Tornados aren't the only hazards associated with thunderstorms. Hail, flash floods and lightning can all be deadly. Hail forms as small objects like ice pellets, water droplets or even insects are circulated by powerful winds inside the storm cloud. Since these storms can reach tens of thousands of feet high, their tops are well below freezing. With each trip from top to bottom, the object picks up another coating of ice and gets bigger. Eventually, this pellet is too heavy to be kept aloft by the winds and it falls to earth as a hailstone.