December 16, 2012

Big Storm: But the Worst South of Seattle

The most powerful storm of the season will hit the Northwest tonight and tomorrow AM, but the strongest winds will be over southwestern Washington and northeast Oregon.

Each run of our computer models have been moving the low southward, and particularly the areas of big pressure gradients, which are associated with high winds. Let me show you a sequence of pressure forecasts from the UW WRF model for 10 PM tonight, 1 AM tonight, and 4 AM tomorrow morning.  At 10 PM a 973 hPa low is offshore our coast, but the area of very large pressure gradient (change) is offshore and swings towards the Oregon coast.  Expect big winds (gusts above 50 mph) along the Oregon coast at this time.

 Three hours later, the area of strong pressure gradient slams into northwest Oregon...this will be a major wind event for them:  expect power outages and tree damage.  The coast could have sustained winds of 30-50 mph, with gusts of 50-80 mph.  This is serious...stay inside if you live there.  The Willamette Valley will also get major, but lesser winds:  sustained of 20-40 mph and gusts to 50-60 mph.  Strong winds offshore of the the WA coast, but nothing really over the Puget Sound lowlands and NW WA at this time.

 Then as the low moves inland, strong southerly winds will move northward into SW Washington, roughly from Seattle southward.  In addition, with a huge east-west pressure difference, a strong westerly wind surge will push eastward into the Strait, where winds could gust to 40-60 mph (from the west).

Here are the near surface sustained (NOT GUSTS) winds forecast by the modeling system (at roughly 30 ft above the surface).   Red are sustained at 50 kts.

At 10 PM big winds offshore and extending to the Oregon coast.

 Three hours later they move to the WA coast and the Willamette Valley.
 And you can see the spread of moderately strong winds up to Seattle and into NW Washington by 4 AM.  Seattle may see 20-30 mph winds over land and double that over the Sound.

 So, the bottom line:  this is a major event for the NW Oregon and SE WA coasts and the Willamette Valley. Seattle will get winds, but it will NOT be one of the big ones here (not the Chanukah Eve storm).  The Strait will also have major westerly winds.

We can check the model runs this evening for a final confirmation.  And yes, there will be huge snows in the mountains.  Here are the 72hr totals for the period ending 4 PM on Wednesday.  MANY FEET. 

When the atmosphere has juice, like in this event, everything seems to happen.  I almost forgot!  They will be a fairly major easterly wind event on the western foothills of the Cascades (Enumclaw, North Bend, you know what I mean).  Winds gusting to 60 mph+ tonight!

So enjoy the storm, but prepare for power outages and stay inside during the big winds.


  1. Thank you for the update cliff. As I expected, the storm is going south of us. I'd really like for a big wind storm in the Seattle area, but I'll keep hoping.

    It seems whenever there is uncertainty, there is no uncertainty - the storm is almost always a miss for the greater puget sound.

    I'm eager to see tonight's model runs, but am not keeping my hopes up for this one.

  2. The mountains are going to get so much snow! This will be great.

  3. Did anyone else get an Emergency alert on their phone?
    "Blizzard warning this area til 6:00 PM PST Mon. prepare. Avoid Travel. Check media. - NWS

    We are in greenwood......

  4. Why has the NWS been sending blizzard alerts to my phone? Supposedly, it's to run through 6 pm Monday night. I could understand this if my cell phone service was based in, say, North Bend, but given that I have a Bellevue address (and have location services on, so my device KNOWS I'm in Bellevue at ~210' ASL), this seems a bit over the top. A good idea that's run amok a little bit, or are we going to have substantial snow with the wind here in the Puget Sound lowlands? I'm not even turning on the TV; they will overhype a dozen flakes, but you will tell us the truth, Cliff (and thanks for that!!)

  5. I'm heading to Victoria on the Clipper @ 8am Monday. What should I expect...a pretty choppy ride?

  6. The alerts people are getting for blizzard conditions apply to the mountains only, but the alerts appear to be going out county-wide because that's just how NWS issues alerts.

  7. Things are getting exciting up in Blaine. Lots of large wet flakes mixed in with the rain and the temperature has dropped 1.5 degrees in the last hour with the NE wind we have.

  8. Hey Cliff, what's adiabatic cooling?

  9. Lots of rain and wind in Hazel Dell, WA since about 5:30pm. says possible snow for us on Tuesday...

  10. WSDOT has closed Snoqualmie pass due to accidents and blizzard conditions. Drive safe if you have to go over the mountains, better yet, stay in the lowlands for now.

  11. WSDOT has closed Snoqualmie pass until at least 9 PM tonight (Sunday) due to accidents and blizzard conditions. Don't go up that way without checking conditions first.

  12. I live on Harstine Island. The barometric pressure at my house right now is 955 millibars! I've never seen it that low before. What does this really mean?

  13. PNW means your barometer is not calibrated! There is no way that your sea level pressure is that low....cliff

  14. The National Weather Service continues to downplay this storm because the low is tracking farther south on each update.

    I don't think this is going to be the big wind event everyone thinks it is, at least not for the major populated areas.

    It's a bit over-hyped, although not by Cliff! He seems to have called this one early on just as it is, moving south to only really effect Oregon and SW Washington.

  15. Cliff, forecast for Snoqualmie Pass was for high of 26 today. Current reports are 33 and rain. What happened?


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

Rain without Clouds, the Upcoming Cooling, and Strong Leeside Winds: All in My New Podcast

The radar image this morning at 5:30 AM showed rain...some heavy... offshore. As shown in the satellite image at the same time, much of that...