White Christmas 2019

We're only a week away from Christmas, so the natural question is "Will it be a White Christmas?"  And as always, the answer is "It depends on where you live."  Just to remind folks, here's the climatological odds of a White Christmas in the Inland Northwest:

But this is based on the Christmases between 1981 and 2010.  What about this year?

As of 17 December 2019, here's where the snow currently resides:

NOHRSC Snow Depth December 17th, 2019

This doesn't look too promising.  Most of the cities/towns are either snowless, or have just a patchy trace of snow.  Is there any hope on the horizon?  Turns out that there is, but it may not deliver what we're hoping for.

Snow outlook this week

We are about to enter a wet pattern.  Initially most areas will get snow, but a warm up will result in snow changing to rain except in the mountains and possibly Methow Valley where heavy snow accumulations are expected.  This is especially true in the Cascades where some peaks will see snow totals in excess of 4 feet!  The Upper Methow Valley and Lake Wenatchee area are forecast to receive 1-2 feet!

NWS Forecast issued Wednesday afternoon for forecast snow Thursday-Saturday (Dec 19-21)

 For the majority of the valleys, these amounts reflect Thursday totals as temperature warm on Friday.


 Warming up

A significant warm up is expected, as noted by this ensemble temperature forecast for Spokane.

12z Dec 18th GEFS forecast of 2-m Temperature (F) for KGEG (Spokane Airport)

Note temperatures rise significantly on the 20th (Friday) and don't fall below freezing until the 22nd or 23rd.  And it's not just Spokane warming up, here are the projected temperatures for Friday. 

NWS Max Temperature Forecast issued Wednesday afternoon valid Friday, December 20th, 2019

Nearly all valleys in the 40s, with mid 50s around the Tri-Cities and Walla Walla areas.  The exception in the Cascades where snow melt will be minimal, with areas of heavy wet snow persisting.   The warm temperatures are expected to melt much of the lower elevation snow.

So what is the cause of this pattern.  A mild southwesterly flow ushering in warmer air.  Below is  one model prediction for Friday and Saturday showing a deep fetch of mild but moist air over the region.

12z/Dec 18th GFS Forecast of 500mb heights and 700-500mb RH valid 4 AM PST Friday, December 20th

12z/Dec 18th GFS Forecast of 500mb heights and 700-500mb RH valid 4 AM PST Saturday, December 21st

So many areas will lose their snow by the end of the week.  The mountains, Cascade valleys, the Republic area, and areas near the Canadian border stand the best chance for hanging onto some snow. 


Christmas Day Outlook

So, you be asking what about Christmas Day itself?  Well here is the projected weather pattern

12z/Dec 18th GEFS forecast of 500mb heights and winds for Christmas Day

This shows a split flow pattern with the jet stream well to our north across northern British Columbia, with a stronger branch of the jet dropping down into Mexico.  This supports dry weather for our neck of the woods.  Christmas Eve looks dry as well.   Now as of this writing this is a 7 day forecast which is subject to change.  There are just a few model runs that still give a little hope of light snow, but at this point a dry Christmas is expected. 

A White Christmas is a good bet for the mountains especially the Cascades as well as the Cascade valleys.  Some northern valley locations may hang onto some snow as well.  Elsewhere a White Christmas is unlikely.