THE CLIMATE OF MONTANA 67 



reference to cold waves in Montana should also include at least mention of the chinooks 

 which so frequently terminate or mitigate them with various degrees of decisiveness 

 and abruptness. As a result of certain air pressure distribution and air movement, 

 rapid rises of 20 to 50 degrees in temperature often occur in one section or another, of 

 greatly varying local extent. A troublesome weather item in the summer months is the 

 hot wind which occasionally arises and rapidly takes up the moisture from crops and 

 soil and grass, leaving them dry and more or less parched, sometimes greatly reducing 

 the grain yield in areas exposed to it and not favored with rain quickly thereafter. 



Precipitation ^he region of Montana's greatest total annual precipitation is that 



, adjoining Idaho in the northwest, particularly western portions of 



Sanders and Mineral counties. A record nine years long for Saltese, 



egions which is near the Idaho line, in a valley between the Bitter Roots and 



the Coeur d'Alenes, shows an average annual total of 34.25 inches. Farther north, 

 between the Coeur d'Alenes and the Cabinet Mountains, a ten year record for Heron, 

 a few miles from the Idaho line, gives an average of 31.90 inches. There may be 

 scattered localities in the mountain valleys and passes, both east and west of the 

 Continental Divide, where these amounts are exceeded, but in places where this may 

 be suspected the records are too brief to establish the fact definitely. There is much 

 variation in the west, through the section marked off by the Continental Divide. Here 

 the precipitation averages 20.37 inches a year. In Glacier Park and the Flathead Valley 

 are totals above 20 and 25 inches. Belton has 26.46 inches. Amounts with few excep- 

 tions between 12 and 19 inches are irregularly distributed over the rest of this area, 

 the least being 11.29 inches at Hamilton. 



From the feet of the Main Range eastward in the counties along the Canadian 

 line, and including also Pondera, part of Teton, western and most of northern Chouteau, 

 and Roosevelt, the average precipitation during the year is a little over 13 inches, the 

 least being 8.27 inches, which is shown by the average for Rudyard. As the Rudyard 

 record began as late as 1916, and the average is of only five years of observations and 

 runs into the most notable drought in the weather history of the state, this figure does 

 not by any means indicate the normal precipitation, and the average will most probably 

 be raised as the record lengthens. Through the entire eastern part of the state there 

 are but limited areas where the annual precipitation averages as much as 15 inches. In 

 central and southwestern counties the distribution is very irregular. It is scant in the 

 high lands of Beaverhead county, and varies mostly between 9 and 14 inches through the 

 upper end of the Missouri Valley where the trend is north-south ; yet it averages 16.84 

 inches for the southwestern part of the state to eastward of the Continental Divide, 

 while the section to northward, notwithstanding the light precipitation in the northern- 

 most counties, averages 15.81 inches. 



Thus the roughest sections of Montana show the greatest local differences in the 

 amount of precipitation and have the highest general averages, and the expanses less 

 varied in topography receive, in general, somewhat less, but more evenly distributed, 

 precipitation. May and June have the greatest monthly amounts for almost the whole 

 of the state, a circumstance highly favorable for agricultural interests. There are, of 

 course, wide local variations in the monthly amounts, but they range from about two 

 inches to four inches, wiht few exceptions, in each of these months. July averages a 

 smaller amount than May or June, but still sufficient for the needs of the growing 

 crops. There is a distinct falling off in the rainfall in August, and a clearly marked 

 increase over the August average in September. Near the Idaho line, in Mineral, 

 Sanders, and Lincoln counties, and on the west slope in Glacier Park, this monthly 

 distribution does not hold; while there are as a rule sufficiently ample amounts in the 

 early summer, the precipitation maximum occurs in the winter, the colder months having 

 a decidedly greater amount of precipitation than the warmer months. The fact points 

 to a heavy snowfall for these sections, and this is shown by the records. This north- 



