Speaking of the possibilities in the current climate we have. Even with the warming we've had in the past 70 years or so January 1950 would still end averaging well below 30 degrees for SEA. Jan 1862 averaged around 21 at Fort Vancouver and 22 and Fort Steilacoom so those would still equate to like 26 or so now.
I know that Nisqually had a very wicked winter in 1833-34, based on diary entries from a person in the Hudson's Bay Company. He made reference to heavy and deep snowfall from a couple of different periods that winter.
I see what your saying, but almost every winter had an insanely good month that decade. December 1884 alone was like 5 or more winters worth of snow now.
I think I would choose the 1860s over the 1880s down your way, because January 1868 had a lot of snow there and here it was just very cold and dry.