Studies on the Distribution and Forecasting of Hail in Western United States *

The highest hail-thunderstorm ratio in the country is found over the western Great Plains and the east slope of the Rocky Mountains in a band extending from the Rio Grande northward to the Canadian border. Point frequency of hail over western United States is of little value in determining relative area exposures to hail. Frequency of hail in a metropolitan area such as Denver is at least ten times as great as random point frequency within that area. Hail probably occurs aloft during the growing stage of each thunderstorm which forms in the Denver Section. Hail is predominantly a post-coldfrontal phenomenon at Denver, but no satisfactory method has been found so far of predicting damaging hail. Airborne radar storm detection equipment offers the greatest hope of avoiding damaging hail in flight.