Not all predators go downwind like coyotes do and coyotes don't always go downwind. Of the ones I have taken in the fog, they were in the open and easy shots as I recall.
Yep songdogslayer, good point. I always set up where I'm looking crosswind or downwind. In the case of fog, upwind would not be a bad idea if you go set downwind say maybe 50 yards.