The distinctive lumpy appearance of mammatus clouds is a striking and fascinating insight into the unusual world of clouds.
Mammatus clouds are some of the most unusual and distinctive clouds formations with a series of bulges or pouches emerging from the base of a cloud. The shape of mammatus formations can vary widely; from the classic protruding shape, to a more elongated tube hanging from the cloud above.
Mammatus clouds are usually formed in association with large cumulonimbus clouds. Typically turbulence within the cumulonimbus cloud will cause mammatus to form, especially on the underside of the projecting anvil as it descends to lower levels. This reverses the usual cloud-forming process of upward growth, making for an uneven cloud base.
Cumulonimbus clouds are also known as thunderstorms, these clouds are huge and often unstable. Mammatus clouds often form on the most unstable cumulonimbus, meaning that there is also a chance of hail, showers and lightning in the vicinity. Sometimes mammatus may form on other cloud types which produce no rain, though this is far less common.
Mammatus comes from the Latin mamma which translates to "udder" or "breast". Their striking appearance is most visible when the sun is low in the sky and their pouches are framed by the sunlight. This supplementary feature is a firm favourite with many meteorologists and cloud enthusiasts.
Mammatus usually form on the base of a cumulonimbus anvil, but they have also been sighted to form on other cloud types, such as stratocumulus, altostratus and altocumulus. Mammatus have also been observed to form on the underside of volcanic ash clouds.
Last updated: 5 August 2016