May 02, 2010

A Weather Odyssey Across the Cascades

The Weather Choice On Saturday

One of the most marvelous aspects of our weather are the contrasts on nearly any day with a little driving...and yesterday (Saturday) was no exception.

Yesterday morning there was a cool, unstable air mass over western Washington in the wake of a Pacific front. In western Washington, a cool day with lots of clouds, scattered showers, a Puget Sound convergence zone, and rain on the western slopes beckoned. At roughly 9 AM, the above cam shot at the UW showed the dismal scene (top image). But the satellite image showed another option (see below).

East of the Cascades, as the air descended down the terrain their was profound drying of of the air mass , with sunny skies and some warmth , even though the air mass was fairly cool. My favorite place in such situations is the Vantage/Quincy area... a low region near the Columbia River that is typically sunny under westerly flow. A look at the Silica Road WSDOT cam was promising (see image). The WSDOT cams and weather observations are a real treasure trove for travelers, by the way (

My family and I were off around 10:30 AM heading across the Cascades on I90. Dry and cloudy until roughly North Bend, and THEN the weather went bad. With a little lift the atmosphere was destabilized, producing growing cumulus and showers, some very heavy. The weather radar showed some of these windward showers (see below).

Moving up towards Snoqualmie Pass (see cam) it was pretty miserable (see image). 43F and pouring. The showers held on across the Pass and only let up around Easton. But then the sky brightened and east of Cle Elum it started to open up.

But as we moved towards Ellensburg, something else was noticeable--gusts were pushing my car around--and that was expected. With deep cool air moving in from the west, a large pressure difference formed across the mountains. With strong downslope flow and warming east of the Cascades, the pressure had dropped over the eastern Cascade slopes (called a pressure trough) and a large pressure difference was accelerating the flow eastward (see pressure and temperature forecast for 2 PM below). The lines are isobars, lines of constant pressure, and you will notice quite a few of the lines across the mountains.

And I knew that such situations produce another, somewhat unwelcome, feature--strong winds, particularly in the Kittitas Valley area near Ellensburg. There is a reason there are lots of wind farms there. There is a weakness in the Cascades...called the Stampede Gap--and when there are large pressure differences across the Cascades, the air is able to accelerate through this gap into eastern WA (see my book for more information on this). The National Weather Service even had a wind warning up.

When we got to Vantage, there were whitecaps on the river, but the sun was glorious. We headed north a bit (getting off I90 at Silica Road) and stopped for a nice lunch at Cave-B winery/inn near the Gorge Amphitheater ( Really good view of the river from their restaurant and then we hiked down to the Columbia from the inn. Beautiful day and views, but it was windy! Here is a video I made with my camera:

click on the arrow!

The air temperature was nearly 65F, with winds around 20 kts, with higher gusts, particularly near cliffs or promontories in the terrain. The ground was warm, wild flowers were all over, and the for the trip back to the Inn we passed by a nice waterfall. And then we stopped at their winery's tasting room on the way out. Sun, wind, scenery, the fragrance of sage, and wine....not a bad way to spend the day.

But then there was the two-hour drive back into the clouds.

On the return, the winds had clearly strengthened (typical, due to heating east of the Cascades), with justs to 40 mph near Ellensburg, and a wall of clouds was waiting for us west of Thorp, near the eastern slopes of the Cascades. In addition, lots of dust was rising off some fields east of Ellensburg...some farmer was losing quite a bit of top soil from his/her newly plowed fields. Loss of topsoil is a major problem in eastern Washington and duststorms have caused serious, and sometimes fatal, accidents.

PS: A strange situation is happening right now (Sunday). Rain is spreading over the region...but NOT over Seattle--we are being rainshadowed by the Olympics! The reason...the unusual combination of westerly flow aloft and a wet system.

PSS: As noted in the side bar, I will be talking about local windstorms on Tuesday, at 7:30 PM at McHugh's Irish Bar in Seattle. Shows what I am willing to do for a beer!


  1. I'd trade sunny/windy for cloudy/calm anyday. I lived near CWU last year, and like Seattle, trees, buildings, fences, etc. lessen the feel, but get into vast open spaces...its miserable.

    Nicest part of the day is 6am - 10am. High wind warning tomorrow! Make it 6 straight days of wind.

    Did you do a gas milage check from Cle Elum to Vantage? Best in the state.

  2. Thanks for this post, Cliff. Being a student in Eburg, I am always fascinated by the winds, and they always blow in just one direction (the trees are all tilted that way too). I always look at the satellite map and see that usually when it is windy, there are clouds west of the cascades and clear east. There is a high wind watch for all of Eastern Washington Monday, it has been windy for the past five days! How is this cold front that will be moving across, different than the typical cloudy west clear east type wind?

  3. I remember those contrasts in weather everytime my family as a kid drove to idaho as a kid and when my husband and I and 2 kids lived in pullman going to WSU.

  4. I live in Cle Elum and went to Ellensburg last Thursday. Drove through a cloud of dust from a plowed field east of Thorp. The paper reported a gust of 58 mph that day.

    The gas mileage is only good if you're heading east...coming back from Eburg can be a real wrestling match with the steering wheel.

    There is a magic line around Easton. If you are heading west, that's where the rain starts. In winter, if it's raining in Cle Elum, it will be snowing at the top of Easton Hill.

    Raining steadily here this evening and the wind has eased.

  5. Crazy that it is raining in Cle Elum when it has been clear to partly sunny all day and currently here in Eburg.

  6. Very windy here at the North Coast tonight....not much rain.

  7. Great day trip and I didn't have to leave my chair! Now that Highway 20 is open how about taking us for a drive next weekend. Thanks Cliff.

  8. Great reminder that a little road trip will pay off with good weather. See you Tuesday night!

  9. I was in Spokane all weekend. It was dry Friday night, rained overnight, then began pooring heavily during the day. I drove up into the hills behind Coeur d'Alene Lake where the weather ended up very spotty in the afternoon: sunny one moment & hail the next minute. Drove back to Spokane where it was beautiful for several hours. By evening the dark clouds rolled in, including a few thunder showers, then it cleared up again and stayed dry through Sunday. Clouds came in Sunday afternoon and the wind picked up.

    I started driving back west from around Pullman in the late afternoon. It was rather windy the whole way back toward ellensburg, but the clouds disappeared about halfway across making for a decent sunset. Of course, as soon as I reached the pass on I-90 the heavy rain started, and continued until around North Bend or issaquah.

    I think I saw just about everything this weekend.

  10. Very windy on Capitol Hill on Sunday night into Monday morning. In fact there was an isolated gust just after 3am that was one of the strongest I can recall in over a decade living here (based on very scientific instrumentation... ie, the creaking and swaying of the building). The buoy out in Elliot Bay says it was 42 kts and the Coast Guard Station at Pier 36 saw the same thing. However, this station (apparently located at 1100 Western Ave) recorded an 89mph gust at 7:36am... which has to be some kind of error, right? (Unless there was a crazy venturi effect from surrounding structures or something). The other nearby stations show more reasonable data with lots of high gusts in around 3am, but nothing that high and nothing notable around 7:30.

  11. It's pretty crazy over here right now, walking on campus is pretty hard! It was sunny and clear, but you could see the wall of clouds by the cascades. Then all of a sudden it got dark and misty, the wind is so strong that it is blowing the rain and clouds from the cascades over into the Kittitas Valley.

  12. Thanks to you, Cliff, I am a regular watcher of the radar images now. NWS forecast a convergence zone for the San Juan/Georgia Straight area while it was still sunny here. It is currently breezy and rainy here in B'ham and sure enough, there is a convergence band over us and one over Puget Sound. I'm getting better at navigating these micro weather events thanks to your blog.


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

A Forecast Failure and the Next Snow Event

 The weather prediction business is a humbling one.      Yes, forecasting systems have gotten far better, but occasionally they disappoint, ...