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The 9 Different Types of Clouds

Clouds are puffy, flat, flaky, wispy or veil-like phenomena made from water droplets or ice crystals that continually move and change shape due to evaporation, wind or air currents. They can come at all altitudes -- a cloud close to the ground is called fog -- and some bring rain, snow, hail or other precipitation. There are at least nine different types of clouds.

Cirrus
- Cirrus clouds are found above 20,000 feet. These long, wispy clouds are made entirely of ice crystals. Species of cirrus clouds include the hairlike cirrus fibratus; cirrus uncinus, clouds that look like a comma or a hook because of wind shear; cirrus spissatus, clouds thick enough to hide the sun; cirrus castellanus, which displays elements like the turrets on a castle; and cirrus floccus, a cloud with little tuft associated with virga, precipitation that dissipates before it can reach the ground.
Cirrocumulus and Cirrostratus
- High-altitude clouds glow at sunset.
  
  Cirrocumulus and cirrostratus clouds form in the highest levels of the atmosphere. Cirrocumulus clouds appear thin, patchy and shadowless, and include several named species. Stratiformis has horizontal as opposed to vertical development, lenticularis takes the form of a lens, castellanus includes high turrets, and floccus is puffy and appears flaked. Cirrostratus clouds lie across the sky like veils and cause halos around the sun or the moon. Species of cirrostratus clouds include fibratus and nebulosus, which is also like a veil with no details.
Altocumulus and Altostratus
- Alto clouds appear between 6,500 and 20,000 feet and can be made up of water droplets or ice crystals, depending upon the time of year and atmospheric conditions. Altocumulus clouds are puffy, white or gray and come in layers or patches. Species of altocumulus clouds include stratiformis, lenticularis, castellanus and floccus. Altostratus are gray and bluish -- never white -- sheets or layers of cloud. They often completely cover the sky, and there may be enough gaps in the clouds to be able to see the sun.
Stratus, Stratocumulus and Nimbostratus
- Clouds and patch of blue over the ocean.
  
  Stratus clouds occur below 6,500 feet. They tend to be flat and gray and may bring rain. Stratus species include nebulosus and fractus, where the cloud elements are irregular but small and look ragged and shredded. These clouds change constantly and quickly. Stratocumulus clouds also lie low but display the puffiness of cumulus clouds. Stratocumulus species are stratiformis, lenticularis and castellanus. Nimbostratus clouds are thick, ominous, dark clouds that produce rain or snow.
Cumulus
- Cumulus clouds, or convective clouds, are substantial-looking clouds that puff upward into the atmosphere due to thermal air currents. They develop vertically and can appear at both low and middle levels of the atmosphere. Cumulus species include fractus and humilis -- pretty, fair-weather clouds. Cumulus mediocris are cauliflower-like clouds that don't bring precipitation, and cumulus congestus is a large, puffy cloud that might bring a lot of precipitation. A cumulonimbus cloud often signals a thunderstorm.

Nature