Dragonsfire: Yeah I've been there done that , where I run into problems is when I need the cloud to have a very specific shape.

I need to create a Supercell that morphs to having an Anvil top and eventually a tornado forming out of it.

The shape changes over a period of time but I can't seem to get the right kind of particle shader to make it look good.

I used the make cold breath tutorial and tried modifying the expressions abit. This is the closest I've come to getting something looking good. I can get them to look good at the beginning of the animation but when the cloud is needed to get bigger then too many particles fill the geometry and I loos any of the subtle contours that were present in the earlier part.

I may have to create several emitters for various parts of the geometry or something.

Thanks for the help guys, please keep it coming. I wish I had fluids at Work.