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We had 2 weeks of high pressure and dry weather in mid-November, but now it’s payback time. I’ve got 3 weather items to cover this evening: stormy night tonight, heavy snow in Cascades/Gorge, & could we see snow in the lowlands later this week.
First, we’ve got a soaker headed into the PACNW right now. It’s a cold front and that’s the leading edge of another “maritime polar” or “maritime arctic” airmass. That means cold/dry arctic air has dumped out over the ocean and is moving toward us. That cold front has a lot of rain associated with it. I expect about an inch of rain (or a bit more) overnight in the western valleys of Oregon and SW Washington. Then the wind; southerly gusts will likely reach the 35-45 mph range around 11pm-2am just ahead of the cold front. Expect a few scattered power outages during the night
Tomorrow will be uneventful in the lower elevations with light wind and scattered showers
For the first time this season we’ve got a (very shallow) cold airmass streaming westward through this sea-level gap in the Cascades. Add in abundant moisture moving in overhead and it’s the perfect recipe for a snow or ice storm. It appears this time it’ll be mainly snow, with a little freezing rain mixed in toward sunrise when the cold airmass thins out. Almost all the action will be east of Multnomah Falls. The cold air is so thin at the west end of the Gorge that it’s barely streaming over the top of Crown Point! Up around 1,500′ nearby it’s well above freezing. The cold air is thick enough on the Washington side to support snow a few more hours of snow NORTH of the Columbia River.
Temperatures will warm tomorrow midday/afternoon and I-84 should be fine the rest of tomorrow.
There is plenty of snow on the ground in the Cascades and we’ll add 1-2′ additional tonight through Thursday morning. This will be the best December 1st snowpack in about 15 years!
Worst travel conditions in the Cascades will be tomorrow morning with lighter snow in the afternoon.
LOWLAND SNOW POSSIBILITIES
This is probably what many of you want to know…Will we get snow in the I-5 corridor between Longview and Eugene? Possibly, but I still don’t see a setup for widespread snow in the cities. The first two “close calls” this week have ended with nothing. That was Monday morning’s snow in the hills, then a brief “flurry storm” in a few spots this morning before the airmass warmed up. Models handled both well, although precipitation arrived a bit early today.
For the next 2 days, I think our commutes are clear except for Thursday morning. On that day we’ll be in a chilly airmass with scattered showers roaming about including during that morning commute. Typically this isn’t a significant snow producer west of the Cascades in the lowlands. BUT, if it snows a Trace to 1″ Thursday morning where YOU live, it’s a big deal to YOU!
The cold airmass behind tonight’s cold front will bring sticking snow down to around 2,000′ late tomorrow and around 1,000′ Thursday morning. Considering it’s just scattered showers, that usually means a few spots in the hills get a dusting and we don’t see anything other than a rain/snow mix in the valleys. BUT, if we get any sort of steady/heavy showers, that sticking snow can come right down into the lowest elevations. For the geeks, we’re bottoming out around 520dm thickness and 850mb temps -6 to -7 Thursday and Friday…that’s cold, but not “guaranteed” category for snow in the lowlands. Some models have been hinting an organized band of showers could develop tomorrow night or Thursday morning. The Canadian HDRPS model, HRRR, & NAM-3km imply this could happen and all 3 are producing measurable snow across at least part of the Portland metro area during that time. So…we will see what the evening GRAF model shows in an hour or so. Right now it thinks a few spots could get “stickage” early Thursday morning…stay tuned!
A repeat is possible Thursday night into Friday morning, but in general I’m thinking the vast majority of us in the I-5 corridor from Longview to Eugene will not see “sleddable” snow through Friday.
It could be a different story after that time…
Another cold upper trough drops down offshore Friday and spins up another wet frontal system. Models are all over the place on this one. The normally cold GFS thinks we’ve got a snow and then ice storm Friday night into Saturday morning. The ECMWF is much drier and has the system farther offshore. But it IS cold enough with a strong easterly Gorge wind that moisture would be in the form of snow/ice. So Friday evening/night is another possible “event” I’m watching closely. There is also plenty of cold/dry arctic air lingering just north of us through early next week. That means at any time some of that could get pulled south and interact with Pacific moisture as we’re seeing this evening. Winter is here for the forecasters and it’s busy!
That’s it for now…enjoy the stormy night.