To be fair a lot of it has to do with micro climates as well.
https://www.worldatlas.com/articles/...francisco.html
This article is just about SF itself but it applies to the whole bay area too - it can be a beautiful, 75 degree sunny day in San Mateo, and 50 degrees with fog and rain on the coast in Half Moon Bay. So you get tourists coming in for a beach day, realizing halfway there the weather sucks, and turning around
Conversely sometimes it's cloudy and overcast and cold inland and nice and balmy and sunny on the coast.