Sunday, February 10, 2019

Slushmageddon

Will update at 10 AM Monday
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You heard about about Snowmageddon in previous blogs.

Well, tomorrow (Monday) it looks like we will transition to Slushmageddon during the evening.

As forecast (and right on time), light snow started falling around Puget Sound around 4 PM and since then 2-4 inches have fallen in most places. Many local roads are covered, so be careful out there...with temperatures near freezing, the roads are slippery.


The latest radar image (8:30 PM) shows most of the action is over from this disturbance for Puget Sound, with the snow band moving east, but a hint of some convergence zone activity in Snohomish County.


Local departments of transportation have overnight to clean this up, so I suspect the main roads will be passable in the morning.

The new model runs are in and confirm that snow will start falling tomorrow afternoon and a messy situation will occur later in the day.

The morning will be fine, but precipitation will reach central Puget Sound between 2 and 3 PM (earlier to the south).  With cold air in place, precipitation will start as snow.  But as the event proceeds, warm air will surge in aloft, and eventually precipitation will transition to cold rain.  And then Slushmagedon will begin.

At 4 PM tomorrow the low will be west of our north coast and a warm front will be pushing in (solid lines are pressure and the colors are temperature, with blue cold enough to snow).   With shallow cold air in place Puget Sound will get snow at that point.

 By 4 AM Tuesday the low will be close to our NW coast and the air will be warm enough for rain to extend over Puget Sound

 The low hardly moves during the next twelve hours, but the air will have warmed and rain will be falling over western WA.  BC is going to get hammered with snow though.


I have a great graphic to illustrate all this, with colors showing snowfall and gray shades indicating rain.  For the 3-h ending 4 PM, expect snow over central Puget Sound, but rain to the SW.

For the next three hours, snow barely holds in Seattle, and extends to the north.  Rain will just be reaching Sea Tac.


By 4 AM Tuesday, rain will extend over the lowlands.

The total snowfall over the region shows mega-snow over the mountains (skiers will rejoice) and perhaps 3-4 inches over Seattle northward.


So you will wake up tomorrow with 2-4 inches of fresh snow.  Midafternoon more snow will start and I expect that around 2-4 PM snow will start again over central Puget Sound.  In the south Sound, precipitation will quickly turn to rain, but from Seattle northward there will be another 2-5 inches before it turns to rain during the evening.  The evening rush hour Monday may be problematic with fresh snow.

And Tuesday morning you will wake up to a slushy mess.

This is the kind of forecast that can easily go wrong.  If the low ends up 100 km farther south, Slushmagedon becomes Snowmagedon.  The ensemble forecasts have a wide spread.  But I believe the above is the most probable evolution at this point.

35 comments:

  1. For commute purposes, is slushmageddon preferred to snowmageddon, or will the slush freeze into an unremovable layer on Tuesday night?

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  2. Mostly great news. That means all the snow, ice and slush will melt quicker and we can get back to "normal" by Valentine's Day.

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    1. Great news if “great” means massive flooding.

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  3. in monroe, its been dumping for the past 4 or so hrs. What would the behavior of the convergence zone be over the next 12 or so hours?

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  4. We got 8 inches of snow here on the Dungeness River SW of Sequim Superbowl Sunday night, then another24 inches on the 8th/9th. We read your forecasts as they are the most specific and accurate I can find. Thx, Cliff.

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  5. Sounds a lot better than what it was looking like in the same timeframe, several days ago.

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  6. Can someone explain what "convergence zone activity in Snohomish County" means?

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    1. https://komonews.com/weather/faq/what-is-a-puget-sound-convergence-zone

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  7. Well, would LOVE to see SNOWMAGEDON, but understand that all good things (snow) must come to an end. Just hoping the transition from snow to rain doesn't result in freezing rain down here in Fircrest (Tacoma)!

    Thanks Cliff, your forecasts for the cold snap and snow have been dead on!

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  8. It will be interesting to see what I get. Right now, I've got about 10" on the ground SSW of Chehalis at ~1200'. It was pretty amazing for about 2 hours. Blustery 30 mph winds and heavy dry snow. If I don't change over to rain, I'll get a foot more easy.
    My current OAT is 30F with moderate snow while KCLS is steady at 36F.

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  9. [Monroe/Woods Creek, 11:20pm] It's been snowing and sleeting steadily at our place with almost no let-up since around 2:30pm. The current radar suggests that it will finally end around midnight. We took our dog for a walk about an hour ago, and there were easily six inches of new snow on the ground, possibly more.

    Looks like this "weak" storm decided to make up for the fact that the last, stronger storm missed us. It'll be interesting to see what develops with the Monday Night storm - we may or may not get warm enough for it to turn to rain.

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  10. All good things must come to an end. Great memories of our old dog behaving puppy like this weekend rolling in the snow and making "snow angels".

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  11. Unfortunately, these over running Pacific born systems are usually our snow killers. I remember many a winter over the last 40+ when snow was called for and all we got was cold rain. Secretly, I'm hoping for all snow Monday night, what's 4-8" more at this point?

    Thank you Cliff for your extra coverage of these recent snow storms and all of your other great explanations of our unique and difficult forecast area.

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  12. Thank God I am so happy the nightmare is over.

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  13. Probably about 4ish inches in Bellingham since 3:00pm @80' above sea level. Still snowing moderately heavy, with a fair amount of wind. Glad we at least got a non prescripition dose before we all come down to reality. Felt like we almost missed out in Whatcom County till now.

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  14. We received 8" + of snow here north of Monroe. If this turns to rain, there are going to be major flooding problems IMHO.

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  15. We got at least 8" of snow today 5 mile northeast of Monroe. If the weather turns to rain, we are going to have more than Slushmagedon…. it will be floodmagedon…

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  16. 7 1/2 inches at three lakes tonight

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  17. We received 7 inches in Sultan last night. Should we expect more snow and less rain today?

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  18. Any idea how much snow is predicted for the Olympic peninsula for round 4? I’ve been hitting the top end of the accumulations each round and just curious if I’m looking at another 12” of snow this one

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  19. When you say BC as the snow recipient throughout does that mean Skagit and Whatcom counties will be spared from that long term or is there a chance...or a higher likelihood that we would be the most likely to stay in the snow zone. We have largely been spared here in the low lying areas but Ive noticed just east of the Sedro area there is a 1-2 foot warning. I assume its for the foothills but is there a decent chance we stay in that snow zone. My yard has been cleared effectively by the sun twice now but last night we received maybe another inch or so. Hoping that we miss the bullet again.

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  20. I am up in Swede Heaven and we got over 2 feet of new snow yesterday from 4 pm till 1 am this morning. Swede Heaven is 6 miles due West of Darrington on the North Fork of the Stillaguamish River.

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  21. Bham looks to stay cold enough to remain in the snow-zone through the week, accd to NWS and WU. Sadly, we'll be lucky to have the schools open at all this week!

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  22. The strangest thing about this post is that there is no NE 66th st at 25th Ave NE.

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  23. Bellingham had it about as bad as i've seen for at least 20 years last night. It was damn near a blizzard on the south hill with 25 mph winds driving snow. 4-5" with some drifts in my yard up to my black labs belly.

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  24. Hard to tell how much we got in Rochester last night because it was so windy and it drifted a lot, but it was at least 4 inches. And as of 7:30 this morning it has already started coming down heavy again.

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  25. No! It’s way worse! Slushmageadob is very dangerous and it will freeze if cold enough.

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  26. Sunday afternoon and night at the Bow,WA strictly unofficial weather reporting station was just a light dusting - plenty of wind blowing it around. Nothing happening this AM at 9:15 - yet. 26 degrees. Stone-on-a-string still white and looking a bit forelorn but hanging in there doing its duty.

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  27. You're really staying on top of the forecasts!

    Impressive, very impressive.

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  28. Minor clarification to the sentence above the first air pressure image. It should say by 4pm TODAY.

    Love your blog Cliff.

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  29. Aberdeen School District started on time and now it is snowing big, fluffy flakes of irony. It's even better when you consider that we all got a phone call for late start and then another call for oops, no late start. Can we please get an irony blizzard over here?

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  30. So this is just a question from a lay person wanting to know more . . . this was supposed to be an El Nino winter, right? Did El Nino set up and then dissipate? Or did it not set up? Or is a two-week period of non-typical El Nino weather just a normal variance within an overall weather trend?

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  31. Nice job scaring people off the roads Friday! The evening commute was a breeze. Really!

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  32. Just an enthusiast. Why does BC flush out with the rotation over the plains. https://www.goes.noaa.gov/dml/west/nhem/nepac/vis.html

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