environmental manipulations (falling to earth from space)
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i never thought about steam, I will look into it
How are you using the Authoring Tools then? 
How are you using the Authoring Tools then?
He means he never thought about using the env_steam entity.
I think that was not meant to be serious.
In my timetravel (concept) map, for the portal opening and closeing effect, I placed several brush behind eachother, textured with a homogen glass (one that has the highest transparency) so each of them reduce the visibility of things behind them by 25-30%. And then I activated them one-by-one so it faded the things behind them into almost full invisibility, but only there, so looking to other directions everything was clear. I dont know if it can be uses withing clouds (if you want it to fall with the player and act as a fog, or just when you enter some fog particle (or floating textures with a fog and transparency) but if you turn several brush with glass on (brushes also can be nonsolid so you can fall into them etc) you may get a cool effect. Or just a glass-brush falling with the player (surrounding him). However since most glass use cubemap reflections, it can be tricky (unless you place cubemaps into small cubes with 0 light or something).
You want the player to see clouds under them in a horizontal cloud-line, and when he falls into one you want some fog-effect? Can the player turn around and look freely, or fixed view?
well its going to be a fixed view, but the player essentially starts the map off being worm-holed to earth. Now that I think about it, I forgot to put that wormhole element in. At any rate, the fading effect is just going to be an env_fade, but it only comes into play after a cloud of particles and steam show up. So I think I got what I need now. I just got to experiment with orientation and volume control.
Thanks for the help