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Clouds are made up of millions of tiny water droplets. Clouds are made when quite warm, moist air rises into the sky where it cools down and condenses. Clouds can form in a few minutes or over a number of hours. There are many different types of cloud and looking at them can help you to predict the weather.

Cloud can be measured through a number of observations. Consider whether the cloud is:

HIGH
(5,500-14,000 meters)
Includes: Cirrus, cirrocumulus, and cirrostratus
MEDIUM
(2,000-7,000 meters)
Includes: Altocumulus, altostratus, and nimbostratus
LOW
(below 2,000 meters)
Includes: Stratocumulus, Stratus, Cumulus, and Cumulonimbus
Name
Colour
Description
Weather
HIGH
White
Thin silky and feathery
Fair
White
Ripples/bumps
Fair
Whitish
Fat, smooth transparent sheet
Worsening
MEDIUM
White/grey
Layers and waves often separated by blue sky
Fair
Greyish
Thin sheets/layers
Rain on way
Dark grey
Thick sheets
Continuous rain/snow
LOW
Grey/white
Layers in rounded rolls. No breaks.
Dry/dull
Grey
Thin sheet blanketing sky
Drizzle
Grey/white
Puffy clouds
Good
Grey/white
Very tall puffy clouds
Storms. Heavy rain/hail/snow
The cloud types above are the most common in the UK, though more unusual clouds may sometimes be seen. In May 2004, mammatus cloud was visible at the base of a cumulonimbus formation over Broad Oak Nature Reserve.

The amount of cloud in the sky is measured in eighths (or oktas by meteorologists). Simple observation can be made such as
Clear - no cloud cover
Partly cloudy - less than half cloud cover
Mainly cloudy - more than half cloud cover but with some breaks in the cloud
Overcast - complete cloud cover