How does hail form from rain?

Hail is rain that has frozen into ice crystals, which are then tossed up and down through vertical cloud currents. When tossed through below-freezing air, the crystals become coated with layers of ice until they are too heavy to be tossed anymore. Then they fall to the ground as hail. The average size of a hailstone is one-quarter inch in diameter, although stones weighing up to seven pounds have been reported. During the warm months of the year, hail most often forms during large, cold thunderstorms that are traveling over large landmasses.