I was a Ren Fair actor at Black Point (Novato, Marin County) for years, and it could go from over 100 F. on stage to 55 F once over the San Rafael bridge to the East Bay.
I always have a jacket in my car. And no matter how i travel to San Francisco, i always bring a jacket - just going a few blocks in SF the temperature can drop 20 degrees F.
It's BART and bus, or transbay bus and local SF bus. It's over at 1833 Union Street (not to be confused with Union Square - nowhere near it). Check out http://511.org - you can put in the address of your destination and either the time you want to leave home or arrive at the destination, and it will give a several possible trips. (and be sure to set the proper day using the tiny calendar)
Yeah, driving around much of SF is really annoying (can't turn left here... nope, can't turn left here... nope, cannot make a #$*%& left turn here either!), not to mention the near impossibility of finding a parking spot.
But i LOVE The City, no matter how many times i go there i still see so many beautiful views.