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.