Cloud Types

Clouds are classified by their height in the atmosphere and appearance.

Clouds 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 cystrals 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)
  • Cirrostratus are high clouds, composed of ice crystals.
  • 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 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 grey 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
  • Appear as low patches or sheets of grey to white cloud, with individual rolls or rounded masses.
  • Do not usually bring precipitation.
Stratus (St)
  • Stratus clouds are low level clouds composed of water droplets.
  • 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 grey clouds with a ragged base. Sometimes they cover the entire sky.
  • Indicate rain in the very near future.
Cumulus (Cu)
  • Cumulus clouds are low level clouds, composed of water droplets.
  • They are have a puffy appearence, a flat base and are white or light grey.
  • Indicate fair weather unless they grow vertically.
Vertically Developed 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.
Other Clouds
  • Contrails are visible trails of condensed water vapour made by the exhaust of aircraft engines.




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