Ahh. I've always had that dilema. I'm born and raised in SF (almost always foggy) but moved to the east bay (HOTT) when I got married. I do a daily commute, so when I leave home, it's nice - it's freezing cold at work then on my way home, it's hot again.
I say play it safe and always expect the unexpected. Although Palo Alto has better season, it's still in the bay. lol.
TOPS: The key is LAYERING. I always start of with tanks (cheap, so if the washer/dryer at your place sucks, you can always get new ones easily.) Lightweight shirts and top it off with Button-up sweaters / cardigans / jean jacket. Bring a nice jacket for your fun nights out too.
Bring a number of good jeans (it doesn't get TOO hot for jeans) and shorts - for days you know it's gonna be good.
Shoes: If you don't mind your toes freezing everynow and then, then go ahead and bring some f.flops. Otherwise, I'd go with versatile ballet flats or sneakers and a good pair of all around heels.
Accessories: A good big purse is a must for me coz i bring all type of things in there. . (recharge water for hot days, a pashmina/scarf for those not so sure days.
Have fun and good luck!!