Not your average winter storm

We have the potential for a significant winter storm to affect the entire Inland Northwest this weekend.  But this isn't just your average winter storm.  Most of our storms go like this:  heavy, wet snow falling with temperatures around freezing and light winds.  Then as the snow ends, the southwest winds increase, and the temperatures warm.  For this weekend, things will be just the opposite; dry fluffy snow, cold winds, bitter wind chills and drifting snow.  Let's take a look.

First, here's the expected snow fall for Friday through Saturday.

Light snow will start early Friday morning across the northern border region.  It should be snowing in the Spokane metro area before sunrise Friday, with about 1-2" of accumulation during the day. 

But the real event will get going Friday night into Saturday, with the main focus for heavy snow in north-central Washington.  The above image is our best forecast at this time (early Thursday morning).  But computer guidance varies greatly.

We'll start off by looking at some forecasts from the traditional models, the NAM and GFS.  Here's their snowfall forecasts for Spokane:

 The blue lines are the GFS, the reddish lines are the NAM.  As you can see, the GFS is on the light side, with just a couple of inches for the metro area, while the NAM is more optimistic of a 5-7" event.

In central Washington, the forecasts are little more impressive.  Here's the forecasts for Wenatchee:

The GFS is again lighter than the NAM for snowfall amounts.  Some of the NAM forecasts are in excess of a foot of snow.  The Okanogan Valley also looks similar to the Wenatchee forecast:

And lastly, here's the forecast for Ephrata (near Moses  Lake):

That's a lot of snow for the Columbia Basin, if the NAM is right.  Even the GFS forecast of 6-8" is respectable.

But that's just 2 models.  There are also multi-model ensembles that we can look at.  We'll start with the GFS ensemble for Spokane:

 
The blue line is the GFS forecast.  The thin grey lines are all of the ensemble members, and the thick black line is an average of all the grey lines.  So 4" looks like a good forecast, but the range could be anywhere between 2" and 6".  

Here's the same forecast graph for Ephrata:

 
You can see that the GFS (blue line) has about 9" of snow, while the ensemble average (black line) is closer to 6".

Lastly, let's take a look at the SREF model, which is actually an ensemble of 26 different NAM models.  Again, we'll start with Spokane:

 The SREF would suggest a forecast of 6", with a possible range of 2" to 11".  

How about Ephrata?

 The average of the SREF members has a forecast of about 8" for Ephrata, but a few members want to go as high as 17".

Wenatchee is even more impressive.

 Yes, you're seeing things correct.  The average of the ensemble is 19" of snow at Wenatchee, and a few members have over 3 feet of snow, while others have less than 10".  The Okanogan valley is similar to Wenatchee.  These extreme forecasts have very little chance of being correct.  It's worth keeping in mind that the 48-hour snowfall record for Wenatchee is 24.7" set back in 1971.

So, as you can see, lots of different computer forecasts, with lots of different snow fall amounts.  But the screaming message is that there could be a LOT of snow for north central Washington.

But so far, we've focused on snowfall.  But during the day on Saturday, cold winds will blow from the northeast.  Here's the forecast wind gusts for Saturday afternoon:

Winds this strong, coupled with dry, fluffy snow, will result in the potential for a lot of blowing and drifting snow.  Drifting snow has the potential to make some roads impassable, especially in the Columbia Basin, the Waterville Plateau and Okanogan Valley.  If you have travel plans on Saturday, you might encounter roads like this:

Lastly, if you're hoping for warmer weather, you're going to have to wait awhile.  Here's the outlook for next week:

Temperatures in the Inland Northwest will remain below freezing for the next week.  And even for the week after that, there's a really good chance that temperatures won't warm much.  A few locations might see a daytime temperature slightly above freezing, but in general, we're looking at staying sub-freezing for the next two weeks.