Curious cloud

[Crosswhinge]

At a safety seminar a photo of a the underside of a darkish and very lumpy cloud was shown. This was said to be dangerous and avoided. What was this warning about?

[john_tullamarine]

Perhaps, this sort of item - https://www.avwxtraining.com/post/a-look-at-mammatus-clouds

Mucho bumps, big time, and one probably is better off staying away from them ....

[deltahotel]

And last night some truly lovely noctilucent clouds