February 03, 2012

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...


  1. Speaking of high temperatures, I'm curious how obviously erroneous temperatures are handled in the records. KBLI showed a high temperature of 68 degrees today, showing 66+ degrees for a period of at least three hours. Meanwhile, every other weather station shown at wunderground for Whatcom County had the temperature below 60, and 90% of them, I'd guess, were within five degrees of 50. At 4pm, it showed 67 degrees. At 5pm, 50 degrees.

    wunderground was reporting a record high temperature in Bellingham yesterday -- Thursday -- at 59 degrees, but I suspect that data was not correct, either.

    There's something funny going on with the thermometer at KBLI, obviously. But are these data retained as official data, or are they discarded at some point?

  2. Drove from Seattle to eastern WA yesterday and was impressed with the very strong winds on the west side from North Bend to top of the pass. Two hands on the steering wheel type weather. Less wind than usual observed in the wind farms and about usual at Vantage. Main roads bare and clear and weather sunny all the way. Rural roads at destination....plenty of ice and little bits of fog in NE Kettle River range.

  3. Thank-you Dr Mass, a very fascinating description of our Chinook Winds (correct me if I've got this wrong). In Europe, this same wind is called the Foehn. I remember well standing on the tarmac at the Innsbruck Airport about 7 am with my cup of coffee. There was a cold chilling steady (katabatic) breeze coming down the river from the west. We kept our hands wrapped around our cups to keep them warm. But then, every fifth minute or so, we'd just get about knocked over by a relatively hot blast of air from the southeast - it'd blow on you like a hair dryer and then be gone. The locals knew this wind well, they just looked at you, smiled and said it's "the Foehn". One fellow, who was a member of the sailplane club on the other side of the airport, said it was going to be a great day for the members - the Foehn always brought the best soaring over those beautiful Austrian Alps.

  4. What a funky winter. You said earlier the typical La Nina ridge has settled more to the east. Imagine what our winter would have been if it settled more to the west.

    I quickly check the NWS 500mb model every morning. The trough out in the western pacific is massive. The flow in Siberia is crazy east to west. Its pretty insane.

  5. The NWS is saying the winds on Monday will be the worst of the weekend. Any chance that the "gap" winds will change to mountain wave winds?

  6. I have noted that for some time now we seem to get a preview of spring for about two weeks in February. Then winter returns with a vengence, crushing all our illusions.

  7. My family moved back from California to Seattle 42 years ago -- I reluctantly, my then-husband happily. It was February 3 and beautiful sunny weather. I thought, "Maybe this won't be as bad as when we were here before." Several weeks later, it shut down again, as Don Carter said.

  8. Unfortunately, a lot of the weather phenomena cited just aren't that interesting in Winter. Oh, I'll take the sunshine reprieve, but some winds and a temp nearing 60 here and there doesn't captivate my attention for a week on end. :)

    That said, I'll gladly take it, so long as the weather doesn't decide to shift into a winter pattern (persistent trough) from April to July for the third year in a row. So knock yourself out Mr. Ridge of High Pressure, just don't let yourself get pushed around come Spring.

  9. Forecaters nailed it. I love this weather. I am getting very ill with Spring Fever.

  10. We barely got to the mid-forties yesterday on the west side of Sinclair Island. At the same time it was 60 in Seattle it was 40 degrees here with a cold fog blowing in from the north.

  11. Right now, it is 26 deg. in Olympia and 44 deg. in Seattle. Cliff has written about the artificially low temps reported from Oly, but this is unreal! There is NO front coming through. What is causing this extreme 18 degree difference?!

  12. That made for a fast flight from Denver yesterday, Tailwinds heading west? yes.

  13. If I wanted to visit Crown Point and experience some high wind, would there be a forecast with enough lead time and reliability to drive down there from Seattle?


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