From ancient times on, people have looked to the sky to find out what the weather holds. Clouds are one way of forecasting the weather.
A cloud is a mass of water droplets or ice crystals that hangs above the surface of a planet. Clouds are visible and usually white in color, but can be gray depending on their density.
PHOTOS: Cloud TypesHigh Altitude Clouds: Clouds at high altitudes (16,000 feet and higher when observed near the equator) are made primarily of ice crystals. These clouds are cirrus clouds, cirrostratus, and cirrocumulus.
Cirrus are made of ice crystals and are shaped like feathery patches or wispy white bands. They are formed high in the sky and can be semi-transparent. Cirrus clouds generally don't forecast thunderstorms.
Cirrus uncinus clouds are long wisps of cirrus cloud that sometimes hook or curl at the end.
Cirrostratus clouds are often semi-transparent and cover the whole sky, sometimes creating a halo effect if they cross the sun or moon.
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Cirrocumulus cloud is formed from cirrus or cirrostratus clouds that are warmed from below. The warming process causes air to move around inside the cloud, making a rippling pattern. This pattern is sometimes called mackerel sky.
Contrails are cloud-like trails of water vapor that can be seen in the wake of airplanes, either from the heat of their exhaust or sometimes from their wing tips.
Lenticular clouds are lens-shaped, smooth-edged clouds that form at high altitudes, often appearing to sit above mountains.
Mid-Level Clouds Mid-level clouds are generally visible between 6,500 and 23,000 feet above the earth. The clouds in the higher ranges are made up of some ice crystals but are mainly composed of small drops of water. The main types of mid-level clouds are altocumulus, altostratus, and nimbostratus.
Altostratus clouds look like gray sheets or layers. These clouds often partially or completely block the sun. These clouds usually mean some type of precipitation, but as the snow or rain falls it often evaporates due to warmer air near the ground.
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Altocumulus is a cloud distinguished by patches of clouds. Often there is a larger middle cloud group, usually white or gray. These clouds are sometimes described as a series of small cotton balls across the sky.
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altocumulus mackerel sky or mackerel sky is a mid-level cloud group in which the clouds ripple like the scales of a fish. Similar to the cirrocumulus clouds, but at a lower altitude.
Altocumulus Castellanus clouds are often taller than they are wide, with towering billows rising from the cloud's base. Castellanus clouds are a sign of air turbulence, and are usually followed by bad weather.
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Nimbostratus cloud is a shapeless dark gray cloud layer. These are rain clouds.
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pileus (Latin for cap) is a small, horizontal cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei usually indicate strong weather.
Low Clouds The low-level cloud group includes those clouds that are found at the earth's surface (which would be fog) or up to about 6,500 feet in the sky. Low cloud types are stratus and stratocumulus.
Stratus clouds are flat, featureless clouds of low altitude that range in color from dark gray to nearly white. These clouds are basically fog that is above ground.
Stratocumulus clouds are large dark masses, usually found in groups, lines, or waves. The individual elements are larger than those in altocumulus.
Cumulus humilis clouds are billowy and flat-bottomed and usually indicate pleasant weather.
Cumulus mediocris is slightly larger in height than Cumulus humilis. This cloud type does not produce precipitation, but may change into clouds such as Cumulus congestus and Cumulonimbus, which do.
Pyrocumulus, or fire cumulus, is a dense cumuliform cloud usually found above fires or volcanic eruptions, usually at around 5000 feet altitude.
Cumulonimbus is a tall, dense, thunderstorm cloud. These clouds can form alone, in clusters, or along a cold front in a squall line.
Cumulus congestus clouds are humilis clouds that grow vertically as heat rises through the air. The bottom often stays flat like the humilis cloud from which it has grown.
