February 08, 2021

Very Cold Air Coming to the Northwest, But Will There Be Lowland Snow?

Will update with latest model forecast by 2 PM Tuesday

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 Very cold air will be coming to the western lowlands, probably the coldest air we have experienced in years.   The cold is pretty much guaranteed.

But snow is something else and the major models are not all on the same page, ranging from a dusting to a major snow event.

Let me give you the latest information.

As predicted, last night brought light snow above roughly 500 ft during a Puget Sound convergence zone event.   Up in the hills of Bellevue, the scene was quite snowy this morning (see below) and some snow got mixed in even near sea level (but no accumulations there).

Image courtesy of Dr. Peter Benda

So what is going to happen now?    The air above us right now is relatively cold (allowing snow even at sea level if there was moisture), but the air will get much colder over the next few days.

The lates NOAA/NWS ensemble forecast for temperature at Seattle based on running the GFS model  many times shows temperatures not getting beyond the low thirties on Thursday and Friday,  with the minima dropping into the lower 20s.

The surface air temperature forecast for 1 PM Thursday shows sub-zero temperatures in the mountains and teens/single digits in eastern WA.  And a plume of cold air will be jetting out from the Fraser river valley and heading to those poor folks on the San Juan islands.


Bottom line:  you can bank on the cold, so protect your plants, remove hoses outside of homes/apartments, make sure your plants are in, among other tasks.

And the large homeless population of our region needs to be moved indoors.  Past events like this have resulted in deaths from exposure.

But what about snow?

Major models have differing solutions, and the ensembles of some of the modelings systems are all over the place.  The issue is not temperature..we will be cold enough... the question is moisture.

Start with European Center, which is generally the best...but not always.

Looking at the EC high-resolution run for total snowfall through Thursday at 4 AM, the lowlands are yet to get hit, except for light snow over NW Washington, and heavy snow over the North Cascades.


But by 1 PM Friday, the situation is VERY different as a Pacific system approaches the Oregon coast.  North Seattle gets light snow, but much heavier amounts are predicted south of Tacoma.  Olympia gets hammered with 7-8 inches and Portland gets several inches.

But the event is not over: total snowfall through 4 PM Sunday really buries SW Washington and Portland get hit hard as well, with roughly a foot.   Seattle gets a few more inches with a huge difference between north and south Seattle. The southern WA and norther Oregon Cascades are just buried.

Keep in mind:  a small northward shift of the precipitation could bury Seattle.

Well, the above it one solution.  What does the European Center ensemble of many forecasts show? (see below).  Looking at many forecasts helps quantify uncertainty.  Each line in the top panel below is a different forecast (there are 51 of them).  The snow totals are color coded.   Time increases from left to right.  The blue line on the bottom panel indicates the high-resolution run and the green bars are the average of all the forecasts (which is normally the best thing to go for).

Bottom line:  the event starts light but most of the runs have significant snow at Sea Tac.


The U.S modeling system...the GFS... is taking the system further south, with far less snow in Seattle.  Check out the smaller 21-member U.S ensemble plot.  MUCH less snow.  A lot of the gray colors (which is an inch or less).


During the next day the differences between these two systems should decrease...and keep in mind that the European Center is usually more skillful--but not always.

Uncertainty is a fact of life with weather prediction, particularly for lowland snow forecasts that require everything to line up right to get a big snow even.    

And one more thing to ponder...even if there is a lot of snow, there won't be a need for a school snow day--one of the most glorious events in the lives of most kids.

22 comments:

  1. Im glad to hear that snow is almost certain... although im hankerin' for a lot...

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  2. Cold yes...but snow...my guess is we will see it but from Tacoma north no more than an inch...some spots might get 2...another bust snow event...southwest Washington into Portland hits the snow lottery...cold and no snow is a waste...bring on spring..

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    1. gus with the negativity again..

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    2. Reality again come on...you know better...I'm hoping but usually disappointed...trying snow reverse psychology

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  3. Maybe a bit off topic, but when I see constant reminders that the Euro model is typically more accurate, I think back to that big recent windstorm where the euro model was completely ignored. I still wonder why seemingly every local forecast and meteorlogist ignored the euro model for the wind storm. It seems now everyone is latching on to the euro models again for snow, even though each subsequent run in the past 36 hours or so has been downplaying the snow event.

    Anytime a big snow storm has 'potential' this far ahead, it almost never actually happens.

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  4. Rats! I was hoping to get my grapefruit tree through the winter without intervention.

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  5. Well I'm bummed. Was hoping to get something in Lynnwood :(

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  6. Wow, Professor, that photo is amazing. I expected to wake up to that, but we were spared (at least for today). I feel horrible for life outside and those stuck inside with limited resources. As you stated, uncertainty in predicting snow is a given in the NW, as is uncertainty of life for those at the whim of nature. We best take care of our planet, to the best of our ability, or the power of uncertainty will become our certainty.

    Thank you for your update. I read your blog regularly, but look for updates in February daily.

    One last thing. It seems to me that what hits us, ends up playing havoc with the rest of the country about a week later (or less), sometimes tragically so. They're already being hit, so I hope this doesn't impact them in even worse ways.

    For those who want snow, I hope you enjoy it. For those who don't, I hope it passes you by. Stay safe and warm; be well.

    I look forward to spring.

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  7. "...there won't be a need for a school snow day--one of the most glorious events in the lives of most kids."

    Still glorious well into adulthood! But, yes, our district isn't doing snow days this year. School will be virtual in the event of a snow day. Technology has finally caught up, for better or worse.

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  8. Thank you for your analysis Dr. Mass! Can't wait to see how it all shakes out the next few days.

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  9. Thanks for the latest update.

    Having seen this scenario several times over the years, my best guess is that the storm system on Thursday heads further south and we just get a glancing blow, with nothing up in Bellingham (where I am).

    It always seems like the cold dense Frasier air needs a moist and strong system heading right into WA State to hit the snow jackpot. Maybe that will happen this week but, as I say, it seems unlikely.

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  10. My un-professional guess... My guess is that MLT, Lynnwood, Everett and North will get snow. We're in the Convergence Zone! I reside and hide near Paine Field in Everett. I've been watching nature, and nature has been naturing up. Birds have been flocking to my wild berry tree and eating all in a frenzy kind of way, which happens before snow. Plus, the outside has been still... When nature is still, watch for the chill; then with a little wind flakes may begin. I think and hope we are gonna get some top shelf snow! And I think flakes will start falling tonight or tomorrow morning, cause nature knows.

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  11. No matter how promising it looks its never certain. This forecast looks similar to the forecast before the 2019 storm so a major snowstorm is possible but more likely we will get little to no snow and it will just be really cold. If the models are still forecasting big totals 24 to 36 hours out then I will get excited. Last year a big snowstorm was forecast but a dry downslope wind developed and the snow was much ligher than expect this storm is comming form the southwest like last years storm so I fear the same thing might happen.

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  12. IT WILL BE ESSENTIAL THAT MODES OF TRANSPORT ARE NOT IMPACTED DUE TO COVID 19. SEATTLE DOT MUST BE READY. PLEASE DO A DEEP DIVE INTO THIS AND SEND YOUR ADVICE TO THE CITY OF SEATTLE DR. MASS. THANK YOU.

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  13. Thank you SO much for this reporting. We have some things to do . . . just in case.

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  14. The effect of the Fraser outflow is significant, far more so for those of us in north Whatcom County than the “poor folks on the San Juan Islands”. Currently single digit wind chill, and this is the appetizer. Not pleasant in the least. Come on, spring!

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  15. If there's that much snow the kids should get at least one day off to play.

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  16. Last time Portland was hit with a massive snow event (a few years back), the local forecasters were all over the map, only coming to a conclusion in the wee hours right before it hit. So I take everything these days with a proverbial grain of salt.

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  17. Snow days might not even be a thing in the future since school districts have set up online learning environments! Crazy!

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  18. Something is strange here. These models are predicting serious (even by our standards) snow here in the mountains, whereas NW Avy center is just predicting piddly amounts. Granted, they only predict 2 days ahead, but they usually mention if something major is on the horizon. Plus NWS spot forecasts are not predicting major snow up here either. Surely they are using same models. ???

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