8 



litLLKTrX 1244, T. S. DEPARTMENT OF AGRICULTURE. 



Table 6 gives the dates of the last killing frosts in the spring and 

 the earliest in the fall, with the length of the frost-free period for 

 the years 1909 to 1922. The average date of the last killing frost 

 in the spring was May 18 and the first in autumn September 20. 

 The average length of the frost-free period was 125 days. The short- 

 est period between killing frosts, 83 days, occurred in 1910. The 

 longest period free from killing frost was 150 days, reported in 1922. 

 The latest killing frost occurred on June 2 and the earliest August 24. 



The average monthly wind velocity, in miles per hour, for the years 

 1909 to 1921 was as follows: April, 8.2; May, 7.9; June, 6.2; July, 

 7.9; August, 5.3; September, 6.1. 6 The seasonal average was 6.9 

 miles per hour. 



Table 6. — Dates of killing frost, the last in spring and first in fall, with the frost- 

 free period at Judith Basin Substation, Moccasin, Mont., in each year from 

 1909 to 1922, inclusive. 



[Data from the records of the Biophysical Laboratory of the Bureau of Plant Industry.] 



Year. 



Last in 

 spring. 



First in 

 fall. 



Frost- 

 free 

 period. 



Year. 



Last in 

 spring. 



First in 

 fall. 



Frost- 

 free 

 period. 



1909 



May 17 

 June 2 

 May 6 



Oct. 12 

 Aug. 24 

 Sept. 18 

 Sept. 15 

 Sept. 9 

 Sept. 12 

 Sept. 11 

 Sept. 13 



Days. 

 148 



83 

 135 



126 

 113 

 123 

 129 



120 



1917 



Mav 30 



Oct. 17 

 Sept. 14 

 Sept. 27 

 Sept. 2s 

 Sept. 9 

 Oct. 5 



Days. 



140 



1910 



1918 . 



May 2s 

 June 1 

 May 2o 

 Mav 2 



May 8 



109 



1911 



1919 



118 



1912 



May 12 

 May 19 

 May 12 



Mav .") 

 May 16 



1920 



126 



1913 



1921 



130 



1914 . 



1922 



isn 





Average 





1916 



May 18 



Sept. 20 



125 







The important climatic features from all stations for which crop 

 data are given in this bulletin are summarized in Table 7. These 

 data do not cover the same period of years at the various stations, 

 which undoubtedly accounts for some apparent discrepancies. The 

 highest average annual and seasonal precipitation is reported at Red- 

 field, S. Dak. Edgeley, N. Dak., stands second in the seasonal aver- 

 age, with only about 1 inch less than at Redfield. The lowest average 

 annual precipitation is recorded for Havre, "Mont., and the lowest 

 seasonal average for Sheridan, Wyo. The seasonal average of 13.25 

 inches, recorded for Ardmore, S. Dak., is undoubtedly above the 

 normal, since the records for that station cover a period of only nine 

 years, which included three or four years of abnormally high precipita- 

 tion. Three stations, Redfield and Ardmore, S. Dak., and Mandan, 

 N. Dak., record a maximum of slightly more than a 30-inch precipita- 

 tion in one year. The lowest annual precipitation recorded is 6.64 

 inches at Belle Fourche, S. Dak. The maximum annual precipita- 

 tion is nearly as great for the stations with the lowest as for those 

 with the highest average annual precipitation. As would naturally 

 be expected, the ratio of precipitation to evaporation is greatest in 

 those sections where the rainfall is lowest , as is the case at Havre and 

 Sheridan. The lowest ratio occurs at Edgeley, and while evapora- 

 tion records are not available for Redfield, it is very likely that there 

 is not much difference in this respect between Redfield and Edgeley. 

 The highest mean seasonal temperatures are reported at Redfield, 



i rom i he records of the Biophysical I laboratory of the Bureau <>r pianl Industry. 



