4 BULLETIlSr 430, U. S. DEPARTMENT OF AGRICULTURE. 



wind, particularly that which passes du'ectly over the ground during 

 the crop season; and (3) temperature, with special reference to the 

 length of the frost-free period in a given locahty. 



PRECIPITATION. 



Rainfall is undoubtedly the most important factor in crop produc- 

 tion in southeastern Wyoming. Table I shows the monthly, 

 seasonal (April to July), and annual precipitation at Cheyenne, 



Wyo., in the 16-year 

 period, 1900 to 1915, 

 inclusive. The sea- 

 sonal and annual 

 precipitation are 

 shown graphically in 

 figure 1. 



Table I shows 

 that the highest 

 monthly precipita- 

 tion during the 16- 

 year period was 7.66 

 inches, in April, 1900. 

 The lowest monthly 

 precipitation during 

 that period was a 

 trace, in November, 

 1901. The highest 

 seasonal (April to 

 July) precipitation 

 recorded during the 

 16 years was 15,36 

 inches, in 1905. The 

 lowest seasonal pre- 

 cipitation was 4.77 

 inches, recorded in 

 1903. The average seasonal precipitation was 8.59 inches. 



The highest annual precipitation recorded during the 16-year 

 period was 22.68 inches, in 1905. The lowest annual precipitation 

 during the same period was 10.85 mches, in 1911. The average 

 annual precipitation for the 16 years was 15.78 inches. 



The monthly precipitation varies widely from year to year. 

 Marked variations are observed also in the seasonal and annual 

 precipitation of the different years. 





vi n' V ^ X \' V "^ 



Q N Oj fh 



S S ^ <5 

 ? 5 9> & 



§ ^ ^ § 



0) 5j ^ 5 



Fig. 1. — Diagram showing the seasonal and the annual precipitation 

 (in inches) at Cheyeime, Wye, for 16 years, 1900 to 1915, inclusive. 



