What causes hail?

Hail forms inside severe thunderstorms with powerful vertical updrafts. Water droplets carried above the freezing level become supercooled or freeze onto an ice nucleus, and as the growing stone is held aloft or recirculated through regions of different moisture and temperature, additional layers of ice accumulate. Cutting a large hailstone open often reveals concentric layers similar to an onion, recording those passes. The stone falls when it becomes too heavy for the updraft to support, which means hailstone size is a direct indicator of updraft strength, and golf ball sized hail implies updrafts around 60 miles per hour while larger stones imply considerably more.

This is why hail is associated with the same storms that produce tornadoes and damaging winds: all three require intense updrafts, and large hail is one of the criteria that defines a severe thunderstorm warning in the United States, along with wind gusts above a threshold. Hail is most frequent in continental interiors with strong surface heating and available moisture, which is why the central United States, northern India, and parts of Argentina and China see it most often. The record stones recovered in the United States have measured around eight inches across.

The damage is economic more than lethal. Hail causes billions of dollars in insured losses annually in the United States alone, primarily to roofs, vehicles, and crops, and hail claims are a substantial driver of rising homeowners insurance costs in affected regions. Practical guidance during a hailstorm: get vehicles under cover if there is time, stay indoors and away from windows and skylights, which can shatter, and do not go outside to move a car once stones are falling, since injuries occur that way. Afterward, document damage with photographs before repairs and be alert to storm-chasing contractors who canvass neighborhoods after events, which is a well-documented fraud pattern.