Mammatus Clouds

Inspired by this page. I picture Mammatus Clouds doing mostly, or entirely, instrumental music. Maybe a bit like Ozric Tentacles.

Most clouds form in rising air, but mammatus clouds form in sinking air, which is cooler than the air around it and has a high liquid water or ice content. They get their name from the fact that they look like cows' udders.

Here is an example: