Largest area "Fog type" spell?

[phaedrusxy]

I'm looking to fill an area with an invisible fog spell to screw over a bunch of invaders that will likely all have True Seeing up. What D&D spells have a massive area and create some kind of non-illusionary vision-obscuring effect? Guards and Wards looks to be the top contender so far, but I'm wondering if I'm missing something.

[rot42]

Would Control Weather work? Storm of Vengeance is not really city friendly but gives reduced visibility. Fimbulwinter in Frostburn gives you a huge area of winter, which can be stormy, much like Control Weather. There is also the Sandstorm spell in (wait for it) Sandstorm, though it only gives Spot penalties, not actual concealment.

[phaedrusxy]

The environment is a huge underground system of caverns, so probably not. Thanks, though.

[X-Codes]

Sleet Storm has a 40' radius, blocks vision better than fog, and screws over movement regardless.

[sirpercival]

I still think a widened G&W is the way to go.  Unless you can come up with some crazy way to use the water in the river, without killing all the fish.

[X-Codes]

Oh, Guards and Wards is on the list... No, that pretty much takes the cake.