Cloud spotting

Stratus clouds tend to be flat and fairly featureless low level clouds with a base of 0 - 1,200ft. The cover the sky in a blanket of grey or white cloud. 

Stratus (St) are the lowest lying form of cloud and sometimes appear like mist or fog. 

Stratus clouds form in calm, stable conditions with gentle breezes. 

They usually mean dry conditions but if thick enough they can lead to light drizzle. 

There are two species of stratus: 'nebulosus' (a featureless and dark layer) and 'fractus' (starting to break up)

The King of Clouds these clouds are recognised for their icy anvil shaped tops. They tower through the troposphere with bases from 1,100 to 6,500ft. 

Cumulonimbus (Cb) clouds bring rain and thunderstorms and are the only clouds that can produce hail, thunder and lightning.

Cumulonimbus clouds grow through convection, often from small cumulus clouds over hot land surfaces. They can store as much power as 10 Hiroshima-sized atom bombs. 

Cb clouds can bring extreme weather including torrential downpours, hail, lighting and tornadoes.

There are three types of Cumulonimbus cloud:

Calvus has a puffy top like a cumulus cloud.

Capillatus has a fibrous top but is contained. It indicates rain soon. 

Incus has an anvil shaped top. It indicates the cloud has reached the top of the atmosphere and must now spread out. 

Cumulus are fluffy cauliflower-shaped clouds and have bases between 1,200 and 6,500ft. 

Cumulus (Cu) clouds are fair weather clouds. They all develop through convection. This means that as air is heated at the surface it rises and cools and water vapour condenses to form clouds.

If cumulus clouds continue to grow during the day they can develop into towering cumulus or cumulonimbus and produce showers. 

There are four types of Cu clouds:

Humilis - wider than they are tall
Mediocris - as wide as they are tall
Congestus - towers
Fractus - breaking up

Stratocumulus clouds are low level clumps or patches of cloud varying from white to grey at the base. They are the most common clouds on earth and have bases between 1,200 and 6,500ft. 

Stratocumulus (Sc) clouds do not usually bring any form of rainfall. 

Stratocumulus indicate a change in the weather. They are usually found near a weather front. 

There are four forms:
Stratiformis - flat based 
Cumulogenitus - when rising cumulus spreads out
Castellanus - turreted tops, these can form cumulonimbus
Lenticularis - lens shaped

Altostratus are large mid-level sheets of thin cloud. They are thin enough in parts to allow you to see the Sun weakly through the cloud. They are often spread over a very large area and form ahead of weather fronts. 

Altostratus (As) has a base between 6,500 and 20,000ft. 

Nimbostratus (Ns) clouds are dark, grey, featureless clouds, which block out the Sun. They have bases between 2,000 and 10,000ft. 


Nimbostratus (Ns) is formed through the thickening of an Altostratus cloud. They are associated with fronts and bring persistent rain.

Altocumulus clouds are small mid-level layers or patches of clouds, called cloudlets, they come in many varieties and shapes with bases 7,000 to 18,000ft. 

Altocumulus (Ac) indicate settled conditions. Any rain that does fall will not reach the ground and is seen as 'virga'.

Altocumulus has many different 'species' including: 

Stratiformis - flat bottomed puffy clouds close together with small 'rivers' of sky in between. 

Lenticularis - lens shaped clouds over hilly areas, they can look like UFOs!

All high clouds are forms of Cirrus. Cirrus are hair like clouds made of ice crystals that look bright white by day and can take the colours of the sunset. They have bases of 20,000 to 40,000ft. 

Cirrus (Ci) form before a warm front and indicate a change in the weather. 

Cirrocumulus clouds are made up of lots of small white clouds called cloudlets. They often look like ripples high in the sky with bases of 20,000 to 40,000ft. 

Cirrocumulus (Cc) appear in fair weather but are often a sign of stormy weather. 

Cirrostratus are transparent high clouds with bases of 20,000 to 40,000ft. They cover large areas of the sky. They sometimes produce white or coloured rings around the Sun or Moon known as halos. 

Cirrostratus (Cs) are usually a sign that a front will arrive within 24hrs.