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Spring showers.

BY Wijke Ruiter

This is the season for the typical afternoon cumulus clouds that often develop a spring shower.

Cumulus clouds look like lumps of cotton wool. They are formed as the sun heats up the ground that in turn the air right above. When air is heated  it will expand and becomes less dense than the surrounding air. Warmer air always rises.

During rising the air will cool down and condense; water vapour will turn into tiny water droplets and a cumulus cloud appears. Actually we see the bottom of the cloud.

As long as the air cloud stays warmer than its environment it will keep on growing and growing into the higher atmosphere. The temperature there is below zero: the clouds water droplets will turn into ice-crystals: and snow is born.

The top of the cloud gets the “anvil-shape”; cumulus has developed into cumulonimbus  (nimbus = rain). At the top of a cumulonimbus there’s always ice and snow.
As this begins to fall we reach a new stage. In the cloud a melting process starts: the drops are too heavy now: they fall down.

On the ground people run to find shelter; looking for an umbrella or simply get wet: it rains.

Characteristic for springtime is the division of the showers above land and sea.

The water of the North Sea is considerably colder than the air above land. So cumulus clouds mainly develop above the warmer grounds. When the air is quite and there are no large low-pressure systems in the neighbourhood; the cumulus clouds concentrate above the land and the sea is clear. This satellite photo gives a beautiful example.

In springtime there are often big differences in temperature between day and night. By night and in early morning the seawater is warmer than the land. Showers can develop above sea; the coastal regions can have rain.
In the afternoon the situation is the other way around: showers develop above land. The coastal regions are clear.