It’s been a very stressful week for weather forecasters in the Pacific Northwest. Lots of uncertainty about the upcoming cold spell, but it’s now coming into clear focus.

HIGHLIGHTS

1.  Cold air arrives tomorrow Friday! Expect east wind to arrive in Portland midday, causing temps to suddenly drop below freezing.

2.  There will be some precip tomorrow, but most of it stays south of Salem. But if anything falls over Portland it will be light snow.

3.  Serious snow arrives Saturday morning and continues until after dark for the Portland metro and SW Washington, probably 3-8” total.  But from Salem to Eugene…serious ice is expected instead. Likely 0.5-1.0″, perhaps even more in spots.

4.  Very cold air dominates Saturday through Monday, with temps in the teens at night almost everywhere west side. In fact, for the first time in 33 years, Portland may not climb OUT of the teens on Saturday!

 

THE PATTERN

It’s great to finally see arctic air on the move in eastern Washington and the Puget Sound. This image for 7pm on the 12z WRF model shows the bitter air spilling into the Columbia Basin tonight:

That cold air will be in the Gorge by early tomorrow morning, and then blast through in the metro around 10 am – noon.  Temperatures will quickly plunge from the upper 30s to the mid 20s, and standing puddles on roads will flash freeze.  Could be a bigger problem if there is cold rain falling in the morning.

Here are the 12z ECMWF (Euro) maps for precip tomorrow and Sunday. The Euro model is usually the most reliable so it’s what I’m using as a reference.  Tomorrow afternoon at 4pm everything is south of Portland still:

(all Euro & GFS maps are from Pivotalweather.com)

But by Saturday midmorning a major ice storm is in effect south of Salem, and snow over Portland:

Why ice in the valley? Because the cold air down there is shallower, and there is a layer of above-freezing air in the middle to melt precipitation before it lands and refreezes. More on the ice in a moment…

Saturday 4pm…heavier snow is pushing north, past Portland and into the uplands of southwest Washington:

Finally, 10pm.  Snow and ice are beginning to die down…this event is nearly over!

Here are the Euro snow totals through 4am Sunday. Snowy, but nothing historic:

Now on to the GFS….it shows more snow over Portland. Part of this is due to 2″ falling tomorrow, but also slightly heavier precip Saturday:

I’m going to split the difference and say that Portland and Vancouver can expect 3-8″ snow from this storm, and little to no pellets or freezing rain. This is just a rough guideline; if someone only gets 2″ or conversely pulls off 9-10″, well…that’s Portland snow for you…

I don’t have access to the Euro’s ice maps so I will have to use the Canadian and GFS.  First, the Canadian:

And the GFS:

That 2″ for Eugene on the GFS is probably too high.  Nonetheless, even 1/2″ to 1″ ice glaze can cause tremendous damage to the power grid, as Portland experienced in February 2021.

Anyway…at the same time that this storm is going on, frigid air is sweeping through Portland from the east. Temps of only 16 at 4pm means HIGH temps likely 18-20 degrees Saturday, making this the coldest day since December 1990!

And then there’s the wind.  The pressure gradient in the Columbia River Gorge goes bat crazy by 7am Saturday morning. At least 15 millibars of east wind from The Dalles to PDX.  Here’s another WRF image showing the barometric insanity!

That means widespread 40-50 mph gusts, maybe even a bit higher. Gusts could reach 70-80 mph at the west end of the Gorge, and likely 100-120 for Crown Point.  Power outages are going to be a big issue at precisely the same time windchills are near 0°F.  Ouch!!!

 

By Sunday evening is done with, except the lingering cold. Temps will likely rebound to the upper 20s/low 30s Sunday and Monday under the sunshine.  But nights will still be very cold, with low to mid teens likely many areas. With several inches of snow on the ground…I wouldn’t be surprised if we even saw a few single digits on the west side!

So, to be prepared:

1.  Hopefully you got most of your basic prep done today (gas, groceries, home supplies, car supplies, chains, etc.).  If you have any last-minute errands to do, get them done by 10-11am tomorrow!

2.  Tomorrow is a good day to say “work from home if possible. ”  If not, then be aware of the flash freeze threat tomorrow, plus the chance for light snow. Carry chains and take you “winter vehicle” if you have one.

3.  Saturday is a mess…don’t plan on going out at all unless it’s absolutely necessary!  Many if not most workplaces will likely be shut down from Longview to Eugene.

4.  Sunday and Monday are dry, but still extremely cold and windy.  Snow and ice will linger on untreated roads and driveways for several days. Use caution accordingly!

 

That’s it! Be safe!

Karl