Hail

Layers...

Hail is made up of frozen raindrops – solid chunks of ice more than 5 mm in diameter. It forms when raindrops are tossed high up by winds inside huge cumulonimbus clouds. They freeze into ice and are continually bounced up and down inside the cloud. As they rise and fall like this, more ice builds up in layers around them.

If a hailstone is cut in half, we can see the layers which look a bit like the layers of an onion. The clear ice forms from the warmer, lower part of the cloud where water freezes slowly. The second layer appears as frosty ice and forms in the colder top of the cloud where water freezes instantly. If we count the layers in this way, it is possible to tell how many times the hailstone was blown up and down in the cloud.

Damage...

Hail is most common in areas with warm summers where there is enough heat to cause the uplift of air. Places such as the American prairies often experience severe hailstorms where the ice can devastate crops and provide a serious climatic hazard. Hailstones as large as golf balls are quite often reported in areas such as this where hot summers allow the formation of large cumulonimbus clouds.

Considerable damage is caused to buildings and crops each year by storms of this size. The picture on the right shows damage caused to a car windscreen by hailstones. The largest hailstone ever found weighed 768g (1.7 lb.) and fell in Kansas, USA in 1970. It was about the size of a melon or large grapefruit. How large are hailstones that fall in your area?

Having looked at hail, let's move on to another cold weather feature - this time it's frost!