Snowflakes - What is Snow?

Snow can be great fun to play in. People enjoy sledging in the snow, making a snowman or having snowball fights! But what exactly is snow? 

The air is full of water vapour which has evaporated from lakes, rivers and the sea. Some of the moisture in the air comes from the leaves of plants and trees. On a cold day, you can see the clouds of water vapour that you breathe out. 

This water vapour rises into the atmosphere and gathers together in clouds. When it falls from the sky, it is called precipitation. Precipitation can fall as rain, snow, hail or sleet depending on the temperature of the air. Sometimes, water vapour freezes into ice crystals, instead of drops of rain. If the temperature is cold enough (it would have to be −35 °C or lower) other water droplets attach to a single first ice crystal, or, in clouds above -35 °C, the freezing droplets can form around a dust or pollen particle. More and more ice crystals form around the first few, creating a snowflake.