White Christmas this year?

Many of you may be wondering about odds of a White Christmas this year.  Snow has covered the ground recently in many areas, but will it stick around until Christmas?  What about the outlook for Christmas Day?

First let's start with the climatological odds of a White Christmas.  As always, the odds depend on where you live as the map below shows

Odds of a White Christmas, defined as 1" of snow or more on the ground, based on historical data shows the odds increase as you travel northward in the Columbia Basin up into the Spokane/Coeur d'Alene area.  And along the East Slopes of the Cascades, northern mountains, and Idaho Panhandle mountains the odds are very high (>90%).  There is a great article explaining this map here that has more background information, including an interactive map.

You may be saying ok these are the historic odds, but what about this year?  Let's start with where we have snow.  The map below from December 13th shows water content in the snow, which isn't much where most people live.  

Modeled Snow Water Equivalent (SWE) valid 4 AM PST Dec 13th, 2020

And the latest CoCoRaHS map from today (Dec 14th) shows many of these locations only have between 1-4" of snow on the ground, except for higher amounts around Republic and the upper Methow Valley.

CoCoRaHS map of Max Observed Snow Depth Dec 13-14th, 2020

For an interactive version of this map, click here

Why all this talk about what is on the ground now?  Because many areas may have a hard time keeping it.  More on that in a minute.  First it is worth mentioning that some areas will get more snow this week.   But snow levels will be gradually increasing.  The latest forecast for your location can be found at weather.gov/spokane

Temperatures are forecast to warm up this week, especially over the weekend.  This may melt much of the snow over the region.

Here are the forecast temperatures this week for Spokane, Omak, Lewiston, and Wenatchee.

NWS Forecast Temperatures issued 3 AM PST Dec 14th, 2020

Why the big warmup this weekend?  A mild Pacific jet stream aimed at the region

12z/Dec 14th GEFS forecast of 250mb winds (shaded), and MSLP valid 4 AM PST Dec 20th, 2020

And this particular model solution depicts warm southwest winds across much of the area.

12z/Dec 14th GFS forecast of 850mb winds (shaded) and heights valid 4 AM PDT Dec 20th, 2020

Mild temperatures and wind can melt snow very quickly.  Thus, there is a good chance of a complete snow melt off across the Columbia Basin, Spokane/Coeur d'Alene area, southward through the Palouse if these model solutions verify.  Tougher call for the northern valleys.  The Cascade valleys should have enough of an established snowpack to keep snow on the ground.

This takes us through December 20th.  So for areas that lose all their snow this weekend, will the snow return in time for Christmas?  This is getting far out into the forecast, but there has been some hint of a potential system with lower snow levels Dec 21-22nd.

12z/Dec 14th GEFS forecast of 500mb heights and anomaly valid 10 PM PST Dec 21th, 2020

Confidence isn't high, but some areas could get some snow out of it.  After that there are signs of high pressure trying to build over the region in time for Christmas.  But it's not very strong which could open the door to some weaker systems.  Of course this is more than a week out so confidence in the details is low.

12z/Dec 14th GEFS forecast of 500mb heights and anomaly valid 4 AM PST Dec 25th, 2020

In conclusion, a white Christmas defined at 1" or more of snow on the ground is a good bet for the Cascade valleys, and possible for the northern valleys into the Idaho Panhandle.  From the Wenatchee area through the Columbia Basin, Spokane/Coeur d'Alene area, Palouse, and Lewiston-Clarkston Valley a White Christmas is possible if new snow coats the landscape after the weekend warm up.