I'm no expert
I've only lived in the Seattle area for about three years so there are others who can certainly give better advice, but I think you'd be fine. It seems like the low soggy clouds usually come in around November and hang around after that. Due to the water nearby our temps are usually too warm for icing if you are willing to stay at the lower altitudes (terrain permitting of course). December above 3,000 - 4,000 different story . . .