Kind of interesting the stuff in NM is thanks to the base of the blocking being so far south. Not at all what is expected for winter. In the winter most forecasts have the base of the blocking much further north so the blocks reach much further north.
Dec 19 in 1998. Incredible they didn't get one until that big blast. 2008 really stands out as well. Both La Nina.
Another thing to note is outlying areas had much earlier freezes in a lot of the years SEA was late. 2016 is the big exception.