Arctic Blast Next Week

December 29, 2016

11pm Thursday…

Models are in very good agreement now that we’re about to experience our first “arctic blast” across the Pacific Northwest in 3 years.  It arrives Sunday night on northerly winds pushing out of Canada and continues the entire rest of the work week.  After Monday we go into a gusty east wind pattern with bitterly cold air moving through the Columbia River Gorge and into the Portland metro area.  Those waterfalls are going to be looking great by midweek all frozen up!

First, will we get snow Saturday night or early New Year’s morning?  I think anything other than flurries or a dusting is quite unlikely.  The showers are pretty much gone by the time the snow level lowers down into the lowlands.  In fact after 7am Sunday we’ll probably be dry.  Take a look at 5 different model forecast of precipitation after 4am Sunday, then the snow that could produce.  Yeah, looks pretty dry:

marksnow_pdx_models

The ECMWF and WRF-GFS model snowfall forecast don’t inspire much confidence for sledding in the lowlands Sunday either.  Click for a closer view:

After Sunday that cold air takes over and we’re likely going to be sunny and dry most or all of the work week.  Take a look at the WRF-GFS cross-section:

kpdx-x-th

Time goes from RIGHT to LEFT.  The right side is Monday morning, left side is next Friday morning.  Clear areas are less than 70% relative humidity…that’s a very dry atmosphere.  The wind barbs are easterly the entire time.  Through Wednesday morning the northeast/east flow extends all the way up to 10,000′.  This is a rare “deep” arctic airmass.  That means unusually cold temps in the mountains too.  Probably only 0-8 degrees at the ski areas Monday!  Northeast wind will be widespread across the region Monday/Tuesday.  After Wednesday it becomes more of an east wind through the Gorge but light wind elsewhere.  That calm wind will allow for very cold nights…5-15 degrees west of the Cascades.

Beyond our 7 day forecast there are hints of moisture returning next Friday, or Saturday, or Sunday, depending on which run of which model you are looking at.  This is the graphic I used for the 12 Day Trend I used this evening at 10pm.  I do this most nights to give viewers a GENERAL idea of what we’re seeing beyond the next 7 days.  It’s very useful in situations like this.  I think there’s a decent chance of getting some sort of snow west of the Cascades between days 8-12.  But it’s unknown at this point if we have a major ice/snow event coming sometime NEXT weekend or beyond.

mark12dayfinal

The cool pattern is going to continue.!

It’s my weekend the next two days but I’ll be back at Sunday.

Have a safe and Happy New Year!

Chief Meteorologist Mark Nelsen