Have you ever seen mammatus clouds, the lumpy sort of cloud formations that look like huge puffs of candyfloss hanging in the sky?
There are many types of clouds: nimbostratus, cumulonimbus, cumulus and cirrus are probably the best known.
But there are also stratus, stratocumulus, altostratus, altocumulus, cirrocumulus and cirrostratus clouds.
And, of course, there's the phenomenon known as noctilucent clouds, or night-shining clouds, which can be seen during summer months.
Mammatus clouds are a little different, because ‘mammatus’ (also known as ‘mamma’ or ‘mammatocumulus’) isn’t a type of cloud at all.
Rather, it’s a very specific feature that can be found on clouds of several types, although it’s most closely associated with cumulonimbus rain clouds.
What mammatus means and why they're lumpy
The word ‘mamma’ means ‘udder’ or ‘breast’ in Latin, which is a clue to the phenomenon we’re discussing here.
‘Mammatus’ clouds have distinctive ‘lumpy’ undersides that look a little bit like the udders of a cow. Sometimes.
We’d say “like looking up at a bucket of popcorn, or a load of cotton wool balls” would be a better description, but to be fair, we’re not sure what the Latin for that would be.
These ‘lumps’ are composed largely of ice, and the mechanism responsible for their formation isn’t entirely understood.
Some have suggested mammatus clouds form when pockets of colder, heavier air descend 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.
However they form, they can be smooth or ragged in their appearance, and range in colour from a brilliant white to near-transparent. But they’re almost never a good sign.
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.
And if you’re doing some outdoor observing, now might be a good time to start packing your gear away.
Similarly, pilots will generally avoid flying through mammatus clouds if they can help it, as they’re extremely likely to cause turbulence.
Photos of mammatus clouds
