Chapter 13, Annex D COMMON CLOUDS

Cirrus

High

High, thin, wispy clouds blown by high winds into long streamers. Cirrus clouds usually move across the sky from west to east. They generally indicate pleasant weather.

Cirrocumulus

High

Appears as small, round white puffs. The small ripples in the cirrocumulus sometimes resemble the scales of a fish. A sky with cirrocumulus clouds is sometimes referred to as a “mackerel sky”.

Altocumulus

Middle

Appear as grey, puffy masses, sometimes in parallel waves or bands. The appearance of these clouds on a warm, humid summer morning often means thunderstorms will occur by late afternoon.

Altostratus

Middle

A grey or blue-grey layer cloud that typically covers the entire sky. In the thinner areas of the cloud, the sun may be dimly visible as a round disk. This cloud appears lighter than stratus clouds.

Stratus

Low

Uniform grey layer cloud that often covers the entire sky. They resemble fog that does not reach the ground. Usually no precipitation falls from stratus clouds, but sometimes they may drizzle.

Nimbostratus

Low

Dark grey layer clouds associated with continuously falling rain or snow. They often produce precipitation that is usually light to moderate.

Stratocumulus

Low

A series of round mass that form a layer cloud. This type of cloud is usually thin enough for the sky to be seen through breaks.

Cumulus

Vertical Development

Puffy clouds, which are thick, round, and lumpy. They sometimes look like pieces of floating cotton. They usually have flat bases and round tops.

Cumulonimbus

Vertical Development

Thunderstorm clouds that form if cumulus clouds continue to build. Violent vertical air currents, hail, lightning, and thunder are associated with the cumulonimbus clouds.