February 11, 2021

The Snow Forecast Update


4 PM in Olympia, Courtesy of Mark Maurer

 Light snow has begun to fall around the region.    Earlier today, flow from the  Fraser River Valley and Strait of Georgia moved southward into the northern Olympics, and being forced to rise, dropped snow around Sequim and north Olympic foothills (see picture along US 101)

And the advertised first low pressure system is now heading towards Oregon (see forecast position at 4 PM), sending a shield of precipitation over northern Oregon and southern Washington


The weather radar image around 1 PM shows the light precipitation associated with this system.  Snow is now observed from SeaTac Airport and to the south,  lighter to the north.  Flurries to the north.


The latest WSDOT cams around Olympia are downright winter-like.



Now that we are close in, I can show you recent high resolution forecasts.  The latest run of the NOAA/NWS HRRR model showing accumulated snowfall is shown below.

First, through 10 PM tonight.  Light snow over most of western WA...but only .1 to 1 inch.  More (as much as 2-4 inches around Olympia and to the south).


The total through 5 AM.  Shows more in the same spots.  But there is a very important issue here...less snow west of the Cascades from Tacoma northward...with the snow deficiency extending to the Sound.  This is due to strong easterly flow (from the east) sinking on the terrain.  Thus, local mayors can sleep well tonight.


Let me show you the wind forecast for 10 PM tonight with a dashed oval indicating the easterly winds. Click to enlarge.  It will be blustery from North Bed to Enumclaw.


So this is stage one of the event.

Now stage two is the threatening and difficult part.  This is not your typical big snow event and Puget Sound is right on the edge for several reasons.

Another low will approach the Washington coast on Saturday.  Which means moisture extending farther north.


The snow totals from this morning European Center model is impressive.   But you will notice the pesky Cascade "snow shadow" due to the drying easterly flow.  Seattle ends up with 5-6 inches of snowfall...perhaps half of that in depth.  But MUCH more west of the Sound and over the south Sound, where some places could get a foot of snow.  


The main U.S. model the GFS, has subtle differences, with far more snow in general, particularly around Puget Sound.  Much less north of Everett.


Is there uncertainty for the snowfall over central Puget Sound?  You bet there is.  Subtle differences in the position of the northern extent of the moisture, the location of the low, and the degree of downslope flow off the Cascades could really change things.

To demonstrate this, here is the ensemble of many forecasts for SeaTac for snow accumulation over time.  The forecast through 4 PM Saturday (00z/14) range from 1 inch to 20 inches!  The higher resolution run (blue line) is about 8 inches.  And I hate to say it....there is another snow event lurking on Monday for many of the ensemble members.


I will blog about this more tomorrow and will do my regular Friday morning podcast, which I will dedicate to the snow event.

The flurries outside are pretty right now.    








34 comments:

  1. Why is there such a great difference between the 12Z UW MM5 and the other models in the total accumulated snowfall? It shows virtually no snow north and east of Seattle.Talk about model inconsistency.....

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  2. Thank you Cliff! Always enjoy your forecasts, even when they aren't terrific or gloom and doom. Native Vermonter. I love it when it snows around here.

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  3. Wow much different forecast than yesterday

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  5. Light snow at 500 feet above hood canal at29 degrees.
    Accumulations are in progress on all surfaces

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  6. No pretty flurries in north Whatcom County, which is for the best. Snow + the northeaster is a very bad combo. Bad enough to have this non-stop battering wind. Single digit wind chill up here since yesterday.

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  7. Here in Tacoma, it's been off and on flurries since 10:30 or so but just after 3pm, I noticed the snow begin to increase to light showers and it's looking steady, so far. I think the snow may have increased a little a couple of minutes ago but still too early to tell how it'll turn out but agree, it's sure purdy out. No snow on the ground, yet.

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  8. We are so tantalizing close to some of those really big numbers. If this can just push 5-10 mile farther north we could be looking at a real snow event. Fingers crossed for that 20”. I have my milk and bananas, so I’m all set.

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  9. I smell FORECAST BUST. As we get closer the snow gets pulled out from under us. That happened with today's "event" and now you see it happening to Friday/Saturday's event. A piddling amount for Seattle and points north justifies the News not taking today or Friday or Saturday very seriously. They look set up to be right for once!

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    1. Yep. On Monday weather underground said the snow was going to hit on wednesday, by Tuesday they were saying it would be Thursday. Now instead of getting 6 in on Thursday like was forecast I'm looking at getting maybe two inches on friday, but I highly doubt it. I knew I shouldn't have told my kids. -Lynnwood

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    2. Don't hold your breath. They never get it right on the stations... I still think we are going to get slammed. I take are of birds around here and they are doing what I usually see them do before a big snow event. Eating like crazy and not chirping alot. Crows are acting different too. LOL

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    3. I agree a couple days ago Renton was forecast to get 5" from this storm and all we got was flurries. It seems like when a storm comes from the west or southwest we inevitably get downslope winds that reduce the snow to almost nothing. To get a big snowfall the storm must come from the northwest and those storms tend to be drier and you luck out only if you are under the convergence zone. If Thursday and Saturdays storm bust it indicates a major flaw in the computer models. I don't know that I can ever trust a snow forecast again if were supposed to get 15" 3 days out and we end up with a third or less of that.

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    4. I think the east winds are very underplayed in the forecasts here. I'm in auburn/lea hill at 500ft. On the radar it looked like we were under snow all day, but in reality we got barely a flurry. We had winds ranging from 5 to 15mph from the N/NE, but that was enough to keep the snow from reaching the ground (air too dry). We weren't suppose to get above 34f, yet we hit 38f.

      For tonight (friday night), I'm expecting the same thing, too much wind keeping the air dry and likely little to no snow, even though latest model runs show 8+ inches. I really think they don't take the wind into account as much as they should.

      I've lived here my whole life, I've seen how this plays out too many times. Big snow prediction, every day it gets closer it gets downplayed...and then it's minimal if at all on the day of the event.

      I'm hoping for tons of snow though, as always!

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  10. I will never be too old to be totally devastated when the forecast goes from "Snowmageddon" to "Snow-ma-nothing". Sincerely, frustrated snow lover in Northwest Washington.

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  11. Looks like that means more snow for clark County!

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  12. At this moment (Thur 5pm) NWS forecast for SEATTLE:
    "Saturday - Snow, mainly before 10am. High near 36. East wind 8 to 13 mph becoming light northeast in the afternoon. Chance of precipitation is 80%. New snow accumulation of 1 to 2 inches possible."
    All that Saturday low has to do it go a bit farther south and it's a bust for the city. I'm hoping we'll get 3-4 inches at 350ft, enough to sled on for an afternoon.

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  13. 4.25 inches measured on my car just outside of Lacey! This isn’t a bust for us down here!

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  14. I sense the “set up for big snow event and then change to small snow event” ruse.

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  15. 5.8" measured on my COCORAHS "snow board" as of 5:20 pm. This is at the south end of the Puget Sound in Olympia.

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  16. the snow event might complicate COVID 19 vaccine efforts

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  17. Hm, choose from 12" or 27" at Longview? Sounds like a record or something.. beats my personal numbers from Portland in '68 and '08 even if only half shows up on the ground.

    Currently 34° with a pinch over 2" on the deck.

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  18. 8:30 pm in West Olympia and we are at nearly 7" with snow still steadily falling. Forecast today was for 1-3" and another 1-3" overnight...this may end up like 2 years ago this week where all the forecasts were on low side in Olympia and we ended up over 26" across 3 days.

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  19. Nothing big will happen, just the brutal frasier valley blasting here in whatcom county. Snow comes when you least expect it and here nothing about it.

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  20. I think you're right, Sulla. I don't know if it will ever be possible to overcome the combination of randomness and huge variations in wx impact over piddling distances that we deal with. The models don't see many of these influences, andn they do you get things like these ensemble members doing their little algorithmic freakout dances.

    Common sense says you fall back on experience. And experience tells us there's no reason to see these snow forecasts as anything but a curuosity. Don't hang your hat on em unless you want to pick it up from a dusting of snow. Or maybe a puddle of slush.

    Prove me wrong, models. I dare you.

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  21. Micro-climates.

    Forecasts for a region just cant do micro-climates so they have to do a blanket snowfall tally.

    Case in point on the Kitsap:

    Silverdale around 4:30-5:00pm Thursday: Nothing on the ground and nothing falling from the sky for the most part. Some on and off earlier. A drive up Anderson Hill towards Seabeck reveals a dusting by Silverdale Cemetery/Anderson Hill Athletic Fields but no further precipitation. Further driving towards the Seabeck Conference center on Seabeck Highway past the General Store....squat. Climbing past Stavis Bay Road towards the uplands...bubkiss on the ground and in the air.

    Between Dragonfly and Cats Paw after a bunch of uphill driving, things begin to whiten up. Once at the post office, there is at least an inch and still snowing. The trip ends at Camp Union with plenty of white and the evident promise of more on the way.

    This drive took 20 minutes. No convergence zone or whatever. Seabeck is "Hood Canal" but even down right at the canal at sea level can mean diddly. So the Seabeck Uplands are a Micro-climate nested in a Micro-climate. A Nano Climate perhaps?

    The forecasts are so complex. They try their best but all the interaction of mountains flanking bodies of water with wind doing this and that, orographic lift and leeward compressive heating/drying....yah. Every neighborhood basically has a snow forecast tug of war going on.

    Given the east wind, ample moisture etc on Friday night/Saturday and even into Sunday/Monday...Seabeck Uplands will be given a good healthy tally. No idea what Silverdale or Bremerton will pick up but it will be notably less, with Seattle even further behind. Not talking much distance as the Osprey flies...

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  22. In Everett and not even a dusting. Dry as a bone up here. This first pass missed us completely.

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  23. Sounds like it’s going to be a dud cliff??? Dang it lol east winds?? It seems to be norm now for this east wind to kill our snow

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  24. I wish there was a summary at the bottom telling us how much you actually think we will get

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  25. Just woke up and checked the pacific satellite and this looks waaaay more interesting for those of us in the Northwest Interior. The storm appears strong and headed directly for WA State which could produce prodigious snow.

    Starting to get excited!

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  26. Cliff, I appreciate your blog and forecasts. Forecasting weather is basically predicting the future in an educated fashion based on model predications that obviously aren't perfect. I want a big snow like most on here but I don't understand the gnashing of teeth when the forecast misses the mark. All the variability due to the landscape of the area, as we know, produces a mixed bag. This past storm was no different and it was the south sounds storm. The next one looks like it will be more of a direct hit as advertised What do people expect, that forecasters will tell them how much snow will be in their front drive with 100% certainty? Get real folks!

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  27. Seems time to revisit "certainty" or odds for the forecasts. Kudos to Cliff for saying he was very confident, but then of course demerit for badly missing the forecast. I wish by rough region there was "Seattle proper" forecast is 6 inches, with only 50/50 or medium confidence.

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  28. Hmmm, well in the last blog post, Cliff said as much as 4 feet in the mountains and a foot in Seattle. That is looking like a hearty exaggeration at this point. The mountains are calling for 5 to 9 inches on NOAA through Monday... let's see how this plays out. Looking like mostly a bust so far. Just not enough moisture. Not sure why Cliff got so excited.

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