A Study of Causes of Hail

Abstract

An analysis has been made of the incidence of hall in southern Alberta during the years 1959?1963. The study has shown that warm air is necessary for major hail. An effective lower limit of ?1C at 700 mb in the vicinity of the storm has been established. Other meteorological variables were examined to try to distinguish days with hall from those without hail. The best clues to the occurrence of hail were: a steep temperature gradient at low levels between Great Falls and Seattle, a high-level vortex over British Columbia, and unstable air over Great Falls. Other variables were also examined, and a relationship with hail was confirmed. Yet among the variables examined no necessary and sufficient conditions were isolated by which one could distinguish a day with severe hail from a day with minor hail or a day without hail.