text size: small medium large Clouds form when the air temperature reaches the condensation point or dew point, which is the point at which water vapor becomes a liquid. When it reaches this point, the liquid collects on dust particles in the air and become visible. If the temperature is far below freezing ice crystals will form instead of water droplets.
An Englishman named Luke Howard (1773-1864) developed a classification for clouds that is still largely in use. Howard noted that there are three basic shapes to clouds:
- heaps of separated cloud masses with flat bottoms and cauliflower tops, which he named Cumulus (Latin for heap);
- layers of cloud much wider than they are thick, like a blanket or a mattress, which he named Stratus (Latin for layer);
- wispy curls, like a child's hair, which he called Cirrus (Latin for curl).
- To clouds generating precipitation, he gave the name Nimbus (Latin for rain).
| Heaps: Cumulus family
fair weather cumulus swelling cumulus cumulus congestus |
Layers: Stratus family
stratus altostratus cirrostratus |
Layered Heaps
stratocumulus altocumulus cirrocumulus |
Precipitating clouds
cumulonimbus cirrus nimbostratus |
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Cirrus clouds are very high, thin, wispy clouds that are made of ice crystals. Sometimes they are called mare's tails because they look like the tail of a horse. |
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Cirrostratus clouds can be so thin that you barely notice them even though they cover the sky like a veil. Because they are made of ice crystals they create colorful shapes around the sun. |
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Cirrocumulus clouds are high and thin and they look like tiny cotton balls in a sheet. They don't block too much of the sun. |
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Altostratus are middle clouds, made of water droplets, that make the sky gray but usually you can see some sunshine through them. |
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Altocumulus are a lot like Cirrocumulus except they are made of water droplets and they are lower than Cirrocumulus. |
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Cumulus are the clouds that look like cotton balls. They can be small, medium, or large. |
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Stratocumulus are low, dark clouds that often bring showers. |
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Stratus clouds are low clouds that can totally block the sun. When they give us steady rain they are called Nimbostratus. |
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Fog is a cloud that is on the ground. Sometimes it is only a few feet thick. Other times it can be hundreds of feet thick. |
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Cumulonimbus is the thundercloud that grows tall and produces lightning, heavy rain, and sometimes hail and tornadoes. |
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A tornado is a cloud of violently spinning air that touches the ground. It is dangerous. |
High clouds include Cirrus, Cirrocumulus, and Cirrostratus. These are higher than 18,000 feet.
Middle clouds include Altostratus, Altocumulus. These can range in height from 6,000 feet to 20,000 feet.
Low clouds include Stratus, Nimbostratus, and fair weather Cumulus. These are typically below 6,000 feet.
The Cumulonimbus is in a special category since Cumulus clouds can grow to over 60,000 feet high!
Even the Post Office had clouds!
