4 



The northern Great Plains is a region of temperature extremes. 

 The temperatures during the long winters may reach a minimum 

 of —20° to —30° F., the lowest recorded at any of the stations con- 

 sidered in this bulletin being —57° F. at Havre. Very high temper- 

 atures occur during the comparatively short summers. A temper- 

 ature of 100° F. or more at least once during the season is not un- 

 common, the highest recorded being 110° F. at Redfield, Edgeley, 

 and Mandan. These extremely hot periods are usually of short 

 duration, and except in the eastern and southern parts the nights 

 are generally cool. Extreme fluctuations occur during the growing 

 season. Temperatures of 102° and 32° F. were recorded at Red- 

 field during September, 1922. Because of the dry atmosphere, 

 however, the extremes of heat and cold are less severe on man and 

 beast; but the winds, winch blow with considerable regularity, are 

 discomforting to man and beast, especially during the winter, and 

 may be destructive to crops during the summer, particularly when 

 accompanied by high temperature. High winds during the growing 

 season greatly increase evaporation from the soil and transpiration 

 from the plant. Were it not for the relatively high latitude of the 

 region and the concomitant factors which produce what is commonly 

 known as an intensive growing season, the annual precipitation 

 would not be sufficient for cereal production except in limited local- 

 ities. 



Frosts have been known to occur at the higher altitudes every 

 month of the year, but are rare in JinV. Early June and late August 

 frosts are not uncommon in much of the region. The average 

 length of the frost-free period ranges from 106 to 137 days at the 

 station given. Never a year passes that more or less damage is 

 not done to growing crops in the northern Great Plains by hail, 

 but such damage is usually more or less local and in many cases is 

 covered by insurance. 



The climatological data for Redfield, S. Dak., and Moccasin 

 and Havre, Mont., are given in detail in the following pages. 

 These points have been chosen particularly because most of the 

 forage-crop data have been obtained from experiments conducted 

 at or near these stations and also because they represent the climatic 

 extremes of the dry-farming section of the region. 



Table 1 gives the precipitation data at Redfield, S. Dak. The 

 average annual precipitation for all years from 1898 to 1922 exclusive 

 of the years 1912, 1913, and 1921 is about 20.33 inches, while that 

 for the last 10 years, exclusive of 1913 and 1921, is 21.1 inches, <>r 

 about three-fourths of an inch more. The average difference in 

 seasonal 2 precipitation for the same periods is a little less than 

 half an inch in favor of the longer period. About three-fourths of 

 the total precipitation, or approximately 1"> inches, occurs from 

 April to September, inclusive. The greatest annual precipitation 

 (30.76 inches) was recorded in 1900, and the minimum (11.98 inched 

 in 1898. The highest and lowest seasonal precipitation occurred 

 during the same years. 



»The "'nil "seasonal" as used in this bulletin includes the mouths from April to September, in- 



