Tuesday, December 27, 2016

The Potential for a Major Cold Spell in the Northwest

Although temperatures have been relatively normal for the last few days, the last month has been decidedly colder than normal over the Northwest, as suggested by this map, which shows the deviation from normal for the past 30 days.  Much of our region has been 2-4F colder than typical during the past month.  Such cold temperatures have brought us a very healthy snowpack.

But the latest model runs are suggesting a much colder period next week, one that would be far colder than we have seen in many years.  

Since we are looking forward in time for an extended period, we must think probabilistically and thus I will show you mainly ensemble (many forecast) output.

We can start with European Center ensemble forecasts (51 forecasts) for surface temperatures (max and min) over Seattle.  The range of their ensembles are shown by the blue bracket, while the ensemble mean (often very skillful) by the green line.  Their single high-resolution run by the black line.  50% of the ensemble members are within the green box.

Note that just after the new year, the high temps drop below freezing and then plateau out around 25-28F.  But uncertainty gets large as well.



The US GFS ensemble, shown below, does something similar (Seattle temperature shown, ensemble mean indicated by the black line, high-res member, blue line).  Much colder next week, but with substantial uncertainty.

The forecast surface weather maps for next week based on the high-resolution NWS GFS model are chilling, with cold air (blue colors) extending over the whole region.


The latest weather.com forecast (which is generally excellent) is going for cold and sunny early next week as the cold, arctic air spreads south.  Is there a chance of snow as the cold air moves in?  The answer is yes...but the uncertainties are too large to speculate on that now.


I feel sorry for those Northwesteners who have travelled to warmer climes over the holidays....they are going to suffer terribly next week, while the cold-hardened folks who remained will be more comfortable.


14 comments:

Dean said...

As a weather forecaster who's had one day off in the last four weeks, _I_ sure don't feel sorry for any vacationers coming back from warmer climes. :-)

Bob said...

This fall/winter is looking more and more like the 1949/1950 pattern. Warm November, cool December - and record setting cold and snow from January into February. Time to turn the cat up to 9...

Scott K. said...

Just bought a space heater today. Looks like good timing!

Matter said...

I thought I saw a blip on the Weather Channel that indicated the cold being carried out for a couple weeks. I used to ice skate on area lakes in the 60s & 70s. Lake Leota would have to have 5" of ice on it before we were allowed out onto it. I have seen Lake Sammamish frozen over and Lake Washington frozen from Kenmore to Magnuson Park. Our family would ice skate at the arboretum as did a lot of UW students.
That kind of ice coverage takes days below freezing. This will test all the new buildings to see how well they have been winterized and give ammunition to climate skeptics....

remnant1978 said...

Not again, just got the frozen pipes thawed.

David said...

Cliff - What could I expect coming over Snoqualmie Pass on New Year's Eve day?

Unknown said...

Cliff, Where does the cold air come from? Or asked another way, Why does the air get cold one week and warm the next? I presume the wind is shifting from the south to the north, and bringing in more arctic air. I note that water temperature in the Salish Sea is warmer than normal. So I am thinking that next week is mostly being driven by a change in wind direction. What's your analysis?

Mark Cullen said...

Congratulations on reaching 30,000,000 page views, Cliff! A well-deserved tribute. I use your blog in my Middle School Geography class all the time - it's a trusted and valued teaching tool. Many thanks!

windlover said...

Will be interesting to see how this all plays out....Will it be as cold, or colder, than the models predict? Will we get any actual accumulating snow that sticks around for more than a few hours before melting? And how Will it all end? A huge dumping of snow before turning to rain? Ice storm like a few years back? The suspense is going to get the best of me! Whatever comes our way, my family and I are ready! Extra food, generator, pipes wrapped, extra pet food and treats, and extra wood brought in for the wood stove. Bring it on! I just really hope we do get snow...it makes the cold so much more worth it!

Unknown said...

Cliff, Where does the cold air come from? Or asked another way, Why does the air get cold one week and warm the next? I presume the wind is shifting from the south to the north, and bring in more arctic air. I note that water temperature in the Salish Sea is above normal. So I am thinking that next week is mostly being driven by a change in wind direction. What's your analysis?

Bryan Black said...

16-day GFS shows the persistent cold troughing over the entire PNW and by the end of next week has another, colder surge of arctic air coming in as well as low pressure systems sliding right along the west coast on that perfect trajectory to bring widespread snowfall to the region. Obviously a lot will change between now and then but I haven't seen the extended models show this kind of stuff since at least December, 2008.

jeff said...

This global warming thing totally sucks

tracksdc89 said...

Very interesting! During that same time period, was October similarly very wet (October 2016 having record rainfall of about 10")?

Bob said...

Looks like October 1949 had just slightly above normal precipitation.