Hail

How does hail form?

Hail develops in thunderclouds where strong updraughts (rising air currents) and downdraughts (falling air currents) move water droplets up and down through the cloud. When these droplets reach the top of the cloud, they freeze due to the cold temperatures. The powerful updraughts can keep hailstones suspended for a long time, allowing them to grow larger as more layers of ice accumulate. Eventually, when hailstones become too heavy for the updraughts to support, they fall to the ground as solid balls of ice. Unlike snow, which can form in various weather conditions, hail only forms in these convective clouds.

When and where does hail occur?

Hail can occur in different places and at different times of the year.

Western Britain

Hail is most common in western regions, most frequently in winter. During this time, the land is colder than the sea, so showers form over the North Atlantic and Irish Sea driven by rising heat energy. These showers often lose strength as they move inland, but under the right atmospheric conditions, hail can reach central and eastern UK.

Eastern England & southeast Scotland

Here, hail is most frequent in spring. The land is warm enough to generate shower clouds, but the air is still cold enough to freeze water droplets in the clouds.

Summer hailstorms

Britain’s most damaging hailstorms usually happen in summer, though they are relatively infrequent. Hot land surfaces create tall shower clouds with cold tops, ideal for hail formation. Summer hail is most common in inland northern and eastern Britain.

How big can hailstones get?

Hailstones are typically spherical or conical, ranging from 5mm to over 50mm in diameter, though most are smaller than 25mm. The largest hailstones form in ‘multicell’ storms, which are more common in places like the United States.