Try moving to New England from San Francisco.

Part of the difference is that you don't realize it's winter in San Francisco. New England winters make you very aware that it is in fact winter, and thus very legitimate about how you feel during said winter (crappy, lethargic, cold).

It also makes you supremely appreciative of life, spring, summer, and the fall that precedes it. I truly believe living in a place with seasons has made me a better, more self-aware person.

I have no doubt that SAD can strike you anywhere, but seriously, I highly recommend moving somewhere with a real winter. It will harden you and give you an invaluable perspective, and surely SAD will not strike you again in California.