Hailstone

A hailstone is a single piece of hail, ice that forms inside strong thunderstorm updrafts within cumulonimbus clouds. It begins when a small ice core or supercooled raindrop is lifted into freezing regions of the storm. As the particle travels through the cloud, supercooled water droplets strike and freeze on contact, causing the hailstone to accrete layers of ice. Repeated cycles through updrafts can yield a multi-layered, roughly spherical form with an onion-like internal structure.

The growth of a hailstone depends on updraft strength and the availability of supercooled liquid water. Stronger updrafts keep the particle aloft longer, allowing more freezing and larger final sizes. If the updraft weakens or a downdraft dominates, the hailstone falls to the ground. Hailstones may be mostly transparent or cloudy, depending on air pockets and impurities trapped during formation. They are distinct from graupel or sleet, which form under different atmospheric conditions.

Sizes vary widely. They can range from small pea-sized hail to golf-ball or larger stones, with extremely large stones being rare. Hail is most common in mid-latitude regions during spring and summer and is associated with severe thunderstorms and elongated storm cells.

Impact and observation: hailstones can damage crops, vehicles, roofs, and property, and may pose safety risks to people outdoors. Meteorologists study hail formation using radar and storm observations to issue warnings and assess risk in affected areas.