How does hail form? An explanation from the experts

Thunderstorms can bring a range of hazards, including lightning, heavy rain, strong winds, and hail. Hailstones are pieces of ice that fall from thunderstorms and can get large enough to do much damage.

So how does hail form? The answer is thunderstorm updrafts. Hail forms when strong updrafts, areas of rising air in a thunderstorm, carry water droplets high into the atmosphere, freezing into ice crystals. The wind can then carry these ice crystals and collide with other supercooled water droplets, which freeze onto the ice crystals and grow in size.

The stronger a storm's updraft, the larger the hailstone grows. As the hailstones grow larger and heavier, gravity takes over, and the storm's updraft can no longer support the weight of the hailstones, causing them to fall to the ground.

The size of the hailstones can vary depending on the strength of the updrafts and the amount of time the hailstones spend in the cloud, growing in size. Supercell thunderstorms tend to produce the largest hail due to their strong updrafts.

In some cases, multiple layers of ice can form around the hailstones as they are carried up and down through the cloud by the updraft. If a hailstone is picked up by a storm's rising air, or updraft, and thrown back into the atmosphere above the freezing line, it refreezes and grows more. This situation can produce large hail, especially if the cycle repeats several times.

The largest hailstones can be as large as grapefruits or softballs and can cause significant damage to buildings, crops, and vehicles. A hailstone found in Vivian, S.D., currently holds the record for having the largest diameter (18.62 inches) and being the heaviest (1 pound, 15 ounces) hailstone found in the U.S. This hailstone was produced by a severe thunderstorm on July 23, 2010.