With the weather that we have in the United Kingdom, there are usually quite a few clouds in the sky! Most people can tell if it looks like it is going to rain, but there are many different types of clouds.

Clouds are all named in a way that describes their height and shape. Their shape is described by the words 'cirrus', 'cumulus', 'nimbus' and 'stratus'. Cirrus literally means 'a curl of hair', cumulus 'heap', nimbus 'rain-bearing' and stratus means 'layer'.

Two words describes their height; 'cirr' is used for high-level clouds and 'alto' for medium-level. A high-level cloud has its base between 5,000m and 14,000m (16,500ft and 45,000ft), medium-level between 2,000m and 5,000m (7,000ft and 16,500ft) and low-level clouds under 2,000m (7,000ft).

If a cloud forms at the cold high-levels, it will be usually be made of ice crystals, so will tend to look rather thin and wispy. High-level clouds include 'cirrus', the commonly seen delicate white tufty clouds, and 'cirrocumulus', which is made up of many small round clouds. A sheet of 'cirrostratus' is generally more uniform. It is often translucent and can give a 'halo' around the sun.

Medium-level clouds usually look thicker. Because they are lower, they are mostly made of water droplets, although they can also contain some ice particles too. Some of the medium-level clouds are similar to the high-level clouds; 'altocumulus' is made of larger puffs of clouds than the high-level cirrocumulus, and the grey layer of 'altostratus' is a denser version of cirrostratus. There is also a thick dark rain-bearing cloud at this height too - nimbostratus.

Low-level clouds are usually made solely of water droplets. As well as the grey featureless layer of 'stratus', there are many types low-level of cumulo clouds too. There is the rather squashed looking 'stratocumulus', and the fluffy cotton-wool 'cumulus' clouds. There is also the 'cumulonimbus'. Cumulonimbus clouds can be so tall that it can reach up into the high-level. This is why it is sometimes classed as a 'vertically developed' cloud. This cloud can bring thunderstorms, or showers of rain, snow or hail.

One rare, but beautiful cloud is the noctilucent cloud that appears to glow in the sky. It is usually about 85 km above the surface of the earth and believed to be composed of ice crystals. However, because it is so high and forms in such a dry part of the atmosphere, it is a bit of an enigma in the world of clouds.

Other features in the Weather Basics series
Air Pressure
Day and Night
Fog and Mist
Fronts
Frost
High Pressure
Humidity
Jet Streams
Lightning
Low Pressure
Mirages
Northern Lights
Rain or Showers?
Thunder
Watercycle