May is lovely, but from June through August the skies are overcast and the temp is cool until about August when the sun finally shines on through the fall. But you can't beat the beauty of the area all year long.... more
Your info is correct...the weather in Tam Valley, with all due respect; sucks!
I lived near the intersection of Northern and Marin Avenue and couldn't wait to move. The fog rolls down Shoreline just after it swallows Sausalito, then it sits in the valley for the best part of many days. If you are unfortunate enough to be on the south side of the slope, with a northern exposure, you will be lucky to get 1 hour of sun in Winter.
I frankly would not even consider a house there outside of "Birdland", or well exposed sunny slopes in Tennesee Valley.
Prices are lower, and you will soon understand why.
All the best,