9pm Monday...

We ended up with 0.7″ snow officially in Portland on Sunday. That was a mix of Sunday morning and again Sunday evening. That brings our winter total to 1.1″

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Luckily no freezing rain so far and none in sight!

Today the southern edge of that cold arctic airmass moved through the metro area. That was right around sunrise. A northwest breeze kicked in, bringing the 25-28 degree air south. The high at PDX was right after midnight…34 degrees. It bottomed out at 26, now has risen back to just under freezing for most of us as the thin layer of arctic air mixes in with surrounding air. There’s no fresh supply of cold air coming from the north or east until Wednesday morning. So it’s plenty cold, in fact the 850mb temp of -9.9 degrees at Salem means it’s about 18 degrees at 4,000′ overhead! That’s also the coldest measured over Salem since the arctic outbreak of December 2013.

It’s snowing again tonight! I see a dusting all across the metro area and the boss says he’s got 1/2″ (fresh) in Lake Oswego. Most of the lower elevations west of the Cascades are under a Winter Weather Advisory. Anything over 1″ triggers that advisory. I remember in the 1990s when the criteria was either 2″ or 3″, but then after a few events it became obvious Portland can come to a standstill with 1-2″ snow, so an advisory typically means at least 1″ snow is expected. I think a Trace to 2″ covers it for tonight, although gut feeling says the majority of us get an inch.

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I think roads will be mainly fine midday and tomorrow afternoon, assuming we really only do get less than 2″. Side roads in neighborhoods of course could remain snow covered all day

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A “BC Slider” (a weak surface low that moves quickly down the Pacific Northwest coastline) is providing lifting, clouds, & light snowfall. The low is well west of Astoria right now

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By 4pm tomorrow, the low has weakened and spread out a bit on the southern Oregon coastline. We won’t see much wind from any direction these next 24 hours because it’s so weak.

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This light snowfall continues through tomorrow morning with flurries following the rest of the day. Temperatures remain below/near freezing most of the time. All models produce between 1/2″-2″ snowfall, most around 1″. The contour here is the HRRR. The GFS is much wetter/whiter…producing 3-5″ in the Salem/Albany areas by tomorrow evening! That’s due to another weak wave coming down south in the upper atmosphere later tomorrow, prolonging the precipitation. There is a decent “bust potential” in the lowlands with this event…

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After the low dies to our south tomorrow evening, a fresh surge of that modified arctic air pours through the Columbia River Gorge. That should bring drier air, sunshine, and high temps only around freezing or so Wednesday. That will be our third day around the freezing mark. A chilly 12 days of Christmas indeed!

I’m watching the next system for Wednesday night & Thursday closely. All models agree that one more little “slider” comes down the coastline, but moves inland across the central part of Washington this time. That gives us a gusty southerly wind for at least a few hours that day. We’ll probably climb into the mid-upper 30s at some point Thursday with the warming onshore wind, but not before somewhere between 1-3″ snow falls.

That’s it for this evening…enjoy the snow! Chief Meteorologist Mark Nelsen

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