Not from SF but live in the Bay Area, just down the road from Concord.
Lots of microclimates. That said, SF in particular rarely has extremes of any weather. Some heavy rains on occasion, one or two hot days. Otherwise, cool and beautiful.
If you plan to visit, remember what Mark Twain said: "the coldest winter I ever spent was a summer in San Francisco." It's true, despite the temps being mild, the wet, sea air and wind sends many tourists to the junk shops to buy a hoody and sweatpants. Best weather is in Sept and Oct.
Quakes are the major deal, obviously. Speaking of SF proper, "the city" as us locals call it, is on the end of a peninsula. It's not that big a city, less than a million I think, all crammed into that spot.
Much of the areas near the bay are built on landfill--very, very unstable in earthquakes. Such land can "liquify" in a quake. Anything sitting on them is FUBAR. Also, a lot of dwellings use natural gas for some appliances, which is why so many structures burned in the Loma Prieta quake of 1989.
It's a difficult city to get out of, and would be really messed up if a quake severed the bridges. The sizeable chunk of the Bay Bridge, linking SF to Oakland, collapsed. Several others were closed for inspection. By that time the damage was done. Lots of folks stuck where they were, at home, or in cars. The only way out of the city if the bridges are clogged or blocked is south.
Keep in mind that there are 100 cities in the area and around 7 million people. Want to get to the mountains from SF? You are SOL and probably better off walking.
I would not want to be there for a quake. I was in Berkeley for Loma Prieta and my wife was not too far from there. Never forget it. BTW, it was not "the big one" but it was bad enough.
It's possible there could also be tsunami as well, and of course terrorism. SF is a major financial center.
Lots of other places to live in the area w/o being actually in SF.