May 09, 2016

Cooler West, Windy East

During the last day, winds have surged to amazingly levels in eastern Washington with gusty easterly winds reaching  60 mph.   Strong enough that it blew down a power line and started the first significant fire of the season (now about 50 acres) near Entiat, Washington (near the Columbia River).
 Here are the max gusts for the 24h ending 7 PM Monday for a domain stretching from southern Puget Sound to Walla Qalla.   The red numbers are winds over 50 mph.

In the spring, the winds increase rapidly when cool, Pacific air floods western Washington and Oregon as it did on late Saturday night.     Cool air is denser than warm air and is associated with higher pressure.  With the Cascades blocking much of cooler air on the west side, a large pressure difference (or gradient) develops across the Cascades.  In addition, the flux of cool air is often forced by an upper trough, which results in pressure declines east of the Cascades as it passes through.

Let me illustrate the development of a large pressure gradient across the Cascades with the sea level pressure forecasts for 8 AM Sunday.   The shading shows low-level temperatures, with green temperatures being cooler and orange/red warmer.   You can see the contrast in air temperature across the Cascades.  The solid lines are isobars (lines of constant pressure).  You note a lot of lines (strong pressure gradient) across the Cascades.    Such large pressure gradients produce strong winds as air accelerates from high to low pressure, particularly within the lower areas of the central Cascades.

There is a weakness in the Cascades north of Mt. Rainier called the Stampede Gap, so some of the strongest winds are around Ellensburg.  There is a reason there are a lot of wind turbines around there.  

Modern numerical models run at high resolution can forecast the strong winds along the eastern slopes of the Cascades fairly well.   Here is the sustained wind speed prediction for 8 AM on Sunday from the UW high resolution WRF model.  You see the strong winds along the lower Cascade slopes?

And here is a blow-up from our uber-resolution (4/3 km grid spacing) WRF model forecasts for gusts at the same time.  The model had isolated locations reaching 60 knots--not bad.

This is the windy season on the eastern Cascade slopes--with cool marine air on the west side and the eastern side warming rapidly (producing low pressure).  Wind power season.

Major news:  the proposed coal terminal near Cherry Point (near Bellingham) has been stopped by the US Army Corps of Engineers.   Their reason:  to honor the treaty rights of the Lummi tribe to use those waters.  This is a huge victory for those concerned about coal dust, traffic backups near rail crossings, and the climatic effects of sending huge amounts of coal to Asia.


  1. Awesome news on the proposed coal terminal! Thank you for your advocacy Dr Mass.


  3. Really interesting data - even w/ the big pressure differentials west of the crest, the strong winds aren't actually there (As I would have assumed previously).

  4. I'm always confused about wind direction.

    According to some dictionaries "If something moves in an easterly direction, it moves towards the east. 'The yacht was continuing in an easterly direction.' However, an easterly wind blows from the east. 'There was an icy easterly wind blowing off the sea.'"

    Are you using this convention? Thanks.


  5. Windsport enthusiasts were enjoying the phenomenon out at Arlington, OR, Sunday where the local readings were 40G50+ mph. Some of the action captured by a professional photographer

  6. On a completely different note I'm glad to see that the NWS has stopped screaming in the Forecast Discussions. That all caps thing was like something from the early days of computers, much better now.

  7. Thanks Mr. Triggs. So all those wind barbs showing the wind coming from the west means that the winds were westerly, right?

  8. I was out sailing near the south end of Whidbey in sunshine on Saturday afternoon when, after light-moderate winds from the south, around 3:30 the wind changed to northerly and got very strong. I had exciting sailing into Port Madison, anchored in the lee of the land. Good thing I did. South wind and clouds the next day.

  9. Pardon for the off-topic, but after a great many years the National Weather Service teletype-d Area forecast discussion has just the last day or so decided to incorporate lowercase ASCII characters. It rather leaves one feeling nostalgic somehow; what's next, emojis?

  10. Dr. Mass,

    Fascinating info! I would love to hear your thoughts on this springs extreme temperature swings as well! I don't ever remember a time when we were so bipolar in day to day temp swings. On Friday, Portland, OR. is supposed to crack the 90 degree mark, Saturday we won't make it out of the 60's. It's been the same for the last 5-6 weeks!


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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