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ART OF CLOUDS Clouds that look like things Mammatus clouds The word ‘mamma’ means ‘udder’ or ‘breast’ in Latin. ‘Mammatus’ clouds have distinctive ‘lumpy’ undersides that look a little bit like the udders of a cow. Sometimes. These ‘lumps’ are composed largely of ice, and the mechanism responsible for their formation isn’t entirely understood. Some have suggested they form when pockets of colder, heavier air descends through the cloud while, warmer, lighter air is causing the cloud as a whole to rise, but other proposed mechanisms have ranged from thermodynamics to the effects radiation. Stormy weather ahead If you spot mammatus on the undersides of nearby clouds, it’s often a pretty reliable indicator that a storm or other extreme weather event is on its way.