Lifelong Great Valley of California boy chiming in, here. I grew up near Fresno, and live near Sacramento.
Autumn—particularly after a summer drought—is the season of implacable wildfire. The so-called Camp Fire a few miles from here killed nearly a hundred people and destroyed 2/3 of the city of Paradise. The worst damage took place over the course of a single afternoon.
Winter doesn’t bring snow, here. But between the infrequent rains, when the air grows still and a couple of nights are clear and cold, you can expect the fog. Epic, apocalyptic, Barovia-level fog, blanketing everything for days or weeks. Fog so thick it’s common not to be able to see the color of stoplights, or read the numbers on a house—which is bad, when you are a paramedic trying to find someone who needs your help. But that’s in the city. If you get out into the surrounding farm country, a common practice was to creep up to an intersection because if you went too fast you’d miss the stop sign. Once you stopped at the edge of the intersection, you turned off your motor and radios and rolled down your windows. If you didn’t hear another vehicle approaching, then you started up again, with every light as bright as you could make it and your siren wound as tight as it would go.
That being said, there is one things I love about the fog. It muffles sound so much that the usual background of street noise, and neighbors, is absent. And, valley fog requires still air and an inversion layer (cold, heavy air acting like a lid on the bowl of the Great Valley, trapping warmer, water-saturated air underneath). It’s so still that you often can’t hear anyone else at all, and the inversion means that it’s really not that cold.
Anyway...I hope that gives you some ideas.
“To day is a good day to die for all the things of my life are present." --Crazy Horse, prior to the battle of Little Big Horn