Hail forms in thunderstorms that include strong updrafts. Water vapor condenses in a cloud and is then pulled up by the updraft, where they are frozen. The hailstones grow as additional water vapor is deposited on the surface. Eventually, the hailstones acquire enough weight to escape the updraft and fall to earth. Pieces of ice exceeding 5 mm in diameter are called hail; smaller pieces are called small hail or snow pellets.
