Thanks!

pikachu: You are absolutely right. There should be some turbulence and a sense of depth as well as some coloring. I doubt that such effects will be part of this pack anyway.
It`s great to have a former meteorologist here and I am happy about any hints.

This cloud was in fact one of the first attempts at creating a towering cumulus cloud. At that time I was happy to get some kind of realistic shape and texture. But this cloud is still not the thing that we see when we look at cumulus clouds in real life.
For example the lit side is kind of over exposed and the details get lost and the shadow part to the right looks like a patch of grey instead of maintaining some subtle details.

Below are some more images which are all just test renders and experiments, but they show some other aspects and development stages.

http://www.eonmusic.ch http://www.artmatica.ch