Make sure to buy vitamin D supplements, a sunlight lamp, and generally check in with yourself during the wet months. I'm from LA and went to Seattle for college. I ended up transferring because SAD fucked me up pretty badly.
Definitely not saying this to discourage you, it's a great city. Depending on where you live it's super walkable, the public transit has greatly improved in recent years and there's fantastic food (especially in the ID). I just wish I would've been better prepared so I could've taken advantage of more that Seattle had to offer.