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IRRIGATED FARMING IN TWIN FALLS COUNTY, IDAHO a 
The monthly precipitation for the four years of this study and 
the normal monthly precipitation are shown in Figure 3. The dis- 
trict has the characteristic inter-mountain type of rainfall—very 
dry summers and wet winters. The average monthly precipitation 
of July and August is less than 0.5 of an inch and that of June, 
September, and October is less than an inch. Table 1 presents the 
general climatic conditions of the district. On the average there 
are but 76 rainy days (days having at least 0.01 of an inch of pre- 
cipitation) durmg the year. Six of these rainy days fall in June, 
3 in July, 2 in August, 4 in September, and 5 in October. Fair 
NORMAL MONTHLY AND MONTHLY PRECIPITATION AT TWIN FALLS, IDAHO 
te | a: = INCHES - 
1920 
2 2 
| | 
0 0 
INCHES INCHES 
2 2 
4 Bi Norma/ 
1 I % a jn WA 
Joeb--M SAMs Jats As SiO) UN. 'D- ic Mos A a IM eum OL oA tome tOr aN Da 
Fic. 3.—This district has the Pacific type of rainfall, dry summers and wet winters. During the 
years 1919, 1920, and 1921, the monthly precipitation varied greatly from the normal. (Compiled 
from reports of the Weather Bureau) 
weather, therefore, usually prevails when most of the crops are being 
harvested. In 1920, however, there were 14 rainy days in September, 
12 in October, and 12 in November. This caused considerable 
damage to the bean crop and the third cutting of alfalfa. The 
jength of the frost-free period, as seen from Table 1, is about 129 days. 
Because of the variations in the dates of the last killing frost in the 
spring and the first in the fall, crops may be damaged by low tem- 
perature at either end of the growing season. Occasionally hail 
storms sweep across the country and do more or less damage where 
they strike. 
