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Cloud Formation and Weather Fronts - Windows to the Universe

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Cold air is more dense than warm air, so when a warm air mass meets a cold air mass, the cold air ends up below the warm air. Once the air has risen, it cools and clouds can form.
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Cloud Formation and Weather Fronts

Weather fronts can cause clouds to form. Fronts happen when two large masses of air collide into each other at the Earth's surface.

Warm fronts produce clouds when warm air replaces cold air by sliding above it. Many different cloud types can be created in this way: altocumulus, altostratus, cirrocumulus, cirrostratus, cirrus, cumulonimbus (and mammatus clouds), nimbostratus, stratus, and stratocumulus.

Cold fronts happen when heavy cold air moves the lighter warm air, pushing it upward. Cumulus clouds are the most common cloud types that are produced by cold fronts. They often grow into cumulonimbus clouds, which produce thunderstorms. Cold fronts can also produce nimbostratus, stratocumulus, and stratus clouds.

Last modified May 21, 2009 by Becca Hatheway.

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Weather Fronts

Weather fronts can cause clouds, rain, thunderstorms, gusty winds, and even tornadoes. Usually the skies clear once the front has passed. Weather fronts happen because not all air is the same. In some...more

Altocumulus

Altocumulus clouds are part of the Middle Cloud group. They are grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups. Altocumulus clouds are about...more

Altostratus

Altostratus clouds belong to the Middle Cloud group. An altostratus cloud usually covers the whole sky. The cloud looks gray or blue-gray. The sun or moon may shine through an altostratus cloud, but will...more

Cirrocumulus

Cirrocumulus clouds belong to the High Cloud group. They are small rounded puffs that usually appear in long rows. Cirrocumulus are usually white, but sometimes appear gray. Cirrocumulus clouds are the...more

Cirrostratus

Cirrostratus clouds belong to the High Cloud group. They are sheetlike thin clouds that usually cover the entire sky. The sun or moon can shine through cirrostratus clouds. When looking at the sun through...more

Cirrus

Cirrus clouds are the most common of the High Cloud group. They are made of ice crystals and have long, thin, wispy streamers. Cirrus clouds are usually white and predict fair weather. ...more

Cumulonimbus

Cumulonimbus clouds belong to the Clouds with Vertical Growth group. They are also known as thunderstorm clouds. A cumulonimbus cloud can grow up to 10km high. At this height, high winds make the top...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF