Hail is frozen precipitation in the form of balls or irregular clumps associated with thunderstorms. It is formed as small pieces of ice are held aloft by an updraft within the thunderstorm, and grow by accretion as they collect supercooled water droplets. They can grow anywhere from the size of peas to softballs, and 3/4 inch is the severe criteria. Since a strong updraft is needed to support such weight, hail is typically produced by very strong thunderstorms. In fact, to support a grapefruit sized stone, an updraft wind speed of approximately 100 mph is needed.