I will follow up with the weather and concur that it is very variable. At the very least you can be assured that it will be wet and cool to cold. But that is the Pacific Northwest in late November.
I lived in Vancouver, BC for 10 years, so I know the weather well.
The only year I did the Seattle Marathon I had to pull out at 10 miles with a severe calf cramp that I believe came on in part due to the 5 degree C weather and pouring rain! The only running/triathlon DNF of mine in the last 20 years.
If you are looking for Pacific NorthWest marathons in the future. I highly reccomend both the Portland Marathon in Late September and the Victoria( BC, Canada) Marathon on the second weekend in October. Both are well run events with typically, better weather.
Steve Fleck @stevefleck | Blog