The best map to look at this time of the year is wunderground, here is the link. I like this map a lot as it shows LOCAL weather in different parts of Marin and you can watch as the fog comes in and the different temperatures in such a small County.
You'll likely have to plug in our zip code to center the map:
I LOVE this map! I use it at my Marin Seminar: http://www.MyMarinHouse.com