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gb
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PostTue Dec 13, 2022 6:57 am 
I had been kind of surprised looking at Windy and scrolling North that the interior of BC has not really had cold temperatures lately - like 10-20 degrees F. But reading the NWS Discussion https://forecast.weather.gov/product.php?site=sew&issuedby=sew&product=AFD&format=CI&version=1&glossary=1, the prolonged moderate ridge forecast (most recently) through the weekend has disappeared. Western Washington will apparently be pleased to welcome the first (and perhaps only) period of snow and Arctic cold late next weekend through the following week. This looks like the real McCoy. Take a glance at Windy, Seattle by both the GFS and ECMWF really gets nailed with continually falling temps through Thursday of next week. The likelihood of snow looks pretty good, but of course, the amount of snow is not yet any kind of certainty. But both models show mid-20's or teens initially, then single digits late next week. Of course, this is not typical for Seattle and W Washington, so it might be overstated (understated), but cold temps look very likely. Meanwhile, BC 100-300 miles north of the border sees -20 to -30 F temps (both of those models via Windy), so there is a lot of support for a very real incursion of Arctic air into W Washington. At the end of a period like this, whenever it happens, about 90% of the time within a couple of days mountain freezing levels shoot up and either you get warm and wet or warm and dry after warm and wet...so not typically great for skiing. So, there may be no joy in Mudville longer term...... Oh, somewhere in this favored land the sun is shining bright; The band is playing somewhere, and somewhere hearts are light, And somewhere men are laughing, and somewhere children shout; But there is no joy in Mudville—mighty Casey has struck out. Ernest Thayer Casey at the Bat

Bramble_Scramble, PowderPawn, Aussie, SpookyKite89
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Chief Joseph
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PostTue Dec 13, 2022 8:13 pm 
Finally have a weather window, so plan to head to Priest lake Thursday. I think they have nearly 3' of snow there already. Conditions look clear and cold all the way, hopefully no freezing fog..

Go placidly amid the noise and waste, and remember what comfort there may be in owning a piece thereof.
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joker
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PostTue Dec 13, 2022 9:19 pm 
From the NWS Seattle office's forecast discussion just now
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.LONG TERM /SATURDAY THROUGH TUESDAY/...A cold upper trough develops over British Columbia through the weekend. Looking at the 00z GFS temps--afternoon temps over Western Washington Sunday are forecast to be in the 30s while just a hundred miles north over British Columbia, north of the arctic front, where temps are below zero. Cold Fraser outflow is likely to develop early next week into into the Bellingham area and the San Juans. There should be a good chance of snow at some point with Monday and Tuesday now looking better than the weekend if you favor the GFS--although it is interesting that the 00z GFS confines the snow to Skagit and Whatcom county Monday and Tuesday with rain to the south. The 12z ECMWF is drier but colder--it has a modified arctic front moving through Western Washington Sunday afternoon or night with just some scattered snow showers on Monday before taking the interesting frontal wave into northern California late Tuesday. 19

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PostWed Dec 14, 2022 9:11 am 
I am flying out of seatac next wednesday so its definitely going to snow that day. Other than that models are flipping all over the place. Going back and forth between 0-20 inches. Probably means an inch of rain snow mix. For the lowlands. Obviously theres way more likely for the mountains.

rossb
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kiliki
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PostWed Dec 14, 2022 11:44 am 
Quote:
I am flying out of seatac next wednesday so its definitely going to snow that day.
I had a flight cancelled during that last round of cold/snow which made me miss an international connecting flight at LAX. It wasn't because Seatac couldn't deal with the snow--there was only a trace--but it turns out the contractor that does de-icing is short staffed and they just can't de-ice all the planes. You might keep this in mind and make sure you have plenty of time to get where you need to be.

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PostWed Dec 14, 2022 12:28 pm 
We arnt connecting which helps but its still iffy. We wernt connecting last year either and delta still failed and stranded us for days.

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PostThu Dec 15, 2022 6:20 am 
That's just terrible

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joker
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PostThu Dec 15, 2022 10:41 am 
the latest NWS discussion
Quote:
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The more notable weather will occur in the extended period this week with more widespread wintry precipitation. As noted in the previous discussion, there is still some uncertainty in how far south the developing modified Arctic cold front dives. The general consensus still brings the front into western Washington Sunday and Sunday night. The bitterly cold Arctic air will stay north and east of our region on the lee side of the Rockies but both nearly all of the global ensemble guidance brings a period of well below normal temperatures into the region by the middle of next week. Largely stuck with the NBM on the forecast into next week, but trended temperatures down a degree or two Tuesday through Thursday given a look at the EC ensemble guidance. A series of shortwaves will pivot through the region as they eject from a longwave trough over the north-central Pacific. The first round of precipitation will quickly dive southward ahead of the modified-Arctic front Sunday, brining lowland rain and mountain snow. Snow levels drop below 500 feet over Whatcom and Skagit counties, remaining between 1000 and 1500 feet further south into the Seattle metro. These drop through Sunday night as the front continues to dig south into the area, looking to drop below 250 feet even over the Seattle metro by Monday night according to the NBM. Thus, by Monday we will likely see even more transition from lowland rain and mountain snow to more snow Monday. After the front settles into the area, there look to be two more distinct shortwaves and attendant surface lows to watch. The first of these being Tuesday and Tuesday night and also being the weaker/ less dynamic of the two. The second system looks to enter the area in the Wednesday night through Thursday night timeframe. There looks to be a stronger warm surge ahead of this surface low. There is also an inherent growing concern for some mixed precipitation if this scenario plays out and colder air remains locked around Puget Sound and adjacent lowland areas. All three of the GFS, EC, and CMC suggest there is some sleet and freezing rain potential somewhere in the area Wednesday night as the front attempts to lift northward as a warm front. This will need to be closely monitored in future forecasts. While it is still too early to discuss exact snowfall amounts, there is the potential for several accumulating snowfalls, totalling up to a few inches even into the Seattle-Tacoma metro by Thursday. Global ensemble guidance all suggest this for KSEA, with the GFS, EC, and CMC mean ensemble member snowfall totals by Friday morning ranging from one to several inches. Keep in mind this is over a range of several days from Monday afternoon through Thursday night. There is still a substantial range in totals, so further refinement will need to occur. The NBM forecast seems reasonable for now, though I have a feeling the snowfall ratio used might be a little too high. The NBM forecast does support this consensus for several inches of snow potential through the metro. Also opted stick to a rain/snow mix through the extended for now, but as mentioned above, the freezing rain potential will need to be closely monitored.

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gb
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PostThu Dec 15, 2022 4:40 pm 
Pretty wild swings back and forth from GFS to ECMWF from succeeding runs. Yesterday showed Thursday temps of -44 at Williams Lake and +52 at Astoria, a 100 degree difference over 500 miles. Not looking as extreme now, but the European model has the NW snowing Tuesday/Wednesday, but rain by Thursday. GFS shows a longer period of snowy weather but shows warm rain with a 8000' freezing level by Saturday. Originally, when I posted it just looked very cold with 7 to 10 F in Seattle for much of the week. It looked very definitive with GFS and ECMWF both agreeing. Apparently the cold blast will stay north, but it looks to be cool enough temps for snow with overrunning moisture from our SW. We could see quite a bit of snow before it all turns to a typically messy slush in Seattle, etc. The forecast changes have been really pretty astronomical.

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PostFri Dec 16, 2022 2:26 pm 
Yet a few days later, 12/23, models are currently showing "summer" like 50deg temps west of the crest. With rain at the Pass and east side of the crest in Leavenworth etc. Talk about an extreme bounce. What's the chance's this comes to pass? I'm hoping that its wrong, since warm rain over the holiday weekend seems pretty grim.

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PostFri Dec 16, 2022 8:52 pm 
That sounds like a PNW early winter classic

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gb
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PostFri Dec 16, 2022 8:58 pm 
dixon wrote:
Yet a few days later, 12/23, models are currently showing "summer" like 50deg temps west of the crest. With rain at the Pass and east side of the crest in Leavenworth etc. Talk about an extreme bounce. What's the chance's this comes to pass? I'm hoping that its wrong, since warm rain over the holiday weekend seems pretty grim.
Think of it this way: To get really cold, the air has to come from the north which means a high amplitude ridge offshore. Move the ridge east and what comes next is strong southerly flow. Voila. When we get arctic air here, there is something like a 90-95% chance that it ends this way. We just have to hope it doesn't stay like it did last year for 2-1/2 months...

HikingBex, dixon
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altasnob
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PostSat Dec 17, 2022 6:59 am 
I had to look up what the "!" symbol means on windy. Freezing rain bawl.gif

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PostSat Dec 17, 2022 1:00 pm 
Yeah, tomorrow may be an epic day for powderhounds - epic driving conditions that is. Per NWS forecast dicussion from this morning
Quote:
Some hi-res guidance has also suggested there is potential for freezing drizzle/mist as the snowfall begins and as snow levels lower through Sunday morning. Collaborated with NWS PDT and issued a Winter Weather Advisory for eastern King and Snohomish County to account for the freezing rain/drizzle and following snowfall from 4 PM Saturday through 10 PM Sunday. This is primarily for potentially dangerous driving conditions on Stevens and, especially, Snoqualmie Passes. Guidance is hinting on a potential Puget Sound Convergence Zone across northern King and Snohomish county Sunday evening, due to the frontogenetic forcing along the modified-Arctic frontal boundary. Expect precipitation to increase in coverage and intensity through the evening and overnight within this band, where locations could get more than an inch or two.

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gb
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PostSun Dec 18, 2022 9:07 am 
Now looking at what must be record high lowland temperatures just after XMAS. GFS and ECMWF both showing Seattle at 57 and Tacoma at 59F. Freezing level peaks at 10,500'! Hopefully, this is not an endless stretch of warm and dry and warm and wet.

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