4 BULLETIN 430, U. S. DEPARTMENT OF AGRICULTURE. 
wind, particularly that which passes directly over the ground during 
the crop season; and (3) temperature, with special reference to the 
_length of the frost-free period in a given locality. 
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 
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Fic. 1—Diagram showing the seasonal and the annual precipitation 
(in inches) at Cheyenne, Wyo., for 16 years, 1900 to 1915, inclusive. 
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 inches, 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. 
