Magazine article Geographical

Weatherwatch with Helen Willetts: May Clouds, Those Ever-Visible and Ever-Changing Parts of the Weather, Are Something with Which the British Are Very Familiar. Helen Willetts Explains How to Tell Your Cirrus from Your Cumulus

Magazine article Geographical

Weatherwatch with Helen Willetts: May Clouds, Those Ever-Visible and Ever-Changing Parts of the Weather, Are Something with Which the British Are Very Familiar. Helen Willetts Explains How to Tell Your Cirrus from Your Cumulus

Article excerpt

Clouds are so ubiquitous in the UK that we usually take them for granted, but their appearance can give us clues as to what is happening with the weather. The system of classifying clouds, developed in the early 1800s by English chemist Luke Howard, is based on the clouds' appearance and height.

There are ten main cloud types, split into three groups according to height above the ground. Cirrus, cirrocumulus and cirrostratus are high clouds, found between 5,500 and 10,500 metres--the range within which aeroplanes cruise. Altocumulus, altostratus and nimbostratus are medium-level clouds--between 2,500 and 5,500 metres. And stratus, stratocumulus, cumulus and cumulonimbus are found below 2,500 metres. These clouds sometimes reach ground level, causing fog.

A cloud's shape offers several clues about what is happening in the atmosphere, and forecasters often make use of these visual signals. Flat-looking clouds, which often cover a large area and may indicate imminent rain, usually have 'strato' or 'stratus' in their name--from the Latin for layered. Examples are altostratus and cirrostratus. Clouds with a 'bubbly' or 'cauliflower' appearance have spread vertically through the atmosphere and have 'cumulo' in their name, which means heaped. …

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