More snow by Christmas?

Are you hoping for a White Christmas this year?   Is more snow on the way?  We'll examine this further in this blog, so lets get started.

When talking White Christmas, it's always good to see who has snow, and who doesn't.  Here is this morning's modeled analysis...

NOHRSC modeled SWE (Snow Water Equivalent) valid 17z (9 AM PST) Dec 21st, 2017

As of today (Dec 21), areas along the East Slopes of the Cascades, northern valleys, and into the Idaho Panhandle had snow on the ground while across much of the Columbia Basin, Spokane area, Palouse, and Lewiston-Clarkston Valley snow cover was spotty or non-existent.  The weather pattern ahead will be cold and thus areas with snow on the ground now look good for a White Christmas.

But what about more snow opportunities you ask?  There will be two more opportunities.  The first arrives tonight into Friday with the bulk of the moisture hitting the Idaho Panhandle, Blue Mountains, Palouse, the Lewiston-Clarkston Valley, and the southern Columbia Basin.  Here is our forecast snowfall as of 2 PM today.

NWS snowfall forecast issued 2 PM Thursday, valid through Friday

Cold and dry weather is expected Saturday, before the next system arrives Sunday (Christmas Eve).
Here is one model solution (GFS) showing an increase in moisture moving across the area on Sunday.

12z/21st GFS model run of 500mb heights & 700-500 mb Relative Humidity valid 18z Sunday (10 am PST)

This solution would bring widespread light to moderate snow accumulations for all of Central and Eastern Washington into North Idaho giving all areas a White Christmas.  However as of this writing quite a bit of uncertainty remained with how much this system will hold together as it passes through.  A different model (European) takes the system further south mainly into Oregon, clipping southern Washington and the Lewiston-Clarkston Valley.

To further convey the uncertainty, ensemble forecasts can be used which is a set of forecasts run with slightly different initial conditions to see what range of outcomes exist.  Here is one ensemble forecast (GEFS) showing snow accumulations for Spokane.

EMC's GEFS plumes for snow at KGEG (Spokane Airport) from 12z/21st December run

This shows most solutions giving Spokane a dusting of snow early on the 22nd (Friday), followed by a second and more significant round of snow on the 24th (Christmas Eve) possibly extending into early Christmas Day.  But note the spread in amounts.  The solid black line is the average which shows about 2 inches, with most members in the 1 to 2.5 inches range.  Stay tuned to the latest forecasts on our web site found here

In general, a combination of snow on the ground now in some areas combined with the potential for more snow Friday and again Christmas Eve should give most locations a White Christmas this year.