john smith schrieb:

I've seen plenty of photo's of little titties on the bottom
of storm clouds, (I think they are usually Nimbo Stratus,
but not always), that dissipated.

Cumulo Mamatus

Close. Mammatus or mamma is not a cloud, but a special form of the cloud
base. It mostly appears on CBs, but can also appear with any other cloud
form. And yes, it's called mammatus because it resembles mammae, making
it one of the most erotic cloud forms.

So a cumulonimbus mammatus is a cumulonimbus with that special cloud base.