Indian Summer.

San Francisco doesn't really have seasons, it just has periods where:

(A) It's rainy, cold, damp and miserable. This has happened to me in January and June.

(B) It's perfectly clear and warm and sunny and amazing. This has happened to me in September and December.

Other then those two "extremes" the rest of the weather out here reminds me of Indian Summers back in the Midwest. This magical time of year happens on a lucky October where the first frost has already gilded a chilly morning and leaves have already begun to fall from the trees. You usually notice it as you are walking to work and decide it's too warm for a jacket. Then you stop to notice all the birds singing and by the time you start walking again you realize that you need to put your jacket back on. The weather cannot make up its mind and neither can you. But by the time you have begun your shift you are already pining for the walk home, and wondering if it will still be light out. It is the time of year for long meandering bicycle rides, crisp apples, afternoon naps in dappled sunlight, and impossibly blue skies. Every so often the north wind begins to blow, a taste of the long cold winter to come and a reminder that everything is fleeting.