An "asperatus" cloud rolls over New Zealand's South Island in an undated picture. This apparently new class of clouds is still a mystery. Photograph courtesy Merrick DaviesExperts suspect asperatus clouds' choppy undersides may be due to strong winds
Big Sky CUMULONIMBUS Cloud - II A little later, as the sun set, the storm looks quite different. This kind of complete view of a thunderstorm cloud is typical of the US Great Plains - Big Sky country. Photo by Kay Cunninghan, a Texas rancher, May
Mammatus, also known as mammatocumulus (meaning “mammary cloud” or “breast cloud”), is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. Photograph by Matt Saal.