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.
In fact, most clouds are formed by rising air. But mammatus clouds are interesting in part because they’re formed by sinking air. And 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 clouds from 2022
Mammatus clouds from 2021
Mammatus clouds from 2020
Bottom line: Mammatus clouds are bubbly-looking, low-hanging clouds often associated with thunderstorms. Learn more about them here and see photos.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. 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. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. 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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