses). Mean p r e c i p i t a t i o n p e r snow storm was l e s s than t h a t p e r r a i n storm except at 1060 m and 1260 m i n the w i n t e r 1969-70. 6.1 .2 Comparison w i t h o t h e r l o c a l s t u d i e s Walker (1961), O r l o c i (1964), and S c h a e f e r and N i k l e v a (1973) have d i s c u s s e d v a r i a t i o n s o f annual p r e -c i p i t a t i o n w i t h e l e v a t i o n on the N o r t h Shore Mountains. Walker and O r l o c i suggest a maximum o f p r e c i p i t a t i o n s h o u l d e x i s t somewhere between 620 m and 810 m, the exact e l e -v a t i o n v a r y i n g w i t h the season. Above t h i s e l e v a t i o n , p r e c i p i t a t i o n amounts s h o u l d d e c r e a s e . Maximum p r e -c i p i t a t i o n from some storms d i d o c c a s i o n a l l y o c c u r midway up the mountain ( F i g . 6 . 2 ) , but over the two w i n t e r s , the above comments are not s u b s t a n t i a t e d by the d a t a o f t h i s study ( F i g . 6 . 1 ) . I f an e l e v a t i o n o f maximum p r e -c i p i t a t i o n does e x i s t , i t must o c c u r above 1260 m. Many workers (e.g. Walker, 1 9 6 l , B a r r y and C h o r l e y 197D have p o s t u l a t e d t h a t the e l e v a t i o n of maximum p r e c i p i t a t i o n i s c l o s e t o t h e mean c l o u d base, s i n c e the maximum s i z e 137 6 0 -F e b r u a r y 1 9 7 0 4 0 -1 2 0 -. o- 44 o-4-8 0 6 0 H O c t o b e r 1 9 7 0 4 0 ~\ 2 0 H 1 0 0 300 5 0 0 7 0 0 9 0 0 E l e v a t i o n ( m e t e r s ) 1 1 0 0 1 3 0 0 F i g . 6 .2 V a r i a t i o n s of p r e c i p i t a t i o n with eley'ation f o r storms of s e l e c t e d months. Storms are iden-t i f i e d by number, top f o r winter 1969-70, and bottom f o r winter 1970-71 138 and number of f a l l i n g p r e c i p i t a t i o n p a r t i c l e s ' w i l l o c c u r at t h i s l e v e l . W i t h - ' d r i e r a i r below, the p a r t i c l e s w i l l t e n d t o e v a p o r a t e and. l o s e .mass-. The mean c l o u d bases of w i n t e r storms on Mount Seymour i s a t about 500. m,.but s i n c e the l e v e l of maximum p r e c i p i t a t i o n g e n e r a l l y o c c u r s above t h i s e l e v a t i o n , t h i s p r o c e s s does not seem t o be i m p o r t a n t h e r e . There are- a number o f o t h e r p o s s i b l e reasons why e a r l i e r workers might c l a i m a lower e l e v a t i o n o f maximum p r e c i p i t a t i o n . Wright (.1966b) and S c h a e f e r and N i k l e v a (1973) p o i n t ' o u t t h a t the p r e c i p i t a t i o n at-/-Seymour F a l l s (200 m), i n the Seymour V a l l e y , i s g r e a t e r t h a n t h a t a t the h i g h e r H o l l y b u r n Ridge (950 m) and Mount Seymour CBUT s t a t i o n s (870 m). They suggest m o i s t u r e l a d e n winds are f u n n e l l e d up the v a l l e y , where -convergence and u p l i f t combine t o g i v e a h e a v i e r f a l l t h a n on the more exposed s o u t h e r n f l a n k s of the mountains. These p r e v i o u s workers d i d not d i s t i n g u i s h between s t a t i o n s w i t h d i f f e r e n t exposures or a s p e c t s , so were i n f a c t c o n s i d e r i n g d i f f e r e n t p o p u l a t i o n s . I n a d d i t i o n they used the r e c o r d s of r e g u l a r c l i m a t i c s t a t i o n s as b a s i c d a t a . These are v e r y few at e l e v a t i o n s above 300 m,. and have unequal p e r i o d s , of re'cord ( s e c t i o n 2.5), so do not form an .adequate- sample.. More s e r i o u s l y , t h e s e s t a t i o n s do not measure a c t u a l water e q u i v a l e n t o f s n o w f a l l , but e s t i m a t e t h i s from ' 139 measured depth, o f new snow, .'and by. assuming a d e n s i t y , o f 10 0. kg/m 3 . The mean de n s i t y , o f new snow measured'- a t the end o f storms f o r both, w i n t e r s o f t h i s study was- 25.0 kg/m 3 at the e l e v a t i o n of H o l l y b u r n R i d g e , and' 230 kg/m 3 at the e l e v a t i o n of Mount Seymour CBUT (Table 6.2). A l l o w i n g f o r some compaction o f new snow d u r i n g the sto r m , the d e n s i t y o f f r e s h l y f a l l e n snow may be e x p e c t e d t o be l e s s t h a n t h e s e v a l u e s , but would c e r t a i n l y seem t o be g r e a t e r than 100 kg/m 3. For t h i s r e a s o n , w i n t e r p r e c i p i t a t i o n at the h i g h e l e v a t i o n c l i m a t i c s t a t i o n s where s n o w f a l l i s more f r e q u e n t , has p r o b a b l y b e e n , u n d e r e s t i m a t e d . T h i s e r r o r would g e n e r a t e an apparent decrease i n p r e c i p i t a t i o n at the s e h i g h e r e l e v a t i o n s . I n t h i s c o n n e c t i o n O r l o c i (1964, pg.6) s t a t e s : " Maximum p r e c i p i t a t i o n may be ex p e c t e d t o o c c u r a t an e l e -v a t i o n lower t h a n 2700 f e e t , except d u r i n g the summer months, where the maximum may o c c u r a t , or n e a r , the h i g h e s t a v a i l a b l e e l e v a t i o n . " The f a c t - a n e l e v a t i o n of maximum p r e c i p i t a t i o n was s a i d t o occur o n l y i n w i n t e r , and not i n summer when t h e r e i s not s n o w f a l l , s u p p o r t s the above argument. 6.1.3 W i n t e r p r e c i p i t a t i o n at s t a t i o n s w i t h a l o n g e r  p e r i o d o f r e c o r d Mean p r e c i p i t a t i o n r e c o r d s f o r w i n t e r are g i v e n i n Appendix F2 f o r two h i g h e r e l e v a t i o n s t a t i o n s , and f o r 140 TABLE 6.2 . Means and s t a n d a r d d e v i a t i o n s of d e n s i t y o f newly, f a l l e n snow: i n open areas -• w i n t e r s 1969-70 197-0-71 W i n t e r 19.69-70.. W i n t e r 1970-71: E l e v a t i o n / i - \ number s t n . number s t n . (meters) storms ...mean dev. storms mean dev. sampled (kg/m 3) (kg/m 3) sampled (kg/m 3) .(kg/m 3) 1260 26 268 78 35 252 71 1060 27 263 70 38 249 74 970 21 255 80 34 247 73 870 14 234 75 30 221 72 790 10 235 61 27 218 68 710 5 283 54 21 197 50 590 1 160 - 18 201 53 490 12 196 54 400 10 195 • 60 • 330 7 206 59 220 1 206 - 6 230 84 120 1 200 - 4 250 61 Note: D e n s i t y of newly f a l l e n snow i s the d e n s i t y of new snow measured at the end o f the storm. I t may. be g r e a t e r t h a n t h e d e n s i t y o f f r e s h l y  f a l l e n snow,.defined as the d e n s i t y of new snow measured'during the storm. 141 Vancouver I n t e r n a t i o n a l A i r p o r t . The d a t a s h o u l d be t r e a t e d w i t h c a u t i o n • because o f the f a c t j u s t , • d i s c u s s e d , and because the lengths- o f r e c o r d are u n e q u a l . The Mount Seymour CBUT d a t a i s e s p e c i a l l y b i a s e d because many o b s e r v a t i o n s are m i s s i n g d u r i n g heavy- snow months. Mean p r e c i p i t a t i o n between October and May i s 882 mm o r 85 p e r -cent o f the mean an n u a l at Vancouver, i s 2438 mm or 82 p e r -cent at H o l l y b u r n R i d g e , and 2420 mm or 83 p e r c e n t o f the mean an n u a l at Mount Seymour CBUT. December i s n o r m a l l y the w e t t e s t month at a l l t h r e e s t a t i o n s , w h e r e a f t e r p r e -c i p i t a t i o n g r a d u a l l y d e c r e a s e s . Over 40 p e r c e n t o f the mean annual p r e c i p i t a t i o n o c c u r s i n the t h r e e months November,. December, J a n u a r y . Mean w i n t e r p r e c i p i t a t i o n at the mountain s t a t i o n s i s almost t h r e e t i m e s h i g h e r than at Vancouver I n t e r n a t i o n a l A i r p o r t . 6.1.4 V a r i a t i o n of storm p r e c i p i t a t i o n . w i t h e l e v a t i o n V a r i a t i o n s of p r e c i p i t a t i o n w i t h e l e v a t i o n f o r storms of s e l e c t e d months are g i v e n i n F i g . 6.2. (See Appendices E and F l f o r complete d a t a f o r a l l s t o r m s ) . C l e a r l y the i n c r e a s e o f p r e c i p i t a t i o n w i t h e l e v a t i o n was not always l i n e a r , nor c o n s i s t e n t from storm t o storm. As a l r e a d y n o t e d , an e l e v a t i o n o f maximum p r e c i p i t a t i o n d i d oc c u r f o r some stor m s . The a n a l y s i s and p r e d i c t i o n of storm p r e -c i p i t a t i o n v a r i a t i o n s w i t h e l e v a t i o n i s c o n s i d e r e d more f u l l y i n Chapter 9• 14 6.2 S n o w f a l l phenology 6.2.1 Dates' of f i r s t and l a s t s n o w f a l l The dates o f the f i r s t and l a s t - s n o w f a l l , and the l e n g t h o f the s n o w f a l l season at v a r i o u s ' e l e v a t i o n s are g i v e n i n Appendix C f o r the two w i n t e r s 1969-70-, 1970-71-The f i r s t snow f e l l on Mount Seymour toward the end o f October i n b o t h w i n t e r s . The l a s t snow f e l l i n mid-May i n 1970. D i s c u s s i o n s w i t h Mount Seymour Park r a n g e r s , and s k i l i f t o p e r a t o r s , i n d i c a t e d t h i s was " U s u a l " . T h i s was c o n f i r m e d by the dates of f i r s t and l a s t snow-f a l l s from the l o n g e r p e r i o d of r e c o r d at H o l l y b u r n Ridge (950 m) and Mount Seymour (CBUT) tower (870 m) (Table 6.3) I n 1971, t h e l a s t snow was u n u s u a l l y l a t e , f a l l i n g on the 24th J u n e , when a c o l d low produced l i g h t 'snow down t o 1060 m; and the f i r s t snow i n autumn 1971 was u n u s u a l l y e a r l y , f a l l i n g at about 1000 m on the 29th September. 6.2.2 S e a s o n a l v a r i a t i o n o f new s n o w l i n e s The new s n o w l i n e s from most storms i n t e r s e c t e d the mountain at some e l e v a t i o n above i t s base ( F i g s . 4.1, 4.3) From November t o March, t h e s e s n o w l i n e s formed over the t o t a l range o f e l e v a t i o n s sampled. I n p a s t y e a r s , snow has a l s o f a l l e n i n Vancouver i n A p r i l . On the othe r * h a n d 143 TABLE 6.3 F i r s t - and l a s t s n o w f a l l , by. month, a t two h i g h - e l e v a t i o n c l l m a t o . l o g i . c a l s t a t i o n s on the' North; Shore Mountains F i r s t s n o w f a l l S t a t i o n E l e v a t i o n (meters) Month of o c c u r r e n c e & number o f events l e n g t h of r e c o r d ( y e a r s ) Sept. .Oct. Nov. H o l l y b u r n Ridge 950 1 12 2 15 Mt. Seymour CBUT •870 0 3 7 10 L a s t s n o w f a l l Q S t a t i o n E l e v a t i o n (meter s) Month of o c c u r r e n c e & number o f events l e n g t h of r e c o r d ( y e a r s ) A p r i l May June H o l l y b u r n Ridge 950 5 11 0 16 Mt. Seymour CBUT 870 2 8 0 10 Notes: ( i ) Compiled from "Monthly Record", D.O.T., Met. Branch. ( i i ) D ata f o r H o l l y b u r n Ridge f o r the p e r i o d 1954-69, and f o r Mt. Seymour f o r the p e r i o d 1958-67. 144 even i n m i d - w i n t e r , r a i n occurred, to. the top o f the mountain. D e s p i t e these• v a r i a t i o n s , t h e r e d i d e x i s t some s e a s o n a l t r e n d of new- s n o w l i n e s , with, snow more common at the low e s t l e v e l s i n December, January and F e b r u a r y . The two w i n t e r s p r e s e n t e d a marked c o n t r a s t i n p r e -c i p i t a t i o n t y p e , d e s p i t e the f a c t each had an almost i d e n -t i c a l number o f storms (Table 6.4). I n the w i n t e r 1969-70, fewer storms d e p o s i t e d snow on the mountain. I t r e p e a t -e d l y was r e s t r i c t e d t o h i g h e r e l e v a t i o n s (Table 6.5), and the l e n g t h o f the s n o w f a l l season was l e s s , e s p e c i a l l y at lower l e v e l s (Appendix C ) . C o n v e r s e l y , the w i n t e r 1970-71 e x p e r i e n c e d more snow storms. T h i r t e e n storms d e p o s i t e d snow t o sea l e v e l , compared w i t h o n l y one the p r e v i o u s w i n t e r . I n bo t h w i n t e r s , t h e r e were r e l a t i v e l y few storms w i t h snow at h i g h e r e l e v a t i o n s i n the- m i d - w i n t e r months o f January and F e b r u a r y , a l t h o u g h t h e s e months were amongst the s n o w i e s t at low e l e v a t i o n s (Table 6.5). 6.2.3 Snowlines on t r e e s The minimum e l e v a t i o n s of the l i n e s o f snow l o a d s on t r e e s ( d e f i n e d i n S e c t i o n 3.7) are g i v e n f o r two w i n t e r s i n F i g s . 6.3, 6.4. There was c o n s i d e r a b l e f l u c t u a t i o n s throughout the w i n t e r s , .depending on the n a t u r e (.and q u a n t i t y ) of the storm p r e c i p i t a t i o n . The fr e q u e n c y o f r a i n - storms ensured t h a t snow d i s a p p e a r e d from t r e e s 145 TABLE 6.4 Summary, of storm p r e c i p i t a t i o n t y p e , Mount Seymour, w i n t e r s 1969-70, 19 70-71 w i n t e r 1969-70 Storm p r e c i p i t a t i o n type Month W i n t e r 1969-70 . Oct Nov Dec J a n Feb Mar Apr May R a i n t o top o f mountain (no snow) 7 4 3 1 4 1 2 6 28 Mixed r a i n and snow a t top of mountain 0 0 1 4 1 3 4 0 13 Snow o n l y at top of mountain, r a i n below 1 6 9 3 3 3 5 1 31 Snow at a l l e l e v a t i o n s on mountain 0 0 0 1 0 0 0 . 0 . 1 TOTAL 1969-70 8 10 13 9 8 7 11 7 73 W i n t e r 1970-71 Storm p r e c i p i t a t i o n t y p e Month W i n t e r 1970-71 Oct Nov Dec J a n Feb Mar Apr May R a i n t o top of mountain (no snow) 4 2 0 5 2 1 1 4 19 Mixed r a i n and snow at top of mountain 1 3 2 2 1 2 4 1 16 Snow o n l y at top of m o u n t a i n , r a i n below 2 1 5 2 . 3 1 3 1 18 Snow at a l l e l e -v a t i o n s on mountain * . 0 , 3 5 2 4 7 0.. 0 . 21 . TOTAL I97O-.7I 7 9 „ 12 , 11 10 . 11 ' 8 6 74 i n c l u d e s storms where not p r e s e n t at end of snow was storm. o b s e r v e d t o f a l l , but was 146 TABLE 6 . 5 Frequency o f storms, d e p o s i t i n g SHOW at. .each  s a m p l i n g site.*: - w i n t e r s 1 9 6 9 - 7 0 , 1970-71 X * i n c l u d e s t r a c e ' a m o u n t s o f new snow (<0.5 cm deep) w h i c h were n o t m e a s u r e d ) E l e v a t i o n o f sa m p l i n g a r e a (meters) Month W i n t e r Oct Nov Dec Jan Feb Mar Apr May • 1969-70 1260 1 6 10 8 4 6 9 1 45 1060 1 5 10 8 4 6 . 8 1 , 43 970 1 3 10 7 4 5 8 1 39 870 1 8 7 4 1 8 29 790 1 4 6- 4 1 7 23 710 4 6 4 6 20 590 3 6 3 3 15 490 2 2 2 1 7 400 2 1 3 330 1 1 220 1 1 120 1 1 E l e v a t i o n o f s a m p l i n g a r e a (met ers) Month W i n t e r Oct Nov Dec Jan Feb Mar Apr May 1970-71 1260 3 7 12 6 8 10 7 2 55 1060 2 • 5 12 6 8 10 7 2 52 970 1 4 11 6 8 10 6 2 48 870 ' 1 4 11 6 - 8 10. / 5 . 1 46 790 . 1 4 - 11 5 8 8 4 ' 41 710 1 4 11 5 7 6 3 37 590. . 4 9 4 5 6 2 30 . 490. . 4 7 . 4 3 3 1 22 400 4 6 3 3 3 1 20 330 . 4 5 3 3 ' 3 18 220 3 . 5 3 3 1 15 120 3 4 2 3 1 13 1200 H 1000 H i _ -«-> <u E c o 800 H 600 H o I U 400 200 H Winter 1969-70 — — — Heavy Load Line Light Load Line OCT NOV DEC JAN FEB MONTH MAR APR MAY F i g . 6.3 E l e v a t i o n a l coverage of snow on trees., winter 1969-70 i - , , — " r HI 'ji • NOV DEC JAN FEB MAR ~ APR MONTH F i g . 6.4 E l e v a t i o n a l coverage of snow on t r e e s , w i n t e r 1970-71 149 s e v e r a l times d u r i n g m i d - w i n t e r . While heavy snow l o a d s were o f t e n o b s e r v e d , e s p e c i a l l y at h i g h e r e l e v a t i o n s where r i m i n g o c c u r r e d , they were seldom s u s t a i n e d f o r l o n g p e r i o d s . I n the w i n t e r 1969-70, the l o n g e s t p e r i o d w i t h heavy snow l o a d s on t r e e s was 18 days, compared w i t h 40 days the f o l l o w i n g w i n t e r . No measurements of a c t u a l l o a d s on t r e e s were made. However, the v a r i a t i o n s w i t h e l e v a t i o n of snow mass and d e n s i t y and o f t h e new s n o w l i n e s from s u c c e s s i v e storms ( F i g s . 4.1, 4.3), i n d i c a t e d t h a t l o a d s must change con-s i d e r a b l y w i t h e l e v a t i o n . T h i s i s an i m p o r t a n t p o i n t , not r e f e r r e d t o i n t h e l i t e r a t u r e , and worthy of f u r t h e r s t u d y . 6 . 3 Snow d e p o s i t i o n 6.3-1 V a r i a t i o n of w i n t e r snow d e p o s i t i o n w i t h e l e v a t i o n W i n t e r snow d e p o s i t o n v a r i e d w i t h e l e v a t i o n i n w e d g e - l i k e f a s h i o n , t a p e r i n g o f f t o s m a l l amounts at low e l e v a t i o n s ( F i g s . 6.1, 6.5). T h i s r e s u l t e d because b o t h the number o f storms w i t h snow, and the mean amount of snow per snow storm i n c r e a s e d w i t h e l e v a t i o n (Table 6.1). E x c e p t i o n s t o t h i s l a t t e r t r e n d o c c u r r e d at 120 m and 220. m, a consequence of snow d e p o s i t i o n a s s o c i a t e d w i t h A r c t i c 3 0 0 0 2 5 0 0 H 2 0 0 0 1500 •o 1000 'in 8. m g 5 0 0 0 o 0 Winter 1970-71 0 p O Winter 1 9 6 9 - 7 0 sampling site o c l e a r i n g s open areas c a n o p y edge b e n e a t h c a n o p y c l o s e to t r e e t r u n k s o p e n a r e a s c l e a r i n g s c a n o p y edge b e n e a t h c a n o p y c l o s e t o t r e e t r u n k s 200 4 0 0 6 0 0 c?00 E l e v a t i o n ( m e t e r s ) 1000 1200 I 1400 F i g . 6.5 V a r i a t i o n 1970-71 of w i n t e r - snow d e p o s i t i o n w i t h e l e v a t i o n , w i n t e r s 1969-70, 151 a i r o u t b r e a k s (.e.g. see storm. - 3 5 , 1969-70 .in F i g . 6 . 8 ) . The w i n t e r snow d e p o s i t i o n wedge bears a s t r i k i n g s i m i l -a r i t y t o t h e snow a c c u m u l a t i o n wedge d i s c u s s e d e a r l i e r ( F i g . 4 . 1 0 ) . W i n t e r snow d e p o s i t i o n was g r e a t e s t i n open a r e a s , e x cept i n t h e w i n t e r 1970-71 where i t was exceeded by t h a t f o r c l e a r i n g s above 790 m. Otherwise t h e f o r e s t s t r a t a -c l e a r i n g s , canopy edge, beneath the canopy, t r e e t r u n k s -r e c e i v e d p r o g r e s s i v e l y l e s s snow. Snow d e p o s i t i o n c l o s e t o t r e e t r u n k s was o f t e n e q u i v a l e n t t o t h a t i n open areas at an e l e v a t i o n 300 m l o w e r . S u b s t a n t i a l l y more snow was d e p o s i t e d i n t h e w i n t e r 1 9 7 0 - 7 1 . Even c l o s e t o t r e e t r u n k s i t exceeded t h e p r e v i o u s w i n t e r ' s d e p o s i t i o n i n open a r e a s . 6 . 3 . 2 Importance o f snow d e p o s i t i o n t o w i n t e r p r e c i p i t a t i o n Snow d e p o s i t i o n became l e s s i m p o r t a n t t o w i n t e r p r e c i p i t a t i o n w i t h d e c r e a s i n g e l e v a t i o n ( F i g . 6 . 1 , Table 6 . 1 ) . Snow d e p o s i t i o n was l e s s i m p o r t a n t at most e l e v a t i o n s i n 1969-70 , although, the two w i n t e r s are not d i r e c t l y comparable, because 9 storms C a l l r a i n storms) were not sampled i n t h i s w i n t e r . However, even i n 1 9 7 0 - 7 1 , which had c l o s e t o t h e maximum snow a c c u m u l a t i o n r e c o r d e d ( F i g . 3 . 6 ) , o n l y 69 p e r -cent-, o f the p r e c i p i t a t i o n f e l l as snow at the h i g h e s t 152 e l e v a t i o n sampled. Whi l e t h i s r e p r e s e n t e d a l a r g e amount, t h e r e was s u b s t a n t i a l w i n t e r r a i n f a l l . T h i s r a i n at h i g h e l e v a t i o n s i s an i m p o r t a n t f a c t o r i n p r o d u c i n g the r e l a t i v e l y h i g h d e n s i t y o f the l o c a l snowpacks ( F i g . 4.14). I t i s i n t e r e s t i n g t o compare t h i s d a t a w i t h s t a t i o n s w i t h a l o n g e r p e r i o d of r e c o r d . Mean s n o w f a l l at Vancouver I n t e r n a t i o n a l A i r p o r t i s o n l y 5 p e r c e n t of w i n t e r p r e c i p -i t a t i o n . At H o l l y b u r n R i d g e , 34 p e r c e n t of w i n t e r p r e c i p -i t a t i o n n o r m a l l y f a l l s as snow. At Mount Seymour CBUT the f i g u r e i s 19 p e r c e n t (Appendix F2). S c h a e f e r and N i k l e v a (1973) d i s c u s s t h e s e d a t a f u r t h e r , but f o r reasons p r e v i o u s l y d i s c u s s e d i n S e c t i o n s 6.1.2-3, the s n o w f a l l w a t e r e q u i v a l e n t and hence p r e c i p i t a t i o n a t t h e s e mountain s i t e s are p r o b a b l y u n d e r e s t i m a t e d . H i g h e r e l e v a t i o n s d u r i n g the m i d - w i n t e r months of January and F e b r u a r y r e c e i v e d r e l a t i v e l y l e s s snow th a n i n o t h e r months (Table 6.6). At lower e l e v a t i o n s the o p p o s i t e was t r u e . T h i s was a consequence of o c c a s i o n a l r a i n storms at the h i g h e r e l e v a t i o n s i n these months, w h i l e some storms gave snow t o low e l e v a t i o n s ( F i g s . 4.1, 4.3). Even at the h i g h e s t e l e v a t i o n sampled (1260 m), r a i n f a l l always c o n s t i t u t e d at l e a s t 8 p e r c e n t and u s u a l l y s u b s t a n t i a l l y more of the monthly p r e c i p i t a t i o n . 153 TABLE 6 . 6 Percentage of monthly p r e c i p i t a t i o n f a l l i n g  as snow at each e l e v a t i o n , open areas -winters 1 9 6 9 - 7 0 , 197.0-71 E l e v a t i o n Month (meters) Oct 1 Nov Dec . Jan Feb Mar Apr May Winter 196< }-70 1260 6 0 . 9 92.1 8 6 . 3 6 5 . 5 58.6 59-8 8 .5 1060 5 9 . 7 84.6 84 .5 66.2 3 7 . 3 61.2 5.2 • 970 5 3 . 9 43.2 5 8 . 3 59.8 5.6 46.6 1-1 . 870 5 . 3 1 8 . 9 3 5 . 5 , 3 4 . 9 2 6 . 3 790 1.2 15.4 24.6 3 0 . 9 15 .9 710 6 .5 1 8 . 7 21 .7 8.1 590 3-5 5 . 9 7.6 2 . 3 490 0.6 1.1 1.8 0 .7 400 0.8 1.0 330 0 .5 220 5.1 120 5.1 Winter 1970-71 1260 3 5 . 7 41.4 86.6 56.6 75.6 &6.6 84.0 3 4 . 1 1060 7.7 35.6 84.2 5 8 . 9 75.2 85.2 75.2 2 7 . 3 970 2 . 3 3 2 . 9 7 1 . 3 5 1 . 9 6 9 . 6 80 .2 5 6 . 7 27.8 870 1.4 2 5 . 9 62.6 39 .4 52.6 68.6 3 9 . 3 790 24.2 59.8 3 8 . 3 47.6 66 .9 3 6 . 5 710 . 24 .3 52.2 3 7 . 3 38.0 5 0 . 3 32 .2 590 2 1 . 5 3 9 . 7 32.1 3 2 . 9 40 .7 20 .3 490 . 22 .3 22.0 24 .5 2 8 . 3 24.6 2 .9 400 . 19 .1 20 .9 19 .6 2 5 . 7 16 .2 1 .7 330 . 1 2 . 5 9.0 1 2 . 9 21 .9 13-9 220 9 . 5 5 . 9 16 .1 2 3 . 3 10 .0 120 8.0 5.2 17.1 2 7 . 3 7-8 154 6.3.3 V a r i a t i o n of storm snow, d e p o s i t i o n w i t h e l e v a t i o n To i l l u s t r a t e some v a r i a t i o n s o f snow d e p o s i t i o n w i t h e l e v a t i o n and w i t h i n the f o r e s t , and the s i g n i f i c a n c e o f s n o w f a l l t o storm p r e c i p i t a t i o n , d a t a f o r s e l e c t e d storms are shown i n F i g s . 6.6-6.9 (Snow d e p o s i t i o n f o r each s t r a t u m and e l e v a t i o n f o r a l l w i n t e r storms i s g i v e n i n Appendix G). The storms were chosen from f o u r a r b i t r a r y groups. (a) Storms g i v i n g snow at h i g h e l e v a t i o n s o n l y ( g r e a t e r than 800 m) Snow from t h e s e storms was always d e p o s i t e d as a wedge whose t h i c k n e s s i n c r e a s e d w i t h e l e v a t i o n ( F i g . 6.6). F r e e z i n g l e v e l s from t h e s e storms were j u s t below, or above, the top o f the mountain. M e l t i n g o f some new snow below the f r e e z i n g l e v e l produced t h i s wedge. Above the e l e v a t i o n o f the i n c o m p l e t e new s n o w l i n e ( H Q ) , p r e c i p i t a t i o n f e l l as both snow and r a i n , w i t h snow d e p o s i t i o n i n c r e a s i n g r a p i d l y at the expense o f r a i n f a l l . For most of these storms t h e r e was an e l e v a t i o n on t h e mountains (H e) where snow d e p o s i t i o n i n open areas e v e n t u a l l y e q u a l l e d p r e -c i p i t a t i o n , but whether o r not t h i s o c c u r r e d depended on th e t h i c k n e s s o f t h e a t m o s p h e r i c m e l t i n g l a y e r , and on v a r i a t i o n s of f r e e z i n g l e v e l d u r i n g the storm. H e i s here 155 100 3 0 0 500 700 900 1100 1300 E l e v a t i o n ( m e t e r s ) F i g . 6.6 Two examples o f d e p o s i t i o n from storms which gave snow at h i g h e r e l e v a t i o n s o n l y 156 40 Storm 29 Winter 1969-70 100 300 500 700 900 1100 1300 Elevation (meters) F i g . 6.7 Two examples o f d e p o s i t i o n from storms w h i c h gave snow at h i g h e r and i n t e r m e d i a t e e l e v a t i o n s . Symbols as f o r F i g . 6.6 157 F i g . 6.8 D e p o s i t i o n from a storm w i t h snow t o low e l e v a t i o n s . Symbols as f o r F i g . 6.6 158 140 I i I : l i ; I 1 100 300 500 700 900 1100 1300 Elevation (meters ) F i g . 6.9 D e p o s i t i o n from a storm w i t h l a r g e amounts of snow. Symbols as f o r F i g . 6.6 159 termed t h e " e q u i . y a l e r i t e l e y a t i o n " . The r e g i o n between H 0 and H e i s c a l l e d the "wet snow zone". The r e g i o n below H 0, where no new snow was d e p o s i t e d i s c a l l e d the " r a i n zone" . At a l l e l e v a t i o n s , p r o g r e s s i v e l y l e s s snow was d e p o s i t e d at the canopy edge, beneath the canopy and c l o s e t o t r e e t r u n k s . Immediately above H 0 t h e r e was f r e q u e n t l y no snow d e p o s i t i o n beneath t r e e s . L o c a l v a r i a t i o n s i n t h i s p a t t e r n sometimes r e s u l t e d from d r i f t i n g i f winds were stro n g , . o r - from snow s l i d i n g o f f t r e e s t o the canopy edge. (b) Storms g i v i n g snow t o h i g h and i n t e r m e d i a t e e l e v a t i o n s ( g r e a t e r t h a n 400 m) These storms a l s o d e p o s i t e d snow i n wedge form ( F i g . 6.7). I n the wet snow zone, s i m i l a r t r e n d s t o those d i s c u s s e d above were o b s e r v e d . Above H e p r e c i p i t a t i o n f e l l as snow o n l y . T h i s was termed the "snow zone". As i n the wet snow zone, d e p o s i t i o n became p r o g r e s s i v e l y l e s s from open areas t h r o u g h t o " c l o s e t o t r e e t r u n k s " . I n some sto r m s , s u b s t a n t i a l d r i f t i n g o c c u r r e d above 1000 m, so t h a t a f u r t h e r " d r i f t snow zone" i s r e c o g n i s e d . Here snow beneath t r e e s , c l o s e t o t r e e t r u n k s and i n c l e a r i n g s , was s u b s t a n t i a l l y g r e a t e r t h a n i n open a r e a s . Wind scour a t the canopy edge, and f o r m a t i o n o f c o r n i c e s were a l s o 160 c h a r a c t e r i s t i c f e a t u r e s . The development of t h i s zone o c c u r r e d o n l y I f storms g e n e r a t e d s t r o n g winds. The d r i f t snow zone marked the upper l i m i t of the snow zone. On Mount Seymour t h i s l i m i t never o c c u r r e d below 1000. m. However, on mountains w i t h l e s s dense, or no f o r e s t c o v e r , i t may ex t e n d t o lower e l e v a t i o n s . The r a i n , wet snow, and snow zones are a l l d e f i n e d w i t h r e s p e c t t o the storm f r e e z i n g l e v e l . On the o t h e r hand, the d r i f t snow zone i s d e f i n e d i n terms of wind i n d u c e d d e p o s i t i o n a l f e a t u r e s . F o r a storm w i t h s t r o n g winds t h i s zone c o u l d e x t e n d down t o H e, and hence e l i m i n a t e the snow zone. T h i s s i t u a t i o n n ever o c c u r r e d on Mount Seymour, but may e l s e w h e r e . (c) Storms g i v i n g snow t o low e l e v a t i o n s (below 400 m) I f the f r e e z i n g l e v e l from th e s e storms was at sea l e v e l , the shape of the snow wedge was l e s s developed s i n c e no r a i n o r wet snow zones o c c u r r e d . However, t h e r e was s t i l l some i n c r e a s e i n s n o w f a l l w i t h e l e v a t i o n , because of the u s u a l o r o g r a p h i c i n c r e a s e of p r e c i p i t a t i o n . I f the f r e e z i n g l e v e l was above sea l e v e l , wet snow and/or r a i n zones formed, and a snow wedge was produced. Storms w i t h snow t o low e l e v a t i o n s were o f t e n a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , w h i c h were o v e r - r i d d e n by m o i s t 161 P a c i f i c a i r . I n some of t h e s e storms a l a y e r o f warmer a i r and a l o c a l minimum o f s n o w f a l l o c c u r r e d at i n t e r m e d i a t e e l e v a t i o n s (e.g. storm 3 5 , 1 9 6 9 - 7 0 , F i g . 6 . 8 ) . (d) Storms w i t h l a r g e amounts of s n o w f a l l ( s n o w f a l l > 80 kg/m 2) These o c c u r r e d w i t h s n o w l i n e s at v a r i o u s e l e v a t i o n s . P r e c i p i t a t i o n at the base of t h e mountain (120 m) was u s u a l l y g r e a t e r t h a n 40 mm. F e a t u r e s o f t h e s e storms were o t h e r w i s e s i m i l a r t o t h o s e d i s c u s s e d above ( F i g . 6 . 9 ) . These examples show the wedge shape p a t t e r n o f d e p o s i t i o n w i t h e l e v a t i o n t o be a p e r s i s t e n t f e a t u r e o f s torms, except i n the few cases where the. f r e e z i n g l e v e l o c c u r s a t sea l e v e l . T h i s c o n s i s t e n c y must be a major f a c t o r i n t h e development of the s i m i l a r wedge-shaped d i s t r i b u t i o n of w i n t e r snow d e p o s i t i o n ( F i g . 6 . 5 ) and u l t i m a t e l y i n t h a t o f snowpack a c c u m u l a t i o n ( F i g . 4 . 1 0 ) . T h i s i s i l l u s t r a t e d i n f u r t h e r d e t a i l i n F i g . 6 . 1 0 , where the d e p o s i t i o n o f snow from each storm i s accumulated f o r the w i n t e r . The a d d i t i v e snow-wedges from each storm combine t o form a composite wedge. S u b t r a c t from t h i s the p r e f e r e n t i a l m e l t i n g at l o w e r e l e v a t i o n s t h a t t a k e s p l a c e d u r i n g and between s t o r m s , and i n t h e s p r i n g , and the wedge shape i s f u r t h e r enhanced. 162 The a d d i t i v e e f f e c t of snow d e p o s i t i o n from each storm. Data f o r open areas f o r each w i n t e r , 1969-70 (.top) and w i n t e r 1970-71 (bottom). Snow d e p o s i t i o n from each storm i s added t o t h a t of the p r e v i o u s storms t o g i v e a composite' snow wedge f o r the whole w i n t e r . Drawn by computer. 163 6.3.4 A q u a l i t a t i v e model of snow d e p o s i t i o n 'from a  storm on a west, c o a s t m i d l a t i t u d e mountain Based on the p r e v i o u s d i s c u s s i o n , a q u a l i t a t i v e d e s c r i p t i o n of snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n i n open areas i s p r e s e n t e d i n s c h e m a t i c form i n F i g . 6.11a. F o r c o n v e n i e n c e , the v a r i a t i o n s o f snow d e p o s i t i o n • w i t h e l e v a t i o n are shown as l i n e a r f u n c t i o n s , but t h e s e need not be so. A l l zones o f t h e snow wedge may not be produced by each storm: when winds are l i g h t , t he d r i f t snow zone w i l l not e x i s t , c o n v e r s e l y , t h i s zone can e l i m i n a t e the snow zone i f winds are s t r o n g ; i f the st o r m f r e e z i n g l e v e l o c c u r s much above the top o f the mountain, o n l y wet snow and r a i n zones are formed, but th e s e zones are e l i m i n a t e d i f the f r e e z i n g l e v e l i s at or "below" the base o f the mountain. Except f o r the d r i f t snow zone, a l l zones o f the diagram are d e f i n e d i n terms o f the f r e e z i n g l e v e l . As the f r e e z i n g l e v e l s h i f t s i n e l e v a t i o n from storm t o st o r m , or w i t h i n a s t o r m , so too do t h e s e zones. Thus the diagram s h o u l d be e n v i s a g e d as a moving system o f zones o r co-o r d i n a t e s a p p l i e d t o the f i x e d c o - o r d i n a t e s o f e l e v a t i o n of the mountain. As l o n g as the f r e e z i n g ; l e v e l d u r i n g a storm remains r e l a t i v e l y c o n s t a n t and below the top of the mountain, the 164 (o) N o l o r c of deposit ion on mountoln (simple i t o r m ) drift s n o w xone N o t u r e of d e p o s i t i o n In f o r e s t In e a c h l o n e Ho (Incomplete n e w roin zone (b) N o t u r e Of d e p o s i t i o n o n m o u n t a i n ( c o m p o s i t e s t o r m ) N o t u r e of d e p o s i t i o n p o s t f r o n t o l freezing^ level P°&t frontoI Ho F i g . 6.11 Schematic diagram of snow d e p o s i t i o n from a storm on a west c o a s t m i d l a t i t u d e mountain (a) Storm w i t h r e l a t i v e l y c o n s t a n t f r e e z i n g l e v e l (b) Composite storm w i t h f l u c t u a t i n g f r e e z i n g l e v e l 165 model of F i g . 6 . 11a w i l l a p p l y . However, f o r some storms the. f r e e z i n g l e v e l o c c u r s s u c c e s s i v e l y at two or more d i f f e r e n t e l e v a t i o n s . I f t h e r e has been s u b s t a n t i a l p r e -c i p i t a t i o n at each p o s i t i o n of the f r e e z i n g l e v e l , t h e n the storm may have t o be d i v i d e d i n t o s ubstorms, and the model a p p l i e d t o each i n t u r n . The most common of t h e s e cases i s where the f r e e z i n g l e v e l - i s below the top o f the mountain f o r but p a r t o f the sto r m , so t h a t b o t h r a i n ' a n d snow f a l l at the h i g h e s t e l e v a t i o n s ( F i g . -6 .11b) . The snow-wedge s t i l l f o r ms, u s u a l l y by d e p o s i t i o n from the c o l d e r a i r a f t e r a f r o n t a l p a s s a g e , but- a p r e v i o u s a d v e c t i o n of warmer a i r ahead o f the f r o n t may have produced rainV'at a l l e l e v a t i o n s on the mountain. The p r e c i p i t a t i o n i s d i v i d e d i n t o s ubstorms, so t h a t H e i s now d e f i n e d as the e l e v a t i o n where p o s t f r o n t a l snow d e p o s i t i o n e q u a l s p o s t f r o n t a l p r e c i p i t a t i o n . O f t e n H e can be i d e n t i f i e d by a r e d u c t i o n i n s l o p e of the new snow-wedge (e. g . storm 6 2 , F i g . 6 . 6 , where H e i s about 1050 m). D u r i n g the two w i n t e r s o f measurement, t h e r e were a l s o . a few more c o m p l i c a t e d storms where the f r e e z i n g l e v e l , was seldom c o n s t a n t . At the b e g i n n i n g o f the storm the f r e e z i n g l e v e l and hence s n o w l i n e would be a t low e l e -v a t i o n , t h e n r i s e t o aboye the mo u n t a i n , t h e n descend a g a i n . The q u a l i t a t i v e model can handle t h e s e composite storm 166 t y p e s , when broken down i n t o separate, substorms. However, d i v i s i o n i n t o , substorms i s o f t e n d i f f i c u l t i f based o n l y on e v i d e n c e observed i m m e d i a t e l y a f t e r the storm. C o n t i n u a l m o n i t o r i n g o f the type o f p r e c i p i t a t i o n d u r i n g t h e s e c o m p l i c a t e d storms at a number o f d i f f e r e n t e l e v a t i o n s would a l l o w such s u b d i v i s i o n , but l o g i s t i c a l l y t h i s was not p o s s i b l e I n t h i s s t u d y . T h i s q u a l i t a t i v e model o f storm snow d e p o s i t i o n w i t h e l e v a t i o n i s t r a n s l a t e d i n t o q u a n t i t a t i v e forms i n Chapter 9• 6.4 Rime a c c r e t i o n 6 . 4 . 1 R e s u l t s Large q u a n t i t i e s of rime•on t r e e s , b u i l d i n g s , w i r e s and p o l e s are a f e a t u r e o f the w i n t e r l a n d s c a p e o f Mount Seymour a f t e r some storms ( F i g . 6 . 1 2 ) . The s i z e and fre q u e n c y o f th e s e rime d e p o s i t s suggests t h a t they make a s i g n i f i c a n t c o n t r i b u t i o n t o th e water i n p u t at h i g h e r e l e v a t i o n s on Mount Seymour. F o r the two y e a r s o f t h i s s t u d y , no rime was- o b s e r v e d below 790 jn. Above t h i s , t he number o f storms w i t h rime i n c r e a s e d l i n e a r l y w i t h e l e y a t i o n . However, the t o t a l l e n g t h o f rime i n c r e a s e d e x p o n e n t i a l l y (Table 6.7,5 F i g - 6 . 1 3 ) , 167 F i g . 6.12 Rime d e p o s i t s a c c r e t e d onto 0.5 cm d i a m e t e r r e c e p t o r s t a k e ( t o p ) and onto t r e e s (bottom) E l e v a t i o n 1260 m, March 1971 168 TABLE 6 .7 Amount of rime accreted on 0..5 cm diameter  stakes' ab.oVe the snow surface• -6 December 197.0.-31 May 197.1 E l e v a t i o n (meters) 12 60 . 106.0 970 . 870 790 . T o t a l h o r i z o n t a l length (cm) 146 35 20 10 3 Number of storms with rime a c c r e t i o n 26* 16 11 6 2 Mean length/storm w i t h rime (cm) 5.6 2.2 1.8 1.7 1.5 % of snow storms with r i m e • a c c r e t i o n 72 44 31 17 6 % of a l l storms with rime a c c r e t i o n 46 29 20 11 4 Estimated water equivalent of rime a c c r e t i o n (mm)** 438 . 105 60 30 9 Estimated rime a c c r e t i o n as % of t o t a l winter p r e c i p i t a t i o n 12.5 3.0 2.1 1.1 0.3 Included one case with, two d i r e c t i o n s of r i m i n g from one storm. Estimated assuming density, f o r rime of 300 kg/m3 (see t e x t ) . 169 30 P i g . 6.13 H o r i z o n t a l length.'of rime a c c r e t e d on. 0 .5 cm d i a m e t e r s t a k e s , by e l e v a t i o n and d i r e c t i o n of growth," -6 December 1970 -.31 May 1971 170 with, l a r g e i n c r e a s e s ab.oye 106.0 jn.'. The l a r g e s t a c c r e t i o n measured on the 0 . 5 cm s t a k e s •from one storm was 16 cm l o n g ( s t o r m 2 8 , 1 9 7 0 - 7 1 ) . The dominant wind d i r e c t i o n (as•measured at'Vancouver I n t e r n a t i o n a l A i r p o r t ) f o r r i m i n g was from the e a s t ( p r e f r o n t a l c o n d i t i o n s ) . There was a l s o s u b s t a n t i a l rime a c c u m u l a t i o n from winds w i t h westerly-a s pect ( p o s t f r o n t a l c o n d i t i o n s ) . i t i s g e n e r a l l y b e l i e v e d rime grows d i r e c t l y i n t o the wind, but S c o r e r ( 1 9 7 2 , pg . 1 3 2 ) r e p o r t s rime a c c r e t i o n about 30° on e i t h e r s i d e o f t h a t d i r e c t i o n . T h i s may h e l p e x p l a i n d i f f e r e n c e s i n the shapes o f the wind and rime r o s e s i n P i g . 6 . 1 3 ) . Only one storm produced r i m i n g from two s e p a r a t e d i r e c t i o n s . R i m i n g was obser v e d t o form d u r i n g , or i m m e d i a t e l y a f t e r , snow s t o r m s , but not a l l snow storms a c c r e t e d r i m e . 6 . 4 . 2 Rime on t r e e s Rime d e p o s i t s - from a s i n g l e storm o f t e n had a-s h a r p l y d e f i n e d l ower e l e v a t i o n a l l i m i t . T h i s produced an apparent " s n o w l i n e " t h a t was c l e a r l y v i s i b l e on the m o u n t a i n s i d e . I n f a c t t h i s o n l y marked the l i m i t o f rime on t r e e s , and new snow o f t e n f e l l t o e l e v a t i o n s below t h i s l i n e . At h i g h e r e l e v a t i o n s , rime sometimes p e r s i s t e d on t r e e s between s t o r m s , so was a b l e to. b u i l d t o c o n s i d e r a b l e . 171 t h i c k n e s s . Trees, t h e n became completely, c o v e r e d w i t h rime and compacted snow, a p p e a r i n g as l a r g e h a r d ' i c e p i l l a r s w i t h no f o l i a g e v i s i b l e . 6.4.3 Water e q u i v a l e n t o f rime a c c r e t e d The measurements i n d i c a t e d t h a t rime might form an i m p o r t a n t i n p u t i n t o the w i n t e r water b a l a n c e , e s p e c i a l l y above 1000 m. Rime c o l l e c t e d by t r e e s was o f t e n o b s e r v e d t o f a l l t o the snowpack beneath. It-was a l s o observed t o have grown d i r e c t l y onto the snowpack, e s p e c i a l l y on the w a l l s of snow or s c o u r h o l l o w s . I n t h i s study the a c t u a l water e q u i v a l e n t of rime was not measured. However, t h i s may be c a l c u l a t e d f o r the u n i t c r o s s s e c t i o n a l a r e a exposed t o an a i r str e a m i f the d e n s i t y o f rime i s known. Some e s t i m a t e s o f d e n s i t y were made by measuring the dimensions o f rime • depo'sits t o f i n d t he volume, t h e n s u b s e q u e n t l y w e i g h i n g the sample. V a l u e s ranged from 3^0 kg/m 3 t o 610 kg/m 3. E s t i m a t e s o f the volume were s u b j e c t t o e r r o r as the rime was f e a t h e r y and i r r e g u l a r i n shape. H e i k i n h e i m o ( i n M i l l e r 1966) r e p o r t e d d e n s i t i e s o f 150-300 kg/m 3 f o r rime and' snow p l a s t e r e d on t r e e s by s t r o n g winds i n N o r t h e r n F i n l a n d . I n a l a b o r a t o r y s t u d y o f f r o s t growth on a f l a t p l a t e h e l d at s u b f r e e z i n g t e m p e r a t u r e s ( e q u i v a l e n t t o the f o r m a t i o n 172 o f r i m e ) , Trammell e t a l (.196.8). found a d e n s i t y o f 216 kg/m 3, a f t e r one hours growth. A f t e r . 24. hours growth Chung and A l g r e n (1958) measured a d e n s i t y of 500. kg/m 3. Only t h i c k n e s s e s o f a few mm- c l o s e t o the rim e d o b j e c t were c o n s i d e r e d i n b o t h s t u d i e s . Trammell e t a l b e l i e v e d t h a t i f growth c o n t i n u e d f o r s e v e r a l months .the d e n s i t y would r i s e t o 800 kg/m 3. F r o s t d e n s i t i e s were i n c r e a s e d by h i g h e r s p e c i f i c h u m i d i t i e s and h i g h e r wind v e l o c i t i e s . The temperature o f the a i r s t r e a m had l i t t l e e f f e c t , e x cept i n c o n t r o l l i n g t he temperature o f the m a t e r i a l on which the f r o s t J w a s g r o w i n g . The lower t h i s t e m p e r a t u r e , the lower the d e n s i t y . Tramwell e t a l a l s o r e p o r t e d t h a t the d e n s i t y o f a f r o s t l a y e r i n c r e a s e d w i t h depth and the d e n s i t y o f any s u b l a y e r i n c r e a s e d w i t h t i m e . From t h i s e v i d e n c e i t appears- the d e n s i t y o f rime on Mount Seymour must v a r y from storm t o s t o r m , depending on weather c o n d i t i o n s , and amount o f rime accreted.. F o r want o f b e t t e r e v i d e n c e a d e n s i t y o f 300 kg/m 3 was assumed. The' t o t a l h o r i z o n t a l l e n g t h o f rime a c c r e t e d was m u l t i p l i e d by t h i s assumed d e n s i t y t o g i v e an e s t i m a t e o f the water e q u i v a l e n t per u n i t v e r t i c a l a r e a exposed t o an a i r s t r e a m . The 438 mm at 126.0 m i s s u b s t a n t i a l (Table 6 . 7 ) , and has been e x p r e s s e d as a pe r c e n t a g e o f the t o t a l w i n t e r p r e c i p -i t a t i o n , w h i c h o f course is.measured w i t h r e s p e c t t o a u n i t h o r i z o n t a l a r e a . Thus the v a l u e o f 1 2 . 5 p e r c e n t o f 173 t o t a l w i n t e r p r e c i p i t a t i o n at 1260 m i s somewhat hypo-t h e t i c a l i n t h a t rime grows o n l y on s p e c i f i c o b j e c t s i n the way o f the a i r s t r e a m , and t o a l i m i t e d e x t e n t on some n e a r - h o r i z o n t a l snow s u r f a c e s , whereas p r e c i p i t a t i o n o c c u r s over the e n t i r e s u r f a c e . N e v e r t h e l e s s , i t i s i n t e r e s t i n g t o compare t h i s d a t a w i t h f i n d i n g s o f o t h e r r e s e a r c h e r s . For example, Berndt and Fow l e r (1969) thought rime c o u l d c o n t r i b u t e as much as 75 t o 100 mm m o i s t u r e i n an e n t i r e w i n t e r on upper f o r e s t e d s l o p e s i n E a s t e r n Washington. T h i s c o u l d be up t o 10 p e r c e n t o f t h e t o t a l y e a r l y m o i s t u r e i n p u t . E s t i m a t e s o f 50 t o 130 mm a d d i t i o n a l m o i s t u r e have been made f o r t i m b e r e d areas above 1500 m i n south e a s t e r n A u s t r a l i a ( C o s t i n e t a l 1961). G e i g e r ' s (1965) r e v i e w o f German work c i t e s Grunow, who c a l c u l a t e d dew and rime supplement from f o g t o be 20 p e r c e n t o f an n u a l p r e c i p i t a t i o n at about 1000 m. Care must be t a k e n i n i n t e r p r e t a t i o n o f t h e s e r e s u l t s , s i n c e F o w l e r and Berndt (1971) have shown t h a t a c c u m u l a t i o n of rime i s c o n t r o l l e d not o n l y by m e t e o r o l o g i c a l c o n d i t i o n s , but a l s o by t h e s i z e and shape o f r e c e p t o r . Thus the above r e s u l t s cannot be s t r i c t l y compared, s i n c e the r e s e a r c h e r s used d i f f e r e n t t y p e s o f r e c e p t o r s . F o w l e r and Berndt show the r a t e o f rime a c c u m u l a t i o n decreases e x p o n e n t i a l l y w i t h i n c r e a s e d r a d i u s o f r e c e p t o r t o some c r i t i c a l d i m e n s i o n , where c e s s a t i o n of growth can be ex p e c t e d . The c r i t i c a l 174 d i m e n s i o n i s p r o p o r t i o n a l t o wind v e l o c i t y and t o the square o f the s u p e r c o o l e d d r o p l e t r a d i u s (Kuroiwa 1965). I t i s p o s s i b l e t h a t i n t h i s study,' t h e r e c e p t o r s i z e o f 0.5 cm may have on o c c a s i o n s exceeded the c r i t i c a l dimen-s i o n , so t h a t rime growth ceased, a l t h o u g h rime c o n t i n u e d t o a c c r e t e on s m a l l e r d i a m e t e r r e c e p t o r s such as c o n i f e r n e e d l e s . There i s a l s o a p o s s i b l e r e d u c t i o n i n c o l l e c t i o n e f f i c i e n c y d u r i n g a s t o r m , due t o i n c r e a s i n g c r o s s s e c t i o n a l a r e a and t o changes i n aerodynamic p r o f i l e w i t h rime growth. 6.5 C o n c l u s i o n T o t a l w i n t e r p r e c i p i t a t i o n i n c r e a s e s l i n e a r l y w i t h e l e v a t i o n on Mount Seymour, w i t h no ev i d e n c e o f an i n t e r -mediate e l e v a t i o n where a c o n s i s t e n t p r e c i p i t a t i o n maximum o c c u r s . T h i s i s c o n t r a r y t o the f i n d i n g s o f e a r l i e r w o r k e r s , but they have tended t o u n d e r e s t i m a t e w i n t e r p r e -c i p i t a t i o n t h r o u g h use o f a snow d e n s i t y o f 100 kg/m 3 t o co n v e r t s n o w f a l l t o water e q u i v a l e n t . The t r u e d e n s i t y o f newly f a l l e n snow i s a t l e a s t t w i c e t h i s , v a l u e . However, the v a r i a t i o n o f storm p r e c i p i t a t i o n w i t h e l e v a t i o n i s ex t r e m e l y v a r i a b l e from storm t o s t o r m , and on o c c a s i o n s a maximum can o c c u r below the base o f t h e mountain. R a i n f r e q u e n t l y f a l l s a t t h e top o f t h e mountain even i n mid-w i n t e r . C o n v e r s e l y , snow may f a l l t o sea l e v e l on o c c a s i o n s . 175 Snow d e p o s i t i o n from each, storm i n c r e a s e s with, e l e v a t i o n i n wedge l i k e form. T h i s p e r s i s t e n t wedge shape, from s u c c e s s i v e storms- u l t i m a t e l y h e l p s produce the snow-wedge of snowpack a c c u m u l a t i o n . Less snow i s d e p o s i t e d i n the f o r e s t t h a n i n open a r e a s . Rime adds an a p p r e c i a b l e amount t o w i n t e r w a t e r i n p u t , but the amount a c c r e t e d depends on the number, shapes and s i z e s o f r e c e p t o r s w i t h i n the a i r f l o w , as w e l l as on m e t e o r o l o g i c a l v a r i a b l e s . A q u a l i t a t i v e model i s proposed t o d e s c r i b e snow d e p o s i t i o n v a r i a t i o n s w i t h e l e v a t i o n . I t i d e n t i f i e s a s e r i e s of zones of d e p o s i t i o n which are l i n k e d t o the e l e -v a t i o n o f the storm ( o r substorm) f r e e z i n g l e v e l and t o wind v e l o c i t y . T h i s model, f u r t h e r a n a l y s e s of snow d e p o s i t i o n d a t a and a f o l l o w i n g d i s c u s s i o n of the c l i m a -t o l o g y of snow storms are the f o u n d a t i o n f o r q u a n t i t a t i v e p r e d i c t i o n f u n c t i o n s developed i n Chapter 9-176 CHAPTER 7 7. ANALYSIS OF SNOW DEPOSITION The e x t e n s i v e s a m p l i n g network o f t h i s s t u d y was de s i g n e d t o a l l o w use o f a n a l y s i s o f v a r i a n c e t e c h n i q u e s . The r e s u l t s o f t h i s a n a l y s i s , p r e s e n t e d i n t h e next s e c t i o n , l e a d t o d i s c u s s i o n of the e f f i c i e n c y of the s a m p l i n g n e t -work, t e c h n i q u e s f o r r e d u c i n g the network, and t h e f e a s -i b i l i t y o f computing the t o t a l mass of snow over a meso-s c a l e a r e a . 7.1 A n a l y s i s o f v a r i a n c e o f snow d e p o s i t i o n . Snow d e p o s i t i o n from t h e 82 storms sampled was examined by a n a l y s i s o f v a r i a n c e t e c h n i q u e s t o d i s c o v e r i f t h e r e were: (a) any s i g n i f i c a n t d i f f e r e n c e s among s t o r m s , (b) any s i g n i f i c a n t d i f f e r e n c e s , among e l e v a t i o n s , (c) any s i g n i f i c a n t d i f f e r e n c e s among the f o r e s t s t r a t a . As a f i r s t s t e p , the a n a l y s i s o f v a r i a n c e model i n T able 7-1 was a p p l i e d t o a l l d a t a o f the w i n t e r 1 9 6 9 - 7 0 . The model r e q u i r e s e q u a l sample s i z e s f o r s t r a t a and e l e v a t i o n s . 177 TABLE 7 . 1 A n a l y s i s o f v a r i a n c e models used t o examine  snow d e p o s i t i o n A. Model and r e s u l t s f o r a l l d a t a - winter. 1 9 6 9 - 7 0 Source d f SS ms F Storms 37 2604 70 . 4 1868 ** E l e v a t i o n s 12 11267 938 .9 24920 ** S t r a t a 4 703 175 • 7 4663 ** Storm X E l e v a t i o n 444 7089 16 .0 4 2 4 * * S t r a t a X E l e v a t i o n 4 8 1184 . 2 4 .6 655 ** S t r a t a X Storm 1 4 8 426 2 .9 76 ** S t r . X E l e v . X Storm 1 7 7 6 1891 1 .1 28 ** E r r o r 12350 465 0 . 0 4 TOTAL 14819 25629 ** s i g n i f i c a n t at 99% c o n f i d e n c e l e v e l B. • Model f o r a n a l y s i s o f each storm s e p a r a t e l y - w i n t e r s 1 9 6 9 - 7 0 , 1970-71 Source df E l e v a t i o n s S t r a t a E l e v a t i o n s X S t r a t a E r r o r ; H-1 • S-1 (H-1) (S - 1 ) HS (R - 1 ) TOTAL HSR-1 Where, H = e l e v a t i o n , H = l , 2 , . . . . n , • n£ l 2 , depending on e l e v a t i o n o f storm s n o w l i n e S = s t r a t u m , S = 1 , 2 , . . 5 R = number r e p l i c a t i o n s i n each s t r a t u m , R = 1,2 . . .6 178 T h i s i n t r o d u c e s the d i s a d v a n t a g e - t h a t z e r o v a l u e s must be a s s i g n e d and a n a l y z e d f o r e l e v a t i o n s below the s n o w l i n e . On the o t h e r hand, i t p o s s e s s e s the u s e f u l advantage t h a t i n t e r a c t i o n s can be examined. The r e s u l t s i n d i c a t e - t h a t snow d e p o s i t i o n i s s i g n i f i c a n t l y d i f f e r e n t , a t the 99 p e r -cent c o n f i d e n c e l e v e l , among s t o r m s , e l e v a t i o n s and s t r a t a . More i m p o r t a n t l y , a l l the i n t e r a c t i o n s are h i g h l y s i g n i f i -cant . T h i s shows the b e h a v i o u r of the mountain t e r r a i n segment t o snow d e p o s i t i o n v a r i e s from s t o r m t o s t o r m , from e l e v a t i o n t o e l e v a t i o n , and from s t r a t u m t o s t r a t u m . The i n t e r a c t i o n between storms and e l e v a t i o n s i s e x p e c t e d , s i n c e on a west c o a s t m i d l a t i t u d e mountain the new s n o w l i n e s n o r m a l l y v a r y from storm t o storm. The i n t e r a c t i o n s between f o r e s t s t r a t a and e l e v a t i o n , and between s t r a t a and storms are more i n t e r e s t i n g . They i n d i c a t e new snow i s d i s t r i b u t e d d i f f e r e n t l y i n the f o r e s t at d i f f e r e n t e l e v a t i o n s , and d u r i n g d i f f e r e n t s torms. S e v e r a l i m p o r t a n t i m p l i c a t i o n s f o l l o w . F o r example, a snow gauge s i t e d at one e l e v a t i o n w i l l be unable t o i n d e x d e p o s i t i o n a d e q u a t e l y on the mountain t e r r a i n segment. I n f a c t , s i n c e e l e v a t i o n - f o r e s t i n t e r a c t i o n s o c c u r , even a network of gauges s i t u a t e d at v a r i o u s e l e v a t i o n s , say i n c l e a r i n g s , as i s a common p r o c e d u r e , w i l l be i n a d e q u a t e . The i n t e r a c t i o n s a l s o suggest m e t e o r o l o g i c a l c h a r a c t e r i s t i c s 179 o f storms are an i m p o r t a n t i n f l u e n c e i n t h e a r e a l d i s t r i -b u t i o n o f new snow. The presence o f the s e i n t e r a c t i o n s i n snow d e p o s i t i o n must a l s o be an i m p o r t a n t p a r t o f the e x p l a n a t i o n f o r the snowpack water e q u i v a l e n t i n t e r a c t i o n s d i s c u s s e d i n Chapter 5. Data f o r the w i n t e r 1970-71 were not a n a l y s e d i n t h i s way, because a s i m i l a r r e s u l t was e x p e c t e d . I n s t e a d , an a n a l y s i s o f v a r i a n c e was performed f o r each storm. The model used i s a l s o g i v e n i n Table 7.1. T h i s model a n a l y s e s o n l y those snow d e p o s i t i o n v a l u e s above the new s n o w l i n e from each storm.' Thus zer o v a l u e s below the s n o w l i n e are not i n c l u d e d , and a d i s a d v a n t a g e of the f i r s t model i s e l i m i n a t e d . Of t h e snow storms sampled, f i v e were not s u i t a b l e f o r a n a l y s i s because snow f e l l a t o n l y one e l e v a t i o n (1260 m). Of the 77 storms s u b s e q u e n t l y a n a l y s e d , a l l show s i g n i f i c a n t d i f f e r e n c e s i n snow- d e p o s i t i o n among e l e v a t i o n s and among s t r a t a . A l l but t h r e e storms show h i g h l y s i g n i f i c a n t e l e v a t i o n s - s t r a t a i n t e r a c t i o n e f f e c t s . Thus, a l t h o u g h d i f f e r e n c e s i n snow d e p o s i t i o n o c c u r among e l e -v a t i o n s and among s t r a t a , the b e h a v i o u r o f the f o r e s t t o snow d e p o s i t i o n v a r i e s from e l e v a t i o n t o e l e v a t i o n . Some of t h i s v a r i a t i o n may be due t o the changing n a t u r e o f the f o r e s t w i t h e l e v a t i o n ( F i g s . 2.7 S 2.8), e s p e c i a l l y 180 since the data includes a wide v a r i e t y of storms with a wide v a r i e t y of new snowlines ( P i g s . 4.1, 4.3). M e t e o r o l o g i c a l f a c t o r s that vary with e l e v a t i o n may a l s o be important. Of those storms which show no s i g n i f i c a n t e l e v a t i o n -f o r e s t s t r a t a i n t e r a c t i o n , one deposited very small amounts of snow (storm 70, 1970-71)- The other two (storm 21, 1970-71; storm 36, 1970-71) had moderate s n o w f a l l s , but were p r i n c i p a l l y c h a r a c t e r i s e d by very l i t t l e t a p e r i n g of the new snow wedge ( i . e . a very narrow wet snow zone). This suggests the e l e v a t i o n - f o r e s t i n t e r a c t i o n of other storms i s a ssociated w i t h the developemnt of the wet snow zone where reduced, or zero, snow amounts are deposited w i t h i n the f o r e s t . The d i f f e r e n t p a t t e r n of snow d e p o s i t i o n at the more exposed e l e v a t i o n s above 1000 m, where winds may erode snow from open areas to be deposited beneath-trees, a l s o c o n t r i b u t e s to the i n t e r a c t i o n term (e.g. storm 55, F i g . 6.6). To i n v e s t i g a t e these comments f u r t h e r , Duncan's New M u l t i p l e Range Test was performed on e l e v a t i o n , stratum, and i n t e r a c t i o n means. This t e s t i n d i c a t e s which snow de p o s i t i o n means are not s i g n i f i c a n t l y d i f f e r e n t , that i s those which are homogeneous. Unf o r t u n a t e l y , the r e s u l t s f o r i n t e r a c t i o n means proved hopelessly complicated and impossible to f o l l o w . However, a summary of storms where 181 a d j a c e n t e l e v a t i o n s , or f o r e s t s t r a t a , had snow d e p o s i t i o n means t h a t were homogeneous, i s i n s t r u c t i v e (Table 7-2). F o r the b u l k o f s t o r m s , snow d e p o s i t i o n means were s i g n i f i c a n t l y d i f f e r e n t between each e l e v a t i o n sampled. The p r i n c i p a l e x c e p t i o n s were between 790-870 m, and between 400-490 m, but t h e s e s a m p l i n g e l e v a t i o n s are a l s o c l o s e r t o g e t h e r t h a n most. To examine whether snow d e p o s i t i o n means are l i k e l y t o be more homogeneous as s a m p l i n g e l e -v a t i o n s became c l o s e r , F i g . 7.1 was c o n s t r u c t e d . The r e s u l t s i n d i c a t e t h i s t o be g e n e r a l l y t r u e , but o t h e r f a c t o r s appear i m p o r t a n t . F i r s t , i n 38 p e r c e n t of the storms sampled, snow d e p o s i t i o n means at t h e t h r e e e l e v a t i o n s i m m e d i a t e l y above the d i s c o n t i n u o u s new s n o w l i n e were not s i g n i f i c a n t l y d i f f e r e n t . Second, storms w i t h snow t o the l o w e s t e l e v a t i o n s a l s o had a h i g h p e r c e n t a g e of homogeneity of s n o w f a l l means between a d j a c e n t s a m p l i n g s i t e s . Such storms u s u a l l y r e s u l t from the same b a s i c s y n o p t i c p a t t e r n , m o i s t P a c i f i c a i r , o v e r r i d i n g e n t r e n c h e d A r c t i c a i r (see C hapter 8). I t would seem, t h e r e f o r e , t h a t homogeneity of s n o w f a l l means between a d j a c e n t e l e v a t i o n s depends on the a c t u a l e l e v a t i o n of the sample, and.the storm t y p e , as w e l l as on the e l e v a t i o n d i f f e r e n c e between the s a m p l i n g s i t e s . . Snow d e p o s i t i o n means were almost always s i g n i f i -c a n t l y d i f f e r e n t between c l e a r i n g s and.the canopy edge, and between the canopy edge and beneath the canopy (Table 7-2). TABLE 7 .2 Number of storms where adjacent e l e v a t i o n s and f o r e s t s t r a t a had snow  d e p o s i t i o n means that were homogeneous, at the 95$ confidence l e v e l . Analysed w i t h Duncan's New M u l t i p l e Range Test A. E l e v a t i o n means E l e v a t i o n (metres) 1260 - 1060 - 970 - 870 - 790- - 710 - 590 - • 4 9 0 - 400 330 - 220 - 120 Winter 1969-70 Winter 1970-71 2 6 2 1 3 5 9 14 5 9 0 3 0 3 4 14 1 5 0 6 1 5 T o t a l Winters 1969-71 8 5 6 23 14 3 4 17 6 6 6 % of those snow storms sampled 10 7 11 45 30 8 15 74 38 55 50 B. Stratum means Stratum open - c l e a r i n g canopy edg ?e - beneath canopy - tree trunk Winter 1969-70 \. Winter 1970-71 ] 15 23 5 4 8 4 16 23 T o t a l winters 1969-71 - 38 9 12 39 % of those snow " storms sampled 46 11 15 48 183 100 c o V E c O O a. v o c w <L) L V sz X) t) a E o tn </> E i_ o t> CD C Q-E c a> u •a o c V -t-> «J X) I/) n o c V cn o E o v u 80 60 h 40 I-20 50 100 150 200 F i g . 7.1 Elevation interval between sampling sites ( meter s ) Homogeneity of means o f - s t o r m snow d e p o s i t i o n between a d j a c e n t s a m p l i n g s i t e s , as a. f u n c t i o n " of the e l e v a t i o n i n t e r v a l between s a m p l i n g s i t e s . 184 T h i s j u s t i f i e s the measurements beneath t r e e s , and i n d i c a t e s t h a t i n a f o r e s t e d west c o a s t m i d l a t i t u d e mountain e n v i r -onment, such areas s h o u l d be sampled i f e s t i m a t e s are t o be made of the t o t a l mass o f snow d e p o s i t e d . I n - a l m o s t h a l f the s t o r m s , t h e r e were no s i g n i f i c a n t d i f f e r e n c e s between c l e a r i n g s and open a r e a s , and between the a r e a c l o s e t o t r e e t r u n k s and beneath t r e e s . I n summary, the p r e v i o u s a n a l y s e s show t h a t on a west c o a s t m i d l a t i t u d e mountain, snow d e p o s i t i o n i s s i g -n i f i c a n t l y d i f f e r e n t among s t o r m s , e l e v a t i o n s , and f o r e s t s t r a t a , but more i m p o r t a n t l y , t h e r e are a l s o s i g n i f i c a n t i n t e r a c t i o n s . These i n t e r a c t i o n e f f e c t s appear t o be produced by v a r i a t i o n s i n m e t e o r o l o g i c a l parameters between storms and-with e l e v a t i o n , and by <£hexchanging-'nature-'-' of the f o r e s t w i t h e l e v a t i o n . 7.2 T o t a l mass of snow d e p o s i t e d a f t e r each storm 7.2.1 Method o f c a l c u l a t i o n E s t i m a t e s can be made of the t o t a l mass of snow d e p o s i t e d by each storm on the t e r r a i n segment, by a p p l y i n g the t h e o r y o f s t r a t i f i e d random s a m p l i n g (Cochran 1963) . The s a m p l i n g network o f t h i s s tudy was s u f f i c i e n t f o r t h i s p u r pose. A l t e r n a t i v e l y , p r e d i c t i o n f u n c t i o n s t o be e s t a b -l i s h e d l a t e r c o u l d be used t o e s t i m a t e s n o w f a l l i n f o r e s t s t r a t a knowing t h a t i n the open. 185 T o t a l mass r e p r e s e n t s the amount o f snow a v a i l a b l e f o r a c c u m u l a t i o n of the snowpack over the a r e a of the t e r r a i n segment. When combined, w i t h r a i n f a l l measurements and w i t h snow melt f u n c t i o n s ( e.g. U.S. Army 1956), r u n o f f may be p r e d i c t e d . I n t h i s s t u d y , the' t e r r a i n - segment was d r a i n e d ' b y a l a r g e number o f s m a l l s t e e p streams so r u n o f f gauging was i m p r a c t i c a l . Thus no independent water b a l a n c e check on the c a l c u l a t i o n s was p o s s i b l e . There were s e v e r a l problems i n computing the t o t a l mass o f snow from each storm. I n t e r c e p t e d snow t h a t f e l l t o t he snowpack a f t e r s a m p l i n g was not measured u n t i l t he f o l l o w i n g s torm. I f i t m e l t e d p r i o r t o t h i s , i t was not measured at a l l . F u r t h e r unmeasured i n p u t r e s u l t e d from c o n d e n s a t i o n , and from r a i n , o r d r i p from t r e e s , which p e r c o l a t e d i n t o , and was absorbed by the snowpack by f r e e z i n g o r by c a p i l l i a r y t e n s i o n . A f i n a l d i f f i c u l t y r e s u l t e d because the a r e a o f each s t r a t u m had t o be known. Areas o f p r i m a r y s t r a t a were found by p l a n i m e t e r i n g the a r e a of each, e l e v a t i o n a l band from a map--of - s c a l e 1:12,000. The areas o f the secondary s t r a t a were more d i f f i c u l t t o measure. Open areas and c l e a r i n g s were mapped from a i r photographs and p l a n i m e t e r e d . Areas o f t h e t h r e e o t h e r f o r e s t s t r a t a c o u l d o n l y be a s s e s s e d by s a m p l i n g the dimensions and number of t r e e s i n the f o r e s t 186 f o r each e l e v a t i o n a l band. I n view o f the heteorogenous n a t u r e o f t h e f o r e s t on Mount Seymour ( F i g . 2.7), t h i s p r ocedure would be t e d i o u s , and. c o u l d l e a d t o e r r o r s i n s t r a t u m s i z e . The r e s u l t would be a b i a s e d sample e s t i m a t e , t h e g a i n i n p r e c i s i o n from s t r a t i f i c a t i o n would be l o s t , and c o n f i d e n c e l i m i t s would be u n d e r e s t i m a t e d (Cochran 1963). C o n s e q u e n t l y , snow d e p o s i t i o n samples from the t h r e e s t r a t a - canopy edge, beneath t r e e s , and c l o s e t o t r e e t r u n k s - were p o o l e d , t o g i v e a sample s i z e o f 18.• The a r e a of t h i s new s t r a t u m , "the f o r e s t " c o u l d t h e n be more r e l i a b l y a s s e s s e d f o r each e l e v a t i o n a l band from a i r p h otographs. 7.2.2 R e s u l t s An example o f the r e s u l t s from a s i n g l e storm are g i v e n i n Table 7-3. V a r i a n c e , degree of freedom, and 95 p e r c e n t c o n f i d e n c e l i m i t s were computed by methods suggested by Cochran, (1963). For most s t o r m s , c o n f i d e n c e i n t e r v a l s were as l a r g e as 90 p e r c e n t o f the t o t a l snow mass f o r d e p o s i t i o n s c l o s e t o the new s n o w l i n e , but de-c r e a s e d w i t h i n c r e a s i n g e l e v a t i o n , o f t e n t o below 3 p e r c e n t of the t o t a l , except f o r a f u r t h e r i n c r e a s e a t 1260 m. The h i g h e r v a l u e s were a s s o c i a t e d w i t h s m a l l e r amounts o f d e p o s i t e d snow, o r , as at 1260 m, w i t h snow d r i f t i n g . TABLE 7-3 Example o f t h e t o t a l mass o f snow d e p o s i t e d on the Mount Seymour t e r r a i n segment from a stor m (Storm 3 0 , w i n t e r 1969-70) E l e v a t i o n Band ( f e e t ) A r e a (10 3.m 2) Me an Mass (kg/m 2) T o t a l Mass of snow D e p o s i t e d (10 3.m 3) Degrees of Freedom 95$ Confidence L i m i t s o f T o t a l Mass (10 3.m 3) Confidence i n t e r v a l -as percentage o f • t o t a l mass 3600-4200 234 16 .9 3 .96 11 3.59 4 . 3 4 19 3300-3600 387 16 .7 6.46 19 6.19 6 .74 8 3000-3300 815 10 .0 8 .11 26 7.35 8.86 18 2700-3000 619 5 . 1 3-13 17 2.42 3.84 45 2400 -2700 607 3 . 3 1 .98 18 1.76 2 . 2 0 22 2100-2400 764 3 .4 2 . 6 3 17 2 . 2 1 3 . 0 5 30 1800-2100 1019 0 . 9 0 . 9 8 18 0.41 . I . 5 6 117 1500-1800 943 0 . 1 0 . 0 6 8 0 . 0 1 0 .10 164 T o t a l f o r t e r r a i n segment 5388 5 . 1 2 7 . 3 1 90 ' 2 6 . 0 3 2 8 . 6 1 9 r—1 C O — 188 C o n f i d e n c e l i m i t s were a l s o computed f o r the t o t a l mass o f snow d e p o s i t e d on the t e r r a i n segment a f t e r each storm, by p o o l i n g the sample v a r i a n c e s f o r each e l e v a t i o n a l zone. R e s u l t a n t c o n f i d e n c e i n t e r v a l s were l e s s than 15 p e r c e n t o f the- t o t a l f o r 70 o f t h e 82 snow storms a n a l y s e d . Thus, i f i t i s assumed the samples were u n b i a s e d , a c c e p t a b l e e s t i m a t e s of t o t a l snow mass d e p o s i t e d on the t e r r a i n segment were p o s s i b l e . I n the o t h e r cases c o n f i d e n c e i n t e r v a l s were sometimes as h i g h as 70 p e r c e n t o f the t o t a l mass of snow, but t h e s e storms were always t h o s e w i t h s m a l l amounts of d e p o s i t e d snow, and so were r e l a t i v e l y u n i m p o r t a n t . T o t a l snow mass d e p o s i t e d over two w i n t e r s was com-pute d f o r each e l e v a t i o n a l band and f o r the t e r r a i n segment ( F i g . 7-2). .Confidence i n t e r v a l s were l e s s t h a n 10 p e r -cent o f t h e t o t a l f o r most e l e v a t i o n s . The r e s u l t a n t curves r e f l e c t e d t h e r e l a t i v e p r o p o r t i o n o f -forested, c l e a r i n g , and open a r e a at each e l e v a t i o n , and the shape of the h y p s o m e t r i c c u r v e , as w e l l as v a r i a t i o n s o f s p e c i f i c snow mass d e p o s i t i o n w i t h e l e v a t i o n . The curves i n d i c a t e d t h e most s i g n i f i c a n t zone f o r snow d e p o s i t i o n on the t e r r a i n segment was between 900 m and 1100 m i n b o t h w i n t e r s . I f m a n i p u l a t i o n o f the f o r e s t c o v e r can i n c r e a s e snow d e p o s i t i o n , . a n d hence snow a c c u m u l a t i o n , t h i s zone would be the most p r o f i t a b l e t a r g e t a r e a . T o t a l m a s s o f d e p o s i t e d s n o w ( X 1 0 3 ) m 3 w a t e r e q u i v a l e n t . M O o o o _I_ 0) 8 _ i _ CD O O _L_ O O o ro O O 2 z O - I o I-* D_ in ? ' ^ | H O s s a 3 3 681 190 C o n s i d e r a b l y more t o t a l snow was d e p o s i t e d on the t e r r a i n segment i n the w i n t e r 1970-71. However, the shape o f the curv e s a re s i m i l a r , except f o r a s h a r p e r maximum of t o t a l mass at 970 m, and f o r a secondary max-imum at the lowe s t e l e v a t i o n s i n 1970-71. I n t h i s y e a r when snow f r e q u e n t l y f e l l t o low l e v e l s , t o t a l mass d e p o s i t e d a t 120 m was e q u i v a l e n t t o t h a t at 790 m and o n l y a l i t t l e l e s s t h a n t h a t at the top o f the mountain. 7.3 R e d u c t i o n o f the s a m p l i n g network The t r a n s e c t of s a m p l i n g s i t e s up the mountain appeared t o be s u f f i c i e n t t o a d e q u a t e l y d e f i n e v a r i a t i o n s of p r e c i p i t a t i o n and snow d e p o s i t i o n w i t h e l e v a t i o n (Chap-t e r 6 ) . To i n v e s t i g a t e a p o s s i b l e r e d u c t i o n o f t h e number-of s a m p l i n g s i t e s , c o r r e l a t i o n m a t r i c e s o f storm p r e -c i p i t a t i o n were p r e p a r e d f o r each o f the w i n t e r s (Table 7-4). Even though the two w i n t e r s were d i f f e r e n t i n c h a r a c t e r , the m a t r i c e s are q u i t e s i m i l a r . C o r r e l a t i o n d e c r e a s e s as the e l e v a t i o n d i f f e r e n c e between s a m p l i n g s i t e s i n c r e a s e s , but a l s o d e c r e a s e s w i t h h e i g h t , so i s a f u n c t i o n o f the a c t u a l e l e v a t i o n . These m a t r i c e s , the homogeneity o f sto r m s n o w f a l l means between a d j a c e n t s a m p l i n g s i t e s ( F i g . 7-1) and p l o t s o f storm p r e c i p i t a t i o n v a r i a t i o n w i t h e l e v a t i o n s i m i l a r t o F i g . 6.2, a l l i n d i c a t e p r e c i p i t a t i o n v a r i a t i o n s w i t h 191 TABLE 7 .4 Correlation matrices for p r e c i p i t a t i o n at 12 'elevations  Winters 1969070, 1970-71 Winter 1969-70 (57 observations*) Elevation (met.ers) 1260 1060 970 870 790 710 "590 490 400 330 220 120 1260 1.00 1060 0 . 9 2 1 .00 970 0 . 8 8 0 . 8 8 1 .00 870 0 . 8 3 0 . 8 6 0 . 9 2 1 .00 790 0.79 0 .79 0 . 8 7 0 .96 1 .00 710 0.77 0.79 0 . 8 6 0.94 0 . 9 8 1 .00 590 0.77 0 . 7 6 0.84 0 . 9 1 0 . 9 5 0 . 9 8 1 .00 490 0.76 O.76 0.84 0 . 9 1 0 . 9 5 0.98 0 . 9 9 1 .00 , '110 0.76 0 . 7 5 0.84 0 . 9 1 0 .94 0 . 9 7 0 . 9 8 0 . 9 9 1.00 330 0 . 7 5 0 .75 0 . 8 3 .0.90 0 .94 0 . 9 7 0 . 9 9 0 . 9 9 0 . 9 9 1 .00 220 0 .75 0 . 7 4 . 0 . 8 2 0 . 9 0 0 .94 0 . 9 7 0 .99 0 . 9 9 0 . 9 9 0 . 9 9 1 .00 120 0.74 0 . 7 3 0 .82 0 . 8 9 0 . 9 3 0 . 9 6 0 .98 O.98 0 . 9 8 0 . 9 9 0 . 9 9 1 .00 Winter 1970 -71 (68 observations*) Elevation (met ers) 1260 1060 970 870 790 710. 590 490 400 330 220 120 1260 1.00 1060 0 . 9 6 1.00 970 0 . 9 2 0 . 9 3 1 .00 870 0 . 8 9 0 . 8 7 0 . 9 2 1 .00 . 7 9 0 0 . 8 8 0 . 8 5 .0.92 0 . 9 8 1 .00 710 0 .81 0.79 0 . 8 6 0 . 9 4 0'.95 1 .00 590 0 .79 0 . 7 8 0 . 8 5 0 . 9 1 . 0 . 9 2 O.96 1.00 490 0 . 7 7 0 .75 0 . 8 5 0 . 9 1 0.91 0 . 9 5 0 . 9 7 1 .00 410 0 . 7 8 0 . 7 7 0 . 8 5 0 . 9 1 0 . 9 1 0 .94 0 . 9 6 0 . 9 8 1 .00 330 0 . 7 7 0 .74 0 . 8 3 0 . 9 0 0 . 9 0 0 . 9 3 0 . 9 6 0 . 9 6 0 . 9 8 1 .00 220 0 . 7 6 0 . 7 3 0 . 8 3 0 . 8 8 0 . 9 1 0 .9.4 0 . 9 6 ' 0 . 9 5 0.96 0.98 1.00 120 0 . 7 8 0 .75 0.84 0 . 8 9 0 . 9 2 0 . 9 4 0 . 9 6 0 . 9 4 0 . 9 4 . 0 . 9 7 0 . 9 9 1 .00 * In most cases one observation represents p r e c i p i t a t i o n from one storm. In a few. cases p r e c i p i t a t i o n from two storms i s combined. 192 e l e v a t i o n on the t e r r a i n segment c o u l d be more e f f i c i e n t l y sampled by measurements at 120 m and 790 m, and above t h i s at 200 m i n t e r v a l s . T h i s scheme s h o u l d be c o n f i n e d t o r a i n storms or snow storms where no snow f a l l s below 790 m. O t h e r w i s e a d d i t i o n a l samples would be needed below 790 m, so as t o d e f i n e the d i s c o n t i n u o u s s n o w l i n e , and the shape o f t h e new snow wedge. Too much s i m p l i f i c a t i o n o f t h e e x p e r i m e n t a l d e s i g n , as used i n t h i s s t u d y , can l e a d t o l a r g e e r r o r s i n e s t i m -a t i n g the t o t a l mass of snow d e p o s i t e d on t h e t e r r a i n segment.. (Table 7-5). I n g e n e r a l , t h e r e i s i n c r e a s i n g o v e r e s t i m a t i o n as the e l e v a t i o n i n t e r v a l between s a m p l i n g . s i t e s becomes l a r g e r . The p e r c e n t a g e d i f f e r e n c e between e s t i m a t e s u s i n g s a m p l i n g s i t e s at 200 m and 100 m e l e v a t i o n i n t e r v a l s i s s m a l l , and about the same as t h e computed 95 p e r c e n t c o n f i d e n c e I n t e r v a l s . Hence, t h e r e i s no apparent b e n e f i t from s a m p l i n g at about 100 m e l e v a t i o n i n t e r v a l s , as was done i n t h i s s t u d y . A scheme w i t h s a m p l i n g s i t e s a t 200 m w i l l more e f f i c i e n t l y p r o v i d e s t a t i s t i c a l l y s i m i l a r e s t i m a t e s o f t o t a l mass d e p o s i t e d on the t e r r a i n segment. I f t h e e x p e r i m e n t a l d e s i g n must be s i m p l i f i e d f u r t h e r , i t i s b e t t e r t o i n c r e a s e the e l e -v a t i o n i n t e r v a l , r a t h e r than e l i m i n a t e measurements w i t h i n the f o r e s t . 193 TABLE 7.5 I n f l u e n c e o f s i m p l i f i c a t i o n o f the e x p e r i - m e n t a l d e s i g n on e s t i m a t i o n o f t o t a l mass  of snow d e p o s i t e d on the t e r r a i n segment Percentage d i f f e r e n c e from t o t a l mass computed w i t h the e x p e r i m e n t a l d e s i g n o f t h i s s t u d y . (Sampling s i t e s at about 100 m i n t e r v a l s and measurements i n t he f o r e s t ) Proposed s i m p l i f i c a t i o n Storm 30* W i n t e r 1969-70 W i n t e r 1969-70 W i n t e r 1970-71 Sampling s i t e s at 200 m e l e v a t i o n i n t e r v a l s . Measurements i n f o r e s t . 13 6. 6 Sampling s i t e s at 300 m e l e v a t i o n i n t e r v a l s . Measurements i n f o r e s t . 18 38 1 Sampling s i t e s at 400 m e l e v a t i o n i n t e r v a l s . Measurements i n f o r e s t . 67 26 24 Sampling s i t e s as f o r t h i s s t u d y , but no measurements t a k e n i n the f o r e s t . 65 98 82 * T o t a l mass o f snow d e p o s i t e d on t h e t e r r a i n segment i s e s t i m a t e d f o r t h i s storm i n Table 7-3 u s i n g the experi^-m e ntal d e s i g n o f t h i s s t u d y . 194 The r e s u l t s o f the a n a l y s i s o f v a r i a n c e support the c o n t e n t i o n t h a t s a m p l i n g snow d e p o s i t i o n w i t h i n the f o r e s t i s n e c e s s a r y i f adequate e s t i m a t e s o f t o t a l mass of snow d e p o s i t e d are t o be o b t a i n e d . These r e s u l t s show t h a t measurements s h o u l d c e r t a i n l y be t a k e n at the canopy edge (where snow may s l i d e o f f t r e e s ) and beneath, the canopy (where i n t e r c e p t i o n o r wind s c o u r may reduce t h e amount o f snow d e p o s i t e d ) . Sampling i n " c l e a r i n g s " , and " c l o s e t o t r e e t r u n k s " would be e l i m i n a t e d , s i n c e f o r many' storms snow d e p o s i t i o n i n t h e s e areas i s w e l l r e p r e s e n t e d by t h a t i n "open areas"-, and "beneath t r e e s " , r e s p e c t i v e l y . The o n l y e x c e p t i o n s are. f o r storms w i t h h i g h w i n d s , and storms w i t h low d e n s i t y snow, where t u r b u l e n c e may in d u c e g r e a t e r d e p o s i t i o n i n c l e a r i n g s t h a n i n open a r e a s , o r where wind may p i l e snow a g a i n s t t r e e t r u n k s . 7 .4 C o n c l u s i o n The e x p e r i m e n t a l d e s i g n i n t h i s study appeared adequate t o d e f i n e v a r i a t i o n s of storm p r e c i p i t a t i o n and storm snow d e p o s i t i o n w i t h e l e v a t i o n , and snow d e p o s i t i o n w i t h i n the f o r e s t . I t seems a s a m p l i n g scheme almost as d e t a i l e d as used here i s n e c e s s a r y i f good e s t i m a t e s o f the t o t a l mass o f snow d e p o s i t e d ' on a t e r r a i n segment are d e s i r e d . Measurements s h o u l d be t a k e n a t about 200 m e l e v a t i o n i n t e r v a l s , except below the s n o w l i n e , where the 195 i n t e r v a l may be l a r g e r (say 300 m). Samples of-snow de-p o s i t i o n must be o b t a i n e d i n the f o r e s t , p a r t i c u l a r l y beneath t r e e s and beneath t r e e canopy edges. Here, snow d e p o s i t i o n can be v e r y d i f f e r e n t from t h a t i n the- open-. The degree of d i f f e r e n c e i s not c o n s i s t e n t , but dependent on the m e t e o r o l o g i c a l c o n d i t i o n s p r e v a i l i n g d u r i n g storms ( e s p e c i a l l y the e l e v a t i o n and movement o f the f r e e z i n g l e v e l , and wind s p e e d ) , and on the n a t u r e of the f o r e s t at a p a r t i c u l a r e l e v a t i o n . I t has been e s t a b l i s h e d t h a t the two w i n t e r s of t h i s s tudy were v e r y d i f f e r e n t i n c h a r a c t e r , y e t i n b o t h , the e l e v a t i o n zone between 900 and 1100 m, was- the most i m p o r t a n t f o r t o t a l mass o f snow d e p o s i t e d . F u t u r e s t u d i e s o f snow h y d r o l o g y i n t h e ' N o r t h Shore Mountains s h o u l d t a k e t h i s i n t o a c c o u n t . L i k e w i s e , because o f t h e i r l a r g e r e l a t i v e a r e a , low e l e v a t i o n s can make i m p o r t a n t c o n t r i -b u t i o n s t o the snow h y d r o l o g y of west c o a s t m i d l a t i t u d e m o u n t a ins, even though f a l l s o f snow are s m a l l and i n f r e q u e n t . U n f o r t u n a t e l y , no independent check of the c a l c u -l a t i o n s was p r a c t i c a l , but i f , as i s b e l i e v e d , the e x p e r i -m e n t a l d e s i g n o f t h i s s tudy produced u n b i a s e d e s t i m a t e s , then the t o t a l mass o f snow d e p o s i t e d on the t e r r a i n segment i s w i t h i n ±5 p e r c e n t of t h a t c a l c u l a t e d f o r each w i n t e r , and w i t h i n ±8 p e r c e n t f o r most st o r m s . Thus i t i s p o s s i b l e 196 t o s a t i s f a c t o r i l y e s t i m a t e , by s a m p l i n g the t o t a l mass of-d e p o s i t e d snow over a mesoscale a r e a . However, a l a r g e amount of work i s needed t o s e r v i c e the' e x p e r i m e n t a l d e s i g n of t h i s s t u d y , even w i t h the s u g g e s t e d , more e f f i c i e n t m o d i f i c a t i o n s ( e . g . i t sometimes took most of a day t o sample d e p o s i t i o n from a s i n g l e s t o r m ) . Such e f f o r t w i l l seldom be p r a c t i c a l over a catchment, where a number of t e r r a i n segments of d i f f e r e n t s l o p e and a s p e c t would have t o be sampled. Thus, t o r o u t i n e l y e s t i m a t e t h e t o t a l mass of snow d e p o s i t e d over r i v e r catchments on most west c o a s t m i d l a t i t u d e mountains, t h e r e i s no a l t e r n a t i v e - b u t • t o e s t a b l i s h f u n c t i o n s t o e s t i m a t e v a r i a t i o n s o f d e p o s i t i o n w i t h e l e v a t i o n , and w i t h i n t h e f o r e s t , f r o m a s e r i e s o f base s t a t i o n s . The problem i s l e s s d i f f i c u l t on mountains where t h e r e i s no f o r e s t " c o v e r (as f o r some i n New Z e a l a n d ) . The e x p e r i m e n t a l d e s i g n can t h e n be s i m p l e r . However, the number of samples w i l l s t i l l need t o be l a r g e because of the v a r i a b i l i t y i n d u c e d by i n c r e a s e d l i k e l i h o o d of snow d r i f t i n g . 197 CHAPTER 8 8. CLIMATOLOGY OF SNOW STORMS I t has been e s t a b l i s h e d t h a t the w i n t e r s 1969-70 and 1970-71 d i f f e r e d s u b s t a n t i a l l y i n the amount o f snow r e c e i v e d , and i n the e l e v a t i o n s a t which i t f e l l . The s y n o p t i c storm s i t u a t i o n s of thes e w i n t e r s gave r i s e t o bot h near minimum, and near maximum r e c o r d e d s n o w f a l l s . T h e r e f o r e , i t i s u s e f u l t o examine d i f f e r e n c e s i n the sy n -o p t i c c l i m a t o l o g y of thes e w i n t e r s . T h i s l e a d s t o an an-a l y s i s o f the c o n t r i b u t i o n o f v a r i o u s storm t y p e s t o snow d e p o s i t i o n at each e l e v a t i o n . Storm f r e e z i n g l e v e l s are a l s o examined i n t h i s c h a p t e r , because they l a r g e l y determine the lower l i m i t s of s n o w f a l l . The h o r i z o n t a l f l u x o f atm o s p h e r i c water vapour i s computed as a p o s s i b l e i n d i c a t o r of m o i s t u r e s o u r c e s . I d e n t i f i c a t i o n o f d i f f e r e n c e s i n wat e r vapour f l u x between the two w i n t e r s may h e l p e x p l a i n t h e observed c o n t r a s t s i n p r e c i p i t a t i o n and s n o w f a l l . 8.1 S y n o p t i c f e a t u r e s o f w i n t e r storms The b r o a d s c a l e s y n o p t i c f e a t u r e s of w i n t e r weather and a i r mass c l i m a t o l o g y o f the B r i t i s h Columbia c o a s t have 198 been o u t l i n e d p r e v i o u s l y i n S e c t i o n 2.2. On Mount Seymour, most storms d u r i n g t h e study w i n t e r s were f r o n t a l ( T a ble 8.1) and dominated by mP' or mA a i r m a s s e s . Storms adve'cting mA a i r onto Mount Seymour were p a r t i c u l a r l y prominent J u r i n g the w i n t e r 1970-71, so the a s s o c i a t e d c o m b i n a t i o n o f low f r e e z i n g l e v e l s and u n s t a b l e a i r produced snow t o low e l e -v a t i o n s and a l a r g e o r o g r a p h i c component of p r e c i p i t a t i o n . T h i s w i n t e r a l s o had a l a r g e r number (8) of A r c t i c A i r o u t -b r e a k s r e a c h i n g the Vancouver a r e a compared w i t h the p r e -v i o u s w i n t e r , when t h e r e was o n l y one. Both w i n t e r s e x p e r i e n c e d a few storms c o n t a i n i n g mT a i r . These u s u a l l y gave r a i n - t o a l l e l e v a t i o n s on the mountain, o r i f snow o c c u r r e d i t was o f t e n mixed w i t h r a i n , and c o n f i n e d t o h i g h e r e l e v a t i o n s . G e n e r a l l y , c o l d e r a i r i n v a d e d the r e g i o n b e h i n d most f r o n t s , so a f r o n t a l passage l o w e r e d the f r e e z i n g l e v e l . Thus f o r some st o r m s , snow f e l l o n l y from p o s t f r o n t a l c o n d i t i o n s . However, i n most cases the b u l k o f storm p r e c i p i t a t i o n was p r e f r o n t a l . T h e r e f o r e , when the f r e e z i n g l e v e l was s u f f i c i e n t l y low, most o f the s n o w f a l l at h i g h e l e v a t i o n s r e p r e s e n t e d p r e f r o n t a l c o n d i t i o n s . The source o f a i r ahead o f , and b e h i n d , fronts.-,, and i t s soj.ourn over the ocean may be deduced by t r a j e c t o r y a n a l y s i s . T r a j e c t o r i e s are u s u a l l y c o n s t r u c t e d u s i n g a f i n i t e - d i f f e r e n c e p r o c e s s ( P e t t e r s s e n 1956), but un c e r -199 TABLE 8 . 1 P e r c e n t a g e f r e q u e n c y o f stor m t y p e s f o r a l l s t o r m s , and f o r snow storms -w i n t e r s 1 9 6 9 - 7 0 , 1970-71 Storm t y p e s were i d e n t i f i e d from s u r f a c e s y n o p t i c c h a r t s . There were 73 storms i n w i n t e r 1969-70 and 74 storms i n w i n t e r 1970-71 A l l Storms | Snow Storms Storm Type . 1969-70 1969-70 1970-71 1970-71 A. F r o n t a l 77 89 45 65 1) M a r i t i m e c o l d '7 f r o n t s 12 19 15 2) M a r i t i m e f r o n t s w i t h a warm s e c t o r 15 18 7 10' 3) M a r i t i m e o c c l u d e d f r o n t s 48 39 30 27 4) A r c t i c f r o n t s a s s o c i a t e d w i t h 8 8 m a r i t i m e f r o n t 2 1 5) A r c t i c f r o n t s not a s s o c i a t e d w i t h m a r i t i m e f r o n t s , but w i t h m o i s t P a c i f i c a i r f l o w s 0 5 0 5 ' B. N o n - f r o n t a l 23 • 11 15 8 6) C o l d lows 6 0 1 0 7) Other lows w i t h no f r o n t , or f r o n t w e l l t o S 5 4 6 3 8) Troughs ( u s u a l l y a s s o c i a t e d w i t h W o r NW a i r f l o w 2 5 1 4 9) SW air.streams 3 1 3 0 10) W air.streams 0 1 0 1 11) NW a i r s t r e a m s 4 0 3 0 12) L i g h t p r e c i p i -t a t i o n a s s o c -i a t e d w i t h h i g h 0 p r e s s u r e c e l l s 3 0 1 TOTALS FOR WINTER 100$ 100$ 61$ 73$ 200 t a i n t i e s i n estimates of wind speed and d i r e c t i o n cause e r r o r s i n t r a j e c t o r i e s , e s p e c i a l l y i f there are organised v e r t i c a l motions i n the atmosphere (Munn 1970) . For example, assuming h o r i z o n t a l flow, Durst and Davis- (1957) have suggested a c l i m a t o l o g i c a l average e r r o r of 13 km/ hour i n wind estimates from synoptic maps. This technique was considered i n a p p r o p r i a t e f o r storms a f f e c t i n g the B r i t i s h Columbia coast because organised v e r t i c a l motions are common during storms, and because maps of the wind f i e l d over the eastern P a c i f i c Ocean are based on few measurements, and are l a r g e l y estimates. More p r a c t i c a l a n a l y s i s may be made by considering storm t r a c k s and storm types. 8.1.1 Tracks of winter storms The t r a c k s of the low pressure centres of storms were p l o t t e d from d a i l y surface synoptic charts f o r the study w i n t e r s . Eight g e n e r a l i s e d t r a c k s could be recognised ( F i g . 8.1). Storms along t r a c k s E, G and H have e a s i e s t access to cold a i r sources. This i s e s p e c i a l l y true of the a i r s t r e a m behind the f r o n t a s s o c i a t e d w i t h most low pressure centres. Such a i r i s unstable and has low f r e e z i n g l e v e l s . Because of a p e r s i s t e n t ridge of high pressure i n the eastern P a c i f i c i n the winter 1970-71 ( F i g . 3.3), storms often followed these t r a c k s i n November to February 60 170 160 150 140 130 120 110 150 140 F i g . 8.1 G e n e r a l i s e d t r a c k s of stor m s , w i n t e r s 1969-70, 1970-71 Each t r a c k i s i d e n t i f i e d by a- l e t t e r . The a s s o c i a t e d number r e p r e s e n t s the percentage of. storms which f o l l o w e d each t r a c k and produced snow on Mount Seymour. The numbers at the end of the arrows i n d i c a t e the f r e q u e n c y . o f snow sto r m s , w i t h those f o r 1970-71 i n b r a c k e t s 202 of• the same w i n t e r . They produced a l a r g e r o r o g r a p h i c component of p r e c i p i t a t i o n and l o w e r s n o w l i n e s . Storms f o l l o w i n g t r a c k s A and B do not g e n e r a l l y have low f r e e z i n g l e v e l s , u n l e s s they dominate the e a s t e r n P a c i f i c c i r c u l a t i o n . They t h e n may have access t o the c o l d a i r of t h e B e r i n g Sea or A l a s k a . I f these storms are f o l l o w e d by a b u i l d i n g r i d g e o f h i g h p r e s s u r e , a s t r o n g n o r t h - w e s t e r l y f l o w of c o l d u n s t a b l e a i r may develop b e h i n d f r o n t s , g i v i n g snow t o mod e r a t e l y low e l e v a t i o n s on Mount Seymour. More u s u a l l y , storms f o l l o w i n g t h e s e t r a c k s advect warm, mo i s t .'-stable a i r onto the c o a s t . They o f t e n o c c u r as a f a m i l y o f storms w i t h a new stor m d e v e l o p i n g t o the sout h - w e s t , on the f r o n t of i t s p r e d e c e s s o r . These storms g e n e r a l l y b r i n g r a i n t o the top of the mountain, or snow t o h i g h e l e v a t i o n s o n l y . Storms f o l l o w i n g t h e s e t r a c k s were e s p e c i a l l y common i n the w i n t e r 1969-70 ( F i g . 8.1), because the e a s t e r n P a c i f i c was p e r s i s t e n t l y dominated by a deep a r e a o f low p r e s s u r e ( F i g . 3-3)-Storms caught up i n a z o n a l f l o w ( t r a c k s E, C ) , ten d t o adve'c't a i r i n e q u i l i b r i u m w i t h the ocean s u r f a c e over which i t p a s s e s . S i n c e the s u r f a c e t emperature of the ocean grows c o l d e r as the w i n t e r p r o g r e s s e s (Sverdrup 19^2), such storms g i v e snow t o lo w e r e l e v a t i o n s i n A p r i l t h a n i n November. A i r b e h i n d the f r o n t s o f thes e storms can o f t e n f l o w d i r e c t l y from c o l d a i r s o u r c e s . These storm t r a c k s were much more f r e q u e n t i n the w i n t e r 1970-71-203 F i g . 8 . 1 s h o u l d be i n t e r p r e t e d w i t h c a u t i o n , f o r t h r e e r e a s o n s . F i r s t i t i n d i c a t e s the t r a c k s o f low p r e s s u r e c e n t r e s and not f r o n t s . F o r t r a c k s such as B, D and F, f r o n t s may become uncoupled from t h e i r a s s o c i a t e d low. They then move eas t w a r d a c r o s s the B r i t i s h Columbia c o a s t , w h i l e the lows swing n o r t h i n t o the G u l f o f A l a s k a . S e c o n d l y , the t r a c k o f a s t o r m g i v e s o n l y a g e n e r a l i n d i -c a t i o n o f f r e e z i n g l e v e l , and hence the e l e v a t i o n o f the s n o w l i n e . As p r e v i o u s l y d i s c u s s e d , the a c c e s s o f the , storm t o s o u r c e s of c o l d a i r and the season are a l s o i m p o r t a n t c o n s i d e r a t i o n s . F i h a l l y , F i g . 8 . 1 does not i n d i c a t e A r c t i c a i r o u t b r e a k s . Storms f o l l o w i n g any t r a c k can g i v e snow t o low e l e v a t i o n s i f A r c t i c a i r l i e s over the Van-couver a r e a . 8 . 1 . 2 Frequency of storm t y p e s Storms were d i v i d e d i n t o two c a t e g o r i e s , f r o n t a l and. n o n - f r o n t a l . The f r o n t a l storms were f u r t h e r c l a s s i f i e d by t y p e o f m a r i t i m e f r o n t , and by type o f s t o r m a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s . A v a r i e t y o f n o n - f r o n t a l storms were r e c o g n i s e d (Table 8 . 1 ) . The type of storm was i d e n t i f i e d from e x a m i n a t i o n o f d a i l y s u r f a c e s y n o p t i c c h a r t s . The w i n t e r 1969-70 produced 73 s t o r m s , o n l y one l e s s t h a n i n 1 9 7 0 - 7 1 . There were 10 more snow storms i n 1 9 7 0 - 7 1 . 204 F r o n t a l storms dominated both w i n t e r s . Walker (196l) reported a s i m i l a r s i t u a t i o n f o r the per i o d 1954-58. The higher frequency of storms a s s o c i a t e d with A r c t i c a i r outbreaks i n the snowier winter 1970-71 represents the most importance d i f f e r e n c e from 1969-70. The winter 1970-71 was also marked by fewer occluded f r o n t s , and. non-f r o n t a l storms, and by more c o l d f r o n t s and troughs. Geostrophic wind d i r e c t i o n s were assumed to be p a r a l l e l to the isobars of surface synoptic c h a r t s . Geostrophic wind d i r e c t i o n s were obtained f o r p r e f r o n t a l and p o s t f r o n t a l a i r f l o w s when the storm was shown c l o s e s t -to 'Mount Seymour. Wind d i r e c t i o n ahead of f r o n t s v a r i e d from e a s t , through south, to west. E a s t e r l y and south winds dominated snow storms i n 1970-71, while southerly and south-westerly were important- i n the previous winter (Table 8.2). Winds behind f r o n t s vary from south, through west, -to north. North-west and north winds were more prominent i n the winter 1970-71. These produced post-f r o n t a l snow to lower e l e v a t i o n s . However, even south-west winds behind f r o n t s can advect c o l d a i r onto the mountain-if t h i s a i r has had a short passage over the ocean. 205 TABLE 8.2 Percentage f r e q u e n c y of g e o s t r o p h l c a i r f l o w  ahead o f , and b e h i n d f r o n t s , f o r a l l s t o r m s , and f o r snow storms -w i n t e r s 1969-70, 1970-71 A l l storms Snow storms 1969-70 1970-71 1969-70 1970-71 G e o s t r o p h i c A i r f l o w ahead o f f r o n t s E or SE 20 30 15 29 S 46 52 . 48 57 SW 27 15 27 11 W 7 3 10 3 Geostr'pphic A i r f l o w b e h i n d ' f r o n t s S • 2 0 0 0 SW 48 49 36 45 W 32 18 39 23 NW 16 32 21 26 N 2 1 4 6 20 6 8.1.3 Importance o f each, storm type f o r w i n t e r s n o w f a l l  a t each, e l e v a t i o n Storms d i s t r i b u t e snow d i f f e r e n t l y on the m o u n t a i n , depending on t y p e . Thus some storms o n l y c o n t r i b u t e a s i g n i f i c a n t p o r t i o n o f w i n t e r s n o w f a l l at c e r t a i n e l e v a t i o n s . For example, snow d e p o s i t i o n from f r o n t s w i t h warm s e c t o r s , and from o c c l u d e d f r o n t s i s more i m p o r t a n t w i t h i n c r e a s i n g e l e v a t i o n ( F i g . 8.2, 8.3). Most o t h e r storm t y p e s are more i m p o r t a n t w i t h d e c r e a s i n g e l e v a t i o n . Examples o f snow d e p o s i t i o n from some of the more common storm t y p e s are g i v e n i n Appendix J . At h i g h e l e v a t i o n s (above 800 m), t h e o c c l u d e d f r o n t i s the major so u r c e o f w i n t e r s n o w f a l l , but c o l d f r o n t s and s o u t h - w e s t e r l y a i r s t r e a m s a l s o make s i g n i f i c a n t c o n t r i b u t i o n s . These h i g h e r e l e v a t i o n s are the o n l y p a r t of the mountain where warm s e c t o r f r o n t s are i m p o r t a n t . At m i d d l e e l e v a t i o n s (400.-800 m), n o n - f r o n t a l s o u r c e s of s n o w f a l l become prominent s o u r c e s o f snow d e p o s i t i o n , a l t h o u g h o c c l u d e d f r o n t s remain the dominant i n f l u e n c e . Storms a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s and w i t h c o l d f r o n t s i n c r e a s e i n i m p o r t a n c e . Storms a s s o c i a t e d w i t h A r c t i c a i r t e n d t o dominate s n o w f a l l at low e l e v a t i o n s ( l e s s than 400. m) . T h i s con-t r a s t s w i t h h i g h e r e l e v a t i o n s where t h e i r r e l a t i v e c o n t r i -b u t i o n i s s m a l l . . C o l d f r o n t s and t r o u g h s , a l s o make l a r g e 100 c o (/> o a. <u Q o c (/> i_ c 5 80 H 60 -1 40 20 fl ^ ^ a ' t h e r S.W. A i r s t reams £"£ 200 400 600 800 E levat ion ( m e t e r s ) 1000 1200 1400 F i g . 8.2 • Influence of storm type i n determining- winter/snow d e p o s i t i o n (.water equivalent) at each e l e v a t i o n , winter 1969-70 0 2 0 0 4 0 0 6 0 0 8 0 0 1,000 1200 1400 Elevation (meters) F i g . 8:3:. I n f l u e n c e o f storm type i n d e t e r m i n i n g w i n t e r snow d e p o s i t i o n (water e q u i v a l e n t ) at each e l e v a t i o n , w i n t e r 1970-71 209 c o n t r i b u t i o n s . Occluded f r o n t s produce s n o w f a l l at low e l e v a t i o n s i f they have access to cold a i r sources by f o l l o w i n g storm t r a c k s E, G and H of F i g . 8 : . l . Geostrophic winds ahead of, and behind, f r o n t s do not produce such c l e a r . t r e n d s with e l e v a t i o n (Tables 8.3, 8.4). However, west and north-west winds behind f r o n t s do appear to be dominant sources of snow d e p o s i t i o n w i t h decreasing e l e v a t i o n . Mean s n o w f a l l at each e l e v a t i o n from each' storm type was computed f o r the combined data of both winters (Table 8.5). The r e s u l t s should be t r e a t e d with caution f o r those types where few storms were sampled. A l l types show an increase i n mean s n o w f a l l w i t h e l e v a t i o n . This i s produced by the increased frequency of snow as the form of p r e c i p i t a t i o n at higher e l e v a t i o n s , and by orographic increase of p r e c i p i t a t i o n . At high elevations,' the greatest s n o w f a l l per storm comes from south-west a i r s t r e a m s , storms ass o c i a t e d w i t h A r c t i c a i r , and c o l d f r o n t s . At middle e l e v a t i o n s , A r c t i c a i r storms, cold f r o n t s , and a number of n o n - f r o n t a l types produce heaviest s n o w f a l l s . At low e l e v a t i o n s , by f a r the heaviest snowfalls r e s u l t from A r c t i c a i r storms. 210 TABLE 8 . 3 Percentage of s n o w . d e p o s i t i o n (water e q u i v a l e n t )  at each e l e v a t i o n a s s o c i a t e d w i t h g e o s t r o p h l c  a i r f l o w d i r e c t i o n - w i n t e r 1 9 6 9 - 7 0 E l e v a t i o n (meters) 1260 1 0 6 0 9 7 0 870 790 710 590 490 100 3 3 0 220 120 G e o s t r o p h l c a i r f l o w ahead o f f r o n t s E o r SE 22 20 16 20 1 3 1.4 25 20 45 100 100 100 •' S 18 ,*5 16 1)1) 54 55 62 80 55 0 0 0 SW 19 25 2 8 24 21 26 13 0 0 0 0 0 w 11 10 10 12 12 5 0 0 0 0 b 0 G e o s t r o p h l c a i r f l o w b e h i n d f r o n t s S sw H2 37 3 3 3 3 3 3 42 55 6 0 100 100 100 100 w 29 32 D3 47 46 50 45 40 0 0 0 0 NW 26 27 22 18 18 5 0 0 0 0 0 0 H 3 1 2 2 3 3 0 0 0 0 0 . 0 TABLE 8 . 4 Percentage of snow d e p o s i t i o n (water e q u i v a l e n t )  at each e l e v a t i o n a s s o c i a t e d with g e o s t r o p h l c  a i r f l o w d i r e c t i o n - w i n t e r 1970-71 E l e v a t i o n (meters) 1 2 6 0 1 0 6 0 9 7 0 8 7 0 7 9 0 7 1 0 5 9 0 I 9 0 400 3 3 0 2 2 0 1 2 0 G e o s t r o p h l c a i r f l o w ahead o f f r o n t s E o r SE 30 30 26 27 26 31 32 31 3 1 35 46 11 S 5 1 49 50 5 1 50 16 35 30 32 35 2 7 2 2 SW 15 17 18 16 17 19 2 1 25 2 8 25 2 3 2 8 W 4 4 6 8 7 1 9 1 1 9 5 4 1 G e o s t r o p h l c a i r f l o w b e h i n d f r o n t s S SW 47 16 44 47 47 15 15 38 10 3 5 ' 29 2 2 W 24 . 2 3 24 22 2 1 16 11 17 14 - 2 1 22 35 • NW 24 25 2 7 2 8 2 8 31 38 11 16 12 37 1 2 N 5 6 5 3 4 5 3 1 0 2 2 1 211 TABLE 8 .5 Mean snow d e p o s i t i o n (mm water e q u i v a l e n t ) p e r  type o f storm at each e l e v a t i o n  Data f o r w i n t e r s 1 9 6 9 - 7 0 , 1970-71 combined. Storm t y p e s are i d e n t i f i e d i n Table 8 . 1 Storm. Type No. Storms sampled E l e v a t i o n (meters) 1260 1060 970 870 790 710 590 490 400 330 220 210 A 122 26 24 16 10 10 7 5 3 3 2 2 1 1 23 35 36 25 19 18 16 12 9 8 5 4 4 2 24 21 19 12 5 3 2 0 0 0 0 0 0 3 64 29 25 17 11 10 6 4 2 2 1 1 0 4 7 31 30 • 25 14 11 8 7 5 5 4 4 4 5 4 43 42 34 32 37 38 32 32 24 19 21 20 B 25- : 21 23 17 11 11 8 5 3 2 l 1 2 6 4 5 5 1 0 0 0 0 0 0 0 0 0 7 7 28 30 20 17 17 15 9 2 1 0 .0 0 8 4 27 34 27 16 21 16 15 11 10 8 9 10 9 3 65 64 49 32 25 14 0 0: 0 0 0 0 10 2 21 16 6 3 0 0 0 0 0 0 0 0 11 3 16 14 :."9 :-6 '.2 0 0 0 0 0 0 0 12 2. . 0 0 0 0 0 0 0 0 0 0 0 0 212 8.2 F r e e z i n g l e v e l s of w i n t e r storms F r e e z i n g l e v e l s f o r a l l weather c o n d i t i o n s i n f l u e n c e the manner i n which snow d e p o s i t i o n and melt of the snow-pack v a r y w i t h e l e v a t i o n . Thus the heavy snow a c c u m u l a t i o n w i n t e r o f 1970-71 e x p e r i e n c e d g e n e r a l l y lower f r e e z i n g l e v e l s at P o r t Hardy t h a n the l i g h t snow w i n t e r of 1969-70 (Table 8.6). F r e e z i n g l e v e l s d u r i n g s t o r m p e r i o d s determine t h e lower e l e v a t i o n l i m i t s of s n o w f a l l . Storm f r e e z i n g l e v e l s at b o t h P o r t Hardy, and at Mount Seymour were- h i g h e r d u r i n g the w i n t e r o f 1969-70. I n t h i s w i n t e r , mean f r e e z i n g l e v e l s f o r snow storms were near n o r m a l l y d i s t r i b u t e d w i t h a marked c o n c e n t r a t i o n between 700-1000 m ( F i g . 8.4).. T h i s phenomenon was d i r e c t l y r e s p o n s i b l e f o r t h a t w i n t e r ' s s t e p l i k e n o n - l i n e a r v a r i a t i o n o f snow a c c u m u l a t i o n w i t h ' e l e v a t i o n p r e v i o u s l y d e s c r i b e d i n Chapter 4. L i t t l e snow f e l l below 500 m, because t h e r e were few storms w i t h f r e e z i n g l e v e l s below t h i s e l e v a t i o n . The l o w e r s n o w l i n e s o f the w i n t e r 1970-71 r e f l e c t the lower f r e e z i n g l e v e l s d u r i n g storms ( F i g . 8.4). Over h a l f o f th e s e f r e e z i n g l e v e l s were below 500 m. The w i d e r d i s t r i b u t i o n o f f r e e z i n g l e v e l s c o r r e l a t e s w i t h a more l i n e a r d i s t r i b u t i o n o f snow a c c u m u l a t i o n w i t h e l e v a t i o n . A l t h o u g h the concept of mean storm f r e e z i n g l e v e l i s u s e f u l , i t must be used w i t h c a u t i o n . Large f l u c t u a t i o n s 213 TABLE 8 .6 Mean f r e e z i n g l e v e l s d u r i n g storms -P o r t Hardy ( i n g e o p o t e n t i a l metres)  and Mount Seymour ( i n m e t e r s ) -W i n t e r s 1 9 6 9 - 7 0 , 1970-71 Month P o r t Hardy P o r t Hardy Mount Seymour Mount Seymour 1969-70 1970-71- 1969-70 1970-71 Oct 1909 2138 — > 130 0 Nov 1505 1270 1150 1190 Dec 1083 593 970 590 J an 874 •132 7 880 : 350 Feb 983 1127 1120 740 Mar 1024 578 1080 650 Apr 898 760 910 960 May 1778 1418 > 1300 1300 Notes: ( i ) P o r t Hardy data- from "Monthly B u l l e t i n o f Canadian Upper A i r Data". ( i i ) Mount Seymour d a t a computed from f i e l d t e m perature r e c o r d s at s i x e l e v a t i o n s t o 1260 meters. 214 30-20H o c t) n. cr £ 10 Winter 1969-70 200 400 600 800 1000 1200 Freezing level (meters ) 1400 30-20-o c V cr J| 10-U. Winter 1970-71 200 400 600 800 1000 Freezing level (meters) 1200 1400 Pig. Comparison of the d i s t r i b u t i o n s of mean f r e e z i n g l e v e l s on -Mount Seymour, snow storms f o r t he w i n t e r s 1 9 6 9 - 7 0 , 1970-71 215 i n f r e e z i n g l e v e l s do o c c u r w i t h i n some storms (see Appendix J f o r exa m p l e s ) . F o r example, f r e e z i n g l e v e l s v a r i e d over a range g r e a t e r t h a n 1300 m i n 7 p e r c e n t o f a l l snow--' st o r m s . However, t h e mean range f o r a l l snow storms was 550 m (± 400 m), w i t h 60 p e r c e n t of a l l storms h a v i n g a-range l e s s t h a n t h i s mean, and.one t h i r d h a v i n g a range l e s s t h a n 200 m. There was a l s o c o n s i d e r a b l e v a r i a t i o n i n f r e e z i n g l e v e l among snow s t o r m s , but t h e r e are some g e n e r a l t r e n d s f o r t h o s e o f the same s y n o p t i c type (Table -8.7). The h i g h e s t f r e e z i n g l e v e l s are produced by snow storms w i t h a warm s e c t o r , . w i t h o c c l u d e d f r o n t s , c o l d f r o n t s , non-f r o n t a l s i t u a t i o n s , and storms a s s o c i a t e d w i t h A r c t i c a i r . t e n d i n g t o have p r o g r e s s i v e l y l ower f r e e z i n g l e v e l s . Two d i s t i n c t i v e p o p u l a t i o n s o f c o l d f r o n t s can be r e c o g n i s e d . One p o p u l a t i o n has f r e e z i n g l e v e l s o f about 200 m, and. advects a i r over the ocean from the c o l d s o u r c e s o f the Yukon and A l a s k a . The o t h e r p o p u l a t i o n b r i n g s a i r . o f more P a c i f i c o r i g i n and has a h i g h e r f r e e z i n g l e v e l at about 900 m. S i m i l a r l y n o n - f r o n t a l snow storms produce f r e e z i n g l e v e l s c e n t e r e d around 200 m ( u s u a l l y c o l d lows and n o r t h -west a i r f l o w s ) and 600 m ( o t h e r s ) . Most storms a s s o c i a t e d w i t h A r c t i c a i r t e n d t o have mean f r e e z i n g l e v e l s c l o s e t o the s u r f a c e , a l t h o u g h a few r a i s e f r e e z i n g l e v e l s t o h i g h e r t h a n 400 m. 216 TABLE 8.7 V a r i a t i o n o f mean f r e e z i n g l e v e l of show  storms w i t h s y n o p t i c storm type  Data f o r w i n t e r s 1969-70, 1970-71 combined Storm type Mean (m) St.Dev. (m) Nature o f f r e q u e n c y d i s t r i b u i t o n m a r i t i m e c o l d f r o n t 729' 361 Bimodal w i t h p e a k s - a t 200 m and 900 m m a r i t i m e f r o n t s w i t h a warm s e c t o r 891 179 n o r m a l l y d i s t r i b u t e d m a r i t i m e o c c l u d e d f r o n t s 770 264 n o r m a l l y d i s t r i b u t e d storms a s s o c i a t e d w i t h A r c t i c a i r - 295 225 P o s i t i v e skew d i s t r i b u t i v e w i t h the mode at 100 m n o n - f r o n t a l storms : 589 292 Bimodal w i t h peaks- at 200 m and 600 m 217 8 . 3 The f l u x o f a t m o s p h e r i c water vapour d u r i n g w i n t e r The f l u x o f a t m o s p h e r i c water vapour over an a r e a has o f t e n been used t o examine m o i s t u r e s o u r c e s ( e . g . B a r r y 1966, Rasmusson 1 9 6 7 ) . The r a d i o s o n d e network about the west co a s t of N o r t h America i s not s u f f i c i e n t l y dense t o a l l o w an a r e a l a n a l y s i s i n the same way-. However, t e m p o r a l d i f f e r e n c e s i n vapour f l u x e s between the two winters"may be examined at a s i n g l e r a d i o s o n d e s t a t i o n . I d e n t i f i c a t i o n o f t h e s e d i f f e r e n c e s may l e a d t o u n d e r s t a n d i n g t h e r e a s o n s f o r the o b s e r v e d c o n t r a s t s i n p r e c i p i t a t i o n and s n o w f a l l . A c c o r d i n g l y , vapour f l u x e s were computed f o r b o t h w i n t e r s from r a d i o s o n d e d a t a c o l l e c t e d at P o r t Hardy. P r e v i o u s s t u d i e s o f l a r g e s c a l e water vapour movement over the P a c i f i c c o a s t i n d i c a t e t h a t vapour f l u x e s a t t h i s s t a t i o n are s i m i l a r t o those at Q u i l l a y u t e , the o t h e r r a d i o s o n d e s t a t i o n r e l e v a n t t o the Mount Seymour a r e a (Rasmusson- 1 9 6 7 ) . 8 . 3 . 1 Data and method of computation Vapour f l u x e s were computed from r a d i o s o n d e a s c e n t s at P o r t Hardy f o r 0000 GMT and 1200 GMT f o r the p e r i o d s November 1969 t o May 1 9 7 0 , and November 1970 t o May 1971 . Data a t - t h e s u r f a c e , lOOOmb, and at 5'0 mb i n t e r v a l s , up t o 400 mb were used. 218 The z o n a l f l u x at a s i n g l e l e v e l i s given-.; by Pz = 77 q u and the m e r i d i o n a l f l u x by Fm = h Q v where g = a c c e l e r a t i o n due t o g r a v i t y •( cm/sec 2.) q = s p e c i f i c h u m i d i t y (gm/kg) u, v =-.zonal and m e r i d i o n a l components o f wind v e l o c i t y (cm/sec) The v e r t i c a l l y i n t e g r a t e d z o n a l f l u x i s g i v e n by 400 mb Q z = J / q u dp P s and the v e r t i c a l l y i n t e g r a t e d m e r i d i o n a l f l u x by 400 mb-Qm = | / q v dp where P s = p r e s s u r e at the s u r f a c e . The i n t e g r a t i o n was performed by a p p l y i n g the t r a p e z o i d a l r u l e . 219 V a l u e s o f F z , Fnu-Qz and Q m were computed f o r each ascent and the mean t a k e n f o r each'month. The v e r t i c a l l y i n t e g r a t e d t o t a l mean monthly f l u x of water vapour above' a p o i n t on the e a r t h ' s s u r f a c e was then g i v e n by Q = Qz i + Qm 1 where 1 , ~j , are u n i t v e c t o r s d i r e c t e d p o s i t i v e l y t o the e a s t and n o r t h r e s p e c t i v e l y , and Qz and Qm are. means f o r a month. The monthly means were a l s o o b t a i n e d f o r tho s e a s c e n t s d u r i n g s t o r m s , and f o r those a s c e n t s d u r i n g snow storms on Mount Seymour. I t was n e c e s s a r y t o ta k e i n t o account the d i s t a n c e a p a r t o f P o r t Hardy and Mount Seymour, and t h e movement o f p r e s s u r e systems. I t was assumed t h a t r a d i o -sonde a s c e n t s at P o r t Hardy measure upper a i r c o n d i t i o n s which o c c u r 8 hours l a t e r over Mount Seymour. The mean monthly f l u x f o r storms i s analogous t o the c o m p u t a t i o n a l q u a n t i t y , the"eddy component o f the f l u x " , f r e q u e n t l y used by o t h e r workers ( e . g . B a r r y 1966 ) . 8.3.2 D i s c u s s i o n of r e s u l t s P o r t Hardy l i e s a c r o s s the p a t h o f one o f the two main c u r r e n t s o f wa t e r vapour e n t e r i n g t h e N o r t h American c o n t i n e n t (Rasmusson 196"7) so t h e v e r t i c a l l y i n t e g r a t e d f l u x e s o f water vapour are l a r g e ( F i g . 8 . 5 ) . The f l u x e s 220 F i g . 8 .5 Mean monthly v e r t i c a l l y i n t e g r a t e d water vapour . f l u x v e c t o r s , P o r t Hardy, w i n t e r s 1 9 6 9 - 7 0 , 1970-71 221 f o r a l l weather c o n d i t i o n s a r e f i r s t c o n s i d e r e d . I n the w i n t e r 1969-70 t h e s e were comparable I n magnitude and d i r e c t i o n t o those found by Rasmusson f o r the p e r i o d 196l t o 1963. The f l u x e s d u r i n g the w i n t e r 1970-71 were l e s s s i m i l a r . They a l s o d i s p l a y e d g r e a t e r monthly v a r i a b i l i t y t h a n i n 1969-70. F l u x e s d u r i n g storm p e r i o d s were e q u a l t o or g r e a t e r t h a n f l u x e s f o r a l l weather c o n d i t i o n s . I n a d d i t i o n they o f t e n d i s p l a y e d a s t r o n g e r p o s i t i v e m e r i d i o n a l component. Comparing the two w i n t e r s , the f l u x e s d u r i n g storms were l a r g e r i n 1969-70, except d u r i n g J a nuary and F e b r u a r y . T h i s i s an i n t e r e s t i n g r e s u l t , c o n s i d e r i n g the g r e a t e r p r e c i p i -t a t i o n o f the second w i n t e r . There e x i s t s t he p o s s i b i l i t y t h a t P o r t Hardy d a t a may not be r e p r e s e n t a t i v e of upper a i r c o n d i t i o n s on Mount Seymour, e s p e c i a l l y s i n c e the v e r t i c a l l y i n t e g r a t e d f l u x v e c t o r s were u s u a l l y not i n the d i r e c t i o n o f the mountain ( F i g . 8.5) However, o t h e r workers have a l s o n o t e d t h a t t r a n s p o r t o f water vapour over an a r e a may p r o v i d e l i t t l e g u ide t o p r e c i p i t a t i o n amounts ( B a r r y 1966, Rasmusson 1967). R a t h e r , p r e c i p i t a t i o n i s r e l a t e d t o the di v e r g e n c e ( o r convergence) o f vapour f l u x , as g i v e n by the a t m o s p h e r i c water b a l a n c e e q u a t i o n . U n f o r t u n a t e l y , the r a d i o s o n d e network around Mount Seymour i s not s u f f i c i e n t l y dense t o a l l o w e s t i m a t e s of 222 divergence or convergence. However, the smaller f l u x e s of the winter 1970-71* but l a r g e r storm p r e c i p i t a t i o n , suggest a greater p r e c i p i t a t i o n e f f i c i e n c y during t h i s winter. To i n v e s t i g a t e t h i s hypothesis f u r t h e r , the p r e c i p i t a t i o n e f f i c i e n c y was defined a f t e r S e l l e r s (1965) as, P PE = - . 100 (percent) W where P = mean d a i l y p r e c i p i t a t i o n f o r the winter (mm) W = mean p r e c i p i t a b l e water at Port Hardy (mm) PE represents the f r a c t i o n of the average moisture overhead which f a l l s as p r e c i p i t a t i o n on an average day. Values f o r both winters were c a l c u l a t e d f o r Mount Seymour at 120 m and 1260 m, and f o r Port Hardy. The r e s u l t s were as fol l o w s ( i n percent) Winter 1969-70 Winter 1970-71 Mount Seymour 120 m 48 • 63 Mount Seymour 1260 m 71 123 Port Hardy 44 48 223 P r e c i p i t a t i o n e f f i c i e n c i e s were about one t h i r d h i g h e r on Mount Seymour i n the w i n t e r 197-0-71, even t o the e x t e n t of b e i n g g r e a t e r t h a n 100 3 but at P o r t Hardy t h e r e was l i t t l e d i f f e r e n c e . T h i s s u g gests t h a t l a r g e r amounts of m o i s t u r e were a d v e c t e d over Mount Seymour than over P o r t Hardy. These may have come from-convergence o f vapour f l u x , from l o c a l e f f e c t s such as the i n f l u e n c e o f the' S t r a i t of G e o r g i a , or from more a c t i v e o r o g r a p h i c p r e c i p i t a t i o n p r o c e s s e s . The f l u x e s o f water vapour d u r i n g snow storms are of major i n t e r e s t t o t h i s s t u d y . There were s e v e r a l c o n t r a s t s between the two w i n t e r s . An i m p o r t a n t d i f f e r e n c e was t h e l a r g e f l u x e s d u r i n g t h e c o l d e r p a r t o f w i n t e r 1970-71 (January t o A p r i l ) . I n January o f t h i s w i n t e r the f l u x e s were a l s o d i r e c t e d from the west. Large q u a n t i t i e s of snow were d e p o s i t e d t o low e l e v a t i o n s i n t h i s month. I n most o t h e r months o f b o t h w i n t e r s f l u x e s d u r i n g snow storms were d i r e c t e d from the s o u t h or s o u t h -west. Examples o f t h e f l u x d u r i n g the. more commonly o c c u r r i n g snow storm t y p e s are g i v e n i n Appendix J.. S i n c e a mountain i s a t h r e e d i m e n s i o n a l o b j e c t , the- v a r i a t i o n s o f f l u x e s w i t h e l e v a t i o n s h o u l d a l s o be con-s i d e r e d . The top o f Mount Seymour i s at about 850 mb. The z o n a l f l u x o f water /vapour v a r i e s w i t h e l e v a t i o n i n a c o n f i g u r a t i o n t h a t i s ' c o n s i s t e n t from month t o month ( F i g . 8. 224 Snow storms produce s t r o n g e a s t e r l y f l u x e s at the s u r f a c e . However, at about 850 mb the .zonal f l u x becomes p o s i t i v e i n c r e a s i n g t o a maximum at 800 t o 700. mb , t h e n more s l o w l y d e c r e a s i n g at h i g h e r l e v e l s . Many p r e v i o u s workers (e.g. Rasmusson 1967) assume the f l u x above 400 mb t o be n e g l i g i b l e , but i t i s i n t e r e s t i n g t o note t h a t the f l u x at 400 mb above P o r t Hardy can sometimes r e a c h one gm (cm mb s e c ) - 1 . T h i s may be h a l f t h a t - o f the maximum (e.g. as i n March 1 9 7 0 ) . The s n o w i e r w i n t e r , 1 9 7 0 - 7 1 , produced weaker e a s t e r l y f l u x e s i n most months, and d u r i n g the c o l d e s t months of the w i n t e r ( J a n u a r y , F e b r u a r y , March) the w e s t e r l y f l u x e s a l o f t were l a r g e r . The m e r i d i o n a l f l u x o f water vapour d u r i n g snow storms i s o v e r - w h e l m i n g l y from the south at most l e v e l s ( F i g . 8 . 7 ) . The maximum m e r i d i o n a l f l u x o c c u r s a t 900 t o 800 mb.. The g e n e r a l l y c o n s i s t e n t shape o f the c u r v e s from month t o month g i v e n i n F i g s , 8 . 6 , 8 . 7 undoubtedly r e f l e c t s ..the l a r g e number of f r o n t a l d i s t u r b a n c e s ' which produce' snow. Those months t h a t d i s p l a y the m o s t ' i r r e g u l a r curves ( e . g . J a n uary 1971) e x p e r i e n c e d f r e q u e n t A r c t i c a i r o u t b r e a k s or o t h e r n o r t h e r l y f l o w s . The h i g h e r s n o w l i n e s o f the w i n t e r 1969-70 may be r e l a t e d t o t h a t w i n t e r ' s l a r g e r f l u x e s of water vapour from th e s o u t h . 400 ' 500 XI £ 600-Si 7 0 ° " in tv c Q- eoo-900-1000 400-500-" \ \ ' :  \ \ Nov VV Dec \ \ Jan \ \ * \ • \\ l \ \ \ \ \ \ \ i\ \ \ » \ \i \ i ' \ * \ \ \ \ \ \ \ A \ \ \ \ 1 \ i \ \ N ' \ • \ V \ \ N \ N ' J * ) • \ ^ 1 ' A 1 1 J 1 / ^ / / j t / / -2 -3 - 2 -1 ^| 600-3 700-ui in <U at eoo-900-1000-- -* Winter 1969-70 '-f—Winter 1970-71 - 2 -1 0 I T -3 - 2 -1 F i g . 8.6 Mean monthly z o n a l f l u x e s d u r i n g snowstorms. Based on d a t a from s t a n d a r d p r e s s u r e l e v e l s at P o r t Hardy f o r the w i n t e r s 1969-70, 1970-71. P o s i t i v e f l u x e s are d i r e c t e d from the west. U n i t s are gm (cm mb s e c ) - 1 ro 4 0 0 -5 0 0 -6 0 0 -.1 TOO-v a. 8 0 0 9 0 0 H 1 0 0 0 - f -1 4 0 0 -5 0 0 H 6 0 0 -i OJ 3 700-I in a. arxH 9 0 0 H 1 0 0 0 - f -1 Winter 1969-70 -1 0 FLUX - 1 F i g . 8.7 Mean monthly m e r i d i o n a l f l u x e s d u r i n g snow storms. Based on d a t a from s t a n d a r d . p r e s s u r e l e v e l s at P o r t Hardy f o r the w i n t e r s 1969-70, 1970-71. P o s i t i v e f l u x e s are d i r e c t e d from the so u t h . U n i t s are gm(cm mb s e c ) - 1 ro ro CA 227 8 .4 C o n c l u s i o n s F r o n t a l storms dominate p r e c i p i t a t i o n at a l l e l e -v a t i o n s on Mount Seymour. Most f r o n t s are o c c l u d e d b e f o r e they r e a c h the co a s t and they u s u a l l y advect mA or mP i n t o t h e r e g i o n . Storms f o l l o w i n g n o r t h e r l y - t r a c k s are more l i k e l y t o produce snow on Mount Seymour because they have e a s i e s t access t o the c o l d a i r s o u r c e s . However, storms a p p r o a c h i n g the a r e a from t h e s o u t h can produce snow on the mountain i f they can draw on c o l d a i r by d o m i n a t i n g the c i r c u l a t i o n i n the E a s t e r n P a c i f i c . The storms of the c o l d e r , s n o w i e r , w i n t e r (1970-71) f o l l o w e d n o r t h e r l y t r a c k s more o f t e n than the p r e v i o u s w i n t e r . They thus tended t o advect a i r w i t h lower f r e e z i n g l e v e l s , p r o d u c i n g lower s n o w l i n e s . Such a i r a l s o tends t o be u n s t a b l e , so the o r o g r a p h i c component of p r e c i p i t a t i o n was g r e a t e r . T h i s w i n t e r produced s u b s t a n t i a l l y more storms a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , a c r i t i c a l s i t u a t i o n f o r p r o d u c i n g snow t o low e l e v a t i o n s . There were a l s o more c o l d f r o n t s and more trough's'.;. Assuming the r e s u l t s from the two w i n t e r s are r e p -r e s e n t a t i v e o f a wide range o f p o s s i b l e w i n t e r s n o w f a l l c o n d i t i o n s , storms may be ranked i n importance at each e l e v a t i o n as f o l l o w s : / 2 A. By storm type High e l e v a t i o n s C8Q0-1260 m) Occluded' f r o n t s , c o l d f r o n t ' s , warm f r o n t s , s o u t h -w e s t e r l y a i r s t r e a m s . M i d d l e e l e v a t i o n s (-400.-800 m) Occluded f r o n t s , n o n - f r o n t a l s o u r c e s , c o l d f r o n t s storms a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s . Low e l e v a t i o n s (below 400. m) Storms a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , c o l d f r o n t s , t r o u g h s . B. By mean s n o w f a l l p e r storm H i g h ' e l e v a t i o n s (800-1260 m) S o u t h - w e s t e r l y a i r s t r e a m , m o i s t P a c i f i c airflows.-, a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , c o l d f r o n t s t r o u g h s . M i d d l e e l e v a t i o n s (-400-800 m) M o i s t P a c i f i c a i r f l o w s a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , c o l d f r o n t s , t r o u g h s . ,Low e l e v a t i o n s (below 400. m) M o i s t P a c i f i c a i r f l o w s a s s o c i a t e d w i t h A r c t i c a i r o u t b r e a k s , t r o u g h s , o t h e r A r c t i c a i r s t o r m s , c o l d f r o n t s . 229 The w i n t e r 1970-71 d i s p l a y e d lower mean storm f r e e z i n g l e v e l s . T h i s produced l o w e r s n o w l i n e s . F r e e z i n g l e v e l s were - s t r o n g l y grouped about 900 m in" T9'6'9-70 . T h i s h e l p e d g e n e r a t e the o b s e r v e d n o n - l i n e a r i n c r e a s e o f snow a c c u m u l a t i o n w i t h e l e v a t i o n . F r e e z i n g l e v e l s are r e l a t e d t o storm t y p e . The t o t a l f l u x e s o f wa t e r vapour were l a r g e , and g e n e r a l l y showed c o n s i s t e n t p a t t e r n s from n o r t h t o south',.; and w i t h h e i g h t . F l u x e s d u r i n g snow storms were l a r g e r t h a n f o r o t h e r weather c o n d i t i o n s . I n 1970-71, they o f t e n showed s t r o n g e r p o s i t i v e z o n a l components, e s p e c i a l l y d u r i n g the c o l d e r months o f the y e a r . However, d i f f e r e n c e s i n t he vapour f l u x f i e l d s were not as l a r g e as the d i f f -e rences i n s n o w f a l l and p r e c i p i t a t i o n might .suggest. i 230 CHAPTER 9 9. PREDICTION OP NEW SNOW DEPOSITION The f o c u s of t h i s c h a p t e r i s the development of a model t o p r e d i c t snow d e p o s i t i o n from a storm on a west coa s t m i d l a t i t u d e mountain. Input t o the model i s r e s t r i c t e d t o p r e c i p i t a t i o n and temperature measurements at the base of the mountain., and t o d a t a from r a d i o s o n d e a s c e n t s and s y n o p t i c c h a r t s . As a f i r s t a p p r o x i m a t i o n , snow d e p o s i t i o n a t v a r i o u s e l e v a t i o n s 'could be e s t i m a t e d u s i n g the mean f i g u r e s f o r each storm type g i v e n i n T a b l e 8.5. However, except f o r the f i r s t t h r e e storm t y p e s , the number of samples i s low and the e s t i m a t e s l i k e l y t o l a r g e e r r o r . There i s a l s o con-s i d e r a b l e v a r i a t i o n i n snow d e p o s i t i o n about each mean be-cause of d i f f e r e n t f r e e z i n g l e v e l s , i n t e n s i t i e s and t r a c k s o f storms of the same s y n o p t i c t y p e . 9 .1 A p r o posed model More r e l i a b l e e s t i m a t e s of storm snow d e p o s i t i o n can be a c h i e v e d i f the q u a l i t a t i v e model dev e l o p e d i n s e c t i o n 6.3.4 I s t r a n s l a t e d i n t o q u a n t i t a t i v e terms and i n t e g r a t e d w i t h the s y n o p t i c d a t a . To t h i s end, t h e d e s c r i p t i v e model 231 of F i g . 6.11 i s p r e s e n t e d i n more, f o r m a l terms i n F i g . 9.1. For c o n v e n i e n c e , the- v a r i a t i o n o f snow d e p o s i t i o n and p r e -c i p i t a t i o n w i t h e l e v a t i o n are shown as l i n e a r f u n c t i o n s , but t h e s e need not be so. The f o l l o w i n g parameters must be e s t i m a t e d ( i n o r d e r ) : (a) P(H) = p r e c i p i t a t i o n i n open areas at any e l e v a t i o n H (b) H Q = the e l e v a t i o n o f t h e ' i n c o m p l e t e new s n o w l i n e (c) H e = the l o w e s t e l e v a t i o n where storm (or substorm) snow d e p o s i t i o n e q u a l s storm ( o r substorm) p r e c i p i t a t i o n . T h i s i s the e q u i v a l e n t e l e v a t i o n . (d) M(H) = S p e c i f i c new snow mass d e p o s i t e d i n open areas at any e l e v a t i o n where H > H e, i . e . d e p o s i t i o n i n the snow, or d r i f t zone. (e) M l(H) = s p e c i f i c snow mass d e p o s i t e d i n open areas at any e l e v a t i o n H, where H D < H < H e , i . e . d e p o s i t i o n i n the wet snow zone. ( f ) Where, because o f f l u c t u a t i n g f r e e z i n g l e v e l s b o t h snow and r a i n f a l l a t the top of the mountain, i t i s co n v e n i e n t t o r e c o g n i s e the r a t i o R, where R " PTHTT 232 Elevation(H) (b) S t o r m s w h e r e R < 1 S P(Hi) M(H0 He Elevation (H) F i g . 9.1 Proposed .model of snow d e p o s i t i o n i n . open areas from . a st o r m on west coast m i d l a t i t u d e mountain: (a) Storm w i t h r e l a t i v e l y c o n s t a n t f r e e z i n g l e v e l and snow o n l y at top o f mountain (R=l)-(b) A composite storm w i t h f l u c t u a t i n g f r e e z i n g l e v e l Snow mixed w i t h -rain at top of the mountain (R<1) A l l terms a re d e f i n e d i n the t e x t 233 Hj i s the e l e v a t i o n of the top of the mountain. Thus R gives the p r o p o r t i o n of the storm p r e c i p i -t a t i o n deposited as snow at the top of the mountain. When R = 1.0, only snow f a l l s at the top of the mountain. I f R = 0.0, then no snow i s - deposited. v I f 0.0 < R < 1.0, then both r a i n and'snow f a l l at the top of the mountain and the storm i s of a com-p o s i t e type. In terms of the proposed model i l l u s t r a t e d i n F i g . 9.1b M(H) = R.P(H) f o r H > H e . (g) Snow d e p o s i t i o n i n f o r e s t e d areas can be estimated from that i n open areas. 9.2 P r e d i c t i o n of storm p r e c i p i t a t i o n w i t h e l e v a t i o n P(H) 9.2.1 Orographic component of p r e c i p i t a t i o n To examine v a r i a t i o n s of p r e c i p i t a t i o n with e l e v a t i o n f u r t h e r , the maximum storm p r e c i p i t a t i o n ( P m a x ) a wherever recorded w i t h i n the study network of gauges, was p l o t t e d against p r e c i p i t a t i o n P(120) at e l e v a t i o n 120 m, here regarded as the base of the mountain. The data was analysed by simple l i n e a r r e g r e s s i o n (Fig.'9.2) to give Pma.x = l ^ - 1 + i - 1 * P(120) 6 20 40 60 80 Storm Precipitation at base of mountain Rl20)(mm) rv> - t F i g . 9-2" Maximum p r e c i p i t a t i o n r e c o r d e d from a storm on Mount Seymour, as a f u n c t i o n o f storm p r e c i p i t a t i o n at the base"of the mountain 235 w i t h r 2 = O..69, but t h e r e i s a good d e a l o f s c a t t e r a t l a r g e r storm p r e c i p i t a t i o n amounts. There e x i s t s a s t r a i g h t l i n e • l o w e r envelope g i v e n by, P'max = P ^ 2 0 ) t o t he assemblage - of p o i n t s . F o l l o w i n g E l l i o t t and S c h a f f e r (1962), the amount by which storm p r e c i p i t a t i o n exceeds t h i s envelope i s known as the o r o g r a p h i c component of p r e c i p -i t a t i o n . Thus, ^oro = ^max ~ p'max The s c a t t e r about the r e g r e s s i o n l i n e r e s u l t s from v a r i -a t i o n s i n t h i s component f o r d i f f e r e n t s torms. As sto r m p r e c i p i t a t i o n i n the v a l l e y i n c r e a s e s , t he o r o g r a p h i c com-ponent tends t o become more marked. T h i s i s i n accordance w i t h W a l k o t t e n and P a t r i c s (1967) f i n d i n g near H o l l i s , A l a s k a . There a l s o e x i s t s an upper envelope g i v e n ( i n mm) ^ P"max = 6 0 + 2 P(120) i n d i c a t i n g some unknown c o n s t r a i n t t o the magnitude o f the o r o g r a p h i c component. The maximum s i z e o f the o r o g r a p h i c component i s t h e r e f o r e g i v e n ( i n mm) by p"max - p , m a x = 60 + P(120) 236 These s i m p l e r e l a t i o n s h i p s are u s e f u l f o r crude e s t i m a t e s o f p r e c i p i t a t i o n on Mount Seymour, and may have a p p l i c a t i o n f o r some purposes such as f l o o d d e s i g n , but are i n s u f f i c i e n t l y p r e c i s e f o r e s t i m a t i o n of P(H) f o r i n d i v i d u a l storms. 9.2.2 E m p i r i c a l p r e d i c t i o n e q u a t i o n s V a r i a t i o n s o f storm p r e c i p i t a t i o n w i t h e l e v a t i o n might be p r e d i c t e d u s i n g t h e known p r e c i p i t a t i o n at the base of the mountain and e l e v a t i o n i n the f o l l o w i n g form, P(H) = f [ P ( l 2 0 ) , H, P ( 1 2 0 ) , H, P(120.) 2, H 2 J where P(H) = storm p r e c i p i t a t i o n (mm) at some e l e v a t i o n H. 0 < P(H) < 151 mm H = e l e v a t i o n (m). 120 m < H < 1260 m P(120) =.storm p r e c i p i t a t i o n at the base o f the mountain (H = 120 m). 0 < P(120) < 83 mm The d a t a were analysed, by m u l t i p l e s t e p w i s e r e g r e s s i o n p r o -c e d u r e s . The r e s u l t a n t b e s t f i t e q u a t i o n s f o r each w i n t e r 237 ( e q u a t i o n s 1,2). and f o r a l l data- combined ( e q u a t i o n 3) e x p l a i n e d c l o s e t o 80%. of the v a r i a t i o n i n P ( H ) . ( T a b l e 9-1). S i n c e a wide v a r i e t y o f storm t y p e s was i n c l u d e d i n the 125 a n a l y s e d , and the r e s i d u a l s from t h e r e g r e s s i o n l i n e f o r a l l . d a t a combined were homogeneous and n o r m a l l y d i s -t r i b u t e d , e q u a t i o n 3 was c o n s i d e r e d a p p r o p r i a t e f o r p r e -d i c t i o n ( a f t e r Draper and Smith 1966). However, the s t a n d a r d e r r o r of 12.1 of t h i s e q u a t i o n i s f a i r l y l a r g e . T h i s does not a l l o w v e r y p r e c i s e e s t i m a t e s o f P ( H ) , so ways of r e d u c i n g the s t a n d a r d e r r o r of p r e d i c t i o n e q u a t i o n s are now examined. The p e r s i s t e n t anomalies i n p r e c i p i t a t i o n v a r i a -t i o n s w i t h e l e v a t i o n a t 490 m, and 870-970 m ( F i g . 6.1)• may have been due t o the p r o x i m i t y - of thes e s a m p l i n g s i t e s t o the top of the r i d g e ( F i g . 2.3). To examine t h i s h y p o t h e s i s , r e s i d u a l s from r e g r e s s i o n e q u a t i o n 3 were themselves r e g r e s s e d a g a i n s t the d i s t a n c e from the sam p l i n g s i t e t o the r i d g e . No s i g n i f i c a n t r e l a t i o n s h i p was f o u n d . S i n c e the anomaly p e r s i s t e d t h r o u g h a wide v a r i e t y o f storm t y p e s , i t was u n l i k e l y t o have been p r o -duced by m e t e o r o l o g i c a l f a c t o r s , but by- o t h e r t o p o g r a p h i c p a r a m e t e r s . R e g r e s s i o n e q u a t i o n s which i n c l u d e d s l o p e and aspect o f the sa m p l i n g s i t e as independent v a r i a b l e s were a l s o t e s t e d , but no improvement i n p r e d i c t i o n o f p r e -c i p i t a t i o n r e s u l t e d . I t was t h e r e f o r e c o n c l u d e d t h e s e anomalies must be due t o l o c a l s i t e c o n d i t i o n s . 238 TABLE 9 . 1 Regression liquations for estimating storm p r e c i p i t a t i o n with elevation Equation No. Notes Equation n • R2 S.E. of Estimate 1 Winter 1969-70 P ( H ) = - 2 . 8 + 1 . 0 5 P ( 1 2 0 ) + 0 . 0 1 0 H 627 0 . 8 1 9 . 7 2 Winter 1 9 7 0 - 7 1 P ( H ) = - 9 . 7 + 1 . 2 1 P Q 2 0 ) + 0 . 0 2 H H 7JI8 0 . 7 8 1 3 . 2 3 Combined data Winters 1 9 6 9 - 7 1 P ( H ) = - 6 . 8 + 1 . 1 5 P ( 1 2 0 ) + 0 . 0 1 7 H 1375 0 . 7 9 1 2 . 1 1) Combined data for elevations below 870 m P ( H ) = 2 . 9 1 + 0 .86 P ( 1 2 0 ) + 0 . 0 0 0 5 P ( 1 2 0 ) . H 1375 0 . 8 9 7 . 8 5 Combined data for elevations above 870 m P ( H ) = i t . 8 2 + 0 . t 7 P ( 8 7 0 ) + 0 . 0 0 0 5 P ( 8 7 0 ) . H 1375 O.78 1 1 . 3 6 Maritime cold fronts P ( H ) = -7.1) + 1 . 2 1 ) p ( i 2 0 ) + 0 . 0 1 6 H 168 0 . 8 2 1 1 . 7 7 Maritime fronts with warm sector P ( H ) = - 7 . 2 + 1 . 2 1 P (120) ' <+• 0 . 0 1 7 H 160 0 . 7 7 IH.3 8 Maritime occluded fronts P ( H ) = - 8 . 6 + 1 . 1 7 P ( 1 2 0 ) + 0 . 0 2 1 H 1)21) 0 . 8 0 1 1 . 5 9 Non frontal Systems P ( H ) = -1).6 + 1 . 0 1 ) P ( 1 2 0 ) + 0 . 0 1 8 H 2 0 0 0 . 6 8 1 2 .9 10 A r c t i c fronts associated with maritime fronts P ( H ) = - 0 . 9 + 1 . 0 9 P ( 1 2 0 ) + 0 . 0 0 7 H 1)8 0 . 8 1 1 1 . 0 NOTES: ( 1) Based on data for 5 7 storms in winter 1 9 6 9 - 7 0 and 68 storms i n winter 1 9 7 0 - 7 1 . Includes some few cases where two consecutive storms were sampled.as one. ( 11) A l l regression equations were s i g n i f i c a n t at the 99% confidence l e v e l . ( i i i ) P ( H ) = storm precipitation (mm) at some elevation H , where 120 < H < 1260 m. P ( 1 2 0 ) = storm precipitation at base of mountain (120 m) 239 When the d a t a was r e a n a l y s e d i n the o r i g i n a l way, but w i t h o b s e r v a t i o n s at 490_,m,- 870 m and 790 m o m i t t e d , , a s l i g h t r e d u c t i o n i n s t a n d a r d e r r o r r e s u l t e d , but' the co-e f f i c i e n t s o f the r e g r e s s i o n e q u a t i o n were p r a c t i c a l l y t he same as f o r e q u a t i o n 3, Table 9.1. I t was p o s t u l a t e d t h a t more p r e c i s e e s t i m a t e s f o r most e l e v a t i o n s might r e s u l t i f i t was assumed p r e c i p i t a t i o n was a l s o measured at some p o i n t h i g h e r on the mountain. For example, i f measurements were made at 120 m and 870 m, improved e s t i m a t e s f o r e l e v a t i o n s between t h e s e l e v e l s , and' f o r above 870 m might be g i v e n . When t e s t e d , t h i s was t r u e f o r e l e v a t i o n s below 870 m ( e q u a t i o n 4, T a b l e 9.1), but not f o r e l e v a t i o n s above 870 m ( e q u a t i o n 5), where a l a r g e r s t a n d a r d e r r o r o f e s t i m a t e r e s u l t e d , t h a n when o n l y P(120) was used. A f u r t h e r s m a l l i n c r e a s e i n the p r e c i s i o n o f e s t i m a t i n g the v a r i a t i o n o f p r e c i p i t a t i o n w i t h e l e v a t i o n can b e . o b t a i n e d i f the d a t a are a n a l y s e d s e p a r a t e l y f o r each s y n o p t i c s t o r m t y p e (Table 9.1, e q u a t i o n s 6 t o 10).. There i s a s i g n i f i c a n t d i f f e r e n c e between the s l o p e s of th e s e r e g r e s s i o n l i n e s , w i t h t h o s e f o r o c c l u d e d f r o n t s and hon-f r o n t a l systems, t h o s e f o r f r o n t s w i t h warm s e c t o r s and. c o l d f r o n t s , and t h a t f o r A r c t i c a i r a s s o c i a t e d w i t h m a r i -time f r o n t s , f o r m i n g d i s t i n c t s e t s . The above o r d e r i n g a l s o r e f l e c t s a d e c r e a s i n g s l o p e of the r e g r e s s i o n l i n e , 240 that i s a decreasing orographic component of p r e c i p i t a t i o n . Thus the excess of mountain o v e r - v a l l e y winter p r e c i p i t a t i o n i s greatest f o r occluded f r o n t s and l e a s t . f o r A r c t i c a i r associated with maritime f r o n t s . On the whole, the equations of Table 9.1 f o r storm p r e c i p i t a t i o n • p r o v i d e greater explanation and p r e c i s i o n over a wider range of p r e c i p i t a t i o n s and e l e v a t i o n s than those produced f o r d a i l y r a i n f a l l s by Woo (1972) at the-nearby UBC Re-se'arch Forest at Haney. 9.2.3 More t h e o r e t i c a l approaches Several t h e o r e t i c a l models f o r e s t i m a t i n g orographic p r e c i p i t a t i o n have been proposed (e.g. Sawyer 1956, Walker 1961, E l l i o t t and Shaffer 1962, Danard 1971). Sawyer notes that such models must consider m e t e o r o l o g i c a l aspects at three d i f f e r e n t s c a l e s . F i r s t , there are the large scale synoptic f a c t o r s which determine the c h a r a c t e r i s t i c s of the airmass c r o s s i n g the mountains. A strong wind perpendicular to a mountain r i d g e , an airmass which i s moist i n depth,and an airmass w i t h a near n e u t r a l lapse rate without markedly st a b l e l a y e r s o r - i n v e r s i o n s , are e s p e c i a l l y conducive to heavy orographic p r e c i p i t a t i o n . 2 4 l Second, t h e r e I s the dynamics of the a i r m o t i o n over a mountain r i d g e . The amount o f water condensed when a i r f l o w s over h i l l s depends on the amount o f m o i s t a i r l i f t e d and the h e i g h t t o which i t i s l i f t e d . These f a c t o r s are' c o n t r o l l e d by the wind v e l o c i t y and d i r e c t i o n , the wind shear and the s t a b i l i t y of the atmosphere. Thus Danard (1971) uses as h i s b a s i c p r e d i c t o r , t he mean v e r t i c a l w ater vapour t r a n s p o r t t h r o u g h a h o r i z o n t a l u n i t - a r e a due t o f l o w over u n d u l a t i n g t e r r a i n . T h i r d , t h e r e i s the m i c r o p h y s i c s of the c l o u d and p r e c i p i t a t i o n w hich determines the amount of w a t e r condensed and whether i t reaches the ground. I n o r o g r a p h i c c l o u d s over Mount Seymour p r e c i p i t a t i o n i n w i n t e r i s p r o b a b l y always formed-by the B e r g e r o n - F i n d e i s e n p r o c e s s . As the snow p a r t i c l e s f a l l w i t h i n t he c l o u d , they grow by sweeping out s u p e r c o o l e d water d r o p l e t s d u r i n g t h e i r f a l l . U n f o r t -u n a t e l y we u n d e r s t a n d l i t t l e about the motion of a i r w i t h i n c l o u d s , and. the laws g o v e r n i n g the growth and a g g r e g a t i o n of i c e p a r t i c l e s are not y e t f i r m l y e s t a b l i s h e d . Moreover, the l a r g e v a r i a t i o n s i n the c o n c e n t r a t i o n and p r o p e r t i e s o f atm o s p h e r i c a e r o s o l s , and the g r e a t c o m p l e x i t y of atmos-p h e r i c motions make i t d i f f i c u l t t o c o n s t r u c t a d e t a i l e d , g e n e r a l t h e o r y o f p r e c i p i t a t i o n development (Mason 1971), l e t a lone a p p l y i t t o a mountain a r e a . 242 Thus some a s p e c t s of the t h e o r y o f o r o g r a p h i c p r e -c i p i t a t i o n are s t i l l l i t t l e u n d e r s t o o d . Many o f t h e t h e o r i e s a p p l y t o i d e a l s i t u a t i o n s (e.g. an i n f i n i t e l y l o n g smooth mountain r i d g e ) , and some i n c o r p o r a t e terms which cannot be dete r m i n e d w i t h p r e c i s i o n (e.g. p r e c i p i t a t i o n e f f i c i e n c y , t e r m i n a l v e l o c i t y o f p r e c i p i t a t i o n p a r t i c l e s , v e r t i c a l v e l o c i t y o f s t o r m s ) . Walker (1961) and Danard (1971) have a p p l i e d t h e i r t h e o r i e s t o v a r i o u s areas o f B r i t i s h C o lumbia, but b o t h seek t o e s t i m a t e s e a s o n a l o r ann u a l p r e c i p i t a t i o n f o r mountain areas w h i c h have been t o p o g r a p h i c a l l y smoothed over 200 km 2 or g r e a t e r . D i r e c t use o f t h e i r methods was not c o n s i d e r e d s u i t a b l e f o r t h i s s t u d y , where p r e d i c t i o n o f o r o g r a p h i c p r e c i p i t a t i o n i s sought a f t e r i n d i v i d u a l storms f o r a mountain of a r e a l e s s t h a n 15 km 2. F o r thes e r e a s o n s , i t was c o n s i d e r e d i n -a p p r o p r i a t e t o ap p l y t h e o r e t i c a l models t o Mount Seymour, which i s not an i n f i n i t e l y l o n g , smooth r i d g e , and where t h e r e i s no knowledge of the mesoscale s t r u c t u r e o f a storm. R a t h e r attempts are made t o develop f u r t h e r , improved, e m p i r i c a l p r e d i c t i o n e q u a t i o n s i n c o r p o r a t i n g v a r i a b l e s which the t h e o r y o f p r e c i p i t a t i o n (as d i s c u s s e d by t h e above a u t h o r s ) i n d i c a t e s a re i m p o r t a n t . T h i s approach has been j u s t i f i e d by E l l i o t t and S h a f f e r (1962). By u s i n g such v a r i a b l e s , they were b e t t e r a b l e t o p r e d i c t the o r o g r a p h i c component o f p r e c i p i t a t i o n f o r t h e c o a s t a l mountains o f 243 C a l i f o r n i a t h a n they were by a t t e m p t i n g t o use t h e t h e o r y i t s e l f . A c c o r d i n g l y , the f o l l o w i n g v a r i a b l e s were s e l e c t e d , or computed, from the r a d i o s o n d e d a t a at P o r t Hardy. The d a t a was c o n f i n e d t o thos e a s c e n t s which t o o k p l a c e d u r i n g storms . W = p r e c i p i t a b l e w ater from the s u r f a c e t o 750 mb Q = v e r t i c a l l y i n t e g r a t e d z o n a l f l u x o f water vapour Q m = • v e r t i c a l l y i n t e g r a t e d m e r i d i o n a l f l u x o f water vapour V(850) = maximum wind v e l o c i t y d u r i n g t h e storm at 850 mb V(750) = maximum wind v e l o c i t y d u r i n g the storm at 750 mb DB(750) = p r e f r o n t wind d i r e c t i o n at 750 mb DA(750) = p o s t f r o n t wind d i r e c t i o n at 750 mb B = v e r t i c a l wind shear from the s u r f a c e t o 750 mb. I f t h e r e was more th a n one asc e n t d u r i n g the st o r m , t h e n t h e maximum v a l u e was chosen. 3 was c a l c u l a t e d i n cm/sec . 100 m 244 SI(950) = s t a b i l i t y i n d e x from t h e s u r f a c e t o 950 mb SI(850) = s t a b i l i t y i n d e x from 950 mb t o 850 mb SI(750) = s t a b i l i t y i n d e x from 850 mb t o 750 mb HTTT- = mean h e i g h t o f the f r e e z i n g l e v e l r Li d u r i n g the storm The s t a b i l i t y i n d e x i s the d i f f e r e n c e between the obs e r v e d t e m p e r a t u r e at one l e v e l (say 750 mb) and t h e temperature o f the s a t u r a t e d a d i a b a t i c a s c e n t t o t h a t l e v e l , from some lower l e v e l (say 850 mb). I f S I i s n e g a t i v e , a t m o s p h e r i c i n s t a b i l i t y e x i s t s . N e u t r a l c o n d i t i o n s p r e v a i l i f SI i s z e r o , and the atmosphere i s s t a b l e when SI i s p o s i t i v e . When t h e r e was more th a n one r a d i o s o n d e a s c e n t d u r i n g a s t o r m , t h e most u n s t a b l e v a l u e was chosen. ' The c o r r e l a t i o n s between t h e o r o g r a p h i c component of p r e c i p i t a t i o n ( P o r o ) and t h e s e v a r i a b l e s are poor (Table 9.2). The l a c k o f c o r r e l a t i o n may be due t o t h e i n f l u e n c e o f o t h e r v a r i a b l e s not measured by the r a d i o s o n d e a s c e n t s 245 TABLE 9 • 2 Simple, c o r r e l a t i o n .'.coefficients between  the' o r o g r a p h i c component o f p r e c i p i t a t i o n  and v a r i a b l e s from r a d i o s o n d e data-The v a r i a b l e s a re i d e n t i f i e d i n the t e x t V a r i a b l e 1 2 3 4 5 W - 0 .10 • . - 0 . 1 9 . - 0 .04 0 . 0 5 0 .22 Qz - 0 .01 - 0 .05 - 0 .01 0 .12 0 .20 Qm 0 .12 0 .21 0 .15 • 0 .11 0 .03 V ( 8 5 0 ) 0 .25 0 .24 0 .27 0 .14 0 . 2 1 V ( 7 5 0 ) 0 .20 0 .18 0 .20 0 .11 - 0 .15 DB(750) - 0 . 0 1 0 .09 • - 0 . 1 1 - 0 .12 - 0 . 0 3 DA(750) 0 .02 0 . 0 1 0 . 0 8 - 0 .10 - 0 . 0 3 e 0 .07 0 .05 0 . 0 8 - 0 .01 0.04. S K 9 5 0 ) - 0 .09 - 0 . 1 8 - 0 .02 0 . 0 9 . - 0 .02 SI ( 8 5 0 ) - 0 . 1 9 - 0 . 3 0 . - 0 . 1 1 - 0 ..07- ' 0 .01 S K 7 5 0 ) - 0 .19 - 0 .22 - 0 .22 0 .02 0 .01 H P L - 0.04 0 .25 - 0 . 1 6 0 .15 - 0 .13 No. o f Storms 120 54 66 36 47 NOTES Column 1 Column 2 Column 3 Column 4 Column 5 U s i n g d a t a f o r a l l storms* U s i n g d a t a f o r a l l storms:^ w i n t e r 1969-70 U s i n g d a t a f o r a l l s t o r m s , w i n t e r 1970-71 U s i n g d a t a from snowstorms, w i n t e r 1969-70 U s i n g d a t a from snowstorms, w i n t e r 1970-71 a l l storms r e f e r s t o a l l a v a i l a b l e storms. Some storms were not i n c l u d e d i n the a n a l y s i s f o r a v a r i e t y o f reas o n s ( e . g . m i s s i n g r a d i o s o n d e d a t a , t r a c e amounts, o f p r e c i p i t a t i o n o n l y , p r e c i p i t a t i o n from two or more storms measured t o g e t h e r , e t c .) 246 (e.g. t h o s e r e l a t e d t o m i c r o p h y s i c a l p r o c e s s e s o p e r a t i n g i n o r o g r a p h i c c l o u d s ) , and t o t h e l i m i t e d sample o f t h e storm s t r u c t u r e p r o v i d e d by what i s o f t e n a s i n g l e a s c e n t . In a d d i t i o n , P o r t Hardy r a d i o s o n d e d a t a may not be r e p r e -s e n t a t i v e o f a i r over Mount Seymour. Other e v i d e n c e w i l l be p r e s e n t e d i n s e c t i o n 9 - 3 - 2 t o support t h i s c o n c l u s i o n . No s t a t i s t i c a l l y s i g n i f i c a n t e q u a t i o n s r e s u l t e d from s t e p w i s e r e g r e s s i o n a n a l y s i s of P w i t h the v a r i a b l e s 1 " oro from r a d i o s o n d e a s c e n t s p l u s p r e c i p i t a t i o n at the base o f the mountain, P ( 1 2 0 ) , except f o r P o r o = 1 0 + ° - 3 5 P ( 1 2 0 ) + 2.69 V ( 8 5 0 ) - 1.55 V ( 7 5 0 ) P r e c i p i t a t i o n i s i n mm and wind speed i n m/sec. The e q u a t i o n was based on 47 snow storms i n the w i n t e r 1970-71-No s i m i l a r s i g n i f i c a n t r e l a t i o n s h i p was found f o r the w i n t e r 1969-70' . I n a d d i t i o n t h e r e i s low e x p l a n a t i o n (R 2 = 0.24) f o r the above e q u a t i o n , the s t a n d a r d e r r o r o f the e s t i m a t e i s r e l a t i v e l y h i g h (23 mm), so t h a t t h e e q u a t i o n i s not v e r y u s e f u l f o r p r e d i c t i o n . I t i s t h e r e f o r e c o n c l u d e d t h a t no advantage i s t o be g a i n e d by u s i n g v a r i a b l e s from r a d i o s o n d e d a t a a t P o r t Hardy, even though the t h e o r y of o r o g r a p h i c p r e c i p i t a t i o n i n d i c a t e s they are i m p o r t a n t . Thus t h e r e seems l i t t l e a l t e r n a t i v e but t o e s t i m a t e the v a r i a t i o n o f p r e c i p i t a t i o n w i t h e l e v a t i o n w i t h t h e e m p i r i c a l r e l a t i o n s h i p s d e v e l o p e d i n the p r e v i o u s s e c t i o n and shown i n T a b l e 9-1-247 9 . 3 P r e d i c t i o n of new s n o w l i n e s The next s t e p i n the development o f a model t o e s t i m a t e snow d e p o s i t i o n a f t e r each storm i s t o p r e d i c t the e l e v a t i o n o f the i n c o m p l e t e new s n o w l i n e H 0. At the same t i m e , t h e e l e v a t i o n of the complete new s n o w l i n e i s o f i n t e r e s t . 9 . 3 - 1 P r e d i c t i o n e q u a t i o n s The e l e v a t i o n s of b o t h the complete and i n c o m p l e t e new s n o w l i n e s can be r e a s o n a b l y w e l l e x p l a i n e d by the mean storm f r e e z i n g l e v e l ( P i g . 9 . 3 ) . The s i m p l e l i n e a r r e g r e s s i o n r e l a t i o n s h i p s were s i g n i f i c a n t at the 99 p e r c e n t c o n f i d e n c e l e v e l . Mean storm f r e e z i n g l e v e l s were computed from two-h o u r l y storm t e m p e r a t u r e s at s i x e l e v a t i o n s (120 m t o 1260 m). Only t h o s e storm f r e e z i n g l e v e l s below 1400 m were used t o compute t h i s mean. H i g h e r f r e e z i n g l e v e l s c o u l d not be c o n f i d e n t l y e s t i m a t e d , and would be u n l i k e l y t o produce snow on the mountain. The mean storm f r e e z i n g l e v e l , or l i n e o f u n i t s l o p e ( H c = HJTJT-) , s e p a r a t e d the two new s n o w l i n e s . The r e g r e s s i o n r e l a t i o n s h i p s i n d i c a t e d snow may be d e p o s i t e d at sea l e v e l w i t h the f r e e z i n g l e v e l at 90 m. A l t e r n a t i v e l y , w i t h the f r e e z i n g l e v e l at the s u r f a c e , the complete new s n o w l i n e was about 100. m h i g h e r . The e l e v a t i o n a l d i f f e r e n c e between the two new s n o w l i n e s was 184 m at sea l e v e l , but i n c r e a s e d by 30 m f o r each 1000 m i n c r e a s e i n f r e e z i n g l e v e l . Other f a c t o r s 248 E l e va t i on of m e a n s t o r m f r e e z i n g l e v e l , H F L . ( m e t e r s ). F i g . 9.3 R e l a t i o n s h i p s between new s n o w l i n e s and mean storm f r e e z i n g l e v e l Diagram i s s c a t t e r p l o t f o r two s e t s o f d a t a (a) P l o t o f complete new s n o w l i n e a g a i n s t mean storm f r e e z i n g l e v e l w i t h the r e g r e s s i o n r e l a t i o n s h i p f o r t h i s d a t a r e p r e s e n t e d by the heavy s o l i d l i n e (b) P l o t of i n c o m p l e t e new s n o w l i n e and mean storm f r e e z i n g l e v e l w i t h the r e g r e s s i o n r e l a t i o n s h i p r e p r e s e n t e d by the heavy dashed l i n e . 95% c o n f i d e n c e l i m i t s g i v e n by l i g h t dashed l i n e s 249 a f f e c t e d the complete new s n o w l i n e . I t tended t o be lower w i t h heavy s n o w f a l l s , o r i f t h e f o r e s t was open. Thus the complete new s n o w l i n e approached the f r e e z i n g l e v e l at h i g h e l e v a t i o n s . The r e g i o n between the f r e e z i n g l e v e l and lower l i m i t of s n o w f a l l i s known as the m e l t i n g l a y e r ( P i n d e i s o n 1940) and i s u s u a l l y 100-200 m deep (Wexler 1955)- The r e g i o n between th e mean storm f r e e z i n g l e v e l and the i n c o m p l e t e new s n o w l i n e i s g i v e n by t h e l a y e r (H=r - H ). T h i s l a y e r was r b O not as deep as t h e m e l t i n g l a y e r a t lower e l e v a t i o n s , b e i n g about 90 m at sea l e v e l ( F i g . 9 . 3 ) . The d i f f e r e n c e r e s u l t e d because some snow t h a t was d e p o s i t e d below t h e f r e e z i n g l e v e l m e l t e d d u r i n g the storm. Such melt was l e s s i m p o r t a n t at h i g h e r e l e v a t i o n s , where new snow o f t e n r e s t e d on the c o l d s u r f a c e o f the e x i s t i n g snowpack. Thus w i t h h i g h e r storm f r e e z i n g l e v e l s the depth o f the ( I f e ? — H ) l a y e r tended t o approach t h a t o f the m e l t i n g l a y e r (e.g. the (Hpj- _ H ) l a y e r was 170 m t h i c k at 1000 m, almost t w i c e t h a t a t s e a l e v e l ) . Because t h e m e l t i n g o f some o f the new snow depended on the e l e v a t i o n o f the e x i s t i n g snowpack, the ( f f e = — H ) l a y e r c o u l d r Li O vary from storm t o s t o r m , even at the same e l e v a t i o n . T h i s accounted f o r some o f t h e s c a t t e r about the r e g r e s s i o n r e l a t i o n -s h i p f o r the i n c o m p l e t e new s n o w l i n e . Other s c a t t e r may have r e s u l t e d from v a r i a t i o n s i n i n t e n s i t y o f storm p r e c i p i t a t i o n , w h i c h a l s o c o n t r o l s the t h i c k n e s s o f t h e m e l t i n g l a y e r ( A t l a s et a l 1 9 6 7 ) , and from f l u c t u a t i o n s o f t h e f r e e z i n g l e v e l Cr-ab out the storm mean. 250 The s c a t t e r ahout the r e g r e s s i o n l i n e r e s u l t s i n 95 p e r c e n t c o n f i d e n c e l i m i t s , computed about an e s t i m a t e o f the i n c o m p l e t e s n o w l i n e , t h a t are l a r g e (± 284 m). U n f o r t u n a t e l y , t h e f a c t o r s p r o d u c i n g the s c a t t e r , and d e s c r i b e d above, are d i f f i c u l t t o q u a n t i f y , o r • a r e not a v a i l a b l e from t h e f i e l d d a t a , so no improvement i n the p r e -d i c t i o n e q u a t i o n can be o b t a i n e d . On t h e o t h e r hand, p l o t s o f the r e s i d u a l s from t h e r e g r e s s i o n l i n e s were examined as recommended by Draper and Smith ( 1 9 6 6 ) . These p l o t s suggested the assumptions o f r e g r e s s i o n a n a l y s i s were not v i o l a t e d , so i n t h i s r e s p e c t the p r e d i c t i o n e q u a t i o n s are adequate. 9 * 3 . 2 P r e d i c t i o n o f storm f r e e z i n g l e v e l s I f the new s n o w l i n e s are t o be e s t i m a t e d w i t h the p r e d i c t o r e q u a t i o n s of the p r e v i o u s s e c t i o n , t h e n v a l u e s f o r the mean storm f r e e z i n g l e v e l must be found. I n most mountain s i t u a t i o n s a network o f s t a t i o n s r e c o r d i n g temp-e r a t u r e w i t h e l e v a t i o n i s not a v a i l a b l e t o compute the mean storm f r e e z i n g l e v e l . E i t h e r the mean must be o b t a i n e d from r a d i o s o n d e a s c e n t s , or from t e m p e r a t u r e s a t • the base o f the mountain by e x t r a p o l a t i o n a l o n g a g i v e n l a p s e r a t e . 251 To examine the f i r s t method, f r e e z i n g l e v e l s from t w i c e d a i l y r a d i o s o n d e a s c e n t s a t P o r t Hardy were r e l a t e d by s i m p l e l i n e a r r e g r e s s i o n w i t h f r e e z i n g l e v e l s on Mount Seymour e i g h t hours l a t e r . A time l a g of 48 km per hour was a l l o w e d f o r the average movement o f p r e s s u r e systems. Only t h o s e i n s t a n c e s where storms were i n p r o g r e s s and f r e e z i n g l e v e l s i n t e r s e c t e d Mount Seymour were c o n s i d e r e d i n t h e a n a l y s i s . P r e f r o n t a l and p o s t f r o n t a l s i t u a t i o n s were i d e n t i f i e d by f a l l i n g and r i s i n g p r e s s u r e tendency r e s p e c t i v e l y , at P o r t Hardy. Computer p l o t s o f Mount Seymour v e r s u s P o r t Hardy f r e e z i n g l e v e l s i n d i c a t e d wide s c a t t e r i n the d a t a , and t h a t no advantage would be g a i n e d by u s i n g o t h e r t h a n a l i n e a r model. The c o r r e l a t i o n o f t h e r e s u l t a n t e q u a t i o n s (Table 9-was not as good as t h a t s u g g e sted by an e a r l i e r more sub-j e c t i v e a n a l y s i s o f P e t e r s o n (1964). P o r t Hardy r a d i o s o n d e a s c e n t s g i v e f a i r e s t i m a t e s o f Mount Seymour f r e e z i n g l e v e l s under p o s t f r o n t a l c o n d i t i o n s when no ' A r c t i c a i r i s p r e s e n t . P o r t Hardy a s c e n t s p r o v i d e poor e s t i m a t e s under p r e f r o n t a l c o n d i t i o n s . C e r t a i n s y n o p t i c s i t u a t i o n s can l e a d t o d i v e r s e f r e e z i n g l e v e l s between the two l o c a l i t i e s (e.g. a slow moving f r o n t a l system between P o r t Hardy and Mount Seymour, A r c t i c a i r o v er Vancouver only)'. A l t e r n a t i v e l y , t h e t ime l a g o f e i g h t hours used i n the a n a l y s i s might be i n c o r r e c t . 252 TABLE 9•3 Simple l i n e a r r e g r e s s i o n e q u a t i o n s r e l a t i n g  f r e e z i n g l e v e l s on Mount Seymour '(Y)to. t hose of r a d i o s o n d e as cents' at P o r t Hardy 'QQ S i t u a t i o n P r e f r o n t a l c o n d i t i o n s A l l s torm s i t u a t i o n s Storms where no A r c t i c a i r p r e s e n t Storms where f r e e z i n g l e v e l s a t P o r t Hardy were l e s s t h a n 1300 m and' no A r c t i c a i r p r e s e n t E q u a t i o n Y= 590 + 0 .12 X Y= 637 + 0.14 X Y= .337 + 0 .52 X n 10 4 80 59 0 .05 0 .10 0 .29 S t . E r r o r of E s t i m a t e 334 254 232 P o s t f r o n t a l c o n d i t i o n s A l l s torm s i t u a t i o n s Storms where no A r c t i c a i r p r e s e n t Storms where f r e e z i n g l e v e l s at P o r t Hardy were l e s s t h a n 1300 m and no A r c t i c a i r p r e s e n t Y= 319 + 0 . 4 7 X Y= 662 + 0 . 1 8 X 107 69 0 .12 0 .16 Y= 450. + 0 .48 X 56 0 . 3 2 272 201 172 NOTES ( 1) ( i i ) ( i i i ) ( i v ) F r e e z i n g l e v e l s on Mount Seymour computed from i n t e r -p o l a t i o n among s i x temperature s t a t i o n s between 120 m and 1260 m. P o r t Hardy f r e e z i n g l e v e l s a r e p u b l i s h e d i n " B u l l e t i n o f Canadian Upper A i r Data". Only t h o s e s i t u a t i o n s w i t h f r e e z i n g l e v e l s on^Mount Seymour below 1260 m were c o n s i d e r e d . Data was f o r storms November- t o May 1969-70 and October t o May 1 9 7 0 - 7 1 . A l l c o r r e l a t i o n c o e f f i c i e n t s ( r ) s i g n i f i c a n t at the 95 p e r c e n t c o n f i d e n c e l e v e l . 253 However, the g e n e r a l low c o r r e l a t i o n suggests t h a t the at m o s p h e r i c t h e r m a l regime b e l ow 1260-m,.near Mount Seymour, i s s i g n i f i c a n t l y m o d i f i e d compared w i t h the f r e e a i r s i t u -a t i o n at P o r t Hardy. That t h i s i s s o , even f o r p o s t f r o n t a l c o n d i t i o n s , when a i r i s o f t e n moving from the v i c i n i t y o f P o r t Hardy towards Mount Seymour, i s y e t f u r t h e r e v i d e n c e t h a t r a d i o s o n d e d a t a from t h i s s t a t i o n i s not' r e p r e s e n t a t i v e o f s t o r m c o n d i t i o n s above t h e study a r e a . I t i s i n t e r e s t i n g t o note t h a t t h e s e d i f f e r e n c e s are not n e a r l y as pronounced when mean monthly f r e e z i n g l e v e l s are c o n s i d e r e d (see Ta b l e 8.7)• The p r e v i o u s d i s c u s s i o n s u g g e s t s t h a t e s t i m a t i o n of storm f r e e z i n g l e v e l s might b e t t e r be made by e x t r a -p o l a t i o n from t e m p e r a t u r e s at the base o f the mountain. A s u i t a b l e l a p s e r a t e must th e n be found. Lapse r a t e s between 120 m and 1260 m on Mount Seymour were computed d u r i n g s t o r m p e r i o d s . These are s u b j e c t t o an e r r o r of about 10 p e r c e n t because o f p o s s i b l e e r r o r s i n measurement of temperature and e l e v a t i o n . The mean l a p s e r a t e f o r p e r i o d s o f s t e a d y p r e c i p i t a t i o n ( u s u a l l y p r e f r o n t a l c o n d i t i o n s ) was 0 . 6 8 °C/100 m (st.dev-. of ± 0 . 1 8 ) , and 0 . 7 1 °C/100 m ( s t . d e v . o f ± 0 . 1 7 ) f o r showery p r e c i p i t a t i o n ( u s u a l l y p o s t -f r o n t a l c o n d i t i o n s ) . These r e s u l t s are not s t a t i s t i c a l l y d i f f e r e n t from each o t h e r , nor d i f f e r e n t from 0 . 7 °C/100 m,. which f o r 254 p r a c t i c a l purposes i s a c o n v e n i e n t number t o use. A 95 p e r -cent c o n f i d e n c e band about an e s t i m a t e l e a d s t o a range of about ±50 m, or a 100. m t h i c k , l a y e r on the mountain, w i t h i n which the f r e e z i n g l e v e l c o u l d l i e . A v a l u e of 0 . J 0 ±0..l8 °C/100 m then seems s u f f i c i e n t l y adequate t o g i v e e s t i m a t e s of the f r e e z i n g l e v e l t h a t are more r e l i a b l e t han t h o s e from r a d i o s o n d e a s c e n t s . T h i s method has the f u r t h e r advantage t h a t f r e e z i n g l e v e l s d u r i n g storms may be computed f o r any time i n t e r v a l f o r which t h e r e are t e m p e r a t u r e s a v a i l a b l e a t the base of t h e mountain. F r e e z i n g l e v e l s from r a d i o s o n d e a s c e n t s are o n l y a v a i l a b l e every 12 h o u r s . 9 . 4 P r e d i c t i o n o f the e q u i v a l e n t e l e v a t i o n The e q u i v a l e n t e l e v a t i o n (H e) i s the l o w e s t e l e v a t i o n where new snow d e p o s i t i o n e q u a l s p r e c i p i t a t i o n from the storm. H e marks the upper l i m i t of the wet snow zone, and must be e s t i m a t e d i f the shape of the new snow wedge i s t o be d e f i n e d . V a r i a t i o n s i n H e are w e l l e x p l a i n e d by v a r i a t i o n s i n mean storm f r e e z i n g l e v e l ( F i g . 9 . 4 ) and e x a m i n a t i o n s of r e s i d u a l s i n d i c a t e s the r e s u l t a n t r e g r e s s i o n e q u a t i o n i s a good model (Draper and Smith 1 9 6 6 ) . However, t h e r e i s con-s i d e r a b l e s c a t t e r about the r e g r e s s i o n l i n e , so t h a t the 95 p e r c e n t c o n f i d e n c e l i m i t s are a g a i n l a r g e (± 284 m). F l u c t u a t i o n s o f the f r e e z i n g l e v e l about the mean storm e l e v a t i o n i s the main g e n e r a t o r of t h e s c a t t e r . 255 F i g . 9.4 R e l a t i o n s h i p between the e q u i v a l e n t and mean storm f r e e z i n g l e v e l e l e v a t i o n 256 9 . 5 P r e d i c t i o n of snow, d e p o s i t i o n , with: e l e v a t i o n 9 - 5 . 1 Simple cases The new snow wedge can now be c o n s t r u c t e d f o r tho s e storms where the f r e e z i n g l e v e l i s r e l a t i v e l y c o n s t a n t , and p r e c i p i t a t i o n a t the top of the mountain i s e n t i r e l y .in the form o f snow (see F i g . 9'vl) . The n e c e s s a r y i n p u t d a t a are storm p r e c i p i t a t i o n at the base of the mountain (here P ( 1 2 0 ) ) , and tempe r a t u r e s r e c o r d e d , say two h o u r l y d u r i n g the storm, a l s o at the base o f the mountain. The v a r i a t i o n of p r e c i p i t a t i o n ( i n mm) w i t h e l e -v a t i o n can be e s t i m a t e d w i t h one of the r e l a t i o n s h i p s - f o r P(H) shown i n T a b l e 9 . 1 . F o r example t h a t f o r e q u a t i o n 3 P(H) = - 6 . 8 +.1.15 P (120) + 0.017H The p o s i t i o n o f the lower l i m i t o f snow d e p o s i t i o n H 0 i s o b t a i n e d w i t h (.in meters) H Q = - 7 9 . 8 + 0 . 9 2 H j ^ where , the mean h e i g h t of the sto r m f r e e z i n g l e v e l i s g i v e n by ( i n meters) n T(120) T T i =i l a p s e r a t e FL ~ — n With T(120) = temperature a t the base o f the mountain, i n °C. 257 V a l u e s o f 0 .0. ± T(120.X ± 9 ..8 are. the o n l y ones, used on Mount Seymour. TC-120.). g r e a t e r t h a n 9-.8°C would g i v e ' f r e e z i n g l e v e l s above 1400.m a and hence snow would be un-l i k e l y t o f a l l on the mountain. l a p s e r a t e = 0 . 7 . 10" 2 °C/m n = number of o b s e r v a t i o n s of T(.120). t a k e n d u r i n g the storm. The p o s i t i o n o f the e q u i v a l e n t e l e v a t i o n , H e i s g i v e n by ( i n meters) H e = 125 + 0 . 9 8 The v a r i a t i o n o f snow d e p o s i t i o n between H Q and H e i s assumed t o be a s t r a i g h t l i n e r e l a t i o n s h i p . There seems l i t t l e p o i n t i n p o s t u l a t i n g any o t h e r ^type of r e l a -t i o n s h i p , s i n c e the 95 p e r c e n t c o n f i d e n c e l i m i t s f o r e s t i m a t e s of H Q and H e o v e r l a p . Thus f o r the e l e v a t i o n a l range H 0 < H <T H e, the s p e c i f i c new snow mass - d e p o s i t e d i n open areas ( i n mm water e q u i v a l e n t , or kg/m 2) i s g i v e n by M' (H) 5 " HQ . P ( H P ) H e - H 0 e F o r e l e v a t i o n s above H e, t h e s p e c i f i c new snow:mas.s-d e p o s i t e d i n open areas i s g i v e n by M(H) = P(H) 258 9 - 5 - 2 . Comple-x cases. For- storms where t h e r e are l a r g e changes i n f r e e z i n g l e v e l , b e t t e r r e s u l t s w i l l be o b t a i n e d i f t h e storm i s d i v i d e d i n t o substorms. , Each substorm i s a p e r i o d d u r i n g which the f r e e z i n g l e v e l i s r e l a t i v e l y c o n s t a n t . The model of the p r e v i o u s s e c t i o n i s then a p p l i e d t o each substorm. T h i s approach re quire's t h a t at l e a s t two h o u r l y measurements of p r e c i p i t a t i o n and temperature are made at the base of the mountain. F o r storms where b o t h r a i n and snow f a l l at the top of the mountain ( H ^ ) , a s l i g h t l y d i f f e r e n t model i s p r o -posed. F i r s t i t i s n e c e s s a r y t o f i n d the p r o p o r t i o n of storm p r e c i p i t a t i o n f a l l i n g as snow at t h e top of t h e moun-t a i n ( F i g . 9 . 1 b ) , t h a t i s , t o f i n d R = p^j j • T h i s may be done w i t h the r e l a t i o n R = p'(H^j = - 0 . 0 2 •+ 1 .03 I Where I = number of hours when the f r e e z i n g l e v e l d u r i n g the storm i s below 1400 m, d i v i d e d by the l e n g t h of the storm i n h o u r s . Then the f r e e z i n g l e v e l i s found as b e f o r e TC120). Hpt- ~ l a p s e r a t e 259 The c r i t i c a l h e i g h t of 1400. in f o r the. f r e e z i n g l e v e l p e r t a i n s t o Mount Seymour, but f o r o t h e r mountains c o u l d be t a k e n as 150 m above the top of the mountain. The- p r e - • d i c t i o n e q u a t i o n f o r R i s v a l i d f o r most storms w i t h r a i n and snow at the top o f the mountain ( F i g . 9 . 5 ) . T h i s i s because f o r t h e s e storms snow f a l l s i n c o l d e r p o s t f r o n t a l a i r a f t e r p r e f r o n t a l r a i n , and hence tends to-be p r e s e r v e d . T,he good r e l a t i o n s h i p found between R and I i m p l i e s t h a t p r e c i p i t a t i o n i n t e n s i t y i s c o n s t a n t f o r each' substorm, or t h a t t h e r e are s e l f - c a n c e l l i n g v a r i a t i o n s . Once R has been e s t i m a t e d , the s p e c i f i c new snow mass d e p o s i t e d above the e l e v a t i o n H e i s g i v e n by ( F i g . 9.1 ) M(H) = R . P(H) T h i s assumes t h a t R found f o r t h e - t o p of the mountain i s t r u e f o r a l l o t h e r e l e v a t i o n s above H e. No t e s t was made of t h i s assumption . I n the e l e v a t i o n a l range H Q < H < H e the s p e c i f i c new snow mass w i l l be g i v e n by M'(H) = ^ . R . p ( H e ) Hence the new snow wedge i s c o n s t r u c t e d f o r t h e storm. However, f o r storms where snow f a l l s f i r s t , and s u b s e q u e n t l y t u r n s t o r a i n , t h i s method does not appear s u i t a b l e , presumably because much new snow m e l t s d u r i n g 260 I F i g . '9-5' R e l a t i o n s h i p between the r a t i o . R and the r a t i o I . A l l terms are. d e f i n e d i n the t e x t . Data i s f o r a l l ' s t o r m s where b o t h snow and r a i n - f e l l at the h i g h e s t s a m p l i n g s i t e (.1260 m) . Such storms t h a t were a s s o c i a t e d w i t h A r c t i c A i r are i n d i c a t e d by c r o s s e s and were not i n c l u d e d i n the r e g r e s s i o n r e l a t i o n s h i p 261 the storm (.e.g. storms w i t h warm P a c i f i c a i r a s s o c i a t e d w i t h a r c t i c a i r out breaks, F i g . 9 - 5 ) • The.se storms can be so complex, that best estimates of snow d e p o s i t i o n are probably made from the c l i m a t o l o g i c a l values f o r each storm type given i n Table 8 . 5 , t a k i n g i n t o account the estimates of p r e c i p i t a t i o n w i t h e l e v a t i o n P(H). F o r t -unately, such storms are r a r e , and are- l i k e l y to make- a very small c o n t r i b u t i o n to t o t a l winter snow d e p o s i t i o n except at low e l e v a t i o n s . 9 . 6 P r e d i c t i o n of snow d e p o s i t i o n i n the f o r e s t 9 . 6 . 1 P r e l i m i n a r y p r e d i c t i o n equations I t i s more convenient to estimate snow d e p o s i t i o n i n the f o r e s t from that i n open areas, r a t h e r than to e s t a b l i s h a set of r e l a t i o n s d e s c r i b i n g snow d e p o s i t i o n v a r i a t i o n s with e l e v a t i o n f o r each of the f o r e s t s t r a t a . Because the r e l a t i o n s h i p between sn o w f a l l i n the f o r e s t . and that i n the open v a r i e d w i t h e l e v a t i o n , an i n t e r a c t i o n term should be inc l u d e d i n any p r e d i c t i o n equation. Accord-i n g l y the f o l l o w i n g general model was t e s t e d , using stepwise r e g r e s s i o n procedures: M s = f(.Mi, H, MiH, H 2, M i 2 ) 262 where M s = s p e c i f i c new snow mass (mm water e q u i v a l e n t ) d e p o s i t e d i n a g i v e n f o r e s t s t r a t u m S, (S = 2,3...5) a t ' a n e l e v a t i o n H. Mi . = s p e c i f i c snow mass (mm water e q u i v -a l e n t ) d e p o s i t e d i n open areas at an e l e v a t i o n H. H = e l e v a t i o n (metres) The use o f the squared term ( M j 2 ) r e c o g n i s e s the r e s u l t s o f s t u d i e s by Watanabe, and O z e k i (1964) and S a t t e r l u n d and Haupt (1967), who have shown i n t e r c e p t i o n by conifero'.us crowns f o l l o w s l o g a r i t h m i c 'growth' c u r v e s , which t e n d a s y m p o t i c a l l y t o st e a d y s t a t e c o n d i t i o n s as s n o w f a l l con-t i n u e s . Snow t h r o u g h f a l l i n c r e a s e s s t e a d i l y as snow f a l l s , u n t i l the t r e e branches- become so lo a d e d t h a t they bend, s h e d d i n g a d d i t i o n a l snow, a f t e r which t h r o u g h f a l l ' becomes d i r e c t l y p r o p o r t i o n a l t o s n o w f a l l i n t h e open. S n o w f a l l i n c l e a r i n g s i s w e l l p r e d i c t e d (Table 9.4), but as s t r a t a from canopy edge th r o u g h t o t r e e t r u n k s are c o n s i d e r e d , t h e r e i s a decrease i n e x p l a n a t i o n ( R 2 ) and i n c r e a s e d s c a t t e r about t h e r e g r e s s i o n l i n e ( s t a n d a r d e r r o r of e s t i m a t e ) . T h i s suggests the v a r i a b i l i t y of p r o c e s s e s a f f e c t i n g snow d e p o s i t i o n becomes g r e a t e r from c l e a r i n g s TABLE 9.4 Regression equations between snow de p o s i t i o n i n f o r e s t s t r a t a  and i n open areas Stratum Equation n R 2 S.E. of estimate (mm) Cl e a r i n g M2 = -1.3 + l.OMi 511 0.95 6.9 Canopy-edge M3 = -3-3 + O .6M1 + 0.0002MJ.H - 0.0024M! 511 0.83 9.9 Beneath canopy MIJ = -1.3 + 0.2Mj + 0.0002MaH + 0.0013M 2 511 0.78 9.8 Tree trunk M5 = -1.7 + O.lMj + 0.0003Mi_H + 0.0015M* 511 0.75 10 .6 NOTES: ( i ) A l l equations were s i g n i f i c a n t at the 99 percent confidence l e v e l . ( i i ) Mi = s n o w f a l l i n open-areas (mm water equivalent) M s = s n o w f a l l i n f o r e s t s t r a t a (mm water equivalent) S (S = 1,2,.. .5) H = e l e v a t i o n (metres) (H = l , 2 , . . . n , where n < 12) ( i i i ) Data i s f o r winters 1969-70, 1970-71. C O 264 through t o t r e e t r u n k s . A f e a t u r e o f t h e b e s t f i t equa-t i o n s i s t h e presence o f MiH terms i n d i c a t i n g t h a t the r e l a t i o n s h i p between s n o w f a l l i n t h e open and i n t h e f o r e s t depends on e l e v a t i o n , t h a t i s , t h e r e i s an e l e v a t i o n -f o r e s t s t r a t a i n t e r a c t i o n . 9.6.2 The e l e v a t i o n - f o r e s t s t r a t a i n t e r a c t i o n . To see where the above p r e d i c t i o n r e l a t i o n s c o u l d be improved, and t o g a i n f u r t h e r i n s i g h t s i n t o t h e e l e v a t i o n -f o r e s t s t r a t a i n t e r a c t i o n , s e p a r a t e a n a l y s e s were made f o r each e l e v a t i o n u s i n g s t e p w i s e r e g r e s s i o n p r o c e d u r e s . These were o f the form, M s = f ( M l 3 Mi 2 ) The r e l a t i o n s a r e p l o t t e d f o r each e l e v a t i o n a c c o r d i n g t o f o r e s t s t r a t a ( F i g . 9.6", T a b l e 9 - 5 ) . Some o f the r e g r e s s i o n l i n e s a r e undoubtedly not s i g n i f i c a n t l y d i f f e r e n t from one a n o t h e r , but each i s p r e s e n t e d s e p a r a t e l y here because p h y s i c a l s i g n i f i c a n c e can be a t t a c h e d t o t h e changing s l o p e s o f - t h e l i n e s w i t h i n c r e a s i n g e l e v a t i o n . I t i s not i n t e n d e d the l i n e s be used as p r e d i c t o r r e l a t i o n s , but as a means t o u n d e r s t a n d i n g changes w i t h e l e v a t i o n i n the i n f l u e n c e o f the f o r e s t on snow d e p o s i t i o n . As w i t h t h e p r e v i o u s a n a l y s i s , the s c a t t e r about the r e g r e s s i o n l i n e s i n c r e a s e s , Snowfall In Open ( mm water equivalent) CTs F i g . 9-6 Best f i t r e g r e s s i o n r e l a t i o n s . f o r each e l e v a t i o n of snow d e p o s i t i o n i n f o r e s t s t r a t a as a f u n c t i o n of snow d e p o s i t i o n -i n open areas 992 TABLE 9-5 . D e t a i l s o f r e g r e s s i o n e q u a t i o n s between snow d e p o s i t i o n i n open and i n f o r e s t s t r a t a . Each e l e v a t i o n a n a l y s e d s e p a r a t e l y . FOREST STRATUM E l e v a t i o n (metres) Sample-S i z e C l e a r i n g s R 2 S.E. Canopy Edge R 2 S.E. Beneath Canopy R 2 S.E. Tree R 2 Trunk S.E. 1260 82 0 . 9 1 11 .4 0 . 7 3 14 . 5 0 . 7 3 15 .2 0 . 6 9 16 .5 1060 78 0 . 9 6 7 .1 0 . 7 7 13-5 0 . 7 3 12 .6 0 . 6 8 13 .6 970 73 0 . 9 6 5 . 2 0 . 80 11.0 0 .75 10 .2 0 .69 11.7 870 57 0 . 9 7 4 . 3 0 .88 6 . 3 0 .88 5 . 7 0.84 6 . 7 790 51 0 . 9 8 3 . 2 0 . 9 1 6 . 0 0 . 8 1 6 . 8 0 . 7 7 6 . 8 710 47 0 . 9 9 2 .2 0 . 9 4 4 .5 0 . 8 3 6 . 3 0 .80 6 . 4 590 36 0 . 9 6 3 . 7 0 . 8 9 4 . 7 0 . 8 9 - 2 .7 0 . 8 8 2 .7 490 27 0 . 9 8 3 . 0 0 . 8 8 3 .6 0 . 9 1 2 .9 0 . 8 8 2 .9 400 23 0 . 9 2 4 .6 0 . 9 0 3 . 8 0 . 9 1 3 . 1 0 . 8 8 3 . 1 NOTES: ( i ) Based on s t e p w i s e r e g r e s s i o n a n a l y s i s of e q u a t i o n M s = a..o + a i M i + a 2 M i where M = s n o w f a l l i n f o r e s t s t r a t a (mm water e q u i v a l e n t ) S (S = 1 , 2 , . . . 5 ) Mi = s n o w f a l l i n open (mm water e q u i v a l e n t ) ( i i ) A l l e q u a t i o n s were s i g n i f i c a n t at the 99 p e r c e n t c o n f i d e n c e l e v e l . ( i i i ) R 2 = c o e f f i c i e n t o f d e t e r m i n a t i o n SE = st'andard e r r o r of e s t i m a t e 268 and the e x p l a n a t i o n d e c r e a s e s , from c l e a r i n g s t h r o u g h t o c l o s e t o t r e e t r u n k s . The. same t r e n d s are also, found with, i n -c r e a s i n g e l e v a t i o n (-Table 9 . 5 ) . Thus the. v a r i a b i l i t y o f p r o c e s s e s a f f e c t i n g s n o w f a l l must be g r e a t e r with, i n c r e a s i n g e l e v a t i o n . The b e s t f i t r e g r e s s i o n r e l a t i o n s f o r c l e a r i n g s show t h a t below 790 ra, s n o w f a l l i s d e c r e a s i n g l y s m a l l e r than i n open areas ( F i g . 9 . 6 ) . Only above 870 m i s . t h e r e s u b s t a n -t i a l excess s n o w f a l l i n c l e a r i n g s . T h i s excess becomes more pronounced as s n o w f a l l i n c r e a s e s , e s p e c i a l l y a t 1260 m f o r f a l l s e x c e e d i n g 100 mm. Snow d e p o s i t i o n at the canopy edge r e l a t i v e t o t h a t i n the open a l s o d e c r e a s e s w i t h de-c r e a s i n g e l e v a t i o n . At a l l e l e v a t i o n s i t i s l e s s than t h a t i n the open. The c u r v i l i n e a r r e l a t i o n s a t , and above, 1060 m r e s u l t from wind s c o u r , which f r e q u e n t l y c r e a t e h o l l o w s a t t h e canopy edge. Wind s c o u r i s u s u a l l y a s s o c i a t e d w i t h the most a c t i v e .storms which produce the h e a v i e s t snow-f a l l s and s t r o n g e s t winds. The r e g r e s s i o n r e l a t i o n s f o r storm s n o w f a l l f o r "beneath the canopy" and " t r e e t r u n k " s t r a t a show c u r v i l i n e a r r e l a t i o n s at 870 m and below. These n o n - l i n e a r r e l a t i o n s are i n p a r t induced.by d e p o s i t i o n of non-zero amounts of snow beneath t r e e s , a t t i m e s when s n o w f a l l i n open areas i s con-s i d e r a b l y l a r g e r . T h i s t o t a l , or near t o t a l , i n t e r -c e p t i o n of snow by t r e e s i s most e f f e c t i v e i n the wet snow zone. Here, f a l l i n g snow p a r t i c l e s b e g i n 269 t o m e l t , and c o a l e s c e - a s snow.flak.es. These have a h i g h e r f a l l v e l o c i t y CNakaya 1954). and hence a h i g h e r a n g l e of i n c i d e n c e a g a i n s t the f o r e s t . F o r t h i s r e a s o n , and. because t r e e canopy c l o s u r e i s g r e a t e r , t h i s - p r o c e s s i s most obvio u s at t h e l ower e l e v a t i o n s . I n a d d i t i o n , as s n o w f a l l amounts i n c r e a s e , the t r e e f o l i a g e becomes l o a d e d , and b e g i n s t o shed snow t o the snowpack.beneath i n the manner d e s c r i b e d by S a t t e r l u n d and Haupt (1967) . I n t e r c e p t i o n i s t h e n l e s s e f f e c t i v e , and hence t h r o u g h f a l l r e l a t i v e t o s n o w f a l l i n open areas i n c r e a s e s a t a more r a p i d r a t e . S i n c e the Mount Seymour f o r e s t i s not homogeneous w i t h e l e v a t i o n ( F i g . 2.1), and because th e s e p r o c e s s e s are de-pendent on s i z e , shape and branch c h a r a c t e r i s t i c s o f t r e e s , the curves do... not behave r e g u l a r l y w i t h e l e v a t i o n as do t hose f o r c l e a r i n g s and the canopy edge. The.: c u r v i l i n e a r r e l a t i o n found f o r 1260 m i s gen-e r a t e d by the same p r o c e s s e s , but i n - a d d i t i o n , f a l l i n g snow at t h i s exposed s i t e i s o f t e n blown from open areas t o the s h e l t e r e d a r e a beneath t r e e s . T h i s i s e s p e c i a l l y marked when s m a l l amounts o f low d e n s i t y snow f a l l onto a snowpack w i t h a h a r d s u r f a c e c r u s t . 9 . 6 . 3 Improvement'of p r e d i c t i o n e q u a t i o n s The p r e v i o u s a n a l y s e s suggest t h a t the o r i g i n a l r e g r e s s i o n r e l a t i o n f o r a l l e l e v a t i o n s can be improved by 270 c o n s i d e r i n g snow d e p o s i t i o n s e p a r a t e l y i n the t h r e e zones d e f i n e d i n s e c t i o n 6 . 3 . - 3 . A c c o r d i n g l y data' was . r e a n a l y s e d f o r t he g e n e r a l model but i n the f o l l o w i n g zones: (a) d a t a at 1260 m, r e p r e s e n t a t i v e of e l e v a t i o n s from 1100 t o 1300 m (the d r i f t snow zone)-, (b) d a t a below the e q u i v a l e n t e l e v a t i o n , H e (the wet snow z o n e ) , (c) d a t a above the e q u i v a l e n t e l e v a t i o n , H e, e x c e p t i n g t h a t f o r 1260 m, (.the snow. zo n e ) . The l a t t e r two of these zones are- c o n t r o l l e d by the f r e e z i n g l e v e l and v a r y up and down the mountain from s t o r m t o storm. S i n c e m e t e o r o l o g i c a l v a r i a b l e s i n each of t h e s e subzones are l i k e l y t o be b r o a d l y s i m i l a r , some assessment may be made of the e f f e c t of changing f o r e s t c h a r a c t e r i s t i c s w i t h e l e v a t i o n . When compared w i t h the o r i g i n a l e q u a t i o n s (Table 9 . 4 ) the new e q u a t i o n s reduce t h e s t a n d a r d e r r o r o f e s t i m a t e by s m a l l amounts i n the snow zone (Table 9 - 6 ) . There i s sometimes a decrease i n the amount of v a r i a n c e e x p l a i n e d a l t h o u g h t h i s i s p r o b a b l y a f u n c t i o n of reduced sample s i z e , and reduced range of o b s e r v a t i o n s . The l a r g e s t r e d u c t i o n i n s t a n d a r d e r r o r from the o r i g i n a l e q u a t i o n s o c c u r s i n the wet snow zone, but a g a i n , 2 71 TABLE 9.6 Regression equations between snow deposition In forest strata and In  open areas. Data analysed In subzones for winters 1969-70 , 1970-71-. (A) Data at 1260 m (snow d r i f t zone) Stratum Equation n R 2 S.E. of Estimate (mm) Clearing M2 = 9.4 + O.5M1 + 0.00H7MI 2 82 0.91 11.4 Canopy Edge M3 = -2.5 + l.OMi - 0.0025MJ2 82 0 . 7 3 14.5 Beneath Canopy M„ = 6.0 + 0.2Mi + 0.004lMi 2 82 0.73 '15.2 Tree Trunk M5 = 10.6 + 0.0059Mi2 82 0.69 16.5 (B) Data above the equivalent elevation of a storm, but below 1260 m (snow zone] Stratum Equation n R 2 S.E. of Estimate (mm) Clearing M2 = -2.0 + l.OMi 188 0.95 • 6.1 Canopy Edge M3 .= -5.8 + O.lMj + 0 . 0 0 0 7 M j H - 0 . 0 0 4 2 M ! 2 188 0 . 8 0 10 .4 Beneath Canopy M„ = -1.4 + 0.0006NUH 188 0 . 7 4 9.1 Tree Trunk M5 = -2.6 + 0.0005MJH 188 O.69 10 .1 (C) Data below the equivalent elevation of a storm (wet snow zone) Stratum Equation n R 2 S.E. of Estimate (mm) Clearing M2 = = -0.0 + 0.9Mi 178 0.95 2.9 Canopy Edge M3 = = -1.1 + 0.2Mi + O.OOOHMJH 178 0.76 5.5 Beneath Canopy Mi, = -0.7 + 0.0004MiH 178 0.51 5.2. Tree Trunk Ms .= = -0.9 + 0 . 0 0 0 3 M i H 178 0.16 4.9 NOTES: ( 1) A l l equations were s i g n i f i c a n t at the 99 percent confidence l e v e l . ( i i ) Mj, ,M5,H are as for Table 9.4 272 t h e r e i s a decrease i n . e x p l a n a t i o n . T h i s zone, v a r i e s with ' e l e v a t i o n . from storm .to s t o r m , and'..is where i n t e r -c e p t i o n o f snow by t r e e s ' i s most e f f e c t i v e . S i n c e i n t e r -c e p t i o n i s , i n p a r t , a f u n c t i o n of canopy s i z e and canopy c l o s u r e , and s i n c e t h e s e v a r y c o n s i d e r a b l y w i t h e l e v a t i o n , i t was thought t h a t i n t h i s c a s e , the reduced e x p l a n a t i o n ' was a l s o a d i r e c t r e s u l t of the v a r i a t i o n s o f v e g e t a t i o n w i t h e l e v a t i o n . However, when mean ' p r o j e c t e d canopy a r e a and canopy c l o s u r e i n d e x f o r each s a m p l i n g s i t e were i n c l u d e d as independent v a r i a b l e s i n the r e g r e s s i o n equa-t i o n s t h e r e was no i n c r e a s e i n e x p l a n a t i o n . E i t h e r o t h e r , unknown, f o r e s t v a r i a b l e s are i m p o r t a n t , or o t h e r unmeasured m e t e o r o l o g i c a l v a r i a b l e s s h o u l d be c o n s i d e r e d . To i n v e s t i g a t e the c o r r e c t n e s s o f t h e s e models, r e s i d u a l s from th e r e g r e s s i o n l i n e s were examined (Draper and Smith 1 9 6 6 ) . R e s i d u a l s from th e o p e n - c l e a r i n g e q u a t i o n s show l i t t l e s c a t t e r and are always homogeneous and randomly-d i s t r i b u t e d , i n d i c a t i n g the models t o be good. F o r a l l o t h e r o p e n - f o r e s t s t r a t a r e l a t i o n s h i p s , r e s i d u a l s show g r e a t e r v a r i a n c e , but are g e n e r a l l y homogeneous, except f o r storms 'with snow amounts g r e a t e r t h a n 60 mm water e q u i v a l e n t . I n t h e s e c a s e s , s c a t t e r about the r e g r e s s i o n l i n e s i n c r e a s e s w i t h s i z e of s n o w f a l l , so the models are not as r e l i a b l e . The 95 p e r c e n t c o n f i d e n c e l i m i t s about an e s t i m a t e o f new snow d e p o s i t i o n i n the f o r e s t are about 273 ±30. mm i n the snow, d r i f t zone . Those l i m i t s - are l a r g e , because the amount and l o c a t i o n o f d r i f t i n g v a r i e s . - f r o m s t o r m t o s t o r m depending on m e t e o r o l o g i c a l c o n d i t i o n s , and on the p r e v i o u s c o n f i g u r a t i o n of the snow s u r f a c e . The 95 p e r c e n t c o n f i d e n c e l i m i t s i n the o t h e r two zones are-more a c c e p t a b l e b e i n g about ±15 mm i n the snow zone and. about ±10 mm i n the wet snow zone. On the whole, b e t t e r r e s u l t s w i l l come from the use o f the more awkward e q u a t i o n s i n T a b l e 9 . 6 , t h a n from th e s i m p l e r s e t i n T a b l e 9 . 4 . Use o f the s i m p l e r s e t o f p r e d i c t o r e q u a t i o n s , i n e f f e c t , argues t h a t the changing n a t u r e of the f o r e s t w i t h e l e v a t i o n d etermines the r e l a t i o n -s h i p between snow d e p o s i t i o n i n f o r e s t s t r a t a and t h a t i n the open, r e g a r d l e s s o f the n a t u r e of t h e s torm. On the o t h e r hand, the more complex s e t of p r e d i c t o r e q u a t i o n s i n T a ble 9 . 6 argues t h a t m e t e o r o l o g i c a l c o n d i t i o n s are most i m p o r t a n t , but s t i l l a l l o w s f o r the changing n a t u r e of the f o r e s t up the mountain by i n c l u d i n g ^ the e l e v a t i o n a l t e rm, H, i n some e q u a t i o n s . 9•7 Adequacy of the model The adequacy of an e m p i r i c a l model can be ex:amined i n a number- of d i f f e r e n t ways. F i r s t , c o n f i d e n c e l i m i t s can be e s t a b l i s h e d about an e s t i m a t e produced by the model. 274 Second, the model can be t e s t e d a g a i n s t a s e t of i n d e p e n -dent d a t a , and t h i r d , assessment can be made i n terms of how w e l l t h e model r e p r e s e n t s p h y s i c a l p r o c e s s e s b e l i e v e d t o be o p e r a t i n g . 9 . 7 - 1 C o n f i d e n c e l i m i t s - a b o u t an e s t i m a t e o f the new  snow wedge f o r a storm The model t o p r e d i c t snow d e p o s i t i o n i s c o n s t r u c t e d from a. s e r i e s o f e m p i r i c a l r e l a t i o n s h i p s , each.of w h i c h has been a s s i g n e d 95 p e r c e n t c o n f i d e n c e l i m i t s . Thus the dependent v a r i a b l e of one r e l a t i o n s h i p sometimes becomes the independent- v a r i a b l e of t h e n e x t . F o r example, an e s t i m a t e o f Hp^- i s used t o e s t i m a t e H Q and H e . Here, new c o n f i d e n c e l i m i t s can be computed by p o o l i n g the r e s p e c t i v e e r r o r s . T h i s l e a d s t o 95 p e r c e n t c o n f i d e n c e l i m i t s of ±290 m about e s t i m a t e s of H Q and H e. U n f o r t -u n a t e l y , the s i t u a t i o n becomes more complex f o r e s t i m a t e s of snow d e p o s i t i o n i n the wet snow zone between H Q and H e, where t h e r e are i n t e r s e c t i n g c o n f i d e n c e l i m i t s ( F i g . 9--7)-C a l c u l a t i o n of 95 p e r c e n t c o n f i d e n c e l i m i t s i s a d i f f i c u l t s t a t i s t i c a l problem i n t h i s zone. However, some i d e a of the p r e c i s i o n of an e s t i m a t e of the new snow wedge f o r a sto r m may be o b t a i n e d f o r the above case i f the w i d e s t . p o s s i b l e range between 95 p e r c e n t c o n f i d e n c e l i m i t s i s taken- ( F i g . 9 - 7 ) . T h i s range 275 100 8 0 9 5 % C L . about Ho SO E £ ~ 40 c o HO 9 5 % C L . about He He. a. 2 0 es t possible range 95 % confidence 100 300 5 0 0 7 0 0 E l e v a t i o n ( m e t e r s ) 9 0 0 1100 1300 F i g . 9 . 7 An example of confidence l i m i t s ; a b o u t an estimate of the new. snow wedge for. a storm. Freezing l e v e l = 600 m , , p r e c i p i t a t i o n at base of mountain (120 m) = 2 8. mm 276 r e p r e s e n t s the d i f f e r e n c e between "worst: case" s i t u a t i o n s where p o p u l a t i o n parameters are always l o c a t e d at the o u t e r f r i n g e o f t h e c a l c u l a t e d c o n f i d e n c e l i m i t s , i n such a way t h a t t h e r e are no compensating v a r i a t i o n s i n the p a r a -meters . I n r e a l i t y , t h i s i s u n l i k e l y t o o c c u r . F o r example, e s t i m a t e s o f H 0 and H e w i l l t e n d t o v a r y i n the same d i r e c t i o n , . s i n c e b o t h are dependent on t h e f r e e z i n g l e v e l . N e xt, e s t i m a t e s o f the w i d e s t p o s s i b l e range and of the p r e d i c t e d snow wedge can be t r a n s l a t e d i n t o snow d e p o s i t i o n averaged over the t e r r a i n - s e g m e n t , by r e l a t i n g the e s t i m a t e d v a l u e s a t each e l e v a t i o n t o the h y p s o m e t r i c c u r v e . The v a l u e s of the w i d e s t p o s s i b l e range averaged over the t e r r a i n segment can t h e n be e x p r e s s e d as a per--centage of the p r e d i c t e d v a l u e , a l s o averaged over the t e r r a i n segment. T h i s g i v e s an a p p r o x i m a t i o n of the p r o b a b l e v a r i a t i o n o f the p o p u l a t i o n mean about the e s t i m -a t e d mean snow d e p o s i t i o n over the t e r r a i n segment. The p e r c e n t a g e , c a l c u l a t e d as d e s c r i b e d above, v a r i e s depending on storm p r e c i p i t a t i o n and on the storm f r e e z i n g l e v e l ( T a ble 9.7). The p e r c e n t a g e i s l a r g e , e s p e c i a l l y f o r s m a l l e r p r e c i p i t a t i o n amounts and h i g h e r f r e e z i n g l e v e l s . On t h i s e v i d e n c e , i t would appear t h a t the p o p u l a t i o n mean snow d e p o s i t i o n over t h e t e r r a i n segment w i l l not be e s t i m a t e d w i t h h i g h p r e c i s i o n . However, TABLE 9.7 Nature o f c o n f i d e n c e l i m i t s about an  e s t i m a t e - O f the snow d e p o s i t i o n from a storm averaged o v e r t h e t e r r a i n segment V a l u e s are c a l c u l a t e d f o r v a r i o u s storm f r e e z i n g l e v e l s and p r e c i p i t a t i o n , . Storm p r e c i p i t a t i o n at base o f mountain (mm) Storm F r e e z i n g L e v e l (m) 200. . 500. . 80 0. , 1100. . 15 E M WPR# 11.8 \27% 8.2 228$ 4.7 217$ 0.9 553% 50 E M . WPR# 39 .1 87$ 29 .0 127% 10.7 177* 2 .2 437$ BD S M WPR$ 75.0 77% 52.7 12 4J6 20 .9 156% 4.0 . 431$ E M = storm snow d e p o s i t i o n averaged over the t o t a l a r e a of the t e r r a i n segment -C i n mm water e q u i v a l e n t ) WPR$ = w i d e s t p o s s i b l e range of the 95 p e r c e n t c o n f i d e n c e l i m i t s (see F i g . 9-7) _ e x p r e s s e d as a perc e n t a g e of M. 278 the p r o b a b i l i t y a s s o c i a t e d w i t h t h i s i n t e r v a l i s l i k e l y t o be much h i g h e r - t h a n 95 percent,, and when compensating e r r o r s o c c u r , the e s t i m a t e s w i l l he c o n s i d e r a b l y c l o s e r t o the t r u e v a l u e s . Hence i t may be e x p e c t e d e s t i m a t e s w i l l always be as good as tho s e i n Table 9 . 7 , . a n d p r o b a b l y much b e t t e r . Improvements i n p r e c i s i o n o f t h e whole model c o u l d be o b t a i n e d i f more p r e c i s e e s t i m a t e s are.made o f H Q and H e. T h i s would have the e f f e c t of r e d u c i n g the w i d e s t p o s s i b l e range i n the wet snow zone. S i n c e much of the s c a t t e r about e s t i m a t e s o f H 0 or H e i s produced by v a r i a -t i o n s i n f r e e z i n g l e v e l d u r i n g the s t o r m , t h i s c o u l d be a c h i e -ved i f e s t i m a t e s were made w i t h substorm f r e e z i n g l e v e l s , r a t h e r t h a n w i t h the coa r s e parameter o f mean storm f r e e z i n g l e v e l . The d a t a o f t h i s study were not amenable f o r t e s t i n g i n t h i s way, because no o b s e r v a t i o n s o f H Q were made d u r i n g t h e storm. 9 . 7 . 2 A t e s t o f the model a g a i n s t independent st o r m d a t a The r e a l t e s t o f any model i s i n i t s a b i l i t y t o p r e -d i c t . A c c o r d i n g l y , e s t i m a t e s o f snow d e p o s i t i o n a f t e r a storm were compared w i t h an independent s e t o f d a t a from the 1968-69 w i n t e r . These t e s t d a t a were c o l l e c t e d f o r a n o t h e r s t u d y , and do not a-lways conform w i t h the 279 e x p e r i m e n t a l d e s i g n d e s c r i b e d i n C h a p t e r 3. D u r i n g the 1968-196.9 w i n t e r o c c a s i o n a l measurements, of new snow depth and d e n s i t y were made i n the c a r p a r k at 106.0 m. I n a d d i t i o n , numerous sno w p i t s were dug a t v a r i o u s e l e v a t i o n s d u r i n g t h i s w i n t e r . I n f o r m a t i o n on t h e ' w a t e r e q u i v a l e n t o f new snow l a y e r s was e x t r a c t e d from f i e l d n o tes o f the s e p i t s . F o r t h e - t e s t r u n s , e s t i m a t e s had t o be made f o r i n p u t parameters t o the model, s i n c e they were not measured at the base of the mountain d u r i n g the 1968-69 w i n t e r . P r e c i p i t a t i o n at the base of the mountain was assumed t o be 2.13 t i m e s t h a t at Vancouver I n t e r n a t i o n a l A i r p o r t , a r e l a t i o n s h i p e s t a b l i s h e d from d a t a f o r the two f o l l o w i n g w i n t e r s . Storms c o u l d not always be r i g o r o u s l y d e f i n e d from such d a t a , and may have r e p r e s e n t e d s e v e r a l s y n o p t i c e v e n t s . F r e e z i n g l e v e l s were e s t i m a t e d from h o u r l y temperature d a t a at Vancouver I n t e r n a t i o n a l A i r p o r t by assuming a l a p s e r a t e o f 0 .7°C/100 m. I n t h i s way, mean "storm" f r e e z i n g l e v e l s were o b t a i n e d . I n a l l , 23 o b s e r v a t i o n s o f snow d e p o s i t i o n at f i v e d i f f e r e n t e l e v a t i o n s from 330 m t o 1260 m were a v a i l a b l e t o t e s t the model. T h i s r e p r e s e n t e d d a t a from 13 "storms" where the mean istorm f r e e z i n g l e v e l v a r i e d from 0 m t o 1030 m. T h e r e . i s good agreement between the p r e d i c t e d v a l u e s o f snow d e p o s i t i o n , u s i n g the model, and t h i s t e s t 2 80 120 100 120 Measured Snow deposition ( mm water equiv. ) F i g . 9.8 T e s t of the model about an independent d a t a , s e t f o r Measurements were made on the the w i n t e r 1 9 6 8 - 6 9 . f o l l o w i n g d a t e s : 26 December 1968 30 December 1968 .6 January 1969 9 January 1969 1 6'January . I969 19 January 1969 26 January 1969 3 F e b r u a r y 1969 7 F e b r u a r y 1969 15 F e b r u a r y 1969 2 March 1969 5 March 1969 22 March 1969 281 d a t a ( F i g . 9 . 8 ) . Thus on t h i s .evidence, the model appears t o be. s a t i s f a c t o r y - 3 a l t h o u g h i t s h o u l d be. s t r e s s e d t h a t the t e s t d a t a i n c l u d e d o n l y t h r e e o b s e r v a t i o n s from the wet snow zone. F u r t h e r , t h e r e were i n s u f f i c i e n t t e s t d a t a t o examine the model over the whole e l e v a t i o n range of' the new snow wedge f o r a s p e c i f i c s torm. 9 -7?3 C o n f i d e n c e l i m i t s about an e s t i m a t e of t o t a l w i n t e r  snow d e p o s i t i o n I f the model i s used t o p r e d i c t snow d e p o s i t i o n f o r each storm d u r i n g the 1 9 6 9 - 7 0 , 1970-71 w i n t e r s , t h e n 95 p e r c e n t c o n f i d e n c e l i m i t s about the t o t a l p r e d i c t e d w i n t e r snow d e p o s i t i o n can be computed from n M ± t„ -where n = t o t a l number of storms f o r the w i n t e r M = mean p r e d i c t e d snow d e p o s i t i o n f o r w i n t e r storms at each e l e v a t i o n t = s t u d e n t ' s " t " d i s t r i b u t i o n w i t h a = 0 . 0 5 s = an e s t i m a t e o f the s t a n d a r d d e v i a t i o n o f the p r e d i c t e d snow d e p o s i t i o n f o r w i n t e r storms a t each e l e v a t i o n . 282 F i g . 9 . 9 C o n f i d e n c e l i m i t s • a b o u t an" e s t i m a t e o f t o t a l w i n t e r snow d e p o s i t i o n , 19-69-70,. 1 9 7 0 - 7 1 . The a c t u a l measured d e p o s i t i o n i s shown f o r comparison 283 The v a l u e s of n M (.the p r e d i c t e d t o t a l w i n t e r snow de-p o s i t i o n ) t h e 95 p e r c e n t c o n f i d e n c e l i m i t s about t h i s p r e d i c t i o n , and the a c t u a l measured o b s e r v a t i o n s are shown i n F i g . 9 - 9 - The c o n f i d e n c e l i m i t s • e n c l o s e d the measured v a l u e s at a l l e l e v a t i o n s , v a r y i n g from ±23 p e r c e n t t o ±45 p e r c e n t o f the t o t a l p r e d i c t e d w i n t e r snow d e p o s i t i o n . S i m i l a r c o n f i d e n c e l i m i t s f o r the whole t e r r a i n segment are ±15 p e r c e n t ( f o r the 1969-70 w i n t e r ) and ±26 p e r c e n t ( f o r the 1970-71 season) of the p r e d i c t e d t o t a l w i n t e r snow d e p o s i t i o n . ' These l i m i t s are r e a s o n a b l e f o r many h y d r o l o g i c a l p u r p o s e s , e s p e c i a l l y c o n s i d e r i n g the n o t o r i o u s d i f f i c u l t y o f a c h i e v i n g e s t i m a t e s by o t h e r methods i n such t e r r a i n . I n the c a l c u l a t i o n o f t h e s e c o n f i d e n c e l i m i t s , t he model i s used t o p r e d i c t snow d e p o s i t i o n • f o r those w i n t e r s from which the model was c o n s t r u c t e d . N o r m a l l y t h i s p r o c e d u r e i s o f l i t t l e v a l u e , except i n t h i s case the w i n t e r s r e p r e s e n t e d a wide range o f l i k e l y c o n d i t i o n s , and hence i n d i c a t e the g e n e r a l magnitude o f t h e c o n f i d e n c e l i m i t s f o r o t h e r w i n t e r s . 9 . 8 C o n c l u s i o n I t i s p o s s i b l e t o c o n s t r u c t a workable model t o e s t i m a t e snow d e p o s i t i o n a f t e r a sto r m based on sto r m p r e c i p i t a t i o n and two h o u r l y t e m p e r a t u r e s r e c o r d e d a t t h e 284 base o f a west c o a s t m i d l a t i t u d e m ountain. There i s good agreement between p r e d i c t i o n s from t h i s model and an independent d a t a s e t from the 1 9 6 8 - 1 9 6 9•season. P r e d i c -t i o n s from the model are l e a s t s a t i s f a c t o r y i n the wet snow zone, and when t h e r e are l a r g e f l u c t u a t i o n s i n f r e e z i n g l e v e l d u r i n g the s t o r m , e s p e c i a l l y i f t h e r e i s A r c t i c a i r p r e s e n t . I t i s d i f f i c u l t t o e s t i m a t e the p r e c i s i o n of the model, s i n c e d e f i n i t i o n of the c o n f i d e n c e l i m i t s i s complex. However, 95 p e r c e n t c o n f i d e n c e l i m i t s about p r e d i c t i o n s f o r the t o t a l w i n t e r i n p u t o f snow would appear t o be s m a l l . Good e s t i m a t e s of snow d e p o s i t i o n i n the f o r e s t from t h a t i n the open are p o s s i b l e i n the snow and wet snow zones. Because o f d r i f t i n g snow, l e s s s a t i s f a c t o r y e s t i m -a t e s can be made i n the d r i f t snow zone. The changing a f f e c t o f the f o r e s t on snow d e p o s i t i o n i s documented w i t h e l e v a t i o n i n t h i s c h a p t e r . T h i s e l e v a t i o n - f o r e s t i n t e r -a c t i o n i s produced because t r e e s change- i n s p e c i e s and form, and hence i n t e r c e p t i o n c h a r a c t e r i s t i c s , w i t h e l e v a -t i o n , and because the p r o p e r t i e s o f f a l l i n g snow, e s p e c i a l l y t emperature and wind v e l o c i t y , a l s o change w i t h e l e v a t i o n . T h i s i n t e r a c t i o n i s seldom mentioned i n the l i t e r a t u r e . The e q u a t i o n s o f t h i s study are l i k e l y t o be more r e l i a b l e i n e s t i m a t i n g t h r o u g h f a l l i n mountain f o r e s t s , t h a n t h o s e o f Woo (1972) where no i n t e r a c t i o n i s r e c o g n i s e d . 285 On Mount Seymour t h e r e seems t o be a maximum o r o -g r a p h i c component o f p r e c i p i t a t i o n o f IP(.120.). + 6 0 j mm. P r e d i c t i o n o f p r e c i p i t a t i o n v a r i a t i o n s w i t h e l e v a t i o n i s -p o s s i b l e w i t h a l i n e a r r e g r e s s i o n model. The 95 p e r c e n t c o n f i d e n c e l i m i t s about an e s t i m a t e are ±24 mm. A v a r i e t y o f attempts were made t o i n c r e a s e t h i s p r e c i s i o n , but w i t h l i t t l e s u c c e s s . P a r a m e t e r s " I m p o r t a n t i n the t h e o r y o f o r o g r a p h i c p r e c i p i t a t i o n were c a l c u l a t e d from P o r t Hardy r a d i o s o n d e d a t a , but d i d l i t t l e t o h e l p e x p l a i n Mount Se-ymour p r e c i p i t a t i o n . However, t h e r e i s o f t e n an improve-ment i n p r e c i s i o n i f s e p a r a t e e q u a t i o n s are used f o r stor m types d etermined from s u r f a c e s y n o p t i c c h a r t s . The lower l i m i t s o f s n o w f a l l and the e q u i v a l e n t e l e v a t i o n can be p r e d i c t e d i n s i m p l e l i n e a r f a s h i o n w i t h the mean stor m f r e e z i n g l e v e l . The 95 p e r c e n t c o n f i d e n c e l i m i t s are ±284 m, which are not ve r y p r e c i s e , but the r e l a t i o n s h i p s are b e l i e v e d t o be sound. I n those complex storms where b o t h r a i n and snow f e l l at the top o f the mountain, the p r o p o r t i o n of storm p r e c i p i t a t i o n f a l l i n g as snow can be w e l l p r e d i c t e d by the p r o p o r t i o n o f the time the storm f r e e z i n g l e v e l i s below 1400 m. 286 CHAPTER 10 10 . • DISCUSSION 10 .1 Main achievements o f t h i s study Measurements of the wedge o f snow a c c u m u l a t i o n on west c o a s t m i d l a t i t u d e mountains have been made e l s e -where . T h i s study extends t h i s knowledge by e x p l a i n i n g the shape and b e h a v i o u r o f the snow wedge i n terms of the i n p u t o f snow t o the h y d r o l o g i c c y c l e . The snow de-p o s i t i o n measurements made w i t h i n a c a r e f u l l e x p e r i m e n t a l d e s i g n , have a l l o w e d d e t a i l e d d e f i n i t i o n .of t h i s i n p u t over a mesoscale a r e a , f o r two complete w i n t e r s r e p r e s e n t i n g a wide range o f p r o b a b l e c o n d i t i o n s on Mount Seymour. A c l i m a t o l o g y of snow storms i s e s t a b l i s h e d . T h i s p r o v e d an i m p o r t a n t ' a s p e c t o f t h i s s t u d y , because storm t y p e , magnitude and f r e q u e n c y p l a y a major r o l e i n d e t e r m i n i n g the s p a t i a l d i s t r i b u t i o n o f snow a c c u m u l a t i o n w i t h e l e -v a t i o n and w i t h i n the f o r e s t . Of c o u r s e , snow melt i s a l s o i m p o r t a n t , but not examined .here. A d e t e r m i n i s t i c model, w i t h p a r t i a l system s y n t h e s i s , i s e s t a b l i s h e d w i t h a s e t o f r e g r e s s i o n f u n c t i o n s . When combined, t h e s e f u n c t i o n s can e s t i m a t e the s t o r m snow d e p o s i t i o n w i t h e l e v a t i o n and w i t h i n the f o r e s t , u s i n g d a t a measured at the base o f the mountain-. 287 10.2 Improvements' i n p r e c i s i o n o f t h e model The e x a c t c o n f i d e n c e l i m i t s about an e s t i m a t e of storm snow d e p o s i t i o n u s i n g the model are d i f f i c u l t t o d e t e r m i n e , but do not appear t o be s m a l l . Much c o u l d be done t o i n c r e a s e t h i s p r e c i s i o n i f the component p a r t s o f t h e model were t o i n c o r p o r a t e more o f t h e a c t u a l p h y s i c a l p r o c e s s e s b e l i e v e d t o be o p e r a t i n g . F o r example, the l a r g e c o n f i d e n c e l i m i t s about e s t i m a t e s o f the incom-p l e t e new.snowline and the e q u i v a l e n t e l e v a t i o n are d i r e c t l y produced by the e q u a l l y l a r g e f l u c t u a t i o n s o f f r e e z i n g l e v e l d u r i n g some storms. The parameter, mean storm f r e e z i n g l e v e l , i s t h e n too g r o s s . A b e t t e r approach would be t o d i v i d e the storm i n t o substorms o f , s a y , two hours d u r a t i o n , and compute the snow d e p o s i t i o n from each substorm u s i n g the same method o f t h i s s t u d y . The new snow wedges f o r each substorm c o u l d be summed t o o b t a i n a composite f o r t h e storm. A check o f t h e v a l i d i t y o f the e q u a t i o n s of- t h i s s tudy over such s h o r t time i n t e r v a l s , would r e q u i r e measurements of the i n c o m p l e t e new s n o w l i n e , the e q u i v a l e n t e l e v a t i o n , and the new snow mass d e p o s i t e d f o r each two h o u r l y i n t e r v a l , or substorm, a f o r m i d a b l e t a s k . U n e x p e c t e d l y , the r a d i o s o n d e d a t a from P o r t Hardy was o f l i t t l e use i n e s t i m a t i n g storm f r e e z i n g l e v e l or o r o g r a p h i c p r e c i p i t a t i o n on Mount Seymour. The monthly 288 f l u x e s o f a t m o s p h e r i c water vapour suggest t h a t d a t a from another r a d i o s o n d e s t a t i o n , Q u i l l a y u t e , U.S.A., .may have been more a p p r o p r i a t e . However, the a i r above t h i s s t a t i o n must s t i l l c r o s s mountains and water b o d i e s b e f o r e r e a c h i n g Mount Seymour. Recent work a l s o i n d i c a t e s a i r may be a l t e r e d by c r o s s i n g a c i t y l i k e Vancouver (Semonin and Changnon 1 9 7 4 ) . I t i s thought l i t t l e would be g a i n e d by u s i n g Q u i l l a y u t e • r a d i o s o n d e d a t a . R e c a l l t h a t d a i l y f r e e z i n g l e v e l s on Mount Seymour showed l i t t l e c o r r e l a t i o n w i t h t h o s e above P o r t Hardy, even when the wind was from t h a t d i r e c t i o n . However, the p r e c i s i o n of e s t i m a t i n g o r o g r a p h i c p r e c i p i t a t i o n may be improved w i t h b a l l o o n a s c e n t s and r a d a r soundings o f c l o u d s c l o s e r t o o r above the study mountain. E s t i m a t i o n o f snow i n the f o r e s t has been l a r g e l y e m p i r i c a l i n t h i s s t u d y . Improved p r e c i s i o n was p o s s i b l e when s e p a r a t e e q u a t i o n s were deve l o p e d f o r each zone o f t h e new snow wedge. There i s s c o p e . f o r f u r t h e r study o f snow on t r e e s , p a r t i c u l a r l y o f the p h y s i c a l p r o c e s s e s o f snow i n t e r c e p t i o n . T h i s study i n d i c a t e s t h a t t h e s e p r o c e s s e s v a r y w i t h b o t h e l e v a t i o n and storm c h a r a c t e r i s t i c s . 1 0 . 3 E x t r a p o l a t i o n o f the model t o o t h e r areas. I n i t i a l l y , i t was i n t e n d e d t o produce a model, t h a t i n c o r p o r a t e d as many p h y s i c a l p r o c e s s e s as p o s s i b l e , so as 289 t o a l l o w e x t r a p o l a t i o n • t o o t h e r a r e a s . It. t r a n s p i r e d t h a t the l i m i t a t i o n s o f the i n p u t d a t a , p l u s l a c k o f knowledge of some p r o c e s s e s o f snow d e p o s i t i o n (.e.g. m i c r o p h y s i c a l processes»in the .clouds above the m o u n t a i n ) , meant a l a r g e degree o f e m p i r i c i s m had t o be i n t r o d u c e d . T h i s r e n d e r s the model l e s s - p o f t a b l e , s i n c e many o f the c o e f f i c i e n t s i n the e s t a b l i s h e d r e g r e s s i o n r e l a t i o n s h i p s w i l l a l t e r from mountain t o mountain.. I n p a r t i c u l a r , s e p a r a t e f u n c t i o n s f o r P(H) must be e s t a b l i s h e d f o r each mountain ( a l t h o u g h the e q u a t i o n s d e v e l o p e d i n t h i s study c o u l d p r o b a b l y be s a f e l y a p p l i e d t o o t h e r N o r t h Shore. M o u n t a i n s ) . On•the o t h e r hand, the f u n c t i o n s f o r e s t i m -a t i n g H 0 and H e from s t o r m f r e e z i n g l e v e l s a r e - b e l i e v e d t o be more f u n d a m e n t a l , and hence g e n e r a l , so c o u l d be used on o t h e r mountains. The r e l a t i o n s h i p between R and I may w e l l a p p l y e l s e w h e r e , but s h o u l d be t e s t e d f i r s t . O b v i o u s l y , the model p r e s e n t e d here i s not com-p l e t e l y g e n e r a l . However, at each stage the model attempts t o r e p r e s e n t the p h y s i c a l p r o c e s s e s o c c u r r i n g . The same b a s i c p r i n c i p l e s s h o u l d a p p l y t o o t h e r west c o a s t m i d l a t i t u d e m ountains, and hence the r e g r e s s i o n r e l a t i o n s o f the model c o u l d q u i c k l y be e s t a b l i s h e d f o r each. 290 1 0 . 4 E x t e n s i o n s o f t h i s s tudy I t s h o u l d be p o s s i b l e t o e s t a b l i s h the e x a c t con-f i d e n c e l i m i t s about e s t i m a t e s o f sto r m snow d e p o s i t i o n i f a s i n g l e f u n c t i o n i s used t o d e f i n e the new snow wedge. Fo r example, a form o f the W e i b u l l f u n c t i o n c o u l d be t r i e d : M(H) = (1 - e x p [ - ( c H ) d ] ) (a + bH) where M(H) = v a r i a t i o n o f snow d e p o s i t i o n w i t h e l e v a t i o n , H c, d = c o n s t a n t s , r e l a t e d t o f r e e z i n g l e v e l and i t s f l u c t u a t i o n s a = c o n s t a n t , r e l a t e d t o p r e c i p i t a t i o n at the base o f t h e mountain b = c o n s t a n t , r e l a t e d t o t h e o r o g r a p h i c component o f p r e c i p i t a t i o n T h i s model would a l s o be more e f f i c i e n t t o use, t h a n the s e v e r a l i n t e r s e c t i n g f u n c t i o n s o f t h e study model. More d e t a i l e d s t u d i e s w i t h i n i n d i v i d u a l storms would h e l p improve such models. The model o f t h i s study s h o u l d a l s o be t e s t e d on o t h e r west c o a s t m i d l a t i t u d e mountains. An obvious e x t e n s i o n i s t o i n c o r p o r a t e snow 291 m e l t f u n c t i o n s t o the. model to. o b t a i n estimates, of snow a c c u m u l a t i o n . Yet a g a i n the model c o u l d be a p p l i e d t o a s m a l l mountain catchment w i t h measured stream f l o w , and a water b a l a n c e performed. T h i s s t u d y , has i l l u s t r a t e d t h a t f o r management purposes the i m p o r t a n t zone of the west coast m i d l a t i t u d e mountain i s i n the i n t e r m e d i a t e e l e v a t i o n s . The upper p a r t of the mountain r e c e i v e s the most snow, but has l i t t l e a r e a . The l o w e r , g r e a t e r a r e a p a r t o f the mountain r e c e i v e s snow i n f r e q u e n t l y . Thus much of the s e a s o n a l snow i s l o c a t e d i n the i n t e r m e d i a t e r a n g e , so r e s e a r c h s h o u l d be c o n c e n t r a t e d h e r e . 292 REFERENCES Ager, B., 1967. 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Experiment on the snow crown of the Japanese cedar. Japanese Government F o r e s t  Experiment . S t a t i o n B u l l e t i n I69 121-140. 9 303 West, A . J . , 196.1. Cold, a i r d r a i n a g e - i n f o r e s t o p e n i n g s . U n i t e d State's: F o r e s t S e r v i c e R e s e a r c h Note PSW-I80 . Wexler, R., 1955. The ..melting l a y e r . Mete or l o g i c a l Radar St'udies No.3, H a r v a r d U n i v e r s i t y , (Blue H i l l O b s e r v a t o r y ) . W i l l i a m s , P. and Peck, E.L., 1 9 6 2 . T e r r a i n i n f l u e n c e s on p r e c i p i t a t i o n i n t h e i n t e r m o u n t a i n west as r e l a t e d t o s y n o p t i c s i t u a t i o n s . J o u r n a l o f A p p l i e d  M e t e o r o l o g y 1 3 4 3 - 3 4 7 -W i l s o n , W.T., 1954. D i s c u s s i o n on paper " P r e c i p i t a t i o n at Barrow A l a s k a , g r e a t e r t h a n r e c o r d e d " , by R.F. B l a c k . T r a n s a c t i o n s American G e o p h y s i c a l Union 35(2) 2 0 3 - 7 . Woo, M-K, 1972 . N u m e r i c a l s i m u l a t i o n of snow h y d r o l o g y f o r management pur p o s e s . Ph.D. t h e s i s , U n i v e r s i t y of. B r i t i s h Columbia, Department of Geography. Work, R.A., S t o c k w e l l , H.J., Freeman, T.G. and Beaumont, R.T., 1964. Accuracy of f i e l d snow s u r v e y s i n w e s t e r n U n i t e d S t a t e s i n c l u d i n g A l a s k a . U n i t e d S t a t e s  Department of A g r i c u l t u r e , S o i l C o n s e r v a t i o n S e r v i c e , P o r t l a n d , Oregan. World M e t e o r o l o g i c a l O r g a n i s a t i o n , 1961 . Guide t o metero-l o g i c a l i n s t r u m e n t s and o b s e r v i n g p r a c t i c e s . W r i g h t , J.B., 1 9 6 6 a . Long term t r e n d s i n Vancouver's weather. Canada Department of T r a n s p o r t , M e t e o r o l o g i c a l B r a n c h , CIR - 4 3 7 5 , TEC - 5 9 6 . W r i g h t , J.B., 1966b. P r e c i p i t a t i o n p a t t e r n s o ver Van-couver c i t y and the Lower F r a s e r V a l l e y . Canada  Department o f T r a n s p o r t , M e t e o r o l o g i c a l B r a n c h , CIR - 4 4 7 4 , TEC - 6 2 3 . W r i g h t , J.B. and Trenholm, C.H., 1 9 6 9 . G r e a t e r Vancouver p r e c i p i t a t i o n . Canada Department -of T r a n s p o r t , M e t e o r o l o g i c a l B r a n c h , TEC - 7 2 2 . Y o u n k i n , R . J . , 1 9 6 8 . C i r c u l a t i o n p a t t e r n s a s s o c i a t e d w i t h heavy s n o w f a l l over the w e s t e r n U n i t e d S t a t e s . Monthly Weather Review 96(12) 8 5 1 - 8 5 3 . APPENDICES APPENDIX A : D e t a i l s of the f o r e s t c over on Mount Seymour A l : Measures o f - t h e f o r e s t c h a r a c t e r i s t i c s of the t e r r a i n segment. A2 : Photographs of the f o r e s t near each o f the snow s a m p l i n g s i t e s . 305 APPENDIX A l Measures of the f o r e s t c h a r a c t e r i s t i c s of the t e r r a i n segment • -in L v +-* 2 0-6 05 CD S3 JSZ 04 D 4) c_ CD 03 0-2 c <u +-> E D b 0-1 200 -r 400 1^ S t a n d a r d d e v i a t i o n n =25 \ m e a n ± JL T 600 800 Elevation( Meters) 1000 1200 Diameter at breast height of 25 randomly chosen trees at each sampling s i t e 3 0 25 L. 20 +> X <L> „ U 10 I-1 S t a n d a r d d e v i a t i o n ) n = 2 5 \ m e a n 200 400 600 800 Elevation (Meters) 1000 1200 Height of 25 randomly chosen trees at each sampling s i t e APPENDIX A l Co n t i n u e d 306 ~ 120 1. v 4) o cu C_ D >, D-O C D U "D -f-> O dl c7 D_ 100 80 60 40 20 200 400 1 standard deviation \ n = 2 5 mean J -600 800 Elevation(Meters) 1000 1200 P r o j e c t e d canopy a r e a / t r e e at each s a m p l i n g s i t e 80 60 in f 2 40 o c 8 20 c o Q 00 200 1 Standard deviation n=25 \ mean X 400 600 800 Elevation (Meters) 1000 1200 Index o f "openess" o f the f o r e s t at each s a m p l i n g s i t e The d i s t a n c e t o the n e a r e s t t r e e i s measured from 25 randomly-; chosen p o i n t s 220 m (1 March 1 9 7 D W 1 ft 1 330 m (1 March 1971) APPENDIX A2 : The f o r e s t near each of the snow s a m p l i n g s i t e s 308 309 710 m (1 March 1 9 7 D 790 m (1 March 1 9 7 D 870 m (1 March 1 9 7 D 310 970 m (1 March 1970) 1060 m (1 March 1 9 7 D 1260 m (9 January 1970) APPENDIX B : R e s u l t s of p i l o t s t u d i e s w i t h l a r g e samples B l : S t a t i s t i c s o f p i l o t s tudy w i t h l a r g e samples o f new snow d e n s i t y t hroughout the f o r e s t , W i n t e r 1968-I969. B2 : S t a t i s t i c s of p i l o t s tudy w i t h l a r g e samples of new snow depth. APPENDIX B l : S t a t i s t i c s o f p i l o t s t u d y , new snow d e n s i t y throughout the f o r e s t W i n t e r 1968-69 Date of Sample 17.1 .69 21.1 .69 28.1 .69 4.2.69 9.2 .69 11.2 .69 14.1 .69 21.1 .69 28.1 .69 2.69 ,2 .69 11.2 .69 2.3.69 7.3 .69 4 9 14 . 1 . 6 9 2 1 . 1 . 6 9 2 8 . 1 . 6 9 4 .2 9 . 2 1 1 . 2 . 6 9 16 . 2 . 6 9 2 . 3 . 6 9 7 . 3 . 6 9 9 . 3 . 6 9 69 69 E l e v a t i o n (meters) 400 400 400 ::4oo .400 400 590 590 590 590 590 590 590 590 790 790 790 790 790 790 790 790 790 790 Sample S i z e 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 Mean (kg/m 3) 154 184 187 233 265 382 142 150 135 150 172 353 388 327 134 195 130 130 137 322 250 347 370 374 S.D. (kg/m 3) 5 9 12 8 12 16 1 15 20 15 8 9 17 10 12" 2 11 15 15 9 14 12 19 V a r i a n c e 28 81 144 64 144 249 64 1 225 400 217 67 83 289 109 150 4 118 225 225 80 201 132 363 C.V. (%) 3 5 7 3 5 4 5 1 11 13 9 2 2 5 6 • 2 8 11 5 4 4 3 5 ±95$ c o n f i d e n c e l i m i t s about the mean (kg/m 3) 5 , 9 13 8 13 17 8 1 16 21 16 • 8 9 18 • 10 13 2 12 16 16 9 15 13 20 APPENDIX B l : C o n t i n u e d ... ±95% c o n f i d e n c e Date of Sample l i m i t s about Sample E l e v a t i o n S i z e Mean S.D. V a r i a n c e C.V. the mean (meters) (kg/m 3) (kg/m 3) (*) (kg/m 3) 2 1 . 1 . 6 9 1060 6 134 5 25 4 5 2 8 . 1 . 6 9 1060 6 93 10 100 11 10 4 . 2 . 6 9 1060 6 110 9 80 8 9 9 . 2 . 6 9 1060 6 243 9 81 4 9 1 1 . 2 . 6 9 1060 6 264 20 387 7 21 1 6 . 2 . 6 9 1060 6 187 8 64 4 8 2 . 3 . 6 9 1060 6 139 14 196 10 15 7 . 3 . 6 9 1060 6 230 9 81 4 9 9 . 3 . 6 9 1060 6 205 8 64 4 8 6 . 4 . 6 9 1060 6 307 9 81 3 9 1 1 . 1 . 6 9 1260 6 152 6 .36 4 6 9 . 2 . 6 9 1260 6 220 1 1 1 r 1 6 . 2 . 6 9 1260 6 170 11 122 6 12 2 . 3 . 6 9 1260 6 145 14 196 10 15 7 . 3 . 6 9 1260 6 242 8 57 3 8 9 . 3 . 6 9 1260 6 212 10 100 5 10 2 8 . 3 . 6 9 1260 6 301 4 16 1 4 6 . 4 . 6 9 1260 6 260 6 36 2 6 APPENDIX B2 : S t a t i s t i c s o f l a r g e samples of new snow depth ±95$ c o n f i d e n c e Storm No. -. Date o f Secondary Sample l i m i t s about (1970-•71) Sample - E l e v a t i o n Sample S i z e Mean S.D. V a r i a n c e -C.V. the mean (meters) (cm) (cm) (cm 2) 45 19 .2 .71 '• 870 Open 50 10 .1 0 . 7 0 . 5 7.1 0 . 2 . 45 19 .2 .71 870 Canopy edge 50 7.4 1.4 1.8 18 .3 0 . 3 45 1 9 . 2 . 7 1 870 Beneath canopy 50 5 .4 0 . 7 0 . 5 15.7 0 . 2 61 2 . 4 . 7 1 790 Open 50 5 . 1 0 . 5 0 . 2 9 . 0 0 .1 61 2 . 4 . 7 1 870 Open 50 5 .6 0 . 7 0 . 4 11.6 0 . 2 61 2 . 4 . 7 1 870 C l e a r i n g 50 5 . 3 0 . 7 0 . 5 13 .8 0 ,2 61 2 . 4 . 7 1 ' 970 Open 50 6 . 4 0 . 8 0 . 6 11 .8 0 . 2 61 2 . 4 . 7 1 970 C l e a r i n g 50 5 . 6 . 0 . 6 0 . 3 10 .1 0 . 2 61 2 . 4 . 7 1 ; 970 Canopy edge 50 4 . 3 0 . 5 0 . 3 12 .2 0 .2 61 2 .4 .71 1060 Open 50 779 0 . 8 0 .7 10 .5 0 . 2 61 2 . 4 .71 1060 C l e a r i n g 50 8 . 1 0 . 7 0 . 5 8 .8 0 . 2 61 2 . 4 . 7 1 1060 Canopy edge 50 6 . 2 0 . 7 ' 0 . 6 11.9 0 . 2 61 2 . 4 ; 7 1 1060 Beneath canopy 50 4 . 6 0 . 8 0 . 6 16 .7 0 . 2 61 2 .4 .71 1260 Open 50 9 . 0 0 . 9 0 . 7 9.6 0 . 3 61 . 2'; 4 .71 1260 C l e a r i n g 50 9 . 8 1.0 0 . 9 10 .0 0 . 3 61 2 . 4 . 7 1 1260 Canopy edge 50 15 .7 2.4 5 .9 15 .4 0 . 7 61 2 . 4 . 7 1 1260 Beneath canopy 50 5.. 8 1 5 2.4 26 .6 0 . 4 APPENDIX B2 : C o n t i n u e d ... Storm (1970-No. •71) Date of Sample E l e v a t i o n (meters) Secondary-Sample Sample S i z e Mean (cm) S.D. (cm) V a r i a n c e (cm 2) C.V. (%) ±95$ c o n f i d e n c e l i m i t s about the mean 62 7 . 4 . 7 1 1060 Open 50 6 . 2 0 . 7 0 . 5 10.9 0 . 2 62 7 . 4 . 7 1 1060 C l e a r i n g 50 6 . 0 0 . 5 0 . 3 8.9 0 . 2 62 7 .4 ; 7 1 1260 Open 50 10 .6 1.0 9-7 0 . 3 62 7 . 4 . 7 1 1260 C l e a r i n g 50 11 .0 1.4 2.0 12 .8 0 .4 62 7 . 4 . 7 1 1260 Canopy edge 50 9.4 1.5 2 . 3 16 .2 0 .4 62 7 . 4 . 7 1 1260 Beneath canopy 50 4 . 7 1 . 1 1.2 24 .0 0 . 3 64 1 2 . 4 . 7 1 790 Open 50 20 .0 0 . 7 0 . 6 3 .7 0 . 2 64 1 2 . 4 . 7 1 1260 Open 50 40 .7 3 .6 12 .9 8 .8 1.0 APPENDIX C : Snow cover phenology f o r w i n t e r s 1969-70, . 1970-71 APPENDIX C :' Snow Phenology - Winters 1969-70, 1970-71 E l e - Date of Date of Snowfall Date when Duration of. Season -of Winter v a t i o n f i r s t l a s t season snow l a s t snow cover snow cover (meters) snowfall snowfall (days) present on ground (days)* (days)** com-plete incom-plete com-plete incom-p l e t e 1969-70 1260 Oct 24 May 11 200 June 30 222 236 . 235 250 1060 Oct 24 May 11 200 June 20 147 198 165 240 970 Oct 24 May 11 200 May 12 69 175 163 201 . 870 Nov 17 Apr 27 161 May . 4 48 135. 123 168 790 Nov 17 Apr 27 161 Apr 30 33 93 120 164 710 Dec 8 Apr 27 140 Apr 29 21 69 10 8 142 590 Dec 8 Apr 8 121 Apr 10 2 45 2 123 490 Dec 23 Apr 8 10 6 Apr 9 2 21 2 107 88 400 Jan 10 " Feb 6 27 Apr 8 2 15 2 330 Jan 17 Jan 18 1 Jan • 19 1 2 1 2 220 Jan 17 Jan 18 1 Jan 19 1 2 1 2 ' 120 Jan 17 Jan 18 1 Jan 19 1 2 1 2 1970-71 1260 Oct 20 Jun 24 247 Jul y 20 235 271 252 274 1060 Oct 22 Jun 24 245 Jul y 10 210 244 210 262 970 Oct 24 May 19 208 July 3 192 229 192 253 870 Oct 24 Apr 24 183 June 10 182 204 182 230 790 Oct 24 Apr 24 183 May 25 168 186 172 214 ' 710 Oct.24 Apr 11 170 May 8 147 168 161 197 . 590 Nov. 20, Apr 11 166 Apr 26 117 156 137 181. . ' 490 Nov 20 Apr' 11 166 Apr 15 78 144 113 170 400 Nov 20 Apr 11 166 Apr . 12 54 123 10 3 167 330 Nov 20 Mar 27 127 Mar' 28 40 85 100 128 220 Nov 20 Mar 7 10 7 Mar 15 25 72 95 115 120 Nov 20 Mar 7 10 7 Mar 14 18 66 92 114 Act u a l number of days with snow on ground ^ Number of days between date of f i r s t sniowfall and date when snow f i n a l l y melted 318 APPENDIX D : Summary s t a t i s t i c s , of the snowpacks. of the N o r t h Shore Mountains D l : Mean water e q u i v a l e n t D2 : Extremes o f wa t e r e q u i v a l e n t D3 : C o r r e l a t i o n m a t r i x D4 : Mean snow d e n s i t y 319 APPENDIX D. : Summary s t a t i s t i c s of the snowpacks of North  Shore Mountain snow courses CSee Tables 4.1, 4.2, f o r f u r t h e r d e t a i l s ) TABLE D.l - Mean water equivalent (cm) North Shore Mountain snow courses Snow Course E l e v a t i o n Record Feb Mar Apr May May June (meters) began 1 1 1 1 15 1 Grouse Mountain 1158 1936 82 100 123 132 Mount Seymour 1113 I960 111 141 162 188 174 140 Dog Mountain 1082 1945 130 Hollyburn 1022 1945 114 147 Loch Lomond 1097 1945 124 Burwell Lake 884 1945 113 Palisade Lake 884 1945 109 160 166 TABLE D.2 - Extremes of water equivalent (cm) recorded on A p r i l 1, North Shore Mountain snow courses Snow Course E l e v a t i o n (meters) maximum minimum extreme range years of record Grouse Mountain 1158 249. 38 211 34 • Mount Seymour 1113 .234 85 149 10 Dog Mountain 1082 209 .58 151 25 Hollyburn 1022 244 . 90 154 25 Loch Lomond ' 1097 371 41 ' 330 22 Burwell Lake 884 261 47 214 20 Palisade Lake 884 284 65 219 23 320 APPENDIX D : Continued ... TABLE D.3 - C o r r e l a t i o n matrix, A D r i l 1 water equivalent, f o r p e r i o d 1960-70 on North Shore Mountains . Snow Course Grouse Mt. Seymour Mt. Dog Mt. H o l l y -burn Loch Lomond Palisade Lake Grouse Mountain 1.00 Seymour Mountain 0.92 1.00 Dog Mountain o .98 0.87 1.00 Hollyburn 0.95 0.89 0 .94 1.00 Loch Lomond- 0.86 0 .69 0.89 0.82 1.00 Palisade Lake 0.92 0.80 0.93 o .96 0,91 1.00 TABLE D.4 - Me an snow density 3) fo v oer iod 1960-69 on North Shor e Mountain snow cour ses Snow Course E l e v a t i o n Feb Mar Apr May May June (meters) 1 1 1 1 15 1 Grouse Mountain 1158 397 406 429 477 Mount Seymour 1113 427 452 4.58 516 532 561 Dog Mountain 10 82 425 Hollyburn 1022 408 439 Loch Lomond 1097 427 Palisade Lake 884 424 416 499 NOTES: ( i ) Compiled from "A Summary of Snow Survey Measurements 1935-1965, B.C." and "B.C. Snow Survey B u l l e t i n s " , Water I n v e s t i g a t i o n s Branch, Water Resources S e r v i c e , Dept. of Lands, Forest and-Water Resources, V i c t o r i a , B.C. ( i i ) Observations taken i n A p r i l only, p r i o r to 1950 ( i i i ) Compiled from a l l data p r i o r to 1970. APPENDIX E : L i s t of storms- f o r w i n t e r s 1 9 6 9 - 7 0 , 1970-71 322 WINTER 1969-70 MlNTER 1970-71 D A T E D A T E L E N G T H OC NOV NOV NOV _ NOV 11 NOV 14 NOV I? NOV 16 NOV 22 NOV 24 NOV • DEC 21 OCT 24 OCT 26 OCT 27 OCT 29 OCT 31 3 OCT NOV NOV NOV NOV NOV NOV 19 DEC 20 DEC 21 DEC 23 D E C 25 O E C 27 OEC 8 JAN 10 JAN 13 JAN 17 JAN 20 JAN 22 JAN 24 JAN 26 JAN 3§ m 5 F E B 5 F E B 6 FE8 12 F E B 14 F E B 15 F E B 16 F E B 5 MAR MAR MAR MAR MAR MAR 22 MAR 1 APR 3 APR 4 APR 5 APR 7 APR 8 APR 18 APR 22 APR 23 APR 24 APR 29 APR 4 MAY 6 MAY 12 MAY 16 MAY 21 MAY 25 MAY 27 MAY 9 13 16 ....18 NOV 20 NOV 23 NOV 25 NOV 4 OEC 9 DEC i f m 15 OEC ie oil 20 DEC 21 OEC 22 OEC 24 DEC 26 DEC • 1 r-rtM A 13 MS 1 DEC JAN JAN JAN JAN JAN JAN JAN JAN JAN FEB FEB FEB FEB FE8 FE8 FEB FES MAR MAR MAR MAR MAR MAR MAR APR APR APR 6 APR I APR 9 APR 19 APR 23 APR 24 APR 27 APR 29 APR MAY MAY MAY 30 9 Ii 20 21 24 I* 3l 5 3 5 .6 18 6 7 11 12 4 6 2l 4 5 16 MAY 22 MAY 25 MAY 29 MAY 60 46 46 36 12 46 24 36 24 36 46 46 12 36 36 6 12 46 46 24 12 >§ 22 16 !! 81 22 M 84 24 46 55 24 i i IS 12 6 }<> ie 6 24 if 24 8 24 24 24 13 30 10 A 82 4 4 24 2 41 PRtC« 3 f 1 1 3 3 3 i 2 3 1 2 3 1 3 2 2 3 1 2 3 3 3 P B C C l P l T i T T n N , r n n F . I R A I N TO TOP I tfcnE ONLY AT TOP OF MOUNTAIN. RAIN « SNOW AT AtL ELEVATIONS ON MOUNTAIN - f l r ' n ' ^ t ^ M ° U N T A 1 N ( N O S N O « ) !!iXtD_RA_lN.ANO SNOH AT TOP OF M O U N T A I N P  T A I N . A I N BtL OH APPENDIX F : W i n t e r p r e c i p i t a t i o n F l : V a r i a t i o n of w i n t e r p r e c i p i t a t i o n w i t h " e l e v a t i o n f o r each storm. F2 : Mean w i n t e r p r e c i p i t a t i o n at Vancouver and at h i g h e r c l i m a t o l o g i c a l s t a t i o n s on t h e N o r t h Shore M o u n t a i n s . 324 TOTAL P R E C I P I T A T I O N Ci STORM: OPEN AREAS 1969-70 (MM) STORM ELEVATION (METERS! NO. 1260 1060 970 870 790 7 10 490 510 400 330 220 120 4 14 17 14 16 18 17 16 16 14 14 13 12 *• 12 25 25 22 19 29 26 17 20 20 15 14 16 13 3 3 2 3 5 5 4 4 5 4 4 6 14 1 1 1 1 1 1 1 1 1 2 3 4 15 23 22 25 20 16 10 9 10 11 10 5 7 16 53 52 28 30 43 32 29 28 30 27 24 25 17 45 43 66 41 48 45 42 46 48 44 39 37 IB 4 4 4 2 2 2 2 1 1 1 1 1 19 58 55 25 38 39 39 32 31 35 34 30 23 20 39 37 39 29 24 33 36 33 35 36 34 36 21 78 74 71 79 78 62 55 55 54 53 53 58 * - 23 70 53 59 60 6 1 41 45 42 42 41 40 33 * 25 10 10 10 1 7 14 15 16 15 14 13 11 11 26 14 14 14 14 15 15 12 11 12 10 9 9 28 90 86 85 81 80 85 83 83 83 83 83 83 29 31 32 11 13 16 22 22 25 24 22 21 15 30 17 17 13 10 19 9 6 11 10 10 9 9 31 5 5 5 8 6 7 5 4 5 6 6 5 32 3D 44 26 32 32 30 30 30 29 29 26 25 33 19 18 11 1 1 1 2 9 8 8 5 4 4 4 34 22 33 29 30 37 38 36 35 36 34 32 31 35 54 45 77 94 98 92 73 68 70 68 67 63 36 2 4 24 24 28 37 36 37 34 36 35 31 32 37 15 15 13 1 4 1 7 15 15 14 I 3 13 12 11 38 73 71 59 42 36 34 18 17 15 15 1'; 13 39 4 12 12 12 11 9 5 5 4 4 5 5 40 48 87 38 68 56 60 47 47 47 46 43 42 41 19 42 33 21 36 33 24 23 23 21 20 19 * 43 23 31 22 39 39 39 2 1 19 19 17 13 13 44 B 8 8 8 9 8 6 5 5 5 4 4 45 28 28 3b 42 46 48 37 42 45 42 38 34 •* 47 31 31 23 26 34 32 32 39 35 33 30 29 48 63 58 51 52 46 29 26 26 27 26 24 23 49 26 33 13 20 25 28 24 24 25 23 2 1 15 50 41 41 32 24 30 29 24 24 26 23 20 25 51 6 3 1 1 1 1 1 1 1 1 1 1 52 75 46 25 25 28 29 31 26 28 27 28 29 # 54 67 51 51 50 59 59 54 49 49 50 48 45 55 51 40 28 21 29 24 19 19 18 18 15 11 56 1 3 2 2 4 4 3 4 4 4 3 2 57 60 57 40 22 15 5 1 I 1 1 1 1 58 69 68 64 76 116 99 91 88 ao 80 80 79 59 68 66 65 64 60 56 40 52 54 47 44 40 60 28 27 37 28 30 25 17 18 25 22 19 17 61 75 55 53 42 50 49 43 42 43 40 39 39 62 70 91 77 57 49 51 49 47 44 41 40 39 63 40 36 28 27 27 26 28 26 26 26 22 21 64 47 48 47 39 36 32 26 25 25 25 22 19 65 33 39 36 27 22 16 12 10 8 7 7 7 66 3 9 6 6 7 6 5 4 6 4 4 4 67 1 1 1 1 1 1 1 1 1 1 1 1 68 28 26 23 23 25 23 19 20 21 19 20 20 69 3 4 2 1 2 2 2 1 2 I 2 3 70 11 12 12 12 10 10 7 8 8 8 8 7 71 13 15 15 13 15 14 12 12 10 11 11 12 72 1 1 1 1 1 1 1 1 1 1 1 1 73 8 12 13 1 7 22 22 19 26 28 31 31 31 NOTE:AN ASTERISK INDICATES THAT THE VALUE GIVEN INCLUDES THE P R E C I P I T A T I O N FROM THE PREVIOUS STO^M(S) . THESE STORMS WERE NOS. 11,22,24,27,42,46,53 THE STORMS NOT SAMPLED WERE NOS. 1,2,3,5,6,7,8,9,10 325 TOTAL PRECIPITATION t)Y STORM: OPEN AREAS 1970-M (MM) STORM NO. 1260 1060 970 870 ELEVATION (METERS) 790 710 490 510 400 330 220 120 1 12 15 15 19 19 19 13 12 11 9 7 5 2 13 15 15 16 17 16 16 15 14 14 14 14 3 8 9 9 9 9 9 7 7 7 6 6 6 4 35 41 34 28 29 28 23 19 18 16 15 15 5 47 52 38 47 49 50 43 41 39 38 35 33 6 39 30 17 21 22 22 22 20 18 18 . 1U 19 7 57 60 48 53 58 36 51 52 52 51 50 49 B 34 26 22 23 22 23 20 20 18 17 17 16 9 66 58 47 47 50 48 44 41 40 39 38 38 10 76 61 42 65 69 72 67 62 65 68 55 48 11 45 44 32 33 34 33 29 25 25 25 26 26 12 8 8 8 8 7 5 5 8 7 6 5 4 13 14 8 6 5 5 5 2 2 . 2 4 4 4 14 67 70 54 50 62 57 48 47 46 46 46 45 15 22 26 23 15 15 21 23 18 11 8 5 4 16 78 74 50 50 49 43 34 42 39 26 18 14 ¥ 18 58 56 45 44 44 42 66 65 66 68 56 50 19 82 82 80 78 76 76 72 73 74 74 63 53 20 107 64 78 7 7 79 64 59 53 56 59 45 50 21 103 65 54 61 76 63 40 46 45 44 43 42 22 107 90 48 59 5.5 49 48 37 39 38 38 38 23 30 37 36 36 36 36 29 32 29 30 27 28 24 2 2 2 2 2 2 3 2 2 2 2 2 •tr* 27 35 56 49 44 46 48 44 46 60 39 35 33 28 85 94 67 22 31 33 46 41 45 39 34 33 29 95 116 69 46 43 45 29 37 38 36 34 33 30 61 58 57 57 79 82 72 70 48 47 64 63 31 60 5 7 50 29 33 30 33 29 31 26 24 23 32 39 38 36 34 33 32 30 24 24 31 24 22 33 33 32 22 22 21 27 21 20 18 15 14 12 34 32 53 41 29 36 19 15 16 15 6 4 3 35 98 85 90 82 77 80 61 90 77 55 46 42 36 105 102 99 99 99 98 84 85 87 89 79 69 37 3S 37 38 4 1 58 47 35 35 36 37 33 28 38 69 61 76 82 97 90 84 88 89 89 83 76 39 36 33 41 44 52 49 45 48 48 48 44 40 40 112 122 104 105 106 93 92 74 70 55 50 61 41 50 50 48 47 46 43 43 39 38 38 33 32 42 50 4 9 48 4 7 58 48 42 43 44 46 39 34 43 137 114 115 96 110 91 88 74 75 77 76 74 44 21 16 8 9 5 5 5 5 5 5 4 3 45 45 53 37 29 34 23 33 27 27 28 21 18 46 103 103 82 77 78 39 34 34 33 32 29 27 47 119 135 97 94 102 91 65 60 56 55 51 45 ¥r 49 44 50 57 23 31 37 43 33 31 33 37 40 50 69 52 46 43 48 49 35 29 31 39 42 42 51 151 149 131 84 91 60 55 51 55 53 51 49 52 89 85 47 54 61 36 36 26 39 33 26 33 53 51 49 48 40 36 23 37 30 36 30 26 26 54 76 64 27 23 23 23 24 23 20 17 15 14 55 41 46 28 29 24 17 17 11 15 13 11 9 * 57 73 72 71 71 70 66 65 60 '59 60 59 50 58 70 78 63 52 53 47 31 35 45 44 40 37 59 51 51 50 45 46 68 54 48 58 55 46 41 60 3 4 4 4 4 3 3 3 3 2 3 2 61 21 19 17 19 14 8 6 7 7 7 7 6 62 25 25 19 11 10 10 11 9 9 9 9 7 * 64 90 95 54 67 75 78 75 57 70 62 55 50 65 15 9 6 6 5 4 2 1 1 1 1 1 66 24 24 16 1 1 1 1 10 9 8 9 a 8 9 67 14 16 12 8 8 6 7 6 6 6 5 5 68 11 16 15 17 2 0 18 14 12 13 9 7 5 69 2 4 3 3 4 2 3 3 3 2 2 1 70 16 24 24 18 19 17 17 15 15 15 13 10 71 13 12 11 1 5 16 13 14 12 12 8 8 5 72 32 38 41 20 27 23 21 21 20 19 18 18 73 8 9 9 9 9 8 7 7 7 7 7 6 74 3 2 2 2 3 2 2 2 2 2 2 1 NOTE:AN ASTERISK INDICATES THAT THE VALUE CIVEN INCLUDES THE PRECIPITATION FROM THE PREVIOUS STORM(S). THESE STORMS WERE NOS. 17,25 AND 26,48,56,63 THE STORMS NOT SAMPLED WERE : NIL 326 APPENDIX F2 : Mean w i n t e r p r e c i p i t a t i o n (mm) at Vancouver and at h i g h e r c l i m a t o . l o g i c a l s t a t i o n s ' on the' N o r t h Shore Mountains MONTH Vancouver I n t e r n a t i o n a l A i r p o r t (5 m) H o l l y b u r n Ridge C951 m) Mount Seymour CBUT (866 m) October 117 397 429 November 138 398 396 December 164 428 441 January 140 371 341 F e b r u a r y 120 283 248 March 96 246 227 A p r i l 58 195 188 May 49 120 150 W i n t e r s n o w f a l l 36 820 451 W i n t e r p r e c i p i -t a t i o n 882 2438 2420 Annual p r e c i p i -t a t i o n 1039 3004 2927 NOTES: ( i ) Compiled from the "Monthly R e c o r d , M e t e o r o l o g i c a l O b s e r v a t i o n s i n Canada", D.O.T., Met. B r . , T o r o n t o . ( i i ) Vancouver d a t a f o r s t a n d a r d p e r i o d 1931-60 H o l l y b u r n d a t a f o r 16 y e a r p e r i o d 1954-69 Seymour d a t a f o r p e r i o d 1958-68 (some m i s s i n g data) ( i i i ) S n o w f a l l water e q u i v a l e n t and hence p r e c i p i t a t i o n may be u n d e r e s t i m a t e d at H o l l y b u r n Ridge and Mount Seymour CBUT (.see d i s c u s s i o n i n t e x t ) . ( i v ) W i n t e r i s p e r i o d October t o May i n c l u s i v e . 327 APPENDIX G :. V a r i a t i o n s o f snow d e p o s i t i o n w i t h e l e v a t i o n f o r each storm T a b l e s o f snow d e p o s i t i o n (mm water e q u i v a l e n t ) f o r open a r e a s , c l e a r i n g s , canopy edge, beneath the canopy and c l o s e t o t r e e t r u n k s f o r t h e w i n t e r s 1 9 6 9 - 7 0 , 1 9 7 0 - 7 1 . 328 S N O W F A L L W A T E R E Q U I V A L E N T ( M . M »KG/SQ*M) I O P E N A R E A S 1 9 6 9 - 7 0 S T O R M NO « 4 12 1 7 ia 1 9 2 0 2 1 2 3 2 4 2 8 2 9 3 0 I 2 3 3 3 4 3 5 3 8 3 9 4 0 4 1 4 3 4 7 4 8 4 9 I? 5 2 5 4 5 5 5 7 5 9 6 0 6 2 6 3 6 4 6 5 6 8 1 2 6 0 1 0 6 0 9 7 0 8 7 Q E L E V A T I O N C M E T E R S ) 7 9 0 7 1 0 4 9 0 5io 4 0 0 3 3 0 2 2 0 1 2 0 1 4 2 3 2 2 4 5 4 5 6 3 9 7 8 4 1 2 9 9 0 3 1 1 7 3 0 1 9 2 2 5 4 7 0 4 4 8 1 9 2 3 9 6 0 2 6 6 6 5 1 1 7 5 1 6 0 3 5 2 6 6 5 4 0 4 4 2 1 6 1 7 3 0 0 2 2 2 1 6 2 2 1 8 0 0 4 3 4 9 0 0 4 2 0 0 5 5 2 5 4 0 3 7 3 9 2 9 2 4 7 4 3 2 0 0 2 3 4 0 0 0 0 0 0 8 6 2 0 1 0 3 3 2 1 1 1 3 1 6 1 7 1 3 1 0 1 2 4 0 1 5 5 2 1 6 1 1 1 0 9 2 4 3 0 0 4 5 3 5 2 7 1 7 7 1 5 9 4 2 3 6 1 0 9 6 6 8 7 3 8 2 6 1 3 4 2 3 3 1 9 2 0 3 1 2 2 2 2 2 6 0 0 0 0 5 8 ' 4 8 2 5 1 9 1 9 3 0 0 4 2 0 0 3 0 0 0 1 4 0 0 0 0 0 0 0 4 0 5 0 0 5 7 4 0 2 2 1 5 3 4 3 1 2 3 1 4 2 6 3 4 2 4 2 2 8 1 3 5 5 0 3 6 2 8 7 7 4 2 2 0 8 0 3 0 2 4 1 4 9 4 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 7 4 1 0 0 0 0 7 4 1 0 0 0 0 % 0 0 0 0 0 0 1 5 2 1 0 0 0 0 1 0 0 0 0 0 0 0 8 1 1 1 1 2 1 2 2 4 0 0 0 0 0 0 5 1 0 0 0 0 0 1 4 2 0 0 0 0 0 1 0 2 0 0 0 0 0 2 6 9 3 2 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 4 0 0 0 0 0 0 1 7 7 2 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 o 0 0 0 0 0 0 0 329 S N O W F A L L H A T E R E Q U I V A L E N T < M M = K G / S Q « M ) t C L E A H I N G S 1 9 6 9 - 7 0 S T O R M N O , 1 2 6 0 1 0 6 0 4 1 8 1 6 1 5 2 3 2 2 1 6 2 0 1 9 1 7 4 1 3 9 1 6 4 4 1 9 5 7 5 5 2 0 4 0 3 6 2 1 6 3 6 0 2 3 4 6 2 3 2 4 2 7 0 2 d 7 6 7 2 2 9 3 1 1 7 3 0 2 3 1 9 3 2 2 6 4 5 3 3 1 7 1 6 3 4 3 9 1 6 3 5 . 3 9 4 4 3 8 6 6 6 6 3 9 6 7 4 0 6 9 9 1 4 1 2 1 4 0 4 3 4 9 4 7 4 7 9 0 4 8 3 7 5 4 4 9 3 8 1 7 5 0 4 4 5 1 6 3 5 2 4 9 2 0 5 4 1 7 0 I? 3 3 3 6 6 3 6 0 5 9 2 7 2 6 6 0 3 7 3 5 6 2 4 4 7 7 6 3 3 8 3 4 6 4 4 6 4 3 6 5 2 3 3 0 6 8 5 4 E L E V A T I O N ( M E T E R S ) 9 7 0 8 7 0 7 9 0 7\Q HVQ 5 1 0 4 0 0 3 3 0 2 2 0 1 2 0 2 'I 2 3 3 6 2 9 6 0 IF 1 4 1 1 1 2 3 3 4 5? 4 9 3 3 2 2 0 3 4 3 0 0 0 6 4 6 3 7 3 § ?! 2? 0 0 0 0 0 0 0 0 0 6 4 0 0 0 0 .0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 2 1 2 8 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 2 1 0 0 0 0 0 0 8 1 6 6 3 1 0 0 0 0 1 0 8 7 5 1 0 0 0 0 3 1 1 0 0 0 0 0 0 6 8 6 5 1 1 0 0 0 0 0 0 0 0 0 0 0 0 2 6 1 7 1 0 8 2 3 3 1 3 1 2 2 9 4 0 2 1 0 0 0 0 0 0 7 6 5 1 0 0 0 0 0 1 3 1 1 1 3 2 0 0 0 0 0 1 7 1 6 1 1 2 0 0 0 0 0 2 8 2 8 2 7 9 3 1 0 0 0 0 0 0 0 0 0 0 0 0 1 7 1 6 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 9 1 4 3 0 0 0 0 0 0 2 3 2 2 3 0 0 0 0 0 0 1 4 2 0 1 7 5 2 0 0 0 0 4 0 0 0 0 0 0 0 0 6 5 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 1 7 9 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 330 SNOWFALL WATER EQUIVALENT <MM=KG/SQ.M)» CANOPY EDGE 1 9 t > 9 - 7 0 S T O R M N 0 » 1260 1060 4 1 0 15 17 16 16 10 9 17 14 13 16 0 0 19 61 56 20 36 35 21 58 56 23 25 1 24 K 0 28 71 29 2 5 20 30 15 14 32 14 52 33 16 15 34 15 2 7 35 40 20 38 "64 74 39 6 11 40 75 67 41 2 5 33 43 22 45 47 4 0 46 43 42 49 21 50 7 2 51 6 0 52 24 12 54 6 0 5 5 39 41 57 51 46 59 31 29 60 24 23 62 41 61 63 30 19 64 23 23 65 30 27 68 4 2 E L E V A T I O N (METERS) 970 87Q 790 7IQ H9Q 5lo 400 330 2 2 0 120 0 0 0 0 0 0 0 0 0 0 5 2 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11 0 0 0 0 0 0 0 0 0 32 9 2 0 0 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 5 0 0 0 0 0 0 0 0 16 13 4 0 0 0 0 0 0 0 11 8 3 4 2 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 10 5 5 4 2 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 16 10 10 4 2 0 0 0 5 6 63 24 29 6 0 0 0 0 0 0 6 5 3 2 1 0 0 0 0 0 24 10 8 7 0 0 0 0 0 0 25 11 13 2 0 0 0 0 0 0 22 17 13 13 5 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40 6 9 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 40 11 6 0 0 0 0 0 0 0 19 21 12 2 0 0 0 0 0 0 15 12 10 9 3 0 0 0 0 0 24 3 0 0 0 0 0 0 0 0 13 4 2 0 0 0 0 0 0 0 11 5 0 0 0 0 0 0 0 0 21 15 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 331 SNQHfALL WATER EQIJ I y A L £ N T ( MM»KG/SQ t M ) t B E N E A T > C A N O P Y 1969*70 S T O R M N O t 1260 4 1 15 6 U 6 17 9 18 0 19 9 20 21 21 57 23 26 24 18 28 43 29 21 30 9 32 37 33 11 34 23 35 32 36 53 39 9 40 47 41 26 43 16 47 0 46 45 49 2 50 1 51 2 52 2 54 0 55 44 57 42 59 20 60 13 62 24 63 16 64 42 65 45 68 2 U , • E L E V A T I O N ( M E T E R S ) 97Q 87Q 790 7io 49 0 5 l o 4 Q 0 330 220 120 0 0 0 0 8 5 3 0 6 0 0 0 8 9 0 0 0 0 0 0 9 0 0 0 20 5 0 0 55 11 0 0 0 0 0 0 0 0 0 0 41 10 5 0 11 4 3 0 9 2 2 2 26 4 0 0 10 6 4 3 11 0 0 0 18 10 9 6 44 41 16 7 6 2 3 2 46 16 7 3 16 5 5 4 18 1? 7 9 0 0 0 0 17 18 2 3 4 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 10 0 0 0 40 16 7 0 19 5 8 5 12 13 a 6 17 3 0 0 7 5 2 0 19 10 4 0 27 14 13 3 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 3 4 4 0 0 0 0 0 0 1 0 0 0 0 0 0 2 0 0 0 0 0 0 2 0 0 0 0 0 0 6 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 7 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 332 SNOWFALL WATER EQUIVALENT (MM=KG/SQ.M)ICLOSE TO T.TRUNK 19&9-70 STORM NO* 1260 4 0 15 7 \i 3 17 7 18 0 19 2 20 13 21 52 23 27 24 13 28 49 29 l£ 30 7 32 48 33 7 34 • 31 35 27 38 53 39 11 40 65 41 26 43 15 47 0 48 40 49 2 50 1 51 2 52 2 54 0 55 38 57 16 59 11 60 13 62 i 8 63 14 64 40 65 37 66 2 1060 9 7 0 87Q EL E V A T I O N (METERS) 79Q 7 i o 4 9 0 5 1 0 4Q0 330 2 2 0 120 0 0 0 0 0 0 0 0 0 0 0 7 5 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 7 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 13 5 0 0 0 0 0 0 0 0 0 49 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 46 9 2 0 0 0 0 0 0 0 0 4 3 2 0 0 0 0 0 0 0 0 4 2 2 2 2 0 0 0 0 0 0 28 5 0 0 0 0 0 0 0 0 0 7 6 2 2 1 1 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 14 10 9 4 2 0 0 0 0 3 3 27 4 ? 7 6 5 0 0 0 0 0 0 5 1 1 1 0 0 0 0 0 0 0 49 25 4 2 0 0 0 0 0 0 0 9 5 3 3 2 0 0 0 0 0 0 21 20 4 4 3 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 13 16 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 18 7 3 0 0 0 0 0 0 0 0 10 3 2 2 1 0 0 0 0 0 0 12 9 6 6 5 2 0 0 0 0 0 15 2 0 0 0 0 0 0 0 0 0 4 2 I 0 0 0 0 0 0 0 0 11 8 4 0 0 0 0 0 0 0 0 22 'U 13 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 333 SNOWFALL HATER E Q L ) I V A L E N T (MM»KG/SO•M ) l OPEN AREAS 1 9 7 0 - 7 1 STORM 970 87o E L E V A T I O N (METERS) NO. 1260 1060 790 710 4 9 0 5 1 0 400 330 220 120 5 3 0 0 0 0 0 0 0 0 0 0 0 6 16 5 0 0 0 0 0 0 0 0 0 0 7 57 12 4 3 0 0 0 0 0 0 0 0 10 33 3 0 0 0 0 0 0 0 0 0 0 13 14 8 6 5 5 5 2 2 2 2 2 2 14 23 22 14 7 7 5 1 0 0 0 0 0 15 22 26 23 15 15 21 21 15 7 2 1 0 16 78 74 50 50 49 43 34 42 39 26 18 14 18 58 55 42 22 9 6 3 0 0 0 0 0 20 107 60 31 22 15 11 0 0 0 0 0 0 21 103 65 52 58 73 53 29 5 2 0 0 0 22 107 90 46 59 55 31 19 3 I 0 0 0 23 30 37 36 36 36 36 29 29 26 20 16 14 27 35 56 4 ? 44 46 48 39 22 25 3 2 1 28 85 94 67 22 31 29 41 26 30 5 0 0 29 95 116 69 46 43 45 17 4 4 2 0 0 29 61 58 57 57 79 82 72 70 48 4 7 64 63 31 55 52 45 9 6 3 7 3 5 0 0 0 34 32 53 41 29 36 19 15 11 10 1 0 0 35 98 85 90 82 77 75 53 45 33 12 8 8 36 . 32 19 0 0 0 0 0 0 0 0 0 40 112 122 104 105 106 93 92 74 65 46 42 51 43 70 51 51 30 25 3 0 0 0 0 0 0 44 21 16 6 3 0 0 0 0 0 0 0 0 45 45 53 37 25 23 11 5 0 0 < 0 0 0 4$ . 9 8 6? 54 49 5 0 0 0 0 0 0 47 119 129 91 57 37 38 29 7 3 2 0 0 0 49 44 50 23 31 37 43 33 31 33 37 40 50 69 .52 46 43 4 8 49 35 29 27 31 32 24 51 151 149 83 89 36 24 9 0 0 0 0 52 89 85 47 54 61 36 36 26 29 16 0 0 53 51 49 4 8 28 24 12 7 0 0 0 0 0 54 76 64 27 7 0 0 0 0 0 0 0 0 55 41 46 26 29 24 16 14 0 0 0 0 0 58 70 78 63 52 53 47 29 13 2 1 0 0 59 37 31 24 13 7 0 0 0 0 0 0 0 61 16 J * 12 14 9 3 0 0 0 0 0 0 62 16 13 6 0 0 0 0 0 0 0 0 0 64 90 89 47 38 42 41 25 3 2 0 0 0 65 15 9 0 0 0 0 0 0 0 0 0 0 66 19 15 5 0 0 0 0 0 0 0 0 0 67 11 12 7 2 1 0 0 0 0 0 0 0 £2 7 7 6 0 0 0 0 0 0 0 0 0 72 18 17 19 0 0 0 0 0 0 0 0 0 334 SNOWFALL WATER EQUIVALENT ( M M A K G / S Q « M ) t CLEARINGS 1 9 7 0 - 7 1 STORM NO* 1 2 6 0 1 0 6 0 9 7 0 8 7 0 7 9 0 nv°u I E T F R S ) 5 1 0 4 0 0 3 3 0 2 2 0 1 2 0 5 3 0 0 0 0 0 0 0 0 0 0 0 6 1 6 5 0 0 0 0 0 0 0 0 0 0 7 5 6 1 1 3 3 0 0 0 0 0 0 0 0 } o 3 4 4 0 0 0 0 0 0 0 0 0 0 1 3 1 5 6 7 6 6 6 3 3 3 2 2 2 U 3 0 2 9 1 9 7 9 5 1 0 0 0 0 0 1 5 5 0 2 8 2 3 1 4 2 1 2 0 1 9 1 5 7 2 1 0 J 6 7 7 7 3 5 0 5 1 5 0 4 4 3 5 4 1 3 9 2 5 1 8 1 4 1 6 7 8 7 4 2 5 9 9 4 2 0 0 0 0 0 2 0 9 2 6 5 4 1 1 4 1 6 1 0 0 0 0 0 0 0 2 1 1 2 7 7 9 5 5 6 4 8 4 4 3 2 1 4 2 0 0 0 2 2 1 0 1 9 5 4 4 6 5 5 2 3 1 1 0 2 1 0 0 0 3 0 4 0 38 3 6 3 6 3 5 2 8 3 1 2 7 2 8 1 6 1 5 2 7 5 8 6 6 6 3 3 7 4 1 4 3 2 9 1 7 2 0 2 1 1 2 8 1 0 0 7 7 6 1 2 0 3 2 2 9 2 4 1 6 1 0 3 0 0 2 9 1 1 5 1 1 7 7 9 5 1 4 8 5 0 1 6 4 3 1 0 0 3 0 5 9 5 6 5 3 5 7 7 6 8 1 7 0 6 3 3 5 4 0 6 5 6 0 3 1 5 1 4 9 3 6 1 1 4 3 8 2 4 0 0 0 3 4 1 2 5 2 4 1 3 2 4 2 1 8 1 4 7 4 1 0 0 3 5 1 0 2 8 4 9 0 8 4 7 9 7 5 5 4 3 0 2 2 1 1 1 2 8 3 6 3 7 3 6 1 9 0 0 0 0 0 0 0 0 0 4 0 ! H 1 2 3 1 0 4 1 0 6 1 0 4 9 0 7 5 6 2 5 7 4 6 4 5 4 8 4 3 5 4 2 8 1 9 2 0 0 0 0 0 0 4 4 1 9 1 5 7 2 0 0 0 0 0 0 0 0 4 5 6 5 6 6 4 1 2 4 2 2 1 1 5 0 0 0 0 0 4 6 1 0 7 1 0 1 7 3 5 0 4 9 5 0 0 0 0 0 0 4 7 1 3 4 1 3 1 8 6 3 7 3 5 2 7 6 2 1 0 0 0 4 9 §° 5 6 5 6 . 2 4 2 7 4 0 3 6 3 2 3 1 3 0 3 2 4 0 5 0 7 3 6 0 5 1 4 3 4 8 4 3 3 3 2 8 2 6 3 0 3 2 2 3 5 1 2 2 7 1 7 8 1 4 3 8 3 8 8 3 7 2 5 7 0 0 0 0 5 2 9 6 9 1 5 1 5 8 6 3 3 6 3 3 2 6 2 9 1 5 0 0 5 3 6 6 6 5 5 0 2 7 2 4 9 7 0 0 0 0 0 5 4 8 1 5 8 3 6 7 0 0 0 0 0 0 0 0 5 5 4 0 4 6 3 2 2 9 2 3 1 4 1 2 0 0 0 0 0 5 8 8 1 8 2 6 3 5 2 5 3 4 6 3 0 1 3 2 1 0 0 5 9 4 3 4 1 2 6 1 2 6 0 0 0 0 0 0 0 6 1 1 8 1 3 1 0 1 4 9 3 0 0 0 0 0 0 6 2 1 6 1 3 8 0 0 0 0 0 0 0 0 0 6 4 9 0 9 6 4 7 3 5 4 0 3 9 2 4 2 1 0 0 0 6 5 1 3 8 0 0 0 0 0 0 0 0 0 0 66 I 9 ) 6 5 0 0 0 0 0 0 0 0 0 6 7 7 0 1 2 1 1 6 2 1 0 0 0 0 0 0 0 7 7 6 0 0 0 0 0 0 0 0 0 7 2 1 7 1 6 1 9 0 0 0 0 0 0 0 0 0 335 SNOWFALL WATER EQU IVALENT (MM 3 KG/SQ«M)> CANOPY EDGE 1970*71 STORM NO* 1260 5 0 6 5 7 24 IS 3? li 1? 16 63 id 98 20 66 21 83 22 62 23 23 32 26 36 29 36 29 79 31 91 34 17 35 53 36 43 40 63 43 61 44 14 45 65 95 4? 83 49 30 50 32 51 100 52 83 53 50 54 46 55 24 58 46 59 35 61 29 62 18 64 97 65 17 66 20 67 9 to 5 72 5 E L E V A T I O N (METERS) 970 8 7 0 790 7IQ 4*0 510 400 330 220 120 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 5 5 3 3 3 2 2 2 1 1 1 14 6 5 4 4 0 0 0 0 0 0 16 10 8 9 16 9 4 1 1 0 0 60 48 40 41 33 18 14 13 12 8 5 93 67 A 4 0 0 U 0 0 0 0 59 46 12 19 d 0 0 0 0 0 0 61 70 47 63 31 5 1 0 0 0 0 93 46 52 45 22 3 0 0 0 0 0 40 37 35 28 2d 17 10 13 10 9 5 43 56 4? 39 40 20 8 10 0 0 0 69 66 17 29 25 19 8 9 0 0 0 56 69 23 23 23 5 3 2 0 0 0 1% 5 8 48 54 52 36 2 3, 18 32 "3 35 87 31 12 13 0 0 0 0 0 0 0 23 20 18 19 11 6 4 3 0 0 0 54 70 47 58 55 37 29 16 5 4 5 41 30 0 0 0 0 0 0 0 0 0 92 104 71 85 86 63 39 48 24 22 15 37 28 7 2 0 0 0 0 0 0 0 10 4 0 0 0 0 0 0 0 0 0 51 40 18 17 7 3 0 0 0 0 0 90 6£ 26 22 3 0 0 0 0 0 0 34 43 23 24 19 5 0 0 0 0 0 36 43 18 18 22 29 17 21 21 23 26 38 39 38 35 3d 27 20 17 20 20 17 104 93 78 57 26 25 3 0 0 0 0 79 48 43 39 25 23 16 20 4 0 0 47 46 21 17 6 3 0 0 0 0 0 54 36 3 0 0 0 0 0 0 0 0 36 26 20 7 5 4 0 0 0 0 0 51 52 39 29 28 19 8 1 0 0 0 28 20 5 4 0 0 0 ; o 0 0 0 10 8 9 4 0 0 0 0 0 0 0 4 2 0 0 0 0 0 0 0 0 0 63 53 32 19 19 27 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 11 12 1 0 0 0 0 0 0 0 0 5 4 0 0 0 0 0 0 0 0 0 5 7 0 0 0 0 0 0 0 0 0 336 SNQHFALL WATER EQUIVALENT (MM=KG/SQ.M) I BENEATH CANOPY 1 9 7 0 - 7 1 STORM 1 2 6 0 8 7 0 E L E V A T I O N (METERS) NO* 1 0 6 0 9 7 0 7 9 0 7 1 0 4 9 0 5 1 0 4 0 0 3 3 0 2 2 0 1 2 0 5 0 0 0 0 0 0 0 0 0 0 0 0 6 3 0 0 0 0 0 0 0 0 0 0 0 7 8 2 0 0 0 0 0 0 0 0 0 0 1 0 7 0 0 0 0 0 0 0 0 0 0 0 1 3 6 4 3 2 2 2 1 1 1 1 1 1 1 4 1 1 10 5 4 2 3 0 0 0 0 0 0 1 5 2 3 1 0 7 6 8 9 5 2 1 1 0 0 1 6 6 9 6 6 4 9 3 4 3 8 2 6 1 0 9 9 4 0 0 1 6 5 3 5 0 2 8 5 0 0 0 0 0 0 0 0 2 0 8 9 5 4 2 6 5 6 3 0 0 0 0 0 0 2 1 1 1 1 6 6 5 3 2 8 4 4 1 2 0 0 0 0 0 0 2 2 6 1 6 7 2 2 2 5 2 4 1 7 1 0 0 0 0 0 2 3 4 0 2 4 1 8 2 0 1 8 1 5 6 6 9 8 2 0 2 7 7 8 4 7 4 4 4 0 3 6 4 0 1 0 5 6 0 0 0 2 6 3 4 5 2 5 7 J 6 1 ? 1 2 6 8 7 0 0 0 2 9 6 6 6 3 4 5 1 6 1 1 1 0 2 2 0 0 0 0 3 0 5 0 4 7 4 1 4 0 2 6 2 7 2 4 2 5 1 6 1 8 3 3 3 2 3 1 6 1 5 6 2 8 1 1 1 5 0 0 0 0 0 0 0 3 4 1 5 2 2 2 6 1 4 1 9 1 1 3 3 2 0 0 0 3 5 5 5 5 6 5 4 5 1 3 6 4 7 1 8 1 8 1 3 4 2 4 3 6 4 0 3 8 2 3 0 0 0 0 0 0 0 0 0 4 0 8 0 9 9 9 4 7 2 7 7 7 8 3 5 3 9 4 2 2 1 1 2 1 1 4 3 3 4 1 6 1 5 1 0 0 0 0 0 0 0 0 4 4 7 6 1 0 0 0 0 0 0 0 0 0 4 5 4 0 4 3 2 1 1 1 6 4 1 0 0 0 0 0 4 § 7 3 7 0 3 6 - . 1 8 9 1 0 0 0 0 0 0 4 7 8 7 2 5 2 1 1 3 9 9 2 0 0 0 0 0 4 9 2 7 3 7 3 6 1 5 1 5 1 4 1 4 1 4 1 6 1 4 1 4 1 4 19 . 3 2 4 0 4 1 2 5 2 8 2 7 2 0 1 7 1 5 1 6 1 5 1 3 . 5 1 1 6 1 9 9 8 4 6 8 3 5 2 3 8 2 0 0 0 0 5 2 4 9 4 7 3 5 3 4 3 1 1 8 1 2 6 8 1 0 0 5 3 2 9 2 8 3 5 1 9 1 4 3 1 0 0 0 0 0 5 4 4 9 4 2 4 1 0 0 0 0 0 0 0 0 0 55 2 7 3 0 2 3 1 2 5 3 0 0 0 0 0 0 5 8 2 3 4 2 3 2 2 7 1 5 1 3 5 1 0 0 0 0 5 9 3 3 2 6 1 8 4 1 0 0 0 0 0 0 0 6 1 9 7 5 6