Cumulus clouds - clouds that are piled up
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Cumulus clouds

Cumulus clouds
Cumulus clouds

July 2016 - 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. They're usually low-level clouds, only about 1000 meters (3300 feet) above the ground.

Cumulus cloud
More cumulus clouds

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.

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. White clouds are thin and let a lot of sunlight through them - that's why they look white. Gray clouds are thicker, with more water, and less of the sunlight can get through them.

Learn by doing: making a cloud
More about clouds

Bibliography and further reading about the atmosphere:

Learn by Doing - Clouds
More about clouds
More about Thunderstorms
More about Weather
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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