Thursday, January 9, 2020

Snow Update

Some flakes are falling over the western Washington lowlands right now--but this is not a serious issue.  Roads are still quite warm and there is some minor accumulations on grass for some higher elevation locations (see the picture below at the intersection of I-90 and SR 18 east of Issaquah.



The freezing level (and thus the snow level) has dropped considerably over the past day, with the freezing level (the temperature aloft where the atmosphere cools to 32F) now around 800 ft (see image from Seattle SnowWatch below).  A few melting flakes have reached sea level as a weak weather system moves through this morning.
But if you live at a higher elevation, the scene was more winterlike (take a look at the picture at 1170 ft in Bellevue at the home of Dr. Peter Benda).


A stronger weather system is approaching the Northwest and will reach us tonight...and we will have some cooler air in place.   This is not an ideal situation for lowland snow (temperatures are marginal), but with higher precipitation rates and cooler air holding a bit over northwest WA, there will be light snow, particularly away from the water (see the snowfall total forecast for the 24 h ending 4 PM Friday) north of Everett.  Potentially 1-2 inches. 

Again, roads are still relatively warm, so I don't expect travel issues in the lowlands.  But look at the mountains...they are going to be hit relatively hard, with a foot of snow in places.


Snow will continue in the mountains through Saturday, but no snow over the Puget Sound lowlands on Saturday and early Sunday.    Then we get the next snow threat.   A low center will move down the coast, while cold air is found over British Columbia (see forecast surface weather map at 10 AM Sunday). 

The path of this low is critical.  If it were 100 miles south, we could have a snowstorm over much of western Washington, but the current forecast path brings is across northern Washington (see sea level pressure map for 4 PM Sunday below).  Cold air will move into Northwest Washington before the low makes landfall (through the Fraser River Valley) and behind that system after it passes, while onshore flow off the relatively warm Pacific will keep things rain from Seattle southwards.


To illustrate this, here is the 24-h snowfall total ending 4 PM Sunday.  Bellingham will be whitened as will the folks from Sequim to Port Angeles.  Note the STRONG northeasterly winds pushing out of the Fraser Valley gap across the San Juans.  Cold air (the "arctic front") will be entering western Washington.  Also note the heavy snow in the mountains.  Skiers will be all set.


But these snow events are just the preliminaries for what could be a major snow event over western Washington and Oregon on Wednesday and Thursday.  Very cold air will be in place and a potent weather system will be approaching our coast (see surface forecast map for 4 PM on Wednesday). 


Wow--this has potential.  But I have learned from hard experience never to get excited about snowstorms that far out (I have a personal 120hr rule.  If the forecast is beyond 120 hours, I try to keep my emotions in check and prevent myself from stocking up on milk and bread).

The amount of snow and where the snow falls will depend critically on the path of the Pacific low and there is considerable uncertainly that far in the future.

 We do have an exciting new tool right now to help with this forecast---a line of unmanned weather observation sailboats a few hundred mile offshore.  We will see if they help!


38 comments:

  1. How new are those unmanned sailboats; how long have you been able to use their data?

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    1. https://www.saildrone.com/

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    2. Thanks for the info on the technology. How long have they been there, of help to Northwest forecasting??

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    3. The Wave Glider by Liquid Robotics is another cool autonomous platform. https://www.liquid-robotics.com/

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  2. so will it still snow on monday and tuesday? your previous post noted a few inches over southwestern wa ( Olympia area). will this still happen?

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  3. Hi Cliff, super curious when/if roads will be super icy on the hills in Seattle? I'm guessing winter tires by Thursday? Or should we make sure they're on sooner for early morning commutes? Thank you so very much!

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    1. If you're worried about it get them on now before there's a rush. I got mine on last Sunday

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    2. Last Sunday? Hell, I got mine November 5th. No crowds at all!

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  4. Bring it on! We have about an inch at 300ft elevation in northeast Puyallup. Road was white, but has turned to slush at 34degrees.

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  5. We have quite a bit of snow in Bonney Lake at about 500 feet of elevation. It was sticking to the roads, but it's melting off rapidly. We had at least as much accumulation as your Bellvue picture. Kids even managed to make a small snowman.

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  6. Would love to see some snow in Portland, but given prior disasterous attempts at dealing with it here via the city and county crews, perhaps some discretion would be in order.

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  7. What happened to the 72 hour rule. Do we really have forecasts of accuracy at 120 hours now? I really thought anything past 72 hours was heavily impacted by climatology data. Thanks. Troy

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    1. When to choose the the 72 or 120 hour rule is directly proportionate to how excited you are for the potential weather event.

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  8. Looks like the arctic outbreak will be over by next weekend if not sooner. Models are already becoming unstable and waffling.

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  9. My experience is that we'll see the most snow and most wind on the days it's not suppose to be windy or snowy. And the forecast will only be accurate about 12 to 24 hours prior to the event.

    Happens almost every time with wind/snow events around here, long-range forecast (i.e. anything over 24 hours) is about as accurate as throwing a dart at the dartboard with your eyes closed, drunk, after being spun around 7 times while only wearing one shoe.

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    1. The GFS model in particular assumes the oceans and stuff are the same as it was 50 years ago and this is what happened with the conditions then so it should work like that now right? (wink wink). And you want these kinds of computers to drive our cars for us? I don't think so bro.

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    2. The comments here are what Mark Nelson originally intended not to be arguing over models.

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  10. The NWS is forecasting temperatures below freezing in the lowlands ALL week next week. We are sure to get something in the form of snow.

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  11. Got about an inch and a half 3 miles NNE of Monroe, and it did stick to the roads here, about 400 feet elevation. it also snowed in Monroe but the roads were pretty clear around 9:30 when I went into town.

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  12. And what do you mean by "major snow event? are you talking 4-5 feet of snow.

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    1. Be realistic. Who living around here now has seen 4 to 5 feet of snow on Seattle or Tacoma streets??

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    2. In the Seattle area anything more than 3 inches is a major snow event. Seriously: schools will close, the freeway will be a parking lot, people will take days off work, and supermarket shelves will go bare. The forecast I'm looking at now is predicting about 6 inches over 2 days. If that holds it will be a major event!

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  13. Portland has 56 snowplows now. In 2003 they only had 12.

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  14. Bummer.

    The NWS says the Weds/Thursday storm is mostly headed for California now.

    :(

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  15. The big February 2019 snow was on again off again in the forecast. It really wasn't "on" until it was for the most part over! Lots can change in 5-6 days.

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  16. Yep, just saw the event has been cancelled. Good thing Cliff held to his 72 hour rule. Of course the local TV channels won't let this go yet. :)

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  17. Thus far (and a lot can change) this has the makings of a classic Seattle Snow Miss. Sunday/Monday the moisture is too far north, which means rain. Next week is too far off, but a lot of the models bring in the moisture too far south.

    A pity as it's a waste of a great weather pattern for snow.

    But perhaps the models will still change or a CZ will pop up Sunday/Monday to have someone win the snow lottery.

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  18. Bring it on, especially east of the mountains! Here in north-central WA at over 3500' we've only had about 26" (snowfall) since Thanksgiving. We should have had at least twice that by now. Temps kept warming and snow would change to rain - then freeze. Very icy roads, accidents. Hope we are beyond all that and it's pure snow here on out. Wind chill predictions for next week are currently at -25.

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  19. this is a 50/100 for us at this point if the emb assembles go they right way we could get a huge snow event. hz models are showing us in not record breaking news atm but you never know at this point this could be orons winter guys that just how mother nature works but mother nature could throw a curve ball at orgon and it misses them and goes into us which would be a snow lover biggest dream for now orgon could see 2 feet of snow while we watch the action which we don't want this could be the biggest hype winter in washington history but yet be remembered for the biggest blow out of all time

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  20. Cold air will be shifting south through British Columbia over the
    weekend. A weather system on Sunday will arrive as cold Fraser
    outflow develops. Precipitation should change to snow around
    Whatcom county and the San Juans on Sunday. Cold wind chill will
    develop and blowing snow with poor visibility will be possible
    into early next week in the Bellingham area and San Juans. good news for us if it shifts into stevens pass for way more good snow lets hope washington snow lovers win this fight mother nature has been good at practicing curve balls she will nail it maybe this time to washington

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  21. I'm curious about those weather observation sailboats too, Cliff.

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  22. They are usually pretty good about treating the freeway (except!for 2008 when they were caught off guard with sudden chill) City streets are the problem.

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  23. What exactly is the Fraser outflow?

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    1. What is an Arctic outflow?
      A squamish (also known as an Arctic outflow wind in winter months) is a strong and often violent wind occurring in many of the fjords, inlets and valleys of British Columbia, Canada These winds in winter can create high windchills by coastal standards of −20 to −30 °C (−4 to −22 °F).

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  24. Okay, Cliff, so we're supposed to fly NEXT Friday morning...advice and suggestions would be appreciated!

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  25. When traveling in winter, you need to keep warm. Some outdoor sports fans need to protect themselves in winter. They need to prepare corresponding equipment, such as anti-skid boots, gloves, hats, etc. of course, for the sake of safety, you should try not to go out as much as possible, especially not to do outdoor sports.

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