Some sort of mist layer which truncates abruptly. It seems to only happen with the FSX online generated weather. It looks like ####. Anyone have any ideas?

That's the haze layer, and it was implemented the same way in FS9, just bigger this time around. Its just a giant plane of translucent polygons that follows you around whenever the nearest weather station is showing reduced visibility below your current altitude. Activesky was able to disable that ugly thing in FS9, but currently I know of no way to get rid of it in FSX yet, other than figuring out which texture it uses and making it black with zero alpha channel.If you don't want to see it though, just make sure there are no large shifts in visibility layers in your weather settings. Make one visibility layer only, and you shouldn't see it.With "real world weather" though, you'll end up with those at various weather stations.

The real thing is pretty ugly as well... http://arvamont.com/AK-Images/04-07%20olym...20mt%20hood.jpg...although I guess the sim doesn't make it dense or smooth enough to look realistic.

It does do a better job of for overcast conditions.http://forums.avsim.net/user_files/161915.jpg