California normally has outstandingly good weather, unless it doesn’t due to rain or fog
Ever heard the Mamas and the Papas song, “It never Rains in California”?
Especially Southern California, when you can probably count on nine or ten months or more in a row without a single drop of rain.
Fog, on the other hand, can creep in when the inland valleys cool off at night and pull in the moist ocean air over land that has cooled off in the evening due to the clear skies, then you can get a very dense fog that takes a while to burn off in the morning.
Not quite the same as the notorious Tule fog farther north in California, which I can tell you is utterly miserable to drive through, but something similar.
https://en.wikipedia.org/wiki/Tule_fog
Tule fog is a radiation fog, which condenses when there is a high relative humidity (typically after a heavy rain), calm winds, and rapid cooling during the night. The nights are longer in the winter months, which allows an extended period of ground cooling, and thereby a pronounced temperature inversion at a low altitude.
Anyway, as mentioned on the aforementioned thread, the pilot expected a straight shot on his usual route, but was diverted due to the fog, then tried to fly under it along a roadway, then into it rather than land, and did not succeed in reaching his destination.