All the morning maps/models are in. Here’s the latest
WINTER STORM WARNING METRO
Snow showers arrive in the metro area around 5-6pm this evening
At that point temperatures will be several degrees above freezing everywhere except northern Clark County, near/above 1,000′ (West Hills), and right around the west end of the Gorge.
For most of us the snow won’t stick to roads initially and most likely the evening commute will be fine. But watch out in northern Clark County plus near the Gorge.
During the night snow continues and temperatures fall to freezing north and east metro near the Gorge, plus in the hills. Much of west and south metro may stay a few notches above freezing with little snow accumulation.
By sunrise, most roads north, central, & east metro should be snowy and/or frozen as cold east wind returns from the Gorge. Many roads west of the West Hills and Clackamas county south into the valley will likely be wet or just slushy
HIGHLIGHTS SATURDAY DAYTIME
Snow showers continue, although not much additional accumulation after noon
Many roads where not much snow fell (west/south metro) may be just wet or in pretty decent shape. But lots of snow on roads in Clark county and eastern Multnomah County close to the Gorge.
The Columbia River Gorge will be snowy and frozen Saturday
SATURDAY NIGHT AND SUNDAY
Mainly dry with little/no additional snow accumulation. EVERYONE SEES FREEZING BY SUNDAY A.M.
HOW MUCH SNOW?
TRACE – 4″ IN THE METRO AREA, highest totals north and east metro, could be very little for some out in western and southern areas (Hillsboro, Sherwood, Wilsonville, Molalla). A tough call though, if we get lucky ALL of us see 2-4″. I just want to warn you, at this point I see a possibility you may not get “sleddable” snow west/south metro. I’ll be happy to be wrong on this one
2-5″ northern Clark County, St. Helens, and on up through Longview
4-10″ Columbia River Gorge, blowing and drifting snow west end as east wind returns by sunrise
TRACE-2″ Willamette Valley from Wilsonville south to Eugene
TRACE-2″ Oregon and SW Washington coastline, higher amounts Cannon Beach north, lesser down on central coast, and most of that late tomorrow after temps fall to freezing
TECHNICAL TALK FOR WX GEEKS
As models started showing yesterday evening, there are very strong hints that a southerly breeze will be lifting the sticking snow level off the valley floor this evening and into a good part of the overnight hours. It’s already beginning to show up at Salem with a temp near 40 and dewpoint up to 30. ALL models show a “warm tongue” of air moving north to the middle of the metro area this evening and tonight. Even the Euro has a 20 mph wind just 300′ off the surface all the way up to PDX. Sure it’s not very warm to the south but warm enough to lift the snow level up around 500′ or beyond for these southern areas.
Right now pressure gradient trends support this. At noon we’ve got a 3 millibar south-north gradient Eugene to Olympia and Gorge gradient down to under 2 millibars. That’s because a surface low is developing to the north. Now by 4am the surface low is west of us, we lose the southerly breeze, and cold Gorge wind is returning, EVERYONE in metro area can see sticking snow at that point. I think it’s likely all of us in the metro area wake up to at least a coating of white.
and by 10am Saturday it’s all about the cold east wind pouring out of the Gorge
So I see a setup where it’s tough to get much sticking snow south/west metro through a good chunk of the night (when most precipitation is falling) and it stays just barely cold enough for a nice dumping central/north/east metro. Then many of those same areas will drop to or below freezing by sunrise. Messy roads there. You see the lack of snow west metro and into the valley on the ECMWF snowfall accumulation map. Even this model has backed off a bit from previous runs. I also don’t want to neglect the GEM model from Canada. It alone is trying for 4-8″ in the metro area! Those Canadians are always crossing the border with their snow…so annoying.
The WRF-GFS, NAM, NAM-MM5, NAM-WRF, HDRPS, and GFS all say we get very little snow in the metro area with 2″ confined to hills and northern Clark County. A good example is the NAM-WRF.
If my forecast works out correctly (it’s never EXACTLY as we expect!), much of the night and the daytime tomorrow we’ll see pretty decent road conditions for lower elevations south of the metro area.
I’ll be on TV all evening, and fresh model info will come in between 7-10pm. Plus as precipitation starts falling we should know within a couple of hours which way this is going to go, will the mild southerly breeze keep snow off much of valley floor or not? Oh the drama…
I’ll tackle Sunday night and Monday’s snow event in a later post, likely tomorrow, but for now you can assume there will be at least some additional snow at that time.
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Chief Meteorologist Mark Nelsen