January 30, 2011

Dry, Sun, and Modified Arctic Air

Well folks, the threat of snow around here is over for a while. Cool, dry, modified arctic air is pushing over the region, showers are rapidly dissipating, and the sun is breaking out. If the models are even half correct, the next 3-5 days will be generally dry here without any significant weather activity other than a cool down (mainly east of the Cascades) and strong easterly flow in the gaps, such as the Columbia Gorge and the Fraser.

In sharp contrast, the East Coast is going to get hit AGAIN Tuesday by a major snowstorm.

Is there a connection between our opposite weather regimes? You bet there is. As shown in this upper level map for Tuesday, when we have a big ridge, a major trough tends to build downstream (east) of us--bringing stormy weather to the central and eastern U.S. Think of the atmospheric flow aloft as analogous to a rope that you are swinging up and down. There are a series of undulating waves in the rope. The wavelength of the waves (the distance between ridge to ridge or trough to trough) in the atmosphere has a typical scale of thousands of kilometers, for reasons I won't get into now, but which is based on basic physics. So the persistent ridging over us, bringing dry, cool weather this week over the NW, brings the opposite to those poor folks east of the Rockies. Want dry weather with lots of sun...forget Florida...head to Seattle.

Locally, the cold, dry air started pushing through the Fraser Valley into Bellingham and NW Washington yesterday. Here is the latest surface weather plot for NW Washington:You can see the northeasterly flow passing over the San Juans and then moving south and west. Winds have been gusting to 40 mph and more in some locations around Bellingham from this Fraser outflow. It is interesting that the first sign of this continental air from the BC interior is often not temperature, but humidity, or rather dew point. Look at the lower, right red numbers (dewpoint) on these plots and you will see what I mean. And here is the high resolution forecast for 10 AM this morning of the winds..the Fraser outflow is quite clear.

Taking a look at the latest visible satellite image, you will see a residual band of clouds over the middle of the state (with lots of holes) and completely clear skies to the north. This full clearing will move south during the day. With cooler, drier air over us and clearing skies tonight, expect cold overnight temps--20s everyhere and some lower values in valleys and cold spots. Protect your plants!

Even colder air is surging southward into eastern Washington (see plot of current observations)
--and that will help strengthen an east-west pressure difference (higher to the east), which will accelerate the winds in the Cascade passes and the Columbia Gorge. Here is a forecast plot of the pressure pattern today...you can see the packing of the isobars...lines of constant pressure..near the Cascade crest. The colors provide lower-atmosphere temperatures and you can see the colder air (blue colors) east of the Cascade crest.

I wanted to mention that I will be speaking next Saturday (Feb 5) at Port Townsend HS at 3:30 PM about regional implications of global warming...more information is found in the link to the right.

Finally, thanks to all of you that have contributed so far....you have provided funds that are sufficient for two uninterruptable power supplies for our main modeling cluster ($900 each).


  1. Seeing snow this morning in Ellensburg, but it isn't really accumulating yet, big, fluffy flakes. The temperature does seem much cooler than the last few days

  2. Cliff, not much snow in bothell just a couple of flurries.

  3. I was pleased to get out this morning and work up a sweat on a 6 mile hike. The air is so still and I even saw new green leaves on Indian Plum.

    I was happy to send a donation to your program as I have learned so much here. I never make plans without considering what Professor Mass has been covering and what the Prob-cast is saying

  4. Question about the current situation, if only as a potential topic for a future blog. Both you and the National Weather Service are predicting (mostly) sunny skies for this week, but when I look at the GOES W images, I see a fair amount of water vapor (e.g., http://www.ssd.noaa.gov/goes/west/nepac/flash-wv.html).

    Am I seeing the "mostly" part of the forecast? Is there anyway to tell from these images whether the coming weather will be rain and what will be "mostly sunny"?

    I know there's more to forecasting than just looking at one series of images, but usually the satellite images more closely support the predictions and I'm interested in what's different this time.

  5. Cliff,
    When I hear the term "retrogression" as far as high pressure systems, I realize that it means the high is moving west. Knowing how our weather, for the most part, moves from west to east in the Northern Hemisphere, how does this retrogression work?

  6. The UW mesoscale models have cloud forecasts, you can see the clouds thin and dissipate over Western Washington in this loop

    Or go to this link
    and look for the various cloud products under the wrfgfs--"looks like infrared satellite" is a favorite of mine.

    I'm a NWS forecaster--we obviously have models of our own which show the same thing, but ours are mostly RH graphics for various layers and levels. But the UW cloud forecasts are worth a look and I use them too.

    I will say, our upper ridges of late have not been giving us as much sunny weather as they might, and you're right, a lot of overrunning clouds keep breaking through. But Tuesday might finally be sunny around Western Wa.

  7. Actually, that cloud forecast is
    "Outgoing Longwave Radiation (similar to IR satellite)"
    hit a control F and just search for longwave to find it.

    Note, the other cloud forecasts are just above that, low mid and high clouds, Column-integrated cloud water, Near surface Cloud Water is good for marine stratus, good luck!

  8. Zathras, thanks for the links. Fascinating.

  9. Feb. still looking very La Nina-like in the latest http://www.cpc.ncep.noaa.gov/ forecast released today.

  10. The major winter storm that is developing right now and is expected to hit Kansas City, MO; Chicago, IL; New York and a bunch of other big cities is extraordinary! Cliff, you should explain the storm and what is going on. Also, the arctic blast happening in Montana/North Dakota/Minnesota is crazy cold! -55 degree windchill! Brrrr

  11. The earth has been going through warming and cooling cycles since time and eternity. I am sure it will be doing the same thing long after we are gone.

    Man made global climate change is pure unadulterated bovine scatology. When I was in college 30 odd years ago, the worry was global cooling, for thelast 15-20 years it has been global warming. Man has not yet been able to change the tides or ocean levels much less the temperature of the seven seas. Mount St. Helens eruption in 1981 and Mt. Pinatubo in 1991 have put far more CO2 into the atmosphere than all of the industries on earth for the last 150 years.

  12. This storm taking over our nation deserves a post of its own. Even Dallas is going to get hammered. Just got back from Panama City, Florida where we had to de-ice our MD88. It was 29F in North Florida...yikes! Going back to Florida next week for work and chose to connect in Dallas vs. Chicago. This winter is becoming legendary east of the Rockies.

    Thanks for such informative, insightful blog entereis Prof. Mass...and for being so responsive to our requests as readers/commenters. I'll be donating a little bit soon! Thanks again, Harrison

  13. Almost 8:00 pm and we are still waiting for it to get dry! Didn't see a single ray of sun today....misty, rainy, foggy all day! Highest wind gust was out of the NNW at 5 mph.....hope tomorrows forcast holds more true and the sky clears a bit and we see a glimmer of sunshine!

  14. From our POV, this is certainly the most boring winter I think I've seen in a long time -- a bummer given the lead up hype that La Nina would give us some fun. Blech.


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