It is a phenomenon that is distinctly Californian. Other places might have radiation fog or something technical like that...we have Tule Fog. (say "tooley") Named for the tule reeds that grow in marshes and the Tule Elk that were native to the Central Valley.
Sometime this winter or next you will turn on your evening news and read of a "massive pileup" on a Central Valley highway. Sometime in the next five years I will call my mom and tell her "I wasn't in it" because one will be local. You may catch The Discovery Channel showing one such incident with our then Fire Chief giving the play by play. Someone Normy worked with never got to work that day. It took several days to identify his remains from that fiery crash. Four others died with him that day on I-5. The cause? Driving too close too fast in fog that reduced visibility for cars to "barely past your bumper". Big rigs probably had better visibility.
Because of the Tule Fog.
At this time of year, the Tule Fog isn't deadly. It does come in and stay for a week. You won't see today's Tule Fog on satellite weather photos like you will in January. The Tule Fog is a curiosity. It just sits there. On the side of the road. It doesn't cross the road. It doesn't "roll in" like the marine fog of the coast. It just rises up out of the ground. It is most dense at the ground and is less so at higher points. Sometimes you can walk through Tule Fog and see just fine. But sit down on the ground and you are in the soup.
Dropping the child at school these days means driving past the Tule Fog. Not through. Past. The catch basins just hold the fog like soup in a bowl. Tule Fog seeks the lowest point. It will rise out of the field and sink into the catch basin, floating on top of the water. As the sun rises and warms the damp fields, the Tule Fog will get more dense and rise higher. Tule Fog requires warmth. But not too much. Too much warmth and it evaporates. In January, it will be so dense it won't let the sun through to warm us up and we will be socked in for a week.
The only cures for the Tule Fog are wind and rain. A new storm will wash it away (and set up conditions for another round) and wind will blow it away and allow the sun to shine again.
But for now.... I will enjoy watching fog rise from the ground and sit by the side of the road. I know that later it will hide the schmuck who comes upon it suddenly and slams on his brakes causing all the other schmucks following too closely to slam into him and each other. Later it will be deadly. But now? Now I will enjoy the spooky wonder of the Tule Fog.