There are ten main types of cloud which can be separated into three broad categories according to the height of their base above the ground: high clouds, medium clouds and low clouds.
These are usually composed solely of ice crystals and have a base between 18,000 and 45,000 feet (5,500 and 14,000 metres).
Cirrus - white filaments.
Cirrocumulus - small rippled elements.
Cirrostratus - transparent sheet, often with a halo.
Medium clouds
These are usually composed of water droplets and ice crystals, and have a base between 6,500 and 23,000 feet (2,000 and 7,000 metres).
Altocumulus - layered, rippled elements, generally white with some shading.
Altostratus - thin layer, grey, allows sun to appear as if through ground glass.
Nimbostratus - thick layer, low base, dark, rain or snow may fall from it.
Low clouds
These are usually composed of water droplets, though cumulonimbus clouds include ice crystals, and have a base below 6,500 feet (2,000 metres).
Stratocumulus - layered, series of rounded rolls, generally white with some shading.
Stratus - layered, uniform base, grey.
Cumulus - individual cells, vertical rolls or towers, flat base.
Cumulonimbus - large cauliflower-shaped towers, often 'anvil tops' sometimes giving thunderstorms, or showers of rain or snow.
Most of the main cloud types are often subdivided further on the basis of their shape, structure and degree of transparency.
