by David Murphy
Hail is made of pieces of ice that drop from a thunderstorm. Most hail is small (about the size of a pea). But hail can be much larger. Golf ball-sized hail can cause property damage as well as damage to crops. It can also cause injury to people and animals. Some hail is actually the size of a baseball and even a grapefruit! The largest hail ever to fall in the U.S. was in Vivian, South Dakota, on July 23, 2010. The stone was 18 5/8 inches wide, and weighed a record 1.9375 pounds.
Hail forms as drops of water within a thunderstorm are blown high into the top of the storm by a fast-moving column of rising air known as the updraft. The air temperature at the top of large thunderstorms is below freezing, so as the water drops pass into this freezing level, they turn to ice. Additional water drops then adhere to the ice and also freeze, growing the hailstone. Eventually, the hailstone becomes so large and heavy, its weight can no longer be supported by the updraft and it falls. On the way down, the hail re-enters the warmer portion of the storm and begins to melt. Small hailstones melt entirely and turn back into raindrops before they hit the ground, but if the hail is large enough, it makes it all the way to the surface as ice.
By the way, hail should not be confused with sleet, which is generally smaller and only falls during the winter. Check out the Weather Class topic What is sleet?, which is in the Snow group.