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9:00 pm Tuesday...

Quick dinner break and now checking out maps/models again. Many times, in our snow-starved climate, I'll downplay expected snow because...well, many times it doesn't happen. It's tough for all the factors to come together.

This isn't one of those times; at this point I'm feeling this could be one of the big snow/ice storms of my career.

THE MAIN POINTS THIS EVENING

  • An approaching snow/ice storm from late Thursday through early Sunday could be an epic one for some of us in the lowest elevations. That's for any time in winter, but especially so this late in the season. This could be the biggest February snowstorm of my career for at least parts of the metro area! Somewhere between 2-12" is a first good estimate of total snow during that time. Heaviest north and east metro, including Longview/Kelso. Lighter south & west due to more of the precip falling as freezing rain instead of snow.
  • As some models have been hinting, two waves of precipitation from Thursday through Saturday likely won't be separate "storms", but seem like one continuous event. However there should be a bit of a break before a third, and warmer system arrives later Sunday.
  • Much of the metro area will remain mainly frozen from Thursday night to Sunday morning
  • Wind gusts 50-75 mph in the western Gorge will likely lead to blizzard conditions at times from east of Troutdale to Multnomah Falls. That's beginning Thursday night. I would expect I-84 to be closed for at least a day or two. Possibly longer if more than 15" of snow falls out there.
  • Mammoth snowfall is likely in the Gorge and Cascades. This could be a February storm we talk about for a long time. If precipitation is as heavy as most models show, I see 15-30" east of Troutdale to The Dalles. Add in the wind and I see some serious drifts in the usual windy areas. This hasn't happened since 2008 in the western Gorge.
  • That 3rd system eventually turns wind southerly all across the area, a classic southwesterly "Chinook Wind" after a cold spell. So we're confident we pop out into warmer air Monday, if not Sunday afternoon/night.

TOMORROW I'LL GIVE YOU MORE SPECIFIC FORECASTS SINCE WE'LL BE WITHIN 24 HOURS OF THE EVENT

TECHNICAL INFO

Why such a big event? It's all about the perfect combination setting up. Plenty of low level cold air from the metro area north and east. And now models are really pumping in tons of moisture. It's reminding me of the January 1998 event. In that one, 10-18" fell in the north/east metro areas over 2-3 days, but mainly freezing rain with a couple inches snow in south and west metro.

A weak surface low approaches the coastline in a perfect position to pull cold air out of the Gorge at 4am Friday. It doesn't get any better than this if you want a blast of winter in Portland and the Gorge.

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Look at forecast precipitation from the 12z ECMWF through Sunday morning. Wet, or white in this case

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And that produces a snowfall map like this...

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It IS possible to get more than a foot of snow west of the Cascades. January 2017 is one example, although maybe January 2012 is a better. That one was more widespread...something like 10-18" in one night throughout SW Washington and around Columbia County Oregon.

Notice how little falls south of Portland. That's because the boundary of cold arctic air won't progress very far south of Portland, and warmer air overhead will keep precipitation type as liquid through much of the event. Clearly we're going to see a large gradient of snow accumulation. North and east is the big snow, south and southwest not so great. West metro should do okay (Hillsboro/Banks) with some decent snow.

Notice a significant amount of icing (from freezing rain) forecast by ECMWF model from south metro down in the central Willamette Valley

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That's it for now since I'm out of time. I'll be on at 10/11pm tonight and of course every day the next week...it's showtime!

More details tomorrow...Chief Meteorologist Mark Nelsen

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