Rapid City Mammatus Clouds
October 11, 2006
The remarkable mammatus clouds shown above were photographed from Rapid City, South Dakota, at sunset, on July 26, 2006. These reddened sky pouches formed after a 45 minute rain storm at the close of a hot summer's day. Mammatus clouds most often result from down-drafts of cold air within mature thunderstorm cells and are usually observed on the underside of a spreading cumulonimbus anvil. Displays of mammatus clouds can last anywhere from a few minutes to an hour or more.