Saturday, February 23, 2019

A Very Difficult Snow Forecast

The ingredients for lowland snow, somewhere in the region, are now evident:  cold air will be moving in aloft during the next days, an upper level trough is approaching, and a low pressure center will be approaching the Northwest coast.

How these pieces will come together is the issue and I will give you may take based on the latest forecast models.   Either Portland or Seattle is going to get a lot of snow, and I suspect it will be the former.

This will be a performance in four acts.

First Act:  Showers Coming Today

There is a band of showers moving in this morning and afternoon, as illustrated by the radar image at 10:40 AM


But at this point, the freezing level is relatively high (around 1400 ft), which means the snow level (the level where all the snow is melted), is around 400 ft (see observed temperatures below, from the Seattle SnowWatch website).  So most lowland residents will only see rain, perfects with a few flakes mixed in during the heavy showers). 


There will be snow showers in the mountains, near the Hood Canal, and for those of you living at higher elevations.  The UW forecast snow totals ending 4 AM Sunday, tells the story.

Act 2:  Cold Air Moves in As an Upper Trough Approaches

As in any good play, some of the protagonists reveal themselves in the second act.   An upper level trough will be building and moving south into our region (see upper level-500hPa-- map for Sunday at 4 AM).   Such a trough results in upward motion (which can produce clouds and precipitation) and can push cold air southward at low levels.


 In fact, the forecast surface chart at 10 AM Sunday shows cool air moving into our region (blue colors) and a weak low center of SW Washington.

The predicted configuration is close but not quite right to give a substantial snow event over western Washington.   The trough is extending too far offshore, the upward motions over us is weak, and the low center is not very strong.  But small differences in the trough position and shape could make a huge difference.  So let's try to tease out the uncertainty by looking at the total accumulated snowfall at Sea Tac Airport using the NWS GEFS multi-run ensemble.  There is some variability, but the average is about .5 inches.  Accumulation on the ground would be less.  And remember this is at Sea-Tac, which is relatively high (452 ft). (Note...time is in UTC, with 12Z/24 being 4 AM Sunday)

 The UW has another, and higher resolution ensemble (run by my group).  There is a lot of uncertainty, but the average is about .8 inches.

So the bottom line of the second act, is that some light snow is possible tomorrow, but it won't add up to much.  Perhaps .5-.75 inches falling out of the sky, with relatively little accumulation.

Third Act:  The Real Threat Emerges

In my plays, the real action occurs in the third act, and this weather situation is no different.  The tension is palpable.  The villain (or whatever you want to call it), will be modest low pressure system that will approach our coast from off the Pacific.  The U.S. GFS model and the UW model that is driven by it, takes the low center into southern Oregon (see below), leaving Puget Sound in dry, cold conditions (4 AM Monday is shown).

As shown by the 48-hr snowfall totals ending 4 AM Tuesday, this forecast produces little snow north of Olympia, but Portland gets several inches, and central/southern Oregon gets huge amounts of the white stuff.   


The vaunted European Center models brings the system a bit further northward--see below.

And the resulting 48-hr snow total from the European Model brings very light snow to Puget Sound and notably more to Portland (6 inches or more).  Salem and Eugene would be snowbound.

There is substantial uncertainty for Puget Sound snowfall, but it looks like we will get little, with Portland "enjoying' the brunt of the action in the third act.

Fourth Act:   More Snow Later This Week?

In a typical fourth act, there is a denouement, where all the plot twists are resolved.  But not in this play.   The European Center Ensemble prediction of accumulated snowfall, shows the potential next week on Tuesday and later.  The fuel and matches are around and our forecasts would not have to be off much to bring significant snow back into western WA.  But this blog is long enough, and this dramatist has to go outside and clean up debris in his yard.


For never-resting time leads summer on 
To hideous winter and confounds him there, 
Sap checked with frost and lusty leaves quite gone, 
Beauty o'er-snowed and bareness every where 

...William Shakespeare






28 comments:

  1. I love your comment about the 'dramatist' needing to go clean up in the yard! Thank you for sharing your expertise in forecasting!

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  2. I'm addicted to Cliff's blog so I plan to continue visiting it. But I need someone to clarify why a delete symbol has appeared more than once next to my comment. I tried to figure it out but was unable to. Please help, and thank you.

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  3. I think too, this sort of play has bystanders that make comment now and again .. one such is the Bow, WA weather condition reporting rock-on-a-string. As of now, 1:00 PM Saturday, all is calm and dry. But will be ever vigilant as the drama progresses.

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  4. “Tease out the uncertainty”.
    Cliff is to weather what Beethoven is to music and Shakespeare to poetry.

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  5. Looks like Portland will get its snow wish

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  6. Fascinating to watch how the GFS and Euro models disagree and then converge. Looks like they are both meeting in the middle for this one.

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  7. @Twinkie .. if it is a little garbage can it means that you can delete you comment if you want. Others don't see it ...

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  8. NWS out of Portland just updated at 3pm...says precip won't go north of Astoria...so Kelso appears to be the northern fringe...

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  9. Gus Bus said...

    "NWS out of Portland just updated at 3pm...says precip won't go north of Astoria...so Kelso appears to be the northern fringe..."

    But it is a watch not a warning and they are not predicting very much snow - maybe 1.5" over 24 hours, with locally greater accumulations (perhaps near the gorge and higher hills). Predicted temperature is not very low. Not hardly Cliff's 6" snowbound forecast. We'll see who is right.

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  10. I really hope Portland learned from last winter...

    There was ice on the freeway for weeks!

    Glad I don't have any plans that bring me anywhere near Portland. Though I'm sure Multnomah falls will be stunning with all the snow.

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  11. Nothing happened last winter in Portland, but two years earlier was almost epic in terms of the number of snow and ice events. The city was paralyzed for days on end, leading to the first purchase of road ice and the outfitting of trucks with spreaders and plows. They were up practicing their technique on the slopes of Mt. Hood this past Fall, so we'll see how they do if this predicted snowfall occurs.

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  12. if you are, by any chance, forced to disrupt your routine by a weather event caused by our disruption of the climate, you could maybe listen to the UK's Professor Kevin Anderson, talking about how we MIGHT be able to keep warming below 1.5C above baseline and carbon budgets etc....


    Kevin is one of the first people i listened to about climate disruption, around 2014.... i checked out what he had to say then, and couldnt find anything to refute his statements..... i also listened to Mayer Hillman and Al Bartlett (who explains the exponential function in terms of human population growth and energy and resources) and Guy McPherson.... then i spent two weeks poring over all the research i could find in every single field i could think of that was connected to this issue..... because scientists work in SILOS and there's very little cross pollination of data and insights between their specialties.... and i found the same things going on in the different environments ---- broken weather patterns, with extreme events, die offs in plant and animal species, deterioration in soils, ice melt, ocean and atmospheric currents disrupted, threats to/decreases in food production - all related, connected, interdependent...

    and then i came to the conclusion that yes indeed, we are screwed.... and i spent the next six months or so in shock....

    and since then, it's been a journey of grief, cycling through the various stages and figuring out how to live with integrity in this time..... and being pulled back into the grief regularly by the fact that so many of us are not awake and aware and that our society is refusing to accept reality and prepare for what's coming...

    Kevin - in the past - was quite clear on the fact that we are screwed..... here he is in 2019, trying to hang on to some hope that we might still be able to turn things around..... that's called the BARGAINING stage in the grief cycle.... i guess we all have to do something with our anger and our time and there's no harm in trying to mitigate things in some way.... his focus is on total system change and social justice, in not making the (brown-skinned) poor pay for our excesses.....

    i dont think he really believes we can do this, but he needs to spend his energy doing something, and this is what he is choosing to focus on

    https://youtu.be/7BZFvc-ZOa8

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  13. Cliff,

    Weather analysis, theater's rhythm and sublime poetry. How delightful can a weather blog possibly aspire to be!

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  14. I’m imagining Shakespeare doing daily chores, raking the leaves, feeding his cat, buying toulet paper... I forgot what my point was

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  15. Thank you Cliff, for your wonderful insights and easy prose.

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  16. Tough forecast indeed.

    Here in Redmond Oregon it rained right through the first Winter Storm Warning we were under last night as we hovered 1-2C above freezing. Mother nature basically flipped the bird at the fine folks in Pendleton. Some snow has finally started falling in higher areas (Sisters, etc.).

    Temps are cooling from the north, slowly. We are now under another WSW that covers the next 3 days in aggregate - probably a wiser approach: "uh, it's the high desert, it's gonna get colder, looks like some moisture with this, so, er, let's go with 7-12" snow across the next three days. Probably. Is it summer yet? Those forecasts are way easier!"

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  17. Nice little snow underway near Sequim at 1000'. Nearly an inch so far and snowing moderately with temps right at 32.

    Based on the number of mornings I've woken up to new snow this month, not to mention the big snowfalls, this will be a February to remember.

    But one of the delightful things about snowfall here is that its always a surprise. To everyone.

    Now I'm off to buy a heated hummingbird feeder. We've been rotating out regular feeders in and out since the weather got cold, but our over-wintering Anna hummers have been getting up before daylight to wait by a cold and sometimes frozen feeder until we get up. Time to give them a cozy, warm spot to warm their feet and their bellys as soon as they wake.

    And based on the way the weather gods work, if I buy this thing and wire it up, then it won't get cold or snow again.

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  18. @Sahila: Well one can always fall back on George Carlin for some relief ...

    https://www.youtube.com/watch?v=EjmtSkl53h4

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  19. @Eric Blair, you're right. The years run together for me sometimes.

    Glad to hear they purchased some equipment as a result of the chaos.

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  20. 5" this morning above hood canal at 500 ft.

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  21. Really enjoy your blog and the other comments. Fun to get updates from places like.... Lilliwaup humptulips quilcene

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  22. Cliff, please devote a blog to when you think this pattern will shift and spring will get the upper hand. Some of us are getting tired of this!

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  23. @Rabbits' Guy..... i am a fan of Carlin's clear thinking and plain speaking..... it's always encouraging to know there are people who see things for what they are! Pity he wasnt around now to call out the continued BS...

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  24. @Sahalia, a question: Do you think that correct English is tyranny, or that your broken version somehow makes you sound smart? Asking for a friend.

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