Obviously it's not 100% certain since it hasn't happened yet, but models have been extremely persistent about sending a Polar Vortex into Canada (at least), and blasting much of the northern tier of the US with "Arctic air" (however Arctic that can be in November).
How far west/east this cold air makes it is still a major question mark, but lots of model runs/ensemble members do bring the Arctic air into the Pacific Northwest at some point or another. The most favorable thing, in my opinion, is how long the large blocking ridge off the coast is expected to last. This should give Seattle/Portland numerous opportunities for cold shots, with snow a distinct possibility at times. If we can time a shortwave perfectly to coincide with the sagging south of a lobe of the polar vortex (and associated strong Arctic high just to the north), we could see a true Arctic outbreak in the Pacific Northwest (think November 1985 or 1955). That's still a relatively unlikely event, but that it's even a possibility is somewhat impressive.
One potential outcome is that the cold might be hung up at some point on its southward journey. Will it be north of the Canadian border? Seattle? Will it make it all the way to Portland? Will cold air east of the Cascades filter through the Gorge to Portland? These are all specifics that will have to wait several days, at least, for an answer. Until then, buckle up and enjoy the model ride!
gogo
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