Here in Puget Sound we have ordinary days with temperatures in the 40's and high 30's and occasional tender-plant-destroying arctic blasts with lows in the teens. Those are really the only reason our official zones are in the 7 to 8 range.
But..... these low temperatures rarely last for more than a week, often less. Pots of florist's cyclamen and baskets of fuchsias that live on a porch can be tucked indoors for the duration. Bright light is best, but even a dark basement is fine.
A San Francisco garden on a Seattle porch? Why not?
A few things to remember:
Use plants that naturally do well in cooler weather, either annuals that bloom until frost or perennials that live over in zones 9 and 10. Those that don't bloom through winter will make a quick start in spring.
Herbs are naturals for pot gardens. Cilantro, in particular, does well through cool months.