6 



BULLETIN 430, U. S, DEPARTMENT OF AGEICULTURE. 



April is naturally much lower than that during the warmer months. 

 In the only year in which a good crop was obtained, the- precipitation 

 was high and the evaporation low, making a ratio of 1 :2. 



Table II. — Monthly and total precipitation and evaporation from a free water surface 

 at the Cheyenne Experiment Farm, Archer, Wyo., in the months of April to July, 

 inclusive, for 1913, 1914, and 1916. 



[Data (in inches) obtained by the Ofliee of Biophysical Investigations of the Bureau of Plant Industry, 



except as noted.] 





April. 



May. 



June. 



July. 



Total. 



Ratio, 



Year. 



Pre- 



cipi- 



ta- 



tion. 



Evap- 

 ora- 

 tion. 



Pre- 

 cipi- 



ta- 

 tion. 



Evap- 

 ora- 

 tion. 



Pre- 

 cipi- 

 ta- 

 tion. 



Evap- 

 ora- 

 tion. 



Pre- 



cipi- 



ta- 



tion. 



Evap- 

 ora- 

 tion. 



Pre- 

 cipi- 



ta- 

 tion. 



Evap- 

 ora- 

 tion. 



•itation 



to 

 evapo- 

 ration. 



1913 



01.35 

 2.54 

 4.90 



6 3.217 

 3.574 

 3.160 



02.22 

 1.46 

 1.78 



6 5.304 

 5.703 

 4.701 



1.51 

 1.12 

 1.83 



7.104 

 8.317 

 5.557 



2.06 

 1.43 

 1.65 



7.756 

 7.987 

 6.638 



7.14 

 6.55 

 10.16 



23.381 

 25.581 

 20.056 



1:3.27 



1914 



1:3.91 



1915 



1:1.97 











a Data from United States Weather Bureau at Cheyenne, Wyo. 



6 Interpolated. 



Wind velocities have been recorded at Cheyenne during a long series 

 of years. The average wind velocity in miles per hour, by months, 

 from April to July of each year, in the 16-year period from 1900 to 

 1915, inclusive, is given in Table III. Strong winds are quite com- 

 mon in southeastern Wyoming, and crops are damaged at times by 

 the drifting soil. The highest velocities are recorded during the late 

 fall and winter months. April has the highest average hourly velocity 

 for the months under discussion, 11.2 miles, and July the lowest, 8.5 

 miles, per hour. The anemometer was located at a height of 64 feet 

 above the ground. These readings, therefore, probably are higher 

 than they would have been if the anemometer had been located just 

 above the surface. Evaporation usually increases with wind velocity. 

 In the winter months the snowfall is, as a rule, blown to the lower 

 levels, leaving the winter crops exposed. For this reason winter- 

 killing of fall-sown crops is common. 



Table III. — Average wind velocity at Cheyenne, Wyo., by months, from April to July 

 of each year, during the 16-year period, from 1900 to 1915, inclusive. 



[Data (ia miles per hour) from the records of the United States Weather Bureau.] 



Year. 



April. 



May. 



June. 



July. 



Aver- 

 age. 



Year. 



April. 



May. 



June. 



July. 



Aver- 

 age. 



1900 



9.3 

 10.1 

 10.2 

 11.6 

 12.0 



9.9 

 10.8 

 11.6 

 11.9 



9.5 

 9.9 

 10.1 

 11.0 

 10.5 

 10.0 

 10.3 

 10.0 

 11.5 



9.5 

 9.4 

 10.6 

 8.4 

 8.9 

 10.2 

 11.9 

 9.8 

 9.3 



8.5 

 8.2 

 8.6 

 9.9 

 8.5 

 7.9 

 7.1 

 7.9 

 7.3 



9.2 

 9.4 

 9.9 

 10.2 

 10.0 

 12.0 

 10.0 

 9.8 

 10.0 



1909 



11.6 

 11.8 

 11.6 

 11.6 

 10.1 

 13.5 

 11.8 



12.5 

 10.1 

 11.6 

 11.9 

 8.6 

 11.1 

 12.1 



8.2 

 10.1 

 8.9 

 9.1 

 10.2 

 12.1 

 12.1 



8.2 

 8.1, 

 8.9 

 8.3 

 8.5 

 9.7 

 10.8 



10.1 



1901 



1910 



10.0 



1902 



1911 



10.3 



1903 



1912 



10.2 



1904 



1913 



9.4 



1905 



1914 



11.6 



1906 



1915 



11.7 



1907 



Average 





11. 2 1 10. 7 



9.9 



8.5 





1908 



9.8 













