Hail Storms over Lyneham
23rd March 2004

Over the last couple of days, we have been experiencing large deluges of hail.

Within a couple of minutes, the pea-size hail stones have laid a white frozen carpet over the village.

How Hail is formed
Large hailstones develop in huge thunderstorm-clouds. These clouds are cumulonimbus clouds. In such a cloud are falling and rising airstreams; called down and updrafts. The cloud base may be 2,000 feet above the ground with tops at 30,000 feet. Much of the cloud will be composed of super cooled water droplets. As the hailstone falls it will collect tiny water droplets which freeze and form a layer of ice.

Perhaps the hailstone will then be caught in a vigorous updraft. As it is carried back higher into the cloud, it collects more minute water or ice particles to form another layer of ice. Thus layers build up on the hailstone ice) and the cycle may be repeated until the stone is so big that the updraft can't lift it anymore; and it will fall to earth.

Sometimes the updraft - and the connecting downdraft - in a thunderstorm is gets impulses of a jet stream at higher altitude. (Jet streams are strong winds at about 9 - 10 kilometre (30.000 - 33.000 feet) high in the atmosphere, with a force of 65 mph or more.) When this is the case the up and downdrafts can be very violent. And really heavy hailstones are easily lifted up again and again. Its not hard to imagine that such huge thunderstorms with such severe up- and downdrafts can enlarge enormous hailstones - to the size of tennis-balls.

While crops are the major victims, hail is also a hazard to vehicles, aircraft and windows. Deaths are rare in the United Kingdom.

In May 2003, the most recent notable hailstorm experience was when huge hailstones cause flight 'mayhem' on a passenger jet leaving a hole the size of a football in the plane which had more than 200 passengers on board.

The BMI Airbus was flying to Manchester Airport from Cyprus when it encountered heavy turbulence. One passenger described the experience as like "a roller coaster ride".

Deaths and injuries are more common in other parts of the world, especially places where many people live in poorly constructed buildings. In the USA, hailstorms are most common on the Plains, especially just east of the Rockies. Other parts of the world that have damaging hailstorms include China, Russia, India and northern Italy.

Hailstone facts
Heaviest Hailstones
The heaviest hailstones on record, weighing up to 1 kg (2.2 lb.), are reported to have killed 92 people in the Gopalganj district of Bangladesh, on April 14, 1986.

The Eighties hailstorm wasn't the first time citizens of the Indian subcontinent have been struck by such freak weather conditions - hailstones thought to be the size of baseballs killed scores of people and 1,600 cattle in 1888, in the Moradabad and Beheri districts of India.

The largest hailstone recorded in the British Isles weighed 142 grams (5 oz) and occurred at Horsham, West Sussex on 5 September 1958. Certainly anything approaching golf-ball size is remarkable, but hailstones can grow large enough to dent cars, shatter greenhouses and even injure people.