SOIL SURVEY

-17-The effect of altitude on climate is of primary importance in Yoho . In genera lthe temperature falls an average '4° C per 100 m (3 .3° F per 1,000 feet) of increase i naltitude . However, in mountainous terrains, this estimated lapsed temperature shoul dbe used with caution except for general evaluations . The variations in lapse rate i nmountain topography are of high significance as indicated by frequent temperatureinversions, when cool air is trapped at lower elevations by overriding warm air masses .Theoretically in humid regions, precipitation increases with increases in elevation,reaching a maximum at 1,000 to 1,700 m (Volobuev 1964) .However, in th etopographical conditions of British Columbia, as the moist Maritime masses moveeastward they are forced to ascend on the windward side and may descend on th eleeward side of the successive northwest-southeast ranges of mountains . This resultsin markedly higher precipitation on the windward slopes than on the lee slopes bu talso in a general decrease of precipitation from west to east as air becomes progressivelydrier (Chapman 1952) .The local climate of the Yoho National Park is characterized by a mea nannual temperature of 2 .80 C with five months of winter temperatures below 0 0 Cand four months with a mean temperature higher than 50 C . In July the mea ntemperature is higher than 15 ° C . Total yearly precipitation is about 56 cm, o fwhich 40% falls as snow (Table 1) . The dryest month is April .June has the highes tprecipitation (about 70 mm), closely followed by December and January (Table 1 ,Figure 9) . From given data the climate of Yoho National Park could be classified a sdominantly humid to subhumid cold Cryoboreal (Soil Research Institute and Plan tResearch Institute Staff 1972) . However great local variations result from th einfluence of topography on the distribution of solar radiation, precipitation and ai rflow patterns .Detailed evaluation of local climate is very difficult because of th eincompleteness and the discontinuity of the available meteorological data . Complet edata are available for the period 1923 - 1936 from the station at Field . Later dataare available from 1967 to 1971 for the Hector station located at 51 ° 25 ~ N and116° ~ 22 W, altitude 5,225 ft (1,585 m) ; for the Ottertail station (located at 51 °19 N and 116° 35 W, altitude 5,000 ft (1,516 m)) which was relocated in 1971