Tule fog. Winter pea soup fog-apalooza in the Central Valley of California. I just rolled into town day before yesterday from spending a week in Northern California so had to drive through the whole deal from Sacramento (near San Fran) south to the Tejon Pass, as the road ascends into the Angeles Natl Forest north of LA, about 6 hours. I was carrying a large piece of artwork so driving to CA made more sense this year than the normally easy 1 1/2 hr flight from Phoenix.
Tule fog can be incredibly thick, causing big driving hazards too. It is a radiation fog variety that has Californians staring wishfully, hoping for any glimpse of veiled-out sunlight, for weeks at a time in December. There are even road signs along California highways that test for impaired fog visibility. They say - 100 ft, 50ft, 10ft, etc.
Quite often, especially the late night through early morning hours, tule fog can cause zero vis on the roadways. On a couple occasions where a patch takes drivers off guard, I have had to roll my window down and listen, using sound for driving enhancement, as headlights are often useless. Tule fog easily obscures even close objects. I remember one time the tule fog hid an entire locomotive, which I only knew was coming from the sound.
My perma-cure for winter sunlight deprivation when I lived there? Take up skiing. The more you ski, the more you get out of the fog layer and spend time on the sunny Sierra Nevada slopes within an hour's travel time, and have access to some of the best snow in the world (although it is wetter snow than the kind in Colorado). That's how I dealt with winter tule fog. In addition, driving trips or flights in the afternoons are better. The other way I dealt with it is I moved to the Arizona desert!
