Per my last post on the window for winter quickly closing, we have an interesting weather pattern materializing across the northeastern Pacific the next week to ten days. A series of rather benign frontal systems have pushed through the PNW the past week or so, bringing a rather climatological amount of precipitation with them. Nothing that’ll get us further toward normal, or further away from normal. Also, for the most part, the freezing level or snow level has remained above 3000ft, thus sparing most of low-land snowfall and associated plowing hazards.
A somewhat more dynamic series of systems including the current strong downslope wind in the Columbia basin associated with a strong zonal flow across the Cascades, and better chances for more significant “frozen” precipitation this weekend along with a much colder airmass.
Flash forward to this weekend. Above is a snapshot from the University of Washington’s extended GFS-WRF analysis of 300mb winds for Saturday evening. The northwestern trajectory of the jet stream is part of a larger hybrid omega blocking pattern over the northern Pacific. Unlike previous blocking patterns this winter, this one is positioned much further west and allows for the advection of cold air from the lee-side of the block (i.e., from Alaska) to our doorstep. The model run shown here produces a jet streak (or locale intensification of upper-level winds) across OR/WA that should enhance uplift in the right exit region which includes much of north-central Idaho. The University of Washington’s extended GFS-MM5 run has some details on snowfall amounts and timing. However, as we are looking at nearly 120 hours out, the caveat is that details to change from run-to-run and we’ll likely have more confidence in numbers come Friday. On the surface, it appears that Moscow-Coeur d’Alene-Spokane could see 3-6 inches over the course of the weekend.
After this system moves through, the large-scale flow pattern becomes even more loopy and includes the possibility of a continental arctic air mass cameo for the northern and eastern portions of the inland northwest next week.
The map above, showing 500mb wind (vectors) and temperatures (colors), shows strong northerly flow advecting much colder air from interior BC/Yukon our way. Fortunately, the Rockies tend to form a barrier of sorts that inhibit the coldest air masses from infiltrating westward. However, if this materializes and follows on the wake of a good 3-6 inches of fresh snow, we could very likely see our coldest temperatures of the winter at the very end of February (just like last year coincidentally). Beyond the end of February some models are hinting at the cold air mass hanging around for the first week of March, but it is a bit early in the game to pen anything in at this point.