cloud

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

Altitude	Name	Colour	Description	Weather
HIGH	Cirrus	White	Thin silky and feathery	Fair
	Cirrocumulus	White	Ripples/bumps	Fair
	Cirrostratus	Whitish	Fat, smooth transparent sheet	Worsening
MEDIUM	Altocumulus	White/grey	Layers and waves often separated by blue sky	Fair
	Altostratus	Greyish	Thin sheets/layers	Rain on way
	Nimbostratus	Dark grey	Thick sheets	Continuous rain/snow
LOW	Stratocumulus	Grey/white	Layers in rounded rolls. No breaks.	Dry/dull
	Stratus	Grey	Thin sheet blanketing sky	Drizzle
	Cumulus	Grey/white	Puffy clouds	Good
	Cumulonimbus	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