Hail, one of the most destructive forms of precipitation, goes through a relatively lengthy evolution.
It can begin as either rain or snow, but then proceeds through layers of atmosphere that alternate between above and below freezing.
Because of the changing temperature, there are forceful updrafts of wind that reverse the course of the hail back upward. The hail freezes, partially thaws, refreezes, and partially thaws, on and on as it travels back and forth through the layers of atmosphere.
With each trip, the hailstone grows in size until it finally makes its way through the entire atmosphere to Earth’s surface.