Why does it snow?

You wake up, peek outside, and the whole world is white and quiet. Soft flakes drift down from the sky. But what exactly are they, and where do they come from?

Water hiding in the air

High up in the sky there is water you cannot even see, floating about as a kind of invisible mist called water vapour. On a warm day it just stays up there. But when the air gets very, very cold, something magical begins.

Tiny ice crystals are born

When it is cold enough, the water vapour does not turn into rain drops. Instead it freezes straight into teeny-tiny pieces of ice called ice crystals. Each crystal is so small you could balance lots of them on your fingertip.

More and more crystals bump together and stick, building up into a snowflake. When a snowflake grows big and heavy enough, it floats gently down to you.

Always six sides

Here is the amazing part: almost every snowflake has six sides, like a little star. That is just the way water freezes — it always builds in sixes. And because each flake takes a different path through the cold air, no two snowflakes look exactly the same.

Wonder fact: Snow looks white, but ice crystals are really clear! All their tiny surfaces bounce the light around, and that mix of light looks white to your eyes.