CLIMATE 45 



of 10.71 inches, the average of 11 years of observation. Missoula, 

 near the mouth of the Bitter Root Valley and on a direct line 

 some 30 miles from the higher Bitter Root summits, has an 

 annual record of less than 16 inches, the average of over 30 years 

 of observation. Similar comparisons may be made in various 

 other places. The heavy precipitation at Snowshoe in the Cab- 

 inet Range may be due to the position of the lake country in 

 northern Idaho, lying as it does directly to the west, and to the 

 fact that the southwestern winds have few opposing altitudes 

 to diminish their moisture before striking this range. To the 

 east lies the broad basin of the Flathead Valley with about one- 

 fifth the total annual rainfall which occurs at Snowshoe. 



The more amply watered western slopes of the Bitter Root. 

 Coeur d'Alene and Cabinet Ranges are heavily forested, and 

 support a type of vegetation more mesophytic than is to be found 

 in other parts of the region, with some few and limited excep- 

 tions. In this feature some portions of northern Idaho may be 

 included and in all such areas in western Montana and northern 

 Idaho there is a conspicuous element in the flora suggestive 

 of Pacific Coast humid conditions and undoubtedly derived from 

 that source. The areas of this character in western Montana 

 are few and are mostly confined to the moister valleys of the 

 Flathead drainage. 



East of the Divide the annual precipitation is on the average 

 less. It varies from 10 to 22 inches, but for most places from 

 10 to 15. The lower plains have less and the amount increases 

 with the altitude. Red Lodge, Babb and Lewistown, situated 

 among or near mountains, have about 21, 22 and 20 inches re- 

 spectively. The mountainous areas, due to the greater rainfall, 

 have forests of considerable extent, but the plains are devoid of 

 trees except along the streams or under other exceptional con- 

 ditions. 



Relative humidity and the rate of evaporation in Montana 

 have not been established by a sufficient number of observations, 

 but some facts are available from the records of the Weather 

 Bureau at Helena, Havre, Kalispell and Yellowstone Park and 

 from observations by the writer at Missoula, and these are sub- 

 mitted herewith. 



Table 4 summarizes the data from the Weather Bureau's 



