The London Weather Station

Snow is the frozen ice crystals of rain. When clouds are full they pour out rain but in cold weather ice crystals fall out as soft little flakes that are called snowflakes. Sometimes the snow melts and turns into normal water when it touches the ground, but at other times it stays as it is and you can go and try to build a snow man or even get out on a sledge or on skis!

In most parts of the UK the snow doesn't stay for long.
But why does the snow melt? And how is it that rain sometimes turns into snow?

Well, water consists of little elements that are called molecules. These molecules float around constantly when the water has a certain temperature and they do not form a solid object. This is why the water floats everywhere when you spill a glass of water. And when you boil water the molecules go wild and the water makes bubbles and little waves.
But if the water becomes colder, the molecules cannot move around easily anymore. It is too cold to move around. At some point they simply stop moving. Then the water is solid. If you tipp over a glass of frozen water it will not spill everywhere, because the water has turned into a frozen, solid block.

The same thing happens in a cloud. Clouds are high up in the sky, and high up in the sky it is very cold. Sometimes it is so cold that the water in the clouds turns into little crystals of ice. If the water freezes into tiny frozen crystals, snow slowly starts to form. The little crystals grow because water steam gets frozen on them, and the crystals slowly turn into larger snow flakes. Next time it snows, have a closer look at the snow flake! It has a very peculiar and beautiful structure! (also see article on hail storms )

Snow falls out of the cloud when the cloud gets very heavy and sinks to the ground. The snow falls on the ground. Depending on how cold it was the days before the snow fall, the ground may be warm or cold. If the ground is cold enough, the snow stays frozen. If it is too warm, the snow gets warmer and melts. It first turns into "slush" and later into normal, boring water. It also often happens that snow is followed by warmer weather and that rain sets in after a snow fall. The rain is so warm compared to the snow that it will melt any snow on the ground.

If it is very cold, the snow flakes will be rather small and the snow on the ground will feel almost "dry". This is ideal for winter sports like skiing or simply for using your sledge. Larger snow flakes go along with warmer air, and they are rather "wet". These are perfect for building a snow man!

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