Mammatus Over Boulder, Colorado

January 05, 2006

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Provided and copyright by: Claudia Perko, Clara Barton H.S., Brooklyn, NY
Summary authors & editors: Claudia Perko; Jim Foster

The above photo was taken on July 14, 2005, in Boulder, Colorado and shows a beautiful example of mammatus clouds. Since it was my first time seeing such unusual clouds, they kept my attention for a long time, expecting heavy rain any minute. However, these intriguing clouds moved on and not a single drop of rain fell from the sky. My misconception was clarified after reading more about them. Mammatus are typically caused by down-drafts of cold air within mature thunderstorm cells, and they usually form on the underside of the spreading cumulonimbus anvil, which can be some distance from the rising part of the storm cell, where heaviest rains tend to occur. Although they can be quite imposing, the sinking air required to form these clouds actually indicates that the storm cells are diminishing in strength. They don't produce severe weather, nor should they be assumed as an indicator that a violent storm is imminent.

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