| When you look up at clouds in the sky, some clouds seem close enough to touch, and some seem to be very far away. Some days, the clouds even seem to form in neat, clean shapes.
Clouds can float from a few feet above the earth (fog) all the way up to 40,000 feet, and higher. There are eleven different classes of clouds. As the Cloud Chart illustrates, you can tell clouds apart based on how high they are in the sky (altitude) and their shape or how they look.
Cloud Type
Height |
Description |
Cirrus
20,000 to 40,000 feet |
Cirrus clouds are made of very fine ice crystals, which is why they have a somewhat soft, fuzzy appearance. |
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Cirrostratus
20,000 to 40,000 feet |
Cirrostratus clouds are the classical harbinger (sign) of bad weather. They form slowly, like a screen, until they finally cover the whole sky. |
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Cirrocumulus
20,000 to 40,000 feet |
Cirrocumulus clouds usually appear in large patches and are arranged in attractive looking formations. They most often form ahead of warm fronts, when a high-level air stream is blowing from the south. Cirrocumulus clouds are a sign of increasing humidity in the upper air. |
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Altostratus
8,000 to 20,000 feet |
From its looks, an altostratus cloud might be called the most "boring" type. Altostratus clouds most often appear gray in color, but can sometimes appear blue-gray. A growing, thick layer of altostratus clouds usually means it will rain soon, because they usually form when a storm front is approaching. |
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Altocumulus
8,000 to 20,000 feet |
Altocumulus clouds are the most common type of cloud and appear as big fleecy shapes, and are often confused with cirrocumulus clouds. Jet vapor trails, which look like long, straight clouds, form only at cirrocumulus level and help to tell the difference between cirrocumulus and altocumulus clouds. |
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Stratocumulus
below 8,000 feet |
Stratocumulus clouds are the most widespread type of cloud. Seen at sea under almost all weather conditions, they usually appear as a dense, low-hanging cover and usually dissolve quickly. Stratocumulus clouds often darken in the evening, but they are not a sign of bad weather. |
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Nimbostratus
below 8,000 feet |
Nimbostratus is another classic bad weather cloud. Prolonged rainfall usually comes with this cloud, which typically forms and appears with a warm front. Nimbostratus is a layer cloud, extending from just above the earth's surface to the upper boundary of the troposphere (about 7-10 miles above the earth). |
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Cumulus
8,000 to 45,000 feet (base to top) |
There are many different types of cumulus clouds - small, medium, or large size. Cumulus clouds usually formed at or around the spot in the sky where you see them, and almost always disappear within an hour. Their formation means upward movement of the air. |
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Stratus
below 8,000 feet |
Stratus clouds are the lowest-lying type of cloud, and generally appear in the form of fog or mist. When the weather report refers to a high, fog-type cloud, it is referring to a Stratus cloud. Stratus clouds have no structure (shape) and often form over the sea and along the coast. |
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Cumulonimbus
10,000 to 60,000 feet (base to top) |
Cumulonimbus clouds are thunderstorms. They form when a cumulus cloud shoots upwards so strongly that its upper region freezes. Cumulonimbus clouds usually develop a delicate, fuzzy structure, but they also can form caps or collars that resemble cirrus clouds.
When a cumulonimbus cloud's ragged-looking upper region spreads out like an anvil, it has moved against a barrier layer preventing any further upward movement. |
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Fog
Ground-level |
Fog refers to a cloud that lies close to the ground. Fog often forms in low-lying areas, such as valleys. |
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