[ADTech]

The swings in temperature are also likely responsible for the formation of inversion layers which will affect the propagation of signals from almost 60 miles away. Given your proximity to the coast, there also many be a different pattern of marine boundary layers that move in from off-shore and affect the radio path. The winter months are well known for the anomalous propagation conditions in Southern and Central California.

Your best countermeasure is to get some extra height on the receiving antenna since you cannot change the weather. In addition to getting the antenna into what would be expected to be a stronger signal zone, that extra height will also get the antenna further away from the roof which may be causing a destructive "ground bounce". You will likely have to experiment with the exact height (over time) to find what's the best compromise for your specific location.