Cloud Types

Clouds are classified by their height in the atmosphere and appearance and form at three height layers: High Level Clouds form at 16,000 - 45,000 ft (5 - 13 km) - Cirro Prefix, Mid Level Clouds form at 7,000 - 25,000 ft (2 - 8 km) - Alto Prefix, Low Level Clouds form at land surface - 7,000 ft (0 - 2 km) Clouds are also classifed by appearance containing the following words: Cirrus - wispy and thin. Cumulus - Puffy appearance. Stratus - Flat and/or layered. Nimbus - Contain Precipitation.

High Level Clouds


Cirrus (Ci)

Cirrus are high clouds which are composed of ice crystals that originate from the freezing of supercooled water droplets. They are thin and have a wispy appearance, and are often transparent. Usually indicates a change in weather will occur within 24 hours.


Cirrocumulus (Cc)

Cirrocumulus are high clouds, composed of ice crystals. They appear as small individual cloudlets in rows. No shading can be seen on the lower surface. Usually indicate fair weather for the near future.


Cirrostratus (Cs)

Cirrostratus are high clouds, composed of Ice Crystals. Thin and uniform appearance, often covering the whole sky. A halo of the sun or moon can usually be seen through the cloud. Usually indicate rain or snow within the next 12 - 24 hours.

Mid Level Clouds


Altocumulus (Ac)

Altocumulus, sometimes referred to as 'mackerel sky' because of the resemblance to the markings found on mackerel fish, are Mid level clouds composed of water droplets. Similar to Cirrocumulus, but have larger individual cloudlets, and shading can be seen. If seen in the morning, prepare for a thunderstorm in the afternoon.


Altostratus (As)

Altostratus clouds are mid level clouds composed of ice crystals and water droplets. Generally uniform and gray in appearance, and frequently cover the entire sky. The sun or moon may also be seen through them, but is usually quite fuzzy. Tend to indicate a storm some time in the very near future.

Low Level Clouds


Stratocumulus (Sc)

Stratocumulus clouds are low level clouds composed of water droplets.

They appear as low patches or sheets of gray to white cloud, with individual rolls or rounded masses and do not usually bring precipitation.


Stratus (St)

Stratus clouds are low level clouds composed of water droplets. They appear as a uniform greyish layer and often cover the entire sky. They can sometimes cover hill tops. Often bring drizzle or light snow.


Nimbostratus (Ns)

Nimbostratus clouds are low level clouds that might consist entirely of cloud droplets or raindrops, or of ice crystals and snowflakes. They are thick gray clouds with a ragged base. Sometimes they cover the entire sky. Indicate rain in the very near future.

Cumulonimbus clouds

Cumulus (Cu)

Cumulus clouds are low level clouds, composed of water droplets. They are have a puffy appearance, a flat base and are white or light gray. Indicate fair weather unless they grow vertically.

Vertically Developed Clouds

Cumulonimbus clouds

Cumulonimbus (Cb) Cumulonimbus clouds are Vertically Developed Clouds which are composed of water droplets and ice crystals. Appear dark and very tall often extending through all the levels of altitude, and can be several miles wide. They often appear in a shape similar to a mushroom. Usually indicate a storm in the near future. Rain, hail, thunder, lightning.