Hail

Hail is a form of solid precipitation consisting of rounded ice pellets that form inside strong thunderstorms. Hailstones originate when updrafts in a cumulonimbus cloud lift droplets above the freezing level into subfreezing air. There, the droplets freeze into ice and may collide with supercooled water, layering additional ice as the stones circulate within the cloud. The process continues until the hailstone becomes too heavy to be supported by the updraft and falls to the Earth's surface.

Formation requires a combination of strong vertical wind shear and ample moisture, typically in mid-latitude regions during warm seasons. Hail is more common in places with frequent intense thunderstorms, such as plains or maritime climates with convective storms. Not all thunderstorms produce hail, and the diameter of hailstones can vary from small pellets to markedly larger stones in severe storms.

Hailstones are usually spherical or irregular in shape and can range from pea-sized to several centimeters in diameter; very large hailstones, though rare, can cause extensive damage to property, vehicles, and crops, and may injure people and animals. Hail is also a hazard to aviation and can lead to temporary flight disruptions.

After a storm, hail is measured by meteorological services and storm spotters; warnings and forecasts often advise seeking shelter and protecting windows. Hail pads and automated radar observations help assess hail potential and size.