High Pressure Surprises

A ridge of high pressure spreads over the region, with generally clear, skies, lots of sun, and no precipitation.  Time to forget about the weather?  No way...a great deal of interesting action, from extraordinary high temperatures, gale-force winds, air quality problems, freezing fog, and an upper ridge that is amazingly persistent.

With an upper level ridge overhead and the associated high pressure to the east of us, a very large east-west pressure gradient developed over the Cascades, approaching 10.5 mb earlier today. 

Washington State Sea Level Pressure Forecast for 10AM this Morning..big gradient over the Cascades

That is very large for any time of the year.  In fact, large east-west pressure gradients extended over the entire region, resulting in strong easterly flow, particularly in gaps.  For example, the winds accelerated westward to nearly 50 kts (58 mph) at Tatoosh Island on the northwest tip of the Olympics peninsula (see plot)

Our local models knew this was going to happen--here is the forecast winds from last night's run--a little low, but it had the idea:

The areas around Tatoosh was the site of many shipwrecks, with strong easterly winds, fog, and rocks ending the careers of many a vessel. And winds accelerated to 40-50 mph at several locations over the the western side of the Columbia Gorge, with winds at the Crown Point viewpoint reaching 71 kt (82 mph)!

Aloft, there was strong southeasterly flow crossing the Cascades that descended over western Washington and Oregon.  And as that air descended the western Cascade slopes it warmed by compression. Here are the observations from the Seattle profiler (time increases to the left) today.  20-35 knot winds from the SE right above the surface.

The result of this SE flow was that the temperatures surged where it reached the surface, with some locations around Seattle getting into the low 60s.  The forecasts were way too cool today,  mainly in the lower 50s--one forecast error that few people are complaining about.

Have you noticed that at many locations the temperature is staying up even when the sun is down? At 9 PM it is 52F at Renton Airport--a location experiencing moderate southeasterly flow.   But at Olympia it is 32F.  Olympia is in the south Sound dead wind zone and the ground is radiating heat to space, but with little warm air mixing down.   Why is there a dead zone over the south Sound?  Because they are in the lee of Mt. Rainer....a huge obstacle to the southeasterly flow.

And in the dead zones and valleys, where the easterly flow is unable to surface, the radiative cooling fostered by clear skies will allow a cold dead layer to form and air quality to degrade, such as in Pierce County, where a burn ban has been called.   Here is the air quality plot at S. Tacoma provided by the Puget Sound Clean Air Agency:

Take a look at the radiation measurement from the roof of the atmospheric sciences building--little hint of clouds....don't see that often:


This general weather pattern with easterly flow and fine, warm weather should continue at least through Tuesday, and the latest European Center run suggests no precipitation at least through next Friday.  An amazing spell in the middle of winter.  And the rest of the U.S. is also unusually warm., with over a hundred stations breaking daily high max or min records today alone.  January was the third least snowy winter and the warmth has been an economic boon to many---reducing heating costs across much of the nation and allowing construction to continued unabated.  Bad for some ski resorts and sled manufacturers.  But in total it is undoubtedly good for the economy and for a certain political party.

Perhaps high pressure is not so boring after all...