November 26, 2018

Strong Winds and an Atmospheric River Hit the Northwest

Strong winds, some exceeding 50 mph, are hitting some parts of the Northwest today.  And a moderate atmospheric river promises substantial rain in the mountains.

The maximum wind gusts over the past 24 h, shows a fascinating picture of very strong wind in some locations, while lighter winds are evident in others. 45-55 mph gusts in the San Juans and along the coast.  And 40 mph gusts east of North Bend as one ascends towards Snoqualmie Pass.   But light winds around Puget Sound.

Such huge differences result from our terrain and land-water contrasts.

A forecast from the UW WRF modeling system of sustained winds (not gusts) for 10 AM this morning shows the pattern (see below).  In particular, look at the strong winds from the eastern Strait of Juan de Fuca across the San Juans. 

Why are they there?  Blame the Olympic Mountains!   The sea level pressure forecast is shown by the light brown lines.  There is relatively high pressure on the windward (south side) of the Olympics and a leeside pressure trough on the northern side.   This pressure pressure pattern results in a strong pressure difference on the northeast side of the Olympics that accelerates the winds from the southeast.  And strong winds are found on the western side of Snoqualmie Pass because there is a large pressure difference across the Cascades and air is accelerating towards lower pressure to the west.

Smith Island, just west of Whidbey Island, has had recent gusts to 48 knots (SISW1) and  similar winds are being experienced along the coast, such as at Destruction Island (DESW1).   Destruction winds are particularly vicious because of the Olympics as well, since the barrier enhances the pressure gradients in the area.

But winds are only part of the story today.   A moist flow, known as an atmospheric river, is heading right into us, as shown by the infrared satellite image at 7:30 AM (below).  A really juicy frontal cloud band that stretches well into the Pacific.

We can see the plume of moisture clearly in a short-term forecast of total atmospheric water vapor in vertical column of air:

The resulting precipitation over our region during the next 24h  will be substantial, with parts of the Olympics and north Cascades getting over 5 inches of liquid water equivalent:

Note the light precipitation to the NE of the Olympics?   A world-class rainshadow is happening as the air sinks on the lee side of the barrier.  Here is the latest weather radar image--the rainshadow is spectacular:

And then mid-week the jet stream goes south and California gets hit hard by precipitation and mountain snows.  Fire season is over for central and northern CA.

Atmospheric Sciences 101:  Weather

I will be teaching atmospheric sciences 101 during winter quarter at 11:30 AM at UW's Kane Hall. Basic introduction to atmospheric sciences, with a 10 minute "weather discussion" starting every class.


  1. Agree that the NE Olympics rainshadow has been epic during this storm.

    Rainfall on Sunday at my house in Sequim: 0.0"
    Rainful Monday: 0.01 so far.

    No real wind. Broken clouds. Sunshine part of yesterday. See some holes now that might open up. Perfect SW storm to maximize the shadow. Winds are going to have to shift more westerly to drive any moisture down the Strait to us and flatten out the pressure gradient.

    Heck, even my ceanothus bushes are flowering a brilliant blue. Supposed to only do that in June, but they are confused. They think this is late Spring. Weird.

    I should be hoping for rain as we are kind of dry, but I'm not that crazy in late November.

  2. What are the chances that the Hood Canal Bridge will close this evening?

    1. The bridge is closing 10 PM - 4 AM every night for maintenance until Sunday.

  3. Dr. Mass,

    I see the "S" word has crept into the forecast. Too soon?

  4. 51 MPH 1.5 miles SW of KBLI at 12:54PM

  5. King tide this AM as well! I guess Tuesday AM will be even higher what with lo pressure.

    Some of us went to the Kukutali Preserve near LaConner this AM - the tombolo from the mainland to Kiket Island was lowered this summer and a channel cut even lower on the west end of the tombolo. Boy the water was rushing through from the south and carrying quite a lot of small wood through. Moving some big stuff around well too. Going to be some big changes in that beach and piles of driftwood this winter!

  6. A year ago, we escaped Seattle for Klickitat County, which is a much saner and cheaper place to live. We look out at Mt. Adams, about 25 bird miles away. Closer than that, and lower than that, are the Monte Cristo mountains. Word is that snow in the valleys follows snow on the Monte Cristos by two weeks.

    About the middle of last week, we saw the first fresh snow on the Monte Cristos. The two-week rule worked like a charm last year, and wouldn't you know it, the most recent forecast calls for snow this coming Sunday. We shall see.

  7. Yep, hardly a drop in Anacortes today.


  9. in spite of this storm aren't we having an unusually dry late fall? Our power here in Edmonds has yet to go out this season. Something wrong.

  10. When we lived on Lummi Island, we saw and took panorama pics inside rain shadows all the time, it was sweet! Now in Ferndale, we get blasted by Fraser River cold flows in the winter, and we are still getting slapped aroun by winds now...

  11. Excellent forecast again, sir - we are getting HAMMERED in the mountains, near Mt. Baker. This event began at about 1:25 am, and as of this moment (just over 20 hours) I've recorded 3.48" and the UW radar indicates more "incoming." The USGS river gage (12205000) is breaking records again - not the first time this month. When it hasn't rained it's been wintry cold.

    There may be an "unusually dry late fall" happening somewhere..somewhere else. (Cheers, weather watchers)

  12. Again, this was mostly a non-event in Bellingham as far as winds are concerned. The forecasted strong overnight winds associated with the cold front never really materialized. The strongest winds were earlier in the day and were associated with the warm front. Below is a link to the Bellingham airport weather station, which is a half mile north from where we live, and as you can see, sustained winds were very modest and gusts fairly intermittent, with nothing very significant. Since moving from Seattle 3 years ago, we have learned that gusts in the mid 50's at the airport really are not a big deal. The airport is very exposed and tends to experience more severe winds compared to the rest of Bellingham.

    I watched the TV weather folks make a huge deal of an occasional Bellingham Airport gust, which reflects their lack of meteorological expertise. They tend to cherry pick the worst and generalize it to everywhere.

  13. Frequently, the Admiralty inlet will get clipped by the tail end of a post storm convergence zone.

    Did not notice the phenomenon on northern part of the Quimper Penninsula, with this storm??

    A windy but pronounced perfect rainshadow yesterday! The shadow looked to be shifted slightly east?. (Possibly convergence zone was shifted SE also?)

  14. Hi Cliff! Thank you for your excellent predictions and explanations. I wonder if you could tell me why our storms don't have names? Some have been tied to the day they happened like the Columbus Day storm but they don't get names like the hurricanes and typhoons etc. Is it because they aren't big enough or is it because there is a succession of hurricanes/typhoons and they need to be differentiated? I hope you come to Friday Harbor again soon! Shelle Cropper

  15. So far here in Portland, below average Fall precipitation, this latest storm split apart, leaving the bulk to go into WA and the latter half into CA. Oh well, CA needs this more than we do (so far).

  16. "in spite of this storm aren't we having an unusually dry late fall..."

    It is absolutely impossible to stop the drought talk. Absolutely impossible. Every year, in some place in the state, precip can be below normal... but even if it is not remotely statistically significant - or has zero bearing on the environment or water supply - we still hear it as if it was a crisis, ad nauseum (KOMO did a piece a few weeks ago about how dry the ytd was in Seattle - and we were at 95% of normal).

    The Cascades and Olympics - where our water is stored - have been utterly hammered with precip this fall, I mean in some places off the charts. Any articles on that? Any articles about our reservoirs dumping water? No, instead the Seattle Times runs the headline a day ago: "A juicy pineapple express storm is hitting Washington, but it won't make up for dry November"

    Who would write that headline if they knew the truth? Or is there another reason for writing it that way?

    The drought forecasts, the scare-mongering, the misrepresentation of stats and data - all of it gets worse every fall, and you can set your watch to it now. It is 100% predictable. Who believes any of this anymore?

  17. There have been some nice electrical storms rumbling through Vashon today. This was after a couple hours of sunshine around noontime. Still more to come maybe...

  18. Wow... if the hourly totals are right - and the radar would look to be backing it up - Seatac just got deluged for 3 hours straight, and will easily set a record for precip for the 24 hrs.

    Oh but that's right, precip is supposed to fall in perfect daily and weekly average amounts in every location like it used to... said no honest scientist, ever.

    November. What a great month. As unpredictable as it gets.

  19. As evidenced by a couple of earlier comments, Whatcom County is utterly diverse where weather (among other things, lol) is concerned. Quite often non-events in Bellingham are far more significant north and east. Bland weather south of Smith Road is the norm; head toward Baker and/or the border and it’s a different reality.

    ~ Colleen

  20. I had a lot of fun teaching 101 classes, enjoy!

  21. A couple of record breaking rainfall days have really knocked down your deficit for the rain year up in Seattle. Number was -3.15" on the 24th and is -0.54" through yesterday.

    Here in Oregon the rainfall totals have improved but we have been much drier leading up to the recent storm activity. Southern Willamette Valley is around 5" down on the rain year, Portland maybe half that. Recent rain totals (I measured 1.05" & .89" last two days) have lifted my spirits some.

    For what its worth the surfer dude on the Stormsurf site indicated the current MJO cycle is due to generate less activity for a bit picking up again around mid December. As I have been checking that site only for a couple of weeks I have no idea what his track record is like but its interesting seeing his walk through all the NOAA, etc. data.

    Incidentally (and consistent with the Stormsurf discussion) there sure does not seem to be much heating going on in the equatorial Nino index regions ( California nonetheless is getting some decent rain.


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