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ELI5 Yahaaa

Ice going round again

How Does Hail Form?

Hailstones grow in layers by being thrown up through a storm cloud repeatedly.

Thrown up by the updraught Freezesanother layer Falls back down Until tooheavy to liftEach trip= one
An onion built by a storm.

  1. Step 1 of 5

    It needs a violently rising column of air.

    Severe storm updraught150 km/h upwardOrdinary showerfar too weak forhail

    Only a strong thunderstorm has updraughts fast enough — sometimes over 150 km/h — to throw ice upward against gravity.

  2. Step 2 of 5

    A droplet freezes high in the cloud.

    1 A water dropletrises2 Into air wellbelow 0°C3 It freezes —the seed

    Carried into air far below freezing, a droplet turns to ice. That tiny grain is the seed the hailstone will grow around.

  3. Step 3 of 5

    Each trip adds a layer.

    A hailstone cut inhalf Rings, one per tripthrough the cloud

    Falling, it collects supercooled water. Thrown up again, that water freezes on. Every round trip wraps another shell around the stone.

  4. Step 4 of 5

    The layers alternate clear and cloudy.

    Fast freezing Cloudy, bubble-fillediceSlow freezing Clear ice

    Freezing fast traps air bubbles and looks white; freezing slowly makes clear ice. The banding records the conditions on each pass.

  5. Step 5 of 5

    It falls when the updraught cannot hold it.

    A growing hailstoneUpdraught lifts itWeight grows every trip

    Every layer adds weight. Once gravity beats the rising air, the stone drops — so bigger hail means a stronger storm, always.

    The largest recorded hailstone was 20 cm across — the updraught holding it up would have been over 160 km/h.

The short version

Hailstones grow a layer per trip through a storm's updraught, and fall once too heavy to be lifted.

Try it yourself

Cut a large hailstone in half and count the rings. Each one is a journey up through a thundercloud.

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