Cloud Gate - Kind of what I visualize it to be like in the upper cloud level
Here is another: http://www.youtube.com/watch?v=dlKEp-z9yzM
Cloud base is ~48km 1_barstow_pdf_14897.pdf
In that article are some nice pictures I hadn't seen about the lifecycle of the clouds, etc...
clouds-jgt.pdf is a nice whitepaper about real-time rendering (includes the technique I was coming up with on my own which he calls the "imposter ring"
Here is another RTCloudsForGames_HarrisGDC2002.pdf
Tracking map - http://www.turbosquid.com/FullPreview/Index.cfm/ID/608935
Genetica cloud map - http://www.spiralgraphics.biz/packs/terrain_volcanic_gaseous/index.htm?1#anchor
So Genetica is 512x512 ... bases to tops are 10 km max... 32808.4 feet
Clouds are drawn last so they blend with background but they don't have to write Z ... need to work with A channel on render target front to back (sorted internally I suppose?)