Sunday, February 23, 2020

Strong Winds and Heavy Mountain Snows Today

A lot of weather action today.  A strong front has just moved through Puget Sound and is now pummeling the mountains and Portland (see image below for 8:11 AM).   Behind the front is cold, unstable air that is producing convection (including some thunderstorms).  This unstable air will be moving in this afternoon---so expect showers and sunbreaks over western Washington today.


The front was vigorous enough that is brought fairly strong winds, gusting to 40-50 mph in exposed locations, and was even stronger in the eastern Strait of Juan de Fuca (see below).


Why was the front (a cold front) so strong, with powerful winds (some gusting to 60 mph, heavy precipitation, hail, and even thunder?   Because it was associated with a narrow, intense cold frontal rainband-- an intense squall line, with strong thunderstorms and very large changes in temperature. 

This was made clear by the wonderful Langley Hill radar which showed the line offshore over an hour before it hit and which documented the structure immediately before hitting the south Sound (see radar image below).   You see the red line just east of Hoquiam?  THAT is the squall line.




The winds with the front have produced substantial numbers of power outages, particularly over the south sound-- including 25000 household serviced by Puget Sound Energy (see below) and 466 customers served by Seattle City Light (mainly south of the ship canal.



But the even more strong winds are yet to come.   The front is connected to a low pressure center that is now approaching northern Vancouver Island (see larger scale infrared satellite image below).


As shown by the latest UW WRF model forecasts, that low center will move westward, and as it does so, a large north-south pressure difference will develop over western Washington--which should cause a substantial acceleration of winds.  Expect gusts of 30-40 mph over much of western Washington.

Sea level pressure map at 7 AM.

Sea Level Pressure Map at 4 PM

The latest forecast of the National Weather Service HRRR (High Resolution Rapid Refresh) model for 3 PM today shows strong gusts (to 50-60 mph) along the coat and into the Strait of Juan de Fuca.   Not a good day for a ferry ride to the San Juan Islands.  And 40-50 mph gusts over southern Puget Sound
But as in late night commercials...there is more!    The cold, unstable air, driven by strong flow to the west, will be forced to rise by the Cascades and Olympics producing bountiful snow above 3000 ft---as much as 1-2 feet in places (see map of 24-h snowfall ending 4 AM Monday)


The Cascade snow could use a bit of freshening.

And then on Monday we will have clearing skies and some sun, with dry conditions in the lowlands through Friday.

10 comments:

  1. Cliff,

    I'm glad for Monday's sun! It's just what I need this time of year.

    .

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  2. Yay! I'm excited for Friday, looks like it's gonna be a warmer day.

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  3. The Rock-on-a-string weather reporting station in Bow,WA wiggled good at 6:40 PM Sun.

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  4. Cliff, any chance you can align those sunny days with the weekend? Nothing worse than admiring nature's beauty through office tower glass. Also one more request, can you do another of your YouTube videos that explain interesting events like this to us lay folk? The last one was really great! :)

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    1. you get to admire nature's beauty from your desk? sounds pretty good to me as i sit in this windowless cube farm

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    2. Thanks for the perspective Phil, I guess it can always be worse. hopefully you can at least pull up a webcam of mount Rainier :)

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    3. i do that often : )
      https://www.nps.gov/mora/learn/photosmultimedia/webcams.htm

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  5. coming from the Midwest, i'm used to hearing weather forecasters talk about "cold fronts" and "warm fronts" (and sometimes "stationary fronts"). however, you only seem to mention "strong fronts" and "weak fronts". why the difference in terminology? i've tried googling "strong front" but haven't had much luck figuring out what that means, and how it relates to warm vs cold fronts.

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  6. All hype and not much action. Here in the "convergence zone" between Seattle and Everett, which is supposed to be the focus of these things, I got no thunder and almost no rain- just some breeze. A forecast bust?

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