RAINFALL OF THE UNITED STATES 



157 



snow is abundant as in places equally cold where snow 

 seldom falls. 



If raindrops become frozen into little balls in their 

 passage through the air, they fall as hail. Hail usually 

 occurs in summer and is probably caused by ascending 

 currents of air carrying the raindrops to such a height 

 that they are frozen and often mixed with snow before 

 they fall. Sometimes hailstones are more than a half inch 

 in diameter. They occasionally do great damage to crops 

 and to the glass in buildings. 



Sleet is a mixture of snow and rain. 



78. Rainfall of the United States. An examination of a 

 rainfall map of the United 

 States (page 158) will 

 show that the distribution 

 of rainfall can readily be 

 divided into four belts 

 which, although gradually 

 shading the one into the 

 other, are yet quite dis- 

 tinct. These belts may 

 be called the north Pacific 

 slope, the south Pacific 

 slope, the western interior 

 region, and the eastern 

 region. 



In the north Pacific 

 coast region the storms 

 of the " westerlies " are 

 common, particularly in 

 winter, when the westerly 

 winds are strong and stormy. The yearly rainfall here 

 amounts to about seventy inches. 



From central California south the rainfall of the Pacific 



SALMON RIVER DAM, IDAHO. 



A typical irrigation dam in the United 

 States. 



