What You Need to Know:
Name(s): Mammatus, Mammatocumulus, Mamma
Common Altitudes of Formation: 4000m-7500m
Signals: The cloud supplementary feature usually warns of thunderstorm activity or severe weather
Meaning of the Name: Mamma (Latin for udder)
Elaborated, More Comprehensive Information
If a cloud contains a large amount of water or ice and its surrounding air is warmer than the sinking air, mammatus clouds can form. Because of this, these clouds are not very common. The supplementary feature forms under the base of clouds like cumulonimbus cirrocumulus, altostratus, altocumulus and stratocumulus. They are bulging, distinctive protrusions- basically upside down, globular clouds! The time that mammatus clouds remain in the sky for depends on how large the drops of water or ice in the sinking air are. This is because larger drops take longer to evaporate. It is rumoured that Mammatus clouds signal a tornado formation, but this is fiction. Instead of tornadoes, they tend to be associated with thunderstorms and severe weather.
-Photo by Richard Busfield