November 11, 2011

The Weather Takes Its Gloves Off--Strong Winds and Mountain Snow

Missing Dog Update:  My dog Leah was seen near the Moose Casino in Mountlake Terrace--66th Ave W and 220th St SW.  If anyone is in the area and sees here, let us know right away! (see link on right)

We are now going into a very different, and much more active, weather period--and it starts today!

A strong front is now approaching the Washington coast and it will result in VERY strong winds in the Strait of Juan de Fuca, possible damage (power outages, localized flooding on Whidbey Island), blustery conditions and rain elsewhere, and snow in the mountains.  And I don't even want to tell you what the models are suggesting for next weekend. 

Perhaps the most profound weather phenomenon today is one I am actively researching:  a powerful westerly wind surge in the Strait of Juan de Fuca.

 Under the proper conditions, strong westerly winds can surge eastward into the Strait, reaching speeds of 50- 80 mph.  Sometimes called Westerly Strait Surges,  one will occur today.   A particular strong surge destroyed Ivar's Mukilteo Landing restaurant in 2003 (now rebuilt and my favorite restaurant) and another heavily damaged the Washington Ferry Elwha when it was under repair in Everett Harbor (December 1990).  Some pics of the damaged and rebuilt Ivars, which now has a weather theme:

The situation associated with westerly straight surges will occur today:  a broad ridge over the eastern Pacific, northwesterly uper-level flow over western Washington, and a sharp trough pushing into our region in this flow.   Here is the situation predicted for this afternoon at 500 hPa--about 18,000 ft above the surface:

You can see the strong trough embedded in intense northwesterly flow (remember the flow is parallel to the height lines and close spacing means strong winds).  As the trough passes through the winds aloft are aligned with the are the height lines at 850 hPa (around 5000 ft) to illustrate:
You see how the height lines, and thus winds, are parallel to the Strait?  And the strong gradient of the height lines (thus strong winds) are clear.  At the surface, the front is associated with a trough of low pressure, so as it passes eastward an intense low level pressure difference (high to the west, low to the east) develops and air likes to accelerate from high to low pressure. Here is the sea level pressure forecast for this afternoon at 4 PM. Pressure is increasing rapidly up the Strait.

Strong northwesterly winds aloft and big pressure difference down the Strait both support strong westerly winds that can slam in the eastern Strait, with Whidbey Island, Everett, and vicinity taking the brunt of it.  Winds can gust to 40-80 mph.   This one is not completely I would not look beyond 60 mph today.  Here are the WRF model forecasts for this afternoon at 1 PM.  Strong sustained winds of 35 knots have pushed into the Strait (and gusts would be stronger).
Three hours later, strong winds have reached Whidbey Island and the eastern Strait (Port Townsend and the NE tip of the Olympic Peninsula should get a taste of this as well).

The freezing and snow levels should drop as cold air behind the front floods the region.  With the flow directed up the mountains, enhanced precipitation in the form of snow should hit the mountains at and above pass level (more at the higher passes of course).  Here is the forecast 24-h snowfall  ending 4 AM on Saturday.  The model suggests a foot in the northern Cascades dropping to an inch perhaps at Snoqualmie.

Then another system comes in on Saturday with more rain in the lowlands and snow in the Cascades.  Here is the snowfall for the next 24-h--even more!
Good news for skiers!...we are going to start building the base they long for.  Skiing by Thanksgiving may well be in sight.

And now let me tell you something that I shouldn't.   The last few model cycles are suggesting a turn to colder temperatures on Thursday and the potential for lowland snow late Thursday or Friday.  Too early to be sure at this don't get too excited yet.  I went to a meeting run by Seattle DOT this week on winter weather response...these folks are really girding up for battle.  And this year they will have the new UW snow-weather application: SNOWWATCH...which I will describe this week.


  1. As long as the snow is NEXT weekend and not over Thanksgiving... I guess it doesn't matter. I am not excited about it though... don't have the money for the snow tires yet. :-(

  2. How much effect do the elevation structures (hills and mountains) on either side of the Straits have on the direction and velocity of the westerly winds like we will have today?

  3. November & December weather is rarely boring around here. Just don't make it freeze up at rush hour.

    And @JewelyaZ the trouble with snow tires is that they are usually lousy in the rain, and 95% of the time we have rain, unless you are high in the hills on a regular basis.

  4. Cliff,

    Most of this stuff is way over my head.

    However, it appeared on the radar this morning that this system was coming from the North/NW. But as I rode my bike to work, the wind was coming out of the south. Evidenced by the wave against 520.

    Help me understand that.

    Thanks- Jack

  5. The models have been pretty far off this fall so it's difficult to have much confidence in them, but a snow event would be fun.

  6. is today's weather system a relic from the Alaska storm?

  7. Cliff, to me it appears by the maps that you show that Snoqualmie Pass will receive 4-8" Friday into Saturday, and a lot more Saturday into Sunday.

    Snoqualmie pass is nearly directly east of the most southern reaches of Lake Washington. I do see the area in the mountains that is forecasted to receive about an inch of snow, but that seems too far south to be at Snoqualmie (I hope!).

  8. jno62,

    The wind from the south may be due to the fact that the system to the north is low pressure and the system to the south is of higher pressure. In between the systems air from the higher pressure system flows to the lower pressure system creating the wind from the south.

    I am not completely sure of this answer can anybody else expand on this?

  9. The snow can't come early enough for me, especially if it means that Baker opens up soon and I can get some early skiing in.
    I just checked out the new SnowWatch website and it looks really interesting and helpful with all of its maps and data. Hopefully the maps will show color soon.

  10. I've been watching the Snoqualmie Pass Cam and the temp dropped about 10 degrees in the last half hour and the snow is starting.

  11. 3pm and a fearsome wind has suddenly come up from the northwest. Must be blowing sustained 50mph in Rosario Strait. Amazing how fast the water has turned to froth.

  12. Hi Cliff,

    The thing that made me curious about today's storm (Friday) are these very long 'line clouds' out in the Pacific. You've probably explained them before, but can you briefly comment on what causes clouds to form in such a manner?

  13. Just got thunder and lightning at 5:35pm here in N. Seattle. Bring on the exciting weather!

  14. Nice lightning strike followed by enough hail to turn the ground white about 5:30 this afternoon, in Seattle at NE 75th St. & 44th Ave. NE, elevation 300 feet.

  15. Fun times out here on Hood Canal, just north of the bridge. High winds this morning followed by a period of calm, then intense rain with a hail shower. Then the stratus deck came down within a hundred feet of the water. Now a full moon and snow on the Olympics. Followed the whole thing on the UW Radar Loop.

    Re: Snow tires; forget them. This isn't Minnesota or even eastern Washington. Cable chains and knowing how to use them is the cheap insurance. A snow shovel, a small military gas can (filled), some emergency gear like the Ten Essentials and you're good to go almost everywhere except that really important meeting that you can attend on a teleconference.

  16. Snowing in Ellensburg...started sometime after 8pm and continues off and on

  17. @Thompsonized -- and don't forget the wind here in Eburg! According to our backyard weather station, it was averaging about 16 knots with gusts of 27-29. It only lasted a few hours though ... hard to tell how much snow we got since it got blown around so much. Nice and sunny this morning, though. =0)

  18. Snow tires are good in some cases. I have a dedicated set that are studless for my subaru wagon. That car is near unstoppable with those tires on, and they do work great in the rain (better then my summer tires!). I don't think studded tires are really needed in western washington unless you are going to the mountains on a weekly basis. I have been very happy with my studless snow tires though.

  19. Also in Ellensburg, a few miles west of town. We recorded several 45 mph gusts and had near blizzard conditions at times last night. Ended up with about an inch and a half of wet snow and all north facing walls, windows, trees, etc. pasted in white.

  20. Scott Sistek just posted on Facebook that the models are being quite consistent about snow on Friday....and long range models show a wind storm on the 27th? I didn't know they predicted wind storms that far out..... But I hope they are right! Bring on the snow and wind! Especially with this much notice so I can be prepared for anything and just sit back and enjoy it all! So glad La Nina finally decided to show up! I was getting worried for a while there with all of the boring weather we were having! Now it's coming all at once! Yay! Bring it on!

  21. Wild winds continuing tonight (Sunday morning) along the east slopes. WRF-GFS had 30-35 knot gusts forecasted, right on.

    Kinda eerie though. The strong winds must be just above the surface. It'll be dead calm, then crazy, back to calm. Energy must mix down once in awhile.

  22. I just want to know how bad next week!

  23. I just got my sailboat hauled out an hour before the storm hit Port Townsend on Friday!


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