January 19, 2021

Colder Air and Limited Lowland Snow Ahead

Our region will soon experience colder temperatures and substantial snowfall in the mountains.  The snow level will fall and virtually everyone will see some snowflakes.

But the truth is that we will NOT be experiencing the primo Arctic cold air associated with most major lowland snow events, with minimal snow falling around Puget Sound near sea level.

But there is a substantial lowland snow threat and for that one will have to look southward towards Portland and western Oregon.

Portland May Get Much More That A Dusting

The transition starts on Thursday as a low pressure center moves south of us, pulling cooler air southward from British Columbia (see sea level map below for 1 PM Thursday, with blue colors being colder air).


The wind gust forecast for Thursday morning shows northeasterly winds pushing through the Fraser River Valley, across the San Juans, and out the Strait into the Pacific.  Cool, northerly winds will also push southward into the Pacific.

But there will be little moisture and no lowland snow:  the low center is too far south and west to do us much good.

But life is all about second chances, and lowland snow lovers will gaze hopefully at a frontal system approaching early Sunday morning (1 AM sea level pressures and low level temperatures shown below).  Relatively cold air will be in place (blue colors) and this is night when temperatures are cooler.


The front will have precipitation with it, but temperatures near sea level will be marginal for snow.

The UW WRF model's accumulated snowfall (NOT SNOWDEPTH) through 7 PM Sunday, shows half a foot or more in the mountains with the snowfall rapidly decreasing near sea level (very little at the lowest elevations).   Snowflakes will be seen everywhere, but only  minimal amounts near sea level.  The European Center forecast is very similar.


But like a late-night commercial, I must interject:  wait, there's more!

The third act.  

On Tuesday, a MUCH stronger and potent low center will be moving southward off our coast.  One with much more precipitation and forcing of upward motion (see sea level pressure map for1 PM Tuesday). 

Notice the large east-west pressure difference down the Columbia Gorge, which could bring strong (cool) easterlies into Portland and environs, while lots of precipitation is falling into the region.

This pattern can produce substantial snow around the northern Willamette Valley and Portland.

Take a look at the 48-h snowfall ending 4PM next Tuesday.  Portland gets hit with nearly a foot of snow.  And lots in the Oregon Cascades.


If the forecasts are wrong and the low is farther north, then Seattle could get a big event.

Finally, let's look at the excellent European Center ensemble snow forecasts for Seattle, based on running their model 51 times!.  A good way to judge uncertainly.  Each horizontal stripe is one forecast and the cumulative amounts are color coded.  The average of the forecasts are shown by the green bars.  

Nothing to get excited about.  Most ensemble members are predicted some snowflakes at SeaTac airport (which is relatively high at 452 ft).  Total snowfall (not snow depth) of around an inch. There will be less at lower elevations.  Bummer.

But what about Troutdate, at the western exit of the Columbia Gorge and just NE of Portland?  Wow...  a lot more!


We are still a ways out and the forecast can change.  The mountains will get plenty--you can bank on that.  Skiers will be happy.  Water managers will smile.   But those wanting snow near sea level may remain looking longingly at the sky.....











18 comments:

  1. Too many closed, or semi closed cold upper level lows for at least the past several years now.The classic arctic air outbreak with a digging,deep(<520Hpa)upper level low almost seems like a thing of the past now.
    I think there's a better chance of another atmospheric river-- though with lower snow levels--by months end than any significant lowland snow.

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  2. Ahhh seattle needs some snow days :(

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  3. Could you translate this for Eastern WA? How much snow to expect, and when?

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    1. About zilch,unless you live in the Palouse or southward.

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  4. So far, this winter has been a dud, but we've got some time left!

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  5. In conclusion, zero snow. Any prediction of snow this far out is going to be mostly pointless. I don't trust snow predictions more than 6 hours away here in western washington.

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  6. Looks like Portland will get the fun this time

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  7. This has to be the warmest la Nina in Seattle's history. My daffodils and tulips are already up and out, I've mowed the lawn twice because my grass is already growing. So disappointing!! Was really wanting a cold winter and its just not going to happen. Keep seeing the possibility of another atmospheric river set up by end of the month.

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  8. Eh. Our forecaster down here in Portland is basically saying nothing to get excited about. Not sure what to believe.

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  9. I'm guessing everyone who wants snow doesnt have to drive to work. Good riddens hope we have no snow! Having work is a little more important to me then building a snow man

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  10. This is a unacceptable forecast!!!! I do NOT ACCEOT these forecusts!!!!!!!! Predic morE SNOW!!!!!

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  11. A few more years and our economy, with ample assistance from the carbon cycle, should resoundingly assure you that involuntary driving in snow will be unequivocally a thing of the past for pretty much everyone on plant Earth. Sure, you can probably still find snow, but it will probably fall only where very few people live or work. Enjoy it while you can!

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    Replies
    1. @BAMCIS
      A few more years? Change that to a few more decades and I might agree. Boston and Great Falls, Mt., for example, just had their snowiest decade since 1900. Hard to imagine that they would go from snowiest to no snow at all in so short a timeframe.

      Here’s an interesting, historical look at US snowfall totals:

      https://www.wunderground.com/cat6/US-Snowfall-1900-2019-Decade-Decade-Look

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  12. In other words...if you want snow...head to the mountains...

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  13. Too warm. Many of the plants I didn't dig up from last year are still growing outside, since it's frozen maybe, what, twice this year? Flowers on some...in January...really? Never seen anything like it.

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  14. A low snow year in the mountains. Out here in North Bend the mountains are bare of snow after those atmospheric rivers washed it all away. Cliff, higher snow levels and more rain is what you predicted when climate change effects came to the PNW. What data do you have to suggest this time isn't now and the effects we are experiencing are directly due to ACC?

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  15. "Mountains will see substantial snow" is an interesting take. NWAC, NOAA, and WSDOT all have very low snow amounts in the forecast through the middle of next week. If Cliff thinks 1-3 inches is a lot, then I guess he doesn't ski much...

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