Cloud names and classifications

Cloud spotting

Clouds are continually changing and appear in an infinite variety of forms. This is a guide to the 10 main named groups of clouds.

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.

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.

Cloud level (ft)Cloud type

High clouds (CH)

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

Medium clouds (CM)

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

Low clouds (CL)

Base usually below 6,500 ft over British Isles.

The many possibly 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. For a more detailed guide on cloud spotting including species and cloud codes, view our Cloud types for observers Cloud types for observers (PDF, 4 MB)  guide.

Names for clouds

The names for clouds are usually are combinations of the following prefixes or 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

Last updated: 3 October 2013