February 09, 2021

A Major Lowland Snowstorm over Western Washington is Highly Likely

 There is an excellent chance that western Washington is going to be hit by a major lowland snow event.  

And yes, the mountains will be buried as well.

It is possible that some lowland areas will experience more than a foot of snow and February snow records will be broken at some locations.  Can I absolutely guarantee this?  No.  Is a major event highly probable?  Yes.

Convergence

A big issue yesterday was the substantial difference in the snow forecasts of the American and European Center models, with the European model--generally the more accurate one-- going for much more snow over western Washington.

Overnight the American model has moved towards the European solution.

Let me show you the accumulated snowfall over time from the European model.  And let me stress, snow depth will be LESS than total snowfall (what falls out of the sky), due to melting, settling and compaction, and other reasons.

The snow will begin on Thursday.  The snowfall total through 10 PM Thursday shows significant snow from north Seattle to Olympia, with the greatest amounts in the south Sound


And the snow deepens by 10 PM Friday, with roughly a foot in the south Sound.  Huge amounts in the Cascades.  Too warm for snow in the Willamette Valley and the Oregon coast.


More snow hits on Saturday, with snow extending to Portland, cooled by air coming through the Columbia Gorge. Nearly a foot up to central Seattle.   Just crazy in the mountains.


As I have told you many times, never look at a single forecast.  One needs to consider uncertainty, and ensembles of many forecasts help quantify it.  The 51 member European Center ensemble for snowfall at SeaTac Airiport is shown below, the top panel having 51 stripes, one for each forecast. Most members are going for a major snowstorm...perhaps 3 or 5 out of the 51 are not.  Nothing is certain.  You must deal with probabilities.


Importantly, the U.S. GFS model ensembles (only 21 members) looks similar, but with a higher percent of the members have less snow.


 The high resolution U.S. GFS forecast (blue line) is going for ALMOST 20 inches of snow by late Monday.  Unbelievable.   And here is the U.S. GFS snowfall forecast through 10 PM Sunday.  24 inches in Tacoma, 20 inches in Seattle.   The mountains would probably be impassable if this forecast comes true.

And there are subtleties that I haven't talked about.  Strong easterly winds on the western slopes of the Cascades that should lessen snowfall between the Sound and the Cascades (because sinking air works against precipitation).  The unusually cold air east of the Cascade crest.  And much more.

I will probably do a special podcast about this event tomorrow (Wednesday).  There are a lot of moving pieces with this event and thus uncertainty...but at this point a major event appears to be in the cards.


74 comments:

  1. Very excited Cliff. That front on Saturday looks fantastic for us Kitsap folks-- classic, nice easterly/southeasterly gradients...could be a great one. Hard to scour out the cold air here under those conditions with decent precip rates. I thought these big Feb snows were rare? Here we are with another potential big one just two years after the biggest Feb snow in like 80 years.

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    1. Yes!!! Hopefully it hits us here in Kitsap. So excited.

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    2. Anyone have any thoughts on the Lake Bosworth / Granite Falls area?

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    3. Anyone have any thoughts on the Lake Bosworth / Granite Falls area?

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  2. This is unbelievable. I'm so excited! Just like February of two years ago.

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    1. We lost three beautiful trees in our front yard in that storm! But I guess we can't lose them again...

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    2. A 100-foot cedar tree fell on my house in that storm, so I'll pass on an event just like that of two years ago!

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  3. Do you think it’s possible that Fraser outflow could enhance snowfall on the northern Olympic Peninsula, like has happened in the past?

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  4. Gather your banannas and tp. See you all in March.

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  5. Oh man, I've got to get over the pass this weekend. Maybe Saturday better than Sunday?

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  6. LOL the two members going for 30 inches... OH MY GOSH THAT WOULD BE INSANE

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  7. Well, well, well. This should be interesting. Should be quite pretty and mostly enjoyable so long as the power stays on!

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  8. The strong east winds are what make me think all of the snow totals are over estimates. Every time it snows and the east wind picks up, the snow pretty much stops.

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  9. Pretty weird that the networks aren't hyping this yet. Fingers crossed for a big snow!

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    1. Yeah, I was commenting to my wife on this today, too- the TV networks are all downplaying this big time, talking about some flakes, maybe a dusting at MOST. Strange that they are not at least hinting that it could be something bigger as was the case two years ago when we had our big snow event.

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    2. I think this is interesting too. Q13 had nary a flake on their 7 day forecast this morning and interesting with most of the major meteorologists in this area on board with some snow coming through at some point.

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    3. If I recall, the 2019 event wasn't much hyped about either. I remember hearing there was a chance for some snow, maybe an inch. Woke up the next morning with 11 inches on the ground and didn't go to work for 2 days. That's weather for ya!

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  10. There appears to be a boundary where the deeper snow potential ENDS before getting to south Snohomish county. Usually it's the reverse, and we bask in our Convergence Zone Snowiness (tm). We will see what happens!

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  11. Thanks, but no thanks‼️ Snow is for the mountains ❄️

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  12. Info for Wahkiakum Co and Cowlitz Co would be appreciated. Thanks

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    1. There are 4 maps in the post showing forecast snowfall totals, covering Thursday through Sunday. They include SW Washington.

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  13. Good grief! Thanks for the update, though. Looking forward to the podcast, if you're able to, that is. Be well and stay safe!

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  14. The only certain thing in this situation is the uncertainty...

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    1. wow, one of the wisest sentences in meteorology

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  15. Thanks so much for the info. We have made our plans to stay inside until it rains, maybe Sunday? Unless everyone goes out to throw snowballs of course. Or make a snowwoman. We will try to avoid shoveling.

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  16. How about the forecast for South Snohomish County?

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    1. Agree! It looks like it might miss us. We’re in Edmonds and surprised that there’s nothing but a dusting in our forecast. Usually the convergence zone means we get hit as much or more as everyone else!

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  17. I’d like to know why the NOAA/NWS forecast doesn’t reflect this. Their accumulation figures amount to a few inches at best through Sunday.

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  18. As of 4:30 Seattle is forecasted to get dusting at most??? Pierce County south is under a winter storm watch, looks as Seattle will get missed once again by a big snow storm.

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  19. I’ll believe it when I see it, but hopeful!

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  20. I am dating myself but these times when we are all wondering whether all of the difficult to predict factors will line up to produce a classic snowstorm...I think back to watching Ray Ramsey and his rotating box. He introduced me to Williams Lake, BC for the first time and whether there was a high enough pressure difference to trigger the Fraser River outflow. He would get just as excited as we are all..with chalk dust flying everywhere when he was drawing the trajectory of the Low down the coast and where it would come inland....just like this upcoming storm. Just had to share this as I learned a lot from Ray...enough to want to take classes from Cliff when it was time to go to college!

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  21. Any specific info for San Juan islands?!

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  22. Its odd that noaa and none of the TV stations are talking about this. With so many ensembles going for heavy snow you'd think they would at least mention that there is a chance of a big storm. Its certainly cold enough its a question of will moisture get far enough north and will we get a dry downslope wind that makes the precip lighter. I'll belive it when I see it there is still a chance this could fizzle into nothing. Noaa doesn't have the most up to date computers but still out of an abundance of caution they should be warning people that heavy snow is possible. I am going to stock up because if this forecast does come true I might not be going anywhere for 3 to 5 days.

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  23. What do you think Bonneylake/Buckley area will look like.

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  24. GFS model, around three feet in Shelton and Olympia? Unbelievable. "Snowmageddon" had only two feet...and that was A LOT.

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  25. GFS model, around three feet in Shelton and Olympia? Unbelievable. "Snowmageddon" had only two feet...and that was A LOT.

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  26. Easterly down sloping winds are going to (once again) dry out the eastside side(I-5 East) work low accumulations. The moisture will be heavier south of Kent. Points N will get 1-3". Saturday looks to be a good ol fashion wide spread snow event. Though, it's only Tuesday...

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  27. And just like that the newest forecast models just took all the snow away from Seattle Thursday and Friday. Ugh! Now Saturday will be the next chance of snow before it warms up right away.

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  28. Have fun, I'll be up north with lows in the high teens and no snow....yuck

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  29. Curious result showing up on Wed 00Z run of GFS v16 model. Shows snow band developing much farther south compared to earlier runs. Stays south of Olympia until Sunday! Admittedly, I don't know anything about these different models, but it appears to be hotshot new version of GSF?

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  30. I think my three day weekend might get extended. :)

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  31. Based on the 3:22 am forecast discussion, there might be 1-2 inches total in Seattle and zero snow up in Whatcom.

    I guess the ECMWF is the only model now going for a snowstorm.

    Let the battle of the models begin!

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  32. Why hasnt a winter storm watch been issued?

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  33. So you're in Seattle and you're Seattle-centric. But you're also working for the U of Washington, and WA State is a whole lot more than the west side. You wrote NOTHING about the rest of the state. Oh well, Seattle hates us. Please don't come over the mountains when you get that big earthquake.

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    1. This is Prof Mass' personal weather blog, not a product of UW.

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    2. Calm down. The man doesn't even have to write about the west side of the state if he doesn't want to. Did you ever consider doing a google search for the weather forecast on the east side of the mountains? Maybe look for a forecast for your home town? You might find what you're looking for.

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  34. Thank you, Cliff! Your blog helps us tremendously as a company that snow plows.

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  35. I see NOAA early morning update having the 1st low maybe moving further south...and the winter storm watch from pierce county south...2 - 13 inches possible...so with the low moving further south does that mean TAcoma 2 inches and then 13 closer to Portland???...if that haooens my guess a few posts back was correct...hmmmm..I was trying reverse psychology on the snow...would like a big dump in Tacoma...

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  36. Two years ago we had that great snow event early Feb. We had 13 inches in Tacoma. My kids and all the neighborhood families had a great time sledding for 3 or 4 days. In 2 short years, my kids have already memorialized that week as the all time/best ever 'snow week'. Fast forward to today, looking at a couple of the forecast models showing 24 inches in Tacoma!! Anything over a foot is noteworthy, but 2 feet of snow here would be pretty wild!! I hope we get anything close to that. Kids have their sleds ready. #:)

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    1. Just reminder that is snow fall. Not snow accumulation on the ground. I was excited to seed 24 inches too, but we will see a lot less on the ground due to melting and compaction.

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  37. Just listened to your podcast..how do we sign up for notifications of new podcasts?

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  38. Looks like NWS is backing off a bit on the big snow, at least north of Pierce County. Let's hope that changes.

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  39. The latest update keeps the theme of the winter - maybe some snow a few days out.

    It seems to always be just out of reach this season, like a mirage in the distance that seems to disappear when you get closer...

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  40. Looking forward to the podcast

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  41. Weather.com (Weather Channel) has substantial snow falling in Portland and less in Seattle. Curious. I don't mind a little but +12 no thanks.

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  42. Want 10 inches of snow in Bothell. What snow gods do we need to pray to, to make that happen :-)

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  43. Where can we see these snow models as they update?

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    1. Found this website a couple days ago.

      https://www.pivotalweather.com/model.php?m=gfs&p=sn10_acc&rh=2021021012&fh=78&r=conus&dpdt=&mc=bl

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    2. Windy.com is a good resource

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  44. Looks like Saturday is the day for snow south of lake tapps

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  45. Cliff, I love ya but your forecasting is less than accurate when get excited and abandon a probabalistic approach. A 50% chance is a coin toss, not "highly likely". Every major forecaster is calling for maybe ainch or two in metro Seattle. I hope you're right but I'm guessing you are not.

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  46. online weather forecasts show none or very little snow in Newcastle/Renton.

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  47. 100 bucks says seattle wont get a drop of snow on Thursday. Friday maybe a couple of inches that's it. Stop celebrating like a bunch of pre teens missing school. Some of us ACTUALLY work and have REAL jobs. I love how meteorology can be the only job your allowed to be be wrong 50٪ of the time and still hold a job

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    1. You can be wrong 100% of the time and hold elected office so....but thanks for qualifying what a "real" job is.

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