How does hail form?
NARRATION: It takes very special conditions to create a hailstone. You need summer thermals, and you need a violent thunderstorm. Because of the height of thunderclouds some of the water droplets inside them freeze.
But the powerful updrafts created by the warm weather, keep the droplets supported in the cloud, where they collect more water, with new layers freezing on in a separate shell.
Until, finally, there are so many layers that they鈥檙e too heavy to be supported and they fall to the ground.
Richard Hammond explores the weather conditions that form hail.
The two variables are summer thermals and powerful thunderstorms. As thunderclouds are very high, the water droplets contained within them freeze.
The upward thermals keep the ice supported in the cloud where new super cooled water enlarges the ice until they are too heavy for the up-drafts to be supported. This is when they fall to the ground.
Teacher Notes
This short film provides a description of the conditions needed for hail formation and an explanation of how hail forms. Your class could investigate other atmospheric conditions that produce hail.
Curriculum Notes
This topic appears in geography and physics at KS3 and KS4 in England, Wales and Northern Ireland and National 5 in Scotland. At GCSE it appears in AQA, OCR A, EDEXCEL, EDUQAS, WJEC and CCEA, in SQA at National 5.
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