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.

What does it mean when you see mammatus clouds?

Mammatus clouds most often signal that a storm is on a weakening trend. These clouds are formed in part by sinking air. ... While mammatus clouds are commonly associated with severe weather, like the storm on the Gulf Coast, they don't cause severe weather themselves, according to NOAA.

How long do mammatus clouds last?

Mammatus clouds are pouch-like protrusions hanging from the undersides of clouds, usually thunderstorm anvil clouds but other types of clouds as well. Composed primarily of ice, these cloud pouches can extend hundreds of miles in any direction, remaining visible in your sky for perhaps 10 or 15 minutes at a time.