 Hail in this region occurs between the months of March and October during the afternoon and evening hours, with the bulk of the occurrences from May through September.Cheyenne, Wyoming is North America's most hail-prone city with an average of nine to ten hailstorms per season.To the north of this area and also just downwind of the Rocky Mountains is the Hailstorm Alley region of Alberta, which also experiences an increased incidence of significant hail events.