2025-2026 ENSO

[MJO812]

Just like that the warmup is gone during the 1st week of December on the gfs thanks to the negative epo

[leo2000]

2 hours ago, donsutherland1 said:

This morning revealed an unwelcome, GEFS AO forecast. If it holds, it could have implications beyond the first week of December. The base case is a generally negative AO at least to start December. But the GEFS has grown more aggressive with the AO+ scenario, with the AO reaching/exceeding +1.000 near the end of the first week in December.

For now, things still remain on course for places like the Upper Midwest, Great Lakes, and central or northern New England in terms of cold an snow through at least the first 7-10 days of December. Severe cold still appears unlikely.

The question afterward concerns whether the pattern will break down near mid-month or late December. The AO+ development would argue for a faster breakdown. I will need to see more data on this, but the risk of a faster breakdown has increased further since yesterday. Let's see where the GEFS and EPS are in a few days. After all, it is November 24 and model skill is weak beyond 10-14 days.

What about the SSW? As @40/70 Benchmark@bluewave@snowman19 have noted on numerous occasions, it is likely to be a reflection event. The late November cold shot and first week of December developments likely have no connection to the SSW. Whether there would be the development/redevelopment or reinforcement of blocking was the wild card. Considering the nature of this event, it increasingly appears that non-stratospheric factors will play the predominant role.

 

When I type on Google asking about the major SSW will it be either reflective or absorptive the answer has changed before it said reflective now it's saying a combined reflective- absorptive event. Starting out as a reflective phase transitioning into an absorptive phase. Which is why the AO is turning positive with the reflective phase then it will transition mid to late December into the absorptive phase which will flip the AO and NAO both negative. This information is compiled by numerous sources. So December is far from toast. The GEFS shows the MJO going into phase 8. Since, someone is confused I am going to copy the information here. 

 

AI Overview

 

 

 

The major Sudden Stratospheric Warming (SSW) event forecast for late November and early December 2025 is anticipated to be a 

potential combined reflective-absorptive event. 

According to current meteorological models and expert analysis, the event exhibits characteristics of both types, which will influence the timing and location of the resulting weather impacts. 

 

Event Type and Expected Progression

• Initial Reflective Phase (Near-term/Early December): The initial phase is expected to be dominated by wave reflection, where upward-propagating planetary waves temporarily bounce off the disturbed polar vortex.
  • Effect: This phase will likely temporarily strengthen the stratospheric polar vortex and accelerate the polar jet stream, leading to a positive Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) and stronger westerlies across northern Europe in the short term.
  • Surface Response: This might result in a temporary Alaskan Ridge (AkR) development in the Pacific.
• Subsequent Absorptive Phase (Medium-term/Mid-late December): The reflective phase is expected to be followed by a dominant absorptive phase, where the waves are subsequently absorbed, leading to a breakdown or displacement of the polar vortex and the downward propagation of wave activity to the troposphere.
  • Effect: This absorption will increase pattern uncertainty and is the phase typically associated with a weakened polar vortex, which allows frigid Arctic air to plunge south into lower latitudes.
  • Surface Response: This second phase is expected to lead to cold air outbreaks and potential snow events across parts of the United States, Canada, and Europe as the polar vortex becomes disrupted. 

The specific classification as a combined event highlights the complexity of this particular SSW and suggests a dynamic, multi-phase impact on Northern Hemisphere winter weather patterns. 

 

 

https://www.linkedin.com/posts/jens-bonewitz-b43002142_potential-ssw-wave-activity-7398315457403064320-w1Uq#:~:text=Jens Bonewitz's Post-,Jens Bonewitz,uncertainty as absorption phase dominates.

[donsutherland1]

1 hour ago, 40/70 Benchmark said:

Expect the hostile trend in the polar domain to continue for later in December.

Yes. I agree. I think only the timing of its onset remains to be seen.

[TheClimateChanger]

Incredible stuff, with NHEM anomalies pushing up towards 2C above the 1981-2010 mean as we head towards the end of the month. This has been one heck of a hemispheric heat wave over the last month or so.

[TheClimateChanger]

8 minutes ago, TheClimateChanger said:

Incredible stuff, with NHEM anomalies pushing up towards 2C above the 1981-2010 mean as we head towards the end of the month. This has been one heck of a hemispheric heat wave over the last month or so.

 

[donsutherland1]

34 minutes ago, leo2000 said:

When I type on Google asking about the major SSW will it be either reflective or absorptive the answer has changed before it said reflective now it's saying a combined reflective- absorptive event. Starting out as a reflective phase transitioning into an absorptive phase. Which is why the AO is turning positive with the reflective phase then it will transition mid to late December into the absorptive phase which will flip the AO and NAO both negative. This information is compiled by numerous sources. So December is far from toast. The GEFS shows the MJO going into phase 8.

 

 

 

 

Right now, the long-range European guidance is suggesting the development of a Scandinavian Block near mid-December onward. That's not an AO-. 

Your location should be ok. Things should also be ok for cities such as Chicago, Detroit, Toronto, Ottawa, Montreal, etc. If the AO is more positive, areas south of New England would typically see a warmer outcome with reduced snowfall prospects. The SE U.S. looks warm, overall, for December, as the predominant regime through most of December is forecast to be NAO+ yielding to a Scandinavian Block.

 

[MJO812]

1 hour ago, MJO812 said:

Just like that the warmup is gone during the 1st week of December on the gfs thanks to the negative epo

Euro has also trended colder

[donsutherland1]

2 hours ago, Stormchaserchuck1 said:

CFS runs 4x a day, and sometimes it will have the whole US below at 12z then the whole US above at 18z. Running more helps tracking scores to improve for more data.. but 2-4 week models haven't proven much more accurate than seasonal models to this point. I personally like the 384hr map on the ensemble means, seeing what the NAO, PNA, AO patterns look like.. that is pretty accurate. There is a pretty big model drop off after Day 15. Maybe they will continue to upgrade the Euro ensembles, but they have had some big misses since coming into inception several years ago. 

That's why CPC using averages for the last 16 cycles on the CFS's maps. It's bad practice to treat the CFS as a deterministic operational model. That doesn't stop the vendors from providing such information to an often unaware audience (unaware of the tool's limitations).

[donsutherland1]

5 minutes ago, MJO812 said:

Euro has also trended colder

The growing concern isn't December 1-10. That still seems on track. The issue concerns what happens afterward e.g., should the GEFS's AO+ scenario develop. The GEFS compounds the issue with the development of an EPO+. The persistent PNA- remains in place.

[MJO812]

8 minutes ago, donsutherland1 said:

The growing concern isn't December 1-10. That still seems on track. The issue concerns what happens afterward e.g., should the GEFS's AO+ scenario develop. The GEFS compounds the issue with the development of an EPO+. The persistent PNA- remains in place.

Huh ?

There's pages in here on how December  1- 7 was supppsed to way above normal with southeast ridge.  We are seeing the models take a step back with the warmth. There is no need to worry about 2 weeks from now when the models cant even get next week right .

[donsutherland1]

12 minutes ago, MJO812 said:

Huh ?

There's pages in here on how December  1- 7 was supppsed to way above normal with southeast ridge.  We are seeing the models take a step back with the warmth. There is no need to worry about 2 weeks from now when the models cant even get next week right .

December 1-10 should start warm but then get cold. The question is whether it remains generally cold into late December or turns milder near mid-month. That’s the part that is increasingly uncertain.

[FPizz]

21 minutes ago, MJO812 said:

Huh ?

There's pages in here on how December  1- 7 was supppsed to way above normal with southeast ridge.  We are seeing the models take a step back with the warmth. There is no need to worry about 2 weeks from now when the models cant even get next week right .

He's uncertain about 3.5 weeks from now, which is just stating the obvious really.  I get there are levels of uncertainty, but 20+ days from now is always going to be low.  Models haven't really been too steady past day 10 or so for the past several weeks.  Look at this eps trend gif for Dec 1 going back a few runs.  Can it flip back, maybe, but having any confidence in longer range right now seems pretty futile.

 

[stadiumwave]

Change of Euro OP over last 3 runs for late period

 

I figured it was worthy to mention since some of the other runs were.

[bluewave]

50 minutes ago, FPizz said:

He's uncertain about 3.5 weeks from now, which is just stating the obvious really.  I get there are levels of uncertainty, but 20+ days from now is always going to be low.  Models haven't really been too steady past day 10 or so for the past several weeks.  Look at this eps trend gif for Dec 1 going back a few runs.  Can it flip back, maybe, but having any confidence in longer range right now seems pretty futile.

 

It’s less important what the long range models are showing since that can vary from run to run. But the long range forecast biases for each type of regime remain more constant over time. Plus the inability of the models to see seasonal repeating patterns until the actual pattern is getting close to occurring. 

[LakePaste25]

The most anomalously cold air in the entire northern hemisphere will reside in Canada, allowing the northern tier of the Eastern US to stay somewhat cool despite the -PNA. 

 

[stadiumwave]

RRWT model, which is based on rosby waves (Josh Herman's model), has persistently shown a cold Christmas for a good while. This was yesterday's update for dates Dec 24-28:

500mb

 

[MJO812]

[GaWx]

9 hours ago, snowman19 said:

I don’t want to jinx you but it’s looking like a very good call on your part with the SPV, along with the increasingly likely flip to RNA/-PNA in December 

Edit: Also have to give credit to @bluewave with the -PNA December call (looks likely now)

 There has been a +PNA in Jan for all 11 cold ENSO winters that had a -PNA in Dec since 1983-4:

-1983-4: -0.31 to +0.97

-1984-5: -1.60 to +1.63

-1996-7: -1.23 to +0.63

-1998-9: -0.09 to +0.16

-2008-9: -1.41 to +0.61

-2010-11: -1.78 to +1.29

-2012-3: -1.01 to +0.55

-2013-4: -0.86 to +0.97

-2016-7: -0.35 to +0.28

-2021-2: -2.56 to +1.01

-2022-3: -0.66 to +0.22

————

What kind of PNA are you expecting in Jan?

[SnowGoose69]

5 hours ago, brooklynwx99 said:

I would argue that the models are underdoing the Pacific jet and + heights near the WC and AK given that kind of tropical forcing

unless the MJO can never get into 8, which I'm sure I'll be told

 

This is about as strong a look we've seen for it to get into phase 8 in several years.  I'd be surprised if it did not get there, and yeah, ensembles just never see a moderate-strong MJO wave impacts it seems.  Its why so often here when we see a raging 3-4-5 forecast but the D16 ensembles look like January 94 you more or less know that look will be way off if that 3-4-5 wave verified.