Mammatus clouds are pouch-like protrusions hanging from the undersides of clouds. You’ll usually find them under thunderstorm anvil clouds. But you might see them under other types of clouds as well. They’re composed primarily of ices and groups of them can extend hundreds of miles in any direction. But they’re fleeting, remaining visible in your local sky for perhaps 10 or 15 minutes at a time.
People associate these cloud pouches with severe weather. And it’s true; they typically appear around, before or after a storm.
Most clouds are formed by rising air. But mammatus clouds are interesting in part because they’re formed by sinking air. You sometimes hear people say that mammatus clouds continue extending downward and can even form tornados, but that’s not true.
They appear ominous. And they do signify storms. But, in a way that’s so common in nature, their dangerous aspect goes hand in hand with a magnificent beauty.
Mammatus cloud photos from EarthSky’s community
Bottom line: A spectacular collection of photos of mammatus clouds.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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