What Is Hail?
Hail is made up of small lumps of ice that sometimes fall during thunderstorms. Hail starts in thunderclouds as rain. As the raindrops form, strong air currents carry them to the upper part of the cloud, where it is freezing cold. There they turn into ice.
As the bits of ice fall down through the cloud, they pick up a coat of rain. Up they go again, over and over, adding more coats of rain and freezing them, until the air currents let them fall.
If many layers gather and freeze on a hailstone before it falls to the ground, it may grow quite large.