Studies of the Army Aviation (V/STOL) Environment. Report No. 8. Hail and its Distribution.
ARMY ENGINEER TOPOGRAPHIC LABS FORT BELVOIR VA
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Although hail occurs from the tropics to the polar regions, the principal world belt of occurrence is between 30 degrees N and 50 degrees N latitude. Northern India is probably the most severe region, but record hail falls have also occurred in the central and high plains of the United States. Mean annual frequency of hail occurrence may be as high as seven or eight hailstorms at a station or as many as 25 or more during the growing season over a section of a state. The number and severity of the hailstorms and their duration can vary markedly from year to year. Hailstones as large as grapefruit have occurred in the central plains of the United States, and accumulations of hailstones to depths of 12 to 18 inches have also been reported. In general, the maximum size of hailstones during storms is much smaller, about one inch but generally less, while accumulations on the ground are a few inches at the most.