Funny, I'll be up there, too. I know from past experience it can go either way, so I'm going to wait until the date is closer and check for forecasts. I have a couple of wool blazers and a suede jacket I'll consider taking.

Maybe this will help. Depending on where you live, 55 average low temp might feel cool enough for a sweater dress, or way too warm for one.

Here is a link that might be useful: Average temps in SF in Sept

San Francisco tends to be warmer and less foggy in September than it is in the summer - but at any time of year the evenings there are often cool. There is usually a substantial temp difference between day and evening.

oilychic-thanks for the average temp site-like here in southern California-sept. tends to be our hottest month. So I am going with the purple dress. Will wait to see how cold it will be in evenings to decide about the blazer or what I need for evenings. I have been to the bay area several times, but always in June or July, and it was freezing.

I live 30 mins south of San Francisco and it is a good rule to always plan for chill in the evenings and nights. Not sure ow much street walking you will do but the streets can be steep and the pavement may need a bit of navigation. Think manhattan with hills. I always prefer pants or dress with tights and very compy shoes with grippy soles when I go up to the "city". A scarf or a wrap is useful as well. Restaurants and places are pretty casual. You can see a lot of folks wearing tee shirts even in a fancy place.