Some render artifacts on this one, apparently where the spheres overlapped. I think this was about a 45 min render, 800 x 600. To make the cloud material, I started with a cumulous vol. cloud mat, made the color white, and messed with the function. I added some rotation to the smooth noise. This makes the clouds look windblown. I also added a fractal layer. Then I had to play with the ambient, diffuse and luminosity till it looked right. Different atmospheres need different settings. The clouds are all primitive spheres that are a little flattened. I think the size of the mat was set to 20. Playing with the size will change the look of the clouds greatly. I'm trying to figure out how to make a good thunderhead. Not there yet!

I have played a lot with volumetric clouds and I have to say these are the best results I have seen yet !

Great work, thanks for sharing how you did it... :)

Attached Link: http://www.expandingwave.com/thunderheads

What an interesting set of experiments! Do you think a simple thunderhead body like this might help. Try the download - it does taper to the back, although not shown in the clip. If this gets even close to helping, I can make another with any tweaks you suggest.

Oh yes, I can roughen up the surface of a model like this, or make it have soft round, but irregular surfaces, or just about anything that might help. I'm really interested in this, so I'll help, if this kind of object is any help. (Sitting here writing really boring logic code for a database for the next 24 hours anyhow.)

When you say that the clouds started as primative spheres, was each cloud one sphere, or a few grouped (or booleaned) together? Great looking clouds btw!

Glad some people are interested in this! Ok, I've tried making clouds with imported objects or boolean objects or terrains and it won't work. It seems the only thing the volumetric materials work on are Vue primitives. You can, however, overlap your spheres to make denser clouds. Just make a copy of one sphere and offset it a little. If you overlap them exactly you will get a lot of noise.