White Christmas?

As of the time of this writing (2 PM Thursday), the Spokane Airport was a mild 45F with rain falling, when the normal high is only 31F.  These mild temperatures sure are interfering with those dreaming of a White Christmas!  Well there is still hope that we will detail in this blog.

Let's begin with historical odds.  This map shows historical chances of having 1" of snow or more on the ground on Christmas Day.

 An interactive version of this map is available at this link.  It shows historical odds are 57% Spokane, 47% downtown Wenatchee, and 16% Lewiston.

So what about this year?  Let's begin with the snow that is out there now with this morning's 10 am snow analysis.

NOHRSC Snow analysis 10 AM PST (18z) December 20th, 2018

Wow!  Not only a lack of snow around our neck of the woods, but most of the US is free of snow cover.  Here is a more zoomed in map of our region.

NOHRSC Snow analysis 10 AM PST (18z) December 20th, 2018

So most locations outside of the mountains, Cascade valleys, and some valleys near the Canadian border need some snow, and soon!  What does the future hold?

Well a storm is forecast to track through the region Saturday night and Sunday as the GFS model shows.

12z Dec 20th GFS forecast of 500mb heights and 700-500mb Relative Humidity valid 4 AM (12z) PST Sun Dec 23, 2018

Looks like temperatures will start off cold enough Saturday night into Sunday morning for snow with the possible exception being the Lower Columbia Basin and around La Crosse and Lewiston-Clarkston Valley.  The I-90 corridor from Moses Lake to Ritzville will be near the rain/snow line. Here is the GFS forecast of precipitation type Sunday morning.

12z/20th GFS forecast of precipitation type/intensity valid 4 AM PST (12z) Sunday, December 23rd, 2018

So the potential exists for light to moderate snow accumulations for most locations Sunday morning.  But will it stick around through Christmas Day? And any more storms after Sunday?  Let's talk temperatures first.  Whether this snow sticks around will depend on how much falls as temperatures for most valleys will warm into the mid to upper 30s Sunday and Christmas Eve resulting in some melting.  Here are the forecast high temperatures for Sunday and Christmas Eve.

Not all that warm, but should see a little melting of snow for most lower elevations.  

So what about the weather on Christmas Eve into Christmas Day?   Another storm approaches but the current model projection from the GFS late on Christmas Eve take the precipitation mostly to our south across Oregon, southern Idaho, and California.

12z/20th GFS forecast of precipitation type/intensity valid 10 PM PST Monday, December 24th, 2018

This particular solution would give the Washington Cascades some snow as well, but other solutions take the storm further south like the Canadian model below.  This morning's European model is similar to the Canadian model.

12z/20th Canadian model forecast of precipitation type/intensity valid 10 PM PST Monday, December 24th, 2018

And here is the GFS model projection for Christmas morning.

12z/20th GFS forecast of precipitation type/intensity valid 10 AM PST Tuesday, December 25th, 2018

Models are trending further south with this storm, but this is still several days out and the track could still change so be sure to monitor latest forecasts.

To summarize, while there is a lack of snow out there now, light to moderate snow accumulations are forecast for most locations Sunday morning.  But expect some melting of this snow prior to Christmas Day.  We will continue to monitor the track of the storm that follows which is currently more likely to impact Oregon, California, and southern Idaho.

As always, forecasts are refined as we get closer so be sure to check our web site for the latest forecasts at this link

Parade of storms

After a quiet beginning to December, the pattern is about to change as a parade of storms track into the region.   This is good news for our mountain snow pack which is running behind.

This map should look much different in a couple weeks.  Let's take a look at the pattern going into the early next week followed by a more detailed analysis of the first two storms expected.

First system arrives today (Sunday) beginning in the Cascades late this afternoon.  While not much of a storm, we will call it Storm #1 for simplicity sake.  Then follows Storms #2, #3, and #4.  These will carry more precipitation as well as the potential for gusty winds.  The yellow lines on the maps that follow show a strong westerly flow across the Pacific Ocean into our region.  The green shaded areas show high moisture content which you will see over our neck of the woods for each storm.  Take a look. 

00z/Dec 9th GFS model forecast of 500mb heights and 700-500mb relative humidity valid 10 PM PST Sunday

00z/Dec 9th GFS model forecast of 500mb heights and 700-500mb relative humidity valid 4 PM PST Tuesday

00z/Dec 9th GFS model forecast of 500mb heights and 700-500mb relative humidity valid 4 AM PST Friday

00z/Dec 9th GFS model forecast of 500mb heights and 700-500mb relative humidity valid 10 AM PST Dec 16th

Several storms moving through will bring unsettled conditions.  You will notice the flow over our region does turn a bit more southwesterly with the last two storms which may bring slightly milder air.  The mountains will see LOTS of snow.  This mild/wet pattern may persist in the 8-14 day time frame per the latest outlooks from the Climate Prediction Center.

CPC 8-14 Day Temperature Outlook issued December 8th valid Dec 16-22

CPC 8-14 Day Precipitation Outlook issued December 8th valid Dec 16-22

Sunday Night/Monday: Snow Timing and amounts

When will the snow start?  Let's begin with this afternoon (Sunday)

00z/Dec 9th GFS Forecast of Precipitation type valid 4 PM PST Sunday

Snow reaches the Cascades late in the afternoon spreading into Central Washington in the evening.

00z/Dec 9th GFS Forecast of Precipitation type valid 10 PM PST Sunday

Snow then moves into Eastern WA and North Idaho overnight. 

00z/Dec 9th GFS Forecast of Precipitation type valid 4 AM PST Monday

Snow becomes confined to far northeast WA, North Idaho Panhandle, and Cascades, mid to late Monday morning.

00z/Dec 9th GFS Forecast of Precipitation type valid 10 AM PST Monday

This should spell light accumulations for most towns.  Here is a look at our forecast issued Sunday morning.

NWS Forecast snow accumulation issued 3 AM PST Sunday valid through 10 AM PST Monday

Tuesday Storm: 
What about the Tuesday storm?  Looks like it will start off as snow for the palouse and most areas north of Moses Lake.

00z/Dec 9th NAM Forecast of Precipitation type valid 10 AM PST Tuesday

Milder air does surge north Tuesday evening, with snow changing to rain in Spokane.

00z/Dec 9th NAM Forecast of Precipitation type valid 7 PM PST Tuesday

Other models suggest a similar scenario for Tuesday but the forecast will continue to be fine tuned.  This storm has the potential for travel impacts especially over the mountain passes and northern valleys.  For the latest forecast updates, please check our forecast here.

Changes next week

After a quiet weather pattern this week, weather changes are on the way.  What kind of changes you ask?  Good question, let's take a look.

We will take a look at a few model solutions for next week but let's begin with today (December 4th).

06z/Dec 4th GFS model of 500mb heights and 250mb wind (image) valid 4 PM December 4th 

This is a pattern typical of El Nino.  The image shows wind speeds up near 30,000 feet MSL with green colors showing winds between 100-140 MPH and orange colors in excess of 140 MPH.  A split jet stream with the southern branch aimed at California and the northern branch staying to our north and east.  Although we are under a weak northerly flow which will bring our region slightly below normal temperatures.

A weak weather system may pass through Saturday for a threat of light snow or flurries.  More significant changes next week.  Check out the pattern for Monday, December 10th.

06z/Dec 4th GFS model of 500mb heights and 250mb wind (image) valid 4 AM December 10th

Noticed a much stronger, consolidated Pacific Jet Stream across most of the Pacific Ocean with a low pressure system off the west coast.  Light precipitation will be possible across Central and Eastern Washington into north Idaho.  It's still a little early to nail down precipitation type so keep checking the forecast for the latest updates as we are monitoring the potential for a wintry mix.

Now look at next Wednesday, December 12th per the GFS model.

12z/Dec 4th GFS model of 500mb heights and 250mb wind (image) valid 4 AM December 12th

Next Wednesday models show the jet stream stretching across all of the Pacific and aimed at Washington, Oregon, and California.  The center of this jet actually had some red colors in there with a maximum value of 225 MPH.  This may bring more significant precipitation to the region including mountain snow, with rain, snow, or a combination of both for the lower elevations.

And it's not just the GFS, here is the Canadian model.

12z/Dec 4th Canadian model of 500mb heights and 250mb wind (image) valid 4 AM December 12th

And finally, the European model.

12z/Dec 4th European model of 500mb heights and 850mb temperature (image) valid 4 AM December 12th

The image is a bit different on this graphic (850mb temperature) but you get the idea with the strong westerly flow noted across all of the Pacific.  So while next week is still a long ways out, the general model agreement gives a boost of a confidence to at least a pattern change.

The 6-10 and 8-14 day outlooks from the Climate Prediction Center for precipitation agree with this idea with elevated odds of wetter than normal.

CPC 6-10 day precipitation outlook issued December 4th valid Dec 10-14, 2018 

CPC 8-14 day precipitation outlook issued December 4th valid Dec 12-18, 2018 

So after a generally dry period through this upcoming Friday, weather changes are likely to follow.