Hail is precipitation composed of balls or irregular lumps of ice. Hail is produced when large frozen raindrops, or almost any particles, in cumulonimbus clouds act as embryos that grow by accumulating supercooled liquid droplets. Violent updrafts in the cloud carry the particles in freezing air, allowing the frozen core to accumulate more ice. When the piece of hail becomes too heavy to be carried by upsurging air currents it falls to the ground.[1]
Hail is formed through a sort of roller coaster ride through intense thunderstorms. Strong convection currents lift small ice pellets high into the middle and upper portions of a cumulonimbus cloud. This is where super-cooled water droplets collide and the ice pellet grows through a process called accretion. Once the pellet is too heavy for the updrafts to keep it within the cumulonimbus, it begins to fall, and if it does not melt completely before reaching ground level, it comes out as hail. In a supercell, this process can result in hailstones the size of a softball.[2]
Hail can be classified into three stages of development, grauple, small hail, and hail stones.[3]