Quick Tuesday Evening Update: Forecast on Track

December 13, 2016

11pm Tuesday…

All evening models are in now.  There will only be one more set of model runs in tomorrow morning before our big event (well, at least big to our south and east).

What’s different?  In the big picture very little.  Cold air is pouring through the Gorge with gusts around 70 mph at Vista House and just below 60 mph at Corbett.  Temperatures in those locations are now down to where they were just before last Thursday’s event.  Evaporational cooling (temp drops when precip falls into a dry airmass) should bring us all down TO freezing when precip arrives early-mid afternoon.

The Portland metro area will be right on the northern edge of a band of snow stretching across much of Oregon.

Two minor changes:

  1. Timing: Models (as a whole) are slightly slower bringing in the precipitation and getting it out of here as well.  I’d be surprised to see anything other than flurries before 1pm.  The ECMWF keeps some sort of snow going until late evening too.
  2. Accumulations:  The GFS/GEM/ECMWF were all SLIGHTLY wetter (whiter in this case).  At most there is enough precip for 3″ of snow.  But in a nod to the tight gradient of no snow to the north to 3″+ at Salem, I’ll leave our 1/2″ to 2″ forecast the same.


This is what I’ve used on-air this evening and I guess it counts as my final forecast…we’ll see what happens!



Chief Meteorologist Mark Nelsen

Valley Snow Storm Wednesday, Some Snow Metro Too

December 13, 2016

11am Tuesday…

36 hours from now (Wednesday evening) much of the Willamette Valley should be covered in white, and here in the metro area we should be on the northern edge of that snow.  There is some good news at midday:  forecast models have come together reasonably well for tomorrow’s snow event.

This forecast could still change a bit this evening or early tomorrow morning if the storm decides to move a bit farther north or south.


  • Wednesday will be a cold, cloudy & windy day
  • I don’t see a big snowstorm for tomorrow, but yes, I know, an inch or so of snow in Portland IS a snowstorm.
  • Light snow arrives by mid-afternoon (2-3pm) and continues through the evening hours as temperatures drop back to & below freezing
  • 1/2″ to 2″ snowfall is most likely, with that heavier total likely south metro (Wilsonville/Oregon City) and maybe even as low as just a dusting up in outer Clark County & western Washington County.
  • Whatever falls will be pretty much finished by 10pm.
  • Freezing rain is NOT expected, Great news!  Too cold overhead for snowflakes to melt into raindrops

Confidence has increased on the timing, so let’s talk commute & school…


  • Morning commute will be dry
  • At some point beyond 3pm roads will likely turn snowy/icy in the metro area
  • Evening commute could be a real mess, especially if we get more than 1″.  All roads will likely be frozen after 5pm.
  • IF YOU WORK A REGULAR SHIFT, I’D SUGGEST A HALF DAY.  NO NEED TO SKIP THE WHOLE DAY.  Leave Noon-2pm.  Plan on being home by 3pm.
  • SCHOOLS:  Half day would be perfect.  Get the kids on the busses around noon or 1pm.  No models show snow before 2pm.  Doing a full day of school would be risky.
  • Thursday AM:  Roads remain frozen with snow on them (assuming it snows tomorrow)


  • Snow arrives 10am south Willamette Valley and works north
  • 2-5″ likely Woodburn to Albany, heaviest south
  • Frozen roads still on Thursday morning
  • Kelso/Longview only get a dusting, or just stay dry


Looks dry, but maybe a rain/snow mix from Newport south, I don’t expect any road impacts.


Same as metro, but 2-4″ totals likely.  Strong wind at the west end will create rough driving with sideways snow tomorrow evening.


  • This is the bullseye of the storm
  • 8-12″ possible Madras to La Pine, 3-6″ elsewhere
  • You can see the big snowstorm all across the eastside of the state on the WRF-GFS snow forecast


It was good to see models come together quite a bit more this morning.  Mainly because the wetter GEM & ECMWF models backed off on their precip forecasts dramatically.  As you read in the previous post, the ECMWF was showing the most snow potential, but even it has come way down on its forecast for us.  That’s because it’s sending the core of the moisture farther south.  Take a look at this morning’s precipitation forecast:


You can still see tomorrow’s storm is a BIG deal to our south and east.  This is a perfect setup for heavy snow south of The Dalles all the way to Klamath Falls along Highway 97.  Also note that you folks in Astoria will likely have a pleasant dry day.  Same thing north of Longview.  Of course any northward/southward shift in this evening’s model runs will affect our forecast dramatically!

Our RPM model and the usually reliable WRF-GFS are pathetic, showing a dusting to 1″ at best for us:



It’s not often that you see Maupin with the highest precipitation total!  That’s excellent news for you folks because that snow melting is great for the wheat next spring.  Check out the “dry hole” over the east PDX metro area on the WRF too.  If these models end up being correct, all we’ll get is flurries in our area tomorrow afternoon/evening.  I’ve given a bit more weight to the slightly wetter ECMWF/GEM models.

Stay tuned, I’m sure there will be some other twists/turns after the evening models come in or maybe even at the last moment tomorrow morning…

Chief Meteorologist Mark Nelsen