You can also use weather effects to create "puffy" fog if you will.
You will need to setup weatherzones for this - check out the sticky tutorial on www.map-center.com.
A quick way of seeing this is to open the console and type:
R_WE HEAVYRAINFOG or
The more you type it in, the more gets added.
This fog swirls and twirls and generally looks okay. If you set it up in Radiant following the tutorial, you can add a _color key to get it to blend in properly with your map.