February 02, 2021

Running Out of Time For Lowland Snow West of the Cascade Crest

The complaints are starting to come in.   

Where is the lowland snow that was "promised?"

This is a La Nina Year?  Right?  La Nina years tend to have above-normal snow at lower elevations west of the Cascade crest?   Right?


And the desperation is getting palpable. 

We are running out of time. The probably of major snow events starts decreasing rapidly after the the third week of February. After, the first week of March, we simply don't get major lowland snow events.

The Facts

It is true we are in a La Nina year.  The latest sea surface temperatures for the central  tropical Pacific show it (see below).   Nino3.4 is an area in the tropical Pacific that we use as an index.  Blue colors indicate cooler than normal, which indicates La Nina.


It is also true that that typically we get more lowland snow during La Nina years, something described in several NOAA and research reports (including some I have worked on).  Here is a sample, showing more snow than normal (blue color) for La Nina years on average.


But there are no guarantees....this is like weighing some dice.  You might get heads more often, but occasionally you will still get tails.  And nearly all studies show the impacts of La Nina on our region are mainly observed AFTER January 1.

What Has Happened so Far?

For much of January, the atmosphere over the eastern Pacific has not been playing by the typical La Nina playbook.    The typical upper level (500 hPa, about 18,000 ft) pattern during La Nina years is shown below.  More exactly, this figure shows the difference of the La  Nina upper level pattern compared to normal (known as the anomaly from normal).

La Nina years tend to have enhanced high pressure over the eastern Pacific (also known as ridging) and lower than normal pressure (troughing ) over western Canada.



This pattern tends to promote cold northerly winds along the coast that enhance the change of lowland snow.

But much of our past January was not like this.  In fact, during the past month, the anomaly (again difference from normal) pattern aloft was quite different from what is expected during a La Nina winter (see below).  For the first half of the month, low pressure extended westward over the ENTIRE north Pacific, with higher than normal pressure to the south.  This produces warm, moist southwesterly flow that brought us warm temperatures and bountiful rain.

The second  half of the month had an offshore ridge, but no troughing (low pressure) over the continent.  We just get moist, mild onshore flow and light precipitation with this pattern.  Just not right.

Looking Forward

OK, we have essentially one month left.  We can look forward with some skill 7-9 days.  What does the best forecast system in the world (the European Center) suggest?  In fact, I will show you the average of their large and excellent ensemble system in which they run the model many times and average the result.  The GOLD STANDARD for prediction.

The forecast upper level (500 hPa) anomaly (difference from normal) from the European Center looks much more La Nina like.  Higher than normal pressures (or heights) offshore (red), with lower than normal values inland (blue color).  It is in the neighborhood for what we were hoping for.


But being in the neighborhood is not good enough:  most of the forecasts are not producing lowland snow for the next week (see below).  Each line is the snow forecast at Seattle for one forecast. Time increases to the right.  A few gray colors---nothing serious.


But I would not give up yet.  The atmosphere seems to be trying to get into the La Nina configuration and perhaps the very specific set up needed for Northwest lowlands snow will happen.   But we are rapidly running out of time.

But one one thing seems clear, the situation should be favorable for snow in the mountains, as suggested by the European Center 10-days snow forecast shown below:













18 comments:

  1. If you're playing with loaded dice, you may get 7/11 more often but you may also roll craps. (Loaded dice have no relation to heads or tails)

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  2. 2020-2021 current snowfall totals:
    Redding CA 1.5
    Jackson MS 1.3
    Austin TX. 1.3
    Tucson AZ. 1.0
    Sea-Tac AP 0.5

    It looks like yet another lowland snow bust in a moderate La Nina year;its up to something like 6 out of the last 7 La Nina winters since the late 1990's.
    Cliff,it may be time to update the statistical research on La Nina winters.What was true in the 1950 to 1990 time period,does not seem to apply anymore to the latest 30 years of climate records.
    Hopefully,there will be greater snow totals next year in a probable ENSO Neutral winter!

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    1. I'm also wondering if perhaps shortening the history comparisons of la nina's statistics will actually provide more accurate forecasts for future la nina winter events.

      There's mountains of data that makes it seem clear that the cold/snowy winters of the past many decades just aren't what we should expect anymore, even if our weather patterns seem to line up with those in the far past.

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    2. The earth's not in the same position it was in for those old skool La Nina's so even under the same configurations it won't hold the same patterns. We are as close as we are going to get modern days to old skool.

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    3. How often are long term forecasts based on various summer/fall set-ups exactly perfect? I'm going with never.

      Long term forecasts are a guide at best. Two years ago we had 2 feet of snow in Seattle in a weak El Nino year. There was nothing "wrong" with the forecast, nothing broken about the modeling. It happened because forecasting weather is enormously complex with a major multiplier for anything past 10 days.

      Fortunately we are lucky enough to have found this blog... this is as good as it gets and I have never once seen Cliff state a long term forecast as a certainty, in fact he consistently is having to dial back the hype (or fear) that inevitably ensues elsewhere based on these predictions. None of that is forecasting. And it most definitely is not science. No reconfiguration of the models or timeframe is going to change that, in fact it will probably only make it worse.

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  3. Spring....let it begin soon...keep the snow in the mountains...I give up on snow this year in the lowlands...definition of insanity hoping for snow down here...moving onto to spring...

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    1. This comment has been removed by the author.

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  4. Echoing Gus Bus. Enjoyed some December snowfall in north Whatcom County, but at this point, bring on spring!

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  5. Yes. Too warm for snow, too cold for swimming or even for running in shorts. Boring!

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  6. Related, then: for us gardeners starting seeds indoors, when is the likely last frost date in the Puget Sound lowlands this year? I was thinking as a La NiƱa year it might be mid-April, but maybe it's more like mid- to late-March after all.

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    1. Molly,

      In Bothell, where I live, I'd say early April typically. About the end of the first or second week. The latest frost I ever saw here in many years was April 24, 2008, when there were 4 inches of snow (really!) Of course it melted in a day or so.

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    2. Here in Duvall, that snow stuck around a bit longer. Strangely enough, about three weeks later, we had our first really hot day of the year, in mid-May.

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    3. Thanks! I recall trying to hack apart some frozen turf with a spade in late March one time a while back--it was probably 2008. I won't rush to put out flowers this year, although we all know the slugs are the real threat!

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  7. Glad to hear I'm not the only snow freak who reads this blog.

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  8. Wonder where this winter ranks on the SWEI. Probably higher than many would expect but this winter has been at the very least monotonous. Even though many are seemingly eager to write this winter's eulogy, it might not be time to put your guard down yet.

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  9. It seems, after all the wait, there is a chance for snow on monday morning after all? In the weather.com forecast for seattle, it reads "Snow showers before noon" on monday

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  10. Scott Sistek recently pointed out on Twitter that the one day where snow was recorded at SeaTac this winter (December 21st) was also day that reached a high of 59!

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