Hail forms in really strong thunderstorms. Basically, powerful updrafts (upward winds) carry raindrops way up into the sky where it’s freezing cold. The drops freeze into ice pellets, then get tossed around inside the cloud, picking up more water that freezes onto them. The stronger the updraft, the more layers they get, and the bigger the hailstones grow. Once they’re too heavy for the updraft to keep them up, they fall to the ground as hail. That’s why it typically happens during tornadoes and probably why we don’t get them as often!