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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 o f O t a g o , 1967 M.A., U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1969  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  t h e Department of Geography  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d :  THE  UNIVERSITY OF BRITISH April,  1975  COLUMBIA  In  presenting  this  an a d v a n c e d  degree  the L i b r a r y  shall  I  f u r t h e r agree  for  scholarly  by h i s of  thesis at  the U n i v e r s i t y  make  that  it  purposes  written  thesis  for  may  financial  is  __  jjjwj  %2£_  of  Columbia,  British  by  for  gain  Columbia  shall  the  requirements I  agree  r e f e r e n c e and copying  of  this  that  not  copying  or  for  that  study. thesis  t h e Head o f my D e p a r t m e n t  understood  of  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  of  for extensive  be g r a n t e d  It  fulfilment  available  permission.  Department  Date  freely  permission  representatives.  this  in p a r t i a l  or  publication  be a l l o w e d w i t h o u t  my  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  iii  ABSTRACT  The  first  o b j e c t i v e o f t h i s study 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 n e t snow  accumulation w i t h e l e v a t i o n over a mesoscale area o f 14 k m  2  on a w e s t c o a s t m i d l a t i t u d e m o u n t a i n .  o b j e c t i v e i s t o measure a n d d e s c r i b e s i m i l a r of  snow d e p o s i t i o n a f t e r e a c h s t o r m  The w i n t e r s s a m p l e d  a wide range o f p r o b a b l e is  second  variations  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 t h e snow i n p u t s y s t e m cycle.  The  of the hydrologic  (1969-70, 1970-71) r e p r e s e n t  conditions.  A related  goal  t h e development o f a c l i m a t o l o g y o f w i n t e r storms.  final  The  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 o v e r a  west coast m i d l a t i t u d e mountain a f t e r a storm. the d e t e r m i n i s t i c model which  Input t o  i s evolved i s r e s t r i c t e d  to  p r e c i p i t a t i o n and temperature  of  the mountain.  d a t a measured a t t h e base  A l l m e a s u r e m e n t s a r e made on Mount Seymour, B r i t i s h Columbia,  within a carefully  design u s i n g a double  structured experimental  stratified  random s a m p l i n g  Measurements a r e c o n f i n e d t o a p a r t l y segment o f c o n s t a n t are presented to  1260  aspect  and s l o p e .  f o r open a r e a s  m f o r 138  storms.  scheme.  forested terrain Precipitation  a t 12 e l e v a t i o n s f r o m  120  data m  T h e s e i n c l u d e d a t a f o r 82 snow  s t o r m s , where a d d i t i o n a l m e a s u r e m e n t s a r e made w i t h i n  iv  defined positions  o f the f o r e s t .  Frequent  n e t snow  a c c u m u l a t i o n m e a s u r e m e n t s a r e a l s o made o f t h e  snowpack.  Continuous t e m p e r a t u r e measurements a t s i x e l e v a t i o n s on a TV mast d e f i n e t h e t h e r m a l r e g i m e  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 a r e r e c o g n i s e d and 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 The because  first  objective  and  their  days.  cannot  e a s i l y be a c h i e v e d  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 b e t w e e n n e t snow  a c c u m u l a t i o n and e l e v a t i o n a r e n o t r e l i a b l e m i d l a t i t u d e mountain.  on a w e s t c o a s t  T h i s i s a consequence  of the  f o r m a t i o n o f a snow wedge on -the m o u n t a i n , whose shape slope i s l a r g e l y  and  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 , e x c e p t at t h e end o f t h e s e a s o n , o r a t e l e v a t i o n s , where m e l t p r o c e s s e s a r e i m p o r t a n t . accumulation i n the f o r e s t  low  Snow  can be e s t i m a t e d f r o m t h a t i n  t h e o p e n w i t h good p r e c i s i o n , p r o v i d e d t h e snowpack i s g r e a t e r t h a n 1 0 0 cm w a t e r  equivalent.  Snow d e p o s i t i o n f r o m e a c h 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 shape o f t h i s new  form.  The  new  snowlines  and  snow wedge a r e m a i n l y d e t e r m i n e d by  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 of the f r e e z i n g l e v e l . l e v e l among and w i t h i n m i d l a t i t u d e mountains.  Large f l u c t u a t i o n s  the  elevation  of the  freezing  storms a r e a f e a t u r e o f west c o a s t Summation o f snow d e p o s i t i o n  f r o m e a c h s t o r m d e f i n e s t h e t o t a l w i n t e r snow i n p u t t o t h e snowpack  (the second o b j e c t i v e ) .  This input also increases  V  with  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 ,  with  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 n e t snow a c c u m u l a t i o n . Contrary  to earlier  increases consistent input  findings, t o t a l winter p r e c i p i t a t i o n  l i n e a r l y with  e l e v a t i o n , w i t h no e v i d e n c e o f a  s t o r m maximum a t i n t e r m e d i a t e  elevations.  The  o f w a t e r by r i m e i s i n d e x e d , a n d f o u n d 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 t h e e f f i c i e n c y o f t h e s a m p l i n g n e t w o r k o f this  study are proposed. The c l i m a t o l o g y  of winter  storms  (the t h i r d  objective)  is  developed from s u r f a c e  synoptic  maps and u p p e r a i r d a t a  by  examining storm types,  t r a c k s , f r e e z i n g l e v e l s and  atmospheric f l u x e s of water vapour. o f t h e two s t u d i e d w i n t e r s climatology. providing  The d i f f e r e n t snow r e g i m e  i s explained  The r e l a t i v e  i n terms o f t h i s  importance o f storm type i n  s n o w f a l l i s a s s e s s e d f o r e a c h e l e v a t i o n on Mount  Seymour. Good a g r e e m e n t i s f o u n d when t h e d e t e r m i n i s t i c m o d e l , which i s developed t o estimate  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  with  o b j e c t i v e , i s t e s t e d by c o m p a r i n g  e l e v a t i o n as i n t h e f i n a l  simulated limits but  snow d e p o s i t i o n w i t h  about t h e p r e d i c t e d e s t i m a t e s  do n o t a p p e a r t o be s m a l l .  forest i s predicted changing w i t h  from t h a t  midlatitude  at i n t e r m e d i a t e  Confidence  are d i f f i c u l t  Throughfall  i n t h e open w i t h  of the seasonal  mountains i s l i k e l y  elevations.  to  assess,  o f snow i n t h e the r e l a t i o n s h i p s  e l e v a t i o n and s t o r m c h a r a c t e r i s t i c s .  i s p r e s e n t e d t h a t management coast  independent data.  Evidence  snow c o v e r on w e s t  t o be most e f f e c t i v e  CONTENTS  Abstract Contents List  of Tables  List  of Figures  List  of Appendices  List  o f Symbols  Acknowledgement s  CHAPTER 1  INTRODUCTION  1.1  Definitions  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 w e s t c o a s t m i d l a t i t u d e mountains•  1.2.2  Some p r o b l e m s i n snow h y d r o l o g y  1.3  Objectives of this  1.4  The p r e s e n t a t i o n o f t h i s  1.5  General relevance of this  CHAPTER 2  study study study  THE STUDY AREA  2.1  G e n e r a l l o c a t i o n o f Mount Seymour  2.2  General s y n o p t i c f e a t u r e s of w i n t e r weather  2.3  The l o c a l  2.4  Characteristics  setting o f t h e measurement  2.4.1  Hypsography  2.4.2  S l o p e and a s p e c t  area  2.4.3 2.5  Vegetation  Available  data  2.5.1  Climatic  2.5.2  Upper a i r d a t a  2.5.3  N e t snow a c c u m u l a t i o n a n d snowfall data  CHAPTER 3  data  PARAMETERS .MEASURED EXPERIMENTAL  3.1  3.2  3.3  AND  DESIGN  M e a s u r e m e n t o f snow d e p o s i t i o n 3.1.1  Method  3.1.2  Measurement  error  The t e m p o r a l s a m p l e 3.2.1  The s t o r m  3.2.2  The p e r i o d o f f i e l d  3.2.3  Nature  observations  o f w i n t e r s sampled  The s p a t i a l s a m p l e o f snow d e p o s i t i o n measurements 3.3-1  The s a m p l e p o p u l a t i o n  3.3.2  The s a m p l i n g  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 stratification)  3.3.5  S i z e o f sample i n t h e secondary straturn  scheme  3.4  Measurement o f r a i n f a l l  3-5  Measurement o f mixed r a i n / s n o w  3.6  Measurement o f rime  3-7  Measurement o f snow c o v e r  3.8  Measurement o f n e t snow  3-9  Measurement o f a i r t e m p e r a t u r e  events  accretion phenology  accumulation  viii  CHAPTER 4.1  4.2  4.3  4.4  4.5  5.2  NET SNOW ACCUMULATION  S n o w l i n e phenology4.1.1  Dates o f f i r s t the ground  4.1.2  Seasonal v a r i a t i o n of snowline  4.1.3  Season and d u r a t i o n  and l a s t  snow on  o f t h e snow  coyer  S e a s o n a l v a r i a b i l i t y o f t h e snowpack 4.2.1  Variability  o f snow c o u r s e r e c o r d s '  4.2.2  Variability  of field  Variations elevation  observations  o f n e t snow a c c u m u l a t i o n  4.3.1  Snow c o u r s e  4.3.2  Field  observations  4.4.1  Snow i n c l e a r i n g s  4.4.2  Snow i n t h e f o r e s t  4.4.3  Snow h o l l o w s  4.4.4  Wind  Snowpack  within  scour  density  4.5-1  S e a s o n a l and y e a r l y  4.5.2  Variations elevation  4.5.3  V a r i a t i o n s o f snow d e n i s t y the f o r e s t  5  with  observations  V a r i a t i o n s o f n e t snow a c c u m u l a t i o n the f o r e s t  CHAPTER 5.1  4  variations  o f snow d e n s i t y  with within  ESTIMATION OF NEW SNOW ACCUMULATION  Introduction Estimation elevation  o f new snow a c c u m u l a t i o n  5.2.1  Analysis o f data t h e snow wedge  5.2.2  Some i m p l i c a t i o n s  with•  ix  5.3  Factors wedge  5.4  E s t i m a t i o n of net the f o r e s t  5.5  Estimation elevation  5.6  6.2  6.3  6.4  snow  snow a c c u m u l a t i o n w i t h i n  o f snowpack d e n s i t y  with  Conclusions  CHAPTER 6 6.1  c o n t r o l l i n g th.e shape of. t h e  WINTER P R E C I P I T A T I O N AND  SNOW DEPOSITION  Precipitation 6.1.1  V a r i a t i o n of t o t a l w i n t e r precipitation•with elevation  6.1.2  Comparison w i t h other  6.1.3  Winter 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 longer 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 of storm with elevation  local  studies  precipitation  Snow p h e n o l o g y 6.2.1  Dates of f i r s t  6.2.2  S e a s o n a l v a r i a t i o n o f new  6.2.3  Snow l i n e s  on  and  last  snowfall snowfall  trees  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 with elevation  6.3.2  I m p o r t a n c e o f snow d e p o s i t i o n winter precipitation  6.3-3  V a r i a t i o n o f s t o r m snow with elevation  6.3-4  A q u a l i t a t i v e m o d e l o f snow d e p o s i t i o n f r o m a s t o r m on a w e s t c o a s t m i d l a t i t u d e mountain  Rime a c c r e t i o n 6.4.1  Results  6.4.2  Rime on  trees  snow  deposition to  deposition  X  6.4.3 6.5  Water e q u i v a l e n t o f a c c r e t e d rime  Conclusions  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 o f snow d e p o s i t e d a f t e r e a c h 7.2.1  Method o f c a l c u l a t i o n  7.2.2  Results  7.3  Reduction o f the sampling  7.4  Conclusions  CHAPTER 8.1  8  network  CLIMATOLOGY OF SNOWSTORMS  Synoptic features of winter  storms  8.1.1  Winter storm  tracks  8.1.2  Frequency  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  o f storm  of winter  types  8.2  Freezing levels  8.3  The f l u x o f a t m o s p h e r i c w a t e r v a p o u r winter  8.4  storms during  8.3.1  Data and method o f c o m p i l a t i o n  8.3-2  Results  Conclusions  CHAPTER 9.1  9  PREDICTION OF SNOW DEPOSITION  A proposed model <  9.2  storm  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 elevation 9-2-1  O r o g r a p h i c component o f precipitation  9-2.2  Empirical prediction  equations  xi  9.2.3 9.3  More t h e o r e t i c a l  approaches  P r e d i c t i o n o f new  snowlines  9.3.1  Prediction  equations  9.3.2  P r e d i c t i o n of storm f r e e z i n g  9.4  P r e d i c t i o n of the equivalent  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 9.5.1 Simple cases 9.5.2  9.6  9.7  Complex  levels  elevation with'elevation  cases  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  Preliminary  equations  9.6.2  The e l e v a t i o n - f o r e s t  9.6.3  Improvement o f p r e d i c t i o n  prediction  strata interaction equations  Adequacy o f t h e model 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 t h e new snow wedge f o r a s t o r m  9-7.2  A t e s t of the model a g a i n s t storm data  9.7.3  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  CHAPTER 10  independent  DISCUSSION  10.1  Main  10.2  Improvements i n p r e c i s i o n o f t h e model  10.3  Extrapolation  10.4  Extensions to this  References Appendices  achievements  of t h i s  study  of the model t o o t h e r areas study  XI  L I S T OF TABLES  S l o p e and a s p e c t o f e l e v a t i o n b a n d s o f t h e 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 t e r r a i n segment  of clearings i n the  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 m e t e r s ) a t 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 Sample s i z e r e q u i r e d t o e s t i m a t e mean snow d e n s i t y  population  Sample s i z e r e q u i r e d t o e s t i m a t e mean snow d e p t h  population  S t a t i s t i c s • o f l a r g e samples o f r a i n f a l l i n s e l e c t e d open a r e a s Mean, s t a n d a r d d e v i a t i o n a n d 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 monthly water e q u i v a l e n t ( c m ) Mount Seymour snow c o u r s e 1969-70  }  Summary s t a t i s t i c s o f w a t e r e q u i v a l e n t ( c m ) , on A p r i l 1, f o r p e r i o d 196O-.7O, N o r t h S h o r e M o u n t a i n snow c o u r s e s R a t e s o f change o f snow a c c o m m o d a t i o n w i t h elevation. Some e x a m p l e s r e p o r t e d i n t h e l i t e r a t u r e , North America Mean w a t e r e q u i v a l e n t i n open a r e a s c o m p a r e d w i t h mean w a 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 - results of " t " test C h a r a c t e r i s t i c s , o f west coast m o u n t a i n s • c h o s e n as e x a m p l e s  midlatitude  XI1  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 o f snowpack w a t e r 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 b a s e d on a c c u m u l a t i o n i n open a r e a s Variation of t o t a l winter precipitation elevation  with  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 o f n e w l y 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, a t 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 t h e N o r t h Shore Mountains Summary o f s t o r m 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 1 9 6 9 - 7 0 , 1970-71 F r e q u e n c y o f s t o r m s d e p o s i t i n g snow a t e a c h s a m p l i n g s i t e , w i n t e r s 1969-70, 1970-71 Percentage 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 a t e a c h e l e v a t i o n , open a r e a s , w i n t e r s 1 9 6 9 - 7 0 , 1970-71 Amount o f r i m e 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 a b o v e t h e snow s u r f a c e , 6 December 1970 - 31 May 1971 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 Number o f s t o r m s where a d j a c e n t e l e v a t i o n s a n d f o r e s t s t r a t a h a d snow d e p o s i t i o n means t h a t w e r e h o m o g e n e o u s , a t t h e 95 p e r c e n t confidence l e v e l ( r e s u l t s o f Duncans New M u l t i p l e Range Test) E x a m p l e s o f t h e t o t a l mas.s o f snow d e p o s i t e d on t h e Mount Seymour t e r r a i n segment f r o m a s t o r m (.Storm 3 0 , w i n t e r 1969-70) Correlation matrices f o r p r e c i p i t a t i o n e l e v a t i o n s , w i n t e r s 1969-70-* 1970-71  a t 12  Influence of s i m p l i f i c a t i o n of the experimental 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 o f snow d e p o s i t e d on t h e t e r r a i n segment  xiv  8.1  Percentage, frequency o f storm types f o r a l l s t o r m s , a n d f o r -snow s t o r m s , w i n t e r s -  3 9 6 9 - 7 0 , 1970-71  8.2  Percentage frequency o f geostrophic 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 1 9 6 9 - 7 0 , 197.0-71  8.3  P e r c e n t a g e o f snow d e p o s i t i o n ( w a t e r 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  P e r c e n t a g e o f snow d e p o s i t i o n ( w a t e r 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 w a t e r e q u i v a l e n t ) p e r type o f storm a t 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 H a r d y ( i n g e o p o t e n t i a l m e t e r s ) a n d 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 o f mean f r e e z i n g l e v e l o f snow storms w i t h s y n o p t i c storm type  9.1  Regression equations 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 t h e b a s e o f t h e m o u n t a i n  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 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 a n d v a r i a b l e s from radiosonde data  9.3  Simple l i n e a r r e g r e s s i o n equations 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 o f r a d i o s o n d e a s c e n t s a t 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 b e t w e e n snow i n f o r e s t s t r a t a a n d i n open a r e a s  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 b e t w e e n snow d e p o s i t i o n i n open a n d 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 b e t w e e n 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 a n d i n open a r e a s  9.7  N a t u r e o f 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 h e snow d e p o s i t i o n f r o m a s t o r m a v e r a g e d o v e r t h e t e r r a i n segment  deposition  L I S T OP APPENDICES  Details  of the forest  c o v e r on Mount Seymour  Al  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 t h e t e r r a i n , segment  A2  Photographs o f t h e 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  Results of p i l o t Bl  B2  studies with large  Statistics of pilot s a m p l e s o f new snow the f o r e s t , w i n t e r Statistics of pilot o f new snow d e p t h  samples  study with large density throughout 1968-69 s t u d y w i t h l a r g e samples  Snow c o v e r p h e n o l o g y Summary s t a t i s t i c s o f t h e snowpacks o f N o r t h M o u n t a i n snow c o u r s e s List  o f storms, winters  Winter  1969-70,  Shore  1970-71  precipitation  Fl  Variation of winter precipitation e l e v a t i o n f o r e a c h s t o r m (mm)  with  F2  Mean w i n t e r p r e c i p i t a t i o n a t V a n c o u v e r and a t 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 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 The d e n s i t y  o f newly f a l l e n  snow  Summary o f snow c r y s t a l t y p e f r o m s t o r m snowfall E x a m p l e s o f snow d e p o s i t i o n , t h e t e m p e r a t u r e 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 t h e f l u x o f w a t e r v a p o u r f o r e a c h o f t h e more common snow s t o r m t y p e s  xvii  L I S T OF  Frontispiece  :  FIGURES  Snow c o y 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  Fig.  1.1  Mount Seymour, t h e w e s t 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  Fig.  1.2  Two s y s t e m s o f 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  Fig.  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  Fig.  2.1  G e n e r a l l o c a t i o n o f Mount  Fig.  2.2  The l o c a l  Fig.  2.3  The t e r r a i n segment c h o s e n f o r t h i s  Fig.  2.4  Views o f t h e chosen t e r r a i n  Fig.  2.5  Hypsographic 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 basins  Fig.  2.6  S l o p e and a s p e c t o f t h e c h o s e n 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  Fig.  2.7  D i s t r i b u t i o n of v e g e t a t i o n type w i t h elevation  Fig.  2.8  Canopy c l o s u r e o f t h e f o r e s t sampling s i t e  F i g . 3.1 Fig.  3.2  Seymour  setting study  segment  at each  P e r c e n t a g e measurement e r r o r f o r s p e c i f i c mass o f new snow d e p o s i t e d D i f f e r e n c e s f r o m n o r m a l (.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 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  xviii  F i g . 3.3  D e p a r t u r e f r o m n o r m a l o f t h e mean 700. mb h e i g h t ( d e c a m e t e r s ) f o r each-month, o f w i n t e r 1969-70,. w i n t e r 197.0-71  Fig.  3.4  P r o b a b i l i t y o f 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 a t H o l l y b u r n R i d g e , 920 m, and V a n c o u v e r C i t y , n e a r s e a l e v e l  Fig.  3.5  M o n t h l y w a t e r e q u i v a l e n t a t Seymour M o u n t a i n and G r o u s e M o u n t a i n - s n o w c o u r s e s f o r w i n t e r s 1969-70, 1970-71 compared w i t h t h e l o n g t e r m records  Fig.  3.6  P r o b a b i l i t y o f recording greater than given w a t e r e q u i v a l e n t on A p r i l 1 a t Seymour m o u n t a i n a n d G r o u s e M o u n t a i n snow c o u r s e s  Fig.  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 u s e d t o e s t i m a t e snow d e p o s i t i o n o v e r t h e t e r r a i n segment  Fig.  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 s t o r m s on CBUT-TV t o w e r a t 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 t h e f o r e s t a t 970 m  Fig.  4.1  E l e v a t i o n a l c o v e r a g e o f new snow a t e n d o f e a c h s t o r m , w i n t e r 1969-70  Fig.  4.2  Seasonal variations, o f snowlines winter  1969- 70 Fig.  4.3  E l e v a t i o n a l c o v e r a g e o f new snow a t e n d o f e a c h s t o r m , w i n t e r 1970-71  Fig.  4.4  Seasonal v a r i a t i o n o f snowlines, w i n t e r  1970- 71 Fig.  4.5  Snow c o v e r p h e n o l o g y , w i n t e r  1969-70  Fig.  4.6  Snow c o v e r phenology., w i n t e r  1970-71  Fig.  4.7  R e l a t i o n s h i p between d u r a t i o n o f complete snow c o v e r a n d w i n t e r maximum o f snowpack water equivalent  Fig.  4.8  Snowpack w a t e r e q u i v a l e n t i n open a n d i n the f o r e s t s t r a t a f o r various e l e v a t i o n s , w i n t e r 1969-70  xix  Fig.  4.9  Fig.. 4.10  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 open in. 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  and  V a r i a t i o n o f snowpack w a 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 t h e f i r s t day o f e a c h m o n t h , open a r e a s , f o r w i n t e r s 1969-70  and 1970-71  Fig.  4.11  Snow h o l l o w s i n m i d - s e a s o n and season  Fig.  4.12  Wind s c o u r a b o u t t r e e s d u r i n g M a r c h a t 1260 m  Fig.  4.13  D e n s i t y o f snowpack i n open a r e a s i n w i n t e r 1969-70 and w i n t e r 1970-71  Fig.  4.14  S e a s o n a l v a r i a t i o n i n a v e r a g e snowpackd e n s i t y , Mount Seymour s n o w c o u r s e C1969-70). and f o r o t h e r a r e a s  Fig.  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 o f snow wedge  Fig.  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 o f water e q u i v a l e n t at the upper sampling l i m i t on t h e m o u n t a i n  Fig.  5.3  S l o p e o f s e c t i o n s 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 o f 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 section  Fig.  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 o f e l e v a t i o n o f the snowline  Fig.  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 ,  Fig.  5-6  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 i n c l e a r i n g s f r o m t h a t i n open a r e a s  Fig.  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 canopy f r o m t h a t i n open a r e a s  late i n 1971  beneath-the  XX  Fig.  6.1  Variation of winter precipitation elevation  Fig.  6.2  Variations of p r e c i p i t a t i o n with elevation f o r s t o r m s o f s e l e c t e d months  Fig.  6.3  E l e v a t i o n a l c o v e r a g e o f snow o n t r e e s , w i n t e r 1969-70  Fig.  6.4  E l e v a t i o n a l c o v e r a g e o f snow on t r e e s , w i n t e r 1970-71  Fig.  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  Fig.  6.6.  Fig.  6.7  Two e x a m p l e s o f d e p o s i t i o n f r o m s t o r m s w h i c h g a v e snow a t h i g h e r e l e v a t i o n s onlyTwo e x a m p l e s o f d e p o s i t i o n f r o m s t o r m s w h i c h gave snow a t h i g h e r a n d i n t e r . mediate e l e v a t i o n s  Fig.  6.8  Deposition elevations  from a storm w i t h  Fig.  6.9  Deposition o f -snow  f r o m a s t o r m w i t h l a r g e amounts  Fig.  6.10  The a d d i t i v e e f f e c t from each storm  Fig.  6.11  S c h e m a t i c d i a g r a m o f snow d e p o s i t i o n f r o m a s t o r m on a west c o a s t m i d l a t i t u d e m o u n t a i n  with  snow t o l o w  o f snow d e p o s i t i o n  (a) Storm w i t h r e l a t i v e l y level (b) C o m p o s i t e s t o r m w i t h freezing level  constant f r e e z i n g fluctuating  Fig.  6.12  Rime d e p o s i t s a c c r e t e d o n t o 0 . 5 cm d i a m e t e r r e c e p t o r stake and t o t r e e s  Fig.  6.13  H o r i z o n t a l l e n g t h o f r i m e 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 a n d d i r e c t i o n o f g r o w t h , 6 December 1970 31 May 1971  xxi  Fig.  7-1  Homogeneity- o f 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 sampling s i t e s , as a f u n c t i o n o f t h e e l e v a t i o n i n t e r v a l between sampling s i t e s  Fig.  7.2  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 s e g m e n t , w i n t e r s 1969-70,. 1970-71  Fig.  8.1  Generalised  tracks of storms,  1969-70, 1970-71  winters  F i g . 8.2  I n f l u e n c e o f storm type i n determining 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 ) a t each, e l e v a t i o n , w i n t e r 1969-70  F i g . 8.3  I n f l u e n c e o f storm type i n determining 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 ) a t each, e l e v a t i o n , w i n t e r 1970-71  F i g . 8.4  C o m p a r i s o n o f t h e d i s t r i b u t i o n s o f 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 t h e w i n t e r s 1969-70, 1970-71  F i g . 8.5  Mean m o n t h l y 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 , Port Hardy, w i n t e r s  1969-70, 1970-71  F i g . 8.6  Mean m o n t h l y z o n a l f l u x e s d u r i n g  F i g . 8.7  Mean m o n t h l y m e r i d i o n a l f l u x e s d u r i n g storms  snowstorms snow-  P r o p o s e d m o d e l o f snow d e p o s i t i o n i n open a r e a s from a s t o r m on west c o a s t m i d l a t i t u d e mountain Fig.  9.1  (a) S t o r m w i t h r e l a t i v e l y freezing level (b) A c o m p o s i t e s t o r m w i t h freezing level All  constant fluctuating  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 f r o m a s t o r m 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 a t t h e base o f the mountain F i g . 9.2  xxii  Pig.  9.3  R e l a t i o n s h i p s b e t w e e n new s n o w l i n e s a n d mean s t o r m f r e e z i n g l e v e l  Fig.  9.k  R e l a t i o n s h i p between t h e e q u i v a l e n t . . e l e v a t i o n and mean s t o r m f r e e z i n g l e v e l  Fig.  9.5  R e l a t i o n s h i p b e t w e e n t h e r a t i o R and t h e ratio I. A l l terms are d e f i n e d i n t h e text  Fig.  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 o f 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 o f snow d e p o s i t i o n i n open a r e a s  Fig.  9.7  An e x a m p l e o f t h e 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 h e new snow wedge f o r a storm  Fig.  9.8  T e s t o f t h e m o d e l a b o u t an i n d e p e n d e n t d a t a s e t f o r t h e w i n t e r 196:8-69  Fig.  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 , w i n t e r s  1969-70, 1970-71  xxiii  LIST  OP  SYMBOLS  cA  =  continental  Arctica i r  C  =  v a l u e o f maximum d u r a t i o n o f snow c o v e r  D  =  d u r a t i o n o f complete  DA  =  p o s t f r o n t a l wind d i r e c t i o n  DB  =  p r e f r o n t a l wind d i r e c t i o n  e  =  base o f n a t u r a l l o g a r i t h m  E  =  desired  confidence  snow c o v e r  (days)  (days)  (degrees) (degrees)  limits  F  M  =  m e r i d i o n a l atmospheric water vapour at a s i n g l e l e v e l (gm/cm/mb/sec)  F  Z  =  z o n a l atmospheric water vapour single level (gm/cm/mb/sec)  g  =  acceleration  h  =  number o f s a m p l i n g  H  =  elevation  (m)  =  elevation  o f complete  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 t h e most r a p i d o f change o f snow c o v e r d u r a t i o n (m)  H  e  =  t h e e q u i v a l e n t e l e v a t i o n (m), i . e . t h e l o w e s t e l e v a t i o n on t h e m o u n t a i n w h e r e s t o r m snow d e p o s i t i o n equals 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 s t o r m f r e e z i n g  Hj_  =  elevation  o f t h e i n c o m p l e t e s n o w l i n e (m)  H  0  =  elevation  o f t h e i n c o m p l e t e new s n o w l i n e  Hi  =  elevation  of top of mountain  i  =  number o f r e p l i c a t i o n s  H  c  due t o g r a v i t y  flux  f l u x at a  (cm/sec ) 2  site  new s n o w l i n e  level  (m)  (m) rate  (m)  (m)  xxiv  unit, v e c t o r d i r e c t e d t o t h e east number o f hours wh.en t h e 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 t h e length, o f the storm i n hours u n i t vector d i r e c t e d t o the north constant r e l a t e d t o r a t e o f i n c r e a s e o f snow cover d u r a t i o n w i t h e l e v a t i o n maritime A r c t i c a i r maritime P o 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 e q u i v a l e n t o r kg/m ) 2  s p e c i f i c new snow mass d e p o s i t e d at e l e v a t i o n H, where H > H . U n i t s are mm water e q u i v a l e n t o r kg/m e  2  s p e c i f i c new snow mass d e p o s i t e d a t e l e v a t i o n H, where Hp < H < H . U n i t s a r e mm water e q u i v a l e n t or kg/m e  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 (mm water e q u i v a l e n t o r kg/m ) 2  storm snow d e p o s i t i o n averaged over t h e t o t a l a r e a o f t h e t e r r a i n segment (mm water e q u i v a l e n t ) s p e c i f i c new snow mass d e p o s i t e d i n open areas (mm water e q u i v a l e n t o r kg/m ) 2  s p e c i f i c new snow mass d e p o s i t e d i n a f o r e s t stratum (mm water e q u i v a l e n t o r kg/m ) 2  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 t h e w i n t e r  (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 t h e mountain from each storm (mm)  XXV  p  oro  P  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  =  =  p r e s s u r e a t t h e surface*! . (jab)  P(l20).  =  p r e c i p i t a t i o n (mm) a t t h e b a s e e l e v a t i o n H - 120 m  q  =  s p e c i f i c humidity  s  (.mm)  of the mountain,  (gm/kg)  Q  m  =  vertically integrated meridional flux of atmospheric water vapour (gm/cm/sec)  Q  z  =  v e r t i c a l l y integrated zonal f l u x of atmospheric water vapour (gm/cm/sec)  R  =  ratio M ( H j ) / P ( H j ) w h e r e Hj. i s e l e v a t i o n a t t h e top o f t h e mountain  s  =  number o f s e c o n d a r y  SI  =  stability  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 o f new snow d e p t h  2  =  e s t i m a t e o f p o p u l a t i o n v a r i a n c e o f new snow density  t  =  value of Students t d i s t r i b u t i o n  T  =  time-  T(H)  =  temperature  u  =  z o n a l component o f w i n d v e l o c i t y  v  =  m e r i d i o n a l component o f w i n d v e l o c i t y  (cm/sec)  V  =  maximum w i n d v e l o c i t y  (cm/sec)  w  =  w a t e r e q u i v a l e n t o f snow p a c k  W  =  p r e c i p i t a b l e water  W  =  mean w i n t e r p r e c i p i t a b l e w a t e r  X  =  freezing  Y  =  freezing level  S  z  Sy  strata  index  (°C) a t e l e v a t i o n H (cm/sec)  during a storm (cm)  (mm)  l e v e l a t P o r t Hardy  (mm) (geopotential  on Mount Seymour  (m)  meters)  xxvi  z  =  new -snow .depth, m e a s u r e d v e r t i c a l l y  a  =  probability  B  =  v e r t i c a l wind shear  Y  =  d e n s i t y of newly  =  variance of population  =  snow a c c u m u l a t i o n i n open a r e a s  0 0  2  o f c o m m i t t i n g a Type T (cm/sec/100  fallen  snow  (m), error  m)  (kg/m ) 3  (cm)  xxvii  A C KN.O.WLED.GEMEN T.S  A g r e a t number o f p e o p l e this  study, both  academically  h a v e g i v e n me  and  g r a t e f u l to the f o l l o w i n g people me  and  in  b e a u t i f u l weather, but  I  T e r r y Day,  Hok  Woo,  P a u l i n e S m i t h and  J.R.  research  and  f i n a n c e on my  t h e s i s committee:  This  study  g i v e n me  by  was  and  Oke, the  efforts  to Drs. M.  B.  l a t e W.W.  to  d u r i n g my  attain  Goodell, J.  Hay,  Jeffrey.  the f i n a n c i a l  t h e C a n a d i a n S c h o l a r s h i p and me  the  especially,  C h u r c h and  made p o s s i b l e by  Committee, which supported  Tustin,  Ames.  b e h a l f , and  Schaerer  snow':  I a n M c Q u i l l a n , Ken  Mackay f o r h i s i n t e r e s t , and  t o g e t h e r w i t h P.  by  f r e q u e n t l y accompanied  a l s o a c k n o w l e d g e t h e a s s i s t a n c e g i v e n by  M a t h e w s , 0. S l a y m a k e r , T.  tance  most  Steve Evans, L a r r y Minnock,  Cliff  members o r a s s o c i a t e s o f my  W.  who  I am  o f t e n i n t h e c o l d , wet  McDonald, John Bottomley,  M i k e and  Dr.  i n the f i e l d .  a s s i s t e d w i t h m e a s u r e m e n t s on Mount Seymour, s o m e t i m e s  Peter Lewis, Bob  assistance i n  Fellowship  s t a y i n Canada,  the Department of Geography, U n i v e r s i t y of B r i t i s h  w h i c h p u r c h a s e d most o f t h e i n s t r u m e n t a t i o n . the w i l l i n g  co-operation  shown me  Mount Seymour P r o v i n c i a l P a r k , who  by  assis-  I  Columbia  appreciate  the personnel  on o c c a s i o n s  and  of  also  the helped  xxviii  dig at  o u t my- v e h i c l e , f r o m t h e snow;. 1260  Regular  measurements  m w o u l d have b e e n i m p o s s i b l e w i t h o u t  of the s k i c h a i r l i f t  operators  were some o c c a s i o n s when t h e y chair l i f t  f o r me  alone.  The  the  generosity  on Mount Seymour; t h e r e  continued  or s t a r t e d  co-operation of the  the Canadian  B r o a d c a s t i n g Corporation i s a p p r e c i a t e d ; they  allowed  o f t h e i r TV  collection  t r a n s m i s s i o n t o w e r and  of temperature The  fearless  ensured the  d a t a , and efforts  o f t e n warmed me  up w i t h h o t  o f s t e e p l e j a c k s L e w i s and  t h a t t h e t h e r m i s t o r c a b l e was  coffee.  Church  securely placed  on  tower. Finally  my  garage f o r  use  I r e c o g n i s e the tremendous c o n t r i b u t i o n of  w i f e , J o a n n a , t o many a s p e c t s  reliable  field  a typist  and  of t h i s  assistant, often i n miserably  completed.  As  a  cold conditions,  e d i t o r , a dogged c h a r t r e a d e r , and  s i a s t when I n e e d e d e n c o u r a g e m e n t , she s t u d y was  study.  an  enthu-  ensured-, t h a t  this  1  CHAPTER 1  1.  INTRODUCTION Many a s p e c t s  repeatedly still  o f t h e h y d r o l o g i c a l c y c l e have b e e n  d o c u m e n t e d and a r e w e l l u n d e r s t o o d , b u t t h e r e  exists a serious  variations tainous  terrain.  V a r i a t i o n s o f s n o w f a l l over a few square  t h e key t o many-aspects o f h y d r o l o g y ,  along with r e l a t e d meteorological  received  little  The  about mesoscale  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-  kilometres•are these,  lack of information  but  v a r i a t i o n s , have'  attention.  mesoscale i s the focus  of this  study.  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 a r e m e a s u r e d o v e r an a r e a o f 14.3  km  2  at twelve  e l e v a t i o n s f r o m 120 m t o 1260 m i n a  f o r e s t e d e n v i r o n m e n t on a w e s t c o a s t All  mountain.  f i e l d m e a s u r e m e n t s a r e made w i t h i n a s t r u c t u r e d e x p e r i -  mental design. replications  In this  of simple  over remote r e c o r d i n g . logistically (Fig. in  midlatitude  1.1),  confined  severe f i e l d  environment  large  manual measurements a r e p r e f e r r e d For t h i s reason,  measurements a r e  t o a s i n g l e m o u n t a i n , Mount Seymour  w h i c h i s e a s y o f a c c e s s by r o a d  and c h a i r l i f t  a l l weather. Snow d e p o s i t i o n a n d r a i n f a l l  e a c h s t o r m f o r two c o n s e c u t i v e  m e a s u r e m e n t s a r e made a f t e r  winters  (1969-70,  1970-71)•  2 V i e w l o o k i n g N.E. across Burrard I n l e t  V i e w l o o k i n g S.W. t o w a r d s t h e Fraser River d e l t a from e l e v a t i o n 1200 m on Mount Seymour  Fig,  l.l  Mount S e y m o u r , t h e w e s t coast m i d l a t i t u d e mountain chosen f o r t h i s study  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 w i n t e r s produced accumulation  1.1  markedly  i n t e r e s t i n g i n that these  different  snow d e p o s i t i o n and  regimes.  Definitions Mount Seymour i s an e x a m p l e o f a "west c o a s t m i d l a t i t u d e  mountain". lines  T h i s i s d e f i n e d as one ©n w h i c h  f r o m most w i n t e r s t o r m s  i t s base.  o c c u r a t some e l e v a t i o n  above  Such m o u n t a i n s a r e t y p i c a l o f t h e w e s t c o a s t o f  l a n d masses w i t h i n t h e b e l t Those o f w e s t e r n and  t h e new snow-  of the d i s t u r b e d w e s t e r l i e s .  North America,  Scotland, NorwayNew  Zealand  C h i l e a r e t h e most n o t a b l e . " The t e r m "snow d e p o s i t i o n " r e f e r s t o t h e amount o f new  snow p r e s e n t on t h e g r o u n d  a t t h e end o f e a c h  storm.  It  r e p r e s e n t s t h e amount o f new snow e n t e r i n g s t o r a g e as p a r t o f t h e s e a s o n a l snowpack.  I t does n o t i n c l u d e new  snow  w h i c h may h a v e m e l t e d b e f o r e t h e end o f t h e s t o r m . "Snow a c c u m u l a t i o n " i s u s e d it  r e f e r s t o the water  i n t h e customary  sense;  e q u i v a l e n t o f t h e 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 t h e e n d p r o d u c t  f o r any p o i n t •  i n t i m e o f t h e sum o f snow d e p o s i t i o n m i n u s snow m e l t . F o r t h i s r e a s o n i t more s t r i c t l y snow a c c u m u l a t i o n " . seasonal i n nature.  c a n be r e f e r r e d t o as " n e t  The snow c o v e r o f t h i s  study i s  4  "winter"  i s used t o designate  1 t o May 31.  This  i s much l o n g e r  the.period  from October  than t h e customary  d e f i n i t i o n , b u t i s u s e d h e r e b e c a u s e a l m o s t a l l ..snow f a l l s b e t w e e n t h e s e d a t e s on t h e N o r t h S h o r e M o u n t a i n s . "Prediction" is,  i s used i n the s t a t i s t i c a l  sense.  no m a t t e r how many t i m e s an e v e n t i s p r o c e s s e d u n d e r a  given  s e t o f i n v a r i a n t c o n d i t i o n s , t h e same outcome  always r e s u l t . meteorological  forecast  sense i n t h a t t h e p r e d i c t i o n equastudy are  designed t o " f o r e c a s t " a f t e r a storm event. given  That' i s ,  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 d a t a a t t h e base o f a  west coast  midlatitude  snow d e p o s i t i o n the  will  The t e r m p r e d i c t i o n i s n o t u s e d i n t h e  t i o n s d e v e l o p e d f o r snow d e p o s i t i o n i n t h i s  storm.  mountain f o r a storm, the r e s u l t a n t  on t h e m o u n t a i n i s t o be p r e d i c t e d  Hindsight  that  storage  after  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 in  That  branches of hydrology  o f w a t e r as snow a l l o w s  more)'.time . f o r  prediction of runoff.  1.2 1.2.1  Review Previous  studies  on w e s t c o a s t  o f snow d e p o s i t i o n  midlatitude  and a c c u m u l a t i o n  mountains  Few s t u d i e s h a v e b e e n made o f snow d e p o s i t i o n a t i o n s w i t h e l e v a t i o n on a w e s t c o a s t The U.S. Army  midlatitude  (1956) h a s c a r r i e d o u t t h e most  vari-  mountain.  extensive  5  analyses  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 , b u t m e a s u r e d  snowfall at r e l a t i v e l y report  examined s e v e r a l a r e a s ,  Snow L a b o r a t o r y  I t c o v e r s 29 k m , i s h e a v i l y 2  of seasonal  e l e v a t i o n have been r e p o r t e d  relevant forested  precipi-  snowpack v a r i a t i o n s  with  f r o m C a l i f o r n i a b y C o u r t (1963)  A n d e r s o n and West (1965), a n d f r o m 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 discusses  snowfall  versity  Only t h e l a s t  simulation  author  Woo (1972)  o f snow s t o r a g e  and melt  on a s m a l l mountain catchment a t t h e U n i -  of B r i t i s h  metres t o t h e east  Columbia Research F o r e s t , o f Mount Sey-mour.  deterministic part  This  a few k i l o study  extends  o f Woo's m o d e l b y i n v e s t i g a t i n g a  w i d e r range o f e l e v a t i o n s detailed  (1969).  over a range o f e l e v a t i o n s .  produced a numerical  water r e l e a s e  and s t o r m s , a n d b y t a k i n g more  s p a t i a l measurements w i t h i n t h e f o r e s t .  Review o f t h e s e s t u d i e s i s known o f s e a s o n a l  indicates that  midlatitude  mountains.  i s known o f snow d e p o s i t i o n 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 o r d e p o s i t i o n a considerable  little  detail  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 t h e  m e s o s c a l e on w e s t c o a s t  but  Basin  temperatures close t o f r e e z i n g .  Other s t u d i e s  the  but the Willamette  of. t h e two a r e a s a r e s i m i l a r w i t h h e a v y  t a t i o n and w i n t e r  has  comprehensive  e x t e n d s f r o m an e l e v a t i o n o f 610 m t o 1680 m. T h e  climates  and  This  i n t h e C a s c a d e Range i s t h e most  t o Mount Seymour. and  few p o i n t s .  Even l e s s  Mesoscale  studies  a r e few i n h y d r o l o g y ,  number- e x i s t i n g l a c i o l o g y .  Some  6  relate  t o west coast 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  19&5»  t o Mount Seymour ( e . g . t h e B l u e G l a c i e r , L a C h a p e l l e -  South  1.2.2  C a s c a d e G l a c i e r , M e i e r and T a n g b o r n 1965)•  Some p r o b l e m s i n snow h y d r o l o g y P r e s e n t methods o f e s t i m a t i n g snowpack  i n mountain areas are l i m i t e d . e s t i m a t e s are based  accumulation  In North America,  on d a t a f r o m snow c o u r s e s , b u t  g i v e o n l y an i n d e x o f t h e snowpack f o r an a r e a . of disadvantages  follow.  f o r e x t r e m e e v e n t s , and  these A number  Snow c o u r s e d a t a do n o t  reveal interaction effects.  readily  Their index value often  i s s u b j e c t t o unknown change  a l t e r a t i o n of the surrounding environment. are u s u a l l y  most  s i t e d i n c l e a r i n g s , which  For example, Court  their actual elevation. of r e c o r d are necessary snow m e l t index.  800  snow  spatial courses  m higher  than  I n a d d i t i o n , a number o f y e a r s to e s t a b l i s h the r e l a t i o n s h i p  s t r e a m f l o w and t h e b e h a v i o u r o f t h e snow Many c o u n t r i e s c a n n o t  afford this  f o r d e s i g n o r 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 schemes.  between  course  time l a g ,  because e s t i m a t e s of stream f l o w are o f t e n wanted  or i r r i g a t i o n  they  a r e a r e a s o f maximum  (1963), f o u n d  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 of s i t e s  through,  Because  accumulation, t h e i r values are b i a s e d estimates of averages.  fails  immediately  stations  7  Most o f t h e s e d i s a d v a n t a g e s tical  estimates o f t o t a l water  areeliminated i f s t a t i s -  s t o r e d as snow a r e b a s e d  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 . the approach Union  i n Japan  ( e . g . Uryvaev  Ce.g- H i g a s h i 1 9 5 8 ) , i n t h e S o v i e t e t a l 1965)* and'more r e c e n t l y  U.S.A. by B a r t o s a n d R e c h a r d spatial variability  Such has been  ( 1 9 7 3 ) , b u t t h e enormous,  o f . t h e snowpack s o m e t i m e s makes  sampling i m p r a c t i c a l over l a r g e mountain areas.suggests  i n the  such  This  a n e e d t o d e v e l o p r e l a t i o n s h i p s b e t w e e n snow  accumulation  and t o p o g r a p h y ,  s o t h a t t h e number o f m e a s u r e -  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  estimates  of  A logical  t o t a l water  first  storage are s t i l l  step i n t h i s  approach  possible.  i s t h e development o f r e l a t i o n -  s h i p s b e t w e e n snow a c c u m u l a t i o n a n d e l e v a t i o n . T h e r e i s an a l t e r n a t i v e a p p r o a c h . of  water  Good e s t i m a t e s  s t o r e d i n m o u n t a i n s n o w p a c k s may come w i t h t h e  development o f t h e o r e t i c a l models d e s c r i b i n g  deposition,  a c c u m u l a t i o n a n d a b l a t i o n o f t h e 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 a r e f e w o f t h e s e i n snow h y d r o l o g y . Jakhelln to  (1965) i n Norway h a s r e l a t e d  variations  i nfreezing level.  snowpack  accumulation  A n d e r s o n a n d 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 m o d e l (SSARR) t o generate  snow a c c u m u l a t i o n a n d r u n o f f f o r a w e s t c o a s t m i d -  l a t i t u d e mountain, investigations.  based  on d a t a f r o m t h e U.S. Army  Several Russian attempts  (1956)  t o estimate  m o u n t a i n snow c o v e r on t h e o r e t i c a l g r o u n d s h a v e b e e n  8  published  (Denisov  since l i t t l e  1967, B o r o i k o v a  However,  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 storm, these the  1968).  characteristics  o f each  m o d e l s a r e w e a k e s t when e s t i m a t i n g i n p u t t o  snowpack.  F o r example, the Russians  assume a l i n e a r  increase of p e r c i p i t a t i o n with elevation.  A n d e r s o n and  Rockwood u s e a 2°F/1000 f e e t l a p s e r a t e , and a t e m p e r a t u r e o f 33°F t o d e l i m i t t h e r a i n / s n o w b o u n d a r y , on t h e s o l e grounds these  values  Thus w h i l e the h y d r o l o g i c  g i v e more r e a l i s t i c  t h e snow c o v e r  1962), l i t t l e  has sought t o d e f i n e  system of the c y c l e and  a b l a t i o n - r u n o f f system o f  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  ( e . g . U.S. Army 1956, L e a f hydrology  output.  research  i n snow  i n d e t a i l t h e snow i n p u t  ( F i g . 1.2).  Studies which  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  especially  attention  describe  topography,  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  m o d e l s o f snowpack e v o l u t i o n a n d h e n c e may i m p r o v e of water s t o r e d i n mountain  realistic  estimates  snowpacks.  R e a l i s t i c m o d e l s 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 should snow s t o r m s . snow c o v e r  also consider  the climatology  Studies which r e l a t e  t o weather are f a i r l y  of winter  the behaviour  common i n snow  of the hydrology  ( e . g . A g e r 1967, McKay 1964, M i l l e r  1955) a n d i n g l a c i o l o g y  ( e . g . H o i n k e s 1968, M a r c u s 1964).  However, t h e r e have  b e e n o n l y a f e w s t u d i e s r e l a t i n g m o u n t a i n snow d e p o s i t i o n and  t h e c l i m a t o l o g y o f snow s t o r m s  ( e . g . Y o u n k i n 1968,  9  Storm  riming  Characteristics  precipitation processes INPUT  SYSTEM  Rainfall Snow D e p o s i t i o n =• E v a p o r a t i o n  snow m e l t processes  Net  Snow  t  Accumulation  OUTPUT SYSTEM t  t  snow m e l t processes  — run-off processes  Run-off  Pig.  1.2  S i m p l i f i c a t i o n o f two s y s t e m s o f 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  Bossolasco  1954).  Thus t h e N a t i o n a l Academy o f S c i e n c e s ,  N.R.C. (1967) recommends t h a t : " A r e a s 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 c o v e r a g e o f 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 prevailing circulation patterns. Average cyclone 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 s t o r m s ... f o r s e v e r a l c o n s e c u t i v e years". " The  m o u n t a i n snow c o v e r i s a m a j o r a n d r e n e w a b l e  hydrological resource.  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 mountain areas. has  of snowfall to winter precipitation i n Management o f t h i s  snow c o v e r  resource  b e e n c o n s i d e r e d by A n d e r s o n (1963) a n d M a r t i n e l l i (1964).  They s u g g e s t  t h e p r i n c i p a l medium f o r a r t i f i c i a l  control  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 t h e f o r e s t Thus- i t becomes i m p o r t a n t forest  cover.  to-know t h e i n f l u e n c e o f t h e  o n snow d e p o s i t i o n .  Many s t u d i e s h a v e d o c u m e n t e d  c h a n g e s i n t h e snowpack r e s u l t i n g f r o m d e l i b e r a t e modification  o f t h e f o r e s t , b u t f e w ( e . g . West 1961, M i l l e r  1966) s e e k t o i s o l a t e  the processes  involved.  coast m i d l a t i t u d e mountains, t h e changing  On w e s t  effect  of the  f o r e s t o n 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 t h e changing the snowline  with different  There a r e o f course hydrology. (1969).  position of  storms.  many o t h e r p r o b l e m s i n snow  Many o f t h e s e h a v e b e e n h i g h l i g h t e d by M e i e r B u t , from t h e f o r e g o i n g review  t h e f o l l o w i n g o b s e r v a t i o n s a r e made :  of the l i t e r a t u r e ,  11  On w e s t c o a s t m i d l a t i t u d e m o u n t a i n s t h e amount o f research has  on s n o w . a c c u m u l a t i o n h a s b e e n s m a l l , and  b e e n n e g l i g i b l e on snow  deposition.  T h e r e i s a n e e d t o d e v e l o p methods t o p r e d i c t accumulation v a r i a t i o n s with  elevation.  Few s t u d i e s measure and d e s c r i b e ;  snow  t h e snow  input  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 terrain. the  Such s t u d i e s  c o u l d be u s e d t o e x p l a i n  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 , a n d t o  a s s e s s t h e i m p o r t a n c e o f s t o r m 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 m o d e l snow  deposition  processes. Previous tainous  m o d e l s o f t h e snow i n p u t  s y s t e m i n 'moun-  t e r r a i n have b e e n b a s e d l a r g e l y on- a s s u m p t i o n  r a t h e r t h a n on measurement o f t h e r e l e v a n t  processes.  More r e a l i s t i c m o d e l s may i m p r o v e p r e d i c t i o n o f snow melt  runoff.  The e f f e c t o f f o r e s t on t h e snow d e p o s i t i o n is  an i m p o r t a n t c o n s i d e r a t i o n  snow c o v e r  resource.  f o r management  process of the  12  1.3  Objectives  of this  This- s t u d y has f o u r  study interrelated objectives.  First,  to describe  a n d a t t e m p t 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 with  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 t h e f o r e s t on a  west coast m i d l a t i t u d e  mountain.  S e c o n d , t o measure a n d d e s c r i b e with two  consecutive  winters.  data w i l l  t h e n be a n a l y s e d  snow a c c u m u l a t i o n p a t t e r n s  p r o d u c e d on w e s t  coast m i d l a t i t u d e hydrological  snow d e p o s i t e d The winter this  This  m o u n t a i n s , t o a s s e s s t h e snow i n p u t t o c y c l e , a n d t o compute t h e t o t a l mass o f  over t h e mesoscale o f a mountain  snow d e p o s i t i o n  data w i l l  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 of winter  of storm type i n producing  a t e a c h e l e v a t i o n on a w e s t c o a s t m i d l a t i t u d e follows  segment.  a l s o be r e l a t e d t o  study i s t o examine t h e c l i m a t o l o g y  especially the influence  This  deposition  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 a f t e r each storm f o r  t o e x p l a i n - the  the  new snow  the proposals of the National  storms, snowfall  mountain.  Academy o f S c i e n c e s  N.R.C. ( 1 9 6 7 ) . The  final  objective  imates, a f t e r a given on Mount Seymour. istics  i s t o construct  a model which  s t o r m , t h e amount o f snow  The m o d e l i s b a s e d on s t o r m  est-  deposited character-  r e c o r d e d a t t h e base o f t h e m o u n t a i n , o r a t o f f i c i a l  meteorological  stations.  This  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 p r o b l e m 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 k n o w i n g o n l y meteorO'logica-l data;.from valley  1.4'  and'radiosonde  stations.  The p r e s e n t a t i o n o f t h i s Pertinent  study  d e t a i l s o f t h e Mount Seymour s t u d y a r e a a r e  g i v e n i n the next  chapter.  B e f o r e m e a s u r e m e n t 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 were t a k e n i t was  considered  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 . design chosen,  sampling•procedures  are d i s c u s s e d i n Chapter  and methods o f m e a s u r e m e n t  three.  The n e x t two c h a p t e r s e x a m i n e t h e f i r s t this  study  : Chapter  The-  f o u r d e s c r i b e s snow  objective of  accumulation  v a r i a t i o n s on Mount Seymour o v e r two w i n t e r s ; a n d five  Chapter  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  before  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 h e n c e more f a m i l i a r .  Further, i fempirical  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 w i t h t o p o g r a p h y ful,  the other objectives of t h i s  t o snow  s t u d y become  estimates  are successless  important  hydrology.  D e s c r i p t i o n a n d 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  objective  s i x and- s e v e n .  of t h i s  study, are presented i n Chapters  The c l i m a t o l o g y o f snow s t o r m s  subject of the f o l l o w i n g chapter.  i s the  This includes discussion  14  of the in  third objective.  The' f i n a l  objective i s attained  C h a p t e r n i n e where a m o d e l 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 developed i n t h i s  or p a r a m e t r i c ,  and  of the  l i n e a r a n a l y s i s type" type  study  is deterministic,  " p a r t i a l system s y n t h e s i s  (Amorocho and  Hart  1964).  This  of model s t r i v e s t o d e s c r i b e the o p e r a t i o n of  winter  snow d e p o s i t i o n s y s t e m "by  l i n k a g e or  with  the  combination  o f components whose p r e s e n c e i s p r e s u m e d t o e x i s t i n  the  s y s t e m and whose f u n c t i o n s a r e known and p r e d i c t a b l e " . This  i s what Amorocho and The  tical  present  of the  call.system synthesis  s m a l l d e g r e e o f k n o w l e d g e and  impossibility  between the  Hart  of e s t a b l i s h i n g accurate  component phenomena do n o t  example, l i t t l e  of the m i c r o p h y s i c s  full  study.  d e t a i l i s known, o r can be  prac-  linkages  permit  snow i n p u t s y s t e m c h o s e n f o r t h i s  the  ( F i g . 1.  For  easily  of p r e c i p i t a t i o n processes  synthesis  obtained,  in  clouds  above Mount Seymour, o r o f a i r f l o w d u r i n g s t o r m s o v e r mountain r i d g e s of the  area.  Thus o n l y p a r t i a l  the  system  synthesis i s possible. Therefore,  this  correlation analysis. (storm  study  Here the  type, p r e c i p i t a t i o n  m o u n t a i n ) and e s t a b l i s h e d by  output  and  linear  r e l a t i o n s h i p between  input  t e m p e r a t u r e a t base- o f  (snow d e p o s i t i o n on t h e m o u n t a i n ) i s  statistical  m e a s u r e d i n p u t and  d e v e l o p s a model u s i n g  m e t h o d s I n v o l v i n g t h e use  output data.  However, the  of  approach  15  PHYSICAL HYDROLOGY  PARAMETRIC. AND STOCHASTIC • HYDROLOGIES  T Y P I C A L TOPICS OF STUDY M e t e o r o l o g y and Climatology Mass  PARAMETRIC METHODS p  Correlation Analysis  ^' P a r t i a l s y s t e m s y n t h e s i s with linear analysis  ^ ^  ^General  ^  f  balance  Energy c o n v e r s i o n and t r a n s f e r  p  system  synthesis  Biosystems Watershed h y d r a u l i c s and hydromechanics  G e n e r a l non l i n e a r  STOCHASTIC METHODS Markov  Chains  Monte C a r l o  methods  M e t h o d s p a r t i c u l a r l y d e p e n d e n t on p h y s i c a l knowledge o f t h e h y d r o l o g i c system. A f t e r Amorocho a n d H a r t (1964).  ^ ^//////////////////y  Fig.  analysis  1.3  T o p i c s and methods o f h y d r o l o g i c  study.  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 t h e v a r i a b l e s , chosen f o r  c o r r e l a t i o n a r e those t h a t e x i s t i n g knowledge are.-'important.  M o r e o v e r some a t t e m p t  the i n t e r n a l mechanics o f t h e system  indicates  i s made t o d e s c r i b e  i nexplicit  f o r m and.  t o g i v e p h y s i c a l meaning t o t h e parameters.  1.5  General relevance of t h i s  study  G e n e r a l l y , s t u d i e s s u c h as t h i s p r o v i d e d a t a , and d e f i n e processes  o f u s e t o h y d r o e l e c t r i c power and w a t e r  development, f l o o d f o r e c a s t i n g ^ avalanche  recreational planning,  s t u d i e s , upland a g r i c u l t u r e , mountain  and m o u n t a i n b u i l d i n g  transportation  codes.  T h i s s t u d y a l s o h a s some l o c a l r e l e v a n c e . of the water  The b u l k  supply f o r t h e g r e a t e r Vancouver p o p u l a t i o n  o f one m i l l i o n , Mountains,  supply  results  where t h i s  from r u n o f f from t h e North  study area i s l o c a t e d . .  Shore  Several  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  close to a large  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  recreational  potential.  S u b u r b a n homes a r e s t e a d i l y b e i n g b u i l t a t  h i g h e r e l e v a t i o n s , s o 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 f r o m r o a d s this  i sincreasingly pertinent.  c o n n e c t i o n , t h e data presented here  cussions o f Schaerer  In  adds t o t h e d i s -  (1970). a n d S c h a e f e r a n d N i k l e v a  (1973).  17  For cipitation  the f i r s t  a n d snow a c c u m u l a t i o n a r e d o c u m e n t e d f o r a  range o f e l e v a t i o n s conditions Densities be  t i m e i n t h e area,, v a r i a t i o n s o f p r e -  f r o m s e a l e v e l t o 1250 m.  f o rthe winter  months a r e a l s o  realistic  Temperature  examined.  o f newly- f a l l e n snow a r e m e a s u r e d .  used t o o b t a i n  These can  factors f o r conversion  s n o w f a l l depth t o water e q u i v a l e n t .  full  of  I n a d d i t i o n , assump-  t i o n s may be made a b o u t many m e c h a n i c a l p r o p e r t i e s - o f t h e local 1962).  snow s i n c e t h e s e c a n b e r e l a t e d t o d e n s i t y  (Bader  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 o f Mount Seymour Mount Seymour l i e s  couver, at l a t i t u d e It  i m m e d i a t e l y t o t h e n o r t h of Van-  49° 23 N, l o n g i t u d e 122°  i s s e p a r a t e d f r o m t h e P a c i f i c O c e a n , 160  by V a n c o u v e r I s l a n d , w i t h m o u n t a i n s above t h e 40 km w i d e w a t e r s o f t h e S t r a i t southwest, t h e mountains  57 W ( F i g .  km t o t h e w e s t ,  2000 m, a n d b y  of Georgia.  To t h e  of the Olympic P e n i n s u l a  (up t o  2400 m h i g h ) f o r m an a d d i t i o n a l b a r r i e r t o t h e u s u a l a i r flow.  In spite  d o m i n a t e d by P a c i f i c  Ocean w e a t h e r s y s t e m s , w i t h i n t h e b e l t  2.2  (Kendrew  onshore  of these f a c t s , the climate of the  Vancouver area i s m a r i t i m e , l a r g e l y  westerlies  2.1).  of the disturbed  and K e r r 1955)-  General synoptic features of winter  weather  From O c t o b e r t o mid-May t h e w e a t h e r o f t h e Mount Seymour a r e a i s d o m i n a t e d by t h e A l e u t i a n Low, a pressure system.  From t h e r e g i o n o f t h i s  spawned a s e r i e s o f l o w p r e s s u r e w h i c h move t o w a r d t h e B r i t i s h four or five  cells  cells  semi-permanent low are f r e q u e n t l y  and a s s o c i a t e d  Columbia coast.  come as a s e r i e s ,  Sometimes  o r " f a m i l y " , t h a t may  d o m i n a t e t h e w e a t h e r f o r two o r t h r e e weeks (Kendrew 1955) .  fronts  and K e r r  19  Fig.  2.1  General l o c a t i o n  Fig.  2.2  The  local  setting  o f Mt.  Seymour  20  Kendrew and may  Kerr recognise  s e v e r a l airmasses  i n f l u e n c e the B r i t i s h Columbia coast i n w i n t e r .  many c a s e s , t h e y  c a n n o t be  t i m e T r o p i c a l (mT) from the  clearly  a i r i s a d e e p , warm- s e c t o r o f  southwest.  More o f t e n , mT  t h e M a c k e n z i e • V a l l e y and  or trough  Yukon r e g i o n s .  coast.  On  On most  c o l d , so by  flurries. the  Pacific  may  be  air.  Cold maritime c o l d dry i n t e r i o r When s u c h  air  o c c u r o n c e i n two  Columbia outbreaks  a i r i s dry snow  as a l a y e r o r dome c l o s e t o  o v e r r i d d e n by  an o n s h o r e f l o w  of  p r o d u c e s heavy- snow t o  1957)•  airmasses  originate  a i r - i s moved o v e r t h e P a c i f i c by  depression  winters  as cA a i r i n t h e  o f n o r t h e a s t A s i a , A l a s k a and  warmed and m o i s t e n e d  and  s e l d o m p r o d u c e s more t h a n a few  This s i t u a t i o n  low e l e v a t i o n s ( J a c k s o n  the  (Baudat  i s deep, or i f a  Continental Arctic  However, i t l i e s  s u r f a c e and  moist  itself  •  may  occasions  i t can r e a c h  continental Arctic  of Georgia  K e r r 1955)  (Kendrew and  a i r (cA)  o f f the southwest B r i t i s h  the average,  around the S t r a i t  and  i f the airmass  intensifies  by  This a i r o r i g i n a t e s from  coast i f a p e r s i s t e n t n o r t h e r l y flow develops 1 9 6 9 ) , and  depressions  ocean.  i s c o n f i n e d east of the R o c k i e s , but  Wright  Mari-  a i r i s raised aloft  At t h e o t h e r e x t r e m e , c o n t i n e n t a l A r c t i c i n f l u e n c e the area i n w i n t e r .  In  distinguished.  o c c l u s i o n o f t h e warm s e c t o r o v e r t h e  it  which  the r e l a t i v e l y  the  Yukon.  i t i s rapidly warm o c e a n .  This-  21  induces  instability  and .much c u m l i f o r m  o f m o d i f i c a t i o n , and depends on t h e the  hence h e i g h t  l e n g t h of sojourn  t r a j e c t o r y of- t h e  cloud.  Kerr  1955).  The  over the  reaches the  coast  Pacific.  The  reaches the  coast  There r e s u l t  Freezing  2 .3  humid.  of Vancouver the North  and  types  (Kendrew  and a i r - (mA),  the  air.is  the generally  c a l l e d maritime Polar a i r  (mP), It  Such storms g e n e r a t e s t r a t i f o r m  t o l e s s showery and  the  precipitation.  a i r i s generally stable.  setting  Mount Seymour i s one a w e l l defined  low,  a  a f t e r l o n g contact w i t h the ocean.  give r i s e  local  broad  c a l l e d maritime A r c t i c  l e v e l s are  l e v e l s are h i g h e r  The  two  frequently recognised  warm t y p e ,  i s u s u a l l y warm and c l o u d s , and  Thus  a f t e r a short d i r e c t passage over  Freezing  unstable.  Pacific.  a i r i s important.  cold type,  degree  o f the. f r e e z i n g l e v e l ,  l a r g e number o f p o s s i b l e s i t u a t i o n s , b u t of maritime a i r are  The  of a s e r i e s of mountains  f r o n t range r u n n i n g  ( F i g . 2.2).  S h o r e Mountains-.  east-west to the  C o l l e c t i v e l y , these  v a l l e y s extending  The  m  f l a n k Mount Seymour.  On  V a l l e y and  a valley  Inlet.  the west l i e s occupied  the by  Two  Shore  eroded of  these  Seymour Indian  as  high,  North  s e v e r a l deep, g l a c i a l l y  north from Burrard  on t h e e a s t  area.  north  are-known  Mount Seymour i s 1451  r e p r e s e n t a t i v e of o t h e r peaks i n the M o u n t a i n s a r e d i s s e c t e d by  forming  Arm.  22  All a  field 14.3  o b s e r v a t i o n s were made on one t e r r a i n  km  2  area of  Mount Seymour w i t h r e l a t i v e l y  a s p e c t and s l o p e (.Figs. 2.3  2.4 2-4.1  segment, constant  and 2 . 4 ) .  C h a r a c t e r i s t i c s o f t h e measurement  area  Hypspgraphy Fig.  2.4  shows h y p s o g r a p h i c  c u r v e s f o r two r i v e r  b a s i n s i n t h e N o r t h S h o r e M o u n t a i n s , a n d f o r t h e Mount Seymour t e r r a i n  segment.  I n t h e C a p i l a n o a n d Seymour  C r e e k b a s i n s , 50 p e r c e n t o f t h e a r e a i s b e l o w 840 m, w h i l e 50 p e r c e n t o f t h e Mount Seymour t e r r a i n 335 m.  The t e r r a i n  segment l i e s b e l o w  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 t h e e l e v a t i o n range i n t h e 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 o f t h e b a s i n a r e a s l i e above t h e highest elevation  2.4.2  (1260  m) • s a m p l e d i n t h i s  thesis.  S l o p e and a s p e c t Slope and a s p e c t o f t h e t e r r a i n  f r o m a map  segment were m e a s u r e d  ( s c a l e . 1 : 1 2 , 0 0 0 ) a t 10 random p o i n t s w i t h i n  e a c h o f 12 e l e v a t i o n a l b a n d s c o n t a i n i n g snow and d e p o s i t i o n s a m p l i n g s i t e s  (Table 2.1,  accumulation  F i g . 2.6).  M o s t 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  sites  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 t h e 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  indicate  Fig.  2.3  The  t e r r a i n , segment c h o s e n f o r  this  study  24  Looking toward the top of Mount Seymour f r o m t h e c a r p a r k , lOBO m (March 1971)  L o o k i n g t o w a r d t h e T.V. t r a n s m i s s i o n t o w e r (on s k y l i n e a t 870 m) f r o m t h e l o w e r p a r t o f t h e r o a d (200 m) Fig-  2.4  Views o f t h e chosen t e r r a i n segment  20001  1—:—i  -1  - i — - l  T-  1  i  Copilano  batln (oreo 193.1 km*)  Seymour  basin (area 185.0 km )  r  1  Mount Seymour terrain segment (area 14.3 km') I500to  1000  500  _1 20  Pig.•2.5  L.  40  %  Area  J 60  I  I 80  -—  100  Hypsographic curves f o r t h e chosen t e r r a i n segment a n d f o r two a d j a c e n t r i v e r basins  Fig.  2.6  Slope and a s p e c t o f t h e chosen t e r r a i n segment a n d o f snow sampling s i t e s  2.1  TABLE  S l o p e a n d a s p e c t o f e l e v a t i o n bands o f t e r r a i n and o f snow s a m p l i n g  Elevation  (metres)  E l e v a t i o n bands of t e r r a i n segment  sites*  Slope  Snow Sampling Site  Terrain me an  segment  (degrees)  segment s t . dev.  Aspect  Snow Sampling Site  Terrain mean  ( d e g r e e s E o f N) segment  s t . dev.  :  1080 - 1280  1260  14  5  14  153  31  990 - 1080  1060  15  7  12** 12  167  23  13 15 20  145  20 20  153 158  7 9  20  157 159 150  9 5  900 -  990  810 720 -  900 810  630 -  720 630  590  540  490  450  400  180 -  360 270  90 -  180  330 220 120  540  -  450 360 27G,-  970 870 790 •  12 16  710  19 19 21 20  19  4 3 3 2 3 2 4  14  5 2  12  5  17  17 19 12 6  Snow Sampling Site  155 210** 145  151 153  150 151  10 16 7  7 9 15  160 163 152 160 167 164 160 156 145  170  Means a n d 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 f r o m a random s a m p l e o f t e n p o i n t s i n each e l e v a t i o n a l band. C o m p i l e d f r o m a map o f s c a l e 1 : 1 2 , 0 0 0 c o n t o u r 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 t h e snow s a m p l i n g s i t e u s e d i n t h e w i n t e r 1969-70, t h e s e c o n d f o r t h e w i n t e r 1970-71.  OA  27  that  t h e t e r r a i n - segment i s r e l a t i v e l y  respect  t o aspect and s l o p e ,  representative•of  with  the sampling s i t e s are  each e l e v a t i o n a l band and t h a t  they are r e p r e s e n t a t i v e  2.4.3  that  homogeneous  o f t h e whole t e r r a i n  together  segment.  Vegetation A s t u d y o f snow d e p o s i t i o n  with  e l e v a t i o n i s comp-  l i c a t e d by t h e f a c t t h a t  vegetation  vation.  t h e l i t e r a t u r e has n o t y e t r e s o l v e d  Unfortunately,  also varies with  which f o r e s t c h a r a c t e r i s t i c s exert influences forest  on snow d e p o s i t i o n .  important  I t i spossible  t h e same  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 i m p o r t a n c e a t  different  elevations.  B a s e d on ,the  forest classification of B r i t i s h  C o l u m b i a p r o p o s e d by K r a j i n a  (1965,  on Mount Seymour i s d i s c u s s e d Orloci  t h e most  ele-  (1964)  and Brooke  1969), t h e v e g e t a t i o n  i n d e t a i l by P e t e r s o n  (1966).  (1964),  B e l o w an e l e v a t i o n o f  900  m, t h e m o u n t a i n l i e s w i t h i n t h e W e s t e r n H e m l o c k Zone.  The  dominant t r e e  species  heterophylla), with  i s western hemlock  occasional  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 and  western r e d cedar  amabilis  f i r (Abies  by l o g g i n g  (Thuja p l i c a t a ) .  e l e v a t i o n s , mountain hemlock amabilis)  (Tsuga  Toward  or f i r e , higher  (Tsuga m e r t e n s i a n a ) and appe- r.' a  V a c c i n i u m a l a s k a e n s e i s t h e most common.  Of t h e many  shrubs  28  The 900  m.  s u b a l p i n e M o u n t a i n H e m l o c k Zone Brooke  begins•above  (.196.6) r e c o g n i s e s t w o subzones-, t h e  Forest  Zone up t o 1100. m, and t h e P a r k l a n d Zone a t h i g h e r e l e v a t i o n s , where t h e t r e e s t h i n out) c o n s i d e r a b l y . t r e e s p e c i e s are mountain hemlock, cedar  (Chamaecyparis  The d o m i n a n t  amabilis f i r ,  yellow  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-  lock a t lower l e v e l s .  The d o m i n a n t  shrub s p e c i e s  are  R h o d o d e n d r o n 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 t h e S u b a l p i n e Zones a r e b e t t e r a d a p t e d t o snowy conditions than those at lower e l e v a t i o n s , i n that branches  a r e more f l e x i b l e  and b e n d downward.  their  This - enables  them t o s h e d i n t e r c e p t e d snow, a n d a v o i d damage f r o m e x c e s s i v e snow  loading.  F i v e v e g e t a t i o n t y p e s were r e c o g n i s e d and mapped f r o m 1963  a i r photographs  o f Mount Seymour ( s c a l e v a r i e d  1:7542 t o 1:12,800).  The a r e a o f e a c h t y p e was p l a n i m e t e r e d ,  and t h e p e r c e n t a g e a r e a c a l c u l a t e d The  f o r the t e r r a i n  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 nature o f the  (Fig.. 2v7).  from  segment.  mountain  Areas o f young t r e e s , d e s c r i b e d as second  growth predominate.  Open a r e a s a n d 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 t h e t e r r a i n s e g m e n t . the r e s u l t s is  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,  c l e a r t h e r e are. wide  d i f f e r e n c e s between  When it"'  elevations.  Open a r e a s a n d c l e a r i n g s a r e 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 t h e snow- d e p o s i t i o n  p r o c e s s '.(Anderson e t a l 1958, H a n s e n 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 o f 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. ( T a b l e 2.2).  M o s t c l e a r i n g s a r e s m a l l e r t h a n 15 m i n d i a m e t e r , near the top of the mountain,  except  and' a t a more r e c e n t l y  logged  a r e a n e a r 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  sampling  s i t e by t h e u s u a l m e a s u r e s o f t r u n k d i a m e t e r , and h e i g h t (Appendix A ) .  H o w e v e r , as R o t h a c h e r  (1963) and  (1970) s u g g e s t , t h e s e p a r a m e t e r s " a l o n e may factory indices  of f o r e s t i n f l u e n c e s  s i n c e t h e y were d e v e l o p e d deficient  i n physical  Miller  f o r other purposes  satis-  deposition, and  are  interpretation.  (1964) d i s c u s s e s some u s e f u l m e a s u r e s o n  n a t u r e o f t h e f o r e s t , and. w h i c h may deposition.  the three d i m e n s i o n a l  be r e l a t e d t o snow  Of t h e s e , an i n d e x o f canopy c l o s u r e  ( F i g 2.8).  o f 25 r a n d o m l y  T h i s was  was  d e f i n e d as the- p e r c e n t a g e '  s e l e c t e d p o i n t s o c c u r r i n g beneath  canopy a t each, s a m p l i n g s i t e . graphs  n o t be  on snow  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  obtained  Curtis  a tree  O t h e r m e a s u r e s and  of the f o r e s t near each.of  t h e 12 s a m p l i n g  photosites  a r e g i v e n i n A p p e n d i x A. Figs.  2.7, 2.8 and  o t h e r data, i n Appendix  the diverse nature of the f o r e s t p r o d u c t ; of' s e l e c t i v e Perhaps  A,  reveal  at the sampling s i t e s , a  l o g g i n g at d i f f e r e n t  t h e most a n o m a l o u s s a m p l i n g s i t e  times i n the p a s t . i s t h a t a t 590 m.  30  100 80 ^  ,  Second  Growth(50°/o) >C  S 60^  * v . . • •  < 2 5  40H  Deciduous  Trees  (15°/o)  ^  x  •  '  ^<fi  0  Mature %Trees(l9°/o)/  ft  .N  2.7  /  < £ /  "  ^ y^Clearings (6°/o) v  ^  "~-  —  K  400  200  Fig.  X  '  600 800 Elevation (Meters)  Distribution  1000  of vegetation•type with  1200  elevation  10  x 0-8  T> _C  V  h  06  c W  o  04 >. o. o § 0-2  U  1 0 = Totally closed canopy 0 0 = Completely open .  U  JL  200  F i g . 2.8  400  600 500 Elevation ( M e t e r s )  Canopy c l o s u r e o f t h e f o r e s t sampling s i t e  1000  a t each,  1200  31  TABLE 2.2  Frequency • d i s t r i b u t i o n i n the t e r r a i n  E l e v a t i o n band (metres)  of. c l e a r i n g s *  segment  Diameter  of Clearing  < 15 m  15-30 m  30-45 m  1080-1280  68$  22$  10$  '990-1080  86$  12$  2$ 6$  900-  990  72$  22$  810-  900  90%  10$.  720-  -310  89$  11$  630-  720  98$  2$  540- 630  62%  35$  450-  540  84$  14$  1$  360-  450  81$  17$  2$  270-  360  92$  7$  1$  180-  270  90$  8$  2$  90-  180  84$  Compiled  from a i r photographs  13$  45-60 m  3$  :  2$  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 .  1$  1$  32  H o w e v e r , 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 . B o t h t r e e h e i g h t and the top  above 900  The  p r e v i o u s l y mentioned t h i n n i n g  m i s also well  illustrated.  C l i m a t i c data Standard temperature  climatic stations recording precipitation d a t a d u r i n g t h e p e r i o d o f t h i s r e s e a r c h were  numerous a t l o w e r  e l e v a t i o n s , but- i n a d e q u a t e  areas.  mountain s t a t i o n , H o l l y b u r n Ridge  Only- one  t o t h e w e s t a t an e l e v a t i o n o f 920 cipitation  and  temperature.  w i t h over t h i r t y  years  m),  A first  o f r e c o r d was  o f Mount Seymour ( F i g .  i n the  recorded order  km  to the  Precipitation  a t H o l l y b u r n R i d g e i n 1954,  10  km pre-  station level  southwest  2.2).  e l e v a t i o n s i n the p a s t .  and  G r o u s e M o u n t a i n (1105  data f o r the years  (15  daily  climate  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  i960.  mountain  l o c a t e d near sea  a t V a n c o u v e r I n t e r n a t i o n a l A i r p o r t , 25  in  towards  A v a i l a b l e data  2.5.1  and  o f canopy t e n d t o d e c r e a s e  of the mountain.  of the f o r e s t  2 .5  size  19 34-40.  higher  measurements-began  temperature m)  at  recorded  measurements precipitation  On Mount S e y m o u r , a  partial  y e a r r e c o r d (1958-68) o f 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  f r o m t h e CBUT t e l e v i s i o n t r a n s m i t t i n g t o w e r (870 Three temporary c l i m a t i c  s t a t i o n s above 900  m).  m measured  33  t e m p e r a t u r e i n a l l s e a s o n s , a n d p r e c i p i t a t i o n d u r i n g snowf r e e p e r i o d s , b e t w e e n 1960-1962 ( P e t e r s o n - 1964, B r o o k e 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 a s p e c t  a i r data is•important.  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 a t V a n c o u v e r . Hardy a t t h e n o r t h e r n the northwest,  o f mountain c l i m a t e , upper  The n e a r e s t  s t a t i o n s are Port  t i p o f V a n c o u v e r I s l a n d , 350 km t o  and Q u i l l a y u t e ( f o r m e r l y a t T a t o o s h  on t h e O l y m p i c P e n i n s u l a , 165 km t o t h e s o u t h w e s t Both s t a t i o n s a r e w e l l exposed t o approaching flows.  Island) ( F i g . 2.1).  Pacific  The m o d i f i c a t i o n i n a i r m a s s - p a r a m e t e r s b y s u b -  sequent passage over Vancouver I s l a n d o r t h e Olympic sula, the Strait n o t known.  of Georgia,  and t h e c i t y  However, P e t e r s o n  (1964)  a good c o r r e l a t i o n between t h e h e i g h t a t P o r t H a r d y a n d Mount Seymour. evidence,  c l a i m e d t o have  I t was d e c i d e d  12 h o u r s .  move c o m p l e t e l y Detailed studies  from  this  and t h e c o n s i d -  cheapness o f t h e Canadian radiosonde  radiosonde  found  of freezing levels  t o use d a t a from o n l y P o r t Hardy i n t h i s At b o t h  Penin-  o f Vancouver i s  t o g e t h e r w i t h t h e ease o f access  erable r e l a t i v e  every  air-  data,  study.  stations, observations  are taken  I t i s p o s s i b l e f o r weather- s y s t e m s t o through  t h e area between  observations.  ( K r e i t z b e r g 1964, 1970) show t h a t t h e  34  spatial is  and t e m p o r a l s a m p l i n g p a t t e r n o f r a d i o s o n d e  often insufficient  stations  to define the detailed structure of  storms.  2.5.3  Snow a c c u m u l a t i o n a n d s n o w f a l l - d a t a T h e r e h a v e b e e n a number o f o t h e r s t u d i e s w h i c h B e t w e e n i 9 6 0 and 1 9 6 2 ,  d i s c u s s snow on Mount Seymour. Peterson  (1964)  and B r o o k e  snow c o v e r p h e n o l o g y by  (.1966), r e c o r d e d snow d e p t h a n d  above 1000 m.  The p r e s s u r e s  induced  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 a n d 1200 m were  r e p o r t e d b y Mathews a n d Mackay ( 1 9 6 3 ) (1967).  S t e i n and Brooke  o f r e d snow on t h e m o u n t a i n .  (1964)  a n d Mackay and Mathews  d e s c r i b e d an o c c u r r e n c e  The maximum g r o u n d  a t 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 m o u n t a i n s a r e p r e s e n t e d by S c h a e r e r  (1970).  snow l o a d s  Columbia 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 p a p e r s t i o n s , based  d i s c u s s s n o w f a l l at lower e l e v a -  on snow d e p t h 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 Wright  1966a, Wright  1966b, Wright  S c h a e f e r and N i k l e v a 1973)leading to heavier f a l l s d e s c r i b e d by J a c k s o n  1957,  and T r e n h o l m  Thomas  1957,  1969,  The s y n o p t i c c o n d i t i o n s  o f snow i n the- V a n c o u v e r a r e a a r e  ( 1 9 5 7 ) a n d B a u d a t and W r i g h t  (1969).-  35  T h e r e were s e v e n snow c o u r s e s o p e r a t i n g i n t h e N o r t h Shore Mountains Appendix  D with their  Grouse Mountain Columbia.  study.  These a r e l i s t e d i n  l e n g t h o f r e c o r d and  elevation.  h a s one o f t h e l o n g e s t r e c o r d s i n B r i t i s h  On Mount Seymour, snow c o u r s e o b s e r v a t i o n s  were t a k e n about at  during this  1 km t o t h e w e s t o f t h e t e r r a i n  segment  t h e b e g i n n i n g o f e a c h month f r o m F e b r u a r y t o J u n e and  on May  15.  frequently.  A l l o t h e r snow c o u r s e s w e r e r e a d  less  36  CHAPTER 3  3.  PARAMETERS MEASURED AND EXPERIMENTAL DESIGN  3•1  M e a s u r e m e n t 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 m e a s u r e d a f t e r e a c h s t o r m a s t h e  s p e c i f i c mass o f new snow, p e r u n i t o f g r o u n d new snow mass  Specific  (M) i s g i v e n b y : M  where  area.  Y z  =  Y  Z  density  =  =  o f n e w l y • f a l l e n snow  new snow d e p t h , m e a s u r e d  vertically.  Snow d e n s i t y and d e p t h o f new snow i n c r e m e n t w e r e m e a s u r e d above a ' s t y r o f o a m  ( a r e a - 250 c m ) ,  snowboard  2  p l a c e d on t h e p r e v i o u s snow s u r f a c e a n d l o c a t e d by a d o w e l . The  snowboard remained  most w e a t h e r  l e v e l w i t h t h e snow s u r f a c e u n d e r  c o n d i t i o n s , e x c e p t d u r i n g r a i n on snow e v e n t s  when t h e s t y r o f o a m d i d n o t s e t t l e s u r r o u n d i n g snow s u r f a c e .  as r a p i d l y  New snow d e n s i t y was m e a s u r e d  b y . w e i g h i n g t h e c o n t e n t s o f - a 500 cm ( l e n g t h 19.6  as d i d t h e  cm, d i a m e t e r 5.7  cm).  3  CRREL snow  sampler,  I f new snow d e p t h was  greater than the length of the sampling tube,  additional  d e n s i t y measurements were t a k e n w i t h d e p t h .  The maximum  depth  o f new snow r e c o r d e d f r o m any s t o r m was 103  snow d e p t h was l e s s t h a n t h e l e n g t h o f t h e t u b e , rather than v e r t i c a l  samples were t a k e n .  cm.  When  horizontal  37  3.1.2  Measurement  error  New snow depth, w a s - m e a s u r e d t o ±0 ..5 cm, o r t o w i t h i n ±0.25 cm f o r d e p t h s l e s s t h a n 4 cm. o f t h e 500 cm  3  CRREL s a m p l e r were e m p t i e d i n t o  j a r s and s u b s e q u e n t l y weighed balance.  The c o n t e n t s airtight  t o ±0.05 gm on a l a b o r a t o r y  Volume o f t h e s a m p l e r was c h e c k e d by m e a s u r i n g  t h e amount o f w a t e r i t c o u l d c o n t a i n . t o be c o r r e c t t o ±1 c m .  I t was e s t i m a t e d  To e n s u r e t h e c o r r e c t  3  volume  i n f i e l d m e a s u r e m e n t s , t h e ends o f t h e snow sample planed o f f with a steel-edged r u l e .  were  These e r r o r s i n  w e i g h i n g and i n t h e volume o f t h e s a m p l e r 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 w h i c h v a r i e s w i t h snow d e p t h ( F i g . 3 . 1 ) .  Actually, there exists  a f a m i l y o f c u r v e s f o r e a c h snow d e n s i t y , b u t w i t h i n t h e d e n s i t y range  100-400 kg/m  3  these curves are very  close  t o g e t h e r a n d c a n be r e p r e s e n t e d b y t h o s e shown. I n a d d i t i o n t o t h e computed measurement f u r t h e r measurement e r r o r s c a n r e s u l t  error,  f r o m 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 h e s a m p l e r , o r f r o m a d h e s i o n o f snow t o t h e sample  tube w a l l .  I n such c a s e s , t h e  volume o f snow w e i g h e d may be g r e a t e r o r l e s s t h a n 500 c m . 3  T h i s e r r o r was r e d u c e d by w a x i n g t h e sample  t u b e , and by  r e j e c t i n g t h o s e s a m p l e s where c o l l a p s e o r a d h e s i o n was suspected.  50  40  0  4  8  12 New  Pig.  3-1  16  20  24  Snow Depth (cm)  P e r c e n t a g e measurement e r r o r f o r s p e c i f i c mass o f new snow d e p o s i t e d  28  39  Assessment o f t h e magnitude o f t h i s is difficult.  s  snow (1.7J8)-. sampler  o f new snow d e n s i t y ,  o f v a r i a t i o n o f 5.0 p e r c e n t .  than f o r depth hoar  error  (.1971) who e s t i m a t e d t h e " w i t h i n  Gary  p l a c e " sample v a r i a b i l i t y a coefficient  subjective  (2.5%),  quoted  T h i s was l a r g e r  o l d d r y snow (2.4$)  and o l d wet  Work e t a l (1964) f o u n d t h e 500 cm  3  CRREL  t e n d e d t o o v e r e s t i m a t e t h e w a t e r e q u i v a l e n t by  7 percent.  H o w e v e r , t h e i r f i g u r e was b a s e d  of water e q u i v a l e n t f o r t h e t o t a l s e r i e s o f samples.  on an e s t i m a t e  snowpack by u s e o f a  F r o m t h i s , i t seems t h a t t h e m e a s u r e -  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 a n  unknown amount, t h a n t h a t shown i n F i g . 3 • 1 , . d e p e n d i n g on t h e s k i l l  o f t h e o p e r a t o r a n d on snow  conditions.  When new snow d e p t h s were l e s s t h a n t h e d i a m e t e r o f t h e s a m p l i n g t u b e , no m e a s u r e m e n t s 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 t h e n c o m p u t e d  by u s i n g t h e d e n s i t y v a l u e f r o m t h e n e a r e s t s a m p l i n g where a measurement c o u l d be t a k e n .  site  I n these cases, 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 k g / m ) , 2  hence a b s o l u t e e r r o r s t o be u n d u l y  from t h i s procedure  were n o t l i k e l y .  large.  3 .2  The t e m p o r a l  3.2.1  The s t o r m • The b a s i c  sample  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  storm, here defined  ated with and  as a p e r i o d  a p a r t i c u l a r synoptic  rainfall  of p r e c i p i t a t i o n associ-  situation.  Snow  were s a m p l e d no l a t e r t h a n w i t h i n  i n most c a s e s w i t h i n  deposition  24 h o u r s a n d  12 h o u r s a f t e r e a c h s t o r m .  were numbered c o n s e c u t i v e l y , a f t e r October 1 (see l i s t  starting with  Storms  t h e f i r s t one  o f storms, Appendix E ) .  Since the bulk 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 ( W a l k e r 1961), t h e r e s e l d o m was any  confusion i n d e l i m i t i n g storms.  However, c e r t a i n  difficulties  d i d arise i n non-frontal  onshore flow  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  situations  s t o r m s - 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  :  I f an  - were  r e c o g n i s e d ; i f p o s t - f r o n t a l s h o w e r s were b r i e f , a s i n g l e storm 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  such r a p i d s u c c e s s i o n that  i t was i m p o s s i b l e  a f t e r each. separately,  t o sample  I n t h e s e c a s e s , t h e s t o r m s were a l t h o u g h t h e sample d i d i n c l u d e  occurred i n  classified  t h e combined  precipitation. For  sampling purposes, the i n i t i a l  decision  what c o n s t i t u t e d  a s t o r m was made a f t e r c o n s u l t i n g  latest  surface- and m o u n t a i n weather  available  as w e l l as t h e s k i r e p o r t v i e w i n g a crude s u r f a c e satellite  as t o 'the  forecasts  f o r l o c a l m o u n t a i n s , and a f t e r  synoptic  picture  and w e a t h e r  p h o t o g r a p h 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  Subsequently, the synoptic weather-office  synoptic  scheme s u c h as t h i s  s i t u a t i o n was e x a m i n e d  charts.  A temporal sampling  i s - o n l y as v a l i d  as t h e w e a t h e r  c a s t s and t h e a c c u r a c y w i t h which t h e a c t u a l patterns  are portrayed  information weather This the  by the- s y n o p t i c  fore-  weather  charts.  Little  i s r o u t i n e l y a v a i l a b l e on t h e s t r u c t u r e o f  systems  below  the synoptic  i s a problem that i s inherent e f f e c t s o f such systems  spatial scale  3.2.2  on o f f i c i a l  scale  (100-1000 k m ) . 2  i nthis  a r e examined  study, wherein  on a l e s s e r  ( a b o u t 10 k m ) . 2  The p e r i o d o f f i e l d  observations  Samples f o l l o w i n g each s t o r m were t a k e n w i t h i n t h e " w i n t e r " p e r i o d O c t o b e r 1 t o May 3 1 , Except f o r these months, f a l l s 1300 m ( C h a p t e r 6 ) .  Some s a m p l e s  from a l l storms w i t h sampled  1969-70, snow.  of density  below  o f newly  1968-69.  snow d e p o s i t i o n was s a m p l e d  I n a d d i t i o n , r a i n f a l l was  f r o m a l l s t'orms e x c e p t t h o s e o c c u r r i n g i n O c t o b e r :  and t h e f i r s t week i n November.  In the winter  c o m p l e t e p r e c i p i t a t i o n was s a m p l e d p r e c i p i t a t i o n - whether  (138 s t o r m s ) .  1970-71,  from a l l storms.  Thus-  r a i n o r snow - was m e a s u r e d by  s t o r m s f o r one c o m p l e t e w i n t e r  two  and 1970-71.  o f snow a r e u n u s u a l  f a l l e n snow were t a k e n i n t h e w i n t e r In the winter  1969-70  and' f o r most o f a n o t h e r  Snow d e p o s i t i o n was m e a s u r e d b y s t o r m s f o r  complete w i n t e r s  C82  storms).  42  3.2.3  Nature of winters The two w i n t e r s  each other  study  about t h e n o r m a l .  c l i m a t i c data recorded  were d i f f e r e n t ifrom they represent  a wide  A s e l e c t i o n of  at Vancouver I n t e r n a t i o n a l A i r p o r t  s e a l e v e l ) show t h e 'Winter o f 1969-70 t o be m i l d e r  (near  that  of this  i n many ways a n d i t i s f e l t  range o f c o n d i t i o n s  and  sampled  d r i e r than normal, i n sharp c o n t r a s t t o t h e wetter followed  (Pig.  3.2).  On t h e 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 i n the general  c i r c u l a t i o n , h e r e i n d i c a t e d by  f r o m n o r m a l o f t h e mean 700 mb h e i g h t winter  differences  departures  (Fig. 3.3).  o f 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  and' s o u t h  The  anomalies  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  t o March.  winter  over  December  T h e s e a n o m a l i e s were a s s o c i a t e d w i t h a g r e a t l y  e x p a n d e d a n d more i n t e n s e A l e u t i a n Low i n t h e n o r t h e a s t . P a c i f i c , which produced p e r s i s t e n t southerly V a n c o u v e r r e g i o n and t h e warmer, d r i e r is potentially the  winter  the snowiest part  o f 1970-71 d i s p l a y e d  anomalies i n the northeast to February.  flows  c o n d i t i o n s i n what  o f the year.  By c o n t r a s t  s t r o n g p o s i t i v e 700 mb  P a c i f i c , e s p e c i a l l y from October  D u r i n g t h i s p e r i o d t h e A l e u t i a n l o w was  weakened o r e l i m i n a t e d by t h e d e v e l o p m e n t o f an ridge i n the eastern  Pacific.  developed, producing  wetter  frequent  over the  outbreaks of A r c t i c  extensive  A persistent northerly  and c o l d e r c o n d i t i o n s a i r t o the P a c i f i c  with  coast.  flow  Fig.  3-2  D i f f e r e n c e s f r o m n o r m a l ( 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  Fig.  3.3  D e p a r t u r e f r o m n o r m a l o f t h e mean 700. mb h e i g h t ( d e c a m e t e r s ) f o r e a c h - m o n t h o f w i n t e r 196-9-70. From M o n t h l y W e a t h e r R e v i e w  Fig.  3-3  (.continued)  D e p a r t u r e f r o m n o r m a l o f . t h e mean 700 mb height' (decameters) f o r each-month o f 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  circulation  between  t h e 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 m o n t h l y mean f r e e z i n g  l e v e l s , as m e a s u r e d a t a d j a c e n t  radiosonde  these  stations f o r  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 o f t h e l o n g  values  (Table  3.1).  w i n t e r 1969-70. experienced  term  S n o w f a l l was l e s s t h a n n o r m a l i n t h e  By c o n t r a s t , t h e w i n t e r o f 1970-71  t h e g r e a t e s t snow amounts m e a s u r e d a t V a n c o u v e r b e g a n i n 1938,  I n t e r n a t i o n a l A i r p o r t since records  includ-  i n g an a l l - t i m e h i g h f o r J a n u a r y o f 122 cm, a l t h o u g h g r e a t e r amounts h a d b e e n r e c o r d e d C i t y weather s t a t i o n .  At t h i s  at the o l d e r Vancouver  latter  station, the winters  o f t h e s t u d y p r o d u c e d s n o w f a l l s w h i c h s p a n n e d 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  (Fig. 3.4).  From  more l i m i t e d d a t a , t h e s n o w f a l l s a t t h e h i g h e r e l e v a t i o n of H o l l y b u r n conditions  (920 m) a l s o seemed t o i n c l u d e a w i d e r a n g e o f  (Fig. 3.4).  Snow w a t e r e q u i v a l e n t s m e a s u r e d a t two N o r t h M o u n t a i n snow c o u r s e s  Shore  were b e l o w n o r m a l i n t h e w i n t e r  1969-70, and above n o r m a l i n 1970-71 ( F i g . 3 - 5 ) .  Grouse  M o u n t a i n , 9 km t o t h e w e s t o f Mount Seymour, i s i n c l u d e d because o f i t s longer p e r i o d o f r e c o r d . of t h i s  s t u d y , Seymour M o u n t a i n r e c o r d e d  water equivalent  (87 cm i n 1 9 7 0 ) ,  (287  since records  c m - i n 1971)  During  the period  i t s lowest  March  a n d i t s h i g h e s t May v a l u e  b e g a n i n I960.,  •  From t h e .36  47  TABLE 3 . 1  Freezing  levels  (geopotential meters)  a t 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, periods  compared w i t h  of record  Longer p e r i o d o f r e c o r d Tatoosh I s . Month  longer  Port  Hardy  Winters o f study Port  Hardy  1969-70 .  Port  Hardy  1970-71  1946-55  1951-60  Oct  2440  2280  2202  2399  Nov  1730  1560  1782  1347-  Dec  1200  1180 .  1292  627  Jan  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  587  574  452  623  Monthly S. D e v .  Notes:  ( ±)  (ii)  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 T a t o o s h I s l a n d ( n o w - Q u i l l a y u t e ) f r o m R a t n e r (1957) . D a t a f o r 1969-70 ,. 197.0-71 computed f r o m "Monthly B u l l e t i n o f Canadian•Upper A i r Data".  r  48 1190  f  Winttr 1970-71  «3<H  A t  650 J  Based on 18years observation  .999  •999  F i g . 3-4  99  995  99  95  95  -90  SO  80  80  70  70  60 5 0 40 -30  60 -50 -40 -30  20  *>  SO  05  -10  05  01  001  01  005  001  P r o b a b i l i t y o f w i n t e r s n o w f a l l s , as t o t a l depth of new snow a t H o l l y b u r n R i d g e , 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 g i v e s t h e 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 depth o f s n o w f a l l  49 SEYMOUR MOUNTAIN Elevation 1113 m. 120 based on period 1960-71  c  £  °  8  Feb  Apr  May  GROUSE MOUNTAIN Elevation 1158m I  I  Mar  120  I  June  based on period 193 6-71  rr 240  c J  o >  8  /  0  '  cr UJ  I  40  ^  ^  ^  > — — —•  "  /  r  /  "  c i)  "  - mean ^1970  ^  U  80  —»—*  F i g . 3.5  i  '  Mar  Apr  -  i  May  cr (-  min  0 Feb  a >  L160  /  ^ ^ ^ ^  c  /  E o  max ^ 1971 •  June  M o n t h l y w a t e r e q u i v a l e n t a t Seymour M o u n t a i n and G r o u s e M o u n t a i n snow c o u r s e s f o r w i n t e r s 1969-70 ,. 1 9 7 0 - 7 1 5 compared w i t h t h e l o n g t e r m records. C o m p i l e d f r o m B.C. Snow S u r v e y Bulletins•  4; -t-> o  50  t o 1971 o f A p r i l r e a d i n g s  years  f i v e years less  a t Grouse M o u n t a i n , o n l y  (1940, 1941, 1942, 1944 ,. 1963) h a v e  snow t h a n i n 1970, a n d o n l y t w o y e a r s  h a v e r e c o r d e d more t h a n  recorded  (1946, 1964),  i n 1971.  A t t h e Seymour snow c o u r s e  the p r o b a b i l i t y  o f having  a l o w e r w a t e r 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  water  i n 1970-71, i s a b o u t 10$ ( F i g . 3-6).  e q u i v a l e n t than  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 f r o m a c t u a l Seymour values  f o r years  a f t e r I960, a n d b a c k t o 1936 f r o m  estimated  v a l u e s b a s e d on t h 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 = 23.98 + 1.07 G with r  2  = O.87 a n d t h e s t a n d a r d e r r o r o f t h e e s t i m a t e =  ± 19.3 cm, a n d w h e r e , S = Seymour w a t e r e q u i v a l e n t i n cm G = G r o u s e w a t e r 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 of t h i s study  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  a r e a sample o f a wide range o f l i k e l y  d e p o s i t i o n a n d snow a c c u m u l a t i o n  3.3  snow  c o n d i t i o n s o n Mount Seymour.  The S p a t i a l s a m p l e o f snow d e p o s i t i o n m e a s u r e m e n t s This 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 general  sense,  51  300  •999 -995-99  -95  •7 -6 -5 -4 -3  01 -005  •001  Probability  F i g . .3.6  Probability of recording e q u i v a l e n t on A p r i l 1 a t M o u n t a i n snow c o u r s e s . .a g i v e n w a t e r e q u i v a l e n t axis  greater than giyen water Seymour M o u n t a i n and G r o u s e The p r o b a b i l i t y o f e x c e e d i n g , i s given along the h o r i z o n t a l  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 graphical factors. are  The i m p o r t a n t  : f r e e z i n g l e v e l , moisture  d i r e c t i o n , airmass s t a b i l i t y , conditions.  The i m p o r t a n t  elevation, slope, aspect, 1968,  Leaf  of slope  1962,  meteorological factors  s u p p l y , w i n d speed and and i n some c a s e s  antecedent  togographical features are-:  e x p o s u r e and v e g e t a t i o n  G r a n t and S c h l e u s n e r  and a s p e c t  1961).  ( Meiman  The e f f e c t s  h a v e b e e n r e d u c e d by c h o o s i n g  a  • t e r r a i n segment on Mount Seymour w h i c h i s r e l a t i v e l y stant with respect  t o these  3.3.1  population  The s a m p l e To o b t a i n . a n  populations  parameters  estimate  a f t e r each storm, separate  ( P i g s . 2.3,  of specific  estimates  con2.6).  snow mass  deposited  o f t h e means o f t h e  o f new snow d e p t h and new snow d e n s i t y were made.  These e s t i m a t e s  refer strictly  t o snow d e p o s i t i o n w i t h i n t h e  c h o s e n t e r r a i n segment ( t h e s a m p l e p o p u l a t i o n ) . probably  topo-  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  t e r r a i n segments e l s e w h e r e i n t h e N o r t h  They a r e similar  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 Results  scheme  of p i l o t  s t u d i e s , using large simple  samples, i n d i c a t e d that s u b s t a n t i a l v a r i a b i l i t y ulations  random  i n t h e pop-  o f new snow d e p t h a n d d e n s i t y o c c u r r e d w i t h  both  53  elevation•and 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 t h e two p o p u l a t i o n s were essential; sampling  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 ,  scheme s i m i l a r , t o t h a t u s e d  random  f o r measurement o f  r a i n f a l l by N k e m d i r i m ( 1 9 6 8 ) , a n d o f snow a c c u m u l a t i o n by (1973) •  B a r t o s and Rechard  The method a n d a d v a n t a g e s o f  s t r a t i f i e d random s a m p l i n g a r e d i s c u s s e d by C o c h r a n and P r e e s e  (1962).  of primary  stratification;  (1953)  E l e v a t i o n was s e l e c t e d a s t h e c r i t e r i o n t h e 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 t h e f o r e s t . Since 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 permits 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  forest  positions.  I t may a l s o be u s e d  and.hence c o m p u t a t i o n  to obtain areal  estimates  o f t h e a b s o l u t e mass o f snow d e p o s i t e d  on t h e t e r r a i n - s e g m e n t . 3.3.3  Sampling  with elevation  I t was n e c e s s a r y  (the primary  t o d e c i d e a t what  i n t e r v a l s a m p l e s s h o u l d be t a k e n . erature discuss this  stratification)  elevational  Pew p a p e r s  i nthe  lit^  t o p i c , a l t h o u g h Nkemddrim  (1968)  suggests  a 100-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 a n d R e c h a r d  (1973) f o u n d e l e v a t i o n b a n d s  o f 200 f e e t t o h a v e s i g n i f i c a n t l y  different  snow  accumulations.  54  Since coast  freezing•levels generally  m i d l a t i t u d e mountains;- the  melting  i n t e r s e c t t h e west  thickness  o f the atmospheric  l a y e r below t h e f r e e z i n g l e v e l i s l i k e l y  important 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 with snow d e p o s i t i o n .  This  t o be a n  elevation of  i s a consequence o f t h e r a p i d  c h a n g e s i n snow p r o p e r t i e s w h i c h o c c u r i n t h e m e l t i n g (Ohtake 1969). depth o f t h i s lapse and  (1940) and'Lumb (1963) show t h e  l a y e r t o be i t s e l f v a r i a b l e , d e p e n d i n g on  r a t e , t y p e o f snow c r y s t a l a n d i t s f a l l v e l o c i t y , A t l a s e t a l (1967)  intensity of precipitation.  a thickness and  Pindeisen  layer  compute  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,  1900 m f o r i n t e n s i t y 10 mm/hour.  Mason (1971) a n d  Wexler  (1955)  radar,  u s u a l l y r a n g e s b e t w e e n 100 a n d 200 m.  agree t h a t  On t h i s  t h i c k n e s s , a s m e a s u r e d on w e a t h e r  e v i d e n c e , 12 s a m p l i n g s i t e s were  established  a p p r o x i m a t e l y e v e r y 100 m up t h e m o u n t a i n t o a n e l e v a t i o n o f 1260 m. atically  T h e s e a r e l o c a t e d i n F i g . 2 . 3 , shown d i a g r a m -  i n P i g . 3«7 a n d 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 w e r e n o t c h o s e n r a n d o m l y , but- w e r e e s t a b l i s h e d w h e r e there be  occurred  conveniently  a s u i t a b l e open a r e a ,  parked o f f the access road.  expected from t h i s procedure. s i t e was e x t r a c t e d (100 f o o t ) an  No b i a s i s  The e l e v a t i o n o f e a c h  f r o m a map ( s c a l e 1:12j000) w i t h  contour i n t e r v a l ,  altimeter.  a n d where a c a r c o u l d  Each-is  and s u b s e q u e n t l y  considered  precise  a 30.5 m  checked  to-±- 6  sampling  with  55.  >  y  THE SAMPLING SITE Secondary stratum - position within forest .  I>  3H'-  Open area  F i g . 3.7  — — ^  \4rJ-3»^  Clearing  i  1  Canopy Beneath edge canopy  , T r e e T r u n k  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 o v e r t h e t e r r a i n segment  56  3.3.4  Sampling w i t h i n the f o r e s t During preliminary  hollows beneath  (the secondary  f i e l d w o r k , f e a t u r e s s u c h as snow  t r e e s , d r i f t i n g i n open a r e a s , w i n d  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 , w e r e observed.  Further, the l i t e r a t u r e  C o s t i n e t a l 1961).  scour,  frequently  suggests t h a t  r e c e i v e more d e p o s i t e d snow t h a n do open a r e a s e t a l 1958,  stratification)  clearings  (Anderson  S l i d i n g o f snow  from  t r e e s t o t h e snow s u r f a c e a t t h e c a n o p y edge i s a l s o cribed  ( M i l l e r 1964,  H o o v e r and L e a f On t h i s  1966,  1967,  S a t t e r l u n d and Haupt  1966). evidence, f i v e secondary  o f s t u d y ) were c h o s e n .  strata  ( o r domains  These were d e l i n e a t e d a t 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  subpopulations  where t h e v a r i a n c e s o f new snow d e p t h p o p u l a t i o n s m i g h t be homogeneous. b e l o w , and a r e shown d i a g r a m a t i c a l l y (i)  Open a r e a s  and d e n s i t y  The s t r a t a a r e d e f i n e d in Fig.  3-7.  : c l e a r areas g r e a t e r than  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 , exposed (ii)  des-  to prevailing  well  winds.  C l e a r i n g s : open a r e a s i n f o r e s t ,  one-quarter  to three tree heights i n diameter. (iii)  Canopy edge  : area immediately beneath the  edge o f t h e c a n o p y o f i n d i v i d u a l t r e e s .  57  (iv)  B e n e a t h canopy  : area beneath the  canopy  of i n d i v i d u a l t r e e s , excluding that included i n (v). (v)  Tree trunks trunks  3.3-5  o f new  infinite,  (n) n e c e s s a r y  n =  where  c  To  2  to estimate  obtained.  the.mean o f  an  confidence  (a/i) 2  = variance of  population  = value  E  = desired confidence  of t d i s t r i b u t i o n , p r o b a b i l i t y  f i n d n, i t i s n e c e s s a r y  of the p o p u l a t i o n variances (a ).  Little  are not  r e p o r t e d i n the l i t e r a t u r e .  type  snow d e p t h  i s known o f t h e s e  m e a s u r e m e n t s does s u g g e s t ,  a  limits  t o have e s t i m a t e s  o f new  density  vary w i t h storm  before  snow mass can be  t  2  t h e means  random s a m p l i n g , i s :  E  2  decided  normal p o p u l a t i o n , to w i t h i n given  l i m i t s , using simple  S  d e n s i t y must be  o f t h e mean o f s p e c i f i c  sample s i z e  the  stratum  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  snow d e p t h and  estimates  metre o f  trees.  S i z e of sample i n the s e c o n d a r y The  The  of  : a r e a w i t h i n one  S , 2  (a ) 2  values, since  A review  of  and they  rainfall  however, t h a t a , a might z y ( H u f f and S h i p p 1 9 6 9 ) , and w i t h t h e 2  2  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). R u s s i a n measurements o f t h e t o t a l a  2  z  i s considerably To  greater  estimate  1968-69.  than a  a , a pilot 2  B a s e d on  s n o w p a c k , i t seems 2  y  that  (Uryvaev e t a l 1965).  s t u d y was made i n t h e w i n t e r  A f t e r e a c h s t o r m , a n d a t 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 r a n d o m l y throughout the f o r e s t . S  2  No s e c o n d a r y s t r a t a were  recognised.  was f o u n d t o be u n i q u e f o r e a c h s t o r m a n d f o r e a c h e l e -  vation  (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 r a n d o m l y w i t h i n t h e f o r e s t w o u l d e s t i m a t e t h e mean p o p u l a t i o n  density  a t t h e 90% c o n f i d e n c e  a t e a c h e l e v a t i o n t o w i t h i n ±10 kg/m  level  (Table  3.2).  3  In the p i l o t  s t u d y , t h e c o r e f r o m t h e CRREL snow s a m p l e r was w e i g h e d  with  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 t h e l a b o r a t o r y balance used f o r a l l other is  d e n s i t y measurements.  The r e s u l t  a l a r g e r measurement e r r o r , w h i c h i s i n c o r p o r a t e d  the  value  of S . Y 2  For this  into  r e a s o n , and because o f s t r a t -  i f i c a t i o n o f the samples, i ti s b e l i e v e d that b e t t e r of population  mean d e n s i t y w e r e o b t a i n e d  d e n s i t y m e a s u r e m e n t s made i n t h e w i n t e r s  from  estimates  subsequent  1969-70',  1970-71.  I n a n o t h e r e x p e r i m e n t , 12 s a m p l e s o f new snow (1260  d e n s i t y w e r e t a k e n f r o m o p e n a r e a s a t one e l e v a t i o n This  gave a mean d e n s i t y  o f ±6 k g / m . 3  to estimate the  From t h i s  o f 160 kg/m data,  the population  95$ c o n f i d e n c e  level.  only  3  and s t a n d a r d  deviation  two s a m p l e s w e r e  mean d e n s i t y  t o ±10 kg/m  m).  3  required at  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 t h r o u g h o u t the, f o r e s t t o w i t h i n ±10 kg/m  3  at a confidence  level  Based on s t a t i s t i c s - o f p i l o t  D a t e o f Sample  Elevation 400  590  790 .  o f 90$.  study-  (Appendix B l )  (metres) 10 6.0'.  11.1.69  1260 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  9  4  8  . 13  4  4  5  11.2.69 16.2.69  2  2.3.69  4  8  7  7  7-3.69  10  6  4  4  12  4  5  9.3.69  2  28.3.69 6.4.69  4  3  60  In  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 h a d d e v e l o p e d  a hard crust.  T h i s e n a b l e d a l a r g e number o f s a m p l e s o f  new snow d e p t h t o be d e t e r m i n e d  f r o m the- s u b s e q u e n t  S u c h m e a s u r e m e n t s were made i n t h e s e c o n d a r y several elevations  and a f t e r s e v e r a l s t o r m s  I t w i l l be n o t e d t h a t S| i s d i f f e r e n t the f o r e s t  snowfall.  strata-, at ( A p p e n d i x B2) .  f o r each p o s i t i o n i n  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 t h e s t a t i s t i c s  of these  d a t a , t h e number o f s a m p l e s 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 new snow d e p t h , i s g i v e n i n T a b l e 3 . 3 .  On t h e  whole,  e s t i m a t e s t o w i t h i n ±1 cm, a t t h e 95% c o n f i d e n c e  level,  c o u l d be made w i t h f e w e r t h a n s i x s a m p l e s .  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 1260 m.  s h o u l d be t a k e n a t  A t 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  allowing frequent d r i f t i n g new snow d e p t h .  A range  e q u i v a l e n t ) , as  u s u a l l y encountered  exposed,  and hence l a r g e v a r i a b i l i t y i n o f ±1 cm i n snow d e p t h r e p r e s e n t s  a s a m p l i n g e r r o r o f ±2 kg/m water  The  2  i n specific  snow mass (±2  c a l c u l a t e d w i t h new snow  mm  densities  on Mount Seymour.  B e c a u s e t h e v a r i a n c e s o f t h e p o p u l a t i o n s o f new snow d e p t h and d e n s i t y a l t e r w i t h e a c h  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 t h e f o r e s t , i t was d i f f i c u l t  t o determine  how many s a m p l e s 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 a f t e r each storm.  of,samples  The u s e o f c o n s t a n t s a m p l e 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 s u c h t e c h n i q u e s as a n a l y s i s  of variance.  61  TABLE 3.3  Sample s i z e r e q u i r e d new  to. e s t i m a t e p o p u l a t i o n mean  snow depth' 'to - w i t h i n ±1 cm, at' a c o n f i d e n c e  level  o f 95%  B a s e d on s t a t i s t i c s - o f l a r g e  Date o f sample  Secondary Stratum •  ( S t o r m no.. )  Elevation  790  open  (45)  canopy edge  9  beneath  4  2.4.71  open  (61)  clearing  canopy  area  3  canopy edge beneath  ( A p p e n d i x B2)  (metres)  870  970  10 6,0  1260  4  4  5-  5  4  3  4  6  3  4  22  4  12  4  19.2 .71  area  samples  canopy  7.4.71  open a r e a  4  6  (62)  clearing ,  3  10 . 11  canopy edge beneath  12.4.71 (64)  7  canopy  open a r e a  4  50 .  62  However, a consequence  of this  strategy i s that the c o n f i -  dence l i m i t s , a n d / o r t h e p r o b a b i l i t y , w i t h w h i c h t h e sample e s t i m a t e s t h e p o p u l a t i o n • m e a n , v a r y on e a c h o c c a s i o n . S i x new snow d e p t h s a n d one new snow d e n s i t y ment w e r e made i n e a c h s e c o n d a r y  stratum.  measure-  An a d d i t i o n a l  s e t o f t h e s e m e a s u r e m e n t s was made i n open a r e a s 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 elevation.  Both t h e p i l o t  w i t h l a r g e samples  with  s t u d i e s and t h e experiments  i n d i c a t e d t h a t t h e c h o s e n sample  were r e a s o n a b l e f o r most s t o r m s .  sizes  T h e r e f o r e , f o r each  s t o r m 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  hsi  =  Yhsi  • hsi z  w h e r e , i = number o f r e p l i c a t i o n s i n e a c h s e c o n d a r y s t r a t u m . For depth  Z,  i = 1 , 2 , . . . 6 , e x c e p t i n open a r e a s , w h e r e , i = 1,2,  F o r d e n s i t y y,  1=1,  12.  e x c e p t i n open a r e a s w h e r e , i =  1,2.  s = number o f s e c o n d a r y s t r a t a , s = 1 , 2 , . . 5 h = number o f 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, w h e r e , n < 12. H e n c e , a t e a c h 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 m e a s u r e m e n t s were o b t a i n e d , g i v i n g 36 s a m p l e s band.  of specific  snow m a s s - f o r e a c h  elevational  63  The above s a m p l i n g scheme was. u s e d  f o r a l l storms  i n t h e w i n t e r 1969-70,. b u t i t was f o u n d i m p r a c t i c a l t o maintain this  scheme on some o c c a s i o n s i n t h e w i n t e r  1970-71, when many s u c c e s s i v e • s t o r m s elevations.  In the l a t t e r  d e p o s i t e d snow to-r l o w ; :  s i t u a t i o n s , complete  ments were a l w a y s made i n open a r e a s , and new - b u t n o t new  snow d e n s i t y  measure-  snow  depths  s a m p l e s - were n o r m a l l y  taken  i n the other f o u r strata-. 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 t h e h i g h e s t (1260  m), where a c c e s s was- by  T h i s d i d not operate i n severe weather; snow m e a s u r e m e n t s f o l l o w i n g day.  chairlift.  i n which  event,  a t t h e h i g h e s t s i t e were t a k e n t h e When b a d w e a t h e r  was p r o l o n g e d , e s t i m a t e s  f o r open a r e a s were made f r o m 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 g a u g e .  3.4  Measurement  of r a i n f a l l  R a i n f a l l was m e a s u r e d i n t h e open a t t h e 12 sites  a f t e r each  storm.  sampling  Standard f i v e - i n c h diameter  g a u g e s and P l u v i u s g a u g e s were u s e d .  In places subject  t o i n t e r f e r e n c e by t h e p u b l i c , a s e r i e s o f e x p e n d a b l e i n c h d i a m e t e r c o f f e e cans was  substituted.  c a l i b r a t e d i n d i v i d u a l l y before use.  a t two  elevations.  five-  T h e s e were  For p a r t of 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 intensity  rain,  64  A vast  literature  discusses  theinherent  from measuring r a i n f a l l w i t h r a i n gauges. reviews  arelargely  o f two t y p e s  m e n t a l s h o r t c o m i n g s and those  - those  c a u s e d by i n s t r u -  by p o o r s i t i n g  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  Rodda  ( 1 9 6 7 ) , a n d R o b i n s o n a n d Rodda  that ther e l a t i v e  Exhaustive  (.1953) a n d I s r a e l s e n (.1967).  a r e g i v e n by K u r t y k a  Errors  errors  o f the i n s t r u -  values.  Further,  ( 1 9 6 9 ) , h a v e shown  c a t c h f o r t h e same t y p e  o f gauge may v a r y  w i t h l o c a t i o n a n d season.. In t h i s and ±0.5  study,  rainfall  i nthe standard  gauges  c o f f e e c a n s c o u l d be m e a s u r e d t o ±0.13 mm, a n d t o mm f o r t h e P l u v i u s g a u g e s .  This  i s a smaller  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. assess  t h e sampling  error for r a i n f a l l ,  measure-  To  gauges were  est-  a b l i s h e d t h r o u g h o u t open a r e a s a t f o u r e l e v a t i o n s .  The  results  gives  f r o m s e v e r a l s t o r m s i n d i c a t e a s i n g l e gauge  a good e s t i m a t e considerably  (Table  lower  3.4).  This  sampling  error i s also  t h a n t h a t f o r new snow mass  (Appendix  B l , , B2) . All  rain  g a u g e s were s o p o s i t i o n e d t h a t t h e ' o r i f i c e '  was p a r a l l e l t o t h e g e n e r a l  slope- o f t h e t e r r a i n , as r e c o -  mmended b y t h e W o r l d 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 n o t e q u i p p e d w i t h w i n d s h i e l d s , a s recommended mountain a r e a s by I s r a e l s e n (1967). e l e v a t i o n s on Mount  Seymour  However, a t l o w e r  open a r e a s a r e e f f e c t i v e l y  for  65  TABLE 3.4  Statistics in selected  o f ..large s a m p l e s o f r a i n f a l l ' open a r e a s  S t o r m No.  Date o f  Elevation  Sample  Mean  S.D.  (1970-7D  Sample  (metres)  Size  (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 f r o m w i n d by t h e s u r r o u n d i n g f o r e s t . .  Ab.oye.900. m,  exposure  so some  t o w i n d i n c r e a s e s as t h e f o r e s t  undercatch would r e s u l t after  each  3.5  here.  thins,  Because  gauges-were  s t o r m , e v a p o r a t i o n l o s s e s were  Measurement o f m i x e d . r a i n / s n o w  rain/snow boundary  may  m i g r a t e up  T h u s , b o t h r a i n . a n d snow may  occur.  negligible.  events  D u r i n g some s t o r m s , t h e f r e e z i n g the  l e v e l and. h e n c e  o r down t h e  a mixed  snow s t o r m r e m a i n s  a m a j o r measurement p r o b l e m  meteorology.  simple procedures used i n t h i s  have n o t s o l v e d t h i s p r o b l e m , b u t a r 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  mountain.  D e t e r m i n a t i o n of the  amounts o f r a i n - and t h e amount o f snow a f t e r  The  emptied  rain/  of hydrostudy  designed to minimise  amounts o f s n o w f a l l  and  rainfall. If all  rain  fell  after  a p e r i o d o f snow, some, i f n o t  o f it,.-was a b s o r b e d by t h e snow;  some c o u l d  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 l a y e r s " . that t h i s  l a t t e r p o r t i o n was  r a i n gauge was The  resulted  To  a b s o r b e d by t h e new  i n an i n c r e a s e d v a l u e o f new  to  but then c r e d i t s  s n o w f a l l a t the expense  of  of the  surface.  snow  layer  snow d e n s i t y .  t h i s procedure 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 precipitation,  ensure  measured, the o r i f i c e  p l a c e d f l u s h w i t h t h e o l d snow  p o r t i o n of the r a i n  also  Thus,  storm  excess water e q u i v a l e n t rainfall.  67  If rainfall  a s t o r m b e g a n w i t h , r a i n , t h e n t u r n e d , t o snow,  was m e a s u r e d i n t h e r a i n gauge a n d s n o w f a l l by  the  procedure p r e v i o u s l y  was  t h e sum o f t h e t w o .  described.  Total  precipitation  I f any s n o w f a l l m e l t e d i t w o u l d  e n t e r t h e r a i n gauge a n d be m e a s u r e d a s r a i n f a l l .  Thus,  t h i s procedure can c r e d i t excess water t o r a i n f a l l a t the to  expense  of snowfall,  However, t h i s  e r r o r was l i k e l y  be s m a l l , s i n c e m e a s u r e m e n t s were made as s o o n as  possible  a f t e r t h e e n d o f t h e s t o r m , b e f o r e any a p p r e c i a b l e  melt could b e g i n .  3.6  Measurement o f rime  accretion  Rime f o r m s on t e r r e s t r i a l driven supercooled airflows.  o b j e c t s exposed  t o wind  The r i m e i s a c c r e t e d by  f r e e z i n g o f 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 t h e y s t r i k e an exposed  surface  ( L a Ch'apelle 1969).  The Mount Seymour w i n t e r e n v i r o n m e n t conditions  conducive t o the development  o f r i m e , b u t to-  a c t u a l l y measure t h e i n p u t o f w a t e r i n t h i s because  can p r o v i d e  form i s d i f f i c u l t ,  much i s a c c u m u l a t e d on t r e e s o r i s m i x e d w i t h  f a l l ' during storms.  The amount o f r i m e a c c u m u l a t e d on  objects i s also a function o f - t h e i r size and'Berndt  1971).  snow-  a n d shape  (Fowler  H e r e , o n l y an i n d e x o f t h e i n p u t o f  water from rime i s o b t a i n e d by measuring the  horizontal  l e n g t h o f r i m e a c c r e t e d f r o m s t o r m s 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, t h e snow  surface.  The d i r e c t i o n o f growth. Calways i n t o , t h e p r e v a i l i n g was a l s o r e c o r d e d f o r e a c h s t o r m .  wind)  C a r e was t a k e n t o  remove a l l r i m e f r o m t h e s t a k e s b e f o r e t h e n e x t O b s e r v a t i o n s were made a t e a c h . s a m p l i n g  site  b e t w e e n 6 December 19 70 a n d 31 May 1971.  storm.  f o r a l l storms  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 t h e p r e v i o u s winter.  3.7  M e a s u r e m e n t o f snow c o v e r On t h e t e r r a i n  phenology  s e g m e n t , t h e e l e v a t i o n s o f t h e snow  c o v e r , o f t h e new snow b l a n k e t a f t e r e a c h  s t o r m , and o f  snow on t r e e s , w e r e r e c o r d e d by s i x z o n e s  d e f i n e d hereunder.  O b s e r v a t i o n s w e r e made on e a c h v i s i t On t h e a v e r a g e , days. are  one v i s i t  The e l e v a t i o n s  t o t h e mountain.  was made e v e r y two o r t h r e e  of t h e lower l i m i t s  of these  zones  somewhat s u b j e c t i v e , b u t c o n s i d e r e d a c c u r a t e t o ±30 m. (a)  C o m p l e t e snow cover.' : t h e zone i n w h i c h t h e snow c o v e r s more t h a n 90 p e r c e n t o f t h e g r o u n d surface. here  (b)  The l o w e r l i m i t  c a l l e d t h e "complete  Incomplete  snow c o v e r  of t h i s  zone i s  snowline".  : t h e zone where some  snow i s o b s e r v e d , b u t g r e a t e r t h a n 10 p e r c e n t of  t h e ground  c a n be s e e n .  I t includes  69  a r e a s where snow h o l l o w s a r o u n d eocposed  the ground  have  s u r f a c e .(cf. Brooke  The l o w e r l i m i t o f t h i s  zone i s h e r e  the "incomplete snowline" (c)  trees  C o m p l e t e new snow c o v e r  196.6). called  (Hj_) .  : t h e zone i n w h i c h t h e  new snow f r o m a s t o r m c o v e r s more t h a n 90 p e r cent of the s u r f a c e . "complete (d)  Incomplete  The l o w e r l i m i t  new s n o w l i n e "  i s the  (H ). c  new snow c o v e r : t h e zone i n w h i c h  some new snow i s o b s e r v e d , b u t g r e a t e r t h a n 10 p e r c e n t o f t h e u n d e r l y i n g s u r f a c e c a n be seen.  The l o w e r l i m i t  of t h i s  zone,  here  c a l l e d t h e " i n c o m p l e t e new s n o w l i n e " and d e n o t e d by H , Q  i s d e f i n e d as t h e l o w e s t  e l e v a t i o n a t w h i c h new snow c o u l d be r e c o g n i s e d . '.(A s t o r m , w i t h a ^ f r e e z i n g l e v e l much l o w e r than normal would  deposit-new  previous snowlines.  snow b e l o w t h e  After this  event, the  e l e v a t i o n s o f t h e s n o w l i n e s and new would (e)  snowlines  coincide).  M o d e r a t e t o h e a v y snow l o a d s - on t r e e s zone i n w h i c h t r e e s bore  : the  a l l p a r t s of-the branches  snow.  The snow must be  to n o t i c e a b l y bend t h e b r a n c h e s .  of  sufficient The  lower  70  e l e y a t i o n of t h i s "heavy  load l i n e " . .  be m e l t i n g Light  zone  i s here c a l l e d the  Usually  from the t r e e s i n t h i s  snow l o a d s on t r e e s  either  no- . snow w o u l d  only parts  zone.  : t h e zone  i n which  o f the branches of t r e e s  b o r e snow, o r t h e snow l o a d on t r e e s d i d n o t n o t i c e a b l y bend'the  branches.  The  first  c o n d i t i o n • o f t e n r e s u l t e d f r o m m e l t d u r i n g aperiod the  o f sunny  weather, o r from a r i s e i n  freezing l e v e l during  subsequent  rain  a storm, with the  a l l o w i n g some snow t o m e l t  or s l i d e o f f branches.  Generally,  t h e snow  was b o r n e by t h e b r a n c h s t e m , n o t t h e f o l i a g e . The s e c o n d c o n d i t i o n r e s u l t e d f r o m a of t h e f r e e z i n g l e v e l and r a i n / s n o w after  the passage  of a front.  in this the  snow r a p i d l y zone.  boundary  I n these  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 Usually,  lowering  light.  disappeared from  The l o w e r l i m i t i s h e r e  " l i g h t load l i n e " .  trees called  71  3 .7  M e a s u r e m e n t o f n e t snow, a c c u m u l a t i o n Measurement o f s n o w p a c k . w a t e r 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 s a m p l e r , w h i c h  Work e t a l (.1964)  s i d e r t o o v e r e s t i m a t e by an average- 8%. s a m p l e s were t a k e n i n e a c h viously,  a t each  sampling  of the f i v e  Two  con-  or three  strata- defined pre-  s i t e - w h e r e snow was  present.  M e a s u r e m e n t s were o b t a i n e d a b o u t e v e r y two w e e k s , b u t o c c a s i o n a l l y more o r l e s s f r e q u e n t l y d e p e n d i n g  on w e a t h e r  conditions. A much b e t t e r e s t i m a t e o f snow p a c k w a t e r alent  equiv-  c o u l d h a v e b e e n made by u s i n g a s e r i e s o f snow  courses;  h o w e v e r , t h i s w o u l d h a v e 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 m e a s u r e m e n t s o f w a t e r e q u i v a l e n t  were a l w a y s  t a k e n a t t h e same p l a c e , h e n c e t h e y  compared.  These measurements d i f f e r  c a n be  from those  o f snow  d e p o s i t i o n , i n t h a t t h e y a r e b u t an i n d e x o f snowpack d e v e l o p m e n t , r a t h e r t h a n an e s t i m a t e , o f t h e p o p u l a t i o n mean w a t e r e q u i v a l e n t . Some o f t h e w a t e r e l e v a t i o n s i n 1971  e q u i v a l e n t measurements a t h i g h  were l a t e r f o u n d t o be l o w when c o m p a r e d  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 a t a d j a c e n t vations.  Ice lenses produced  these erroneous  because they prevented obtainment i n the sampling tubes.  o f complete  Snowpack d e n s i t i e s  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 .  ele-  measurements . snow  cores  computed  However,  from  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 p a r a m e t e r equivalent..  than  is-water  Thus, r e a s o n a b l e e s t i m a t e s o f t h e t r u e  d e n s i t y were p o s s i b l e b e t w e e n two d a t e s f o r w h i c h 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 .  snow  Converted  v a l u e s o f w a t 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 densities  a n d known snowpack d e p t h s .  d e n s i t y a g a i n s t time o f season  Plots  o f snow  4 . 1 3 , 4.14)  (e.g. F i g s .  were a l s o f o u n d u s e f u l i n c h e c k i n g f o r o t h e r e r r o n e o u s water e q u i v a l e n t measurements.  3.9  Measurement o f a i r t e m p e r a t u r e To e x a m i n e t h e a i r t e m p e r a t u r e r e g i m e  tain,  including theelevation of freezing  storm p e r i o d s , a network  on t h e moun-  levels,  o f s i x temperature  during  recording  s t a t i o n s was e s t a b l i s h e d b e t w e e n 120 m a n d 1260 m ( F i g . 2 . 3 ) . Air  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  thermohygrographs  i n s t a n d a r d Department  Casella  o f Transport-  S t e v e n s o n s c r e e n s f o r most o f t h e p e r i o d O c t o b e r t o May for  two y e a r s , 1969-70 a n d 1970^71.  To c a l i b r a t e t h e  r e c o r d , s t a n d a r d p r e c i s i o n maximum a n d minimum were p l a c e d i n e a c h s c r e e n .  Temperatures  were  thermometers extracted  f r o m t h e c h a r t s e v e r y two h o u r s , a n d a r e c o n s i d e r e d a c c u r a t e to  ±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 , e x p o s e d  and' c o u l d be r a i s e d o r l o w e r e d t o a b o u t  one m e t r e  tree  trunks,  above t h e  73  snowpack s u r f a c e ' . blowing  To p r e v e n t  snow., t h e y were l i n e d on t h e i n s i d e w i t h  n y l o n mesh.  During  most s t o r m s i t i s b e l i e v e d  v e n t i l a t i o n was g o o d . r e s u l t e d from p e r i o d s ditions. ibility  t h e s c r e e n s , from, f i l l i n g  Exceptions  with  white that  at the highest  station  of intense riming or b l i z z a r d  con-  O c c a s i o n a l l y a c l o c k would s t o p , o r t h e f l e x of the bimetallic  through formation  s t r i p w o u l d become a l t e r e d ,  o f i c e on t h e t h e r m o h y g r o g r a p h s .  .These c o n d i t i o n s were e s p e c i a l l y common when t h e f r e e z i n g l e v e l lowered r a p i d l y a f t e r a p e r i o d of r a i n . Temperatures during for to  analysis.  At these  storm periods  times  o n l y were u s e d  r a d i a t i o n errors are l i k e l y  be n e g l i g i b l e , a n d v e n t i l a t i o n a r o u n d t r e e t r u n k s a n d  screens  adequate.  above 1000  Brooke  (1966) m e a s u r e d  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  c o m m u n i t i e s .and on e x p o s e d s i t e s .  He r e p o r t s  d i f f e r e n c e s i n maximum t e m p e r a t u r e s d u r i n g but  "temperatures are l a r g e l y  regardless To forest  of vegetation  cover  e q u a l i s e d on  large  sunny w e a t h e r , overcast.days,  and e x p o s u r e " .  e x a m i n e t h e f r e e a i r t e m p e r a t u r e above t h e  canopy d u r i n g s t o r m s , a c a b l e , w i t h  b e a d s a t i n t e r v a l s , was a t t a c h e d tower.  temperatures  thermistor  t o t h e CBUT t e l e v i s i o n  The t o w e r i s l o c a t e d on an e x p o s e d r i d g e a t 870  and  e x t e n d s more t h a n 25 m above t h e f o r e s t c a n o p y .  The  highest  51.3  t h e r m i s t o r was a t an e l e v a t i o n o f a b o u t 920  m above t h e g r o u n d .  T h i s t h e r m i s t o r was  covered  m  m,  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• t h e t h e r m -  i s t o r was m e a s u r e d on a W h e a t s t o n e b r i d g e a n d 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 b o x , f o r 130 s e c o n d s e v e r y minutes.  28  D u r i n g e a c h 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 t h e c i r c u i t of temperature  for calibration.  The v a l u e s  o b t a i n e d f r o m t h e r e c o r d e r c h a r t s were  s i d e r e d a c c u r a t e t o ±0.25°C. taken throughout  con-  T h e s e m e a s u r e m e n t s were  most o f t h e . p e r i o d J a n u a r y  t o May,  d u r i n g t h e two w i n t e r s 1969-70 .and 1970-71. T h e r e i s good a g r e e m e n t b e t w e e n f r e e a i r temperatures recorded temperatures  on t h e t e l e v i s i o n t o w e r a t 920 m a n d  measured a t t h e temperature  a t 970 m ( P i g . 3 . 8 ) . random f r o m  recording station  The d a t a p r e s e n t e d was drawn a t  15 d i f f e r e n t  storms.  On t h i s e v i d e n c e  assumed t h a t d u r i n g most s t o r m s t h e s c r e e n accurately r e f l e c t e d the free a i r thermal The 1:1  line  i t i s  temperatures regime.  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 s t o r m s (see s e c t i o n 9 . 3 - 2 ) .  This lapse rate 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 Smithsonian  lapse rates given i n the  M e t e o r o l o g i c a l Tables  f o r the conditions of  most s t o r m s a t a b o u t 950 m ( i . e . p r e s s u r e temperatures  -10 t o 15°C).  950 t o 850 mb,  75  15  o CM  01  v L.  3 **  O t_ tl  1:1  a E  line allowing  lapse r a t e of  for  0v7°C/100m  <_  1.5 Air  F i g . .3.8  temperature in screen at 970 m  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 a t 920-m w i t h -temperatures i n a s c r e e n i n t h e f o r e s t a t 970 m, The 1:1 l i n e t a k e s i n t o a c c o u n t . t h e d i f f e r e n t e l e v a t i o n s o f t h e temperature s e n s o r s . 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 t h e end  o f 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  product  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 w i t h i n the f o r e s t  (when c o m b i n e d w i t h a m o d e l o f 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 t h e snowpack  t i o n s d i s c u s s e d below.  Conversely, analysis  snowpack v a r i a t i o n s m i g h t s u g g e s t sition  f e a t u r e s t h a t s h o u l d be  particular  of  variathese  snow-depo-  investigated.  This  b e g i n s by d o c u m e n t i n g t h e b e h a v i o u r o f t h e s n o w l i n e t h e l e n g t h o f t h e snow s e a s o n s p a t i a l and  and  on Mount Seymour.  temporal v a r i a t i o n s  o f n e t snow  chapter and  N e x t , •'  accumulation  a r e e x a m i n e d , t h r o u g h t h e f i e l d m e a s u r e m e n t s on  the  Mount Seymour t e r r a i n s e g m e n t , and t h r o u g h  the  p e r i o d of r e c o r d from North Shore Mountain  snow c o u r s e s .  F i n a l l y , behaviour  longer  o f t h e 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 The d a t e s  and l a s t  of the f i r s t  l e n g t h o f t h e s n o w f a l l season  snow on the- g r o u n d a n d - l a s t s n o w f a l l , and t h e  at various elevations,. for  two w i n t e r s , a r e g i v e n i n A p p e n d i x C. of  the f i r s t  Sometimes t h e date  s n o w f a l l was t h e same a t a number o f e l e v a t i o n s .  T h i s was a c o n s e q u e n c e o f a m a r k e d l o w e r i n g o f t h e s n o w l i n e by a s t o 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 . A t t h e t o p o f t h e mountain-, t h e f i r s t the end o f O c t o b e r  i n both  1969  snow f e l l  and 1970..  The' d a t e s when snow was l a s t p r e s e n t ground, a t each sampling  (1113 1st.  11 y e a r s  on t h e  a r e a a r e a l s o g i v e n i n A p p e n d i x C.  These a r e c o m p a t i b l e w i t h t h e l o n g term d a t a During  available.  o f r e c o r d a t t h e Mount Seymour snow  m), t h e r e was a l w a y s  station  (950  course  some snow on t h e g r o u n d on J u n e  F r o m 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  climatic  toward  m), snow was a l w a y s  Ridge  p r e s e n t on t h e  g r o u n d a t t h e e n d o f A p r i l , and d i s a p p e a r e d by t h e e n d o f May on 11 o c c a s i o n s . 4 years.  I t p e r s i s t e d i n t o June, i n the other  Through 9 years  snow m e l t e d  completely  disappeared  i n May.  summer, snow p a t c h e s at  a t Mount Seymour (CBUT) t h e  i n April  i n one y e a r , b u t o t h e r w i s e  I n an u n s e a s o n a b l y  c o o l and  stormy  can s u r v i v e u n t i l t h e f o l l o w i n g w i n t e r  e l e v a t i o n s above 1200. m (.e.g. as i n 1 9 6 4 , D r . 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  a feature of both winters studied  o f s n o w l i n e s were  (Pigs.  4.2, 4.4).  For  t h e 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 t h e new  s n o w l i n e s o f - s u c c e s s i v e storms  Frequently  t h e y were l o w e r e d  (Figs.  4.1, 4.3).  s e v e r a l h u n d r e d m e t r e s 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 , t h e s n o w l i n e sometimes r o s e r a p i d l y , l e s s d r a m a t i c a l l y , when m e l t than u s u a l storm e l i m i n a t e d this  d u r i n g a warmer  a t h i n snow c o v e r . F o r  r e a s o n , and b e c a u s e o f v a r i a t i o n s  existing plete  and r a i n w a s h  though  i n snow d e p t h  snowpack w i t h e l e v a t i o n , t h e c o m p l e t e  snowlines d i d not always  behave  and  of the incom-  similarly.  The d i f f e r e n c e s i n t h e n a t u r e o f t h e i n p u t t o t h e snowpack a t e a c h 4.3),  produced  e l e v a t i o n i n t h e two w i n t e r s ( F i g s . 4.1,  marked c o n t r a s t s i n snowcover.  w i n t e r 196.9-70, t h e c o m p l e t e 1000 m.  T h i s was a l m o s t  In the  s n o w l i n e was u s u a l l y  close to  500 m h i g h e r t h a n t h e f o l l o w i n g  y e a r , when i t d e s c e n d e d 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, t h e s n o w l i n e s seldom  p e r s i s t e d a t t h e 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 t h e end o f A p r i l , steadily  in parallel  were f e w e r new  t h e s n o w l i n e s began t o r i s e  f a s h i o n as m e l t p r o c e e d e d ,  i n p u t s o f snow.  they rose at a r a t e  o f 5.6 m/day.  and t h e r e  I n t h e w i n t e r o f 1969-70,. I n 1970-71, t h e r a t e  Occurrence of rain s t o r m 1200 -  1  t  I I I I  1  •  1 1  i I I I  1  1 1  II  1000-1  ti  1 D  t  800-J  I  et  •  .1 •  1  1  II  1  i»  • 1  i  t II*  ¥  <u 6 0 0 '  E  c o v« o >  4>  •  Hi »•  i , R a i n storm  I  •  I i  I • I •  400-  200H  i  Complete new Snowcover  1  I  Incomplete new Snowcover  OCT  Winter 1 9 6 9 - 7 0  NOV  DEC  JAN  FEB  M A R  APR  MONTH  Fig.  4.1  E l e v a t i o n a l c o v e r a g e o f new snow a t end o f e a c h s t o r m w i n t e r 1969-70  MAY  9  Fig.  4.2  Seasonal 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 •*-*  •' i i i  4)  E C  600  H •  g  Rain s t o r m I i  a > US  400  C o m p l e t e new Snowcover  H  200 H  j 1  I  i.! i  incomplete new Snowcover  OCT  Winter 1970-71  NOV  DEC  FEB  JAN  MAR  APR  MONTH  Fig.  4.3  Elevational  c o v e r a g e o f new snow a t end o f e a c h s t o r m , w i n t e r 1970-71  MAY  -p"  :  NOV  DEC  r-'  1  JAN  "T* FEB  I MAR  | APR  I MAY  JUN  MONTH  Fie.  4.4  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 s w i n t e r 1970-71  co  83  of r i s e , b e g i n n i n g from an e l e v a t i o n - 400. m lower., was 6.5 m/day.  T h i s compares with, a r i s e of. 21 m/day, f o r  the " e q u i v a l e n t s n o w l i n e " o f Court' (.196.3), i n t h e . K i n g ' 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 t h e E a s t e r n A l p s (Landsberg  1958).  L e t a melt degree day be d e f i n e d as  a day w i t h maximum temperature  1°C above f r e e z i n g a t 1260 m.  Then t h e r e was an average o f 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 d a t a , t h e r a t e ' o f r i s e o f t h e s n o w l i n e s was found t o be t h e same f o r both w i n t e r s , 1.1 m/melt degree day.  4.1.3  Season and d u r a t i o n of snow cover The snow season ( p e r i o d between f i r s t and l a s t snow  on the g r o u n d ) , and d u r a t i o n ( a c t u a l number of days w i t h snow on the ground) a t s e v e r a l e l e v a t i o n s f o r two w i n t e r s are g i v e n i n Appendix C, and p l o t t e d i n F i g s . 4.5, 4.6. Both a r e s u b s t a n t i a l l y g r e a t e r at a l l e l e v a t i o n s i n the w i n t e r 1970-71.  S i n c e 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 a t e l e v a t i o n s above 1200 m.  I n another a r e a f o r which;  s i m i l a r d a t a i s a v a i l a b l e , t h e E a s t e r n 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 h i g h e r ( G e i g e r 1965) .  I n t h e years o f t h i s s t u d y , the d u r a t i o n  was u s u a l l y c o n s i d e r a b l y l e s s than t h e snow  season,  8  Fig.  4.6  Snow c o v e r p h e n o l o g y , w i n t e r  1970-71  \  85  b e c a u s e o f m i d - w i n t e r -melt p e r i o d s . this  At higher  elevations,  d i f f e r e n c e d e c r e a s e d , , e s p e c i a l l y i n the. c o l d e r  winter  o f 1970-71. I n g e n e r a l , t h e snow c o v e r i n F i g s . 4.5,  4.6  phenology  behaved i r r e g u l a r l y  parameters  with elevation,  e x c e p t f o r t h e d u r a t i o n o f t h e c o m p l e t e snow c o v e r . c u r v e t e n d e d t o f l a t t e n a t lower- e l e v a t i o n s .  This  Here t h e  d u r a t i o n was c o n s t r a i n e d by t h e s m a l l number o f s t o r m s producing  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 a n d e a r l y summer by an . - i n c r e a s e i n t h e energy a v a i l a b l e f o r melt. increase. tion and  T h e r e a r e two r e a s o n s f o r t h i s  F i r s t , t h e amount o f i n c o m i n g s h o r t - w a v e r a d i a -  grows l a r g e r i n May a n d J u n e as t h e d a y s ' g r o w 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  d o m i n a t e t h e V a n c o u v e r w e a t h e r (Kendrew and K e r r W a l k e r 1961). frequent surface  falls  1955,  S e c o n d l y , f o r most o f t h e w i n t e r , t h e r e a r e o f new snow ( F i g s . 4 . 1 ,  4.3),  s o t h e snow  u s u a l l y h a s 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  a r e g i v e n f o r new snow i n U.S. Army 1 9 5 6 ) . falls  longer,  o f new snow become i n f r e q u e n t  In spring,  o r cease and  consequently,  more o f t h e g r e a t e r i n c o m i n g s h o r t w a v e r a d i a t i o n w i l l 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  shows t h a t t h e d u r a t i o n o f t h e c o m p l e t e snow c o v e r  be  which d i d not  e x c e e d 250 d a y s d e s p i t e t h e m a g n i t u d e o f t h e maximum w i n t e r water  equivalent.  F i g . , 4.7  R e l a t i o n s h i p b e t w e e n d u r a t i o n o f c o m p l e t e snow c o v e r and w i n t e r maximum o f snowpack w a t e r e q u i v a l e n t  87  A s y s t e m where, c o n s t r a i n t s , a c t ..to.' i m p o s e l i m i t s o n g r o w t h a t l o w e r and  u p p e r p o i n t s , can  sigmoid growth f u n c t i o n duration  d a t a i t has D  C L o t k a 1956).  the  =  be. r e p r e s e n t e d When f i t t e d  by  the  to  the  form:  C 1 + ,e- (H-H ) K  d  where  For trial  and  D• =  duration  C  =  value  e  = ' base of n a t u r a l  K  =. c o n s t a n t  H  =  elevation  =  e l e v a t i o n c o r r e s p o n d i n g t o t h e most r a p i d r a t e o f change o f d u r a t i o n ( m e t r e s )  1969-70 t h e s  e r r o r methods D ,= 1  and  o f c o m p l e t e snow c o v e r  o f maximum d u r a t i o n  (this i s r e l a t e d to rate o f i n c r e a s e of d u r a t i o n w i t h elevation) (metres)  r e s u l t a n t equation was,  230 -0.010(H-990).  +  e  +  210 -0..00.6 (H-560).  = 1  e  (days)  logarithm  f o r 1970-71 d a t a , D  (days)  found by i n f o r m a l  88  (Figs.  T h e s e 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  results  4.5,-4.6), e x c e p t above 10 0.0. m i n 1971. •  This  anomaly r e s u l t e d b e c a u s e J u n e 1971, c l o u d i e s t months on r e c o r d .  was  one  of the'coolest,  T h i s meant t h e 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 c o 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 time of y e a r .  The  analysis  s u g g e s t s t h a t t h e maximum  d u r a t i o n o f t h e snow c o v e r . (C) i s n o r m a l l y i n t h e of  this  vicinity  210-230 d a y s f o r Mount Seymour.  4.2  Seasonal v a r i a b i l i t y  4.2.1  Variability The  of the  snowpack  o f snow c o u r s e r e c o r d s  snow c o u r s e s o f t h e N o r t h S h o r e  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, begin to melt  ( A p p e n d i x D, F i g . 3-5).  t h e snowpack b e g i n s t o b u i l d  then  I f i t i s assumed  i n e a r n e s t i n mid  t h e n t h e 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 Seymour (1113  m)  i s 2.41  B e t w e e n F e b r u a r y and May 0.87 first  cm/day.  Average  h a l f o f May,  second h a l f .  December, a t Mount  cm o f w a t e r e q u i v a l e n t / d a y . the average, r a t e o f i n c r e a s e i s  r a t e o f m e l t i s 0.93  i n c r e a s i n g t o 2.18  However, t h e s e r a t e s  cm/day i n t h e  cm/day i n t h e can a l t e r  f r o m month t o m o n t h and y e a r t o y e a r . 1964,  rapidly  markedly  F o r ex;ample, i n  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  least  89  June 1 s t .  I n some o t h e r y e a r s , t h e maximum has  r e a c h e d by A p r i l r a t h e r t h a n May.  been  O c c a s i o n a l l y , t h e snow-  p a c k may  d e c r e a s e r a t h e r t h a n i n c r e a s e i n t h e months  p r i o r to  April. The  standard d e v i a t i o n s of water e q u i v a l e n t at  Mount Seymour o v e r an 11 y e a r p e r i o d a r e a t l e a s t q u a r t e r o f t h e mean, f u r t h e r i l l u s t r a t i n g t h e variability ability  from year to year  (Table 4.1).  i n c r e a s e s w i t h the season, because  one  substantial This  vari-  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 years.  On t h e N o r t h S h o r e M o u n t a i n s  equivalent recorded i n A p r i l 371  was  t h a n 140  4.2.2  ( s n o w p a c k c l o s e t o maximum)  cm a t L o c h Lomond, and t h e l o w e s t , 38  Grouse Mountain extreme  the h i g h e s t water  range  (Appendix D).  of A p r i l  1st  cm,  at  A t a l l snow .courses,, t h e  water e q u i v a l e n t s i s g r e a t e r  cm.  Variability  of f i e l d observations  V a r i a t i o n s o f snowpack w a t e r e q u i v a l e n t t h r o u g h o u t the of  two w i n t e r s 1969-70, 1 9 7 0 - 7 1 a r e p l o t t e d a t a number elevations  i n Pigs. 4.8,  (or sampling s i t e s ) f o r a l l secondary 4.9.  The . pl'ots i l l u s t r a t e - :  b u i l d u p o f t h e snowpack may m e l t p e r i o d s Cas the  strata,  that the steady  be i n t e r r u p t e d by  midwinter  f o r example..in w i n t e r 1 9 6 9 - 7 0 ) ,  r a p i d m e l t o f t h e pack, t o w a r d t h e end o f t h e  and'by season.  90  TABLE 4.1  Mean, s t a n d a r d d e v i a t i o n a n d c o e f f i c i e n t o f 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 ) , .Seymour  M o u n t a i n - s n o w c o u r s e , ' 1960-1970 C o e f f i c i e n t o f v a r i a t i o n o f snow d e n s i t y given f o r comparison Density  Water E q u i v a l e n t MONTH  me an  st.dev.  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  11  May 15  174  -56  31 32  Jun 1  140  68  49  6  TABLE 4.2  Summary  statistics  9  o f w a 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 1960-1970> N o r t h S h o r e M o u n t a i n snow c o u r s e s  Snow c o u r s e  Elevation Cm)  me an  s t .dev.  C.V. %  1158  133  48  36  162  54  33  Dog M o u n t a i n  1113 10 82  127  45  35  Hollyburn  1022  159  52  33  Loch  1097 884  115  47  41  153  55  36  Grouse  Mountain  Mount Seymour  Lomond  Palisade.Lake-  Source:  Computed f r o m d a t a i n " B . C . Snow S u r v e y 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  OCT  NOV  DEC  FEB  JAN  MAR  APR  MAY  JUN  MONTH  80  1060 m  60  -\  3  Clearings  cr  20  -\  Open  Areas  NOV  DEC  1  JAN  FEB  MAR  1 APR  " — T MAY  JUN  MONTH  E 40 u  970 m  c V  /ANn  a cr  UJ  .  L.  V  o 5  0  . NOV  .DEC  '  JAN  '  FEB  '  MAR  APR  '  MAY  JUN  MONTH  P i g . 4.8  Snowpack w a t e r e q u i v a l e n t i n open a n d i n t h e 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  92  260  DEC  JAN  FEB  MAR  APR  MAY  JUN  JUL  MONTH  MONTH  Fig.  4.9  Snowpack' w a t e r e q u i v a l e n t i n open a n d 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  93  160 970 m 120 H  80  40 •  c  S>  0 Estimate based upon known depth and assumed density, Open A r e a s  870 m  t_ v  -o  120  -»  -f  + ._ .  a  S  5 80  40  :  <i -A  A  Clearings  1- Canopy Beneath  Edge Canopy  Close to Tree Trunks  H  DEC  JAN  FEB  MAR  APR  MAY  APR  MAY  MONTH  DEC  JAN  FEB  MAR MONTH  F i g . . 4:.9  Continued..  JUN  JUL  94  The recorded this  Seymour M o u n t a i n - snow course, c o n s i s t e n t l y  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  s t u d y made a t a s i m i l a r e l e v a t i o n on t h e  segment . ...However, t h e  snow c o u r s e  terrain-  i s s i t e d on  s h e l t e r e d p a r t o f t h e m o u n t a i n , and  probably  of  a  records '  water e q u i v a l e n t s greater 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 records a t G r o u s e M o u n t a i n , w h i c h i s 45  those 8.3  values  km  t o the west  (Table  4.3  V a r i a t i o n s of net  4.3.1  Snow c o u r s e  4.2,  greater  m higher  Appendix  and  than only  D).  snow a c c u m u l a t i o n  with elevation  observations  Mean w a t e r e q u i v a l e n t s a t snow c o u r s e s North  S h o r e M o u n t a i n s - show no  their  complete records  are  on  different  t r e n d w i t h e l e v a t i o n when  considered  (Appendix D),  nor 4.2).  e v e n when a common p e r i o d o f r e c o r d i s e x a m i n e d ( T a b l e This  suggests that the e f f e c t  variations  due  accumulation  to other  and  o f 1.0 4 cm  Rushmore  Kittredge per  10$  factors.  by  D i f f e r e n c e s o f snow  o f 2-1.38$ h a v e b e e n r e p o r t e d w i t h a s p e c t  (Meiman 1 9 6 8 ) . crease  o f e l e v a t i o n i s masked  alone  P a c k e r C1962, I d a h o ) s h o w s . a l i n e a r i n per  C1960,. New  10$.  .decrease - i n f o r e s t c a n o p y .  Y o r k ) giye. y a l u e s  (1953, C a l i f o r n i a ) v a l u e s  o f 0.84  f r o m 1.27  cm  t o 5-59  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  Lull and cm,  species.  95  A n d e r s o n and  P a g e n h a r t .0-957, C a l i f o r n i a ) showed  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 , 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 .  that,  and. f o r e s t In  coastal  i British  Columbia distance  from the  sea  affects local •  t e m p e r a t u r e : a n d w e a t h e r m a r k e d l y , so t h a t in  snow a c c u m u l a t i o n can  4.3.2  Field  occur over short  the  two  month and (It  winters  p l o t t e d as  s h o u l d be  was  adjusted  a function  made t w i c e  at  1260  on  a v e r y exposed knob.  of the  is typical  first  of e l e v a t i o n  that  the  of l a r g e  through-  day  of  equivalent  i n 1970-71).  Values  sampling s i t e  areas of the  each  ( F i g . 4.10)..  water  However, t h e y are  was  retained upper  because  part  mountain.  (U.S.  Army, 1956,  alent  (y-axis) increased  from the  snowline.  relationship  F i g . 1,  The  3.3),  linearly  with  Basin,  the  elevation  snow-wedge f o r m  equiv-  (x-axis) linear  x - a x ; i s , f o r m e d a "snow-Wedge" .  were n o t The  Oregon  suggest water  line•representing this  of goodness o f - f i t .  display this  Willamette  Plate  together with  o r i g i n a l data- p o i n t s  given  to the  m seem a n o m a l o u s , b e c a u s e t h e  S i m i l a r p l o t s f o r the  The  distances.  f o r open a r e a s  noted t h a t , f o r c l a r i t y ,  s c a l e i n 1969-70 was  such a s i t e  variations  observations  Snowpack. w a t e r e q u i v a l e n t out  large  shown, and  no  indication  Mount Seymour d a t a  ( F i g . 4.10). a l t h o u g h  also the  96  100  500  600  700  800  900 Elevation  4 00  500  600  700  800  Elevation  4.10  1000  1100  1200  1300  (metars)  900  1000  1100  12 0 0  (metars)  V a r i a t i o n • o f • .snowpack w a t e r e q u i v a l e n t with.' elevation,--; on t h e f i r s t day o f e a c h m o n t h , open a r e a s , f o r w i n t e r s 1969-70 ( t o p and1970-71 ( b o t t o m ) .  13 0 0  TABLE 4.3  R a t e o f change o f snow a c c u m u l a t i o n w i t h Some e x a m p l e s  elevation  reported i n the literature  R a t e o f Change E l e v a t i o n Range' ' (cm w a t e r equiv/100 m) (metres)  LOCATION  SOURCE  California  2500-3420  10 .2  Court  California  1770-2190  18.3  M i x s e l l e t a l (1951)  Alberta  1520-1680  12 .9  Stanton  Colorado  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 M e x i c o  3020-3380  4.5  Gary a n d C o l t h a r p  Idaho  820-1680  8.9  Packer  (1962)  Ben Ohau R a n g e , N.Z.  975-1646  18.1 *  Archer  (1970)  1020-2340  73.4  N.Z. H y d r o l o g y A n n u a l (1968)  647-1500  25.0  U .'S.  0-1260  54.0  This study  Tasman G l a c i e r , Willamette- Basin Mount Seymour  N.Z.  * B a s e d on d e p t h o f snow, n o t w a t e r  (1963) (1966)  (1967)  Army (1956)  equivalent  —a  98  wedges a r e n o t as s i m p l e Willamette As  as t h o s e  j  a r u l e , the slope  constant  o f • the'-'snow wedge  P l a t e 3-3,  i n the Willamette F i g . 2).  The  Basin  snow-wedge  (U.S. Army  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 w e r e much than reported  4.4  on  f o r other areas i n North  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 This  section discusses  field  greater  America (Table  4.3).  w i t h i n the f o r e s t  m e a s u r e m e n t s , comments  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 t h a t i n open  4.4.1  between t h a t i n t h e f o r e s t s t r a t a  from  areas.  Snow i n c l e a r i n g s The amount o f snow i n c l e a r i n g s was n o t  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 , sampled. 4.4..  became  season, but remained  d u r i n g the melt p e r i o d .  behaved s i m i l a r l y 1956,  f o rthe  Basin.  l a r g e r during the accumulation fairly  reported  The r e s u l t s  These r e s u l t s  environments  signifi-  at any-elevation  of "t"--tests are given, i n Table  c o n t r a s t w i t h r e p o r t s from  (.Anderson e t a l 1958,  P o s s i b l e reasons f o r t h i s  conflict  other  C o s t i n e t a l 196l;) . are :  99  TABLE 4 . 4 . Mean water, e q u i v a l e n t  I n open a r e a s  w i t h : mean w a t e r e q u i v a l e n t  compared  i n forest strata  - r e s u l t s of "t"-test  Winter  Forest  1969-70  10 6.0  clearings  ns  ns  canopy  *  edge  970  870".  (metres) 790 . 710  590  — -  ns  —  —  ns-  -  -  — -  -•  -  -  *  *  close to tree trunks  s  *  *.  -  -  -  clearings  ns  ns  ns  ns  ns  ns  ns  canopy  ns  ns  ns  ns  ns  ns  ns  ns  *  ns  ns  ns  *  *  *  *  *  *  *  beneath  canopy  edge canopy  close to tree trunks  Notes  Elevation 1260  beneath  1970-71'  Strata  i)  ii)  (iii)  ns  The " t " - t e s t e x a m i n e s t h e n u l l hypothesis that ]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 w a t e r e q u i v a l e n t . ns = no s i g n i f i c a n t d i f f e r e n c e f o u n d b e t w e e n 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 level). Number o f p a i r e d o b s e r v a t i o n s 9 and, 1 4 .  v a r i e d between  ( i v ) The v a r i a n c e b e t w e e n p a i r e d s a m p l e s were homogeneous, i n a l l c a s e s e x c e p t f o r , t h o s e c o m p a r i s o n s b e t w e e n open a r e a s a n d t r e e trunks at the 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 u n e q u a l v a r i a n c e s was u s e d . ( S t e e l a n d T o r r i e I 9 6 0 , p.8l).  100  (a)  The  d e n s i t y of f r e s h l y  fallen (Chapter  Therefore,  above c l e a r i n g s i s '  turbulence  In s e v e r a l of the above, the  4.9  6).  snow.  studies r e f e r r e d to  snowpack was  sampled a t , or  a f t e r , maximum a c c u m u l a t i o n . i n d i c a t e t h a t snow  Figs.  p a r t of the  latter  not  m a r k e d d u r i n g t h e p e r i o d when t h e  s e a s o n , and  This  connected w i t h m e l t i n g  important  than those  a greater  T h e s e r e s u l t s may m,  so may  that  a r e more  snowpack i n c l e a r i n g s . :  have l e s s v a l i d i t y  a t 970  m,  where the open a r e a s sampled were  not  h a v e b e h a v e d as l a r g e c l e a r i n g s .  remained longer  snow-  of deposition' i n pro-  s u b s t a n t i a l l y greater than four tree heights and  is  suggests  processes  ducing  b e l o w 790  during  the  p a c k i s b u i l d i n g up.  4.8,  accumulation  becomes g r e a t e r i n c l e a r i n g s o n l y  and  on  Mount Seymour i s h i g h  less effective i n d r i f t i n g (b)  snow  i n .diameter, Snow a l w a y s  i n c l e a r i n g s t h a n i n open a r e a s  (Figs.  4.8,  4.9). 4.4.2  Snow i n o t h e r  forest  strata  I n 1970-71', w a t e r e q u i v a l e n t s and  o c c a s i o n a l l y beneath the  at the  canopy, were not  canopy  edge,  significantly  I  101  d i f f e r e n t , f r o m t h a t i n t h e open,. "t"-tests  a r e g i v e n i n T a b l e 4.4.)  t h e r e were s i g n i f i c a n t  well  the t r u n k s of t r e e s  defined  developed  i n t h e s e a s o n , 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 .  T h e s e h o l l o w s became p r o n o u n c e d 4.8,  w i n t e r 1970-71 ( P i g s .  4.4.3  o n l y t o w a r d t h e end' o f t h e  4.9).  Snow h o l l o w s The  (Fig.  I n t h e w i n t e r . 196.9!-70  d i f f e r e n c e s , because  h o l l o w s i n t h e snow a b o u t early  (The r e s u l t s , o f t h e  4.11)  h o l l o w s r e f e r r e d t o above a r e c a l l e d  snow h o l l o w s  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 B r o o k e o f snow by t r e e  (1966).  They a r e c a u s e d by  crowns, wind  s c o u r , melt about  interception the  tree  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 f r o m t h e t r e e , p r e f e r e n t i a l melt beneath melt r e s u l t s because  Preferential  t h e a l b e d o o f t h e snow s u r f a c e i s  d e . c r e a s e d by m e l t d r i p foliage.  the canopy.  and n e e d l e s f a l l i n g  H o l l o w s c a n be a c c e n t u a t e d when  from the  p e r i p h e r y o f t h e canopy.  tree  intercepted  snow s l i d e s o f f a t r e e t o f o r m a r a i s e d r i m b e n e a t h  importance depending  and'  E a c h p r o c e s s assumes  the  different  on t h e n a t u r e and t i m e o f t h e w i n t e r .  Snow h o l l o w s a p p e a r  t o be  a distinctive  feature  o f a w e s t coas't m i d l a t i t u d e m o u n t a i n  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 s u c h as 1969-70 ..  They a r e ' u s u a l l y  102  F i g . 4.11 Snow h o l l o w s i n m i d - s e a s o n ( t u p , e l e v a t i o n 1000 m, J a n u a r y 1969) and l a t e i n s e a s o n ( b o t t o m , 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 I m m e d i a t e l y above t h e s n o w l i n e , 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 a n d m e l t  processes a r e dominant.  As t h e s e a s o n p r o g r e s s e s ,  hollows develop at p r o g r e s s i v e l y higher the  where new snow  elevations  Wind  scour  In t h e c o l d e r , snowier winter tribution  of deposited  wind at e l e v a t i o n s wind scouring  a b o v e 1000  m.  excavated hollows,  snow was p i l e d  against  o f 1970-71, t h e d i s -  snow was s t r o n g l y a f f e c t e d  metre deep, beneath t h e t r e e  played  a different  often greater  t h a n one  canopy edge ( F i g . 4.12)  the trunks  of trees.  In t h i s  and  Consequently dis-  p a t t e r n than at lower e l e v a t i o n s , pr  than i n the previous,  Snowpack  by the  Prom F e b r u a r y t o A p r i l ,  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 t h e f o r e s t  are  on  mountain.  4.4.4  4.5  snow  milder winter  (Fig.  4.9).  density s e c t i o n , snow c o u r s e a n d f i e l d  examined t o assess t h e v a r i a b i l i t y  o f snow  observations density.  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 m e a s u r e d e p t h than the water equivalent  o f t h e snowpack.  Water  a l e n t s may b e c o m p u t e d i n s u c h c a s e s i f e s t i m a t e s made o f snowpack d e n s i t y .  Density  rather equivc a n be  i s also a useful  104  F i g . 4.12 Wind s c o u r a b o u t t r e e s d u r i n g M a r c h 1971 a t 1260 m. Bottom photograph i s a close-up view of a wind scour h o l l o w .  105  parameter f o r a s s e s s i n g c e r t a i n m e c h a n i c a l and t h e r m a l p r o p e r t i e s of snow OB.ader 196.2)..  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 o f snowpack d e n s i t y D u r i n g t h e w i n t e r s o f t h i s s t u d y , snowpack d e n s i t y  tended t o i n c r e a s e through t h e season temporary  ( F i g . 4.13), although  decreases i n t h e d e n s i t y were i n t r o d u c e d by sus-  t a i n e d p e r i o d s o f heavy s n o w f a l l (e.g. A p r i l 1970, February1971) .  The l o n g e r p e r i o d o f r e c o r d from t h e North  Shore  Mountain snow courses a l s o shows a steady i n c r e a s e (Appendix D ) .  As i n d i c a t e d by Seymour Mountain d a t a , t h e  v a r i a t i o n s from year t o year i n snowpack d e n s i t y i s l e a s t d u r i n g t h e 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 o f about 600 kg/m . 3  F u r t h e r i n c r e a s e s i n d e n s i t y can o n l y be made by  firnification,  a p r o c e s s h a l t e d by melt o f t h e snowpack.  The l a r g e r s t a n d a r d d e v i a t i o n s o f t h e a c c u m u l a t i o n p e r i o d r e f l e c t t h e v a r i a b i l i t y o f i n p u t o f d e p o s i t e d snow i n t o the snowpack.  The d e n s i t y o f new snow may range from 100  to  400 kg/m , 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 o r m e l t p e r i o d s may occur at t h i s time  3  of year i n some w i n t e r s .  T h i s was t h e s i t u a t i o n p r i o r  to March 1 1970,. when t h e d e n s i t y at t h e Mount Seymour snow course was 42.3 kg/m . 3  By c o n t r a s t , t h e p e r i o d p r i o r  to March 1971, when t h e d e n s i t y was  352 kg/m , was 3  106  600-  -  —r  i • ' "  1—  I  f  I  i  /i1  X ^ x :  i  ' i  500 H  1  '\ i i  /  ' &  y° 'I A/i V* E ~^400-  6\  0  /  o a  &i i  300-  3 ^  / //  \ x /  Z > 4 \\ \  /1  n  \\\\  \W  4  a  1260m  X  1113m.Mount  A  1060m  •  200-  DEC  I  *  JAN  FEB  Seymour  Snow  -  Course  970m  MAR  APR  MAY  600  JUN  T~~T  500  +  ' O  e> 400  '  ,5  A  A  2  Q 300  v  9 X  •  Pig.  DEC  ~~  4.13  1  JAN  1  FEB  o •  O  %  O  200  Q  x  1  MAR MONTH  1  1113  Mount  •  970m  •  870m  O  790m  A  710m  +  590m  APR  1  Seymour  Snow  Course  MAY  ~~  JUN  R  -Density o f snowpack i n open a r e a s i n w i n t e r 1969-70 ( t o p ) a n d 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, f e w .melt p e r i o d s , a n d a l a r g e number- o f c o l d show s t o r m s d e p o s i t i n g l o w . d e n s i t y The is  snow.  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  different  variability  f r o m t h a t o f snow w a t e r e q u i v a l e n t  4.1 f o r comparison).  Snow d e n s i t y v a r i e s  (see Table  l e s s as melt  p r o g r e s s e s a n d i s a l s o t h e more c o n s e r v a t i v e  parameter.  This small seasonal v a r i a b i l i t y  o f snowpack d e n s i t y h a s  a l s o b e e n n o t e d by F i n d l a y  c  and M Kay  estimates o f water equivalent  (1972).  Thus good  a t any one e l e v a t i o n c a n be  made t h r o u g h o u t t h e s e a s o n w i t h many snow d e p t h a n d 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, a s e l s e w h e r e on t h e N o r t h S h o r e M o u n t a i n s l a t i t u d e mountains  and o t h e r west  coast mid-  s u c h as i n New Z e a l a n d , a r e s u b s t a n t i a l l y  g r e a t e r t h a n t h o s e 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 t h e h i g h e r d e n s i t y o f newly midwinter  f a l l e n snow, t h e f r e q u e n t  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 , a n d c o m p a c t i o n by t h e l a r g e o v e r b u r d e n p r e s s u r e s of the.deep  snowpack.  practical implications.  These h i g h d e n s i t i e s have F o r example,  vertical  several  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 a n y g i v e n d e p t h , . a n d on s l o p e s , s u b s t a n t i a l snow c r e e p p r e s s u r e s ' c a n d e v e l o p  (Mackay  and Mathews 1 9 6 7 ) , which.-may s e v e r e l y damage b u i l d i n g s o r trees.  108  i  IOO  r  FEB  MAR  APR  MAY  MONTH  Fig.  4.14  S e a s o n a l v a r i a t i o n i n a v e r a g e 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 A m e r i c a n 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 f r o m McKay ( 1 9 6 8 ) . New Z e a l a n d d a t a f r o m N.Z. H y d r o l o g y A n n u a l . (1968) i s ' b a s e d 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 Since  the Federal  snow t u b e does n o t m e a s u r e snow-  p r e c i s e l y (Work e t a l 1 9 6 4 ) , i t i s  pack water e q u i v a l e n t difficult  t o compare w i t h  over s m a l l ranges.  confidence  o f snowpack d e n s i t y w i t h  clearly  defined  pattern  elevation  ( F i g . 4.13).  No  emerges b e c a u s e o f t h e d i f f e r i n g  and o t h e r  a t each e l e v a t i o n .  metamorphism p r o c e s s e s 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 f r o m t h e N o r t h S h o r e M o u n t a i n snow c o u r s e d i s p l a y no c l e a r t r e n d w i t h  4.5-3  vary  o f new snow amount, new snow d e n s i t y , snow m e l t ,  overburden pressure operating  snow d e n s i t i e s w h i c h  F i e l d measurements i n d i c a t e a c o n f u s e d  pattern  influences  with-elevation  elevation  records  (Appendix D).  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 t h e f o r e s t Since  the differences  i n snowpack d e n s i t y  between  f o r e s t s t r a t a a p p e a r t o be o f t h e same m a g n i t u d e a s t h e measurement e r r o r o f t h e F e d e r a l  snow t u b e , l i t t l e  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 . general  statement, d e n s i t i e s are higher  of f r e q u e n t  melt-drip  because  o f snow  i s not simple  snow i n o p e n a r e a s ,  (Chapter 6 ) , so t h e v a r i o u s  o f new snow t h a t  near t r e e s  the formation  The d i s t r i b u t i o n o f snow d e n s i t y  trees  H o w e v e r , as a  f r o m t h e f o l i a g e , a n d more r a p i d  m e t a m o r p h i s m o f t h e snow w i t h  some s t o r m s d e p o s i t  c a n be  hollows.  because  but not beneath  strata receive  are different i nquantity  inputs  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 , the  snow f r o m w i n d  4.6  chapter has d e s c r i b e d  Shore M o u n t a i n s .  Prom t h i s  t h e snowpack o f t h e N o r t h  d i s c u s s i o n may be drawn  w h i c h a r e l i k e l y t o be common t o o t h e r  midlatitude 1.  compaction.  Conclusions This  features  because t h e f o l i a g e . p r o t e c t s  west  several coast  mountains :  They a r e c h a r a c t e r i s e d by a deep snowpack w h i c h exists  f o r greater  vations  t h a n 7 months a t h i g h e r  Ce.g. above 1200 m on Mount  Seymour, a b o v e  1600 m on Tasman G l a c i e r , New Z e a l a n d ) . e l e v a t i o n s b e l o w 500 m t h e r e snow i n some w i n t e r s . is  ele-  may be l i t t l e  At o r no  'At a l l ' e l e v a t i o n s t h e r e  substantial variability  i n the winter  equiv-  a l e n t o f t h e snowpack f r o m y e a r t o y e a r . 2.  There a r e l a r g e and f r e q u e n t snowline,  f l u c t u a t i o n s ofthe  c o n t r o l l e d b y p o s i t i o n s o f new s n o w l i n e s  and. t h e common m i d - w i n t e r m e l t 3.  The d u r a t i o n . :of t h e s e a s o n a l  periods.  snow c o v e r i s c o n -  s t r a i n e d a t b o t h upper and lower  elevations.  Ill  Show w a t e r e q u i v a l e n t the  s h a p e o f a snow-wedge.  wedge c h a n g e s w i t h If  varies with elevation- i n The s l o p e o f t h i s  season.  t h e m o u n t a i n i s f o r e s t e d , snow i n c l e a r i n g s  may n o t be s i g n i f i c a n t l y open a r e a s .  different  In milder winters  form around t r e e s .  Scour w i l l  from t h a t i n  snow h o l l o w s occur  about  will trees  e x p o s e d t o s t r o n g w i n d s i n c o l d e r s t o r m s , when t h e d e n s i t y o f s u r f a c e snow i s - l o w . mean snow a c c u m u l a t i o n t h a n i n open  Such  features  w i t h i n the f o r e s t i s l e s s  areas.  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 t h e s e a s o n to  be more c o n s e r v a t i v e  lation.  than those  Thus r e a s o n a b l e  estimates  tend  o f snow accumuo f snow  d e n s i t y a t any one e l e v a t i o n may be made f r o m 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 water  equivalent  This i s  i f snowpack d e p t h i s known.  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 rather than d e p o s i t i o n a l processes Density other  melt-  dominate.  o f t h e snowpack i s g r e a t e r t h a n f o r many  environments.  T h e r e i s no c l e a r p a t t e r n  of v a r i a t i o n of 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  5 .1  Introduction The  NET 'SNOW ACCUMULATION  possibility  of e s t a b l i s h i n g workable  empirical  r e l a t i o n s h i p s b e t w e e n n e t s e a s o n a l snow a c c u m u l a t i o n e l e v a t i o n on w e s t c o a s t m i d l a t i t u d e m o u n t a i n s • a r e in  this  w(H,  chapter.  T h e s e r e l a t i o n s h i p s w o u l d be  T) = f ( H , H-j_), where w i s w a t e r  p a c k a t some e l e v a t i o n H,  concept  examined of the  e q u i v a l e n t of the  The  utility  such  m o u n t a i n s 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  in  the f o r e s t  snow-  o f t h e snow  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  An a t t e m p t  form  and Hj_ i s t h e e l e v a t i o n o f t h e  i n c o m p l e t e s n o w l i n e a t t i m e T. course  and  examined.  i s made t o e s t i m a t e n e t snow a c c u m u l a t i o n  s t r a t a f r o m t h a t i n open a r e a s .  Finally  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 a t t e m p t e d  i n v o l v e snow Apart  estimations w i l l  deposition. f r o m Mount Seymour, snow a c c u m u l a t i o n i s c o n -  s i d e r e d f o r t h r e e o t h e r examples o f 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 b e c a u s e t h e y r e p r e s e n t e x t e n s i v e e a r l y w o r k on type of mountain of concern h e r e .  The  mountains'of  the  .this  TABLE 5•1  C h a r a c t e r i s t i c s o f west  c o a s t m i d l a t i t u d e m o u n t a i n s c h o s e n as e x a m p l e s  Characteristics  Mount Seymour  Willamette Basin  Ben Ohau Range  Tasman G l a c i e r  'Country  B.C. C a n a d a  O r e g o n U.S.A.  South  South  Slope range (degrees) Aspect range (degrees) Elevation (meters)  range  Max. e l e v a t i o n sampled (meters) Max. snow water equiva l e n t sampled (cm)  8  I s . N.Z.  20 .  I s . N.Z.  15  12  25  225  75  75  1260  853  671  1320  1260  1500  1646  2340  236  203  40  596  Vegetation  hemlock Douglas f i r cedar  Douglas f i r hemlock noble 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 observation  1969-71  1949-51  1966  1968-69  Reference  author's observations  U.S. Army  (1956)  Archer  (1970)  N.Z. H y d r o l o g y A n n u a l (1968)  114  b a s i n a r e s i m i l a r t o .Mount Seymour i n t h a t t h e zone o f ' seasonal  snow c o v e r  are not f o r e s t e d .  i s forested.  The New Z e a l a n d  examples  The snow, c o v e r  on t h e Tasman G l a c i e r  may n o t be t y p i c a l o f many m o u n t a i n s l o p e s b u t t h e s e  data  are  up  to  i n c l u d e d because o f t h e great  range o f a l t i t u d e ,  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 o f n e t snow a c c u m u l a t i o n  5.2.1  A n a l y s i s ' o f snow wedge  with elevation  data  P l o t s o f t h e snow wedge f o r t h e W i l l a m e t t e (U.S.  Army 1956,  equivalent  P i g . l , p l a t e 3.3)  (the ordinate)  suggested that  i n c r e a s e d as a s i m p l e  function with e l e v a t i o n (the abscissa)  Basin water  linear  from the  snowline.  H o w e v e r , t h e snow wedges p r o d u c e d on Mount Seymour ( F i g . and  on t h e Tasman G l a c i e r do n o t a l w a y s show  increases  constant.  of water equivalent w i t h e l e v a t i o n .  t h e Mount Seymour d a t a a l l o w a s i m p l e  linear  F o r example, f i t for  J a n u a r y 1970,  a n d up u n t i l M a r c h f o r t h e w i n t e r  but  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.  otherwise  Such c u r v i l i n e a r i t y r e s u l t s  1970-71,  f r o m m e l t a t lower- e l e v a t i o n s ,  when t h e u p p e r p a r t s o f t h e wedge a r e s t i l l r e c e i v i n g f r e s h i n p u t s o f snow.  1  T h i s e f f e c t was most p r o n o u n c e d i n  1969-70 ,. b e c a u s e t h e w i n t e r was u n u s u a l l y m i l d , w i t h frequent  m e l t p e r i o d s , and because few storms  snow b e l o w 900  m.  4.10)  deposited  115  It  i s p o s s i b l e , .to, de.s-cri.be w(H,.. T), f o r  e x a m p l e s w i t h l i n e a r and  c u r v i l i n e a r .functions.  s u c h a p r o c e d u r e w o u l d be' o f l i t t l e i n d i c a t e s t h a t the consistently  shape o f t h e  or d e c r e a s i n g  lation  data  i s not  The  because' P i g .  snow wedge does n o t  U.S.  the  same f r o m y e a r  to  constant Moreover,  of  this  year.  Army (1956) b e l i e v e d t h a t d u r i n g t h e  water equivalent  Basin there  ( F i g . 5.2).  accum-  existed a of-the  a t the. u p p e r s a m p l e l i m i t  simple  snow wedge  of  the  This i m p l i e d that a s i n g l e monthly  measurement o f snowpack w a t e r e q u i v a l e n t mountain would a l l o w d e f i n i t i o n Unfortunately, this t o be  remaining  suggest t h a t the behaviour  season i n the W i l l a m e t t e  mountain  Even  ( F i g . 5.1).  l i n e a r r e l a t i o n s h i p b e t w e e n t h e mean s l o p e and  4.10  behave  to year.  s e a s o n , and  d u r i n g the melt p e r i o d  t h e Mount Seymour  However,  snow wedge c h a n g e s , g e n e r a l l y b e c o m i n g  l a r g e r d u r i n g the accumulation  mean s l o p e  value  f r o m month t o m o n t h , o r y e a r  t h e mean s l o p e o f t h e  these  simple  of the  at the  top  f u n c t i o n w(H,  r e l a t i o n s h i p does n o t  of  the  T).  appear  v a l i d f o r o t h e r west coast m i d l a t i t u d e mountains.  F u r t h e r , f o r t h e Mount Seymour examples, t h e r e l a t i o n s h i p is  different  i n successive  years  of t h i s method t o s a t i s f a c t o r i l y  ( F i g . 5.2). estimate  The w(H,  T)  e v e n more a p p a r e n t when i t i s remembered t h a t t h e surface  of the  as i m p l i e d by  snow we'dge I s " n o t  the  use  failure becomes upper  always" a s t r a i g h t l i n e ,  o f t h e t e r m "mean s l o p e " ;  A  116  SoutharnHamispharaMonth May  D«c  Jun  Jan  Jul  Aug  Fab  Mar  Sap  Apr Northarn  Fig.  5.1  Oct  May Hamisphara  Nov  Jun  Dac  Jul  Jan  Fab  Mar  Aug  Sap  Oct  Month  S e a s o n a l y a r i a t i o n i n mean o f snow wedge  slope  117 80  640 W a t e r  Fig.  5.2  equivalent  at  highest  s a m p l e  point  ot  snow  w e d g e  ( c m )  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 o f w a t e r e q u i v a l e n t a t t h e u p p e r s a m p l i n g l i m i t on t h e m o u n t a i n  120  Mount Seymour S n o w  100  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 9 7 0 - 1 0 6 0 m b e l o w  1970-71  O . •  9 7 0 m  A  80  60  40  W i l l o m e t t e  B a s i n  1949-51  20  OB  ho  40 Water  80 equivalent of  • F i g . 5«3  120  snow  160  at highest wedge  sample  200  240  point  section  S l o p e o f s e c t i o n s 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 o f water e q u i v a l e n t a t t h e upper l i m i t o f each s e c t i o n  118  similar  a n a l y s i s o f t h e Mount Seymour d a t a , but. f o r .homo-  g e n e o u s s e c t i o n s o f t h e snow wedge,, d i s p l a y e d b u t t h e s e were s t i l l or  year to year The're  not. . c o n s i s t e n t , f r o m s e c t i o n t o  (Pig.  section  5.3)•  i s a l s o no a p p a r e n t  r e l a t i o n s h i p between: t h e  w a t e r e q u i v a l e n t o f t h e snowpack a t t h e u p p e r of  some, t r e n d s ,  sampling  t h e snow wedge and t h e p o s i t i o n o f t h e s n o w l i n e  (Fig.  H o w e v e r , t h e p o i n t s on t h e g r a p h do d e s c r i b e a t y p e elliptical  path through the season  ( e . g . Mount Seymour,  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 w e s t c o a s t -  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 t h e f o r m o f a snow wedge.  However, the  s l o p e and r e l a t i o n s h i p w i t h t h e s n o w l i n e o f t h i s  to  year  year.  5.2.2  are  5-4).  of  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 to  limit  not  snow wedge  c o n s i s t e n t f r o m month t o m o n t h , y e a r t o y e a r o r  locality.  I t must t h e n be  r e l a t i o n s h i p s o f t h e f o r m w(H, p r e d i c t i v e m o d e l s on t h i s fails  shape-,  concluded that T) w i l l  empirical  not produce  type of mountain.  locality  The  reliable approach  b e c a u s e t h e s l o p e and e x t e n t o f t h e snow wedge i s n o t  c o n s i s t e n t l y r e l a t e d t o t h e m a g n i t u d e o f t h e snowpack o r time of year.  600  Willamette  Basin  500 o a  c» a. E . a ~ •o E  Mount 400 Tasman  m «» » •c cn ID ^ 'JE «•  Seymour  Glacier  Ben Ohau Ra.  1949  O  1950  O  1951  A  1969 -70  •  1970 -71  •  1968 - 6 9  •  1966  300  ° *o c c  C*  1/1  O  H-  > o  200  cr » t-  a 5  100  h  200  400  600  800  1000  1200  1400  1600  1800 r—  Elevation  Fig.  5.4.  of snowline  Water e q u i v a l e n t a t upper s a m p l i n g l i m i t vation of the snowline  (meters)  o f snow wedge a s a - f u n c t i o n o f e l e -  1  VO  120  On w e s t c o a s t m i d l a t i t u d e m o u n t a i n s ' i t  i s possible  f o r water equivalents, to-be s i m i l a r i n d i f f e r e n t years ( o r m o n t h s ) a t one e l e v a t i o n , b u t t h e d i s t r i b u t i o n equivalent  with  year to year. This  of water  e l e v a t i o n may be m a r k e d l y d i f f e r e n t f r o m  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  played  i n e a r l i e r e x a m p l e s , has been r e p o r t e d  ( P a c k e r 1962,  A n d e r s o n a n d West 1 9 6 5 ) .  dis-  elsewhere  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 c o u r s e a t one e l e v a t i o n provide  For  coast  mountain. t h e h y p o t h e t i c a l e x a m p l e , a snow c o u r s e a t  e l e v a t i o n 1300 1 as i n y e a r 2.  m records  t h e same'water e q u i v a l e n t  Y e t t h e volume o f w a t e r s t o r e d  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 By  cannot  a good i n d e x o f snow a c c u m u l a t i o n on a w e s t  midlatitude  5.5.  A h y p o t h e t i c a l e x a m p l e i s shown i n F i g .  than that  i n year  as  seasonal  i n year  2.  r e l a t i n g t h e shape o f t h e 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 pack at t h e h i g h e s t  e l e v a t i o n s a m p l e d n e e d n o t be i n d i c a t i v e  o f t h e t o t a l amount o f w a t e r s t o r e d Further,  samples o f t h e s h a l l o w  s n o w l i n e assume g r e a t e r with  the r e l a t i v e l y  o f the'snow-  on t h e m o u n t a i n .  snowpack n e a r t h e  i m p o r t a n c e , b e c a u s e when c o m b i n e d  l a r g e a r e a o f any c a t c h m e n t a t t h i s  e l e v a t i o n , t h e y a r e shown t o p r o d u c e a s i g n i f i c a n t bution  seasonal  t o t h e t o t a l w a t e r s t o r e d as snow.  contri-  121  Pig.  5.5  H y p o t h e t i c a l e x a m p l e 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 years  122  5.3  F a c t o r s c o n t r o l l i n g t h e shape o f t h e snow wedge There  are three p r i n c i p a l processes that  control  shape o f - t h e snow wedge : (a)  The  v a r i a t i o n of p r e c i p i t a t i o n w i t h  On most m o u n t a i n s  there i s ' a s t e a d y - i n c r e a s e of  precipitation with elevation. of  elevation.  However t h e  rate  i n c r e a s e , and t h e e l e v a t i o n o f any maximum o f  precipitation, will wind  change w i t h t h e s t a b i l i t y  and  1956).  s h e a r o f t h e s t o r m a i r mass (Sawyer  Hence t h e f r e q u e n c y o f v a r i o u s s t o r m t y p e s  will  determine the v a r i a t i o n w i t h e l e v a t i o n of 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 o f  (b)  the  snowpack.  The  v a r i a t i o n o f snow m e l t w i t h  It  i s characteristic  elevation.  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 b e t w e e n w i n t e r s t o r m s ,  melt w i l l  occur at l e a s t  at  lower-elevations.  However, from y e a r t o y e a r the energy for  melt i s u n l i k e l y  t o be t h e same a t  available each  elevation. (c)  The  e l e v a t i o n of the rain/snow boundary  successive  during  storms.  T h i s boundary  i s largely  freezing levels.  c o n t r o l l e d by  storm'  Winter storm f r e e z i n g  levels  the  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 m o u n t a i n s may move o v e r  a wide range o f e l e v a t i o n i n t h e space  o f a few d a y s Ce.g. a h e a d o f and b e h i n d  a family  of east'moving f r o n t s ) .  of winter  storm  The f r e q u e n c y  f r e e z i n g l e v e l s a t 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 the main f a c t o r  c o n t r o l l i n g t h e shape and s l o p e  o f t h e snow wedge. f o l l o w i n g chapters'. those  s n o w f a l l s may'be  This i s investigated i n I t i s significant  that i n  c o n t i n e n t a l m o u n t a i n r e g i o n s where t h e .  f r e e z i n g l e v e l i s a t - ( o r " b e l o w " ) t h e 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 does n o t a p p e a r t o e x i s t .  effect  Consistent empirical  r e l a t i o n s d e s c r i b i n g w(H, T) m i g h t t h e n be possible  ( e . g . i n Western Colorado,  Conservation Grasnick  5.4  U.S.  Soil;  S e r v i c e , 1965-67, a n d i n Germany:,  1967) .  E s t i m a t i o n o f n e t 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 s n o w p a c k . w a t e r e q u i v a l e n t i s m e a s u r e d i n open 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 regression techniques. by' t h e s t e p w i s e  t h a t i n t h e f o r e s t by of Table  5.2,produced  a l l o w such  estimates  The e q u a t i o n s  regression procedure,  t o be made, f o r any p a r t o f t h e s e a s o n . close to tree trunks - the equation  areas  F o r one  i n c l u d e s a time  stratumelement.  TABLE  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 o f snowpack w a t e r e q u i v a l e n t in  f o r e s t s t r a t a b a s e d on a c c u m u l a t i o n i n open a r e a s  of est(cm) S.E.  Winter  Forest stratum  Regression equation  1969-70  clearing (CL) canopy edge ( C E ) b e n e a t h canopy ( C ) close to tree t r u n k s (TR)  CL= CE= C= TR=  0.8-1.060+0.OO120H  clearing (CL) canopy edge ( C E ) b e n e a t h canopy CC) close to tree t r u n k s (TR)  CL= CE=  5 . . 4 + 0 , 9 40, 1.8+0.750  1970-71  Data from w i n t e r s c l e a r i n g ( C L ) 1969-70, 1 9 7 0 - 7 1 canopy edge ( C E ) b e n e a t h canopy ( C ) combined close to tree t r u n k s (TR)  4.O+O.OOO80H -.0 .7+0 .OOO60H -1.9+0.OOO50H  .  c= -1.2+0.650 TR=  CL= 4.0+0.940 CE= -1.0+0.750 • c = -2.6+0.650, TR=  -7 .0 + 0 . 8 2 0 - 0 . O O 2 0 T  i)  All  (iii)  0 -= H = T =  ( iv)  45 45 45  0.92 0 .86 0 .75  8.5 9.4  45 81. 81 81  0.67 0.96 0.91 0.91  81  0.90  11.6 10.8  126 126  11.1  126  11.1  126  regression  v a l u e s o f r o r R s i g n i f i c a n t a t 99$ c o n f i d e n c e l e v e l . s n o w . a c c u m u l a t i o n i n open a r e a s (cm) a t an e l e v a t i o n , H . e l e v a t i o n o f measurement ( m e t r e s ) t i m e i n d a y s , f r o m December 1 . v a r i a b l e s t e s t e d were :  0H T  0 H T  2 2 2  2  8.1  Regression equations found u s i n g forward stepwise m u l t i p l e  (i i )  R  9.4 10 . 2  9.7 9.6 10 .4  -7.9+0.900-0.OO20T  n  NOTES:  (  (em)  0H 0T HT  0.95 0.90 0.87  ' 0.83  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 melt  around  t h e b a s e o f t r e e s , t h e r e l a t i o n s h i p s betw.een snow accumulation i nthis  s t r a t u m a n d t h a t i n t h e open c h a n g e s w i t h  season. 95  percent  c o n f i d e n c e l i m i t s h a v e b e e n computed  a b o u t a n 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 ( F i g . 5.6) and-beneath the canopy  ( F i g . 5-7)  v a l u e o f a c c u m u l a t i o n i n the open.  clearings  for a given  The c o n f i d e n c e  limits  f o r t h e s e e x a m p l e s s p a n a n i n t e r v a l o f 38 cm a n d 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 t h e 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 t h e open i s g r e a t e r t h a n a b o u t 100 cm w a t e r e q u i v a l e n t . Those e q u a t i o n s based  on t h e c o m b i n e d d a t a f o r  two w i n t e r s a r e n o t v e r y d i f f e r e n t 1970-71.  from those f o r w i n t e r  H o w e v e r , t h e c o m b i n e d a n a l y s i s was  dominated  by d a t a f o r t h e s e c o n d w i n t e r , b e c a u s e o f l a r g e r and a g r e a t e r r a n g e w o u l d be u s e d  of values.  samples  The e q u a t i o n s f o r 1969-70  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 a r e 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 t h e  r e l a t i o n s h i p b e t w e e n snow a c c u m u l a t i o n i n t h e open in theforest produced lines  and-that  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  by t h e d e v e l o p m e n t o f snow h o l l o w s .  (Regression  f o r e x a m p l e s o f e l e v a t i o n s 1260 m a n d 400.. m are-  given i n Figs:  5.6,  5.7).  I f t h e w i n t e r i s c o l d e r , w i t h h e a v y snow accumul a t i o n , t h e e q u a t i o n s f o r w i n t e r 1970-71,  or for a l l '  126  Snowpack  Fig.  5.6  water  equivalent in open  (cm)  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 i n c l e a r i n g s ( C L ) f r o m t h a t i n open a r e a s ( ( J ) ) . . The two e x a m p l e s o f l i n e s f o r a m i l d w i n t e r a r e b a s e d on t h e e q u a t i o n d e r i v e d f r o m 1 9 6 9 - 7 0 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 w i t h e l e v a t i o n term  127  40  80 Snowpack  Fig..5.7  120 water  equivalent  160 in  open  200  240  (cm)  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). f r o m t h a t i n open a r e a s ((J)) . The two e x a m p l e s o f l i n e s f o r a m i l d w i n t e r a r e b a s e d on t h e e q u a t i o n d e r i v e d f r o m 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 w i t h , e l e v a t i o n term-  128  data  c o m b i n e d w o u l d be  (i.e.  high R  values)  2  appropriate. obtained, f o r the  w i n t e r , snow c o u r s e s  i n the  open may  the  f o r e s t adequately.  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)  a snow c o u r s e 2  in  regression equations  snowpack among s t r a t a .  tree trunks.  t e r m becomes of f o r e s t  important, accumulation  behaviour  There are p r o g r e s s i v e  decreases  i n slopes  of the best f i t  There are a l s o p r o g r e s s i v e  close  decreases i n  o f snow a c c u m u l a t i o n  s p e c t r u m become l e s s r e l a t e d t o t h o s e  i n the  down  open.  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  a p p e a r s t o be  density w i l l  season, the nature  be  Therefore, closely  the  distribution  c o n t r o l l e d by  of storms, t h e i r rain/snow boundaries, sities.  As are  o f new  snowfalls  the 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  with elevation.  levels  in  spectrum of s t r a t a from c l e a r i n g s to  F o r most o f t h e  of  snowpack  the p r e v i o u s h i s t o r y and  new  snow d e n -  l o n g as snow s t o r m s w i t h d i v e r s e f r e e z i n g  frequent,  e l e v a t i o n i s t o be  no p e r s i s t e n t o r s t e a d y  expected.  w i t h e l e v a t i o n can be a t 590  accumulation  r e f l e c t the r e l a t i v e  e x p l a n a t i o n because the processes  5.5  relation-  H o w e v e r , i n a m i l d e r w i n t e r , when  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  this  regression  index  provides a poorer index  l i n e s , through the to  explanation  values).  The of the  high  1970-71 d a t a s u g g e s t t h a t i n a c o l d , snowy,  s h i p f o r the  (lower R  The  trend  with  In a d d i t i o n , i n t e r a c t i o n  p r o n o u n c e d ( e . g . snowpack d e n s i t y  m behaved d i f f e r e n t l y  than at h i g h e r  elevations  129  f r o m J a n u a r y t o March- 197.1, F i g . 4..13). 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 r e l a t i o n s h i p s b e t w e e n snow d e n s i t y unlikely to  t o be c o n s i s t e n t  any e m p i r i c a l  and e l e v a t i o n a r e  f r o m month t o m o n t h , o r y e a r  year. E v e n when new  the  T h u s , as w i t h  snowfalls  s i t u a t i o n i s complicated  metamorphism o p e r a t i n g  cease-later  i n the season,  by d i f f e r e n t p r o c e s s e s o f  at d i f f e r e n t elevations.  At l o w e r  elevations, melt-freeze,  and i n c r e a s i n g g r a i n s i z e ,  t e m p e r a t u r e metamorphism  ( S o m m e r f i e l d and L a C h a p e l l e  dominate, but at higher different rates  elevations  1970)  these proceed at  a n d , b e c a u s e o f t h e deep s n o w p a c k , a r e  augmented by t h e b e g i n n i n g s o f p r e s s u r e  5•6  equi-  metamorphism. ,  Conclusions 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 b e t w e e n n e t snow  a c c u m u l a t i o n , o r d e n s i t y , and e l e v a t i o n a r e n o t l i k e l y be r e l i a b l e is  on w e s t c o a s t  midlatitude mountains.  a consequence o f t h e f o r m a t i o n  shape and' s l o p e relative  to  This  o f a snow wedge  whose  a p p e a r s t o be l a r g e l y c o n t r o l l e d by t h e  frequency of various  winter  storm types.  f i n d i n g s i n d i c a t e that a s u c c e s s f u l approach t o  These estimation  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  physically  are d i r e c t l y  b a s e d by i n c l u d i n g v a r i a b l e s t h a t  r e l a t e d to the processes operating.  Proposed models  130  s h o u l d s i m u l a t e on a day t o day o r s t o r m b a s i s t h e v a r i a t i o n s i n e l e v a t i o n of the rain/snow snow d e p o s i t e d . the f o l l o w i n g  boundaries  These p r o c e s s e s  chapters.  and t h e amounts o f  a r e examined f u r t h e r i n  Snow m e l t  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 dealt w i t h here. t h e snow wedge i s p a r t i c u l a r l y the rain/snow inventory  S i n c e t h e shape o f  sensitive to the position of  boundary from s u c c e s s i v e storms, a c l i m a t o l o g i c a l  o f s t o 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 a r e a l s o i n c l u d e d i n t h i s The c h a n g i n g  study.  shape o f t h e snow wedge, a n d r e s u l t a n t  elevation-time i n t e r a c t i o n e f f e c t s , render unsuitable the t r a d i t i o n a l snow c o u r s e w h e r e m e a s u r e m e n t s a r e t a k e n a t a s i n g l e e l e v a t i o n on t h e m o u n t a i n .  More r e l i a b l e  indices  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 c o u r s e s  at d i f f e r e n t  of the snowline.  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  The optimum number o f snow s a m p l e s f o r  a s p e c i f i e d e l e v a t i o n range Reasonable  has y e t t o be  empirical relationships  determined. 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 t h e f o r e s t s t r a t a from t h a t i n t h e open, p r o v i d e d t h a t water These a r e thought  e q u i v a l e n t i s g r e a t e r t h a n 100  t o be g e n e r a l l y a p p l i c a b l e t o t h e t e r r a i n  segment, because t h e w i n t e r s sampled i n c l u d e d a wide of accumulations relations  cm.  recorded i n the l a s t  s h o u l d be u s e d :  36 y e a r s .  range  Separate  one f o r c o l d e r , s n o w i e r w i n t e r s ;  and t h e o t h e r f o r warmer w i n t e r s , when t h e d e v e l o p m e n t o f 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  ele-  v a t i o n b e t w e e n a c c u m u l a t i o n i n t h e open a n d i n t h e 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  precise  estimates  o f snow i n t h e f o r e s t i f b a s e d on open a r e a w a t e r e q u i v alent  l e s s t h a n 100. cm.  I n these  cases, e i t h e r  better  measurement m e t h o d s , o r more s o p h i s t i c a t e d m o d e l s incorporating  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 t h e e s t i m a t e s .  132  CHAPTER 6  6.  WINTER P R E C I P I T A T I O N ; AND SNOW This  chapter  DEPOSITION  reports the results  o f w i n t e r and  s t o r m p r e c i p i t a t i o n m e a s u r e m e n t s , b o t h r a i n a n d 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 o f t h e s e c r i b e d a n d compared w i t h o t h e r  local  elements are des-  studies.  A quali-  t a t i v e m o d e l o f s t o r m snow d e p o s i t i o n i s p r o p o s e d f o r west coast m i d l a t i t u d e mountains. winter precipitation f a l l i n g elevation.  Finally  The p r o p o r t i o n o f  as snow i s a s s e s s e d  an e s t i m a t e  i s made o f t h e 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 . and data  a n a l y s i s of these  Presentation  measurements p r o v i d e s  f o r the f o l l o w i n g chapters  f o r each  the basic  where a c l i m a t o l o g y o f  snow s t o r m s i s d e v e l o p e d and a m o d e l c o n s t r u c t e d t o predict  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  within the forest.  6 .1 6.1.1  Precipitation V a r i a t i o n of t o t a l winter precipitation with elevation Total winter p r e c i p i t a t i o n increased linearly  elevation  ( F i g . 6.1,  Table 6.1).  from t h i s  l i n e a r trend occurred  The p r i n c i p a l  with  anomalies  a t 490 m a n d f r o m 870 t o  133 TABLE 6 . 1  V a r i a t i o n of t o t a l winter p r e c i p i t a t i o n with e l e v a t i o n . A l l data f o r snow expressed i n water  Winter  1969-70  Elevation (meter s)  equivalent.  +  Total Precip. (mm)  Snow Dep. (mm)  Rainfall (mm)  Mean Precip. /storm (mm)  % of precip. falling as snow  Mean snow/ snow storm (mm)  mean r a i n / r a i n storm (mm)  1260  1854  1300  554  28  70 .1  34.2  (38)*  21 .3  1060  1857  1243  6l4  29  35-5  (35)  21 .2  970  1630  719  911  26  66 .9 44 1  21.8  (33) (22)  29 .4 ( 3 D 29 .4 (42)  (18)  31 • 5 (46) 30 .5 (47) 24 • 5 (54)  870  1594  359 268  25 27  16.3  1715  1235 1447  22 5  790  15 .6  710  1585  153  1132  25  9 .7  14.9 9.0  590  1368  H5  1323  21  190  1366  10  1356  21  400  4  1375  22  330  1379 1320  3 3 0 7 0 .3  1  0 1  220  1238  1319 1226  21  12  19  0 9  1 . 3 ( 3) 1.0 ( 1) 12.0 ( 1)  120  1198  12  1186  19  1 0  12.0  (17)  4.5 (10) 1.7 ( 6)  (26)  23 .4 (58) 22 .4 (61) 20 .9  (63)  19 .5  (63)  18 .8 (63)  ( 1)  Winter 1970-71  Elevation (meters)  Total " Precip. (mm)  Snow Dep. (mm)  Rainfall (mm)  Mean Precip. /storm (mm)  % of 'precip. falling as snow  Mean snow/ snow storm (mm)  Mean r a i n / r a i n storm (mir )  1260  ' 3520  2438  1082  48  69.3  1060  3448  1195  47  970  (55) (52)  (19)  65.3  '11.3 43.3  56.4  2873  2253 I676  (22)  1197  54.3  39  870  58.3  34.9  (48)  1208  46.0  (26)  1445  36  790  2653 2832  1206  26.5  (46)  1626  51.6  (28)  39  '15.5 42.6  29.4  710  2556  (41)  930  1626  49.3  (33)  35  36.4  590  2349  25-1  (37)  699  43-9  1650  32  29 . 8  23.5  (30)  490  2230  466  1764  37.5  (37) (44)  31  21.0  21.2  (22)  400  2252  392  i860  31  17.4  19.6  (10)  33.9 34.4  (54)  (52)  330  2130  254  I876  29  (18)  1949  222  33.5  (56)  27  1837  216  14.8  (15)  120  1727 1621  11.9 11.4  14.1  220  25  11.8  16.6  (13)  29.3 26.6  (59) (61)  * f i g u r e s i n brackets give number of storms of each p r e c i p i t a t i o n type sampled at each e l e v a t i o n . + p r e c i p i t a t i o n f o r the period 5 November 1969 to 31 May 1970 + p r e c i p i t a t i o n f o r the period  1 October 1970 t o 31 May 1 9 7 1 .  CD <! !— P CD 4 1  •< H-  ~  0  1000  H  ct  o  -|—i 0  1 200  •  1 400  1 600  '  r-  600  Elevation (meters)  i  1000  1 1200  r  1400  135  970 to  jn.  The f o l l o w i n g l e a s t  square equations  were  fitted  thedata :  F o r w i n t e r 1969-70  P= .1104+0 ..62H  r = 0.91  S.E.= 65  F o r w i n t e r 1970-71  P- 1588+1.48H  r = 0 ..94  S.E.= 131  where  :  2  2  P = winter precipitation  (mm)  H = e l e v a t i o n (m)  The orographic in  slope o f the r e g r e s s i o n l i n e  component o f p r e c i p i t a t i o n ) was much g r e a t e r  the second w i n t e r .  erence suggests be  (and h e n c e t h e  The m a g n i t u d e o f t h e  slope  diff-  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  common f o r w i n t e r  precipitation.  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 the two w i n t e r s were n o t as g r e a t  as i n d i c a t e d , b e c a u s e 9 s t o r m s  s t o r m s ) were n o t s a m p l e d a t t h e b e g i n n i n g 1969-70.  Nevertheless  p r e c i p i t a t i o n per  storm  120  m, a n d 71 p e r c e n t  was  a snowier  i n the w i n t e r  o f the  winter  1970-71, mean  s a m p l e d was 32 p e r c e n t  higher  ( a l l rain  a t 1260 m.  higher at  The w i n t e r  w i n t e r , and hence such r e s u l t s  1970-71  c o u l d be  p r o d u c e d i f t h e r e was a b i a s i n t h e measurement m e t h o d s for  snowstorms, a t t h e expense o f r a i n s t o r m s .  there  seems a more f u n d a m e n t a l p h y s i c a l r e a s o n  s i n c e t h e mean r a i n f a l l  However, i s operating,  p e r r a i n s t o r m 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 . elaborated further later.  This pointi s  S u f f i c e t o say here, that  t h e h i g h e r mean s t o r m p r e c i p i t a t i o n o f t h e 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 t h o s e s t o r m  conducive t o h e a v i e r p r e c i p i t a t i o n  types  (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 s y s t e m s o r more u n s t a b l e a i r m a s s e s ) . Mean p r e c i p i t a t i o n p e r snow s t o r m was l e s s t h a n t h a t p e r r a i n storm except  6.1.2  a t 1060 m a n d 1260 m i n t h e w i n t e r 1969-70.  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  Nikleva  (1964), and S c h a e f e r and  (1973) h a v e d i s c u s s e d v a r i a t i o n s o f a n n u a l  c i p i t a t i o n w i t h e l e v a t i o n on t h e N o r t h Shore Walker and O r l o c i exist  suggest  Mountains.  a maximum o f p r e c i p i t a t i o n  somewhere b e t w e e n 620 m a n d 810 m, t h e e x a c t  v a t i o n v a r y i n g w i t h t h e season.  Above t h i s  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 . cipitation  pre-  f r o m some s t o r m s  should  ele-  elevation,  Maximum p r e -  d i d o c c a s i o n a l l y o c c u r midway  up t h e m o u n t a i n ( F i g . 6 . 2 ) , b u t o v e r t h e two w i n t e r s , t h e above comments a r e n o t s u b s t a n t i a t e d by t h e d a t a o f this  study  ( F i g . 6.1).  I f a n 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 w o r k e r s 197D is  ( e . g . Walker, 1 9 6 l , B a r r y a n d C h o r l e y  h a v e p o s t u l a t e d t h a t t h e 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  c l o s e t o t h e mean c l o u d b a s e ,  s i n c e t h e maximum s i z e  137  60February  40  -1  20  -  1970  .  44  o-  o-480  60  October 1970  H  40  ~\  20  H  100  300  500  700 Elevation ( m e t e r s )  F i g . 6.2  900  1100  1300  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 eley'ation f o r storms of s e l e c t e d months. Storms a r e i d e n t i f i e d by number, t o p f o r w i n t e r 1969-70, and bottom f o r w i n t e r 1970-71  138  and  number o f 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  at t h i s  level.  With-'drier  a i r below, the  t e n d t o e v a p o r a t e and. l o s e .mass-.  The  particles will  mean c l o u d  bases  of w i n t e r  s t o r m s on Mount Seymour i s a t a b o u t 500.  since  l e v e l o f maximum p r e c i p i t a t i o n g e n e r a l l y  the  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 n o t important  occur  m,.but occurs  seem t o  be  here.  T h e r e 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 w o r k e r s m i g h t c l a i m a l o w e r e l e v a t i o n o f maximum precipitation.  Wright  (1973) p o i n t ' o u t  that  (200 the  m),  higher  stations are  i n the  the  m).  f u n n e l l e d up  combine t o g i v e  Ridge  (950  m)  fall  at  Mount Seymour CBUT winds  v a l l e y , where - c o n v e r g e n c e and  a heavier  uplift  t h a n on t h e more e x p o s e d These p r e v i o u s  workers  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 , populations. climatic  and  than that  They s u g g e s t m o i s t u r e l a d e n the  Nikleva  p r e c i p i t a t i o n at-/-Seymour F a l l s  southern f l a n k s of the mountains. d i d not  S c h a e f e r and  Seymour V a l l e y , i s g r e a t e r  Hollyburn  (870  (.1966b) and  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  In a d d i t i o n they used the  s t a t i o n s as b a s i c  elevations  above 300  ( s e c t i o n 2.5),  so  m,.  do n o t  and  data.  records  These are  of  very  regular  few  have u n e q u a l p e r i o d s , of  at  re'cord  f o r m 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 n o t m e a s u r e water equivalent  of s n o w f a l l , but  estimate  this  from  actual '  139  m e a s u r e d depth, o f new snow, .'and by. a s s u m i n g a d e n s i t y , o f 10 0 . kg/m . 3  end  The mean d e n s i t y , o f new snow measured'- a t t h e  o f s t o r m s f o r both, w i n t e r s o f t h i s  s t u d y was- 25.0  a t t h e e l e v a t i o n o f H o l l y b u r n R i d g e , and' 230  kg/m  e l e v a t i o n o f Mount Seymour CBUT ( T a b l e 6.2).  3  kg/m  3  at the  Allowing  f o r some c o m p a c t i o n o f new snow d u r i n g t h e s t o r m , t h e d e n s i t y of f r e s h l y  fallen  snow may be e x p e c t e d t o be l e s s t h a n  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 t h a n 100  For t h i s reason, w i n t e r p r e c i p i t a t i o n at the high  these kg/m .  elevation  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 , h a s probably been,underestimated. an a p p a r e n t elevations.  decrease In this  This e r r o r would  generate  i n p r e c i p i t a t i o n at these higher connection Orloci  (1964, pg.6)  states : " Maximum p r e c i p i t a t i o n may be e x p e c t e d t o o c c u r a t a n e l e v a t i o n l o w e r t h a n 2700 f e e t , e x c e p t d u r i n g t h e summer m o n t h s , where t h e maximum may o c c u r a t , o r n e a r , t h e highest available elevation. " The  f a c t - a n 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 was  s a i d t o o c c u r o n l y i n w i n t e r , a n d n o t i n summer when t h e r e i s n o t s n o w f a l l , s u p p o r t s t h e above a r g u m e n t .  6.1.3  Winter p r e c i p i t a t i o n at s t a t i o n s with a longer period of record 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 a r e g i v e n i n  A p p e n d i x 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 , a n d f o r  3  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 density  o f newly, f a l l e n snow: i n open a r e a s -• winters  1969-70 197-0-71  W i n t e r 1970-71:  W i n t e r 19.69- 70.. Elevation (meters) /  stn. dev. (kg/m )  number storms sampled  ...mean (kg/m )  1260  26  268  78  1060  27  263  970  21  870  i  -  \  3  3  number storms sampled  mean (kg/m ) 3  stn. dev. .(kg/m ) 3  252  71  70  35 38  249  74  255  80  34  247  73  14  234  75  30  221  72  790  10  235  61  218  68  710  5  283  54  27 21  50  590  1  160  -  18  197 201  490  12  196  54  400  10  195  7  206  59  6  230  84  4  250  61  330 220  1  206  120  1  200  Note:  Density  -  o f newly  53 •  60 •  f a l l e n snow i s t h e d e n s i t y  o f new snow m e a s u r e d a t t h e e n d o f t h e s t o r m . 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 f a l l e n snow,.defined  as t h e d e n s i t y  snow m e a s u r e d ' d u r i n g  the storm.  of freshly o f new  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 t h e f a c t and  just, •discussed,  because t h e lengths- o f r e c o r d a r e unequal.  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 b e c a u s e many o b s e r v a t i o n s a r e m i s s i n g d u r i n g heavy- snow m o n t h s . p r e c i p i t a t i o n b e t w e e n O c t o b e r a n d May i s 882 c e n t o f t h e mean a n n u a l cent a t H o l l y b u r n R i d g e , mean a n n u a l  Mean  mm o r 85  a t V a n c o u v e r , i s 2438 mm o r 82 a n d 2420 mm o r 83 p e r c e n t  a t Mount Seymour CBUT.  December i s n o r m a l l y  c i p i t a t i o n gradually decreases.  O v e r 40 p e r c e n t  mean a n n u a l  i n t h e t h r e e months  p r e c i p i t a t i o n occurs  November,. D e c e m b e r , J a n u a r y .  than  at Vancouver I n t e r n a t i o n a l  6.1.4  Mean w i n t e r  i s almost  per-  of the  t h e w e t t e s t month a t 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  at t h e mountain s t a t i o n s  per-  pre-  of the  precipitation  three times  higher  Airport.  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 Variations  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 a r e g i v e n i n F i g . 6.2. E and F l f o r complete d a t a f o r a l l s t o r m s ) .  (See A p p e n d i c e s Clearly 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 n o t a l w a y s l i n e a r , nor c o n s i s t e n t from storm t o storm. noted,  As a l r e a d y  a n 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 o c c u r f o r  some s t o r m s .  The a n a l y s i s a n d p r e d i c t i o n o f s t o r m  pre-  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 fully  i n Chapter  9•  14  6.2  Snowfall  phenology  6.2.1  Dates' o f f i r s t  and l a s t  The d a t e s o f t h e f i r s t  snowfall and l a s t - s n o w f a l l , a n d t h e  l e n g t h of the s n o w f a l l season at various' e l e v a t i o n s are g i v e n i n Appendix The f i r s t  C f o r t h e two w i n t e r s 1969-70-, 1970-71-  snow f e l l  on Mount Seymour t o w a r d t h e e n d o f  October i n both w i n t e r s . in  1970.  The l a s t  snow f e l l  D i s c u s s i o n s w i t h Mount Seymour P a r k r a n g e r s ,  and s k i l i f t  operators, indicated this  was " U s u a l " .  T h i s was c o n f i r m e d by t h e d a t e s o f f i r s t falls (950 In  to  and l a s t  snow-  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 m) and Mount Seymour (CBUT) t o w e r  1971, t h e l a s t  the  i n mid-May  snow was u n u s u a l l y  2 4 t h J u n e , when a c o l d 1060 m; and t h e f i r s t  e a r l y , f a l l i n g a t about  6.2.2  (870 m)  late,  low produced  Ridge  ( T a b l e 6.3)  falling  on  l i g h t 'snow down  snow i n autumn 1971 was  unusually  1000 m on t h e 2 9 t h S e p t e m b e r .  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 f r o m most s t o r m s i n t e r s e c t e d t h e  mountain  a t some e l e v a t i o n above i t s b a s e  ( F i g s . 4.1,  From November t o M a r c h , t h e s e s n o w l i n e s f o r m e d t o t a l range o f e l e v a t i o n s sampled. has a l s o f a l l e n  i n Vancouver  4.3)  over the  I n p a s t y e a r s , snow  in April.  On t h e o t h e 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. m o n t h , a t two  h i g h - e l e v a t i o n cllmato.logi.cal s t a t i o n s on the' N o r t h ; S h o r e  First  snowfall  Hollyburn  Last  Month o f o c c u r r e n c e & number o f e v e n t s  Elevation (meters)  Station  Mt.  Mountains  Sept.  .Oct.  950  1  12  2  15  •870  0  3  7  10  Ridge  Seymour CBUT  snowfall  Q  Month o f o c c u r r e n c e & number o f e v e n t s  Elevation (meter s )  Station  April Hollyburn Mt.  Nov.  Ridge  Seymour CBUT  Notes:  length of r e c o r d (years)  June  May  length of r e c o r d (years)  950  5  11  0  16  870  2  8  0  10  ( i ) Compiled from "Monthly  Record",  D.O.T., M e t . B r a n c h . (ii)  Data f o r Hollyburn period for  Ridge f o r t h e  1954-69, a n d f o r M t . Seymour  the period  1958-67.  144  even i n m i d - w i n t e r , Despite  r a i n o c c u r r e d , to. t h e t o p o f t h e m o u n t a i n .  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  seasonal  t r e n d o f new- s n o w l i n e s , w i t h , snow more common a t t h e lowest  levels The  i n December, J a n u a r y  two w i n t e r s p r e s e n t e d  and F e b r u a r y . 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 t h e f a c t e a c h h a d an a l m o s t tical  number o f s t o r m s  ( T a b l e 6.4).  I n t h e w i n t e r 1969-70,  f e w e r s t o r m s d e p o s i t e d snow on t h e m o u n t a i n .  I t repeat-  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 ( T a b l e the  l e n g t h o f t h e s n o w f a l l s e a s o n was l e s s ,  at lower  levels  (Appendix  1970-71 e x p e r i e n c e d  C).  previous winter. few  Conversely,  more snow s t o r m s .  d e p o s i t e d snow t o s e a l e v e l ,  iden-  6.5), a n d  especially the winter  T h i r t e e n storms  compared w i t h o n l y one t h e  I n b o 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  s t o r m s w i t h snow a t 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 J a n u a r y  and F e b r u a r y ,  w e r e amongst t h e s n o w i e s t  6.2.3  Snowlines The  although  t h e s e months  a t l o w e l e v a t i o n s ( T a b l e 6.5).  on t r e e s  minimum e l e v a t i o n s o f t h e l i n e s o f snow  loads  on t r e e s ( d e f i n e d i n S e c t i o n 3.7) a r e 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. throughout  T h e r e was c o n s i d e r a b l e  fluctuations  t h e w i n t e r s , . d e p e n d i n g on t h e 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 . rain- storms ensured  The f r e q u e n c y o f  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, o f s t o r m p r e c i p i t a t i o n  type,  Mount Seymour, w i n t e r s 1969-70, 19 70-71  w i n t e r 1969-70 Storm type  Winter  Month  precipitation  O c t Nov Dec J a n Feb Mar A p r May  1969-70 .  Rain t o top of m o u n t a i n (no snow)  7  4  3  1  4  1  2  6  28  M i x e d r a i n and snow a t t o p o f mountain  0  0  1  4  1  3  4  0  13  Snow o n l y a t t o p of mountain, r a i n below  1  6  9  3  3  3  5  1  31  Snow a t a l l e l e v a t i o n s on mountain  0  0  0  1  0  0  0.  0.  TOTAL 1969-70  8  10  13  9  8  7  Winter Storm type  11  1 73  7  1970-71 Winter  Month  precipitation  Oct Nov Dec J a n Feb Mar A p r May  1970-71  Rain t o topof m o u n t a i n (no snow)  4  2  0  5  2  1  1  4  19  M i x e d r a i n and snow at t o p o f mountain  1  3  2  2  1  2  4  1  16  Snow o n l y a t t o p of m o u n t a i n , r a i n below  2  1  5  2.  3  1  3  1  18  Snow a t a l l e l e v a t i o n s on mountain * .  0,  3  5  2  4  7  0..  0.  21  7  9 „ 12 , 11  6  74  . TOTAL I97O-.7I  10 . 11  i n c l u d e s s t o r m s where snow was o b s e r v e d not p r e s e n t a t end o f storm.  '8  to f a l l ,  b u t was  146  TABLE 6 . 5  F r e q u e n c y o f storms, d e p o s i t i n g  at. .each  SHOW  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 w h i c h were n o t m e a s u r e d ) Elevation of sampling area  cm d e e p )  Winter  Month Oct  Nov  Dec  Jan  Feb  Mar  Apr  1260  1  6  10  8  4  6  9  1  1060  1  5  10  8  4  6 .  8  1  970  1  3  10  7  4  5  8  1  1 1  8  7  4  1  8  29  4  6-  4  1  23  710  4  6  4  7 6  590  3  6  3  3  15  490  2  2  2  1  7  400  2  1  330  1  1  220  1  1  120  1  1  870 790  Elevation of sampling area  May •  1969-70  (meters)  45 ,  43 39  20  3  Winter  Month  1970-71  (met e r s )  Oct  Nov  Dec  Jan  Feb  Mar  Apr  May  1260  7  12  6  8  10  7  2  55  1060  3 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. /  1  46  790 .  1  4 - 11  5  8  8  5 4  . '  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  18  220  3 . 3  3 2  3  120  5 4  '3 1  3  1  13  41  15  1200  H  1000  H  800  H  i_  -«-> <u E c o  600 H  o  I  U  400  Winter 1969-70 — — —  200  Heavy Load Line Light  H  OCT  NOV  DEC  JAN  FEB  MAR  APR  MONTH  F i g . 6.3  Load Line  E l e v a t i o n a l coverage o f snow on trees., w i n t e r 1969-70  MAY  ,—"r  i-, NOV  DEC  HI JAN  'ji FEB  • MAR  ~  APR  MONTH  Fig.  6.4  E l e v a t i o n a l coverage of  snow on  trees, winter  1970-71  149  s e v e r a l times  during mid-winter.  W h i l e h e a v y snow  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 riming occurred, periods.  w i t h h e a v y snow l o a d s 40  days t h e No  e l e v a t i o n s where  t h e y were seldom s u s t a i n e d f o r  In the w i n t e r  1969-70, t h e  on t r e e s was  loads  longest  long  period  18 d a y s , compared w i t h  following winter. measurements of a c t u a l l o a d s  on t r e e s were made.  H o w e v e r , t h e v a r i a t i o n s w i t h e l e v a t i o n o f snow mass density (Figs.  and 4.1,  o f t h e new 4.3),  snowlines  storms  i n d i c a t e d t h a t l o a d s must change  siderably with elevation. not  from s u c c e s s i v e  r e f e r r e d to i n the  This  i s an i m p o r t a n t  literature,  and  con-  point,  and w o r t h y o f f u r t h e r  study.  6 .3 6.3-1  Snow d e p o s i t i o n 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  varied with elevation 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 a t elevations  ( F i g s . 6.1,  6.5).  This  t h e number o f s t o r m s w i t h snow, and snow p e r  low  r e s u l t e d because b o t h t h e mean amount  of  snow s t o r m i n c r e a s e d w i t h e l e v a t i o n ( T a b l e  Exceptions  to t h i s  l a t t e r trend occurred  a t 120  a c o n s e q u e n c e o f 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  m and  6.1). 220.  Arctic  m,  3000  o clearings  2500  H  0  o  0  Winter  1970-71  0  p  O  Winter  1969-70  sampling  open areas  site  2000  c a n o p y edge  beneath canopy close totree trunks  1500 open  areas  clearings  •o 'in  canopy  1000  edge  8. m  g  beneath canopy close to tree trunks  500  I  200  400  600  Elevation  Fig.  6.5  Variation 1970-71  1000  c?00  1200  1400  (meters)  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,  151  a i r outbreaks The w i n t e r arity (Fig.  (.e.g. s e e s t o r m . - 3 5 , 1 9 6 9 - 7 0 .in F i g .  snow d e p o s i t i o n wedge b e a r s a s t r i k i n g  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  6.8). simil-  earlier  4.10). 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  except i n the winter  i n open  areas,  1 9 7 0 - 7 1 where i t was e x c e e d e d by t h a t  f o r c l e a r i n g s above 790 m.  Otherwise the f o r e s t s t r a t a -  c l e a r i n g s , canopy e d g e , b e n e a t h t h e c a n o p y , t r e e t r u n k s received progressively to tree trunks  l e s s snow.  was o f t e n e q u i v a l e n t  a t an e l e v a t i o n 300 m l o w e r . deposited trunks open  i n the winter  to that  close  i n open a r e a s  S u b s t a n t i a l l y more snow was  1970-71.  i t exceeded t h e previous  Snow d e p o s i t i o n  -  Even c l o s e t o t r e e winter's  deposition i n  areas.  6.3.2  I m p o r t a n c e o f snow d e p o s i t i o n  to winter 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 with decreasing  elevation  (Fig. 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 a t most e l e v a t i o n s i n 1 9 6 9 - 7 0 , a l t h o u g h , t h e two w i n t e r s because 9 storms winter.  are not d i r e c t l y  comparable,  C a l l r a i n s t o r m s ) were n o t s a m p l e d i n t h i s  However, even i n 1 9 7 0 - 7 1 , w h i c h 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 cent-, o f t h e p r e c i p i t a t i o n f e l l  (Fig. 3.6),  only  69 p e r -  as snow a t t h e h i g h e s t  152  e l e v a t i o n sampled. t h e r e was  While t h i s  represented  substantial winter r a i n f a l l .  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 relatively  i s i n t e r e s t i n g t o compare t h i s  itation.  f i g u r e i s 19  Nikleva  34  At H o l l y b u r n R i d g e ,  i t a t i o n normally  falls  as  percent  sites  are probably Higher  January in  and  ( A p p e n d i x F2).  data f u r t h e r , but 6.1.2-3, the  February  true.  rainfall  snowfall mountain  underestimated.  received relatively 6.6).  At  T h i s was  lower  l e s s snow  of  than  e l e v a t i o n s the  higher e l e v a t i o n s i n these  Even at the h i g h e s t  months  a consequence of o c c a s i o n a l  some s t o r m s gave snow t o low  4.3).  and  f o r reasons  e l e v a t i o n s d u r i n g the mid-winter  r a i n storms at the while  Schaefer  hence p r e c i p i t a t i o n a t these  o t h e r months ( T a b l e  o p p o s i t e was  of w i n t e r p r e c i p -  A t Mount Seymour CBUT  previously discussed i n Sections w a t e r e q u i v a l e n t and  data with s t a t i o n s  of w i n t e r p r e c i p -  percent  snow.  (1973) d i s c u s s t h e s e  the  Mean s n o w f a l l a t V a n c o u v e r  5 percent  I n t e r n a t i o n a l A i r p o r t i s only  at  l o c a l snowpacks ( F i g . 4.14).  w i t h a l o n g e r p e r i o d of r e c o r d .  the  This r a i n  f a c t o r i n producing  h i g h d e n s i t y of the  It  a l a r g e amount,  months,  elevations (Figs.  e l e v a t i o n s a m p l e d (1260  always c o n s t i t u t e d at l e a s t  s u b s t a n t i a l l y more o f t h e m o n t h l y  8 percent  4.1, m),  and u s u a l l y  precipitation.  153  TABLE 6 . 6  Percentage of monthly p r e c i p i t a t i o n  falling  as snow a t each e l e v a t i o n , open areas winters  Elevation (meters)  Oct  1  1969-70,  Nov  197.0-71  Month Dec . J a n  May  Feb  Mar  Apr  5.2 • 1-1.  W i n t e r 196<}-70 86.3  65.5  58.6  59.7  92.1 84.6  84.5  66.2  37.3  59-8 61.2  970  53.9  43.2  58.3  59.8  5.6  46.6  870  5.3  18.9  35.5  ,34.9  26.3  790  1.2  15.4  24.6  30.9  15.9  710  6.5  18.7  21.7  590  3-5  5.9  490  0.6  400  1.1 0.8  330  0.5  220  5.1 5.1  1260  60.9  1060  120  Winter  8.5  8.1  7.6 1.8  2.3 0.7  1.0  1970-71 86.6 84.2  56.6  7.7  41.4 35.6  58.9  75.6 75.2  970  2.3  32.9  71.3  51.9  69.6  85.2 80 .2  870  1.4  25.9  39 .4  52.6  68.6  39.3  38.3  66.9  37.3  47.6 38.0  36.5 32 .2 20 . 3 1.7  1260  35.7  1060  &6.6  790  24.2  710 .  24.3  62.6 59.8 52.2  590  21.5  39.7  32.1  32.9  490 .  22 . 3  22.0  28.3  400 .  19 .1  20 .9  24.5 19 .6  40 .7 24.6  25.7  16 .2  330 .  12.5  9.0  12.9  21.9  13-9  220  9.5  5.9  16 .1  23.3  10 .0  120  8.0  5.2  17.1  27.3  7-8  50.3  84.0 75.2  34.1  56.7  27.8  2.9  27.3  154  6.3.3  V a r i a t i o n o f s t o r m snow, d e p o s i t i o n w i t h To i l l u s t r a t e  elevation  some v a r i a t i o n s o f snow d e p o s i t i o n  with  e l e v a t i o n a n d w i t h i n t h e f o r e s t , and t h e s i g n i f i c a n c e o f s n o w f a l l to storm p r e c i p i t a t i o n , data f o r s e l e c t e d are  shown i n F i g s . 6.6-6.9  stratum  (Snow d e p o s i t i o n f o r e a c h  and e l e v a t i o n f o r a l l w i n t e r  Appendix G).  storms  storms i s g i v e n i n  The s t o r m s were c h o s e n f r o m f o u r a r b i t r a r y  groups. (a)  S t o r m s g i v i n g snow a t h i g h  elevations  only  ( g r e a t e r t h a n 800 m) Snow f r o m t h e s e s t o r m s was a l w a y s d e p o s i t e d wedge whose t h i c k n e s s Freezing  increased  with elevation (Fig.  M e l t i n g o f some new snow  b e l o w t h e f r e e z i n g l e v e l p r o d u c e d t h i s wedge. 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 as b o t h snow and r a i n , w i t h  rapidly  6.6).  l e v e l s f r o m t h e s e s t o r m s were j u s t b e l o w , o r  above, t h e t o p o f the mountain.  fell  as a  Above t h e  (H ), precipitation Q  snow d e p o s i t i o n  a t t h e expense o f r a i n f a l l .  increasing  F o r most o f t h e s e  s t o r m s t h e r e was an e l e v a t i o n on t h e m o u n t a i n s ( H ) w h e r e e  snow d e p o s i t i o n i n open a r e a s e v e n t u a l l y c i p i t a t i o n , but whether or not t h i s the thickness variations  occurred  of the atmospheric melting  of f r e e z i n g l e v e l during  equalled  pre-  d e p e n d e d on  l a y e r , a n d on  the storm.  H  e  i s here  155  100  300  500  700  900  1100  1300  Elevation (meters)  Fig.  6.6  Two e x a m p l e s o f d e p o s i t i o n f r o m s t o r m s gave snow a t h i g h e r e l e v a t i o n s o n l y  which  156 40  Storm 29  100  300  Winter 1969-70  500  700  900  1100  1300  Elevation ( m e t e r s )  Fig.  6.7  Two e x a m p l e s o f d e p o s i t i o n f r o m s t o r m s w h i c h snow a t h i g h e r a n d i n t e r m e d i a t e elevations. S y m b o l s as f o r F i g . 6.6  gave  157  Fig.  6.8  D e p o s i t i o n f r o m a s t o r m w i t h snow t o elevations. S y m b o l s as f o r F i g . 6.6  low  158  140  I  i  I  100  300  500  :  l  700  i  900  ;  I  1  1100  1300  Elevation ( m e t e r s )  Fig.  6.9  D e p o s i t i o n f r o m a s t o r m w i t h l a r g e amounts o f snow. S y m b o l s as f o r F i g . 6.6  159  termed the"equi.yalerit e l e y a t i o n " . H  0  and H  e  The r e g i o n  i s c a l l e d t h e "wet snow z o n e " .  The  b e l o w H , where no new snow was d e p o s i t e d  region  i s c a l l e d the  0  "rain  between  zone" . At  deposited  a l l elevations, progressively  l e s s snow was  a t t h e c a n o p y e d g e , b e n e a t h t h e canopy and c l o s e  to tree trunks.  I m m e d i a t e l y above H  no snow d e p o s i t i o n b e n e a t h t r e e s . this pattern  0  there  was  frequently  Local variations i n  sometimes r e s u l t e d from d r i f t i n g i f winds  were  s t r o n g , . o r - f r o m snow s l i d i n g o f f t r e e s t o t h e canopy e d g e . (b)  S t o r m s 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  elevations  ( 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 (Fig.  6.7).  discussed as  snow i n wedge f o r m  I n t h e wet snow z o n e , s i m i l a r t r e n d s  above were o b s e r v e d .  snow o n l y .  This  Above H  e  t o those  precipitation  was t e r m e d t h e "snow z o n e " .  As i n  t h e wet snow z o n e , d e p o s i t i o n became p r o g r e s s i v e l y  less  f r o m open a r e a 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 " . storms, s u b s t a n t i a l d r i f t i n g a further "drift  occurred  substantially the  greater  H e r e snow  and i n c l e a r i n g s , was  t h a n i n open a r e a s .  c a n o p y e d g e , and f o r m a t i o n  I n some  above 1000 m, so t h a t  snow z o n e " i s r e c o g n i s e d .  beneath t r e e s , close t o tree trunks  fell  of cornices  Wind s c o u r a t were  also  160  characteristic features. occurred  only  The d e v e l o p m e n t o f t h i s  I f storms generated s t r o n g winds.  snow zone m a r k e d t h e u p p e r l i m i t Mount Seymour t h i s  zone The  o f t h e snow z o n e .  l i m i t never occurred  On  b e l o w 1000. m.  H o w e v e r , on m o u n t a i n s w i t h l e s s d e n s e , o r no f o r e s t it  may e x t e n d t o l o w e r  drift  cover,  elevations.  The r a i n , wet snow, a n d snow z o n e s a r e a l l d e f i n e d with respect  t o the storm f r e e z i n g l e v e l .  hand, t h e d r i f t induced  snow zone i s d e f i n e d i n t e r m s o f w i n d  depositional features.  winds t h i s  For a storm w i t h  zone c o u l d e x t e n d down t o H , e  t h e snow z o n e .  This  Seymour, b u t may  elsewhere.  (c)  On t h e o t h e r  strong  and hence e l i m i n a t e  s i t u a t i o n never occurred  on Mount  S t o r m s g i v i n g snow t o l o w e l e v a t i o n s ( b e l o w 400 m) I f the f r e e z i n g l e v e l from these  s t o r m s was a t s e a  l e v e l , t h e shape o f t h e snow wedge was l e s s d e v e l o p e d no r a i n o r wet snow z o n e s o c c u r r e d . still  However, t h e r e  since was  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 , b e c a u s e o f  the u s u a l o r o g r a p h i c  increase  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 s e a l e v e l , wet snow a n d / o r z o n e s f o r m e d , a n d a snow wedge was p r o d u c e d .  rain  Storms  w i t h snow t o l o w 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 Arctic  a i r outbreaks,  w h i c h were o v e r - r i d d e n  by m o i s t  161  Pacific  air.  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 (e.g. s t o r m 35,  elevations (d)  I n some o f t h e s e  Storms w i t h  s t o r m s a l a y e r o f warmer  1969-70,  kg/m )  These o c c u r r e d  with snowlines  snowfall  2  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 the mountain u s u a l l y g r e a t e r t h a n 40 mm. otherwise  intermediate  Fig.6.8).  l a r g e amounts o f  ( s n o w f a l l > 80  at  Features  s i m i l a r to those  discussed  (120  m)  of these  was  s t o r m s were 6.9).  above ( F i g .  T h e s e e x a m p l e s show t h e wedge s h a p e p a t t e r n 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 storms, except i n the occurs  at sea  level.  few  a persistent feature  c o n s i s t e n c y must be  f a c t o r i n the development of the  the  is illustrated  a major  s i m i l a r wedge-shaped  snow d e p o s i t i o n  ( F i g . 6.5)  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 This  of  c a s e s where the. f r e e z i n g l e v e l  This  d i s t r i b u t i o n of w i n t e r  of  and  (Fig. 4.10).  i n f u r t h e r d e t a i l i n F i g . 6.10,  where  d e p o s i t i o n o f snow f r o m e a c h s t o r m i s a c c u m u l a t e d f o r  the w i n t e r .  The  a d d i t i v e snow-wedges f r o m e a c h  combine t o f o r m a c o m p o s i t e wedge. the p r e f e r e n t i a l m e l t i n g p l a c e d u r i n g and  at l o w e r  Subtract  from  elevations that  b e t w e e n s t o r m s , and  t h e wedge shape i s f u r t h e r e n h a n c e d .  i n the  storm this takes  spring,  and  162  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 f r o m e a c h storm. D a t a f o r open a r e a s f o r e a c h w i n t e r , 1 9 6 9 - 7 0 (.top) and w i n t e r 1 9 7 0 - 7 1 ( b o t t o m ) . Snow d e p o s i t i o n f r o m e a c h s t o r m i s added t o t h a t o f t h e p r e v i o u s s t o r m s t o g i v e a c o m p o s i t e ' snow wedge f o r the whole w i n t e r . Drawn by c o m p u t e r .  163  6.3.4  A q u a l i t a t i v e m o d e l o f snow d e p o s i t i o n 'from a s t o r m on a west, c o a s t m i d l a t i t u d e  mountain  B a s e d on t h e 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 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  elevation  i n open a r e a s i s p r e s e n t e d i n s c h e m a t i c f o r m i n F i g . 6.11a. F o r c o n v e n i e n c e , t h e v a r i a t i o n s o f snow  deposition•with  e l e v a t i o n a r e shown as l i n e a r f u n c t i o n s , b u t t h e s e n e e d n o t be s o .  A l l z o n e s o f t h e snow wedge may n o t be p r o d u c e d  by e a c h s t o r m :  when w i n d s a r e l i g h t , t h e d r i f t  will  conversely, this  not e x i s t ,  snow  zone  zone c a n e l i m i n a t e t h e  snow zone i f w i n d s a r e s t r o n g ; i f t h e s t o r m f r e e z i n g  level  o c c u r s much above t h e t o p o f t h e m o u n t a i n , o n l y wet snow and r a i n z o n e s a r e f o r m e d , b u t t h e s e z o n e s a r e e l i m i n a t e d if  the freezing  l e v e l i s at o r "below" t h e base o f t h e  mountain. Except f o r the d r i f t  snow z o n e , a l l z o n e s o f t h e  diagram a r e d e f i n e d i n terms o f t h e f r e e z i n g the f r e e z i n g l e v e l s h i f t s  level.  As  i n e l e v a t i o n from storm t o storm,  o r w i t h i n a s t o r m , so t o o do t h e s e z o n e s . s h o u l d be e n v i s a g e d as a m o v i n g ordinates applied to the f i x e d  Thus t h e d i a g r a m  system o f zones o r c o co-ordinates of elevation  of the mountain. As l o n g as t h e 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 r e m a i n s relatively  c o n s t a n t and b e l o w t h e t o p o f t h e m o u n t a i n , t h e  164 (o) N o l o r c  of  deposition  on m o u n t o l n  (simple  itorm )  Noture forest  drift  Ho ( I n c o m p l e t e  snow  of  d e p o s i t i o n In  In e a c h  lone  xone  new  roin zone  (b)  post  Noture  frontol  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  storm)  N o t u r e of  deposition  freezing^ level  P°&t f r o n t o I  Fig.  Ho  6.11  S c h e m a t i c d i a g r a m o f snow d e p o s i t i o n f r o m a s t o r m on a w e s t c o a s t m i d l a t i t u d e m o u n t a i n (a) (b)  Storm w i t h r e l a t i v e l y freezing level Composite storm w i t h freezing level  constant fluctuating  165  model o f F i g . 6.11a  will  apply.  H o w e v e r , f o r some  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 different  elevations.  a t two o r more  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 a t each p o s i t i o n o f t h e f r e e z i n g  level,  t h e s t o r m may h a v e t o be d i v i d e d i n t o s u b s t o r m s , model a p p l i e d t o each  storms  i n turn.  then  and t h e  The most common o f t h e s e  c a s e s i s where t h e f r e e z i n g l e v e l - i s b e l o w t h e t o p o f t h e mountain  f o r b u t p a r t o f t h e s t o 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 highest elevations  ( F i g . -6.11b).  The  snow-wedge s t i l l  f o r m s , u s u a l l y by d e p o s i t i o n f r o m t h e  colder a i r after  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  o f warmer a i r a h e a d o f t h e f r o n t may have p r o d u c e d e l e v a t i o n s on t h e m o u n t a i n . i n t o substorms,  so t h a t H  where p o s t f r o n t a l precipitation.  e  The p r e c i p i t a t i o n i s d i v i d e d i s now  d e f i n e d as t h e e l e v a t i o n  snow d e p o s i t i o n e q u a l s p o s t  Often H  e  rainV'at a l l  frontal  c a n 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 o f t h e new snow-wedge ( e . g . s t o r m 6 2 , F i g . 6 . 6 , where H  e  i s about  1050 m).  D u r i n g t h e two w i n t e r s o f m e a s u r e m e n t , t h e r e w e r e a l s o . a f e w more c o m p l i c a t e d s t o r m s where t h e f r e e z i n g was  seldom  freezing  constant.  At t h e b e g i n n i n g o f t h e storm t h e  l e v e l a n d h e n c e s n o w l i n e w o u l d be a t l o w e l e -  v a t i o n , then r i s e The  level,  t o aboye t h e m o u n t a i n ,  then descend  q u a l i t a t i v e model can handle these composite  storm  again.  166  t y p e s , when b r o k e n down i n t o d i v i s i o n into, substorms  separate, substorms.  However,  i s o f t e n d i f f i c u l t i f based  on e v i d e n c e o b s e r v e d i m m e d i a t e l y a f t e r t h e s t o r m .  only Continual  monitoring 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 these c o m p l i c a t e d s t o r m s a t a number o f d i f f e r e n t a l l o w such s u b d i v i s i o n , b u t l o g i s t i c a l l y possible I n this  elevations  would  t h i s was n o t  study.  T h i s q u a l i t a t i v e m o d e l o f s t o r m snow  deposition  with elevation i s translated into quantitative  forms i n  C h a p t e r 9•  6.4  Rime  6.4.1  Results  accretion  Large q u a n t i t i e s  o f rime•on  trees, buildings, wires  and p o l e s a r e a f e a t u r e o f t h e 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 s t o r m s  ( F i g . 6.12).  The s i z e a n d  f r e q u e n c y o f t h e s e r i m e d e p o s i t s s u g g e s t s t h a t t h e y make a significant  c o n t r i b u t i o n t o the water input a t h i g h e r  e l e v a t i o n s on Mount Seymour. F o r t h e two y e a r s o f t h i s b e l o w 790 jn.  s t u d y , no r i m e was- o b s e r v e d  Above t h i s , t h e number o f s t o r m s w i t h r i m e  increased linearly with eleyation.  However, t h e 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  ( T a b l e 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 o n t o 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 o n t o t r e e s ( b o t t o m ) E l e v a t i o n 1260 m, M a r c h 1971  168  TABLE 6 .7  Amount of rime a c c r e t e d on 0..5 cm d i a m e t e r stakes' ab.oVe the snow s u r f a c e • 6 December 197.0.-31 May 197.1  Elevation 12 60 .  Total horizontal l e n g t h (cm)  146  Number o f storms w i t h rime a c c r e t i o n  26*  Mean l e n g t h / s t o r m w i t h rime (cm)  5.6  (meters)  106.0  970 .  35  20  10  3  16  11  6  2  1.7  1.5  2.2  1.8  870  790 .  % o f snow storms with rime•accretion  72  44  31  17  6  % o f a l l storms w i t h rime a c c r e t i o n  46  29  20  11  4  105  60  30  9  E s t i m a t e d water e q u i v a l e n t of rime a c c r e t i o n (mm)**  438  E s t i m a t e d rime a c c r e t i o n as % of t o t a l w i n t e r precipitation  .  12.5  3.0  2.1  1.1  I n c l u d e d 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/m  3  (see t e x t ) .  0.3  169  30  Pig.  6.13  H o r i z o n t a l l e n g t h . ' o f r i m e 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 o f growth," -6 December 1970 -.31 May 1971  170  ab.oye 106.0 jn.'.  with, l a r g e i n c r e a s e s  m e a s u r e d on t h e 0 . 5 cm s t a k e s long  (storm  28, 1970-71).  The l a r g e s t  accretion  •from one s t o r m was 16 cm  The d o m i n a n t w i n d 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 was  from the east  (prefrontal conditions).  riming  T h e r e was  a l s o s u b s t a n t i a l rime accumulation from winds w i t h  westerly-  aspect  believed  (postfrontal conditions).  r i m e grows d i r e c t l y reports  i t i s generally  i n t o the wind, but Scorer(1972,  r i m e a c c r e t i o n a b o u t 30° on e i t h e r s i d e o f t h a t  direction.  This  may h e l p  explain differences i n the  shapes o f t h e w i n d and rime r o s e s storm produced r i m i n g  i n Pig. 6.13).  O n l y one  f r o m 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 o b s e r v e d t o f o r m d u r i n g ,  or immediately a f t e r ,  snow s t o r m s , b u t n o t a l l snow s t o r m s a c c r e t e d  6.4.2  pg.132)  rime.  Rime on t r e e s Rime d e p o s i t s - f r o m a s i n g l e s t o r m o f t e n h a d a-  sharply an  defined  apparent "snowline"  mountainside. on  lower e l e v a t i o n a l l i m i t . t h a t was c l e a r l y  In fact this  At higher  visible  produced on t h e  only marked t h e l i m i t  t r e e s , a n d new snow o f t e n f e l l  line.  This  o f rime  t o e l e v a t i o n s below  this  e l e v a t i o n s , r i m e s o m e t i m e s p e r s i s t e d on  t r e e s b e t w e e n s t o r m s , s o 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  thickness.  T r e e s , t h e n became c o m p l e t e l y , c o v e r e d w i t h r i m e  and c o m p a c t e d  snow, a p p e a r i n g as l a r g e h a r d ' i c e  w i t h no f o l i a g e  6.4.3  visible.  Water e q u i v a l e n t The  pillars  o f rime  accreted  measurements i n d i c a t e d t h a t r i m e might  f o r m an  important input 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. to f a l l  Rime c o l l e c t e d by t r e e s was o f t e n  t o t h e snowpack b e n e a t h .  t o h a v e grown d i r e c t l y  It-was a l s o  observed  observed  o n t o t h e s n o w p a c k , e s p e c i a l l y on  t h e w a l l s o f snow o r s c o u r h o l l o w s . In t h i s was  study the a c t u a l water e q u i v a l e n t  n o t measured.  the u n i t  of rime  H o w e v e r , t h i s may be c a l c u l a t e d f o r  cross s e c t i o n a l a r e a exposed  t h e d e n s i t y o f r i m e i s known.  t o an a i r s t r e a m i f  Some e s t i m a t e s o f d e n s i t y  were made by m e a s u r i n g t h e d i m e n s i o n s o f r i m e • d e p o ' s i t s t o f i n d t h e volume,  then s u b s e q u e n t l y w e i g h i n g t h e sample.  V a l u e s r a n g e d f r o m 3^0 kg/m t h e volume  3  t o 610 k g / m . 3  Estimates of  were s u b j e c t t o e r r o r as t h e r i m e was f e a t h e r y  and i r r e g u l a r  i n shape.  Heikinheimo ( i n M i l l e r  r e p o r t e d d e n s i t i e s o f 150-300 kg/m p l a s t e r e d on t r e e s by s t r o n g w i n d s In a laboratory  3  1966)  f o r r i m e and' snow i n Northern Finland.  s t u d y o f f r o s t g r o w t h on a f l a t p l a t e  at s u b f r e e z i n g temperatures  held  (equivalent to the formation  172  of r i m e ) , after  Trammell  one h o u r s  thicknesses  if  growth  growth.  i n both studies. continued  Frost  specific humidities  The t e m p e r a t u r e  the  Chung  o f 500. k g / m .  Trammell  were  et a l believed  and h i g h e r  wind  lower the d e n s i t y .  effect,  of a frost  density  o f any s u b l a y e r  The l o w e r t h i s t e m p e r a t u r e , t h e  layer increased increased  that the  w i t h d e p t h and t h e with  time.  From t h i s e v i d e n c e i t a p p e a r s - t h e d e n s i t y on Mount Seymour must v a r y  from storm t o storm,  The' t o t a l h o r i z o n t a l l e n g t h assumed d e n s i t y  equivalent  o f rime depending  c o n d i t i o n s , a n d amount o f r i m e a c c r e t e d . .  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  by t h i s  o f 300 kg/m  o f rime accreted  t o give  an e s t i m a t e  p e r u n i t v e r t i c a l a r e a exposed  The 438 mm a t 126.0 m i s s u b s t a n t i a l ( T a b l e  3  was m u l t i p l i e d o f the water  t o an a i r s t r e a m . 6.7),  i t a t i o n , which o f course is.measured w i t h respect Thus t h e v a l u e  For  was a s s u m e d .  and has  b e e n e x p r e s s e d as a p e r c e n t a g e o f t h e t o t a l w i n t e r  unit h o r i z o n t a l area.  except  o f t h e m a t e r i a l on w h i c h  Tramwell et a l a l s o reported  density  would  velocities.  o f t h e a i r s t r e a m had l i t t l e  frostJwas growing.  that  d e n s i t i e s were i n c r e a s e d by  c o n t r o l l i n g the temperature  on w e a t h e r  Only  3  f o r s e v e r a l months .the d e n s i t y  3  in  3  o f a f e w mm- c l o s e t o t h e r i m e d o b j e c t  r i s e t o 800 k g / m . higher  o f 216 k g / m ,  A f t e r . 24. h o u r s g r o w t h  (1958) measured a d e n s i t y  and A l g r e n  considered  e t a l (.196.8). f o u n d a d e n s i t y  o f 12.5  precipto a  percent of  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 a t 1260 m i s somewhat h y p o t h e t i c a l i n t h a t r i m e grows o n l y on s p e c i f i c the  objects i n  way o f t h e a i r s t r e a m , a n d 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 , w h e r e a s p r e c i p i t a t i o n over t h e e n t i r e s u r f a c e . to  compare t h i s  For  example,  occurs  Nevertheless, i t i s interesting  data with findings of other researchers.  Berndt and F o w l e r  (1969) t h o u g h t r i m e  could  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 u p p e r This  forested slopes i n Eastern  Washington.  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  input.  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 b e e n made f o r t i m b e r e d a r e a s a b o v e 1500 m i n s o u t h eastern Australia  ( C o s t i n e t a l 1961).  r e v i e w o f German w o r k c i t e s and r i m e s u p p l e m e n t  Geiger's  (1965)  Grunow, who c a l c u l a t e d dew  f r o m f o g t o be 20 p e r c e n t o f a n n u a l  p r e c i p i t a t i o n a t about  1000 m.  C a r e 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 s i n c e Fowler and Berndt of  (1971) have shown t h a t  accumulation  r i m e i s c o n t r o l l e d n o t 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 ,  b u t a l s o by t h e s i z e a n d shape o f r e c e p t o r . above r e s u l t s  c a n n o t be s t r i c t l y  Thus t h e  compared, s i n c e t h e r e s e a r c h e r s  used d i f f e r e n t types o f r e c e p t o r s . the  results,  F o w l e r and B e r n d t  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  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 where c e s s a t i o n o f g r o w t h  c a n be e x p e c t e d .  show with  dimension, The c r i t i c a l  174  dimension 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 square o f the supercooled It 0.5  ( K u r o i w a 1965).  droplet radius  i s possible that i n this  and t o t h e  study,' t h e r e c e p t o r  cm may h a v e on o c c a s i o n s  size of  exceeded t h e c r i t i c a l  s i o n , so t h a t rime growth ceased, a l t h o u g h  rime  dimen-  continued  to accrete  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  needles.  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  efficiency  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  area  s u c h as c o n i f e r  sectional  and t o c h a n g e s i n a e r o d y n a m i c p r o f i l e w i t h r i m e  6.5  growth.  Conclusion Total winter  p r e c i p i t a t i o n increases  linearly  with  e l e v a t i o n on Mount Seymour, w i t h no e v i d e n c e o f an i n t e r m e d i a t e 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 occurs.  This  i s contrary  to the findings of e a r l i e r  w o r k e r s , but t h e y have tended t o u n d e r e s t i m a t e w i n t e r c i p i t a t i o n t h r o u g h u s e o f a snow d e n s i t y o f 100 kg/m convert  s n o w f a l l t o water equivalent.  o f n e w l y f a l l e n snow i s a t l e a s t t w i c e the  The t r u e  pre-  3  to  density  this, value.  However,  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 with e l e v a t i o n i s  e x t r e m e l y v a r i a b l e f r o m s t o r m t o s t o r m , and on o c c a s i o n s maximum c a n o c c u r b e l o w t h e b a s e o f t h e m o u n t a i n . frequently f a l l s winter.  a  Rain  a t t h e t o p o f t h e mountain even i n mid-  Conversely,  snow may f a l l  t o s e a l e v e l on  occasions.  175  Snow d e p o s i t i o n i n wedge l i k e successive  f r o m each, s t o r m i n c r e a s e s  form.  with, e l e v a t i o n  T h i s p e r s i s t e n t wedge shape, f r o m  storms- u l t i m a t e l y h e l p s p r o d u c e t h e snow-wedge  o f snowpack a c c u m u l a t i o n .  L e s s snow i s d e p o s i t e d i n t h e  f o r e s t t h a n i n open a r e a s . amount t o w i n t e r  Rime adds an  appreciable  w a t e r i n p u t , b u t t h e amount  accreted  depends on t h e number, s h a p e s and s i z e s o f r e c e p t o r s 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  variables.  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 deposition  variations with  elevation.  series  o f zones o f d e p o s i t i o n  vation  of the storm  wind v e l o c i t y . deposition tology  within  snow  It identifies  a  which are l i n k e d t o the e l e -  (or substorm) f r e e z i n g  This model, f u r t h e r  level  and t o  a n a l y s e s o f snow  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 clima-  o f snow s t o r m s a r e t h e 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  prediction functions  d e v e l o p e d i n C h a p t e r 9-  176  CHAPTER 7  7.  ANALYSIS OF SNOW DEPOSITION The  extensive  designed t o allow The  results  sampling network o f t h i s  use o f a n a l y s i s  of the e f f i c i e n c y  work, t e c h n i q u e s f o r r e d u c i n g  scale  of the sampling  net-  t h e n e t w o r k , and t h e f e a s -  area.  Analysis  of variance  . Snow d e p o s i t i o n e x a m i n e d by a n a l y s i s there  o f snow  deposition  f r o m t h e 82 s t o r m s s a m p l e d was  of variance  techniques t o discover  were: (a)  any s i g n i f i c a n t  differences  (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  (c)  any s i g n i f i c a n t  differences  forest As  a first  i n T a b l e 7-1 The  section,  o f c o m p u t i n g t h e t o t a l mass o f snow o v e r a meso-  7.1  if  techniques.  of t h i s a n a l y s i s , presented i n t h e next  lead t o discussion  ibility  of variance  s t u d y was  among s t o r m s , elevations,  among t h e  strata.  step,  the analysis of variance  model  was a p p l i e d t o a l l d a t a o f t h e w i n t e r  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  1969-70.  and e l e v a t i o n s .  177  TABLE 7 . 1  Analysis snow  A.  o f v a r i a n c e models  deposition  Model and r e s u l t s f o r a l l d a t a -  Source  df  SS  37 12 4 444  Storms Elevations Strata Storm X E l e v a t i o n Strata X Elevation S t r a t a X Storm S t r . X E l e v . X Storm Error  12350  2604 11267 703 7089 1184 426 1891 465  TOTAL  14819  25629  **  B. •  significant  48 148  1776  o f each storm  1969-70,  F  ms .4 .9 •7 .0 2 4 .6 2 .9 1 .1 0 .04  70 938 175 16 .  1868 24920 4663  ** ** **  424  **  655 ** 76 ** 28 **  level  separately  1970-71 df  Source Elevations Strata Elevations Error  winter.1969-70  a t 99% c o n f i d e n c e  Model f o r a n a l y s i s - winters  used t o examine  ;  • X  Strata  H-1 S-1 (H-1) ( S - 1 ) HS ( R - 1 ) HSR-1  TOTAL  Where,  H = e l e v a t i o n , H = l , 2 , . . . . n , • n£l2, depending on e l e v a t i o n o f s t o r m s n o w l i n e S = stratum,  S =  1,2,..5  R = number r e p l i c a t i o n s i n e a c h R = 1,2 . . .6  stratum,  178  T h i s i n t r o d u c e s the a s s i g n e d and On  the  disadvantage-that  analyzed for elevations  o t h e r hand, i t possesses the  interactions  can  snow d e p o s i t i o n  be  examined.  The  is significantly  z e r o v a l u e s must below the  useful  snowline.  advantage  cant .  a l l the  T h i s shows t h e  d i f f e r e n t , at  interactions  b e h a v i o u r of the  segment t o snow d e p o s i t i o n from e l e v a t i o n The  to e l e v a t i o n ,  and  the  on  99  and  highly  per-  strata. signifi-  mountain t e r r a i n  from storm to  storm,  from stratum to  stratum.  elevations  is  mountain  the  a west coast m i d l a t i t u d e  snowlines normally vary from storm to storm.  interactions  between f o r e s t  b e t w e e n s t r a t a and indicate  new  s t r a t a and  storms are  snow gauge s i t e d a t one a d e q u a t e l y on  In f a c t , since  and  during different  as  follow.  elevation the  and They  will  For be  also  storms. example,  unable to  interactions  a  index  o c c u r , even  at v a r i o u s e l e v a t i o n s ,  i s a common p r o c e d u r e , w i l l  interactions  forest  m o u n t a i n t e r r a i n segment.  elevation-forest  network of gauges s i t u a t e d clearings,  elevation,  more i n t e r e s t i n g .  Several important implications  deposition  The  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 t h e  at d i f f e r e n t e l e v a t i o n s ,  The  are  i n t e r a c t i o n b e t w e e n s t o r m s and  expected, since new  varies  that  r e s u l t s indicate- that  c e n t 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 More i m p o r t a n t l y ,  be  be  suggest m e t e o r o l o g i c a l  say  a  in  inadequate. characteristics  179  o f s t o r m s a r e an i m p o r t a n t i n f l u e n c e bution in  o f new snow.  snow d e p o s i t i o n  explanation discussed  i n the areal  The p r e s e n c e o f t h e s e  distri-  interactions  must a l s o be an i m p o r t a n t p a r t  f o r t h e snowpack w a t e r e q u i v a l e n t  i n Chapter  of the  interactions  5. 1970-71 w e r e n o t a n a l y s e d  Data f o r the winter in  t h i s way, b e c a u s e a s i m i l a r r e s u l t was e x p e c t e d .  an  analysis  of variance  was p e r f o r m e d f o r e a c h  The m o d e l u s e d i s a l s o g i v e n analyses only  t h o s e snow d e p o s i t i o n  s n o w l i n e f r o m e a c h storm.'  storm.  This  model  v a l u e s above t h e new  Thus z e r o v a l u e s b e l o w t h e  snowline are not included, first  i n T a b l e 7.1.  Instead,  and a d i s a d v a n t a g e o f t h e  model i s e l i m i n a t e d .  Of t h e snow s t o r m s  sampled,  f i v e w e r e n o t s u i t a b l e f o r a n a l y s i s b e c a u s e snow f e l l a t only  one e l e v a t i o n Of  significant and  (1260  t h e 77 s t o r m s s u b s e q u e n t l y a n a l y s e d , a l l show differences  among s t r a t a .  significant  i n snow- d e p o s i t i o n  A l l but three  among  elevations  s t o r m s show h i g h l y  elevations-strata interaction effects.  although differences vations  m).  i n snow d e p o s i t i o n  o c c u r among  Thus, ele-  and among s t r a t a , t h e b e h a v i o u r o f t h e f o r e s t t o  snow d e p o s i t i o n  varies  from e l e v a t i o n t o e l e v a t i o n .  o f t h i s v a r i a t i o n may be due t o t h e c h a n g i n g n a t u r e o f the  forest with  elevation  ( F i g s . 2.7  S  2.8),  especially  Some  180  s i n c e the d a t a i n c l u d e s a wide v a r i e t y of storms w i t h a wide v a r i e t y o f new snowlines  ( P i g s . 4.1, 4.3).  Meteorological  f a c t o r s t h a t vary w i t h e l e v a t i o n may a l s o be i m p o r t a n t . Of those storms which show no s i g n i f i c a n t  elevation-  f o r e s t s t r a t a i n t e r a c t i o n , one d e p o s i t e d very s m a l l amounts of snow (storm 70, 1970-71)-  The o t h e r 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 o f the new snow wedge ( i . e . a very narrow wet snow zone). suggests  This  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 o f o t h e r storms  i s a s s o c i a t e d w i t h t h e developemnt o f t h e wet snow zone where reduced, the f o r e s t .  or z e r o , snow amounts a r e d e p o s i t e d w i t h i n The d i f f e r e n t p a t t e r n o f 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 t o be d e p o s i t e d a l s o c o n t r i b u t e s t o the i n t e r a c t i o n term Fig.  beneath-trees,  (e.g. storm 55,  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 , and i n t e r a c t i o n means.  stratum,  T h i s t e s t i n d i c a t e s which snow  d e 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 , t h a t i s those which are homogeneous.  U n f 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 h o p e l e s s l y c o m p l i c a t e d and impossible to follow.  However, a summary o f storms where  181  a d j a c e n t e l e v a t i o n s , o r f o r e s t s t r a t a , had  snow  deposition 7-2).  means t h a t were homogeneous, i s i n s t r u c t i v e ( T a b l e For  the  significantly The  bulk  o f s t o r m s , snow d e p o s i t i o n means were  d i f f e r e n t between each e l e v a t i o n were b e t w e e n 790-870 m,  p r i n c i p a l exceptions  400-490 m, together  but  these sampling e l e v a t i o n s  t h a n most.  means a r e  likely  To  t o be  are  more homogeneous as  became c l o s e r , F i g . 7.1  results  indicate this  t o be  f a c t o r s appear important.  was  sampling e l e -  significantly  different.  lowest elevations  new  a high  other  three  the elevations  s n o w l i n e were  Second, storms w i t h  a l s o had  The  percent of  s t o r m s s a m p l e d , snow d e p o s i t i o n means a t t h e discontinuous  deposition  t r u e , but  i n 38  between  closer  constructed.  generally First,  and  also  e x a m i n e w h e t h e r snow  vations  i m m e d i a t e l y above t h e  sampled.  snow t o  percentage of  the  homogeneity  o f s n o w f a l l means b e t w e e n a d j a c e n t s a m p l i n g s i t e s . storms u s u a l l y r e s u l t from the  not  Such  same b a s i c s y n o p t i c  pattern,  moist P a c i f i c  a i r , o v e r r i d i n g entrenched A r c t i c a i r  C h a p t e r 8).  I t w o u l d seem, t h e r e f o r e , t h a t h o m o g e n e i t y  s n o w f a l l means b e t w e e n a d j a c e n t e l e v a t i o n s a c t u a l e l e v a t i o n of the as  on  the  depends on  sample, and.the storm type,  e l e v a t i o n d i f f e r e n c e between the  sampling  Snow d e p o s i t i o n means w e r e a l m o s t a l w a y s cantly and  canopy edge and  beneath the  of  the  as  well  sites..  signifi-  d i f f e r e n t b e t w e e n c l e a r i n g s a n d . t h e canopy  between the  (see  canopy  edge, (Table  7-2).  TABLE 7 . 2  A.  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 t h e 95$ c o n f i d e n c e l e v e l . A n a l y s e d w i t h Duncan's New M u l t i p l e Range Test  E l e v a t i o n means E l e v a t i o n (metres) 1260  W i n t e r 1969-70 Winter 1970-71 T o t a l Winters 1969-71  % o f those snow storms sampled  B.  - 1060 - 970 - 870  - 790- - 710  - 590 - • 4 9 0 - 400  330  - 220 - 120  2 6  2 3  1 5  14  9  5 9  0 3  0 4  14  3  1 5  0 6  1 5  8  5  6  23  14  3  4  17  6  6  6  10  7  11  45  30  8  15  74  38  55  50  S t r a t u m means Stratum open  W i n t e r 1969-70 \. Winter 1970-71 ] Total winters  -  clearing  canopy edg?e  -  beneath  canopy  -  15 23  5 4  8 4  16 23  -  38  9  12  39  % o f those snow " storms sampled  46  11  15  48  1969-71  tree trunk  183  100 c o V  E c  O O  a. v  t>  80  CD C  Q-  E  o c w  c a> u <L) •a L o V sz c  60  h  X)  40  I-  t) a  E o tn </>  E o i_  V  -t-> «J  X) I/)  n o c V cn o E o v u  20  50  100  150  200  Elevation interval between sampling sites ( meter s ) Fig.  7.1  H o m o g e n e i t y o f means o f - s t o r m snow d e p o s i t i o n b e t w e e n 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 t h e e l e v a t i o n i n t e r v a l between sampling s i t e s .  184  This  justifies  t h e measurements b e n e a t h 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 coast onment, s u c h a r e a s s h o u l d be  midlatitude  mountain e n v i r -  be s a m p l e d i f e s t i m a t e s  made o f t h e t o t a l mass o f snow d e p o s i t e d .  h a l f the storms, there  were no s i g n i f i c a n t  b e t w e e n c l e a r i n g s and open a r e a s , to tree trunks  and b e n e a t h  are to  In-almost differences  and between t h e a r e a  close  trees.  I n summary, t h e p r e v i o u s  analyses  show t h a t  on a  west coast  m i d l a t i t u d e m o u n t a i n , snow d e p o s i t i o n  nificantly  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 , a n d f o r e s t  s t r a t a , b u t more i m p o r t a n t l y , interactions.  there  are also  i s sig-  significant  T h e s e i n t e r a c t i o n e f f e c t s a p p e a r t o be  p r o d u c e d 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  s t o r m s a n d - w i t h e l e v a t i o n , a n d by <£hexchanging-'nature-'-' o f t h e forest with  elevation.  7.2  T o t a l mass o f snow d e p o s i t e d  7.2.1  Method o f c a l c u l a t i o n  a f t e r each  storm  E s t i m a t e s c a n be made o f t h e t o t a l mass o f snow deposited  by e a c h s t o r m on t h e t e r r a i n s e g m e n t , by  the  theory  The  sampling network of t h i s  purpose.  o f s t r a t i f i e d random s a m p l i n g  ( C o c h r a n 1963) .  s t u d y was s u f f i c i e n t  A l t e r n a t i v e l y , prediction functions  lished later  c o u l d be u s e d t o e s t i m a t e  s t r a t a knowing that  i n t h e open.  applying  for this  t o be  estab-  snowfall i n forest  185  T o t a l mass r e p r e s e n t s t h e amount o f snow  available  f o r a c c u m u l a t i o n o f t h e snowpack o v e r t h e a r e a o f t h e t e r r a i n segment.  When combined, w i t h r a i n f a l l m e a s u r e m e n t s ( e . g . U.S. Army 1956),  and w i t h snow m e l t f u n c t i o n s may be p r e d i c t e d .  In this  runoff  s t u d y , t h e ' 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 s t r e a m s s o r u n o f f g a u g i n g was i m p r a c t i c a l .  Thus no i n d e p e n d e n t  w a t e r b a l a n c e c h e c k on t h e c a l c u l a t i o n s was p o s s i b l e . T h e r e were s e v e r a l p r o b l e m s i n c o m p u t i n g t h e t o t a l mass o f snow f r o m e a c h s t o r m .  I n t e r c e p t e d snow t h a t  fell  t o t h e snowpack a f t e r s a m p l i n g was n o t m e a s u r e d u n t i l t h e f o l l o w i n g storm.  I f i t m e l t e d p r i o r t o t h i s , i t was n o t  measured a t a l l .  F u r t h e r unmeasured i n p u t r e s u l t e d  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 ,  from  which  p e r c o l a t e d i n t o , a n d was a b s o r b e d b y t h e snowpack by f r e e z i n g o r by c a p i l l i a r y A final difficulty  tension. r e s u l t e d because t h e area o f  e a c h s t r a t u m h a d t o be known.  A r e a s o f p r i m a r y s t r a t a were  f o u n d b y p l a n i m e t e r i n g t h e a r e a o f each, e l e v a t i o n a l f r o m a map--of - s c a l e  1:12,000.  s t r a t a w e r e more d i f f i c u l t  band  The a r e a s o f t h e s e c o n d a r y  t o measure.  Open a r e a s a n d  c l e a r i n g s were mapped f r o m a i r p h o t o g r a p h s  and p l a n i m e t e r e d .  A r e a s 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 t h e d i m e n s i o n s a n d number o f t r e e s i n t h e 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 t h e heteorogenous  o f t h e f o r e s t on Mount Seymour ( F i g . 2.7),  nature  this  p r o c e d u r e w o u l d 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 stratum  size.  The r e s u l t w o u l d be a b i a s e d  sample  e s t i m a t e , t h e gain 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 be  l o s t , and confidence  ( C o c h r a n 1963). from t h e three  underestimated  C o n s e q u e n t l y , snow d e p o s i t i o n s a m p l e s s t r a t a - canopy e d g e , b e n e a t h t r e e s  close t o tree trunks o f 18.•  l i m i t s w o u l d be  would  The a r e a  - were p o o l e d ,  t o g i v e a sample  o f t h i s new s t r a t u m ,  t h e n be more r e l i a b l y  assessed  , and  "the  forest"  size could  f o r each e l e v a t i o n a l band  from a i r photographs.  7.2.2  Results An  given  example o f t h e r e s u l t s  i n T a b l e 7-3.  95 p e r c e n t  confidence  s u g g e s t e d by Cochran,  Variance,  from a s i n g l e storm a r e  degree o f freedom, and  l i m i t s were computed by methods (1963).  F o r most s t o r m s ,  i n t e r v a l s w e r e a s l a r g e a s 90 p e r c e n t mass f o r d e p o s i t i o n s creased  confidence  of the total  c l o s e t o t h e new s n o w l i n e ,  snow  but de-  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 percent  o f t h e t o t a l , e x c e p t f o r a f u r t h e r i n c r e a s e a t 1260 m. The  higher  deposited  values  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  snow, o r , a s a t 1260 m, w i t h  snow  drifting.  TABLE 7-3  Example terrain  o f t h e t o t a l mass o f snow d e p o s i t e d on t h e Mount Seymour segment f r o m a s t o r m  Me an Mass (kg/m )  T o t a l Mass o f snow Deposited (10 .m )  (Storm 3 0 , w i n t e r 1969-70)  Degrees of Freedom  95$ C o n f i d e n c e Limits of T o t a l Mass (10 .m )  Confidence i n t e r v a l as p e r c e n t a g e o f • t o t a l mass  Elevation Band (feet)  Area (10 .m )  3600-4200  234  16 .9  3.96  11  3.59  4.34  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  2.42  3.84  45  2400-2700  607  3.3  1.98  17 18  1.76  2.20  22  2100-2400  764  3.4  2.63  17  2.21  3.05  30  1800-2100  1019  0.9  0.98  18  0.41 . I . 5 6  117  3  2  2  3  3  3  3  19  1500-1800  943  0.1  0.06  8  0.01  0.10  164  Total for terrain segment  5388  5.1  27.31  90  '26.03  28.61  9  r—  1  CO —  188  Confidence  l i m i t s were a l s o computed f o r t h e  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 a f t e r s t o r m , by p o o l i n g t h e s a m p l e v a r i a n c e s f o r e a c h  total each  elevational  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 t h a n  percent  o f the- t o t a l f o r 70  o f t h e 82  snow s t o r m s  T h u s , i f i t i s assumed t h e s a m p l e s were u n b i a s e d ,  15  analysed. acceptable  e s t i m a t e s o f t o t a l snow mass d e p o s i t e d on t h e t e r r a i n were p o s s i b l e .  In the o t h e r cases  were s o m e t i m e s as h i g h as 70 snow, b u t  these storms  percent  were always  o f d e p o s i t e d snow, and  confidence  segment  intervals  o f t h e t o t a l mass o f  t h o s e w i t h s m a l l amounts  so were r e l a t i v e l y  unimportant.  T o t a l snow mass d e p o s i t e d o v e r two w i n t e r s was puted  f o r e a c h e l e v a t i o n a l b a n d and  (Fig.  7-2).  .Confidence  f o r the t e r r a i n  segment  i n t e r v a l s were l e s s t h a n 10  c e n t 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  com-  per-  resultant  curves r e f l e c t e d the r e l a t i v e p r o p o r t i o n of -forested, c l e a r i n g , and  open a r e a a t e a c h e l e v a t i o n , and  hypsometric  t h e most s i g n i f i c a n t  The  curves  b e t w e e n 900  m and  1100  snow  indicated  zone f o r snow d e p o s i t i o n on t h e  I f m a n i p u l a t i o n of the f o r e s t  terrain  m i n both w i n t e r s .  cover  can i n c r e a s e snow  d e p o s i t i o n , . a n d h e n c e snow a c c u m u l a t i o n , t h i s be  the  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  mass d e p o s i t i o n w i t h e l e v a t i o n .  segment was  t h e shape o f  t h e most p r o f i t a b l e t a r g e t a r e a .  zone w o u l d  Total m a s s of d e p o s i t e d s n o w ( X 1 0 ) m 3  M  O o  o o  _I_  0)  8 _i_  3  water  equivalent .  COD O _L_  rOo O  OO o  -I  o  ID_-*  2  in  z  ?  ' ^ |  O  O s s a  3 3  681  H  190  Considerably terrain  more t o t a l snow was d e p o s i t e d  segment i n t h e w i n t e r  shape o f t h e c u r v e s  1970-71.  on t h e  However, t h e  are s i m i l a r , except f o r a  sharper  maximum o f t o t a l mass a t 970 m, a n d f o r a s e c o n d a r y maximum a t t h e l o w e s t  e l e v a t i o n s i n 1970-71.  when snow f r e q u e n t l y f e l l a t 120 m was e q u i v a l e n t  In this  t o l o w l e v e l s , t o t a l mass  t o t h a t a t 790 m a n d o n l y a  year deposited little  l e s s than that at the top o f the mountain.  7.3  Reduction The  of the sampling  t r a n s e c t of sampling  a p p e a r e d t o be s u f f i c i e n t  network s i t e s up t h e m o u n t a i n  t o adequately  define 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 d e p o s i t i o n w i t h e l e v a t i o n ( C h a p ter  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 sampling  sites,  c o r r e l a t i o n matrices  c i p i t a t i o n were p r e p a r e d  o f storm  f o r each o f t h e w i n t e r s  E v e n t h o u g h t h e two w i n t e r s were d i f f e r e n t the matrices  are quite s i m i l a r .  pre(Table  7-4).  i n character,  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 sampling  sites  increases,  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 t h e  actual elevation. These m a t r i c e s , t h e homogeneity o f s t o r m means b e t w e e n a d j a c e n t  sampling  sites  ( F i g . 7-1)  snowfall and p l o t s  of storm p r e c i p i t a t i o n v a r i a t i o n with e l e v a t i o n s i m i l a r to  F i g . 6.2,  a l l indicate precipitation variations with  191  TABLE 7.4  Correlation  matrices f o r p r e c i p i t a t i o n at 12 'elevations  Winters 1 9 6 9 0 7 0 ,  Winter 1 9 6 9 - 7 0  Elevation (met.ers)  1970-71  (57 o b s e r v a t i o n s * )  1260  1060  970  870  790  710  "590  490  400  330  220  120  1260  1.00  1060  0.92  1.00  970  0.88  0.88  1.00  870  0.83  0.86  0.92  1.00  790  0.79  0.79  0.87  0.96  1.00  710  0.77  0.79  0.86  0.94  0.98  1.00  0.77 0.76  0.76  0.84  0.98  1.00  0.84  0.91 0.91  0.95  O.76  0.95  0.98  , '110  0.76  0.75  0.84  0.91  0.94  0.97  0.99 0.98  0.99  1.00  330  0.75  0.83  .0.90  0.94  0.97  0.99  0.99  0.99  .0.82  0.90  0.94  0.99  0.99  0.99  1.00  0.89  0.93  0.97 0.96  0.99  0 .82  0 .98  O.98  0.98  0.99  0.99  1.00  590  490  400  330  220  120  590 490  220  0.75  0.75 0.74  120  0.74  0.73  Winter 1970 - 7 1  (68 o b s e r v a t i o n s * )  Elevation (met ers)  1060  1260  970  870  790  1260  1.00  1060  0.96  970  0.92  0.93  1.00  870  0.89  0.87  0.92  1.00  0.88  0.85  .0.92  0.98  1.00  0.94  . 7 9 0  710.  1.00 1.00  1.00  710  0 .81  0.79  0.86  590  0.79  0.78  0.85  0.91  0'.95 .0.92  490  0.77  0.75  0.85  0.91  0.91  410  0.78  0.77  0.85  0.91  330  0.77  0 .74  0.83  220  0.76  0.73  120  0.78  0.75  1.00 O.96  1.00  0.91  0.95 0 .94  0.97 0.96  0.98  1.00  0.90  0.90  0.93  0.96  0.96  0.98  1.00  0.83  0.88  0.91  0 .9.4  0.96'  0.95  0.98  1.00  0.84  0.89  0.92  0.94  0.96  0.94  0.96 0.94  .0.97  0.99  1.00  * In most cases one o b s e r v a t i o n represents p r e c i p i t a t i o n from one In a few. cases p r e c i p i t a t i o n from two storms i s combined.  1.00  storm.  192  e l e v a t i o n on t h e 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  s a m p l e d by m e a s u r e m e n t s a t 120 this  a t 200  to r a i n 790  790  m.  Otherwise m,  and  above confined  snow f a l l s  a d d i t i o n a l s a m p l e s w o u l d be  below  needed  so as t o d e f i n e t h e d i s c o n t i n u o u s  t h e shape o f t h e new Too  m,  T h i s scheme s h o u l d be  s t o r m s o r snow s t o r m s where no  b e l o w 790 and  m intervals.  m and  snowline,  snow wedge.  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  as u s e d i n t h i s  s t u d y , can  lead to large errors i n estim-  a t i n g t h e t o t a l mass o f snow d e p o s i t e d on t h e segment.. ( T a b l e 7 - 5 ) .  design,  terrain  In general, there 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 t h e e l e v a t i o n i n t e r v a l b e t w e e n s a m p l i n g . s i t e s becomes l a r g e r .  The  estimates using sampling intervals  i s s m a l l , and  95 p e r c e n t apparent  as was  on t h e t e r r a i n simplified  similar  d i f f e r e n c e between m and  100  a b o u t t h e same as t h e  Intervals.  done i n t h i s  s i t e s a t 200  statistically  be  s i t e s a t 200  b e n e f i t from sampling  intervals, sampling  confidence  percentage  m elevation  computed  H e n c e , t h e r e i s no  a t a b o u t 100 study.  m elevation  A scheme w i t h  m w i l l more e f f i c i e n t l y p r o v i d e estimates  segment.  o f t o t a l mass d e p o s i t e d  I f the experimental  d e s i g n must  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  ele-  v a t i o n i n t e r v a l , r a t h e r t h a n e l i m i n a t e measurements w i t h i n the  forest.  193  TABLE 7.5  Influence of simplification  of the experi-  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  Percentage  snow d e p o s i t e d on t h e t e r r a i n  segment  d i f f e r e n c e f r o m t o t a l mass computed w i t h t h e  experimental design of this  study.  ( S a m p l i n g s i t e s a t a b o u t 100 m i n t e r v a l s in the forest)  and m e a s u r e m e n t s  S t o r m 30* Winter 1969-70  Winter 1969-70  S a m p l i n g s i t e s a t 200 m elevation intervals. Measurements i n f o r e s t .  13  6.  S a m p l i n g s i t e s a t 300 m elevation intervals. Measurements i n f o r e s t .  18  38  1  S a m p l i n g s i t e s a t 400 m elevation intervals. Measurements i n f o r e s t .  67  26  24  S a m p l i n g s i t e s as f o r t h i s s t u d y , b u t no measurements t a k e n in the forest.  65  98  82  Proposed  simplification  Winter 1970-71  6  * 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 s t o r m i n T a b l e 7-3 u s i n g t h e e x p e r i ^ mental design o f t h i s study.  194  The r e s u l t s  of the a n a l y s i s of variance  contention that sampling i s necessary deposited  a r e t o be o b t a i n e d .  o f t o t a l mass o f snow  These r e s u l t s  c e r t a i n l y be t a k e n  (where snow may s l i d e  the  snow d e p o s i t i o n w i t h i n t h e f o r e s t  i f adequate e s t i m a t e s  measurements s h o u l d  support  show t h a t  a t t h e canopy edge  o f f t r e e s ) and b e n e a t h , t h e c a n o p y  (where i n t e r c e p t i o n o r w i n d s c o u r may r e d u c e t h e amount o f snow d e p o s i t e d ) .  S a m p l i n g 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 " w o u l d be e l i m i n a t e d , s i n c e f o r many' s t o r m s snow d e p o s i t i o n i n t h e s e in  areas i s w e l l represented  by t h a t  "open areas"-, and " b e n e a t h t r e e s " , r e s p e c t i v e l y .  only exceptions storms w i t h  The  are. f o r storms w i t h h i g h w i n d s , and  l o w d e n s i t y snow, where t u r b u l e n c e  may  induce  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 w i n d may p i l e  7 .4  snow a g a i n s t t r e e  trunks.  Conclusion The e x p e r i m e n t a l  design  i n this  study  appeared  a d e q u a t e t o d e f i n e v a r i a t i o n s o f s t o r m p r e c i p i t a t i o n and 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 snow d e p o s i t i o n within the f o r e s t .  I t seems a s a m p l i n g  d e t a i l e d as u s e d h e r e i s n e c e s s a r y the  t o t a l mass o f snow d e p o s i t e d '  are  desired.  scheme a l m o s t as  i f good e s t i m a t e s  of  on a t e r r a i n segment  M e a s u r e m e n t s s h o u l d be t a k e n  a t a b o u t 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 t h e  195  i n t e r v a l may  be  300  l a r g e r (say  p o s i t i o n must be  obtained  m).  i n the  Samples of-snow  forest, particularly  b e n e a t h t r e e s and  b e n e a t h t r e e canopy edges.  deposition  very  The on  can  be  d i f f e r e n t from that  degree of d i f f e r e n c e i s not the  meteorological  ( e s p e c i a l l y the l e v e l , and  w i n d s p e e d ) , and  H e r e , snow  i n the- open-.  c o n s i s t e n t , but  conditions  e l e v a t i o n and  dependent  p r e v a i l i n g during  movement o f t h e  on  de-  the  storms  freezing  nature of the  forest  at a p a r t i c u l a r e l e v a t i o n . I t has this the  been e s t a b l i s h e d t h a t  s t u d y were v e r y  the  two  winters  different i n character,  e l e v a t i o n zone b e t w e e n 900  1100  and  m,  yet  relative butions  i n t o account. area,  to the  low  Likewise,  elevations  Unfortunately,  p r a c t i c a l , but  mental design then the  of t h i s  w i t h i n ±8  should  make i m p o r t a n t  o f snow a r e  i f , as  midlatitude  small  and  i s b e l i e v e d , the  study produced unbiased  percent of that  on  the  infrequent. calcuexperi-  estimates, terrain  c a l c u l a t e d f o r each  p e r c e n t f o r most s t o r m s .  large  contri-  independent check of the  t o t a l mass o f snow d e p o s i t e d  i s w i t h i n ±5 and  no  studies  because of t h e i r  snow h y d r o l o g y o f w e s t c o a s t  mountains, even though f a l l s  l a t i o n s was  can  most  Future  o f snow h y d r o l o g y i n t h e ' N o r t h S h o r e M o u n t a i n s take t h i s  i n both,  was- t h e  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 .  of  segment  winter,  Thus i t i s p o s s i b l e  196  to  satisfactorily  e s t i m a t e , by  d e p o s i t e d snow o v e r  s a m p l i n g t h e t o t a l mass of-  a mesoscale area.  However, a l a r g e  amount o f w o r k i s n e e d e d t o s e r v i c e t h e ' e x p e r i m e n t a l of t h i s  s t u d y , even w i t h the  modifications  suggested,  s e l d o m be p r a c t i c a l o v e r  sampled.  s l o p e and  Thus, to r o u t i n e l y  o f snow d e p o s i t e d o v e r r i v e r  Such e f f o r t  e s t a b l i s h f u n c t i o n s to estimate  estimate  t h e t o t a l mass  where t h e r e i s no The  experimental  v a r i a t i o n s of d e p o s i t i o n  problem i s less d i f f i c u l t  d e s i g n c a n t h e n be still  of the v a r i a b i l i t y  by  snow  drifting.  on  f o r e s t " c o v e r (as f o r some i n New  t h e number o f s a m p l e s w i l l induced  coast  alternative - but•to  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 The  will  a s p e c t would have  c a t c h m e n t s on most w e s t  m i d l a t i t u d e m o u n t a i n s , t h e r e i s no  base s t a t i o n s .  to  a c a t c h m e n t , where a number o f  t e r r a i n segments o f d i f f e r e n t be  efficient  ( e . g . i t s o m e t i m e s t o o k most o f a day  sample d e p o s i t i o n f r o m a s i n g l e s t o r m ) .  to  more  design  simpler.  n e e d t o be  of  mountains Zealand).  However, l a r g e because  increased likelihood  of  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  and  the winters  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 t h e amount o f snow  received, synoptic  and i n t h e e l e v a t i o n s  a t which i t f e l l .  storm s i t u a t i o n s of these winters  Therefore, optic alysis  snowfalls.  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 t h e s y n -  climatology  of these winters.  of the contribution of various  deposition  a t each e l e v a t i o n .  a l s o examined i n t h i s lower l i m i t s  chapter,  This  leads  t o an a n -  s t o r m t y p e s t o snow  Storm f r e e z i n g l e v e l s a r e because they l a r g e l y determine  of snowfall.  The h o r i z o n t a l f l u x o f a t m o s p h e r i c w a t e r is  The  gave r i s e t o  b o t h n e a r minimum, a n d n e a r maximum r e c o r d e d  the  1969-70  computed as a p o s s i b l e  i n d i c a t o r of moisture  vapour sources.  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 water vapour f l u x the  two w i n t e r s  precipitation  8.1  may h e l p  e x p l a i n t h e observed contrasts i n  and s n o w f a l l .  Synoptic  features  of winter  The b r o a d s c a l e s y n o p t i c and  between  a i r mass c l i m a t o l o g y  storms  features  of the B r i t i s h  of winter  weather  Columbia coast  have  198  b e e n 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 s t o r m s d u r i n g t h e s t u d y w i n t e r s were f r o n t a l and  d o m i n a t e d b y mP' o r mA a i r m a s s e s .  (Table  S t o r m s a d v e ' c t i n g mA  a i r o n t o Mount Seymour were p a r t i c u l a r l y  prominent J u r i n g  t h e w i n t e r 1970-71, s o t h e a s s o c i a t e d c o m b i n a t i o n freezing levels vations  and u n s t a b l e  8.1)  o f low  a i r p r o d u c e d snow t o l o w e l e -  and a l a r g 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 w i n t e r a l s o h a d a l a r g e r number (8)  of Arctic  A i r out-  b r e a k s r e a c h i n g t h e V a n c o u v e r a r e a compared w i t h t h e 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 o n e . experienced  Both  a f e w s t o r m s c o n t a i n i n g mT a i r .  winters 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 t h e m o u n t a i n , o r i f snow occurred  i t was o f t e n m i x e d w i t h r a i n , a n d c o n f i n e d t o  higher elevations. region behind the  Generally, colder a i r invaded the  most f r o n t s , s o a f r o n t a l p a s s a g e  freezing level.  Thus f o r some s t o r m s ,  from p o s t f r o n t a l c o n d i t i o n s . bulk 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 .  snowfall at high elevations represented  its  snow f e l l  source  only  H o w e v e r , i n most c a s e s t h e  when t h e 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  The  lowered  Therefore,  l o w , most o f t h e prefrontal conditions.  o f a i r ahead o f , and b e h i n d ,  fronts.-,, a n d  soj.ourn o v e r t h e o c e a n may be d e d u c e d b y t r a j e c t o r y  analysis.  T r a j e c t o r i e s are u s u a l l y constructed using a  f i n i t e - d i f f e r e n c e process  ( P e t t e r s s e n 1956), b u t u n c e r -  199  TABLE  8.1  Percentage frequency all  storms,  winters  o f storm  types f o r  a n d f o r snow s t o r m s -  1969-70,  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 charts. T h e r e were 73 s t o r m s i n w i n t e r and 74 s t o r m s i n w i n t e r 1 9 7 0 - 7 1  S t o r m Type . A.  Frontal  1)  Maritime cold fronts Maritime f r o n t s w i t h a warm sector Maritime occluded fronts Arctic fronts associated with maritime f r o n t A r c t i c f r o n t s not associated with maritime f r o n t s , but w i t h moist Pacific airflows  2) 3)  4) 5)  B.  Non-frontal  6) 7)  C o l d lows Other lows w i t h no f r o n t , o r front well to S Troughs ( u s u a l l y associated with W o r NW a i r f l o w SW a i r . s t r e a m s W air.streams NW a i r s t r e a m s Light p r e c i p i t a t i o n associated with high pressure c e l l s  8) 9) 10) 11) 12)  TOTALS FOR WINTER  All  Storms  |  synoptic 1969-70  Snow S t o r m s 1969-70  1969-70  1970-71  77  89  45  65  12  19  '7  15  15  18  7  10'  48  39  30  27  2  8  1  8  0  5  0  5 '  23  • 11  15  8  6  0  1  0  5  4  6  3  2 3 0  4  5 1 1 0  1 3 0 3  0 1 0  3  0  1  0  61$  73$  100$  100$  1970-71  4  200  t a i n t i e s i n e s t i m a t e s o f 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 t h e r e are o r g a n i s e d v e r t i c a l motions i n t h e atmosphere (Munn 1970) . example, assuming h o r i z o n t a l f l o w , have suggested  Durst and Davis- (1957)  a c l i m a t o l o g i c a l average e r r o r o f 13 km/  hour i n wind e s t i m a t e s from s y n o p t i c maps. was  For  This  technique  c o n s i d e r e d 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 t h e  B r i t i s h Columbia coast because o r g a n i s e d v e r t i c a l motions are common d u r i n g storms,  and because maps of the wind  field  over t h e e a s t e r n P a c i f i c Ocean are based on few measurements, and are l a r g e l y e s t i m a t e s .  More p r a c t i c a l a n a l y s i s may  be made by c o n s i d e r i n g storm t r a c k s and storm  8.1.1  types.  Tracks o f w i n t e r storms The  t r a c k s o f t h e low p r e s s u r e  c e n t r e s of storms  were p l o t t e d from 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 f o r t h e study w i n t e r s . ( F i g . 8.1).  E i g h t g e n e r a l i s e d t r a c k s c o u l d be r e c o g n i s e d Storms a l o n g t r a c k s E, G and H have e a s i e s t  access t o c o l d a i r s o u r c e s .  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 t h e f r o n t a s s o c i a t e d w i t h most low pressure levels.  centres.  Such a i r i s u n s t a b l e and has low f r e e z i n g  Because o f a p e r s i s t e n t r i d g e o f h i g h p r e s s u r e i n  the e a s t e r n P a c i f i c i n t h e w i n t e r 1970-71 ( F i g . 3.3), storms o f t e n f o l l o w e d these t r a c k s i n November t o February  60  170  160  150  Fig.  8.1  150  140  130  120  110  140  G e n e r a l i s e d t r a c k s o f s t o r m s , w i n t e r s 1969-70, 1970-71 E a c h 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 t h e p e r c e n t a g e of. s t o r m s w h i c h f o l l o w e d each t r a c k and p r o d u c e d snow on Mount Seymour. The numbers a t t h e e n d o f t h e a r r o w s i n d i c a t e t h e f r e q u e n c y . o f snow s t o r m s , w i t h t h o s e f o r 1970-71 i n b r a c k e t s  202  of• t h e  same w i n t e r .  They p r o d u c e d a l a r g e r  component o f p r e c i p i t a t i o n a n d l o w e r  orographic  snowlines.  S t o r m s f o l l o w i n g t r a c k s A a n d B do n o t g e n e r a l l y have l o w f r e e z i n g l e v e l s , u n l e s s Pacific  circulation.  they  dominate t h e e a s t e r n  They t h e n may h a v e a c c e s s  a i r o f t h e B e r i n g Sea o r A l a s k a .  I f these  storms a r e  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 , north-westerly  flow of cold unstable  f r o n t s , g i v i n g snow t o m o d e r a t e l y Seymour.  as  a strong  a i r may d e v e l o p  behind  l o w e l e v a t i o n s on Mount  More u s u a l l y , s t o r m s f o l l o w i n g t h e s e  warm, m o i s t  to the cold  .'-stable a i r o n t o t h e c o a s t .  tracks  They o f t e n  a f a m i l y o f s t o r m s w i t h a new s t o r m d e v e l o p i n g  s o u t h - w e s t , on t h e f r o n t o f i t s p r e d e c e s s o r .  advect  occur  t o the  These  storms  g e n e r a l l y b r i n g r a i n t o t h e t o p o f t h e m o u n t a i n , o r snow t o high elevations only. especially the area  Storms f o l l o w i n g these  1969-70 ( F i g . 8.1),  common i n t h e w i n t e r  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 ( F i g . 3-3)-  o f low p r e s s u r e  Since  the surface  t h a n i n November.  A i r behind  often flow d i r e c t l y  surface  temperature of  o c e a n grows c o l d e r as t h e w i n t e r p r o g r e s s e s  19^2), s u c h s t o r m s g i v e snow t o l o w e r  can  (tracks E,C ) ,  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 t h e o c e a n  over which i t passes. the  because  d o m i n a t e d by a deep  S t o r m s c a u g h t up i n a z o n a l f l o w tend  t r a c k s were  (Sverdrup  elevations i n April  the f r o n t s o f these  from c o l d a i r sources.  s t o r m t r a c k s were much more f r e q u e n t  storms  These  i n the winter  1970-71-  203  8.1  Fig.  three reasons.  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 First  i t indicates  c e n t r e s and n o t f r o n t s . f r o n t s may  t h e t r a c k s o f low p r e s s u r e  For tracks  become u n c o u p l e d  s u c h as B, D and  F,  from t h e i r a s s o c i a t e d low.  They t h e n move e a s t w a r d a c r o s s t h e B r i t i s h  Columbia  coast,  w h i l e t h e lows swing n o r t h i n t o the G u l f o f A l a s k a . Secondly,  the t r a c k of a storm gives only a g e n e r a l i n d i -  c a t i o n of f r e e z i n g snowline.  l e v e l , and h e n c e t h e e l e v a t i o n o f t h e  As p r e v i o u s l y  d i s c u s s e d , the access of the ,  s t o r m t o s o u r c e s o f c o l d a i r and t h e s e a s o n considerations. Arctic  F i h a l l y , F i g . 8.1  a i r outbreaks.  8.1.2  does n o t  S t o r m s f o l l o w i n g any  snow t o low e l e v a t i o n s i f A r c t i c couver  are a l s o  air lies  important  indicate t r a c k can g i v e  over the Van-  area.  Frequency  of storm  types  S t o r m s were d i v i d e d i n t o two and. n o n - f r o n t a l .  The  categories,  frontal  f r o n t a l s t o r m s were f u r t h e r  classified  by t y p e o f m a r i t i m e f r o n t , and by t y p e o f s t o r m a s s o c i a t e d with Arctic  a i r outbreaks.  A variety  storms were r e c o g n i s e d ( T a b l e 8 . 1 ) . i d e n t i f i e d from examination of d a i l y charts.  The  w i n t e r 1969-70 p r o d u c e d  l e s s than i n 1970-71. in  1970-71.  T h e r e were 10  of The  non-frontal type of storm  was  surface synoptic 73  storms, only  more snow  storms  one  204  F r o n t a l storms dominated both w i n t e r s .  Walker  (196l) r e p o r t e d a s i m i l a r s i t u a t i o n f o r the p e r i o d 1954-58. The h i g h e r frequency outbreaks  o f storms a s s o c i a t e d w i t h A r c t i c a i r  i n the snowier w i n t e r 1970-71 r e p r e s e n t s t h e  most importance d i f f e r e n c e from 1969-70.  The w i n t e r  1970-71 was a l s o marked by fewer o c c l u d e d f r o n t s , and. nonf r o n t a l storms, and by more c o l d f r o n t s and t r o u g h s . G e o s t r o p h i c wind d i r e c t i o n s were assumed t o be p a r a l l e l t o the i s o b a r s of s u r f a c e s y n o p t i c c h a r t s . G e o s t r o p h i c wind d i r e c t i o n s were o b t a i n e d 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. from e a s t , through  Wind d i r e c t i o n ahead o f f r o n t s v a r i e d s o u t h , t o west.  E a s t e r l y and south  winds dominated snow storms i n 1970-71, w h i l e s o u t h e r l y and s o u t h - w e s t e r l y were important- i n t h e p r e v i o u s (Table 8.2).  winter  Winds behind f r o n t s vary from s o u t h ,  w e s t , -to n o r t h .  through  North-west and n o r t h winds were more  prominent i n t h e w i n t e r 1970-71.  These produced p o s t -  f r o n t a l snow t o lower e l e v a t i o n s .  However, even s o u t h -  west winds behind  c o l d a i r onto t h e  mountain-if  f r o n t s can advect  t h i s a i r has had a s h o r t passage over the ocean.  205  TABLE 8.2  Percentage  frequency  of geostrophlc  ahead o f , and b e h i n d and  f o r snow s t o r m s  airflow  f r o n t s , f o r a l l storms, -  w i n t e r s 1969-70, 1970-71  All 1969-70  Snow  storms 1970-71  1969-70  storms 1970-71  Geostrophic A i r f l o w ahead of f r o n t s E o r SE  20  30  S  46  52  SW  27  15  29  48  57  15  27  11  7  3  10  3  S •  2  0  0  0  SW  48  49  36  45  W  32  18  39  23  NW  16  32  21  26  2  1  4  6  W  .  Geostr'pphic A i r f l o w behind' fronts  N  20 6  8.1.3  I m p o r t a n c e o f each, s t o r m t y p e f o r w i n t e r  snowfall  a t each, e l e v a t i o n Storms d i s t r i b u t e d e p e n d i n g on t y p e .  snow d i f f e r e n t l y  on t h e m o u n t a i n ,  Thus some s t o r m s o n l y  s i g n i f i c a n t portion of winter  snowfall  contribute  at c e r t a i n e l e v a t i o n s .  For  e x a m p l e , snow d e p o s i t i o n  and  f r o m 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  elevation  ( F i g . 8.2, 8 . 3 ) .  more i m p o r t a n t w i t h snow d e p o s i t i o n are  given  decreasing  sectors,  increasing  storm types are  elevation.  Examples o f  f r o m some o f t h e more common s t o r m  types  i n Appendix J .  At h i g h is  f r o m f r o n t s w i t h warm  Most o t h e r  a  elevations  (above 800 m), t h e o c c l u d e d  the major source of w i n t e r  south-westerly These h i g h e r  airstreams elevations  where warm s e c t o r  s n o w f a l l , b u t c o l d f r o n t s and  a l s o make s i g n i f i c a n t  are the only  f r o n t s are  At m i d d l e e l e v a t i o n s  front  part  contributions.  of the mountain  important. (400.-800 m), n o n - f r o n t a l  o f s n o w f a l l become p r o m i n e n t s o u r c e s o f snow  sources  deposition,  a l t h o u g h o c c l u d e d f r o n t s remain t h e dominant i n f l u e n c e . Storms a s s o c i a t e d fronts increase  with A r c t i c  cold  i n importance.  Storms a s s o c i a t e d s n o w f a l l a t low e l e v a t i o n s t r a s t s with higher bution  a i r o u t b r e a k s and w i t h  w i t h A r c t i c a i r tend t o dominate ( l e s s t h a n 400. m) .  This  e l e v a t i o n s where t h e i r r e l a t i v e  i s small. . Cold  f r o n t s and t r o u g h s ,  concontri-  a l s o make  large  100  ^^a'ther S.W. A i r s t r e a m s  £"£  80 H  c o (/> o a. <u Q  60  -1  o c (/> i_ c  40  5  20 fl  200  400  600  800  1000  1200  1400  Elevation ( m e t e r s )  F i g . 8.2  • I n f l u e n c e o f storm type i n determining- winter/snow d e p o s i t i o n (.water e q u i v a l e n t ) a t each e l e v a t i o n , w i n t e r 1969-70  0  200  400  600  800  1,000  1200  1400  Elevation (meters) Fig.  8:3 . :  I n f l u e n c e o f s t o r m t y p e 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 e q u i v a l e n t ) a t e a c h e l e v a t i o n , w i n t e r 1970-71  (water  209  contributions.  Occluded f r o n t s produce s n o w f a l l at  e l e v a t i o n s i f they have access t o c o l d a i r sources  low  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 o f , and b e h i n d ,  f r o n t s do  not produce such c l e a r . t r e n d s w i t h e l e v a t i o n (Tables 8.3, However, west and north-west winds behind t o be dominant sources  8.4).  f r o n t s do appear  of snow d e p o s i t i o n w i t h  decreasing  elevation. 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 d a t a of b o t h w i n t e r s  8.5).  The  (Table  r e s u l t s 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 f o r  those types where few storms were sampled.  A l l types show  an i n c r e a s e i n mean s n o w f a l l w i t h e l e v a t i o n . produced by the i n c r e a s e d frequency  of snow as the form of  p r e c i p i t a t i o n at h i g h e r e l e v a t i o n s , and by i n c r e a s e of p r e c i p i t a t i o n .  This i s  orographic  At h i g h e l e v a t i o n s , ' 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 a s s o c i a t e d w i t h A r c t i c a i r , and  cold fronts.  At middle  e l e v a t i o n s , 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 , and a number of n o n - f r o n t a l types produce h e a v i e s t s n o w f a l l s .  At  e l e v a t i o n s , by f a r the h e a v i e s t s n o w f a l l s r e s u l t from A r c t i c a i r storms.  low  210 TABLE  8.3  Percentage at  of snow.deposition  each  elevation  airflow  direction  -  with  (meters)  Elevation 1060  22  20  16  20  13  18  ,*5  16  1)1)  54  equivalent)  geostrophlc  1969-70  winter  1260  870 790 710  970  (water  associated  220 120  100 3 3 0  590  490  1.4  25  20  45  55  62  80  55  0  0  0  0  0  b  0  Geostrophlc airflow ahead o f fronts E o r SE •' S  100 100 100  SW  19  25  28  24  21  26  13  0  0  0  w  11  10  10  12  12  5  0  0  0  0  H2  37  33  33  33  42  55  60  50  45  40  0  0  0  0  Geostrophlc airflow behind fronts S  sw  100 100 100 100  w  29  32  D3  47  46  NW  26  27  22  18  18  5  0  0  0  0  0  0  3  1  2  2  3  3  0  0  0  0  0  . 0  H  TABLE  8.4  Percentage at  o f snow d e p o s i t i o n  each  elevation  airflow  direction  associated -  1060  o r SE  30  S  51  equivalent)  geostrophlc  1970-71  winter  Elevation 1260  (water with  (meters)  970  870  790  710  590  I90  400  330  220  120  30  26  27  26  31  32  31  31  35  46  11  49  50  51  50  16  35  30  32  35  27  22  15  17  18  16  17  19  21  25  28  25  23  28  4  4  6  8  7  1  9  11  9  5  4  1  35'  Geostrophlc airflow ahead o f fronts E  SW W  Geostrophlc airflow behind fronts S SW  47  16  44  47  47  15  15  38  10  W  29  22  24 .  23  24  22  21  16  11  17  14  -21  22  35  • NW  24  25  27  28  28  31  38  11  16  12  37  12  N  5  6  3  4  5  3  1  0  2  2  1  5  211  TABLE 8 . 5  Mean snow d e p o s i t i o n type o f storm at each  (mm w a t e r e q u i v a l e n t ) p e r elevation  Data f o r w i n t e r s 1969-70,  1970-71  combined.  Storm types are i d e n t i f i e d i n Table  No. Storm. S t o r m s Type s a m p l e d 1260  Elevation  8.1  (meters)  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 24  35 21  36  19  18  16  12  5  4  4  5  3  2  0  9 0  8  19  25 12  0  0  0  0  64  29  25  17  11  10  6  4  2  2  1  1  0  31  30 •  25  14  11  8  7  5  4  4  43  42  34  32  37  38  32  32  5 24  4  5  7 4  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  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 2.  16  14  :-6  '.2  0  0  0  0  0  0  0  . 0  0  ."9 0  0  0  0  0  0  0  0  0  0  2 3 4  12  :  11  212  8.2  Freezing  levels  of winter  storms  Freezing l e v e l s f o ra l l weather c o n d i t i o n s i n f l u e n c e t h e manner i n w h i c h snow d e p o s i t i o n a n d m e l t o f t h e snowpack vary w i t h e l e v a t i o n . winter  Thus t h e h e a v y snow  o f 1970-71 e x p e r i e n c e d  at P o r t Hardy t h a n t h e l i g h t Freezing lower  g e n e r a l l y lower  of snowfall.  freezing levels  o f 1969-70 ( T a b l e  snow w i n t e r  l e v e l s during storm periods  elevation limits  accumulation  determine t h e  Storm f r e e z i n g l e v e l s  a t b o t h P o r t H a r d y , a n d a t Mount Seymour were- h i g h e r the w i n t e r levels  o f 1969-70.  8.6).  during  I n t h i s w i n t e r , mean f r e e z i n g  f o r snow s t o r m s were n e a r n o r m a l l y  distributed  with  a m a r k e d c o n c e n t r a t i o n b e t w e e n 700-1000 m ( F i g . 8.4).. T h i s phenomenon was d i r e c t l y  responsible f o r that  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 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 C h a p t e r 4. fell  winter's with'  Little  b e l o w 500 m, b e c a u s e t h e r e were f e w s t o r m s  snow  with  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 the  lower  snowlines  of thewinter  f r e e z i n g l e v e l s d u r i n g storms  Over h a l f o f t h e s e  1970-71 r e f l e c t  ( F i g . 8.4).  f r e e z i n g l e v e l s were b e l o w 500 m.  wider d i s t r i b u t i o n of f r e e z i n g levels  correlates with 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 Although is  The  with elevation.  t h e c o n c e p t o f mean s t o r m f r e e z i n g l e v e l  u s e f u l , i t must be u s e d 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 s t o r m s P o r t Hardy  ( i ngeopotential  metres)  and Mount Seymour ( i n m e t e r s ) Winters 1969-70,  Month  Port  Hardy  1969-70  Port  1970-71  Hardy  1970-71-  Mount  Seymour  Mount Seymour  1969-70  1970-71  Oct  1909  2138  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)  > 130 0  —  P o r t Hardy  data- f r o m  "Monthly B u l l e t i n o f Canadian Upper A i r Data". (ii)  Mount Seymour d a t a field  computed f r o m  temperature records  e l e v a t i o n s t o 1260 m e t e r s .  at s i x  214  30Winter  1969-70  20H  o c t) n. cr  £ 10  200  400  600  800  1000  1200  1400  Freezing level (meters )  30Winter  1970-71  20o c  V cr  J| 10U.  200  400  600  800  1000  1200  1400  Freezing level (meters) Pig.  C o m p a r i s o n o f t h e d i s t r i b u t i o n s o f mean f r e e z i n g l e v e l s on -Mount S e y m o u r , snow s t o r m s f o r t h e w i n t e r s 1969-70, 1970-71  215  in freezing J  l e v e l s do o c c u r w i t h i n  f o r examples).  F o r example, f r e e z i n g  (see Appendix  levels  varied  t h a n 1300 m i n 7 p e r c e n t o f a l l snow--'  over a range g r e a t e r storms.  some s t o r m s  H o w e v e r , t h e mean r a n g e f o r a l l snow s t o r m s was  550 m (± 400 m), w i t h  60 p e r c e n t o f a l l s t o r m s h a v i n g a-  r a n g e 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 r a n g e l e s s t h a n 200  m.  T h e r e was a l s o  considerable  variation i n freezing  l e v e l among snow s t o r m s , b u t t h e r e a r e some g e n e r a l f o r t h o s e o f t h e same s y n o p t i c highest freezing  type  ( T a b l e -8.7).  The  l e v e l s a r e p r o d u c e d by snow s t o r m s  a warm s e c t o r , . w i t h  with  occluded 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 t e n d i n g t o have p r o g r e s s i v e l y  has f r e e z i n g  with  lower f r e e z i n g  d i s t i n c t i v e populations of cold fronts One p o p u l a t i o n  trends  Arctic air.  levels.  Two  c a n be r e c o g n i s e d .  l e v e l s o f a b o u t 200 m, and.  advects a i r over t h e ocean from t h e c o l d sources o f t h e Y u k o n and A l a s k a . Pacific 900 m. levels  The o t h e r p o p u l a t i o n  o r i g i n and h a s a h i g h e r f r e e z i n g Similarly non-frontal  the  a i r . o f more  l e v e l a t about  snow s t o r m s p r o d u c e  freezing  c e n t e r e d a r o u n d 200 m ( u s u a l l y c o l d l o w s and n o r t h -  w e s t a i r f l o w s ) a n d 600 m ( o t h e r s ) . with  brings  Most storms  A r c t i c a i r t e n d t o h a v e mean f r e e z i n g surface,  t h a n 400 m.  associated  levels close to  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  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 o f show storms w i t h s y n o p t i c storm type D a t a f o r w i n t e r s 1969-70, 1970-71 c o m b i n e d  Mean (m)  Storm type  St.Dev. (m)  Nature o f frequency distribuiton  729'  361  Bimodal w i t h peaks-at 200 m a n d 900 m  maritime fronts w i t h a warm s e c t o r  891  179  normally  distributed  maritime occluded fronts  770  264  normally  distributed  storms a s s o c i a t e d with Arctic air-  295  225  P o s i t i v e skew d i s t r i b u t i v e with the mode a t 100 m  589  292  B i m o d a l w i t h peaks- a t 200 m a n d 600 m  maritime  cold  non-frontal storms  front  :  217  8.3  The  f l u x of atmospheric water  vapour  The  f l u x of atmospheric water vapour  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 Rasmusson 1 9 6 7 ) .  The  coast of North America  radiosonde network  d i f f e r e n c e s i n vapour  However, t e m p o r a l be  Identification  lead to understanding the  reasons  snowfall.  f l u x e s were computed f o r b o t h w i n t e r s  from radiosonde data c o l l e c t e d at P o r t Hardy. s t u d i e s of large s c a l e water Pacific  the west  dense t o a l l o w  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  A c c o r d i n g l y , vapour  1966,  f l u x e s b e t w e e n t h e two w i n t e r s " m a y  o f t h e s e d i f f e r e n c e s may  has  (e.g. Barry  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 .  f o r the observed  o v e r an a r e a  about  i s not s u f f i c i e n t l y  an a r e a l a n a l y s i s i n t h e same way-.  during winter  Previous  v a p o u r movement o v e r  coast i n d i c a t e t h a t vapour  the  f l u x e s at t h i s  station  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 (Rasmusson-1967).  s t a t i o n r e l e v a n t t o t h e Mount Seymour a r e a  8.3.1  Data  and method o f  computation  V a p o u r f l u x e s were c o m p u t e d f r o m r a d i o s o n d e a t P o r t H a r d y f o r 0000 GMT  and  November 1969  and November 1970  t o May  1970,  1200  D a t a a t - t h e s u r f a c e , lOOOmb, and 400 mb  were  used.  GMT  ascents  f o r the p e r i o d s  a t 5'0 mb  t o May  1971.  i n t e r v a l s , up  to  218  The z o n a l f l u x a t a s i n g l e l e v e l i s given-.; by Pz = 77 q u and t h e m e r i d i o n a l f l u x by Fm =  hQ  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 humidity  (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  integrated zonal f l u x i s given  by  400 mb Q  z  = J  / P  and t h e v e r t i c a l l y  q u dp  s  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 Qm = |  mb/  q v dp  where P  s  = pressure  at the surface.  The i n t e g r a t i o n was p e r f o r m e d by a p p l y i n g t h e t r a p e z o i d a l rule .  219  V a l u e s o f F , Fnu-Qz a n d Q z  were computed f o r each  m  a s c e n t a n d t h e mean t a k e n f o r e a c h ' m o n t h . i n t e g r a t e d t o t a l mean m o n t h l y f l u x  The v e r t i c a l l y  o f w a t e r v a p o u r above' a  p o i n t on t h e e a r t h ' s s u r f a c e was t h e n g i v e n by  Q = Qz i + Qm  1  where 1 , ~j , a r e 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 east  and n o r t h r e s p e c t i v e l y , a n d Qz and Qm a r e . means f o r a month. The m o n t h l y means were a l s o o b t a i n e d f o r t h o s e a s c e n t s d u r i n g s t o r m s , a n d f o r t h o s e a s c e n t s d u r i n g snow s t o r m s on Mount Seymour. the  distance  I t was n e c e s s a r y t o t a k e i n t o  a p a r t o f P o r t Hardy  movement o f p r e s s u r e s y s t e m s . sonde  monthly  flux  I t was assumed t h a t  radio-  o v e r Mount Seymour.  The mean  f o r storms i s analogous t o t h e c o m p u t a t i o n a l  q u a n t i t y , the"eddy by o t h e r w o r k e r s  component o f t h e f l u x " , f r e q u e n t l y  (e.g. Barry  used  1966).  Discussion of r e s u l t s P o r t Hardy  main  a n d Mount S e y m o u r , a n d t h e  a s c e n t s a t P o r t Hardy measure upper a i r c o n d i t i o n s  which occur 8 hours l a t e r  8.3.2  account  lies  a c r o s s t h e p a t h o f one o f t h e two  c u r r e n t s o f water vapour e n t e r i n g t h e North American  continent  (Rasmusson  196"7)  so t h e v e r t i c a l l y  f l u x e s o f water vapour are l a r g e  ( F i g . 8.5).  integrated The f l u x e s  220  Fig.  8.5  Mean m o n t h l y 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 v a p o u r . f l u x v e c t o r s , Port Hardy, w i n t e r s 1969-70, 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 winter  1969-70 t h e s e  d i r e c t i o n t o those  considered.  In the  were c o m p a r a b l e I n m a g n i t u d e a n d  f o u n d by Rasmusson f o r t h e p e r i o d  t o 1963.  The f l u x e s d u r i n g t h e w i n t e r  similar.  They a l s o d i s p l a y e d g r e a t e r m o n t h l y  196l  1970-71 w e r e l e s s variability  t h a n i n 1969-70. Fluxes  d u r i n g s t o r m p e r i o d s were e q u a l  than f l u x e s f o r a l l weather c o n d i t i o n s .  t o or greater  I n a d d i t i o n they  often displayed a stronger p o s i t i v e meridional C o m p a r i n g t h e two w i n t e r s , t h e f l u x e s d u r i n g  component.  s t o r m s were  l a r g e r i n 1969-70, e x c e p t d u r i n g J a n u a r y a n d F e b r u a r y . is  an i n t e r e s t i n g r e s u l t ,  considering the greater  t a t i o n o f t h e second w i n t e r .  This  precipi-  There e x i s t s t h e p o s s i b i l i t y  t h a t P o r t H a r d y d a t a may n o t be r e p r e s e n t a t i v e o f u p p e r 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 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 v e c t o r s were u s u a l l y n o t i n t h e d i r e c t i o n ( F i g . 8.5)  of t h e mountain  However, o t h e r w o r k e r s 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 w a t e r v a p o u r o v e r an a r e a may provide  little  g u i d e t o p r e c i p i t a t i o n amounts  Rasmusson 1 9 6 7 ) . divergence the  Rather,  (Barry  1966,  p r e c i p i t a t i o n i s related t o the  ( o r c o n v e r g e n c e ) o f v a p o u r f l u x , as g i v e n by  atmospheric water balance  equation.  Unfortunately, the radiosonde Seymour i s n o t s u f f i c i e n t l y  network around  Mount  dense t o a l l o w e s t i m a t e s o f  222  divergence  o r convergence.  of t h e w i n t e r 1 9 7 0 - 7 1 *  However, t h e s m a l l e r  fluxes  but l a r g e r storm p r e c i p i t a t i o n ,  suggest a g r e a t e r p r e c i p i t a t i o n e f f i c i e n c y d u r i n g 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 d e f i n e d a f t e r S e l l e r s  (1965)  as, P PE = W  . 100  (percent)  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 w i n t e r (mm) W = mean p r e c i p i t a b l e water a t P o r t Hardy (mm) PE r e p r e s e n t s  t h e f r a c t i o n o f t h e average m o i s t u r e  which f a l l s as p r e c i p i t a t i o n on an average day. f o r b o t h w i n t e r s were c a l c u l a t e d and  overhead Values  f o r Mount Seymour a t 120 m  1260 m, and f o r P o r t Hardy.  The r e s u l t s were as  follows ( i n percent) W i n t e r 1969-70 Mount Seymour  120 m  48 •  Winter 1970-71 63  Mount Seymour 1260 m  71  123  P o r t Hardy  44  48  223  Precipitation higher the  efficiencies  on Mount Seymour i n t h e w i n t e r  extent of being greater  there  were a b o u t one  was l i t t l e  t h a n 100  difference.  This  3  third  197-0-71, e v e n t o but at Port  Hardy  suggests that  larger  amounts o f m o i s t u r e were a d v e c t e d o v e r Mount Seymour t h a n over Port  Hardy.  T h e s e may h a v e come f r o m - c o n v e r g e n c e o f  v a p o u r f l u x , f r o m l o c a l e f f e c t s s u c h as t h e i n f l u e n c e the' S t r a i t  o f G e o r g i a , o r f r o m more a c t i v e  precipitation  of major i n t e r e s t t o t h i s  study.  snow s t o r m s a r e  T h e r e were  b e t w e e n t h e two w i n t e r s .  was t h e l a r g e f l u x e s d u r i n g  several  An i m p o r t a n t  the colder part  1970-71 ( J a n u a r y t o A p r i l ) . the  orographic  processes.  The f l u x e s o f w a t e r v a p o u r d u r i n g  contrasts  I n January of t h i s  o f snow were d e p o s i t e d  t h i s month. during  difference  of winter  f l u x e s were a l s o d i r e c t e d f r o m t h e w e s t .  quantities  of  winter  Large  t o low e l e v a t i o n s i n  I n most o t h e r months o f b o t h w i n t e r s  fluxes  snow s t o r m s were d i r e c t e d f r o m t h e s o u t h o r s o u t h -  west.  Examples o f t h e f l u x  occurring  during  snow s t o r m t y p e s a r e g i v e n  Since a mountain i s a three the- v a r i a t i o n s o f f l u x e s w i t h sidered. The z o n a l  the. more commonly i n A p p e n d i x J.. dimensional  object,  e l e v a t i o n s h o u l d a l s o be c o n -  The t o p o f Mount Seymour i s a t a b o u t 850 flux  configuration  of water /vapour v a r i e s w i t h that  is'consistent  mb.  elevation i n a  f r o m month t o month ( F i g . 8.  224  Snow s t o r m s p r o d u c e s t r o n g e a s t e r l y f l u x e s a t t h e H o w e v e r , a t a b o u t 850  mb  surface.  t h e .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 a t 800  t o 700. mb , t h e n more  decreasing  Many p r e v i o u s  at h i g h e r  R a s m u s s o n 1967) but  assume t h e  f l u x above 400  i t i s i n t e r e s t i n g to note t h a t the  P o r t H a r d y can may  levels.  be  sometimes r e a c h  one  gm  workers t o be  (cm mb  -  (e.g.  negligible,  f l u x a t 400  h a l f t h a t o f t h e maximum ( e . g . as The  mb  slowly  mb  sec)  - 1  above  .  This  1970).  i n March  snowier w i n t e r , 1970-71, produced weaker e a s t e r l y  f l u x e s i n most m o n t h s , and  d u r i n g the  winter  March) the w e s t e r l y  (January,  February,  c o l d e s t months o f fluxes  the  aloft  were l a r g e r . The  m e r i d i o n a l f l u x of water vapour d u r i n g  storms i s over-whelmingly from the (Fig. 800  8.7).  mb..  The The  south  a t most  maximum m e r i d i o n a l f l u x o c c u r s  g e n e r a l l y c o n s i s t e n t shape o f t h e  month t o month g i v e n i n F i g s , 8 . 6 ,  8.7  snow  levels a t 900 curves  undoubtedly  to from  reflects  ..the l a r g e number o f f r o n t a l d i s t u r b a n c e s ' w h i c h p r o d u c e ' snow. T h o s e months t h a t d i s p l a y t h e m o s t ' i r r e g u l a r c u r v e s J a n u a r y 1971)  experienced  or other n o r t h e r l y f l o w s .  frequent The  winter  1 9 6 9 - 7 0 may  fluxes  of water vapour from the  be  Arctic  higher  a i r outbreaks  snowlines  r e l a t e d to that winter's south.  (e.g.  of  the  larger  400'  "\ \ \ \  :  VV Dec  * \ • \ \ \ \ »' \\ * \ \ \  500  XI  1  '  600-  £  '  Nov  '  \ \ Jan \ \ l \ \ \ \ \ \ i \ \ \ \ \ \ \ \  \\  i\  \i A i \  \  \ \ \  •\ V* \) •  \ J  1  1  / ^ / /  in  tv c 900Q- eoo-  j  N  \  A  Si 7 0 ° "  N  /J  N  ^  '  1  /1  t  1000 -3  -2  400-  -2  -1  Winter 1969-70 500-  ^|  600-  3 ui  700-  ' - f — W i n t e r 1970-71  in  <U  at eoo900-  - -*  1000-  -2  Fig.  8.6  -1  0  I  -3  -2  T  -1  Mean m o n t h l y z o n a l f l u x e s d u r i n g s n o w s t o r m s . B a s e d on d a t a f r o m s t a n d a r d p r e s s u r e l e v e l s a t P o r t Hardy f o r t h e 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 a r e d i r e c t e d from t h e west. U n i t s a r e gm (cm mb s e c ) - 1  ro  400-  500-  600-  Winter  .1  TOO-  v  a.  1969-70  800  H  900  1000-f -1 400-  500  H  6 0 0 -i OJ  3  700-I  a.  arxH  in  900  H  1000 -f  -1  -1  0  ro ro  -1  FLUX  Fig.  8.7  CA  Mean m o n t h l y m e r i d i o n a l f l u x e s d u r i n g snow s t o r m s . B a s e d on d a t a f r o m s t a n d a r d . p r e s s u r e l e v e l s a t P o r t H a r d y f o r t h e 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 a r e d i r e c t e d from t h e south. U n i t s a r e gm(cm mb s e c ) 1  227  8 .4  Conclusions F r o n t a l storms  dominate p r e c i p i t a t i o n a t a l l e l e -  v a t i o n s on Mount Seymour.  Most f r o n t s a r e o c c l u d e d  t h e y r e a c h t h e c o a s t and t h e y u s u a l l y the r e g i o n . likely easiest  a d v e c t mA o r mP  into  S t o r m s f o l l o w i n g n o r t h e r l y - t r a c k s a r e more  t o p r o d u c e snow on Mount Seymour b e c a u s e t h e y access  approaching  before  to the cold a i r sources.  have  However, storms  t h e a r e a f r o m t h e s o u t h c a n p r o d u c e snow on t h e  mountain i f they  c a n draw on c o l d a i r b y d o m i n a t i n g t h e  c i r c u l a t i o n i n the Eastern The  storms  Pacific. (1970-71)  of the c o l d e r , snowier, w i n t e r  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 t h a n t h e p r e v i o u s winter.  They t h u s  l e v e l s , producing  tended  t o advect  lower snowlines.  a i r w i t h lower  freezing  Such a i r a l s o  tends  t o be u n s t a b l e , so 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 was g r e a t e r .  This w i n t e r produced  associated with Arctic for producing  s u b s t a n t i a l l y more  a i r outbreaks, a c r i t i c a l  snow t o l o w e l e v a t i o n s .  storms  situation  T h e r e were a l s o  more c o l d f r o n t s a n d more trough's'.;. Assuming the r e s u l t s  f r o m t h e two w i n t e r s a r e 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 r a n k e d  i n importance  a t each  e l e v a t i o n as f o l l o w s : /  2  A.  By s t o r m t y p e C8Q0-1260  High e l e v a t i o n s  m)  O c c l u d e d ' f r o n t s , c o l d f r o n t ' s , warm f r o n t s , westerly Middle  airstreams.  elevations  (-400.-800 m)  Occluded f r o n t s , n o n - f r o n t a l storms a s s o c i a t e d w i t h A r c t i c Low e l e v a t i o n s  sources,  cold fronts  a i r outbreaks.  ( b e l o w 400. m)  Storms a s s o c i a t e d w i t h A r c t i c cold fronts,  B.  south-  a i r outbreaks,  troughs.  By mean s n o w f a l l p e r s t o r m (800-1260  High'elevations South-westerly  m)  a i r s t r e a m , moist P a c i f i c airflows.-,  associated with Arctic  a i r outbreaks,  cold fronts  troughs. Middle  elevations  Moist  Pacific  outbreaks,  troughs.  ( b e l o w 400. m)  Pacific  outbreaks,  airflows associated with Arctic a i r  cold fronts,  ,Low e l e v a t i o n s Moist  (-400-800 m)  airflows associated with Arctic a i r  troughs,  cold fronts.  other A r c t i c  a i r storms,  229  The w i n t e r freezing levels.  1970-71 d i s p l a y e d l o w e r mean s t o r m This produced lower  snowlines.  Freezing  l e v e l s were - s t r o n g l y g r o u p e d a b o u t 900 m i n " T9'6'9-70 . helped  This  g e n e r a t e t h e 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  accumulation  with elevation.  r e l a t e d t o storm  Freezing  levels are  type.  The t o t a l f l u x e s o f w a t e r v a p o u r w e r e l a r g e , a n d generally and  showed c o n s i s t e n t p a t t e r n s  with height.  Fluxes  f r o m n o r t h t o south',.;  d u r i n g snow s t o r m s were l a r g e r I n 1970-71,  than f o r other weather c o n d i t i o n s .  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 c o m p o n e n t s , e s p e c i a l l y d u r i n g t h e c o l d e r months o f t h e y e a r .  However, d i f f e r e n c e s  i n t h e v a p o u r f l u x f i e l d s were n o t as l a r g e as t h e d i f f e r e n c e s 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  i  .suggest.  230  CHAPTER 9  9.  PREDICTION OP The  NEW  focus of t h i s  SNOW DEPOSITION chapter i s the  m o d e l t o p r e d i c t snow d e p o s i t i o n coast  midlatitude  mountain.  development of  f r o m a s t o r m on  Input to the  a  a west  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  t e m p e r a t u r e measurements at the  base  of the  to data from radiosonde ascents  and  mountain., and  synoptic  charts. As  elevations  a first  a p p r o x i m a t i o n , snow d e p o s i t i o n  'could be  estimated  each storm type given the  first  three  the  estimates  the  various  t h e mean f i g u r e s  i n T a b l e 8.5.  storm types,  likely  using  at  for  However, e x c e p t  for  number o f s a m p l e s i s low  to large 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 a b o u t e a c h mean 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 of storms of the  9 .1  same s y n o p t i c  be-  tracks  type.  A proposed model More r e l i a b l e  be  and  and  achieved i f the  6.3.4 with  estimates  o f s t o r m snow d e p o s i t i o n  q u a l i t a t i v e model d e v e l o p e d i 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 t e r m s and the  synoptic  data.  To  this  end,  the  can  section  integrated  d e s c r i p t i v e model  231  o f 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 t e r m s i n F i g . 9.1. For convenience,  the- v a r i a t i o n o f snow d e p o s i t i o n a n d 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 a r e shown as l i n e a r but  t h e s e n e e d n o t be s o .  be e s t i m a t e d  functions,  The f o l l o w i n g p a r a m e t e r s  must  ( i n order) :  (a)  P(H)  =  p r e c i p i t a t i o n i n open a r e a s a t any e l e v a t i o n H  (b)  H  Q  =  the e l e v a t i o n of the'incomplete  (c)  H  e  =  t h e l o w e s t e l e v a t i o n where  new  snowline  storm  ( o r s u b s t o r m ) snow d e p o s i t i o n e q u a l s storm  (or substorm) p r e c i p i t a t i o n .  This i s the equivalent 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 o p e n a r e a s a t any e l e v a t i o n where H > i.e.  (e)  M (H) l  =  H  D  < H < H  d e p o s i t i o n i n t h e wet snow  Where, b e c a u s e o f f l u c t u a t i n g snow and r a i n f a l l  freezing  " PTHTT  e  ,  zone.  levels  both  a t t h e t o p o f t h e mountain, i t i s  c o n v e n i e n t t o r e c o g n i s e t h e r a t i o R, w h e r e  R  zone.  snow mass d e p o s i t e d i n o p e n a r e a s  a t any e l e v a t i o n H, w h e r e  (f)  e  d e p o s i t i o n i n t h e snow, o r d r i f t  specific  i.e.  H ,  232  Elevation(H)  Storms  where  R<1  (b)  S  P(Hi)  M(H0  He Elevation (H)  Fig.  9.1  P r o p o s e d .model o f snow d e p o s i t i o n i n . open a r e a s f r o m . a s t o r m on w e s t c o a s t m i d l a t i t u d e m o u n t a i n : (a) S t o r m 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 a t t o p o f m o u n t a i n (R=l)(b) A c o m p o s i t e 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 Snow m i x e d w i t h - r a i n a t t o p o f t h e m o u n t a i n (R<1) All  terms a r e d e f i n e d i n t h e 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 g i v e s 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 d e p o s i t e d as snow at the top of the When R = 1.0, mountain.  mountain.  o n l y snow f a l l s at the top of the I f R = 0.0,  t h e n no snow i s - d e p o s i t e d . v  I f 0.0  < R < 1.0,  then b o t h r a i n and'snow f a l l  the top of the mountain posite type.  (g)  and the storm i s of a com-  I n terms of the proposed model  illustrated in Fig. M(H)  at  = R.P(H)  9.1b for  H > H  .  e  Snow d e p o s i t i o n i n f o r e s t e d areas can be e s t i m a t e d from t h a t i n open a r e a s .  9.2  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  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  P(H)  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 w i t h 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 r e c o r d e d w i t h i n the study network  (P  m a x  )  o f gauges, was  a g a i n s t 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 r e g a r d e d as the base o f the mountain.  The  m,  ma.x = l ^ -  1  + i- * 1  P(120)  wherever plotted here  d a t a was  by s i m p l e l i n e a r r e g r e s s i o n (Fig.'9.2) t o g i v e P  a  analysed  6  20  40  60  80  Storm Precipitation at base of mountain Rl20)(mm)  rv> -t  Fig.  9-2"  Maximum p r e c i p i t a t i o n r e c o r d e d f r o m a s t o r m on Mount Seymour, as a f u n c t i o n o f s t o r m p r e c i p i t a t i o n a t t h e b a s e " o f t h e m o u n t a i n  235  withr  = O..69,  2  larger  b u t t h e r e i s a good d e a l o f s c a t t e r a t  s t o r m p r e c i p i t a t i o n amounts.  line•lower  exists  a straight  envelope given by, P  'max =  P  ^20)  to t h e assemblage - o f p o i n t s . (1962), t h e amount b y w h i c h envelope  There  Following E l l i o t t  and S c h a f f e r  storm p r e c i p i t a t i o n exceeds  this  i s known as t h e o r o g r a p h i c component o f p r e c i p -  itation . Thus, The  scatter  ations  ^oro  =  about  ^max ~ 'max p  the regression  results  i n t h i s component f o r d i f f e r e n t  p r e c i p i t a t i o n i n the valley ponent  line  w i t h W a l k o t t e n and P a t r i c s  storms.  increases,  t e n d s t o become more m a r k e d .  from  vari-  As s t o r m  t h e o r o g r a p h i c comThis i s i n accordance  (1967) f i n d i n g n e a r H o l l i s ,  Alaska. There ^  also  exists  an u p p e r  P"max = 6 0 + 2  "max -  t o t h e magnitude  of the  The maximum s i z e o f t h e 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 p  ( i n mm)  P(120)  i n d i c a t i n g some unknown c o n s t r a i n t o r o g r a p h i c component.  envelope given  p ,  ( i n mm) b y  m a x = 60 + P(120)  236  These simple 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  h a v e a p p l i c a t i o n f o r some p u r p o s e s  design,  but  are i n s u f f i c i e n t l y  for individual  9.2.2  precise  for estimation  prediction  Variations m i g h t be p r e d i c t e d  P(H)  equations  of storm p r e c i p i t a t i o n w i t h  elevation  u s i n g t h e known p r e c i p i t a t i o n a t  b a s e o f t h e m o u n t a i n and  elevation  i n the f o l l o w i n g  P(H)  = f [ P ( l 2 0 ) , H,  P(H)  = s t o r m p r e c i p i t a t i o n (mm) 0 < P(H)  H  of  storms.  Empirical  where  s u c h as f l o o d  P ( 1 2 0 ) , H,  < 151  = elevation  (m).  P(120.) , 2  The  2  a t some e l e v a t i o n  The  resultant  H.  mm 120  (H = 120  d a t a were a n a l y s e d , by m u l t i p l e  cedures.  form,  H J  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 mountain  the  m).  the  0 < P ( 1 2 0 ) < 83  stepwise regression  best f i t equations  mm  pro-  f o r each w i n t e r  237  ( e q u a t i o n s 1,2). a n d f o r a l l data- c o m b i n e d  ( e q u a t i o n 3) 9-1).  e x p l a i n e d c l o s e t o 80%. o f t h e v a r i a t i o n i n P ( H ) . ( T a b l e Since a wide v a r i e t y  o f s t o r m t y p e s was i n c l u d e d i n t h e  125 a n a l y s e d , and t h e r e s i d u a l s f r o m t h e r e g r e s s i o n l i n e for all.data  c o m b i n e d w e r e homogeneous a n d n o r m a l l y  t r i b u t e d , equation diction  dis-  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 1966).  ( a f t e r Draper and Smith  s t a n d a r d e r r o r o f 12.1 o f t h i s  However, t h e  equation i s f a i r l y  T h i s does n o t 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  large.  o f P ( H ) , so  ways o f r e d u c i n g t h e s t a n d a r d e r r o r o f p r e d i c t i o n  equations  a r e now e x a m i n e d . The  p e r s i s t e n t anomalies  i nprecipitation  varia-  t i o n s w i t h e l e v a t i o n a t 490 m, a n d 870-970 m ( F i g . 6.1)• may  h a v e b e e n due t o t h e p r o x i m i t y - o f t h e s e  sites  t o t h e t o p o f t h e r i d g e ( F i g . 2.3).  sampling To e x a m i n e  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 equation 3 were t h e m s e l v e s sampling was  site  found.  variety  regressed a g a i n s t t h e d i s t a n c e from t h e  to the ridge.  No s i g n i f i c a n t  S i n c e t h e anomaly p e r s i s t e d t h r o u g h  o f storm  t y p e s , i t was u n l i k e l y  parameters. aspect  Regression  equations  o f the sampling  site  a wide  t o have been  d u c e d by m e t e o r o l o g i c a l f a c t o r s , b u t by- o t h e r  and  relationship  pro-  topographic  which i n c l u d e d slope  as i n d e p e n d e n t v a r i a b l e s  were a l s o t e s t e d , b u t no i m p r o v e m e n t i n p r e d i c t i o n o f p r e cipitation resulted. anomalies  I t was t h e r e f o r e c o n c l u d e d  must be due t o l o c a l s i t e c o n d i t i o n s .  these  238  TABLE 9 . 1  Equation No.  Regression liquations f o r e s t i m a t i n g storm p r e c i p i t a t i o n with e l e v a t i o n  Notes  Equation  n  •  R  2  S.E. of Estimate  1  Winter  1969-70  P ( H )  =  - 2 . 8  +  1.05  P ( 1 2 0 )  +  0 . 0 1 0 H  627  0.81  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  7 I8  0.78  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  0.79  1 2 . 1  P ( H )  =  2 . 9 1  +  0.86  P ( 1 2 0 )  +  1375  0.89  7.8  1375  O.78  11.3  1)  Combined data f o r e l e v a t i o n s below 870 m  5  Combined data f o r e l e v a t i o n s above 870 m  6  Maritime fronts  7 8  9 10  0.0005 P(H)  P ( 1 2 0 )  . H  J  = it.82 + 0 . t 7 P(870) + 0.0005  P(870).H  cold P(H)  = -7.1) + 1 . 2 1 ) p ( i 2 0 )  + 0.016H  Maritime f r o n t s w i t h warm s e c t o r  168  0 . 8 2  11.7  P(H)  = -7.2  + 1 . 2 1 P(120)'<+• 0 . 0 1 7 H  160  0.77  IH.3  Maritime occluded fronts  P ( H )  =  -8.6  +  1)21)  0 . 8 0  11.5  Non f r o n t a l Systems  P ( H )  =  -1).6  0.68  12  A r c t i c fronts a s s o c i a t e d with maritime f r o n t s  P(H)  = - 0 . 9 + 1 . 0 9 P(120)  0 . 8 1  1 1 . 0  NOTES:  (  1)  +  1.17  P ( 1 2 0 )  +  0 . 0 2 1 H  1.01)  P ( 1 2 0 )  +  0 . 0 1 8 H  + 0.007H  2 0 0  1)8  Based on data f o r 5 7 storms i n 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 r e g r e s s i o n equations were 99% confidence l e v e l .  (iii)  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 , where 120 < H < 1260 m. P(120)  s i g n i f i c a n t at the  = storm p r e c i p i t a t i o n at base o f mountain (120 m)  .9  239  When t h e d a t a was r e a n a l y s e d i n t h e o r i g i n a l way, b u t w i t h o b s e r v a t i o n s a t 490_,m,- 870 m a n d 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' t h e c o efficients  o f t h e 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 h e  same as f o r e q u a t i o n 3, T a b l e  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 m i g h t r e s u l t  i f i t was assumed  precipitation  was a l s o m e a s u r e d a t some p o i n t h i g h e r on t h e m o u n t a i n . F o r e x a m p l e , i f m e a s u r e m e n t s were made a t 120 m a n d 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 these  f o r a b o v e 870 m m i g h t be g i v e n .  l e v e l s , and'  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 b e l o w 870 m ( e q u a t i o n 4, T a b l e  9.1),  b u t n o t 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 u s e d . A further small increase i ntheprecision of e s t i m a t i n g t h e 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 be.obtained  i f t h e data a r e analysed s e p a r a t e l y f o r each  synoptic storm type is  a significant  ( T a b l e 9.1, e q u a t i o n s  There  d i f f e r e n c e between t h e s l o p e s o f these  r e g r e s s i o n l i n e s , w i t h those f r o n t a l systems,  6 t o 10)..  those  f o r o c c l u d e d f r o n t s and h o n -  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 , forming d i s t i n c t  also reflects  sets.  The above o r d e r i n g  a decreasing slope of the regression l i n e ,  240  t h a t i s a d e c r e a s i n g 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 the excess of mountain o v e r - v a l l e y w i n t e r p r e c i p i t a t i o n i s g r e a t e s t f o r o c c l u d e d f r o n t s and l e a s 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 maritime f r o n t s . On the whole, the e q u a t i o n s 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 g r e a t e r e x p l a n a t i o n and p r e c i s i o n over a w i d e r 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 UBC  by Woo  (1972) at the-nearby  Re-se'arch F o r e s t at Haney.  9.2.3  More t h e o r e t i c a l  approaches  S e v e r a l 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 o r o g r a p h i c p r e c i p i t a t i o n have been proposed  (e.g. Sawyer 1956,  1961, E l l i o t t and S h a f f e r 1962, Danard  1971).  Walker  Sawyer notes  t h a t such models must c o n s i d e r m e t e o r o l o g i c a l a s p e c t s at three d i f f e r e n t s c a l e s .  F i r s t , t h e r e are the l a r g e s c a l e  s y n o p t i c 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 s t r o n g wind p e r p e n d i c u l a r  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 l a p s e r a t e w i t h o u t markedly s t 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 t o heavy o r o g r a p h i c p r e c i p i t a t i o n .  24l  Second, t h e r e I s t h e dynamics a mountain r i d g e . flows over h i l l s  of the a i r motion  The amount o f w a t e r c o n d e n s e d when a i r d e p e n d s on t h e amount o f m o i s t a i r l i f t e d  and t h e h e i g h t t o w h i c h i t i s l i f t e d . c o n t r o l l e d by t h e w i n d v e l o c i t y and t h e s t a b i l i t y  over  These  f a c t o r s are'  and d i r e c t i o n , t h e w i n d s h e a r  o f t h e atmosphere.  Thus D a n a r d  (1971)  u s e s as h i s b a s i c p r e d i c t o r , t h e mean v e r t i c a l w a t e r  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  undulating  terrain.  T h i r d , t h e r e i s t h e m i c r o p h y s i c s o f t h e c l o u d and p r e c i p i t a t i o n w h i c h d e t e r m i n e s t h e amount o f w a t e r and w h e t h e r i t r e a c h e s t h e g r o u n d .  condensed  I n orographic clouds  o v e r 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 snow p a r t i c l e s out  the Bergeron-Findeisen process.  fall  As t h e  w i t h i n t h e c l o u d , t h e y grow b y s w e e p i n g  supercooled water droplets during t h e i r f a l l .  u n a t e l y we u n d e r s t a n d l i t t l e  Unfort-  about t h e m o t i o n o f a i r w i t h i n  c l o u d s , and. t h e l a w s g o v e r n i n g t h e g r o w t h a n d a g g r e g a t i o n of the  i c eparticles  are not y e t f i r m l y  established.  l a r g e v a r i a t i o n s i n t h e 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  a t m o s p h e r i c a e r o s o l s , and t h e g r e a t p h e r i c m o t i o n s make i t d i f f i c u l t  c o m p l e x i t y o f atmos-  t o construct a detailed,  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 let  Moreover,  alone apply i t t o a mountain  area.  (Mason  1971),  242  Thus some a s p e c t s c i p i t a t i o n ares t i l l theories apply  of the theory  little  of orographic  understood.  to ideal situations  pre-  Many o f t h e  ( e . g . an i n f i n i t e l y  long  smooth m o u n t a i n r i d g e ) , a n d some i n c o r p o r a t e t e r m s w h i c h c a n n o t be d e t e r m i n e d  with precision  efficiency, terminal velocity v e r t i c a l v e l o c i t y of storms).  (e.g.  precipitation  of precipitation Walker  particles,  (1961) a n d D a n a r d  (1971) h a v e 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 a r e a s o f British  Columbia, but both  seek t o e s t i m a t e  seasonal or  a n n 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 topographically use  smoothed over  200 k m  2  or greater.  o f t h e i r methods was n o t c o n s i d e r e d s u i t a b l e  Direct f o r this  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 o f area than  15 k m . 2  F o r these  reasons,  less  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 a p p l y t h e o r e t i c a l m o d e l s t o Mount S e y m o u r , w h i c h i s n o t an i n f i n i t e l y  l o n g , smooth r i d g e , a n d w h e r e  t h e r e i s no k n o w l e d g e o f t h e m e s o s c a l e s t r u c t u r e o f a s t o r m . Rather  attempts  a r e made t o d e v e l o p  e m p i r i c a l p r e d i c t i o n equations which the theory authors) justified  improved,  incorporating variables  of precipitation  i n d i c a t e s are important. by E l l i o t t  further,  ( a s d i s c u s s e d b y t h e above T h i s approach has been  a n d S h a f f e r (1962).  By u s i n g  such  v a r i a b l e s , t h e y were b e t t e r a b l e t o p r e d i c t 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 f o r t h e c o a s t a l m o u n t a i n s o f  243  C a l i f o r n i a t h a n t h e y w e r e by a t t e m p t i n g t o u s e t h e t h e o r y itself. A c c o r d i n g l y , t h e f o l l o w i n g v a r i a b l e s were  selected,  or computed, from t h e r a d i o s o n d e d a t a a t P o r t Hardy.  The  d a t a was c o n f i n e d t o t h o s e a s c e n t s w h i c h 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 water from t h e s u r f a c e t o 750 mb  Q  =  vertically  i n t e g r a t e d zonal f l u x o f water  vapour Q  m  =  •v e r t i c a l l y water  V(850)  =  integrated meridional flux of  vapour  maximum w i n d v e l o c i t y  during t h e storm  a t 850 mb V(750)  =  maximum w i n d v e l o c i t y  during the storm  a t 750 mb DB(750)  =  p r e f r o n t w i n d d i r e c t i o n a t 750 mb  DA(750)  =  p o s t f r o n t w i n d d i r e c t i o n a t 750 mb  B  =  v e r t i c a l wind shear from t h e s u r f a c e t o 750 mb.  I f t h e r e was more t h a n one  a s c e n t d u r i n g t h e s t o r m , t h e n t h e maximum v a l u e was c h o s e n . 3 was c a l c u l a t e d  i n cm/sec . 100 m  244  SI(950)  =  stability 950 mb  to SI(850)  =  index from t h e s u r f a c e  stability  i n d e x f r o m 950 mb t o  850 mb SI(750)  =  stability  index from  850 mb t o  750 mb  =  HTTT-  mean h e i g h t o f t h e f r e e z i n g  level  r Li  during the storm  The s t a b i l i t y observed temperature temperature level,  i n d e x i s t h e d i f f e r e n c e between t h e a t one l e v e l  ( s a y 750 mb) a n d t h e  o f the s a t u r a t e d a d i a b a t i c ascent t o that  f r o m some l o w e r l e v e l  negative, atmospheric  ( s a y 850 mb).  instability  exists.  I f SI i s Neutral  c o n d i t i o n s p r e v a i l i f S I i s z e r o , and t h e atmosphere i s s t a b l e when S I i s p o s i t i v e .  When t h e r e was more t h 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 c h o s e n . ' The c o r r e l a t i o n s b e t w e e n t h e o r o g r a p h i c of  precipitation  9.2). of  (P  o r o  )  and t h e s e v a r i a b l e s  component  are poor  (Table  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 t h e r v a r i a b l e s n o t m e a s u r e d by t h e r a d i o s o n d e  ascents  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  Variable  and  variables  from radiosonde  The  variables  are i d e n t i f i e d i n the text  1  2  3  4  5  W  - 0 .10 • .  -0.19.  - 0 .04  0 .05  0 .22  Qz  -0 .01  -0 .05  -0 .01  0 .12  0 .20  Qm V(850)  0 .12  0 .21  0 .15 •  0 .11  0 .03  0 .25  0 .24  0 .27  0 .14  0.21  V(750)  0 .20  0.18  0 .20  0 .11  - 0 .15  DB(750)  -0.01  DA(750)  0 .02  0 .09 • 0.01  e  0 .07  0 .05  SK950)  -0 .09  -0.18  SI(850)  -0.19  -0.30  SK750)  - 0 .19  H  data-  PL  No. o f Storms  NOTES  -0.04 120  -0.11  - 0 .12  -0.03  0.08  - 0 .10  -0.03  0.08  -0 .01  -0 .02  0.09  0.04. .  -0 .02  -0.11  - 0 ..07- '  0 .01  - 0 .22  - 0 .22  0 .02  0 .01  0 .25  -0.16  0.15  - 0 .13  54  66  36  47  .  Column 1  Using data f o r a l l storms*  Column 2  U s i n g d a t a f o r a l l storms:^ w i n t e r  1969-70  Column 3  Using data f o r a l l storms, winter  1970-71  Column 4  U s i n g d a t a from snowstorms, w i n t e r  1969-70  Column 5  Using data from  1970-71  snowstorms, w i n t e r  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 s t o r m s were not i n c l u d e d i n t h e a n a l y s i s f o r a v a r i e t y o f reasons ( 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 f r o m two o r more s t o r m s m e a s u r e d t o g e t h e r , e t c .)  246  (e.g. those r e l a t e d t o m i c r o p h y s i c a l processes i n orographic storm In  operating  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  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 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 n o t be r e p r e -  s e n t a t i v e o f a i r o v e r Mount Seymour. i n s e c t i o n 9-3-2  be p r e s e n t e d  No s t a t i s t i c a l l y from stepwise  ascent.  Other evidence  t o support  significant  this  will  conclusion.  equations  resulted  regression a n a l y s i s of P with the v a r i a b l e s " oro  1  from radiosonde  ascents 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  oro  =  1 0  +  °-35  P r e c i p i t a t i o n i s i n mm  P(120) + 2.69 V(850)  -  1.55  V(750)  a n d w i n d s p e e d i n m/sec.  The  e q u a t i o n was b a s e d on 47 snow s t o r m s i n t h e w i n t e r 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 f o u n d w i n t e r 1969-70'. (R  2  f o rthe  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  = 0.24) f o r t h e a b o v e e q u a t i o n , t h e s t a n d a r d e r r o r o f  the estimate i s r e l a t i v e l y high is  1970-71-  (23 mm),  so t h a t t h e e q u a t i o n  not very u s e f u l f o r p r e d i c t i o n . It  i s t h e r e f o r e concluded  t h a t no a d v a n t a g e 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 f r o m r a d i o s o n d e Hardy, even though t h e theory i n d i c a t e s they  are important.  a l t e r n a t i v e but t o estimate  of orographic  data at Port precipitation  Thus t h e r e seems  the v a r i a t i o n of p r e c i p i t a t i o n  with e l e v a t i o n with the e m p i r i c a l relationships in the previous  little  s e c t i o n a n d shown i n T a b l e  9-1-  developed  247  9.3  P r e d i c t i o n o f new  snowlines  The n e x t s t e p i n t h e d e v e l o p m e n t o f a m o d e l 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  o f t h e i n c o m p l e t e new s n o w l i n e H . 0  elevation  9.3-1  the elevation  A t t h e same t i m e , t h e  o f t h e c o m p l e t e new s n o w l i n e i s o f i n t e r e s t .  Prediction  equations  The e l e v a t i o n s  o f b o t h t h e complete and i n c o m p l e t e  new s n o w l i n e s c a n be r e a s o n a b l y w e l l e x p l a i n e d storm f r e e z i n g  level  (Pig. 9.3).  by t h e mean  The s i m p l e l i n e a r  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 a t t h e 99 p e r c e n t level. hourly  Mean s t o r m f r e e z i n g  compute t h i s mean. confidently  confidence  l e v e l s were computed f r o m t w o (120 m t o 1260 m).  storm temperatures at s i xe l e v a t i o n s  Only those storm f r e e z i n g  regression  l e v e l s b e l o w 1400 m w e r e u s e d t o  Higher f r e e z i n g  l e v e l s could  n o t be  e s t i m a t e d , and w o u l d be u n l i k e l y t o p r o d u c e snow  on t h e m o u n t a i n . The mean s t o r m f r e e z i n g (H  c  = HJTJT-) , s e p a r a t e d t h e two new s n o w l i n e s .  relationships indicated the  l e v e l , or l i n e  freezing  level  100. m h i g h e r .  The  slope  regression  snow may be d e p o s i t e d a t s e a l e v e l  l e v e l a t 90 m.  at the s u r f a c e ,  of unit  A l t e r n a t i v e l y , with  with  the freezing  t h e c o m p l e t e new s n o w l i n e was a b o u t  The e l e v a t i o n a l d i f f e r e n c e  b e t w e e n t h e two new  s n o w l i n e s was 184 m a t s e a l e v e l , b u t i n c r e a s e d  by 30 m f o r  e a c h 1000 m i n c r e a s e  factors  i n freezing  level.  Other  248  E l e v a t i o n 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 ).  Fig.  9.3  R e l a t i o n s h i p s b e t w e e n new s n o w l i n e s a n d mean s t o r m freezing level D i a g r a m 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 c o m p l e t e 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 t h e heavy s o l i d l i n e  (b)  P l o t o f i n c o m p l e t e new s n o w l i n e a n d 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 t h e h e a v y d a s h e d line. 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  affected with the  t h e c o m p l e t e new  heavy  snowfalls,  c o m p l e t e new  high  snowline.  I t t e n d e d t o be  o r i f t h e f o r e s t was  snowline approached  Thus  the f r e e z i n g l e v e l  at  elevations. The  of s n o w f a l l  region  between the f r e e z i n g  i s known as t h e m e l t i n g  and i s u s u a l l y  1 0 0 - 2 0 0 m deep  l e v e l and  layer  s n o w l i n e i s g i v e n by t h e l a y e r  90 m a t s e a l e v e l  about  because  (H=r - H ).  melted during  the storm.  Such m e l t was snow o f t e n  o f t h e e x i s t i n g snowpack. l e v e l s the depth of the  approach  that  Because  of the m e l t i n g  m t h i c k a t 1000 the melting  elevation  The  m,  region  This layer  was  resulted  the f r e e z i n g  level  l e s s important at rested  Thus w i t h  on t h e higher  cold storm  ( I f e ? — H ) l a y e r tended  layer  (e.g. the  almost twice that  o f some o f t h e new  o f the e x i s t i n g snowpack, the  (Hpj-  _  at sea  (ffe=—  level). the  H ) layer  This  a c c o u n t e d f o r some o f t h e s c a t t e r a b o u t  the r e g r e s s i o n  ship  O t h e r s c a t t e r may  resulted  could  O  v a r y f r o m s t o r m t o s t o r m , e v e n a t t h e same e l e v a t i o n .  snowline.  to  H ) layer  snow d e p e n d e d on r Li  f o r t h e i n c o m p l e t e new  new  being  difference  d e p o s i t e d below  freezing  170  The  l a y e r at lower e l e v a t i o n s ,  h i g h e r e l e v a t i o n s , w h e r e new surface  1940)  O  (Fig. 9.3).  some snow t h a t was  limit  l e v e l and t h e i n c o m p l e t e rb  n o t as deep as t h e m e l t i n g  lower  (Pindeison  (Wexler 1955)-  b e t w e e n t h e mean s t o r m f r e e z i n g  was  open.  lower  relationhave  from v a r i a t i o n s i n i n t e n s i t y of storm p r e c i p i t a t i o n ,  which also  controls  the t h i c k n e s s  of the melting  layer  e t a l 1 9 6 7 ) , and f r o m 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 Crab o u t t h e s t o r m mean.  (Atlas  level  250  The 95  percent  s c a t t e r ahout t h e r e g r e s s i o n l i n e r e s u l t s i n confidence  limits,  computed a b o u t an e s t i m a t e  s n o w l i n e , t h a t a r e l a r g e (± 284 m).  of the incomplete  Unfortunately, the factors producing d e s c r i b e d above, a r e d i f f i c u l t available  from t h e f i e l d  d i c t i o n equation plots  t h e s c a t t e r , and  t o q u a n t i f y , or•are not  d a t a , s o no i m p r o v e m e n t i n t h e p r e -  c a n be o b t a i n e d .  On t h e o t h e r  o f t h e 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  e x a m i n e d as recommended by D r a p e r a n d S m i t h plots  suggested  hand, were  (1966).  These  the assumptions of r e g r e s s i o n a n a l y s i s  were n o t v i o l a t e d , s o i n t h i s r e s p e c t t h e p r e d i c t i o n are  adequate.  9*3.2  P r e d i c t i o n o f storm If  t h e new s n o w l i n e s  p r e d i c t o r equations for  equations  t h e mean s t o r m  freezing  levels  a r e t o be e s t i m a t e d w i t h t h e  of the previous  s e c t i o n , then  f r e e z i n g l e v e l must be f o u n d .  values I n most  m o u n t a i n s i t u a t i o n s a n e t w o r k o f s t a t i o n s r e c o r d i n g tempe r a t u r e w i t h e l e v a t i o n i s n o t a v a i l a b l e t o compute t h e mean s t o r m  freezing level.  obtained from radiosonde  E i t h e r t h e mean must be  a s c e n t s , or from temperatures a t •  t h e b a s e o f t h e m o u n t a i n 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 lapse  rate.  251  To  examine t h e  first  method, f r e e z i n g  levels  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 by  simple l i n e a r regression  Seymour e i g h t was  with  hours l a t e r .  a l l o w e d f o r the  freezing  levels  A t i m e l a g o f 48  related on  km  a v e r a g e movement o f p r e s s u r e  i n the  levels intersected  analysis.  Prefrontal  w e r e i d e n t i f i e d by respectively,  Mount Seymour w e r e  falling  and  and  at P o r t Hardy.  systems.  s c a t t e r i n the by  that  no  tendency of  Mount  levels indicated  wide  a d v a n t a g e w o u l d be  gained  u s i n g o t h e r than a l i n e a r model. The  was  d a t a , and  and  situations  r i s i n g pressure  Seymour v e r s u s P o r t H a r d y f r e e z i n g  hour  considered  postfrontal  Computer p l o t s  Mount  per  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 freezing  from  not  jective  as  c o r r e l a t i o n of the good as  analysis  that  resultant  s u g g e s t e d by  of Peterson  an  (1964).  equations  (Table  9-  e a r l i e r more s u b -  P o r t Hardy  radiosonde  ascents give 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  under p o s t f r o n t a l  conditions  levels  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  prefrontal  conditions. Certain freezing  synoptic  situations  l e v e l s between the  two  can  lead  localities  m o v i n g f r o n t a l s y s t e m b e t w e e n P o r t H a r d y and Arctic  a i r o v e r Vancouver only)'.  lag of eight  hours used i n the  to  (e.g.  diverse a  slow  Mount S e y m o u r ,  A l t e r n a t i v e l y , the  analysis  m i g h t be  time  incorrect.  252  TABLE 9 • 3  Simple  l i n e a r r e g r e s s i o n equations  freezing those  l e v e l s on Mount Seymour '(Y)to.  of radiosonde  as cents' a t P o r t H a r d y  Equation  Situation Prefrontal  conditions  All  situations  relating 'QQ  St. Error of E s t i m a t e  n  0.12 X  10 4  0 .05  334  S t o r m s where no A r c t i c a i r present  Y= 637 + 0.14 X  80  0 .10  254  S t o r m s 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 present  Y= .337 + 0 .52 X  59  0 .29  232  Y= 319 + 0 . 4 7 X  107  0 .12  272  S t o r m s where no A r c t i c a i r present  Y= 662 + 0 . 1 8 X  69  0 .16  201  S t o r m s 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 present  Y= 450. + 0 .48 X  56  0.32  172  storm  Postfrontal All  storm  Y= 590 +  conditions situations  NOTES (  1)  F r e e z i n g l e v e l s on Mount Seymour computed f r o m i n t e r p o l a t i o n among s i x t e m p e r a t u r e s t a t i o n s b e t w e e n 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 D a t a " .  ( i i )  Only those 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 Seymour b e l o w 1260 m were c o n s i d e r e d .  (iii)  D a t a was f o r s t o r m s November- t o May 1 9 6 9 - 7 0 and O c t o b e r t o May 1 9 7 0 - 7 1 .  ( iv) All  correlation  95 p e r c e n t  coefficients  confidence  level.  on^Mount  ( r ) s i g n i f i c a n t at the  253  However, t h e 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  a t m o s p h e r i c t h e r m a l r e g i m e b e l o w 1260-m,.near Mount Seymour, is  s i g n i f i c a n t l y modified  a t i o n at Port Hardy.  compared w i t h  the free a i r  situ-  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 m o v i n g f r o m t h e v i c i n i t y Port  of  H a r d y t o w a r d s Mount Seymour, i s y e t f u r t h e r e v i d e n c e  that radiosonde data from t h i s of storm c o n d i t i o n s to note that  s t a t i o n i s not' r e p r e s e n t a t i v e  above t h e s t u d y a r e a .  I t i sinteresting  these d i f f e r e n c e s are not nearly  as p r o n o u n c e d  when mean m o n t h l y f r e e z i n g l e v e l s a r e c o n s i d e r e d ( s e e T a b l e 8.7)• The  previous  d i s c u s s i o n suggests that  estimation  o f s t o r m f r e e z i n g l e v e l s m i g h t b e t t e r be made by e x t r a p o l a t i o n from temperatures a t t h e base o f t h e mountain. A s u i t a b l e lapse  r a t e must t h e n be f o u n d .  Lapse  b e t w e e n 120 m a n d 1260 m on Mount Seymour were during  storm periods.  These a r e s u b j e c t  rates  computed  t o an e r r o r o f  a b o u t 10 p e r c e n t b e c a u s e o f p o s s i b l e e r r o r s i n measurement of t e m p e r a t u r e and e l e v a t i o n .  The mean l a p s e  of steady 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 was  0 . 6 8 °C/100 m (st.dev-.  (st.dev. frontal  of ±0.17)  rate f o r periods  conditions)  o f ± 0 . 1 8 ) , and 0.71  °C/100 m  f o r showery p r e c i p i t a t i o n ( u s u a l l y  post-  conditions). These r e s u l t s a r e n o t s t a t i s t i c a l l y  each o t h e r ,  d i f f e r e n t from  n o r d i f f e r e n t f r o m 0 . 7 °C/100 m,. w h i c h f o r  254 A 95  p r a c t i c a l p u r p o s e s i s a c o n v e n i e n t number t o u s e . c e n t c o n f i d e n c e b a n d a b o u t an a b o u t ±50  m,  o r a 100.  which the  freezing  m  e s t i m a t e leads t o a range  t h i c k , l a y e r on  level  could  lie.  °C/100 m t h e n seems s u f f i c i e n t l y of the  freezing  l e v e l that  radiosonde ascents. that  freezing  are  base of the  a s c e n t s are  9.4  only  where new e  equivalent  marks t h e  upper l i m i t  e s t i m a t e d i f the  in H  i n mean s t o r m f r e e z i n g indicates  the  good m o d e l ( D r a p e r and siderable 95  percent  of the  i s the  than those  further  from  advantage  computed f o r  any  hours.  elevation  (H )  i s the  e  wet  new  level  lowest  snow z o n e , and  elevation  regression  Smith 1966).  freezing  regression are  and  line,  l e v e l about the  be  defined.  variations  examinations  of  equation i s a  However, t h e r e i s  again large  main g e n e r a t o r of the  by  storm.  must  snow wedge i s t o be  ( F i g . 9.4)  resultant  at  l e v e l s from radiosonde  are w e l l e x p l a i n e d  confidence l i m i t s of the  estimates  equals p r e c i p i t a t i o n from the  s c a t t e r about the  Fluctuations elevation  e  ±0..l8  be  equivalent  shape o f t h e  Variations  residuals  Freezing  elevation  snow d e p o s i t i o n  A v a l u e of 0.J0  temperatures a v a i l a b l e  a v a i l a b l e e v e r y 12  P r e d i c t i o n of the The  H  mountain.  within  the  s t o r m s may  of  mountain,  more r e l i a b l e  time i n t e r v a l f o r which t h e r e are the  the  adequate to give  T h i s method has  l e v e l s during  per-  so t h a t (±  284  the m).  mean s t o r m  scatter.  con-  255  Fig.  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 e l e v a t i o n and mean s t o r m f r e e z i n g l e v e l  256  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  The new snow wedge c a n now be c o n s t r u c t e d f o r t h o s e s t o r m s where t h e 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 and p r e c i p i t a t i o n a t t h e t o p o f t h e m o u n t a i n .in t h e f o r m o f snow ( s e e F i g . 9'vl) . data are storm p r e c i p i t a t i o n  constant, i s entirely  The n e c e s s a r y  at t h e base  input  of the mountain  ( h e r e P ( 1 2 0 ) ) , and t e m p e r a t u r e s r e c o r d e d , s a y two h o u r l y d u r i n g the storm, a l s o at t h e base  of the mountain.  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 v a t i o n c a n be e s t i m a t e d w i t h P(H)  shown i n T a b l e 9 . 1 . P(H)  ( i n mm)  0  F o r example t h a t f o r e q u a t i o n 3  = - 6 . 8 + . 1 . 1 5 P ( 1 2 0 ) + 0.017H  i s obtained with H  where  ele-  one o f t h e r e l a t i o n s h i p s - f o r  The p o s i t i o n o f t h e l o w e r l i m i t H  with  Q  o f snow  deposition  (.in m e t e r s )  = -79.8  + 0.92 H j ^  , t h e mean h e i g h t o f t h e s t o 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 m e t e r s )  TT  FL  ~  n i =i —  T(120) lapse rate n  With T(120) = temperature a t t h e base  of the mountain,  i n °C.  257  Values  0.0. ± T(120.X ± 9 ..8  of  TC-120.). g r e a t e r t h a n  Mount Seymour. freezing likely  levels  to f a l l  are. t h e o n l y  above 1400.m on t h e  and  a  =  g i v e n by  ( i  The e  n  e  = 125  H  0  and  H  e  < H <T H ,  areas  °C/m  2  d u r i n g the  o f T(.120).  storm.  +  e  ( i n mm  e  is  0.98  a straight  95  overlap.  percent  o t h e r ^type  confidence  limits  2  5 H  e  " Q - H  .  H  for  relaestimates  P(H ) P  0  e  d e p o s i t e d i n open areas i s g i v e n P(H)  by  e  F o r e l e v a t i o n s above H ,  =  of  snow mass - d e p o s i t e d i n open  w a t e r e q u i v a l e n t , o r kg/m ) i s g i v e n  M(H)  There  Thus f o r t h e e l e v a t i o n a l r a n g e  t h e s p e c i f i c new  M' (H)  and  Q  line relationship.  p o i n t i n p o s t u l a t i n g any  t i o n s h i p , s i n c e the Q  . 10"  v a r i a t i o n o f snow d e p o s i t i o n b e t w e e n H  seems l i t t l e  un-  meters)  i s assumed t o be  of H  h e n c e snow w o u l d be  p o s i 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 , H  H  H  9-.8°C w o u l d g i v e '  number o f o b s e r v a t i o n s taken  The  on  mountain.  lapse rate =0.7 n  ones, u s e d  the by  s p e c i f i c new  snow:mas.s-  258  9-5-2  . Comple-x cases. For- s t o r m s where t h e r e a r e l a r g e  l e v e l , b e t t e r r e s u l t s w i l l be divided into  substorms. ,  which the f r e e z i n g  changes  obtained i f the storm i s  Each substorm i s a p e r i o d  level i s relatively  constant.  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 This  a p p r o a c h r e quire's t h a t a t l e a s t  of p r e c i p i t a t i o n the  i n freezing  two h o u r l y  during  The  model  substorm. measurements  and t e m p e r a t u r e a r e made a t t h e b a s e  of  mountain. F o r s t o r m s where b o t h r a i n  of the mountain posed.  First  (H^), a s l i g h t l y  (Fig. 9.1b),  be done w i t h t h e  d i f f e r e n t model i s p r o of  as snow a t t h e t o p o f t h e moun-  t h a t i s , t o f i n d R = p^jj  •  This  may  relation  R = p'(H^j = - 0 . 0 2 •+ 1.03  Where  at the top  i t i s necessary to f i n d the p r o p o r t i o n  storm p r e c i p i t a t i o n f a l l i n g tain  and snow f a l l  I  I = number o f h o u r s when t h e f r e e z i n g the storm i s below  1400  m,  during  d i v i d e d by t h e  of the storm i n hours. Then t h e f r e e z i n g l e v e l i s f o u n d as b e f o r e TC120). Hpt- ~ l a p s e r a t e  level  length  259  The  c r i t i c a l height  o f 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, b u t be  taken  as  150  m above t h e t o p  d i c t i o n equation and  f o r other mountains of the mountain.  for R i s valid  ( F i g . 9.5).  s t o r m s snow f a l l s  air  a f t e r p r e f r o n t a l r a i n , and  T,he  good r e l a t i o n s h i p  or t h a t there  Once R has  i s constant  .  t h e s p e c i f i c new  P(H) 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 .  No  e  t e s t was  made  assumption . In  new  snow ( F i g . 9.1  i s g i v e n by  e  T h i s assumes t h a t R f o u n d f o r t h e - t o p  of t h i s  I implies that  variations.  been e s t i m a t e d ,  = R  preserved.  f o r each' s u b s t o r m ,  mass d e p o s i t e d a b o v e t h e e l e v a t i o n H M(H)  This i s  hence tends to-be  are s e l f - c a n c e l l i n g  rain  i n colder p o s t f r o n t a l  f o u n d b e t w e e n R and  precipitation intensity  The- p r e - •  f o r most s t o r m s w i t h  snow a t t h e t o p o f t h e m o u n t a i n  because f o r these  could  the e l e v a t i o n a l range  snow mass w i l l be M'(H)  Hence t h e new  given  = ^  H  Q  < H < H  specific  by .  R  .  p(  H e  )  snow wedge i s c o n s t r u c t e d f o r t h e  H o w e v e r , f o r s t o r m s where snow f a l l s subsequently  the  e  first,  t u r n s t o r a i n , t h i s method does n o t  s u i t a b l e , p r e s u m a b l y b e c a u s e much new  storm.  snow m e l t s  and  appear during  )  260  I F i g . '9-5'  R e l a t i o n s h i p b e t w e e n t h e r a t i o . R and t h e r a t i o I . A l l t e r m s are. d e f i n e d i n t h e 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 a t t h e 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 a r e i n d i c a t e d by c r o s s e s and w e r e n o t i n c l u d e d i n t h e r e g r e s s i o n relationship  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 b r e a k s , F i g . 9 - 5 ) • be so complex, t h a t best e s t i m a t e s  The.se storms can  o f snow d e p o s i t i o n are  p r o b a b l y made from t h e c l i m a t o l o g i c a l v a l u e s  f o r each  storm type g i v e n i n Table 8 . 5 , t a k i n g i n t o account the estimates  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 P(H).  Fort-  u n a t e l y , such storms a r e r a r e , and are- l i k e l y t o make- a very s m a l l c o n t r i b u t i o n t o t o t a l w i n t e r  snow d e p o s i t i o n  except a t low e l e v a t i o n s .  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  Preliminary p r e d i c t i o n equations I t i s more convenient t o e s t i m a t e  snow d e p o s i t i o n  i n t h e f o r e s t from t h a t i n open a r e a s , r a t h e r than t o e s t a b l i s h a s e t o f 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 w i t h e l e v a t i o n f o r each o f the f o r e s t s t r a t a . Because t h e 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 f o r e s t . and t h a t 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 s h o u l d be i n c l u d e d i n any p r e d i c t i o n e q u a t i o n . i n g l y t h e f o l l o w i n g g e n e r a l model was t e s t e d , u s i n g regression  procedures: M  = f(.Mi, H, MiH, H , M i ) 2  s  2  Accordstepwise  262  where  M  s  = s p e c i f i c new snow mass equivalent)  deposited  (mm w a t e r i n a given  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  alent) deposited  (mm w a t e r  equiv-  i n open a r e a s a t a n  e l e v a t i o n H. H  =  elevation  The u s e o f t h e s q u a r e d t e r m  (metres)  (Mj ) recognises  o f s t u d i e s by Watanabe, a n d O z e k i and  the r e s u l t s  2  (1964) a n d S a t t e r l u n d  H a u p t (1967), who h a v e shown i n t e r c e p t i o n by conifero'.us  crowns f o l l o w s asympotically tinues.  logarithmic  'growth' c u r v e s ,  t o steady state conditions  Snow t h r o u g h f a l l i n c r e a s e s  which  tend  as s n o w f a l l  con-  s t e a d i l y a s snow  u n t i l t h e t r e e b r a n c h e s - become s o l o a d e d t h a t  they  falls,  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 w h i c h 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. Snowfall but  i n clearings i s well predicted  (Table  9.4),  as s t r a t a f r o m canopy edge t h r o u g h t o t r e e t r u n k s a r e  considered, increased  there  i s a decrease i n explanation  s c a t t e r about t h e r e g r e s s i o n  of e s t i m a t e ) .  This  line  2  (standard  suggests the v a r i a b i l i t y  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  ( R ) and  from  error  of processes clearings  TABLE 9.4  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  strata  and i n open areas  Stratum  Equation  R  511  0.95  6.9  511  0.83  9.9  2  511  0.78  9.8  = - 1 . 7 + O.lMj + 0.0003Mi_H + 0.0015M*  511  0.75  10 .6  Clearing  M  2  = -1.3 + l.OMi  Canopyedge  M  3  = -3-3  Beneath canopy  MIJ = -1.3 + 0.2Mj + 0.0002MaH + 0.0013M  Tree t r u n k  M  NOTES:  (  5  S.E. o f estimate (mm)  n  +  O.6M1  + 0.0002MJ.H -  0.0024M!  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 a t t h e 99 p e r c e n t level.  2  confidence  ( i i ) Mi = s n o w f a l l i n open-areas (mm water e q u i v a l e n t ) M H (iii)  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 e q u i v a l e n t ) S (S = 1,2,.. .5) = e l e v a t i o n (metres)  (H = l , 2 , . . . n , where  n < 12)  Data i s f o r w i n t e r s 1969-70, 1970-71.  CO  264  through t o tree tions  trunks.  A feature  i s t h e p r e s e n c e o f MiH terms i n d i c a t i n g t h a t t h e  r e l a t i o n s h i p between s n o w f a l l forest  depends o n e l e v a t i o n ,  forest  strata interaction.  9.6.2  i n t h e open a n d i n t h e that  The e l e v a t i o n - f o r e s t To  be  i s , t h e r e i s an e l e v a t i o n -  strata interaction .  s e e where t h e a b o v e p r e d i c t i o n  improved, and t o g a i n f u r t h e r  forest  o f t h e b e s t f i t equa-  relations  could  insights into the elevation-  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 w e r e made  f o r each e l e v a t i o n  using stepwise regression  procedures.  T h e s e were o f t h e f o r m , M The to forest lines  s  = f(M  Mi ) 2  l 3  relations are plotted  strata  f o r each e l e v a t i o n  ( F i g . 9.6", T a b l e 9 - 5 ) .  are undoubtedly not s i g n i f i c a n t l y  Some o f t h e r e g r e s s i o n d i f f e r e n t f r o m one  a n o t h e r , b u t each i s p r e s e n t e d s e p a r a t e l y physical  significance  of-the l i n e s with the  elevation.  l i n e s be u s e d as p r e d i c t o r  t o u n d e r s t a n d i n g changes w i t h of t h e f o r e s t  slopes  I t i s not intended  r e l a t i o n s , b u t as a means elevation  on snow d e p o s i t i o n .  a n a l y s i s , the scatter  here because  c a n be a t t a c h e d t o t h e c h a n g i n g  increasing  according  i n the influence  As w i t h  about t h e r e g r e s s i o n  the previous lines  increases,  Snowfall In Open ( mm water e q u i v a l e n t )  Fig.  9-6  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 e a c h e l e v a t i o n o f 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 o f snow d e p o s i t i o n i n open a r e a s  CTs  992  TABLE 9 - 5  . Details of regression and  e q u a t i o n s b e t w e e n snow d e p o s i t i o n  i n forest strata.  Each e l e v a t i o n analysed  FOREST Elevation (metres)  SampleSize  1260  82  1060  Clearings  R  0.91  11.4  78  0.96  7.1  970  73  0.96  870  57  790  Beneath Canopy  S.E.  R  0.73  14.5  5.2  0.77 0 . 80  4.3  0 .88  51  0.97 0.98  3.2  710  47  0.99  590  36  490 400 (  i )  separately.  STRATUM  Canopy Edge  S.E.  NOTES:  R  i n open  Tree Trunk  S.E.  R  0.73  15.2  0.69  16 .5  13-5  0.73  12 .6  0.68  13.6  11.0  0.75  10 .2  0.69  11.7  0 .88  6.7  0.81  5.7 6.8  0.84  0.91  6.3 6.0  0.77  6.8  2.2  0.94  4.5  0.83  6.3  0 .80  6.4  0.96  3.7  0.89  4.7  0.89 -  2.7  0.88  2.7  27  0.98  3.0  0.88  3.6  0.91  2.9  0.88  2.9  23  0.92  4.6  0.90  3.8  0.91  3.1  0.88  3.1  2  2  2  2  B a s e d 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 o f e q u a t i o n M = 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 (mm w a t e r 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 w a t e r e q u i v a l e n t ) s  strata  a t t h e 99 p e r c e n t c o n f i d e n c e  ( 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  (iii)  R = c o e f f i c i e n t of determination SE = st'andard e r r o r o f e s t i m a t e 2  S.E.  level.  268  and  the  explanation  to tree trunks.  decreases, from c l e a r i n g s through to  The. same t r e n d s  creasing elevation  are  (-Table 9 . 5 ) .  also, found with, i n -  Thus the. v a r i a b i l i t y  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  close  greater  of  with, i n c r e a s i n g  elevation. The  best f i t regression  relations for clearings  t h a t b e l o w 790 ra, s n o w f a l l i s d e c r e a s i n g l y (Fig. 9.6).  open a r e a s tial  excess s n o w f a l l i n c l e a r i n g s .  more p r o n o u n c e d as for  O n l y above 870  falls  creasing i n the 1060  to that  elevation.  open.  The  mm.  with  the  falls  This  and  i n the At  canopy de-  i t i s l e s s than  which frequently  m  that  above, create  Wind s c o u r i s u s u a l l y  associated  heaviest  snow-  winds. r e l a t i o n s f o r storm s n o w f a l l  "beneath the  c a n o p y " and  relations  870  i n part  at the  c u r v i l i n e a r r e l a t i o n s a t , and  regression  at  1260  open a l s o d e c r e a s e s w i t h  a l l elevations  canopy e d g e .  strongest  substan-  e x c e s s becomes  most a c t i v e .storms w h i c h p r o d u c e t h e  The  are  m is.there  Snow d e p o s i t i o n  m r e s u l t from wind scour,  hollows at the  than i n  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 at  e x c e e d i n g 100  edge r e l a t i v e  smaller  show  m and  "tree trunk"  below.  s t r a t a show c u r v i l i n e a r  These n o n - l i n e a r  induced.by d e p o s i t i o n  for  relations  o f n o n - z e r o amounts o f  snow  b e n e a t h t r e e s , a t t i m e s when s n o w f a l l i n open a r e a s i s c o n siderably ception zone.  larger.  o f snow by  This  total,  or near t o t a l ,  inter-  t r e e s i s most e f f e c t i v e i n the  H e r e , f a l l i n g snow p a r t i c l e s b e g i n  wet  snow  269  t o m e l t , and  coalesce-as  snow.flak.es.  v e l o c i t y CNakaya 1954). and  fall  incidence  against  the f o r e s t .  t r e e canopy c l o s u r e o b v i o u s at the  is  Satterlund  I n a d d i t i o n , as  Haupt (1967) .  and  p e n d e n t on the  size,  and  by  the  snow a t t h i s  branch c h a r a c t e r i s t i c s of  trees,  the  to the  same p r o c e s s e s , exposed s i t e  canopy  snowpack w i t h  9.6.3  e l e v a t i o n as  f o u n d f o r 1260  but  do  edge.  in- a d d i t i o n ,  m i s genfalling  i s o f t e n b l o w n f r o m open a r e a s  s h e l t e r e d area beneath t r e e s .  m a r k e d when s m a l l  with de-  The.: c u r v i l i n e a r r e l a t i o n erated  relative  homogeneous  behave r e g u l a r l y w i t h  t h o s e f o r c l e a r i n g s and  manner  because these p r o c e s s e s are  shape and  c u r v e s do... n o t  and  a t a more r a p i d r a t e .  t h e Mount Seymour f o r e s t i s n o t ( F i g . 2.1),  snowfall  Interception  hence t h r o u g h f a l l  t o s n o w f a l l i n open a r e a s i n c r e a s e s  elevation  of  i s most  snowpack.beneath i n the  t h e n l e s s e f f e c t i v e , and  Since  angle  t r e e f o l i a g e becomes l o a d e d ,  b e g i n s t o s h e d snow t o t h e by  higher  t h i s r e a s o n , and. b e c a u s e  this-process  lower e l e v a t i o n s .  amounts i n c r e a s e , t h e  described  hence a h i g h e r For  i s greater,  T h e s e have a  amounts o f low  a hard surface  This  density  is especially  snow f a l l  onto  a  crust.  Improvement'of p r e d i c t i o n e q u a t i o n s The  regression  previous relation  analyses  suggest that  for a l l elevations  can  the be  original 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 t h e t h r e e d e f i n e d i n s e c t i o n 6.3.-3. for  A c c o r d i n g l y d a t a ' was . r e a n a l y s e d  t h e g e n e r a l model but i n the f o l l o w i n g  zones:  d a t a a t 1260 m, r e p r e s e n t a t i v e o f e l e v a t i o n s  (a)  f r o m 1100 (b)  t o 1300 m ( t h e d r i f t  snow  zone)-,  data below the e q u i v a l e n t e l e v a t i o n , H snow  (c)  e  ( t h e wet  zone),  d a t a above t h e e q u i v a l e n t e l e v a t i o n , H ,  excepting  e  t h a t f o r 1260 m,  (.the snow. z o n e ) .  The l a t t e r two o f t h e s e freezing level to  storm.  z o n e s are- c o n t r o l l e d by t h e  and v a r y up a n d down t h e m o u n t a i n f r o m  t o be b r o a d l y  may be made o f t h e e f f e c t with  s i m i l a r , some  of changing  forest  assessment  characteristics  elevation. When compared w i t h t h e o r i g i n a l e q u a t i o n s  9.4)  t h e new e q u a t i o n s  reduce t h e standard  sometimes a decrease although  this  There i s  i n t h e amount o f v a r i a n c e e x p l a i n e d  i s probably  and r e d u c e d  (Table  error of estimate  s m a l l amounts i n t h e snow zone ( T a b l e 9 - 6 ) .  size,  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 o f these  subzones are l i k e l y  by  zones  a f u n c t i o n of reduced  sample  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 f r o m t h e o r i g i n a l equations  occurs  i n t h e wet snow z o n e , b u t a g a i n ,  2 71  TABLE 9.6  Regression equations between snow d e p o s i t i o n open areas.  (A)  Data at 1260 m  (snow d r i f t zone)  Stratum  Equation  n  Clearing  M  =  + 0.00H7MI  2  2  Canopy Edge  M  3  = -2.5 + l.OMi - 0.0025MJ  Beneath Canopy  M„ =  Tree Trunk  M  (B)  9.4  + O.5M1  6.0 + 0.2Mi + 0.004lMi  = 10.6 + 0.0059Mi  5  Data above the equivalent  Stratum  S.E. of Estimate (mm)  2  0.91  11.4  2  82  0.73  14.5  2  82  0.73  '15.2  82  0.69  16.5  2  e l e v a t i o n of a storm, but below 1260 m (snow zone]  Equation  n  Clearing  M  M .= -5.8 + O.lMj + 0 . 0 0 0 7 M j H -  Beneath Canopy Tree Trunk  = -2.0 + l.OMi  188  R  S.E. of Estimate (mm)  2  •  6.1  188  0.95 0 .80  M„ = -1.4 + 0.0006NUH  188  0.74  9.1  M  188  O.69  10 .1  2  3  = -2.6 + 0.0005MJH  5  Data below the equivalent  Stratum  Equation  M == -0.0 + 0.9Mi  2  Canopy Edge  M  Beneath Canopy  Mi,  Tree Trunk  Ms .== -0.9  n  2  3  0.0042M!  == -1.1 + 0.2Mi +  O.OOOHMJH  = -0.7 + 0.0004MiH + 0.0003MiH  178  0.76  5.5  178  0.51  5.2.  178  0.16  4.9  Mj,  9.4  S.E. of Estimate (mm) 2.9  (ii)  are as f o r Table  2  0.95  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 . 5  R  178  ( 1)  ,M ,H  10 .4  e l e v a t i o n of a storm (wet snow zone)  Clearing  NOTES:  R  82  Canopy Edge  (C)  In f o r e s t s t r a t a and In  Data analysed In subzones f o r winters 1969-70 , 1970-71-.  272  there  i s a decrease i n .explanation.  This  zone, v a r i e s  w i t h ' e l e v a t i o n . f r o m s t o r m .to s t o r m , and'..is where 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 .  inter-  Since  inter-  c e p t i o n i s , i n p a r t , a f u n c t i o n o f canopy s i z e and c l o s u r e , and i t was was  since these  thought that i n t h i s  also a direct  with elevation. and  vary  result  canopy  considerably with elevation,  case,  the reduced  explanation'  of the v a r i a t i o n s of  vegetation  H o w e v e r , when m e a n ' p r o j e c t e d canopy  canopy c l o s u r e i n d e x  f o r each sampling  site  area  were  i n c l u d e d as i n d e p e n d e n t v a r i a b l e s i n t h e r e g r e s s i o n e q u a t i o n s t h e r e was  no  increase i n explanation.  unknown, f o r e s t v a r i a b l e s a r e  important,  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 To residuals and  i n v e s t i g a t e the  show l i t t l e  correctness  Residuals  s c a t t e r and  are  open-forest  equivalent.  not  unmeasured  of these  models,  from the o p e n - c l e a r i n g a l w a y s homogeneous and  In these  o f new  equations randomly-  For a l l  a r e g e n e r a l l y homogeneous, e x c e p t  cases,  increases with size  an e s t i m a t e  good.  'with snow amounts g r e a t e r t h a n 60 mm  as r e l i a b l e .  (Draper  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 f o r storms  other,  considered.  d i s t r i b u t e d , i n d i c a t i n g t h e m o d e l s t o be  lines  or other  f r o m t h e r e g r e s s i o n l i n e s were examined  Smith 1966).  other  Either  The  95  s c a t t e r about the  water regression  o f s n o w f a l l , so t h e m o d e l s percent  confidence  snow d e p o s i t i o n i n t h e  limits  f o r e s t are  are about about  273  ±30.  mm  i n the  because the  snow, d r i f t  amount and  zone .  Those l i m i t s - are  l o c a t i o n of d r i f t i n g  s t o r m t o s t o r m d e p e n d i n g on m e t e o r o l o g i c a l on  the  previous  95  percent  c o n f i g u r a t i o n of the  confidence  more a c c e p t a b l e a b o u t ±10  mm  On  being  limits  i n the  a b o u t ±15  i n t h e wet  mm  varies.-from conditions,  snow s u r f a c e . other  i n the  two  set i n Table 9.4.  n a t u r e of the  are-  snow zone  and.  come f r o m t h e  Use  of the  than from  simpler  set  i n e f f e c t , argues t h a t the  other  hand, the  i n T a b l e 9.6 important, the  9•7  in  more c o m p l e x s e t  but  still  allows  that  in  On  the  equations  conditions  are  changing nature  i n c l u d i n g ^ the  most  of  elevational  equations.  Adequacy of the  model  a d e q u a c y o f an  e m p i r i c a l model can  a number- o f d i f f e r e n t w a y s .  can be  relation-  storm.  of p r e d i c t o r  f o r the  t h e m o u n t a i n by  i n some  The  nature of the  argues t h a t m e t e o r o l o g i c a l  f o r e s t up  t e r m , H,  of the  the  of  f o r e s t w i t h e l e v a t i o n determines the  open, r e g a r d l e s s  use  changing  s h i p b e t w e e n 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 the  The  snow z o n e .  the whole, b e t t e r r e s u l t s w i l l  predictor equations,  and  zones  o f t h e more awkward e q u a t i o n s i n T a b l e 9 . 6 , simpler  large ,  First,  e s t a b l i s h e d a b o u t an e s t i m a t e  be  ex:amined  confidence  p r o d u c e d by  limits the  model.  274  S e c o n d , t h e m o d e l c a n be t e s t e d a g a i n s t a s e t o f d e n t d a t a , and t h i r d ,  indepen-  a s s e s s m e n t c a n be made i n t e r m s o f  how w e l l t h e m o d e l 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  believed  t o be o p e r a t i n g .  9.7-1  Confidence  l i m i t s - a b o u t an e s t i m a t e  snow wedge f o r a  o f t h e new  storm  The m o d e l 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 f r o m 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 , e a c h . o f w h i c h has  b e e n a s s i g n e d 95 p e r c e n t  the dependent v a r i a b l e t h e independentestimate  new c o n f i d e n c e  respective errors. limits  of the next.  s o m e t i m e s becomes  Q  and H  e  .  Here,  c a n be c o m p u t e d by p o o l i n g t h e T h i s l e a d s t o 95 p e r c e n t  o f ±290 m a b o u t e s t i m a t e s  of H  Q  confidence  and H . e  u n a t e l y , t h e s i t u a t i o n becomes more c o m p l e x o f snow d e p o s i t i o n  Thus  F o r e x a m p l e , an  i s used t o estimate H limits  limits.  o f one r e l a t i o n s h i p  variable  o f Hp^-  confidence  Unfort-  f o r estimates  i n t h e wet snow zone b e t w e e n H  H , where t h e r e a r e i n t e r s e c t i n g e  C a l c u l a t i o n o f 95 p e r c e n t  confidence  confidence  s t a t i s t i c a l problem i n t h i s  limits  limits  and  Q  ( F i g . 9--7)-  is a difficult  zone.  H o w e v e r , some i d e a o f t h e p r e c i s i o n o f an e s t i m a t e o f t h e new snow wedge f o r a s t o r m may be o b t a i n e d f o r t h e above c a s e  i f t h e w i d e s t . p o s s i b l e r a n g e b e t w e e n 95  confidence  limits  i s taken-  ( F i g . 9-7).  This  percent  range  275  100  80 9 5 % C L . about  Ho  HO 95%  C L . about He.  SO  E £ ~  He  40  c  o  20 a.  est  100  300  500 Elevation  F i g . 9.7  700  900  possible range 9 5 % confidence  1100  (meters)  An example o f 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 of t h e new. snow wedge for. a storm. F r e e z i n g l e v e l = 600 m , , p r e c i p i t a t i o n at base o f mountain (120 m) = 2 8. mm  1300  276  r e p r e s e n t s t h e d i f f e r e n c e b e t w e e n "worst: c a s e "  situations  where p o p u l a t i o n p a r a m e t e r s a r e a l w a y s l o c a t e d a t  the  outer fringe  in  a way  of the c a l c u l a t e d  t h a t t h e r e a r e no  meters .  of H  limits,  compensating v a r i a t i o n s  In r e a l i t y , t h i s  example, e s t i m a t e s  confidence  0  i s unlikely  and H  same d i r e c t i o n , . s i n c e b o t h  e  will  such  i n the  to occur.  para-  For  tend to vary i n the  a r e d e p e n d e n t on t h e  freezing  level. Next, estimates  of the widest p o s s i b l e range  o f t h e p r e d i c t e d snow wedge can be  translated into  d e p o s i t i o n a v e r a g e d o v e r t h e t e r r a i n - s e g m e n t , by the e s t i m a t e d v a l u e s at each e l e v a t i o n t o the curve. over  The  values  the t e r r a i n  snow  relating  hypsometric  of the w i d e s t p o s s i b l e range  segment can t h e n be  expressed  averaged  as a p e r - -  centage of the p r e d i c t e d v a l u e , a l s o averaged over terrain  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 the  p r o b a b l e v a r i a t i o n o f t h e p o p u l a t i o n mean a b o u t t h e a t e d mean snow d e p o s i t i o n o v e r t h e t e r r a i n The  percentage,  freezing level especially  ( T a b l e 9.7).  The  percentage  On  t h i s evidence,  above,  on t h e  storm  i s large,  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  freezing levels.  estim-  segment.  c a l c u l a t e d as d e s c r i b e d  v a r i e s d e p e n d i n g on s t o r m p r e c i p i t a t i o n and  and  higher  i t would appear t h a t  t h e p o p u l a t i o n mean snow d e p o s i t i o n o v e r t h e t e r r a i n will  n o t be  estimated with high precision.  However,  segment  TABLE 9.7  Nature o f confidence l i m i t s  about an  e s t i m a t e - O f t h e snow d e p o s i t i o n  from  a s t o r m a v e r a g e d o v e r t h e t e r r a i n segment Values are c a l c u l a t e d f o r various 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)  200. .  500. .  15  11.8  8.2  4.7  \27%  228$  217$  39 .1  29 .0  10.7  127%  177*  75.0  52.7  20 .9  77%  12 4J6  156%  E M WPR#  50 E M . WPR# BD  87$  SM WPR$  EM  WPR$  S t o r m F r e e z i n g L e v e l (m)  =  80 0 . , 1100. . 0.9 553%  2 .2  437$ 4.0 . 431$  s t o r m snow d e p o s i t i o n a v e r a g e d o v e r t h e t o t a l a r e a o f t h e t e r r a i n segment C i n mm w a t e r e q u i v a l e n t )  = w i d e s t p o s s i b l e r a n g e o f 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 ( s e e F i g . 9-7) _ e x p r e s s e d as a p e r c e n t a g e o f M.  278  the p r o b a b i l i t y  associated with this  interval i s likely  95 p e r c e n t , , and when c o m p e n s a t i n g  t o be much h i g h e r - t h a n  e r r o r s o c c u r , t h e 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 to the true values. will  Hence  i t may  a l w a y s be as g o o d as t h o s e  be e x p e c t e d  i n Table  closer  estimates  9.7,.and  probably  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 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 H .  T h i s w o u l d have t h e e f f e c t  e  of H  0  and  Q  or H  e  S i n c e much o f t h e i s p r o d u c e d by  t i o n s i n f r e e z i n g l e v e l during the storm, ved  of H  of reducing the widest  p o s s i b l e r a n g e i n t h e wet snow z o n e . s c a t t e r about e s t i m a t e s  are.made  this  varia-  c o u l d be a c h i e -  i f e s t i m a t e s were made w i t h s u b s t o r m f r e e z i n g  levels,  r a t h e r t h a n w i t h t h e c o a r s e p a r a m e t e r o f mean s t o r m level.  The d a t a o f t h i s  9.7.2  Q  w e r e made  storm.  A test  o f the model a g a i n s t independent storm  The r e a l t e s t dict.  o f any m o d e l i s i n i t s a b i l i t y  Accordingly, estimates  1968-69 w i n t e r .  another  data to pre-  o f snow d e p o s i t i o n a f t e r  s t o r m were compared w i t h an i n d e p e n d e n t s e t o f d a t a the  freezing  s t u d y were n o t amenable f o r t e s t i n g  i n t h i s way, b e c a u s e no o b s e r v a t i o n s o f H during the  could  from  T h e s e t e s t d a t a were c o l l e c t e d f o r  s t u d y , and do n o t a-lways c o n f o r m w i t h t h e  a  279  experimental  design described i n Chapter  3.  During the  1968-196.9 w i n t e r o c c a s i o n a l measurements, o f new snow and  d e n s i t y were made i n t h e c a r p a r k a t 106.0 m.  a d d i t i o n , numerous s n o w p i t s during this winter.  depth  In  were dug a t v a r i o u s e l e v a t i o n s  I n f o r m a t i o n on t h e ' w a t e r  equivalent  o f new snow l a y e r s was e x t r a c t e d f r o m f i e l d n o t e s  of these  pits. F o r t h e - t e s t r u n s , e s t i m a t e s h a d t o be made f o r i n p u t p a r a m e t e r s t o t h e m o d e l , s i n c e t h e y were n o t m e a s u r e d a t t h e b a s e o f t h e m o u n t a i n d u r i n g t h e 1968-69  winter.  P r e c i p i t a t i o n a t t h e b a s e o f t h e m o u n t a i n was assumed t o be 2.13  times  that 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 f r o m d a t a f o r t h e two f o l l o w i n g winters.  S t o r m s c o u l d n o t a l w a y s be r i g o r o u s l y  defined  from such  d a t a , and may have r e p r e s e n t e d  several synoptic  events.  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 hourly  temperature  d a t a a t V a n c o u v e r 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 "storm"  f r e e z i n g l e v e l s were In a l l ,  different  m.  I n t h i s way, mean  obtained.  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 a t f i v e  e l e v a t i o n s f r o m 330 m t o 1260 m w e r e  to t e s t the model.  This represented  available  d a t a f r o m 13  "storms"  where t h e m e a n s t o r m f r e e z i n g l e v e l v a r i e d f r o m 0 m t o i  1030 m. values  T h e r e . i s good agreement between t h e p r e d i c t e d o f snow d e p o s i t i o n , u s i n g t h e m o d e l , a n d t h i s  test  2 80 120  100 Measured Snow deposition ( mm water equiv. )  Fig.  9.8  T e s t o f t h e m o d e l a b o u t an i n d e p e n d e n t d a t a , s e t f o r M e a s u r e m e n t s were made on t h e the w i n t e r 1968-69. following dates: 26 December 30 December .6 J a n u a r y 9 January 16'January . 19 J a n u a r y 26 J a n u a r y  1968 1968 1969 1969 I969 1969 1969  3 7 15 2 5 22  February February February March March March  1969 1969 1969 1969 1969 1969  120  281  (Fig. 9.8).  data  Thus on t h i s .evidence, t h e m o d e l a p p e a r s  t o be. s a t i s f a c t o r y the  test  data  wet  snow z o n e .  3  although  included only  i t should three  be. s t r e s s e d  observations  that  from the  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  test  data  t o e x a m i n e t h e m o d e l o v e r t h e w h o l e e l e v a t i o n r a n g e of' t h e new snow wedge f o r a s p e c i f i c  9 -7?3  Confidence l i m i t s snow  storm.  a b o u t an e s t i m a t e  f o r each storm d u r i n g  the 1969-70,  95 p e r c e n t  limits  confidence  deposition  1970-71 w i n t e r s ,  about the t o t a l  then  predicted  snow d e p o s i t i o n c a n be c o m p u t e d f r o m  n M  where  winter  deposition  I f t h e m o d e l i s u s e d t o p r e d i c t snow  winter  of t o t a l  ±  t„  -  n = t o t a l number o f s t o r m s f o r t h e 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 = student's  " t " d i s t r i b u t i o n w i t h a = 0.05  s = an e s t i m a t e  of the standard  deviation of  t h e 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  Fig.  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 m e a s u r e d d e p o s i t i o n i s shown f o r c o m p a r i s o n  283  The  values  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 d e -  95 p e r c e n t  position)the  confidence  limits  about  this  p r e d i c t i o n , a n d t h e a c t u a l m e a s u r e d o b s e r v a t i o n s a r e shown i n F i g . 9-9values  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 t h e measured  a t a l l e l e v a t i o n s , v a r y i n g f r o m ±23 p e r c e n t  t o ±45  percent  o f t h e 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 .  Similar  confidence  a r e ±15 p e r c e n t ( f o r t h e 1970-71 snow d e p o s i t i o n .  limits  segment  ( f o r t h e 1 9 6 9 - 7 0 w i n t e r ) a n d ±26 season) of t h e p r e d i c t e d t o t a l ' These l i m i t s  h y d r o l o g i c a l purposes, difficulty  f o r t h e whole t e r r a i n  are reasonable  especially  percent winter  f o r many  considering the notorious  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 s u c h  terrain. In the c a l c u l a t i o n of these  confidence  l i m i t s , the  m o d e l i s u s e d t o p r e d i c t snow d e p o s i t i o n • f o r t h o s e f r o m w h i c h t h e m o d e l was c o n s t r u c t e d . procedure  i s of l i t t l e  winters represented  v a l u e , except  Normally i n this  winters  this  case t h e  a wide range o f l i k e l y c o n d i t i o n s ,  and h e n c e i n d i c a t e t h e g e n e r a l m a g n i t u d e o f t h e c o n f i d e n c e limits  f o r other winters.  9.8  Conclusion It  estimate  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  snow d e p o s i t i o n a f t e r a s t o r m b a s e d on s t o r m  precipitation  and two h o u r l y t e m p e r a t u r e s  recorded  at the  284  base o f a west coast m i d l a t i t u d e agreement between p r e d i c t i o n s  mountain.  There i s good  f r o m t h i s m o d e l a n d an  independent data s e t from t h e 1968-1969•season. tions  Predic-  f r o m t h e m o d e l a r e l e a s t s a t i s f a c t o r y i n t h e wet  snow z o n e , and when t h e r e a r e l a r g e  fluctuations  i n freezing  l e v e l during the storm, e s p e c i a l l y i f there i s A r c t i c a i r present. the  I t i sdifficult  model, since  d e f i n i t i o n of the confidence l i m i t s i s  H o w e v e r , 95 p e r c e n t  complex. predictions t o be  to estimate the precision of  confidence l i m i t s  for the t o t a l winter input  o f snow w o u l d  from that zones.  i n t h e open a r e p o s s i b l e Because o f d r i f t i n g  a t e s c a n be made i n t h e d r i f t of the forest  elevation action  appear  small. Good e s t i m a t e s o f snow d e p o s i t i o n  affect  about  i n t h e snow a n d wet snow  snow, l e s s s a t i s f a c t o r y snow z o n e .  on snow d e p o s i t i o n  i n t h i s chapter.  i n the forest  The c h a n g i n g i s documented  This elevation-forest  i s produced because t r e e s  f o r m , and hence i n t e r c e p t i o n  with  inter-  change- i n s p e c i e s and  c h a r a c t e r i s t i c s , with  t i o n , and because t h e p r o p e r t i e s  estim-  of f a l l i n g  t e m p e r a t u r e and w i n d v e l o c i t y , a l s o  eleva-  snow, e s p e c i a l l y  change w i t h  elevation.  T h i s i n t e r a c t i o n i s seldom mentioned i n t h e l i t e r a t u r e . The  equations o f t h i s study are l i k e l y  in estimating  throughfall  t o be more r e l i a b l e  i n mountain f o r e s t s , than  o f Woo ( 1 9 7 2 ) 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 .  those  285  On Mount Seymour t h e r e graphic  seems t o be a maximum  component o f p r e c i p i t a t i o n o f IP(.120.). + 6 0 j  oromm.  Prediction of precipitation variations with elevation isp 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. confidence  limits  a b o u t an e s t i m a t e  The 95  a r e ±24 mm.  percent A variety  o f a t t e m p t s w e r e made t o i n c r e a s e t h i s p r e c i s i o n , b u t w i t h little  success.  Parameters"Important i n the theory of  orographic  p r e c i p i t a t i o n were c a l c u l a t e d f r o m P o r t H a r d y  radiosonde  data, but d i d l i t t l e  Se-ymour p r e c i p i t a t i o n .  H o w e v e r , t h e r e i s o f t e n an i m p r o v e -  ment i n p r e c i s i o n i f s e p a r a t e types  t o h e l p e x p l a i n Mount  equations  determined from s u r f a c e s y n o p t i c The l o w e r  limits  limits  charts.  o f s n o w f a l l and t h e e q u i v a l e n t  e l e v a t i o n c a n be p r e d i c t e d i n s i m p l e t h e mean s t o r m  a r e used f o r storm  freezing level.  linear fashion with  The 95 p e r c e n t  confidence  a r e ±284 m, w h i c h a r e n o t v e r y p r e c i s e , b u t t h e  relationships  a r e b e l i e v e d t o be s o u n d .  s t o r m s where b o t h  rain  and snow f e l l  mountain, the p r o p o r t i o n of storm  I n those  complex  at the top of the  p r e c i p i t a t i o n f a l l i n g as  snow c a n be w e l l p r e d i c t e d by t h e p r o p o r t i o n o f t h e t i m e t h e storm  f r e e z i n g l e v e l i s b e l o w 1400 m.  286  CHAPTER 10  10 .  • DISCUSSION  10 .1  Main achievements  of this  study  M e a s u r e m e n t s o f t h e wedge o f snow  accumulation  on w e s t c o a s t m i d l a t i t u d e m o u n t a i n s h a v e b e e n made where .  This study extends  else-  t h i s knowledge by e x p l a i n i n g  t h e s h a p e and b e h a v i o u r o f t h e snow wedge i n t e r m s o f t h e i n p u t o f snow t o t h e h y d r o l o g i c c y c l e .  The snow d e -  p o s i t i o n m e a s u r e m e n t s made w i t h i n a c a r e f u l l  experimental  d e s i g n , h a v e 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 over a mesoscale a wide range  a r e a , f o r two c o m p l e t e  input  winters representing  o f p r o b a b l e c o n d i t i o n s o n Mount Seymour.  A c l i m a t o l o g y o f snow s t o r m s an i m p o r t a n t ' a s p e c t o f t h i s  i s established.  This  s t u d y , because storm  proved  type,  m a g n i t u d e and f r e q u e n c y p l a y a m a j o r 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  v a t i o n and w i t h i n t h e f o r e s t .  Of c o u r s e , snow m e l t i s  a l s o i m p o r t a n t , b u t n o t e x a m i n e d .here. model, w i t h p a r t i a l  system  A deterministic  synthesis, i s established  with a set of regression functions. functions  ele-  When c o m b i n e d , t h e s e  c a n e s t i m a t e t h e 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 t h e f o r e s t , u s i n g d a t a measured a t t h e b a s e o f t h e mountain-.  287  10.2  Improvements' i n p r e c i s i o n o f t h e m o d e l The  exact confidence l i m i t s  about  an e s t i m a t e  of  s t o r m snow d e p o s i t i o n u s i n g t h e m o d e l a r e  to  d e t e r m i n e , b u t do n o t a p p e a r  be done t o i n c r e a s e t h i s parts  difficult  t o be s m a l l .  p r e c i s i o n i f the  Much c o u l d  component  o f t h e m o d e l were t o i n c o r p o r a t e more o f t h e  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 . the l a r g e confidence l i m i t s p l e t e new.snowline directly  produced  about  and t h e e q u i v a l e n t e l e v a t i o n by t h e e q u a l l y l a r g e  l e v e l , i s then too gross.  A better  d u r a t i o n , and  of, say,  compute t h e snow d e p o s i t i o n f r o m  u s i n g t h e same method o f t h i s  snow wedges f o r e a c h  substorm  f o r the storm.  t h e e q u a t i o n s of- t h i s  c o u l d be A check  study.  The  of the v a l i d i t y  r e q u i r e m e a s u r e m e n t s o f t h e i n c o m p l e t e new  e a c h two h o u r l y i n t e r v a l ,  of mean approach two each new  summed t o o b t a i n  study over such s h o r t time  t h e e q u i v a l e n t e l e v a t i o n , and t h e new for  are  parameter,  hours  would  incom-  The  be t o d i v i d e t h e s t o r m i n t o s u b s t o r m s  a composite  example,  fluctuations  would  substorm  For  estimates of the  f r e e z i n g l e v e l d u r i n g some s t o r m s . storm f r e e z i n g  actual  of  intervals, snowline,  snow mass d e p o s i t e d  or substorm,  a formidable  task. U n e x p e c t e d l y , t h e r a d i o s o n d e d a t a from P o r t Hardy was  of l i t t l e  use i n e s t i m a t i n g s t o r m f r e e z i n g l e v e l  orographic p r e c i p i t a t i o n  on Mount Seymour.  The  or  monthly  288  f l u x e s of atmospheric another  radiosonde  water  s t a t i o n must s t i l l  H o w e v e r , t h e a i r above  c r o s s m o u n t a i n s and w a t e r  r e a c h i n g Mount Seymour. may  be  and  Changnon 1 9 7 4 ) .  g a i n e d by daily  of  little  would  However, t h e  radar soundings  10.3  improved  of clouds  closer  been  largely possible  f o r e a c h zone o f  There i s s c o p e . f o r f u r t h e r study  snow on t r e e s , p a r t i c u l a r l y  processes  precision  I m p r o v e d p r e c i s i o n was  when s e p a r a t e e q u a t i o n s w e r e d e v e l o p e d  snow i n t e r c e p t i o n .  that  mountain.  study.  snow wedge.  be  little  be  E s t i m a t i o n o f snow i n t h e f o r e s t has empirical i n this  (Semonin  above P o r t H a r d y , e v e n when t h e  from t h a t d i r e c t i o n .  o r above t h e s t u d y  before  Recall  on Mount Seymour showed  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  t h e new  bodies  using Quillayute•radiosonde data.  w i t h b a l l o o n a s c e n t s and to  have  this  l i k e Vancouver  I t i s thought  c o r r e l a t i o n w i t h those  from  Recent work a l s o i n d i c a t e s a i r  crossing a city  freezing levels  w i n d was  that data  s t a t i o n , Q u i l l a y u t e , U.S.A., .may  b e e n more a p p r o p r i a t e .  a l t e r e d by  vapour suggest  of the p h y s i c a l processes  This study i n d i c a t e s  v a r y w i t h b o t h e l e v a t i o n and  that  storm  of of  these  characteristics.  E x t r a p o l a t i o n of the model t o o t h e r areas. Initially,  i t was  i n t e n d e d t o p r o d u c e 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  to allow that  extrapolation•to other  areas.  the l i m i t a t i o n s of the input  It. t r a n s p i r e d  data,  plus  lack of  k n o w l e d g e o f some p r o c e s s e s o f snow d e p o s i t i o n microphysical  processes»in t h e .clouds  meant a l a r g e d e g r e e o f e m p i r i c i s m This  above t h e m o u n t a i n ) ,  h a d t o be  introduced.  r e n d e r s t h e m o d e l l e s s - p o f t a b l e , s i n c e many o f t h e  coefficients will  (.e.g.  i n the e s t a b l i s h e d regression r e l a t i o n s h i p s  a l t e r f r o m m o u n t a i n t o mountain..  Inparticular,  separate functions  f o r P ( H ) must be e s t a b l i s h e d f o r e a c h  mountain  the equations developed i n t h i s  (although  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 Mountains).  On•the o t h e r  ating H  e  0  and H  t o be more f u n d a m e n t a l , a n d h e n c e g e n e r a l , u s e d on o t h e r  mountains.  I may w e l l a p p l y  pletely  general.  to represent  f o r estim-  are-believed s o c o u l d be  The r e l a t i o n s h i p b e t w e e n R a n d  elsewhere, but should  Obviously,  N o r t h Shore.  hand, the f u n c t i o n s  from storm f r e e z i n g l e v e l s  study  be t e s t e d  first.  t h e m o d e l p r e s e n t e d h e r e i s n o t comHowever, a t each s t a g e t h e model a t t e m p t s  the p h y s i c a l processes occurring.  basic p r i n c i p l e s should  apply  t o other west coast  m o u n t a i n s , and hence t h e r e g r e s s i o n  The same midlatitude  r e l a t i o n s o f t h e 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 e a c h .  290  10.4  Extensions It  study  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 t h e e x a c t  fidence l i m i t s if  of this  about e s t i m a t e s  of storm  con-  snow d e p o s i t i o n  a s i n g l e f u n c t i o n i s u s e d t o d e f i n e t h e new snow wedge.  F o r e x a m p l e , a f o r m o f t h e W e i b u l l f u n c t i o n c o u l d be  where  M(H)  =  (1 - e x p [ - ( c H ) ] )  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  d  tried:  ( a + bH)  elevation, H c, d  =  constants, related to freezing and  a  =  level  i t s fluctuations  constant, related to p r e c i p i t a t i o n at the base o f t h e mountain  b  =  constant, related t o the orographic component o f p r e c i p i t a t i o n  T h i s m o d e l w o u l d a l s o be more e f f i c i e n t t o u s e , t h a n t h e 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 More d e t a i l e d  model.  studies within individual  would h e l p improve such models.  storms  The m o d e l 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 w e s t c o a s t m i d l a t i t u d e mountains.  An o b v i o u s  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. m o d e l to. o b t a i n e s t i m a t e s , o f snow accumulation.  Yet again  t h e m o d e l c o u l d be a p p l i e d t o a  s m a l l m o u n t a i n c a t c h m e n t w i t h m e a s u r e d s t r e a m f l o w , and a water balance This  performed.  study,  has i l l u s t r a t e d  purposes the important  zone o f t h e w e s t c o a s t  mountain i s i n the intermediate part area.  of the mountain r e c e i v e s The l o w e r ,  snow i n f r e q u e n t l y .  here.  elevations.  midlatitude The u p p e r  t h e most snow, b u t h a s  greater area  part  o f the mountain  Thus much o f t h e s e a s o n a l  located i n the intermediate concentrated  t h a t f o r management  r a n g e , so r e s e a r c h  little receives  snow i s should  be  292  REFERENCES  A g e r , B., 1 9 6 7 . 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M o n t h l y Weather Review 96(12) 851-853.  with  APPENDICES  APPENDIX A  :  D e t a i l s of the forest Mount Seymour  c o v e r on  Al  :  Measures o f - t h e f o r e s t t e r r a i n segment.  c h a r a c t e r i s t i c s of the  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 0-6 in  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 t e r r a i n segment • -  of the  T  -r  05  L  v  +-*  2  ^1 S t a n d a r d  04  n  deviation  =25  CD  S3 JSZ  03  D 4) c_ CD  \  mean  0-2  c  <u +->  E  0-1  D  b 200  400  ±  JL  600  800  1000  1200  Elevation( Meters)  Diameter a t b r e a s t h e i g h t o f 25 randomly chosen t r e e s a t each sampling s i t e  30  25 L.  20  1 Standard )  deviation  n = 25  +>  X  \ mean  <L> „ U 10  I-  200  400  600 800 Elevation (Meters)  1000  Height o f 25 randomly chosen t r e e s a t each sampling  1200  site  APPENDIX A l  ~  306  Continued  120 1.  v 4)  o cu  U  C_ D >, DO C D  "D  -f-> O dl  c7  100 1 standard deviation \n=25  80  60 mean  40  20  D_  J-  200  Projected  400  600 800 Elevation(Meters)  canopy a r e a / t r e e  1000  1200  a t each s a m p l i n g s i t e  80 in  f 60  2  40  1 Standard deviation n=25  o c  \  mean  8 20 c  o Q 00  200  400  X 600  800  1000  1200  Elevation (Meters)  Index o f "openess" o f t h e f o r e s t  a t each s a m p l i n g s i t e  The d i s t a n c e t o t h e n e a r e s t t r e e i s m e a s u r e d chosen p o i n t s  f r o m 25 randomly-;  220 m (1 M a r c h  W 1ft1  330  (1 M a r c h  APPENDIX A2  :  The f o r e s t n e a r e a c h o f t h e snow s a m p l i n g sites  197D  m 1971)  308  309  710 m (1 M a r c h 1 9 7 D  790  m  (1 M a r c h  870 (1 M a r c h  197D  m 197D  310  970 m (1 M a r c h 1970)  1060 m (1 M a r c h 1 9 7 D  1260 (9 J a n u a r y  m  1970)  APPENDIX B  :  Results of p i l o t samples  studies with  large  Bl  :  S t a t i s t i c s o f p i l o t study w i t h l a r g e samples o f new snow d e n s i t y t h r o u g h o u t t h e 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 study with o f new snow d e p t h .  large  samples  APPENDIX B l :  Statistics Winter  Date o f Sample  Elevation (meters)  of pilot  s t u d y , new snow d e n s i t y  throughout  the forest  1968-69  Sample Size  Mean (kg/m ) 3  S.D. (kg/m ) 3  Variance  C.V. (%)  17.1.69 21.1.69 28.1.69 4.2.69 9.2.69 11.2.69  400 400 400 ::4oo .400 400  6 6 6 6 6 6  154 184 187 233 265 382  5 9 12 8 12 16  28 81 144 64 144 249  3 5 7 3 5 4  14.1.69 21.1.69 28.1.69 4 2.69 9 ,2 . 6 9 11.2.69 2.3.69 7.3.69  590 590 590 590 590 590 590 590  6 6  6 6 6  142 150 135 150 172 353 388 327  1 15 20 15 8 9 17  64 1 225 400 217 67 83 289  5 1 11 13 9 2 2 5  14.1.69 21.1.69 28.1.69 4 . 2 69 9 . 2 69 11.2.69 16 . 2 . 6 9 2.3.69 7.3.69 9.3.69  790 790 790 790 790 790 790 790 790 790  6 6 6 6 6 6 6 6 6 6  134 195 130 130 137 322 250 347 370 374  10 12" 2 11 15 15 9 14 12 19  109 150 4 118 225 225 80 201 132 363  6 • 2 8 11 5 4 4 3 5  ±95$ confidence l i m i t s about t h e 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 :  Date o f Sample  Continued  Elevation (meters)  ...  Sample Size  Mean (kg/m ) 3  21.1.69 28.1.69 4.2.69 9.2.69 11.2.69 16.2.69 2.3.69 7.3.69 9.3.69 6.4.69  1060 1060 1060 1060 1060 1060 1060 1060 1060 1060  6 6 6 6 6 6 6 6 6 6  11.1.69 9.2.69 16.2.69 2.3.69 7.3.69 9.3.69 28.3.69 6.4.69  1260 1260 1260 1260 1260 1260 1260 1260  6 6 6 6 6 6 6 6  134 93 110  243  264 187 139 230 205 307 152 220 170  145 242 212 301 260  S.D. (kg/m )  Variance  3  5 10 9 9 20 8  14 9 8 9  6 1 11  14 8 10 4 6  25 100 80 81 387  C.V. (*) 4 11 8  4  81  7 4 10 4 4 3  .36 1 122 196 57 100 16 36  4 1 6 10 3 5 1 2  64  196 81  64  ±95% confidence l i m i t s about t h e mean (kg/m ) 3  5 10 9 9 21 8 15 9 8 9 6  r  12 15 8 10 4 6  APPENDIX B2 :  Statistics  o f l a r g e s a m p l e s o f new snow d e p t h  S t o r m No. -. D a t e o f Sample - E l e v a t i o n ( 1 9 7 0 - •71) (meters) 45 . 45 45  19 .2 . 7 1 '• 19 .2 . 7 1  870 870  19.2.71  870  61 61 61 61 61 61  2.4.71 2.4.71 2.4.71 2.4.71 ' 2.4.71 2.4.71  61 61 61  2.4 .71 2 . 4 .71 2 .4.71  1060 1060 1060  61  2.4;71  1060  61 61 61  2 .4 . 7 1 . 2'; 4 . 7 1 2.4.71  1260 1260 1260  61  2.4.71  1260  ;  790 870 870 970 970 970  Secondary Sample  Sample Size  Mean (cm)  S.D. (cm)  Variance (cm )  -C.V.  ±95$ confidence l i m i t s about t h e mean  2  Open Canopy edge Beneath canopy  50  10 .1  0.7  0.5  7.1  0.2  50  7.4  1.4  1.8  18.3  0.3  50  5.4  0.7  0.5  15.7  0.2  Open Open Clearing Open Clearing Canopy edge Open Clearing Canopy edge Beneath canopy Open Clearing Canopy edge Beneath canopy  50 50 50 50 50  5.1 5.6 5.3 6.4 5.6 .  0.5 0.7 0.7 0.8 0.6  0.2 0.4 0.5 0.6 0.3  9.0 11.6 13.8 11.8 10 .1  0 .1 0.2 0 ,2 0.2 0.2  50 50 50  4.3 779 8.1  0.5 0.8 0.7  0.3 0.7 0.5  12 .2 10 .5 8.8  0 .2 0.2 0.2  50  6.2  0.7  '0.6  11.9  0.2  50 50 50  4.6 9.0 9.8  0.8 0.9 1.0  0.6 0.7 0.9  16 .7 9.6 10 .0  0.2 0.3 0.3  50  15.7  2.4  5.9  15 .4  0.7  50  5.. 8  2.4  26.6  0.4  1  5  APPENDIX B2 :  S t o r m No. (1970- •71)  C o n t i n u e d ...  Date o f Sample  Elevation (meters)  62 62 62 62 62  7.4.71 7.4.71 7.4;71 7.4.71 7.4.71  1060 1060 1260 1260 1260  62  7.4.71  1260  64 64  12.4.71 12.4.71  790 1260  SecondarySample  Sample Size  Mean (cm)  S.D. (cm)  Variance (cm ) 2  ±95$ confidence l i m i t s about C.V. t h e mean (%)  Open Clearing Open Clearing Canopy edge Beneath canopy  50 50 50 50  6.2 6.0 10 .6 11.0  0.7 0.5 1.0 1.4  0.5 0.3 9-7 2.0  10.9 8.9 0.3 12 .8  0.4  50  9.4  1.5  2.3  16 .2  0.4  50  4.7  1.1  1.2  24.0  0.3  Open Open  50 50  20 . 0 40 .7  0.7 3.6  0.6 12 .9  3.7 8.8  0.2 1.0  0.2 0.2  APPENDIX C  :  Snow c o v e r p h e n o l o g y f o r w i n t e r s 1969-70,. 1970-71  APPENDIX C :' Snow Phenology  Winter  1969-70  Elevation (meters)  1260 1060 970 870 790 710  590 490 400  330 220 ' 120 1970-71  1260 1060 970 870 790 710 . 590 490 400  330 220 120  Date o f first snowfall  Oct Oct Oct Nov Nov Dec Dec Dec Jan Jan Jan Jan  24 24 24 17 17  8 8 23 10 " 17 17 17  Oct 20 Oct 22 Oct 24 Oct 24 Oct 24 Oct.24 Nov. 20, Nov 20 Nov 20 Nov 20 Nov 20 Nov 20  -  Winters  Date o f last snowfall  May 11 May 11 May 11 Apr 27 Apr 27 Apr 27 Apr 8 Apr 8 Feb 6 Jan 18 Jan 18 Jan 18 Jun Jun May Apr Apr Apr Apr Apr' Apr Mar Mar Mar  24 24  19  24 24  11 11 11 11 27 7 7  1969-70, 1970-71  Snowfall season (days)  200  200 200  161 161  140  121 10 6 27  1 1 1  247 245  208 183 183 170 166 166 166 127 10 7 10 7  Date when snow l a s t present on ground  Duration of. snow c o v e r (days)*  Season -of snow c o v e r (days)**  complete  incomplete  complete  incomplete  June 30 June 20 May 12 May . 4 Apr 30 Apr 29 Apr 10 Apr 9 Apr 8 Jan • 19 Jan 19 Jan 19  222  236 . 198 175 135. 93 69 45 21 15 2 2 2  235 165 163 123  240 201 .  J u l y 20 J u l y 10 July 3 June 10 May 25 May 8 Apr 26 Apr 15 Apr . 12 Mar' 28 Mar 15 Mar 14  235 210 192 182 168  147  69  48  33  21  2 2 2 1 1 1  147  117 78 54 40  25 18  271  244  229  204  186 168 156  144  123 85 72 66  120  10 8 2 2 2 1 1 1 252 210 192 182 172  161 137 113 10 3 100 95 92  A c t u a l number o f days w i t h snow on ground Number o f days between date o f f i r s t sniowfall and d a t e when snow f i n a l l y melted  250  168  164 142  123 107 88 2 2 2 274 262 253 230 214 '  197 181. . ' 170 167 128 115  114  ^  318  APPENDIX D  :  Summary s t a t i s t i c s , o f t h e snowpacks. of t h e N o r t h Shore Mountains  Dl  :  Mean w a t e r  equivalent  D2  :  Extremes  D3  :  Correlation matrix  D4  :  Mean snow d e n s i t y  of water  equivalent  319  APPENDIX D. :  Summary  statistics  o f t h e snowpacks o f N o r t h  Shore M o u n t a i n snow c o u r s e s  CSee T a b l e s 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 e q u i v a l e n t (cm) N o r t h Shore Mountain snow c o u r s e s Elevation  Snow Course  Grouse  Mountain  (meters)  Record began  1158  1936  1113  I960  1082  1945  Hollyburn  1022  1945  Loch Lomond  1097  1945  B u r w e l l Lake  884  1945  Palisade  Lake  884  1945  TABLE D.2  -  Mount Seymour Dog  Mountain  Extremes on A p r i l  Snow Course Grouse  Mountain  Mount Seymour Dog  Mountain  Hollyburn Loch Lomond Burwell Palisade  Lake Lake  Feb  Mar  Apr  May  1  1  1  1  100  123  132  141  162  188  82 111  1  15  174  140  147 124 113  109  160  166  o f water e q u i v a l e n t (cm) r e c o r d e d 1, N o r t h Shore Mountain snow c o u r s e s  maximum  1158  249.  38  211  1113 1082 1022  .234  85 .58 90  149  ' 1097  371 261 284  884  June  130 114  Elevation (meters)  884  May  209 244 .  minimum  41  47 65  extreme range  151 154 ' 330  years of record  34 10  214  25 25 22 20  219  23  •  320  APPENDIX D :  C o n t i n u e d ...  TABLE D.3  C o r r e l a t i o n m a t r i x , A D r i l 1 water e q u i v a l e n t , f o r p e r i o d 1960-70 on N o r t h Shore Mountains .  -  Grouse Mt.  Snow Course Grouse  1.00 0.92 o .98  Mountain  Seymour  Mountain  Dog M o u n t a i n  0.95 0.86 0.92  Hollyburn Loch  Lomond-  Palisade  Lake  TABLE D.4  -  Mount  Elevation (meters)  Mountain Seymour  Hollyburn Lomond  Palisade  Loch Lomond  Palisade Lake  1.00 0,91  1.00  1.00 0.87 0.89 0 .69 0.80  1.00 1.00 0.82 o .96  0 .94 0.89 0.93  3  Dog Mountain Loch  Hollyburn  Dog Mt.  ) f o v o e r iod Me an snow d e n s i t y on N o r t h Shor e Mountain snow cour ses  Snow Course  Grouse  Seymour Mt.  Lake  1158 1113 10 82 1022 1097 884  Feb  Mar  Apr  May  1  1  1  1  397 427  406 452 408 424  429 477 4.58 516 425 439 427 416 499  1960-69  May  June  15  1  532  561  NOTES: (  i)  Compiled f r o m "A Summary o f Snow Survey Measurements 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. o f Lands, F o r e s t and-Water R e s o u r c e s , V i c t o r i a , B.C. ( i i ) O b s e r v a t i o n s t a k e n i n A p r i l o n l y , p r i o r t o 1950 (iii) Compiled from a l l d a t a p r i o r t o 1970.  1935-1965,  APPENDIX E  :  L i s t o f storms- f o r 1969-70, 1970-71  winters  322 WINTER  1969-70 DATE  _ 11 14 I? 16 22 24 •  MlNTER DATE  21 24 26 27 29 OC 31 NOV 3 NOV NOV NOV 9 NOV 13 NOV 16 NOV 18 NOV 20 NOV 23 NOV 25 DEC 4 9  LENGTH  12  46 24 36 24 36 46 46 12 36 36 6 12 46 46 24 12 >§ 22 16  oil  19 D E C 20 DEC 20 D E C 21 OEC 21 D E C 22 OEC 23 D E C 24 DEC 25 O E C 26 DEC 27 O E C 30 DEC 8 JAN 9 JAN JAN 10 JAN JAN 13 JAN 20 JAN 17 JAN 21 JAN 20 JAN 22 JAN 24 JAN JAN 24 JAN 26 JAN I* JAN JAN FEB § m l 5 F E B 5 FEB FEB 5 FEB FEB 6 FE8 FE8 12 F E B 3 14 F E B 5 FE8 15 F E B .6 FEB 16 F E B 18 FES 5 MAR 6 MAR MAR 7 MAR MAR 11 MAR MAR 12 MAR MAR 4 MAR • 1 MAR r-rtM 6 MAR 22 MAR MAR 1 APR l APR 3 APR 4 APR 4 APR 5 APR 5 APR 6 APR 7 APR I APR 8 APR 9 APR 18 APR 19 APR 22 APR 23 APR 23 APR 24 APR 24 APR 27 APR 29 APR 29 APR 4 MAY MAY 6 MAY MAY 12 MAY MAY 16 MAY 16 MAY 21 MAY 22 MAY 25 MAY 25 MAY 27 MAY 29 MAY  !!  81 22  Ii  3  PRtC«  60 46 46 36  OCT OCT OCT OCT OCT OCT NOV NOV NOV NOV NOV NOV .... NOV NOV NOV NOV OEC DEC  if m 15 OEC  ie  1970-71  3  f1  1 3 3 3  i 2  M  84 24 46 55 24  3  ii  IS12  6  }<>  ie  6 24  3 1 2 3 1 3  if  A  13 MS 1  24 8 24 24 24  2  2 2  3 1  13  2  3  30 10  3 3  A  82 4 4 24 2 41  r . I R A- If lN r ' TO n ' ^TOP t^  PBCClPlTiTTnN,  I «  n n F  °UNTA1N (NO SNO«) !!iXtD_RA_lN.ANO SNOH AT T O P OF MOUNTAIN OP O F M OUNTAIN. RRAIN AIN B t L OH tfcnE ONLY AT TTOP OF MOUNTAIN. M  SNOW AT A t L ELEVATIONS ON MOUNTAIN  APPENDIX F  :  Winter  precipitation  Fl  :  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 e l e v a t i o n f o r each storm.  with"  F2  :  Mean w i n t e r p r e c i p i t a t i o n a t V a n c o u v e r and a t h i g h e r c l i m a t o l o g i c a l stations on t h e N o r t h S h o r e M o u n t a i n s .  324  TOTAL  PRECIPITATION  STORM NO. 1260 *•  **  *  •*  #  4 12 13 14 15 16 17 IB 19 20 21 23 25 26 28 29 30 31 32 33 34 35 36 37 38 39 40 41 43 44 45 47 48 49 50 51 52 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73  14 25 3 1 23 53 45 4 58 39 78 70 10 14 90 31 17 5 3D 19 22 54 24 15 73 4 48 19 23 B 28 31 63 26 41 6 75 67 51 1 60 69 68 28 75 70 40 47 33 3 1 28 3 11 13 1 8  Ci STORM: OPEN AREAS ELEVATION  1060 17 25 3 1 22 52 43 4 55 37 74 53 10 14 86 32 17 5 44 18 33 45 24 15 71 12 87 42 31 8 28 31 58 33 41 3 46 51 40 3 57 68 66 27 55 91 36 48 39 9 1 26 4 12 15 1 12  970 14 22 2 1 25 28 66 4 25 39 71 59 10 14 85 11 13 5 26 11 29 77 24 13 59 12 38 33 22 8 3b 23 51 13 32 1 25 51 28 2 40 64 65 37 53 77 28 47 36 6 1 23 2 12 15 1 13  870 16 19 3 1 20 30 41 2 38 29 79 60 1 7 14 81 13 10 8 32 1 1 30 94 28 14 42 12 68 21 39 8 42 26 52 20 24 1 25 50 21 2 22 76 64 28 42 57 27 39 27 6 1 23 1 12 13 1 1 7  790 18 29 5 1 16 43 48 2 39 24 78 6 1 14 15 80 16 19 6 32 12 37 98 37 1 7 36 11 56 36 39 9 46 34 46 25 30 1 28 59 29 4 15 116 60 30 50 49 27 36 22 7 1 25 2 10 15 1 22  7 10 17 26 5 1 10 32 45 2 39 33 62 41 15 15 85 22 9 7 30 9 38 92 36 15 34 9 60 33 39 8 48 32 29 28 29 1 29 59 24 4 5 99 56 25 49 51 26 32 16 6 1 23 2 10 14 1 22  1969-70  (MM)  (METERS!  490 16 17 4 1 9 29 42 2 32 36 55 45 16 12 83 22 6 5 30 8 36 73 37 15 18 5 47 24 2 1 6 37 32 26 24 24 1 31 54 19 3 1 91 40 17 43 49 28 26 12 5 1 19 2 7 12 1 19  510 16 20 4 1 10 28 46 1 31 33 55 42 15 11 83 25 11 4 30 8 35 68 34 14 17 5 47 23 19 5 42 39 26 24 24 1 26 49 19 4 I 88 52 18 42 47 26 25 10 4 1 20 1 8 12 1 26  400 14 20 5 1 11 30 48 1 35 35 54 42 14 12 83 24 10 5 29 5 36 70 36 I 3 15 4 47 23 19 5 45 35 27 25 26 1 28 49 18 4 1 ao 54 25 43 44 26 25 8 6 1 21 2 8 10 1 28  330 14 15 4 2 10 27 44 1 34 36 53 41 13 10 83 22 10 6 29 4 34 68 35 13 15 4 46 21 17 5 42 33 26 23 23 1 27 50 18 4 1 80 47 22 40 41 26 25 7 4 1 19 I 8 11 1 31  220 13 14 4 3 5 24 39 1 30 34 53 40 11 9 83 21 9 6 26 4 32 67 31 12 1'; 5 43 20 13 4 38 30 24 2 1 20 1 28 48 15 3 1 80 44 19 39 40 22 22 7 4 1 20 2 8 11 1 31  120 12 16 6 4 7 25 37 1 23 36 58 33 11 9 83 15 9 5 25 4 31 63 32 11 13 5 42 19 13 4 34 29 23 15 25 1 29 45 11 2 1 79 40 17 39 39 21 19 7 4 1 20 3 7 12 1 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 S T O ^ M ( S ) . THESE STORMS WERE N O S . 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 STORM NO. 1260 1060  ¥  1 2 3 4 5 6 7 B 9 10 11 12 13 14 15 16 18 19 20 21 22 23 24  •tr* 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47  ¥r 49  *  *  50 51 52 53 54 55 57 58 59 60 61 62 64 65 66 67 68 69 70 71 72 73 74  12 13 8 35 47 39 57 34 66 76 45 8 14 67 22 78 58 82 107 103 107 30 2 35 85 95 61 60 39 33 32 98 105 3S 69 36 112 50 50 137 21 45 103 119 44 69 151 89 51 76 41 73 70 51 3 21 25 90 15 24 14 11 2 16 13 32 8 3  970  15 15 15 15 9 9 41 34 52 38 30 17 60 48 26 22 58 47 61 42 44 32 8 8 8 6 70 54 26 23 74 50 56 45 82 80 64 78 65 54 90 48 37 36 2 2 56 49 94 67 116 69 58 57 57 50 38 36 32 22 53 41 85 90 99 102 37 38 61 76 33 41 122 104 50 48 49 48 114 115 16 8 37 53 103 82 135 97 50 57 52 46 149 131 85 47 49 48 64 27 46 28 72 71 78 63 51 50 4 4 19 17 25 19 95 54 9 6 24 16 16 12 16 15 4 3 24 24 12 11 38 41 9 9 2 2  870  1970-M  ELEVATION (METERS) 790 710 490 510 400  19 19 16 17 9 9 28 29 47 49 21 22 53 58 23 22 47 50 69 65 33 34 8 7 5 5 50 62 15 15 50 49 44 44 78 76 7 7 79 61 76 59 5.5 36 36 2 2 44 46 22 31 46 43 57 79 29 33 34 33 22 21 29 36 82 77 99 99 4 1 58 82 97 44 52 105 106 47 46 4 7 58 96 110 9 5 29 34 77 78 94 102 23 31 43 48 84 91 54 61 40 36 23 23 29 24 71 70 52 53 45 46 4 4 19 14 11 10 67 75 6 5 1 11 1 8 8 17 20 3 4 19 18 1 5 16 20 27 9 9 2 3  19 16 9 28 50 22 36 23 48 72 33 5 5 57 21 43 42 76 64 63 49 36 2 48 33 45 82 30 32 27 19 80 98 47 90 49 93 43 48 91 5 23 39 91 37 49 60 36 23 23 17 66 47 68 3 8 10 78 4 10 6 18 2 17 13 23 8 2  13 16 7 23 43 22 51 20 44 67 29 5 2 48 23 34 66 72 59 40 48 29 3 44 46 29 72 33 30 21 15 61 84 35 84 45 92 43 42 88 5 33 34 65 43 35 55 36 37 24 17 65 31 54 3 6 11 75 2 9 7 14 3 17 14 21 7 2  12 11 15 14 7 7 19 18 41 39 20 18 52 52 20 18 41 40 62 65 25 25 8 7 2 . 2 47 46 18 11 42 39 65 66 73 74 53 56 46 45 37 39 32 29 2 2 46 60 41 45 37 38 70 48 29 31 24 24 20 18 16 15 90 77 85 87 35 36 88 89 48 48 74 70 39 38 43 44 74 75 5 5 27 27 34 33 60 56 33 31 29 31 51 55 26 39 30 36 23 20 15 11 60 '59 35 45 48 58 3 3 7 7 9 9 57 70 1 1 9 8 6 6 13 12 3 3 15 15 12 12 21 20 7 7 2 2  (MM) 330  220  120  9 14 6 16 38 18 51 17 39 68 25 6 4 46 8 26 68 74 59 44 38 30 2 39 39 36 47 26 31 15 6 55 89 37 89 48 55 38 46 77 5 28 32 55 33 39 53 33 30 17 13 60 44 55 2 7 9 62 1 a 6 9 2 15 8 19 7 2  7 14 6 15 35 . 1U 50 17 38 55 26 5 4 46 5 18 56 63 45 43 38 27 2 35 34 34 64 24 24 14 4 46 79 33 83 44 50 33 39 76 4 21 29 51 37 42 51 26 26 15 11 59 40 46 3 7 9 55 1 8 5 7 2 13 8 18 7 2  5 14 6 15 33 19 49 16 38 48 26 4 4 45 4 14 50 53 50 42 38 28 2 33 33 33 63 23 22 12 3 42 69 28 76 40 61 32 34 74 3 18 27 45 40 42 49 33 26 14 9 50 37 41 2 6 7 50 1 9 5 5 1 10 5 18 6 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 and  at higher climato.logical  the' N o r t h S h o r e  Vancouver International Airport (5 m)  MONTH  (mm) a t V a n c o u v e r s t a t i o n s ' on  Mountains  Hollyburn Ridge C951 m)  Mount CBUT  Seymour  (866 m)  October  117  397  429  November  138  398  December  164  428  396 441  January  140  371  February  120  283 246  March  96  April  58  May  341 248 227 188  49  195 120  Winter snowfall  36  820  451  Winter precipitation  882  2438  2420  Annual precipitation  1039  3004  2927  150  NOTES: (  i ) Compiled from t h e "Monthly Record, 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 C a n a d a " , D.O.T., M e t . 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 1 9 5 4 - 6 9 Seymour d a t a f o r p e r i o d 1 9 5 8 - 6 8 (some m i s s i n g d a t a ) (iii)  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 may be u n d e r e s t i m a t e d a t H o l l y b u r n R i d g e a n d Mount Seymour CBUT (.see d i s c u s s i o n i n t e x t ) .  ( i v ) Winter i s p e r i o d October  t o May  inclusive.  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 s t o r m  T a b l e s o f snow d e p o s i t i o n (mm w a t e r 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 , c a n o p y e d g e , b e n e a t h t h e canopy a n d c l o s e t o t r e e t r u n k s f o r the w i n t e r s 1969-70, 1970-71.  328  SNOWFALL  STORM NO « 1 2 6 0 4  12 17  ia 19 20 21 23 24 28 29 30 I3 32 34 35 38 39 40 41 43 47 48 49  I? 52 54 55 57 59 60 62 63 64 65 68  14 23 22 45 4 56 39 78 41 29 90 31 17 30 19 22 54 70 4 48 19 23 9 60 26 6 6 51 17 51 60 35 26 65 40 44 21 6  WATER  EQUIVALENT  1060  970  87Q  17 22 21 43 4 55 37 74 23 0 86 32 17 40 16 24 45 71 10 87 42 31 0 58' 19 4 3 14 0 40 57 34 26 81 36 42 30 4  3 21 8 49 2 25 39 32 4 0 20 11 13 15 11 3 35 59 9 38 33 22 0 48 3 2 0 0 0 5 40 31 34 35 28 20 24 1  0 6 0 0 0 4 29 0 0 0 10 13 10 5 10 0 27 42 6 26 19 22 0 25 0 0 0 0 0 0 22 23 24 5 7 8 14 0  (M.M»KG/SQ*M) I  ELEVATION 790  710  0 2 0 0 0 0 24 0 0 0 3 16 12 2 9 0 17 36 6 13 20 26 0 19 0 0 0 0 0 0 15 14 22 0  0 0 0 0 0 0 6 0 0 0 2 7 7  7  0 9 0  % 1  0 10 24 5 14 10 26 0 5 0 0 0 0 0 0 5 4 17 0 0 0 4 0  OPEN  AREAS  1969-70  CMETERS)  4 9  0  0 0 0 0 0 0 3 0 0 0 0 4 4 0 5 0 8 0 1 2 2 9 0 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0  5io 0 0 0 0 0 0 0 0 0 0 0 1 1 0 2 0 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0  400  330  220  120  0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 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 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  o  0 0  o 0  329  SNOWFALL  HATER  E Q U I V A L E N T  1 0 6 0  9 7 0  STORM NO,  1 2 6 0 4  1 8 2 3 2 0 4 1 4  16 2 2 1 9 3 9 4  1 9 2 0 2 1  5 7 4 0  5 5 3 6  6 3  6 0  2 3 2 4  4 6 2 7  2 3 0  1 5 1 6 17 16  2 d 2 9 3 0 3 2 3 3 3 4 3 5  7 6  7 2  31 2 3  17  2 6 17  4 5 16  3 9 .  3 9  19  1 6 4 4 6 6  0  0  0  0  0  0  0  'I  0  0  0  0  0  0  0  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 2 1 0  0 2 8  0 2 0  0 0  0 0  0  0  0  0 0  0 0  0 0  0 0  0  0  0  5 8 1 0  2 1 6 8  3 6 0  1 8 0  2 6 2 9  17 4 0  2 3 3 6 2 9 6 0  IF 14  11 12 3 34  ?  4 9  2 1 4 9  4 0 4 7  3 3  9 3 7 3 8  0 5 4 17  4 6 4 9  4 3 2 0  17  0 3 6  5 2 5 4  I? 5 9 6 0  3 6 2 3  3 3 7 7  6 0 2 6 3 5  6 2 6 3 6 4  4 4 3 8  7 7 34  4 6  4 3  6 5  2 3 5  3 0  6 8  4  1 2 0  4  9 1  5 0 5 1  2 2 0  0  6 9  4 8 4 9  3 3 0  0  4 0 4 1 4 7  E L E V A T I O N ( M E T E R S ) 7\Q HVQ 5 1 0 4 0 0  7 9 0  6  6 6 6  4 3  1 9 6 9 - 7 0  C L E A H I N G S  2  3 8 3 9  7  8 7 0  <MM=KG/SQ«M)t  5  2 2 0 34  0  0 0  0 0  0 0  0 0  0 0  1 6  0  0 1  0 0  0  3  0  0 0  7  5  1  0  0  0 0  1  0 5 0  0  0  0  0  0  1 0  1 0  0 0  0 0  0 0  8 0  2 0  3 0  3 0  12 0 0  6 0  0  0  7  6  1  0  0  0  11 16 2 8  1 3 11 2 7  2 2 9  0 0 3  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 0 0 0 0  2 8 0 17 0 0  0  0 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  37  2 3 14  2 2 2 0  4 6  0  0 0  10  16 0  0 14  ?  0  0  1 3 17  0 1 9  2  0 0  1 3 0 0  3 0 0 0 6 4 6  ?!  0 0  2 1 5  0  3§  0  0 0 0 0  6  5 0  17  9  0  0  0  0 0 0 0  5  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  2 0  0  0  0  0  0  0  0  0  0  0  0  0  3 3 17  0 0  0 0 0  330  SNOWFALL  WATER  EQUIVALENT  1060  970 0 5 3 9 0 11 32 18 0 0 10 16 11 9 10 3 16 63 6 24 25 22 0 40 0 0 0 0 0 1 40 19 15 24 13 11 21 0  STORM N 0 »  4 15 16 17 16 19 20 21 23 24 28 29 30 32 33 34 35 38 39 40 41 43 47 46 49 50 51 52 54 55 57 59 60 62 63 64 65 68  1260 1 17 10 14 0 61 36 58 25  K  25 15 14 16 15 40 "64 6 75 25 22 4 43  7 6 24 6 39 51 31 24 41 30 23 30 4  0 16 9 13 0 56 35 56 1 0 71 20 14 52 15 27 20 74 11 67 33 45 0 42 21 2 0 12 0 41 46 29 23 61 19 23 27 2  87Q 0 2 0 0 0 0 9 0 0 0 5 13 8 0 5 0 10 24 5 10 11 17 0 6 0 0 0 0 0 0 11 21 12 3 4 5 15 0  <MM=KG/SQ.M)»  CANOPY  EDGE  ELEVATION (METERS) 790 7IQ H9Q 5lo 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 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 3 4 2 0 0 0 0 0 0 0 5 2 4 0 0 0 0 0 0 0 10 4 2 0 29 0 0 6 0 3 0 1 2 0 0 8 7 0 0 0 13 0 2 0 1 13 5 13 0 0 0 0 0 9 0 0 0 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 6 0 0 0 0 12 0 2 0 10 0 9 3 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0  1 9 t > 9 - 7 0  330  220  120  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 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 0 0 0 0 0 0 0 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 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  331  SNQHfALL  WATER  EQIJ  I yAL£NT  7Q  87Q  STORM NOt  4 15 U  17 18 19 20 21 23 24 28 29 30 32 33 34 35 36 39 40 41 4  3  47 46 49 50 51 52 54 55 57 59 60 62 63 64 65 68  1260 1 6 6 9 0 9 21 57 26 18 43 21 9 37 11 23 32 53 9 47 26 16 0 45 2 1 2 2 0 44 42 20 13 24 16 42 45 2  9  0 8 6 8 0 9 20 55 0 0 41 11 9 26 10 11 18 44 6 46 16 18 0 17 4 0 0 2 0 10 40 19 12 17 7 19 27 1  0 5 0 9 0 0 5 11 0 0 10 4 2 4 6 0 10 41 2 16 5 1? 0 18 0 0 0 0 0 0 16 5 13 3 5 10 14 0  U  ,  0 3 0 0 0 0 0 0 0 0 5 3 2 0 4 0 9 16 3 7 5 7 0 2 0 0 0 0 0 0 7 8 a 0 2 4 13 0  •  (  MM»KG/SQ t M ) t  ELEVATION  790  0 0 0 0 0 0 0 0 0 0 0 0 2 0 3 0 6 7 2 3 4 9 0 3 0 0 0 0 0 0 0 5 6 0 0 0 3 0  7io  0 0 0 0 0 0 0 0 0 0 0 0 3 0 2 0 2 4  1 2 2 6 0 0 0 0 0 0 0 0 0 1 7 0 0 0 0 0  49  BENEAT>  CANOPY  1969*70  (METERS) 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 2 0 0 0 0 0  5lo  4Q0  330  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  0 0 0 0 0 0 0