December 2023 Weather in the PNW

[TigerWoodsLibido]

Finally getting around to watching Better Call Saul.

Really good show.

Looks like it's 50F and quite warm outside.

[Kolk1604]

32 minutes ago, Gradient Keeper said:

I kind of want to wait up for the EPS now....

Looks improved to me also looks like our chances are increasing on seeing snow sometime early January. 

[HuskyMaestro]

27 minutes ago, TigerWoodsLibido said:

Finally getting around to watching Better Call Saul.

Really good show.

Looks like it's 50F and quite warm outside.

My body is ready for the January hype train to commence 

[Gradient Keeper]

00z CMCE Day 8-14 Analog Composite.
Yeah. This will do nicely. If only this pattern were to play out.

[SpaceRace22]

1 hour ago, snow_wizard said:

This is a link to the GraphCast, but I think it's the same as the Spire on Weatherbell.  It says this is a google/ ECMWF collaboration on this site.

ECMWF | Charts

You just blew my mind, I thought GraphCast wasn't public yet. This is amazing, thank you.

I think Spire is something completely different though. GraphCast is Google's own proprietary AI model and Spire is a separate company. The patterns are completely different at hr 240 on GraphCast vs hr 240 on Spire, too.

[SpaceRace22]

Looking at the individual members of the EPS really highlights that the 00z was an enormous improvement from the 12z. Almost every member has at least some lowland snow now.

[Slushy Inch]

Mean is up a whole inch. Good number of really cold members.

[Gradient Keeper]

18 minutes ago, SpaceRace22 said:

Looking at the individual members of the EPS really highlights that the 00z was an enormous improvement from the 12z. Almost every member has at least some lowland snow now.

Wow, yeah it did! Thanks for posting this.

Night Shift 6z GFS in 44 minutes

[Slushy Inch]

Member 47 in single digits.

[SpaceRace22]

Here you go, I cherry picked some of the spiciest ensemble members from the last 24 hours just for shits and giggles. Yes, this is completely deranged and a great way to set up for massive disappointment, but I find this kind of thing super interesting because it shows what kind of outcomes are still *technically* possible with the current configuration of the atmosphere.

Some day if computing power becomes more widely accessible and it becomes possible to run forecast models from a home computer, I would loooove to force the Euro to generate thousands of ensemble members on a given run just to see what the theoretically possible extremes are.

[TT-SEA]

10 hours ago, Front Ranger said:

They'll likely drop lower before midnight. Already down to 54.

Looks like the record warm min for December is 55 from 1980, so they avoided that.

63/53 at SEA held... temp got down to 53 again in the evening then briefly spiked back to 57.   

@SilverFallsAndrew yesterday was +16 at SEA and for comparison the peak in June 2021 was +25.    This wasn't June 2021 in December.

[TT-SEA]

06Z GFS shows a significant snow event for the Seattle area within a week... this happens next Friday which is just 6 days away now.

 

[FrozenBites]

25 minutes ago, TT-SEA said:

06Z GFS shows a significant snow event for the Seattle area within a week... this happens next Friday which is just 6 days away now.

 

If you don't mind me asking, what are the temps it's showing?

[TT-SEA]

4 minutes ago, clipper_range said:

If you don't mind me asking, what are the temps it's showing?

This seems to be the coldest point during the event... looks like a broad c-zone in the precip loop.  

[Anti Marine Layer]

No snow yet for South Lake Tahoe. 

[SouthHillFrosty]

1 hour ago, TT-SEA said:

06Z GFS shows a significant snow event for the Seattle area within a week... this happens next Friday which is just 6 days away now.

 

[MossMan]

The Fuzz. PNA still lookin good. 

[Phil]

The 00z EPS has one of the more impressive -NAO signals I’ve ever seen at-range. Pacific blocking is “meh” by comparison (from LF standpoint). Which is actually what you’d expect in an El Niño winter, as basically every El Niño winter with periods of deep western troughing involved the a -NAO suppressing the northern jet in Canada (which would otherwise split up into AK/Yukon). So at face value the idea isn’t outlandish (from a historical standpoint, at least.

In this particular case, (as currently modeled), transition to Siberian trough —> -dAAMt —> Pacific Jet retraction —> chain of anticyclonic wave breaks with increasing amplitude (and poleward jet migration over NPAC) —> slowing of zonal component of flow over Canada —> building -NAO.

This is a more unstable and vulnerable setup than your canonical La Niña/-NPO setup, but (as modeled) HL coupling w/ the SSW/stratwarm seems to be just enough to hold it in place. But even a small bump could dislodge the pattern, so beware last minute model swings.

[SilverFallsAndrew]

That first trough was good on the 06z but the rest of the run kinda sucked. 

[Snownerd3000]

3 hours ago, SpaceRace22 said:

Here you go, I cherry picked some of the spiciest ensemble members from the last 24 hours just for shits and giggles. Yes, this is completely deranged and a great way to set up for massive disappointment, but I find this kind of thing super interesting because it shows what kind of outcomes are still *technically* possible with the current configuration of the atmosphere.

Some day if computing power becomes more widely accessible and it becomes possible to run forecast models from a home computer, I would loooove to force the Euro to generate thousands of ensemble members on a given run just to see what the theoretically possible extremes are.

I think this is what they are working towards with the Ai generated forecast solutions. The future is wild, almost as wild as the ensemble member outcomes you shared. 

[iFred]

7 hours ago, SpaceRace22 said:

You just blew my mind, I thought GraphCast wasn't public yet. This is amazing, thank you.

I think Spire is something completely different though. GraphCast is Google's own proprietary AI model and Spire is a separate company. The patterns are completely different at hr 240 on GraphCast vs hr 240 on Spire, too.

It is on GitHub. You just need a couple thousand of TPUs or around a thousand A100s to take a full data set and churn out a model in under eight hours.

[Phil]

22 minutes ago, Phil said:

In this particular case, (as currently modeled), transition to Siberian trough —> -dAAMt —> Pacific Jet retraction —> chain of anticyclonic wave breaks with increasing amplitude (and poleward jet migration over NPAC) —> slowing of zonal component of flow over Canada —> building -NAO.

Can see this process extraordinary well on the 00z EPS.

- Troughing develops over Siberia, which due to presence of Himalayas/terrain, acts to remove momentum from the NPAC jet, culminating in a series of wavebreaks/meridional flow over the NPAC D5-10

- At the same time, the anticyclone in the Beaufort/western Arctic couples with the stratospheric high/wave-1 (associated with the stratwarm). This process acts to drop NAM/AO. 

- Zonal flow in Canada quickly becomes meridional, dipping the jet in W-Canada and instigating another large wavebreak over NE-Canada/Greenland, culminating in a substantial -NAO that keeps the northern jet suppressed.

Big wrinkle here the in-situ blowtorch airmass in W-Canada, which precludes a rapid buildup of arctic air there (which tends to happen more slowly than modeled anyway). This is despite a seemingly ideal 500mb progression. If it wasn’t so warm up there to start with, this pattern progression (as modeled) would easily have driven arctic air into SW-Canada & W-US. But that is going to be a challenge in this situation. It can be overcome if the pattern holds long enough, though.

[Slushy Inch]

2 hours ago, TT-SEA said:

06Z GFS shows a significant snow event for the Seattle area within a week... this happens next Friday which is just 6 days away now.

 

Moved to the 8th on 12z. Still both troughs are trending stronger.

[Slushy Inch]

[Slushy Inch]

Trends are good!

[Slushy Inch]

[AlTahoe]

12 minutes ago, Phil said:

Can see this process extraordinary well on the 00z EPS.

- Troughing develops over Siberia, which due to presence of Himalayas/terrain, acts to remove momentum from the NPAC jet, culminating in a series of wavebreaks/meridional flow over the NPAC D5-10

- At the same time, the anticyclone in the Beaufort/western Arctic couples with the stratospheric high/wave-1 (associated with the stratwarm). This process acts to drop NAM/AO. 

- Zonal flow in Canada quickly becomes meridional, dipping the jet in W-Canada and instigating another large wavebreak over NE-Canada/Greenland, culminating in a substantial -NAO that keeps the northern jet suppressed.

Big wrinkle here the in-situ blowtorch airmass in W-Canada, which precludes a rapid buildup of arctic air there (which tends to happen more slowly than modeled anyway). This is despite a seemingly ideal 500mb progression. If it wasn’t so warm up there to start with, this pattern progression (as modeled) would easily have driven arctic air into SW-Canada & W-US. But that is going to be a challenge in this situation. It can be overcome if the pattern holds long enough, though.

The end result is more ridging off the coast of California but at least it will colder. Today's "storm" the models have shown for a week fizzled out and we didn't get a single drop or flake.

[Slushy Inch]

Great run snow and gets real cold.

[Slushy Inch]

Canadian.

[SilverFallsAndrew]

This run is sufficiently chilly for kool vibes.

[MossMan]

That was a fun day! Fairly short outage at only 14hrs. 

[SilverFallsAndrew]

In other news another 0.47” of rain overnight. 14.36” on the month. 

[Phil]

32 minutes ago, AlTahoe said:

The end result is more ridging off the coast of California but at least it will colder. Today's "storm" the models have shown for a week fizzled out and we didn't get a single drop or flake.

You’ve had some bad luck w/rt disconjunction of subseasonal forcings for jet extension into CA and the low frequency state. Continued piss-poor rolls of the dice.

The coming -NAM/-NAO significantly improves the low frequency signal there, so assuming it holds through mid/late winter (which it usually does in El Niño winters) the next +dAAMt/jet extension is much more likely to deliver significant snowfall to CA mountains (and overall precipitation to the SW US).

I don’t know what seasonality of niño precipitation is out there in CA (or how it has changed in recent events?) but I think a lot of people misunderstand the true nature of niño climo. People associate El Niño with heavy rains (and mountain snows) in California and big east coast snowstorms, but much of that is exclusively a late winter phenomenon, with a middling, rudderless pattern typically dominating during the first half of winter.

(Graphic from Eric Webb on Twitter/X) Something that might surprise people is that moderate/strong *La Niña* climatology is more favorable for significant snowstorms out here until January 27th, when the switch flips. You’d never know this reading most weather forums, though.  https://x.com/webberweather/status/1741115005158707415?s=46&t=656Z973wLtGKaIyhhq_7QQ

[SilverFallsAndrew]

The GEM is definitely going big at day 10.

[Cascadia_Wx]

9 minutes ago, SilverFallsAndrew said:

The GEM is definitely going big at day 10.

Better than going home.

[SilverFallsAndrew]

Raining again. 

[snow_wizard]

12z is the best run of the day for cold hands down.  Noice!

[Rubus Leucodermis]

Chilly, but not really cold next weekend. Though it will probably feel cold in relation to all the first rate quality torching we have been experiencing.

[Phishy Wx]

[snow_wizard]

19 minutes ago, SilverFallsAndrew said:

The GEM is definitely going big at day 10.

Yup!  Just about to join the high latitude block.