The next 3 days look very nice weatherwise…partly cloudy skies with just a few sprinkles likely on Friday morning. There will be rain and snow to our north in much of Washington later Saturday and Sunday, but at this point it appears it’ll all stay to our north.
I had a grand plan for this evening since I’ll be on vacation tomorrow through Wednesday. I was hoping to put the chance of snow/freezing rain in the Gorge and north central Oregon to rest this evening for the first part of next week and then (see previous post) tell the viewers that winter is pretty much wrapped up in the lowlands of Western Oregon/Washington. But then the 00z GFS came in even a little colder with some “backdoor arctic seepage” Monday and Tuesday. Ewww…what is that? It’s cold air that gradually works its way down from Canada, into Eastern Washington, and then through the Columbia River Gorge and into the Portland metro area. That’s as opposed to an arctic blast that brings cold air across the entire region.
As a result there will be no “Winter is Over” proclamation for now.
Our RPM clearly shows rain approaching the coast quickly on Sunday evening, as does the GFS and ECMWF. At the same time pressures are lowering to our west with an approaching “warm front like” system, high pressure and cold air is building east of the mountains. The result is a very strong east wind (8-10 millibars) through the Gorge. 850mb temps are below zero eastside and just a few degrees above zero westside. It will be a very shallow cold air mass west of the Cascades as a result. My current forecast even assumes the GFS/WRF-GFS is bringing down too much cold air eastside. In fact take a look at the snow forecast from the WRF from late Sunday night through early Tuesday morning:
I think the snow west of the Cascades probably won’t happen as I mentioned, but look at the healthy totals in the Gorge! A good 6-10″ from Bonneville to Hood River! And snow all the way down into central Oregon too as the cold air pushes south. You can also see with the east wind the WRF is trying to create the same heavier snow up against the Coast Range and in Columbia county that we’ve seen a couple of times this winter. Again, I’m assuming it’s bringing too much cold air down at that time. Note the 2 day rain totals from the same model:
IF the air is cold enough in the Gorge, which it appears to be, that’s plenty to support those snow totals. The reason is that moist and mild westerly flow is undercutting the upper level ridge over us.
So it boils down to this:
MONDAY IN METRO AREA: A cold and rainy day in the Portland metro area, instead of high temps around 50 or so on Sunday, temps will hover in the upper 30s to around 40 all day. A gusty east wind 20-30 mph will make it feel colder! Could see freezing rain as close as Corbett and the hills above Washougal in the Gorge.
TUESDAY IN METRO AREA: Still chilly and breezy eastside. Showers taper off, temps creep into the mid 40s.
MONDAY/TUESDAY IN THE GORGE: Some sort of snowfall is looking more likely this evening. Depending on how cold the air mass is, could be just 2-3″ or if it’s as cold as these models show and with plenty of moisture, could be two days of snow with 6-10″ with freezing rain at the western end. Extremely slow warmup Tuesday/Wednesday with cold easterly flow continuing.
Now keep in mind if models warm Monday/Tuesday significantly, none of this will happen. Keep on top of the latest forecasts! And the 00z ECMWF was significantly drier than the GFS. The 00z GEM would be just barely cold enough for that snow too. So still up in the air for sure. Maybe LIKELY is too strong of a word. We’ll see.
Chief Meteorologist Mark Nelsen