Half Moon Bay weather in December

Someone asked what time of day the fog rolls in during late December and got corrected, repeatedly: "fog is more of a summer phenomenon. It is more about clouds and rain in winter." One poster explains the mechanism — "fog is a function of the cold air over the Pacific being drawn to hot inland temps; in winter inland temps aren't hot, and ergo no typical fog" — so if December fog appears at all, it "usually doesn't roll in until around or after dark." What replaces it is storms, and the honest answer to any timing question in December is "it depends entirely on the storms, not time of day." Regulars suggest a Golden Gate webcam over a forecast. The other thing to plan for: "dark is pretty early, around 5pm." Our record: 12 rain days, 126mm, 9.6 daylight hours.