I went outside this morning in Delhi at 7 am and saw all the fog.  Back in Switzerland I flew in fog all winter with no worries.  As long as the plane is bright is very slow, it's not too hard to track and very little chance of it getting lost (don't fly too high or too far!)

I got inspired to fly in this morning's thick fog and made this video.  Visibility was about 10 feet!

http://www.youtube.com/watch?v=AEOJxl0g4Hk&feature=player_embedded

nice flying buddy.