Right now it's summer one day of the week (70s), and winter the next(High: 50s, Low: 30s-40s.) It can get pretty cold in Santa Rosa, because it's far away from the bay.
This route will may you a few minutes compared to 19th Avenue during rush hours and will give you the most spectacular view of the ocean and of the Sunset and Richmond districts of San Francisco.
Well, if you have a few extra minutes, and it's daytime and it's not foggy/raining (it shouldn't be foggy, don't know about rain) then you may want to take one of the following routes from the airport:
When you get your car, take I-380 Wast to I-280. Then get off at CA-1, the exit will be called "Pacifica." If my memory serves me right, it'll be the third exit after you merge onto I280.
Then, stay on CA1 until you see a sign for CA35 North (San Francisco). This is the second exit, after the merge. When the traffic from the first exit merges, you need to change lanes, and take the exit (sounds complicated, in reality it isn't, look at the map).
Then take 35 down the hill to John Muir Drive. Pass John Muir drive, and merge into the left lane. Lake merced will be on the right. At the stop sign, turn left.
Here's the map for this leg of the trip
You'll pass the zoo on your right. The ocean will be on your left. Take the great highway all the way up to Golden Gate Park. (do not go over 35, because the lights are timed at 35). You'll see the windmill on your right in Golden Gate Park.
At this point you have two options: get out for a few minutes and stretch your legs by the ocean if the weather's nice, or continue on to your destination.
Up on the hill will be the newly-restored cliff house (overlooking the ocean). Above, will be a vista point called Point Lobos.
Map for this leg of the trip
View from Point Lobos at night:
If you want to visit the Vista point and get an overview of the Golden Gate Park and/or the Richmond/Sunset districts, park somewhere around
here
After this, take Geary Blvd to 34th Avenue, where you'll make a left.
map
Park there, and take a few pictures of the Golden Gate Bridge and the city.
Then continue on down to Sea Cliff, where you'll see 10+ million-dollar homes.
You'll pass Robin Williams' house on your left
map
From there, keep going straight, and you'll go right into the Presidio of San Francisco. Make sure not to speed here because the Park Police are VERY VERY stingy.
Follow Lincoln Blvd as it winds up the hill, and eventually you'll come to a 4-way stop. Go straight. Right after the stop, you'll pass under the freeway that's leading up to the Golden Gate Bridge. [map=http://maps.google.com/maps?q=El+Camino+Del+Mar+and+Sea+Cliff+Ave,san+francisco,+ca+to+Lincoln+Blvd+and+Vista+Access+Road,+san+francisco,+ca&hl=en]
You have two options: If you make two lefts, you'll get right onto the freeway. If you make a left and go straight, you'll end up at the Golden Gate bridge vista point.
OR if you have a few more minutes, go straight. As you round the curve, you'll get a very spectacular view of the city.
map.
If you look at the map, there's a street called 'hoffman'. You can park along there for a few minutes if you want to get out and take a few shots.
From here, backtrack to the Golden Gate Bridge Vista Point and stop there if you wish. Otherwise, proceed onto the freeway
map.
Proceed north on the Golden Gate Bridge. You can take the first exit after the bridge called 'vista point'. If you do, I still recomend visiting the following site:
Take the second exit (Alexander Ave), make a left at the stop sign, go under the bridge. After this, keep right. Go up the hill. At southern-most place, where you see many parked cars (sharp turn), do the same thing, and hike up to be as close to the GGB as you can.
map.
This is the view you should get (looking south):
[img=http://www.hoffmann.caltech.edu/PlacesVisited/html0001/images/Golden%20Gate%20Bridge%20&%20SF%208-03.jpg]
A good part of the city will be visible.
After you're done, backtrack and go under the bridge. Get onto the freeway (101 North) and go your merry way to Santa Rosa. Petaluma does have a nice historic downtown, but there's not much to see there, IMO.
A few general notes:
I wouldn't attempt to go into downtown during PM peak hour because the traffic is slow trying to get onto the Bay Bridge. That's why I'd recomend using the route that I provided. If you are traveling at other times, you may want to visit downtown. Be forwarned, parking is scarse.
traffic on 101N is usually heaviest during PM peak hour. We have carpool lanes for 2+ occupants on 101N in some places, so be aware of that.
Traffic especially bogs down around Central San Rafael.
For traffic reports every 10 minutes on the 8s turn to KCBS, 740AM.
Sorry for the very long post.
Let me know if you have questions.