Precipitation composed of lumps of ice formed in strong updrafts in cumulonimbus clouds. Individual lumps are called hailstones. Most hailstones are spherical or oblong, some are conical, and some are bumpy and irregular. By definition, hail must have a diameter of at least 0.2 in. (5 mm), and has been known to reach over 6 in. (150 mm). Thus, the largest stones are grapefruit or softball size, and the smallest are pea size.