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Cloud Classification Definitions

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Relatively large cumulonimbus producing most of the damage associated with severe thunderstorms. It can produce giant hail, flash floods, stong straight line wind gusts, wall clouds and tornadoes. Common features include an overshooting bulge through the top of the storm and a long life cycle - typically 2 hours or more. Is consists of mesocyclones which are rotating updraughts within the thunderstorm.
Cumulonimbus Incus Cumulonimbus with an anvil typically known as a thunderstorm. Also known as Cumulonimbus Capillatus.
Cumulonimbus Calvus Cumulonimbus or large cumulus with basically no anvil although the tops may become striated.
Cumulus Congestus Cumulus clouds which are markedly sprouting and are often of great vertical extent with tops resembling a cauliflower. Their heights exceed the dimensions of their bases.
Cumulus Mediocris Cumulus clouds of moderate vertical extent, the tops of which show fairly small protuberances. The base is a similar in width to the cloud height.
Cumulus Humilis Cumulus clouds of only a slight vertical extent. They generally appear flattened. Their bases are much wider than the their heights.
Stratocumulus Forms in layers sometimes hundreds of kilometres across. It usually has a ragged upper surface while the base is relatively flat. The most common cloud type.

Stratocumulus Lenticularis
Stratocumulus in the form of flat lens.

Stratus Stratus clouds form in sheets or layers in the lower parts of the atmosphere. Fog is classified as stratus.
Altocumulus Cumulus in the middle levels of the atmosphere associated with the lifting of a large air mass and instability.

Altocumulus Castellanus
Altocumulus which frequently exhibit turrets or bulges. These indicate instability in the middle layers of the atmosphere.

Altocumulus Lenticularis
Altocumulus in the form of flat lens that usually form as a result of the wind flow over mountains.

Altocumulus Mackerel Sky
Altocumulus in the form of globules or ripples.

Altocumulus Undulatus
Altocumulus clouds in patches, sheets or layers, that exhibit undulations.

Altostratus This cloud is found in the middle levels of the atmosphere and is always a sign of the presence of significant amounts of moisture in those layers. It is typically featureless, ranging from a thin, white veil of cloud through which the sun is clearly visible, to a dense gray mantle that may block out the sun completely.
Nimbostratus Rain producing cloud which varies in thickness and layers mostly occurring in a widespread sheet.
Cirrocumulus High level clouds that appear as small rounded puffs arranged in rows or sheets.
Cirrus Cirrus Fibratus
Ice crystal clouds in the form of thin elements that allow sunlight or moonlight to easily pass through.

Cirrus Dense
Ice crystal clouds which are more dense and allow less sunlight or moonlight to pass through.

Cirrus Uncinus
Ice crystal clouds that are often shaped like a comma, terminating at the top in a hook, or contains tufts in the upper parts.

Cirrostratus Ice crystal clouds that appear in the form of extensive sheets that may cover the whole sky.

Document: define1.htm
Updated: 1st February 2008
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