Saturday, February 10, 2018

What a difference a year makes!

It has been stated before that each La Niña year is different.  Last year was a La Niña year, and this winter is yet another La Niña.  However this winter so far has been a far cry from what last winter brought.  Let's take a look at where we are this year compared to last.  Also, don't give up on winter, as temperatures have turned colder: we'll briefly discuss what lies ahead.

This winter so far
Let's begin with this winter.  Above normal temperatures and precipitation for Washington and northern Idaho.  Drier than normal and very mild to our south in Oregon.  December actually brought normal temperatures; it was the very mild January that contributed to the warmth on the map below.

December 2017-January 2018 Temperature anomaly
December 2017-January 2018 Precipitation Percent of Normal



Last Winter
And last winter, well it was a cold one especially in the Columbia Basin!  Precipitation was just the opposite compared to this winter.  Drier than normal in Washington and northern Idaho and wetter than normal to our south.

December 2016-January 2017 Temperature anomaly

December 2016-January 2017 Precipitation Percent of Normal

Snowpack
The milder temperatures this winter, especially in January and the first part of February have led to quite the difference in lower elevation snow pack this winter compared to last.  Below are maps showing the differences in SWE (Snow Water Equivalent) for February 10th, 2018 vs 2017.

This winter

Modeled SWE (Snow Water Equivalent) 12z (4 AM PST) February 10th, 2018 

As you can see, not much snow is left in the valleys.  Good news is mountain snow pack in Washington is looking good.  Oregon, not so much.  Mountain snowpack typically peaks around April 1st, so these maps could still change by then, stay tuned!

And last winter
Modeled SWE (Snow Water Equivalent) 12z (4 AM PST) February 10th, 2017 

Much more lower elevation snow pack, and Oregon was doing much better.

How does this look with regards to percent of normal?  Here is the February 10th map showing the west.

February 10th, 2018 SWE (Snow Water Equivalent) Percent of Normal

It's not just Oregon, but much of California, Nevada, Utah, New Mexico, and SW Colorado also have much below normal snow pack.

Why?
So what has caused this pattern?  Abnormally strong high pressure over the west.  Typically with La Niña this high pressure is centered further to the west.  Here is this year's pattern.

Mean 500mb heights Dec 1, 2017 to Jan 29th, 2018

And the map below shows the anomaly, with higher than normal pressure over our region as noted by the yellow and orange colors.

Mean 500mb height anomaly Dec 1, 2017 to Jan 29th, 2018

Compared that to last year, which was just the opposite with anomalous ridging to our west with a trough over us as noted by the purple and blue colors.

Mean 500mb height anomaly Dec 1, 2017 to Jan 29th, 2017
This goes to show you that each La Niña is different.  Other factors that we will not get into right now impact the orientation, placement, and strength of the jet steam.

Winter is back!
Now the pattern has shifted a bit with high pressure shifting to our west allowing colder air to drop in from the north.    A reinforcing shot of cooler air arrives Monday (Feb 12) and some models suggest this pattern may stick around for a while.  Here is the Canadian model for next Sunday (Feb 18).

12z/10th Canadian model forecast of 500mb heights, MSLP valid 12z February 18th (4 AM PST)

This model shows a very amplified pattern with a strong ridge in the eastern Pacific and a deep trough over our region.  Other models such as the GFS and European show a similar pattern.  While this pattern looks like a cold one, moisture is the wild card.  This is still a long ways out so stay tuned to the latest forecasts.

And here are the latest 8-14 day outlooks from the Climate Prediction Center which also favor elevated odds for below normal temperatures with about normal precipitation.

CPC 8-14 day temperature outlook issued Feb 10th valid Feb 18-24, 2018

CPC 8-14 day Precipitation outlook issued Feb 10th valid Feb 18-24, 2018

So, despite the mild December, January, and early February, more winter like weather (at least temperature-wise) is expected for the next few weeks.


Sunday, December 31, 2017

Top Weather Events of 2017


As 2017 comes to a close, let's take a look at the weather of the past calendar year. The year began with a cold and snowy January. Then, spring was marred by flooding and landslides. Our summer featured long periods of dry weather with many smoky days during August and September. The fall was relatively quiet followed by a couple of big winter storms during the second half of December.

This chronological list takes a look at ten or the Inland Northwest's top weather events of 2017.



#1. The Central Washington and Palouse Blizzard of Jan 10, 2017 is the first on our list. Drifting snow closed several highways and left cars stranded over portions of Douglas and Grant counties.



#2. The Central Washington Ice Storm: January 17-18. Freezing rain coated the I-90 corridor from Snoqualmie Pass to east of Moses Lake with more than a half inch of ice.



#3. February Ice Jam Flooding. The St Joe River, the Grand Ronde River, and several other creeks and streams in Spokane and Shoshone counties experienced ice jam flooding. Arctic cold in January gave way to heavy rains in February. The subsequent ice jams caused flooding and threatened to damage bridges in southeast Washington and the southern Idaho Panhandle.



#4. March Flooding. Above average rain on top of a deep snowpack pushed many rivers in Idaho and Washington above flood stage. Sprague Washington experienced weeks of high water as the creek entering town flooded fields and streets.


#5. April Landslides. Record amounts of precipitation over the winter combined with the release of frost in our soils caused landslides over the steep terrain of Washington and Idaho.


#6. Number 6 on our list of Top Ten Weather Events of 2017 actually features a day of beautiful weather. During a summer plagued by wildfire smoke and grey skies, eastern Washington and north Idaho enjoyed perfect conditions for viewing the solar eclipse.



#7. Camas Prairie Thunderstorm Wind. Residents of the southern Idaho Panhandle will likely remember number 7 on our list of Top Weather Events of 2017.  Back to back days of damaging thunderstorm winds hit the Camas Prairie on August 29 - 30. Trees were damaged and lightning sparked wildfires.



#8. September Smoke. Number 8 on our list of Top Weather Events of 2017 is a period of weather many of us would like to forget...the wildfire smoke. Cough!  Smoke flooded the Inland Northwest on Labor Day and lingered for the next 4 or 5 days. Spokane experienced some of the worst air quality on record during the first week of September. 



#9. Spokane Record Dry Streak. Our winter and spring featured record amounts of precipitation. Mother Nature did an about face during the summer. From June 29th through September 16th, the Spokane International Airport received no measurable precipitation. 80 consecutive dry days...a new record. 



#10. Heavy Wet Snow: December 19th. A big dump of heavy wet snow rounds out or list of Top Weather Events of 2017. For residents of Sandpoint, Bonners Ferry, and Naples, this storm is still fresh in your memory.  Bonner, Boundary, and Pend Oreille counties receive a foot of heavy wet snow.



Saturday, December 23, 2017

Christmas Eve/Christmas Day snow update

For those hoping for more snow by Christmas morning, we have good news for you.   Are you traveling on Christmas Eve?  When will the snow start?   And how much will it snow?  Let's get started!

TODAY (SATURDAY):

For today (12/23) we are under a dry northerly flow ushering in colder air to the region.  The next system is approaching off the coast as shown below

12z/23rd GFS model forecast of 500mb heights and 700-500mb Relative
Humidity valid 21z (1 PM PST) this afternoon (12/23)

TOMORROW  (CHRISTMAS EVE):

The offshore system begins to spread clouds into the Cascades tomorrow morning as shown below before precipitation begins to spread east in the afternoon and evening.

12z/23rd GFS model forecast of 500mb heights and 700-500mb Relative 
Humidity valid 18z (10 AM PST) Sunday (Christmas Eve)
MONDAY  (CHRISTMAS):

Light snow Monday morning will become focused mainly across SE Washington into North Central Idaho Christmas afternoon.

12z/23rd GFS model forecast of 500mb heights and 700-500mb Relative 
Humidity valid 21z (1 PM PST) Monday (Christmas)

So, have travel plans for Christmas Eve or Christmas Day?  Let's take a closer look at our forecast of snow amounts each 6 hours to get a better idea of when snow will start, and then end.

Sunday (Christmas Eve) Snow amount

4 AM-10 AM

Dry conditions across Central and Eastern Washington into north Idaho.

10 AM-4 PM

Snow spreads into the Cascades and much of Central Washington Sunday afternoon.

4 PM-10 PM

Snow continues to spread northeast, reaching the Spokane/Coeur d'Alene area Sunday evening but with the higher snow intensities around Wenatchee, Yakima, Tri-Cities, and Lewiston.

Christmas Day snow amount

10 PM Christmas Eve - 4 AM Christmas 

Snow over nearly all of the area, except possibly near the Canadian border.  Highest snow intensities over the Palouse, Lewiston-Clarkston Valley, Blue Mountains, and Camas Prairie.

4 AM - 10 AM 

Snow begins to decrease Christmas morning, but still a chance of light snow over most areas.  Steady accumulating snow continues over SE Washington into North Central Idaho.

10 AM - 4 PM

Dry conditions over most of Central, NE Washington, and into the north Idaho Panhandle during Christmas afternoon.

So, how much are we expecting?  Here is our forecast as of 2 PM December 23rd.



The previous blog discussed model uncertainty leading to lower confidence in snow amounts.  Models have come into better agreement, although the European model would support slightly lower amounts than what our current forecast shows.   Snow amounts will continue to be updated as this event evolves.  Please see our web site for the latest forecasts, and winter weather highlights found here

Thursday, December 21, 2017

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.

Thursday, October 5, 2017

La Nina - are you coming back?

Will we have another La Nina winter?  Many of you remember last year's La Nina winter that brought cold and snowy weather with several bouts of ice.   The Climate Prediction Center issued a La Nina Watch on September 14th and the next update will be issued on October 12th.  The latest updates on La Nina can be found here.

So why does La Nina impact the Inland NW?  Colder water in the Pacific Ocean along the equator from the west coast of South America to the dateline suppresses thunderstorms while over Indonesia warmer water results in more thunderstorms.  The wind and convection patterns in these areas impact the jet stream in the mid latitudes.   How is the jet stream different?  See map below


Typically, a common feature of a La Nina is amplified high pressure in the eastern Pacific resulting in a colder northerly flow over western Canada into the northwest.  Meanwhile the pacific jet stream brings in storms from the west.  Colder air plus the moisture equals increased odds for above normal snowfall in the lower elevations.  The NMME (National Multi-Model Ensemble) that was issued in September agrees with this:

NMME Temperature anomaly forecast for Dec 2017-Feb 2018
NMME Precipitation anomaly forecast for Dec 2017-Feb 2018
So since the models are showing a wet winter and possibly colder than normal, can we bank on it?  Unfortunately climate models aren't good enough yet to confidently believe them months out.  But still we can look back at previous La Nina events to get an idea of what historically happens.  If we average snowfall for all La Nina years, this is what we get...

Average snowfall for La Nina (inches)

If you are interested in more snowfall maps related to La Nina and how these numbers compare to normal, check out our La Nina briefing page found here.

So should we expect 59" in Spokane, 29" in Wenatchee, and 22" in Lewiston this winter?  While these are the averages, it doesn't show the variability that occurs with each La Nina.  Let's examine 3 cases of La Nina since 2005 and see what happened

2016-2017 La Nina
Many remember last winter.  It was a cold and brutal winter, and snowy with several episodes of freezing rain for many.  It was the 6th coldest winter on record for Ephrata, WA.  Blowing snow on January 10th created very high snow drifts for portions of the Waterville Plateau into Grant County in the Columbia Basin leading to road closures.  See picture below.

Photo courtesy of Grant County Sheriff Tom Jones
Spokane recorded 14 days of freezing rain or freezing drizzle.  The classic La Nina pattern set up with our area influenced by both the Polar Jet Stream and the Pacific Jet Stream for much of the winter.  Although the Pacific Jet Stream was aimed a bit further south compared to normal across southern Oregon and northern California where the wettest conditions were observed.  Here is how last winter finished.


The winter was especially colder than normal across the Columbia Basin where snow stayed on the ground for most of the winter.  For Lewiston, 39.2" fell making it the snowiest winter recorded since 1968-69.  For Spokane 61.5" fell, close to the La Nina average.

2008-2009 La Nina
This was an unusual winter. A little colder than normal in the Columbia Basin with close to normal precipitation for most.  So why was it unusual?  Who remembers?  Well most of the winter wasn't that bad, except for a three week period which was historic for Spokane and nearby communities.  If you were in Spokane from December 17th through January 5th, I'm sure you didn't forget.  A total of 74" fell in 3 weeks with several roof collapses.  An impressive 2 feet fell in Spokane in about 30 hours on Dec 17th and 18th.   Here are a couple snow pictures during this three week period, including one from downtown.

Downtown Spokane - Photo courtesy of Kerry Jones
Photo courtesy of Spokesman Review
Here is how the final maps ended up.


Except for below normal temperatures in the valleys, these maps don't look that bad.  What is the screaming message you ask?  Even if the winter as a whole finishes close to normal, you can't rule out a brief period of extreme winter weather.  Be prepared!

2005-2006 La Nina
This La Nina was slightly warmer than normal (about 1 degree) but was very wet with precipitation 130-150% of average for most.  With the milder temperatures this meant less snow for most lower elevations.  Wenatchee only got 6.9" for the winter with Spokane at 27.3". 


As you can see, every La Nina is different.  There is a delicate balance between the polar jet and the pacific jet with each of these impacting our weather.  Precisely how these set up over this winter is unknown at this time.  But historically, La Nina brings increased odds for above normal snowfall especially in the valleys.

Since this may be the second La Nina winter following a strong El Nino winter, we went back and looked at five analog years since 1950 where this occurred.  What happened in these cases with the second La Nina?


As you can see, a tendency for cooler and wetter conditions, typical of La Nina.

Finally, we'll leave you with the latest winter outlook from the Climate Prediction Center

CPC winter outlook for December 2017-February 2018 issued September 21st, 2017

Equal chances for temperatures and slightly elevated odds for wetter than normal conditions.