Cloud names and classifications

Clouds are continually changing and appear in an infinite variety of forms. The classification of clouds is based on a book written by Luke Howard, a London pharmacist and amateur meteorologist, in 1803. His book, The Modifications of Clouds, named the various cloud structures he had studied. The terms he used were readily accepted by the meteorological community and are still used across the world today.

Cloud types and groups

The World Meteorological Organization (WMO) has extended Luke Howard's classifications to make 10 main groups of clouds, called genera. These are divided into three levels - cloud low (CL), cloud medium (CM) and cloud high (CH) - according to the part of the atmosphere in which they are usually found.

High clouds (CH)

Base usually 20,000 ft or above, over the British Isles

High cloud types

• Cirrus
• Cirrocumulus
• Cirrostratus

Medium clouds (CM)

Base usually between 6,500 and 20,000 ft over the British Isles.

Medium cloud types

• Altocumulus
• Altostratus
• Nimbostratus

Low clouds (CL)

Base usually below 6,500 ft over the British Isles.

Low cloud types

• Stratocumulus
• Stratus
• Cumulus
• Cumulonimbus

The many possible variations in the shape of clouds and differences in their internal structure have led to the subdivision of most of the cloud genera into species.

Names for clouds

Most of our names for clouds come from Latin and are usually a combination of the following prefixes and suffixes:

• Stratus/strato: flat/layered and smooth
• Cumulus/cumulo: heaped up/puffy, like cauliflower
• Cirrus/cirro: high up/wispy
• Alto: medium level
• Nimbus/Nimbo: rain-bearing cloud

Where these names are combined, we can often build up an idea of that cloud's character. For example, if we combine nimbus and stratus we get 'nimbostratus' - a cloud which is flat and layered and has the potential for rain.