Cumulus clouds - clouds that are piled up
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Cumulus clouds

Cumulus clouds
Cumulus clouds

Cumulus clouds are clouds that are piled up on top of each other. "Cumulus" means a pile in Latin, as in our word "accumulate" meaning to pile up. They are puffy clouds. Sometimes cumulus clouds are white and there are only a few of them in the sky; other times they can be heavy and gray.

Usually you get cumulus clouds when warm air rises from the ground carrying water vapor with it by evaporation. When the warm wet air rises up and meets some cold air, the water vapor gets colder and condenses into drops of water, making a cloud.

Cumulus cloud
More cumulus clouds

When cumulus clouds are white and puffy, that usually means it's not going to rain right away. But if they grow into big gray clouds, you can expect rain.

Bibliography and further reading about the atmosphere:

Learn by Doing - Clouds
More about clouds
More about Thunderstorms
More about Weather home

Copyright 2012-2015 Karen Carr, Portland State University. This page last updated September 2015.

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