November 18, 2015

The Storm

 Yesterday's storm brought substantial rain to our mountains (2-5 inches), as illustrated by the larger 24h totals (ending 7 AM today) shown below.

Piled on top of our previous heavy rain, a number of local rivers are flooding, some with major floods, like the Snoqualmie (see NWS River Forecast Center map below)

As you can see from the hydrograph at the Snoqualmie River at Carnation, the river responds relatively quickly to inputs of heavy rain, and subsides nearly as quickly.  Flood season is here.

Yesterday's winds were substantial but not record breaking, with the Puget Sound region encountering general gusts to 30-45 mph over land and 40-60 mph over water (see max gusts yesterday below)

Some exposed mountain-top stations had gusts above 100 mph.  Perhaps the most notable winds were in eastern Washington.  As the low passed eastward in southern BC an intense pressure gradient was created over that part of the state (see map)
The result were winds gusting to 50-70 mph, producing power outages affecting hundreds of thousands of people.

Another remarkable event yesterday was the amazing radar image of the cold front as it approached our coast.  I show two images below during the early afternoon from the Langley Hill radar near Hoquiam.  You see the narrow line on the radar imagery?  That is the cold front.  An intense line of convection with heavy rain produces than linear features...known in the business as a narrow cold frontal rainband.


  1. Very interesting information, especially that cold front image.

    I'm sure I'm not our only reader who would love to have you include the URLs of images from sites which are available to the public.

  2. The thing that needs to be mentioned is the tremendous shift in the direction of the winds depending on where you are located. There was mention of a strong burst of westerlies coming down the strait--storm force were predicted. I don't know how the restaurant fared in Mukilteo, but a very intense burst of winds form the Northwest slammed western Snohomish County and North King County, which really caused the most power outages in those locations. It was an impressive NW Hurricane as we had 3 to 4 hours of intense South SW winds, an hour of lull and then 3 hours of intense NW winds. I think you should comment on this as a lot of people are confused and wondering what hit em.

  3. This may be the worst windstorm in history over here in Spokane.Sustained winds of 40-50 mph with gusts of 60-70 from 4 to 6 PM yesterday.Many trees down,and a lot of houses with roof shingles blown off.The most bizarre aspect of the windstorm was that a dust storm occurred simultaneously.Only a few hundredths of rain here,but all vehicles and house windows facing the wind are coated in mud.By the way,the drought/rain shadow effect continues over here.Less than two thirds of a inch of rain so far in November,less than one tenth of that on the west side.

    1. Wow, Seattle had record precip yesterday. Amazing how these mountains affect the weather.

  4. Couldn't help but notice that this morning's GFS shows an arctic front and a weak low pressure out of the northwest next week- similar to what you told us was a great scenario for snow here in Puget sound in ATMS 101...too far out for any accuracy, but we will all need to watch that!

  5. 3 miles NNE of Monroe... the southerly winds yesterday were impressive, but I was really impressed once the front came through and shifted the winds. The wind direction completely changed... It was almost like having two storms! One died down and the other picked up. Very cool storm. Was without power for over 18 hours but other than that no significant damage.

  6. Here in northern Idaho about an hour northeast of Spokane we had wind gusts of 55-60 mph with almost an inch of precipitation- some of that falling as 3-4 inches of snow ahead of the switch-over to rain. All of the snow melted yesterday as the temperature soared to 50 degrees with the wind. Then we had an intense small hail/graupel storm last night with the cold front. Today is in the upper 30s with a moderate westerly breeze. Here the drought is pretty much over. We have received over 3 inches of precipitation this month so far.

  7. Strong agreement with James! Amazing forecast result for what was a 1-2 punch for a lot of us. We had strong winds out of the south much of the day and then things started to settle down. It was even quiet for about 45 minutes...then BOOM. The burst of westerlies was INTENSE and relatively sudden. We live in north Lynnwood and it was the worst wind of the day. 15 minutes in the power cut out (we are still waiting for restoration).

  8. Yes, thank you Ben -

    I wanted to inquire about the forecasted freeze next week. I come from the East Coast, and for us, it's obvious how back home it gets extremely cold so quickly (cold fronts diving out of Canada have very few to no obstacles at all reaching the major cities). In stark contrast, Seattle is protected on one side by the Olympic range, and more importantly, the Cascades act as a very effective and strong "wall" blocking the main "arctic air highay" that often sends bitterly cold air as far south as Mexico and Florida.

    How is it that Seattle can get hit by Arctic air? By what route does it come? With its prevailing westerly flow, Seattle's weather coming off the Pacific would not allow a freeze.

    This would be an ideal learning opportunity for many to understand how such a sheltered city like Seattle could still get blasts of Arctic air.

    To me, I cannot see the logic. These formidable mountain ranges are both expansive and very high altitude, more than enough to break up a flow of Arctic air.

    If anything, Seattle would be simply be able of receive what little Arctic air would manage to make it all the way across these mountains, at which point it would be weakened and modified significantly.

    Next week's forecast calls for 20s for Seattle. For this "modified" air to be that cold, then next week's blast much be bringing mega sub-zero temperatures to the Midwest and whatnot. And, it's still only November - the bitter bitter cold normally hits the East Coast in January (and, the East Coast gas been basking in seemingly record warmth this entire month - in contrast to our incessantly rain).

    Could you explain how Arctic air is able to reach Seattle, despite the city's "walled in" nature? That would be most informative. Thank you.

    1. Fraiser River Valley. Think of it as a Canadian export.

  9. The cold front was indeed impressive. I saw it on radar as it approached and thoroughly enjoyed it when it hit! What a downpour and the winds were fantastic. This was around 3pm yesterday in Auburn. Our winds increased at 3pm, but died off quickly after the cold front passed us. No power outage, but a whole ton of lights flickering.

    I need to check for wifi from our sailboat in the marina. If there is some, I know where I'll be working from during the next storm!

    @Ben Green, considering recent weather events, including snow in Auburn and surrounding areas just a couple days ago, the idea of snow for Thanksgiving this year doesn't sound to unreasonable. I'll also be keeping an eye on that low pressure system you mentioned.

    Cheers to Cliff, thanks for all the updates! This is my favorite kind of weather, stormy!

  10. tracsdc89: Arctic air really only has one route into Puget Sound & Seattle, so the pattern that brings it in is easy to spot. You look for very high pressure over western Canada, creating N-NE winds that funnel Arctic air out of the Fraser River Valley down through Vancouver and the Salish Sea. This scenario actually turns the mountains nearby against residents, as the air is too cold and dense to rise very much.

    This keeps the cold air moving like a river as far south as it can before the high pressure center shifts, changing the wind flow direction. Meanwhile, relatively-tropical air from the Pacific Ocean rides up over this "Cold Dome" and precipitates as it is lifted, falling into the cooler air near the surface as snow, ice pellets, or freezing rain. This depends on whether there are multiple freezing layers, and how they are distributed vertically.

  11. I have lived in Portland (and now the Longview hills) all my life. No doubt this is my first 10" rainfall week ever. Two atmos-rivers in one week? Amazing.

  12. Tracksdc89, thank the Fraser river valley for many of your Arctic visits. Like the Columbia gorge pounds Portland but with a bit more travel. Also the Arctic air need only be 3500' deep to sneak over the Cascade passes, and it often does just that.

  13. @tracksdc89

    I do not live in Seattle, but I have been there several times (considered moving there). I live in northern Idaho about an hour northeast of Spokane, WA, so my area is affected by many of the same storms as Seattle. To answer your question, next week a bitterly cold airmass is diving straight down out of Alaska and the Yukon into the western United States. It appears due to jet stream placement that this arctic airmass will go much farther west than many of the systems last year. Hence the east coast will be largely spared. This has to do with jet stream patterns and the fact that the source of this arctic air is Alaska and the Yukon instad of Hudson bay. The brunt of this arctic invasion will hit north central Montana.

    Cut Bank, a small town on the Rocky Mountain front in eastern Montana, has a forecast high of 12 next Wednesday. Low will be subzero. Actually, it will probably be MUCH colder but the NWS goes conservative intially until the models come into better agreement. This will be a deep enough airmass that it will have no trouble breaching the continental divide which will bring strong northeast winds to Western Montana and northern Idaho. Where I am we could see highs in the teens on Thanksgiving day with lows at zero or below. Because this system will come down so far west, a large area of arctic high pressure will be centered in southern interior British Columbia. The pressure gradient that results from this will funnel cold air through the Fraser River valley into the Bellingham and Puget Sound areas. So the cold air will not have to breach the Cascades at all. Expect the coldest windiest area to be Bellingham and Lynden.

    For Portland, Oregon, the cold air will come from Eastern Washington and funnel through the Columbia Gorge.

    Hope this helps.

  14. Those of us who live north of Seattle (I'm in Whatcom County), can offer a three word answer that often applies: Fraser Valley outflow. The Arctic winds you mention sweep down through the plains, through the lower BC mainland, and bring exceptionally strong, cold northeasters. If that air keeps tracking south, it can indeed reach Seattle. There's no "wall" to the north!

  15. @tracksdc89

    I've been very interested in our weather since I was a kid, and I always follow Cliff's Blog as it provides so much great detail in forecasting and analysis.

    I'll try to answer your question about how Seattle can get cold in the winter. Our coldest temps of the year happen when arctic air comes down through the Fraser River Valley, which is a little valley in southern BC, just north of our border. This valley provides a narrow valley to our north that allows cold arctic air to dive into western washington. We have to have N or NE flow at the surface to get this arctic air to make it to Seattle. If we have strong E airflow, we don't typically get the cold air because it runs into the cascades.

    You're generally right about how hard it is to get really cold air into seattle since we often have a West Flow. Pacific Ocean obviously moderates the air, and so it generally doesn't get very cold when we have a west air flow. It can snow in certain circumstances with west airflow, but it's usually the 34 degree kind of wet snow, not extremely cold.

    We typically get our coldest arctic outbreaks with a very strong high pressure system from the far North that moves almost directly N to S. In this scenario, the "modified" arctic air as forecasters call it, can advance as far as california. It can even make locations along the pacific coast very cold. This High Pressure air mass has a N to NE flow that is an off-shore flow, and does not allow moderation from the pacific.

    Our big snow storms seem to happen generally when there is a L pressure system to our SW, which allows for some moisture to come in from the SW, and yet still allows N to NE winds to prevail over us, constantly allowing air to flow from the N or NE, through the Fraser River Valley.

    It is really tricky to predict snow for any one community in western washington. But the "arctic outbreak" is definitely the most recognizable way that we get really really cold in western Washington. And again, this air mostly comes through the Fraser River Valley to get to us. In fact, we can have major wind events out of the N or NE if the pressure gradient is strong enough.

    Hope that helps, And welcome to Western Washington!



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