What is hail?

Imagine it is a warm day, and suddenly tiny balls of ice come bouncing down from the sky. Plink, plink, plink! That is hail — and the surprising thing is, it can fall even when it is not cold outside. So how does the sky make ice on a warm day?

It begins in a giant cloud

Hail is born inside very tall, dark storm clouds. These clouds can be taller than the highest mountain! Down at the bottom it is warm, but high up at the top it is freezing cold, colder than your freezer at home.

Inside these clouds the air rushes up and down very fast. These strong rushes of air are called updraughts.

Ice that grows and grows

A little raindrop gets caught in an updraught and is thrown way up high, where it freezes into a tiny ball of ice. Then it falls, gets caught again, and is tossed back up. Each trip, a new layer of ice freezes around it, like adding coats of paint.

The ice ball grows bigger and bigger with every loop. If you cut a hailstone in half, you can see the layers, like the rings inside an onion!

Down it comes

At last the ice ball is too heavy for the air to hold up. Gravity wins, and it falls all the way to the ground as hail. Most hailstones are small, but big storms can make some as large as a marble — or even a golf ball!

Wonder fact: The biggest hailstone ever found was wider than a grown-up’s hand — almost 20 centimetres across!