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Cloud Formation - Windows to the Universe

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View of cumulus clouds from the Great Sand Dunes National Park and Preserve near Alamosa, Colorado.
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Courtesy of Olga and Sergei Kuznetsov

How Clouds Form

A cloud is composed of tiny water droplets or ice crystals. A series of things have to happen in order for these water droplets or ice crystals to form into clouds in the atmosphere, and different types of clouds form in different ways. The four main ways that clouds can form are:

All of these processes involve the cooling of air. Warm air is able to hold larger amounts of water vapor than cool air, so when air cools it can't hold as much water vapor as when it was warm. This extra water vapor begins to condense out of the air into liquid water droplets.

Water vapor usually needs some sort of particle, such as dust or pollen, to condense upon. These particles are called condensation nuclei. Eventually, enough water vapor will condense upon condensation nuclei to form a cloud. The water droplets in the cloud may eventually fall down to Earth in the form of rain or snow (or other forms of precipitation).

Last modified May 21, 2009 by Becca Hatheway.

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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