2024-2025 La Nina

[Terpeast]

4 minutes ago, 40/70 Benchmark said:

You need to consider this within the context of the modern climate...we aren't getting a -8 month, Larry....anything below normal over the east coast for a monthly mean in the middle of winter is pretty extraordinary....especailly realtive to the general consensus leading in.

We did get the coldest first week of december in 14 years. All other first-week decembers colder than this one are between 2002 and 2010.

[40/70 Benchmark]

For instance, consider a snowmap leading into a storm indicated a 40" snowfall for the megalopolis from Boston to Philly, but there is a disclaimer on the bottom of the image that this is about a 10 percentile occurence and represents the most extreme solution portrayed amongst over 50 ensemble members...raise your hand if you think the vast majority of consumers would refrain from impulsively posting it onto their feed....hell, many wouldn't even read it, never mind pay it any mind. This is what social media is today...an assembly line of rapid fire, fragmented thoughts that is driven by our ever shrinking collective attention span and need for instant gratification.

[40/70 Benchmark]

17 hours ago, GaWx said:

 Fwiw this is the weakest SPV Euro weeklies run yet for late Dec through Jan. I still wouldn’t call this “weak” but it is the weakest yet for then/weaker than avg. There are more members dipping rather sharply Dec 20-23 though there are still only 2 of 100 members (4%) with an actual wind reversal (major SSW) this month. I’ve learned based on the last couple of years that the models actually tend to be slow in catching onto major SSW events. With Dec 20th still being 15 days out, any possible major SSW then would probably be too far out for the bulk of members to see it though I’m by no means predicting one at this point:

 

Edit: Looking back at records for La Niña or cold neutral with a W QBO and having a major SSW, the earliest in the season I could find was that of 12/31/2001. The second earliest is 1/24/2009.

Best shot is Feb or March IMO.

[vegan_edible]

dont want to jump the gun here, but somethings telling me this winter might be singing the tune of the last 2 (at least in the nyc metro). really hoping for a turnaround for the holiday week, but we've been fooled before. i'd be very surprised to see a pattern turn around soon, i know theres been some discourse on the integrity of the dynamical mjo plots but im struggling to see how we're gonna get to 8/1/2 soon

[40/70 Benchmark]

11 hours ago, donsutherland1 said:

This is an example of the hype that I was criticizing earlier:

Now, let's take a look at the BAMWX extreme forecast and historic data for four cities shown in the more extreme parts of the map: Chicago, Great Falls, Indianapolis, and Madison. In three cases, the cold would be unprecedented for the period in question.

While it could be colder than normal, the probability of the kind of cold shown on the map is extremely low. Moreover, one is dealing with a timeframe more than five weeks into the future where model skill is far less than climatology.

Considering the timeframe, the historic data, and the smaller pool of Northern Hemisphere deep cold in the contemporary area, the kind of widespread extreme weekly anomalies shown on the map are exceptionally unlikely. Posting such a map is reckless. Moreover, even as BAMWX focuses on Indiana, the map is disconnected from Indianapolis' historic climate data.

I suspect that the BAMWX forecast will be off by an average of 10° or more for these four cities and can't rule out a miss by more than 20°. I also expect that BAMWX will never verify its extreme idea.

This outlook will be verified here and on X.

 

He was implying that map would verify literally?? I didn't think he was doing that......I agree that is silly if that is the case. Not a fan of posting extreme data myself, but I thought he was just doing it to illustrate a point.

[Terpeast]

3 minutes ago, vegan_edible said:

dont want to jump the gun here, but somethings telling me this winter might be singing the tune of the last 2 (at least in the nyc metro). really hoping for a turnaround for the holiday week, but we've been fooled before. i'd be very surprised to see a pattern turn around soon, i know theres been some discourse on the integrity of the dynamical mjo plots but im struggling to see how we're gonna get to 8/1/2 soon

Both extended Euro and GFS ensembles take the MJO to 7 by January. Euro has trended slightly stronger with the mjo wave, but still weaker than GEFS.

[40/70 Benchmark]

7 hours ago, GaWx said:

Per Joe D’Aleo at WB: “Strat warm favored in west QBO near solar max”

 I checked it and by golly I think he has a point:

Solar DJF 135+/west QBO:

57-8: SSW 1/31/58

59-60: SSW 1/17/60

69-70: SSW 1/2/70

78-9: SSW 2/22/79

80-1: SSW 2/6/81

90-1: no SSW

99-00: SSW 3/20/00

01-02: SSW  12/31/01, 2/18/02

 
-So, of these 8 high solar/+QBO winters, 7 had at least one major SSW and one had two! 

- earliest 12/31

- 3 in Jan

- 3 in Feb 

- 1 in Mar

- So, perhaps one will actually be likely this winter should DJF SSN be 135+.

 

SSN: https://www.sidc.be/SILSO/DATA/SN_m_tot_V2.0.txt

I wrote about this back in the middle of summer, Larry.

https://easternmassweather.blogspot.com/2024/08/preliminary-analysis-of-polar-domain.html

[40/70 Benchmark]

3 hours ago, Stormchaserchuck1 said:

It's not impossible, but a +QBO/La Nina state does favor a cold 10mb about 75% of the time. Last year for example, we had -QBO/El Nino and there were 4 Stratosphere warmings. 2 years ago it was +QBO/La Nina and 10mb stayed mostly cold/

+QBO is strong right now. Here is what we've seen at 10mb for the start of cold season

vs +QBO correlation

2 years ago also had a huge SSW in February....agree that its a great polar analog. That said, I think being near solar max as opposed to ascending 2 years ago is somewhat less favorable.

[GaWx]

45 minutes ago, 40/70 Benchmark said:

He was implying that map would verify literally?? I didn't think he was doing that......I agree that is silly if that is the case. Not a fan of posting extreme data myself, but I thought he was just doing it to illustrate a point.

 I’m very confident BAMwx (and assume Don agrees) wasn’t implying yesterday’s extreme 6Z CFS maps with (near) all-time record cold in mid-Jan would necessarily verify closely/literally. But what I think Don and I agree on is that tweeting that extreme 6Z 12/5 CFS way out at weeks 5-6 (and the typically too cold WB version of it to boot) is hype to get more clicks and is cherry-picking. Many folks looking at that aren’t going to understand that the chance of that verifying even closely is extremely low. He did say that the CFS was “on board” with his ideas when he showed that run. I think it was a poor decision to post that map even though it was just for illustrative purposes. As I posted, the very next CFS run (12Z) was literally 23-5F warmer for that mid-Jan week.

 As I posted on Wednesday, I felt Michael Clark’s Wednesday video was overall well done as far as clearly communicating his general feeling about the warming Dec pattern and cold Jan potential. But then a day later (yesterday) BAMwx tweeted that extreme 6Z CFS, which I didn’t like.

[GaWx]

New Michael Clark (BAMwx) video followup from early this morning: again like the Wednesday video, this is well presented with little or no outright “hype” (unlike yesterday’s tweet about the cherry picked extremely cold mid Jan portion of yesterday’s 6Z CFS) and he does talk about a bunch of models rather than just the CFS and the CFS shown is not a cherry picked extreme WeatherBell map:

 

[40/70 Benchmark]

11 minutes ago, GaWx said:

 I’m very confident BAMwx (and assume Don agrees) wasn’t implying yesterday’s extreme 6Z CFS maps with (near) all-time record cold in mid-Jan would necessarily verify closely/literally. But what I think Don and I agree on is that tweeting that extreme 6Z 12/5 CFS way out at weeks 5-6 (and the typically too cold WB version of it to boot) is hype to get more clicks and is cherry-picking. Many folks looking at that aren’t going to understand that the chance of that verifying even closely is extremely low. He did say that the CFS was “on board” with his ideas when he showed that run. I think it was a poor decision to post that map even though it was just for illustrative purposes. As I posted, the very next CFS run (12Z) was literally 23-5F warmer for that mid-Jan week.

 As I posted on Wednesday, I felt Michael Clark’s Wednesday video was overall well done as far as clearly communicating his general feeling about the warming Dec pattern and cold Jan potential. But then a day later (yesterday) BAMwx tweeted that extreme 6Z CFS, which I didn’t like.

Yea, I'm not a fan of posting extreme images. I defintely would have had some qualifiers such as "while this of a scanrio is unlikely, its does lend support to the return of poleward ridging in the Pacific".

[michsnowfreak]

35 minutes ago, GaWx said:

New Michael Clark (BAMwx) video followup from early this morning: again like the Wednesday video, this is well presented with little or no outright “hype” (unlike yesterday’s tweet about the cherry picked extremely cold mid Jan portion of yesterday’s 6Z CFS) and he does talk about a bunch of models rather than just the CFS: 

 

Very well explained video!

[snowman19]

1 hour ago, 40/70 Benchmark said:

2 years ago also had a huge SSW in February....agree that its a great polar analog. That said, I think being near solar max as opposed to ascending 2 years ago is somewhat less favorable.

I am doubtful of a major SSWE. Not to minimize the study @GaWx found, which was compelling, but just based on the data @Stormchaserchuck1 posted, we are very closely (so far) following the Niña/+QBO/high solar years that featured a very cold stratosphere. Secondly, this year’s +QBO event isn’t just strong. It’s approaching record strong numbers

[40/70 Benchmark]

36 minutes ago, snowman19 said:

I am doubtful of a major SSWE. Not to minimize the study @GaWx found, which was compelling, but just based on the data @Stormchaserchuck1 posted, we are very closely (so far) following the Niña/+QBO/high solar years that featured a very cold stratosphere. Secondly, this year’s +QBO event isn’t just strong. It’s approaching record strong numbers

Actual SSW is somewhat dubious, but I don't expect an extremely +AO/NAO, either.

[snowman19]

27 minutes ago, 40/70 Benchmark said:

Actual SSW is somewhat  dubious, but I don't expect an extremely +AO/NAO, either.

I think the bigger question is this….do we actually see the MJO push into phases 8-1-2 in January or is this just another case of it totally crapping out at the dateline like we’ve seen over and over again? There is still an SSTA furnace in phases 4-7 and law of thermodynamics, that’s where the atmosphere is going to want to put the strongest and most persistent convection. That has not changed one iota. With the marked change toward a La Niña in the ENSO gynre, +SOI, -IOD, EWBs, standing wave convection, I’m not so sure we see a decided push into 8-1-2. The wave may fizzle out in the relatively cooler waters in those phase areas and the enhanced Niña trades may shear the convection apart as it tries to make a push to and beyond the IDL

@bluewave Thoughts?

[40/70 Benchmark]

25 minutes ago, snowman19 said:

I think the bigger question is this….do we actually see the MJO push into phases 8-1-2 in January or is this just another case of it totally crapping out at the dateline like we’ve seen over and over again? There is still an SSTA furnace in phases 4-7 and law of thermodynamics, that’s where the atmosphere is going to want to put the strongest and most persistent convection. That has not changed one iota. With the marked change toward a La Niña in the ENSO gynre, +SOI, -IOD, EWBs, standing wave convection, I’m not so sure we see a decided push into 8-1-2. The wave may fizzle out in the relatively cooler waters in those phase areas and the enhanced Niña trades may shear the convection apart as it tries to make a push to and beyond the IDL

@bluewave Thoughts?

I am quite confident that we well given my research using @bluewave's data regarding usage of the MJO behavior to diagnose periods of deviation from said MC forcing. This is especailly true since La Nina is finally getting the jolt that you and I have been calling for.

[bluewave]

30 minutes ago, snowman19 said:

I think the bigger question is this….do we actually see the MJO push into phases 8-1-2 in January or is this just another case of it totally crapping out at the dateline like we’ve seen over and over again? There is still an SSTA furnace in phases 4-7 and law of thermodynamics, that’s where the atmosphere is going to want to put the strongest and most persistent convection. That has not changed one iota. With the marked change toward a La Niña in the ENSO gynre, +SOI, -IOD, EWBs, standing wave convection, I’m not so sure we see a decided push into 8-1-2. The wave may fizzle out in the relatively cooler waters in those phase areas and the enhanced Niña trades may shear the convection apart as it tries to make a push to and beyond the IDL

@bluewave Thoughts?

We got lucky in 21-22 that the amplified MJO 4-7 during December kept progressing east of the Dateline into phase 8 in January. That’s why it was our last real month of winter for many near the East Coast. The Pacific Jet relaxed and the Pacific blocking was able to run the table for a whole month. But it’s still too early to be sure if we can get a clean progression into 8 or the MJO convection reloads in 4-7 again in January. We probably won’t know for sure which way things will go until we are near the start of January. 

[donsutherland1]

2 hours ago, 40/70 Benchmark said:

I see what you are saying....I can't stand when long range snow maps are posted....or any for that matter. However, in the case of Bamwx, that post that was referrred to as "hype" followed up a video of approximately 15 minutes in length that described in great detail why they felt a colder shift was likely. That long range weekly was then added as a follow up to illustrate the expressed thought. You need to consider it in the proper context....

I guess I agree with your overall point, but not the source you chose to illustrate it. I also think that when you take the time to put forth a seasonal product, like Bamwx does, posting long range guidance that either supports or deviates from the previously stated position is more palatable. People have lives...not every post on social media can be a war and peace novel...its not practical, nor are those mediums really intended for that. Perhaps there should be a disclaimer on every post that the data may not ultimately reflect what will actually happen? But then again, would said disclaimer even be paid any mind by the vast majority of those using these platforms like "X", that are esstentially an assembly line of fragmented thoughts catered towards those with attention spans shorter than a NYC winter , and a proclivity for instant gratification every bit as immense as the blizzards that they crave.

Your issue is with contemporary society and its projected onto long range forecasters.

I think that's a fair point. Were the general public more information literate, my point would have less relevance. But issues exist. There is the public perception that even short-range forecasts are wrong. And one also sees such sentiments in news coverage of events i.e., recent claims that the devastating floods from Helene were "unexpected", comments that forecasters didn't provide sufficient warning that led to tremendous traffic jams in parts of PA, NY, and Ontario from the recent lake effect storm, etc. In such cases, the forecasts were on the mark. People had ample warning and ample time to avoid some of what took place. They chose not to respond appropriately. In cases, people don't respond, because of perceptions that forecasters exaggerate the threats or had been wrong previously.

Indeed, the NWS is struggling to grapple with such matters. That's part of the reason they keep refining and revising the kinds of advisories, watches, warnings, and other products they put out. The NWS is not solely concerned with forecasting accuracy. It is also concerned with how people perceive and respond to their forecasts.

The map in question was posted later in the day on X. When I came across it, I posted it here, as it provided a good example of my concerns.

IMO, there is no credible basis that a map showing unprecedented cold more than 5 weeks in advance should be posted (the same would apply for extreme rainfall, snowfall, heat, etc., at such a timeframe). Posting that map was unprofessional. It provided zero public or commercial benefit.

Even worse, should the map not verify--which is very likely given the extreme nature of what was depicted and low probability associated with such an extreme event--I fully expect only silence on that matter from BAMWX. BAMWX won't revisit the map, much less highlight what could be an enormous forecasting error. The average error for the four cities will likely be much larger than if one simply chose climatology for that period. 

Further, to show the absurdity of the map, I asked AI (GPT-4o) to generate a random anomaly at tenths of degree fahrenheit using the following prompt: "Generate a random one-week temperature anomaly in tenths of a degree Fahrenheit. The mean long-term anomaly is 0. Assume daily anomalies could range from -50 to +50. The deviations are normally distributed." The random 7-day mean output: -1.7°.  I suspect what amounts to a simple guess will also do better.

It may well be colder than normal in some or even all of the highlighted cities (though a warmer outcome can't be dismissed either right now). But an entire week of 20F-30F or more below normal over a large part of the northern U.S. is extremely unlikely (historic climate, warmer climate, inherent error of the guidance at 5 week or longer timeframes). Thus, even a large error will be only part of the problem. The avoidable nature of that error will also be important.

As noted previously, I will post the verification here and on X. 

[GaWx]

2 hours ago, 40/70 Benchmark said:

2 years ago also had a huge SSW in February....agree that its a great polar analog. That said, I think being near solar max as opposed to ascending 2 years ago is somewhat less favorable.

 Based on the analysis I just did due to what Joe D’Aleo said about the correlation of high solar/+QBO to SSWs, I don’t agree with you about ascending vs descending in this particular situation. Here’s why:

 

Solar DJF 135+/west QBO:

57-8: SSW 1/31/58 about right at peak

59-60: SSW 1/17/60 descending 

69-70: SSW 1/2/70 descending

78-9: SSW 2/22/79 ascending

80-1: SSW 2/6/81 descending

90-1: no SSW descending

99-00: SSW 3/20/00 ascending

01-02: SSW  12/31/01, 2/18/02 descending

 

 So, these +QBO major SSWs that occurred during high solar were as follows:

- two ascending

- one near peak

- six descending

- So, three times as many during descending as ascending

- So, I don’t think that if 2024-5 winter turns out to be descending (but still 135+) that that itself would necessarily reduce the chance for a major SSW

- However, the criteria requires DJF SSN to exceed 135. If it falls to below that, then winter 24-5 wouldn’t even qualify as high solar (135+) and thus the correlation of high solar/W QBO to SSW frequency would no longer be relevant.

https://www.sidc.be/SILSO/DATA/SN_m_tot_V2.0.txt

[40/70 Benchmark]

6 minutes ago, GaWx said:

 Based on the analysis I just did due to what Joe D’Aleo said about the correlation of high solar/+QBO to SSWs, I don’t agree with you about ascending vs descending in this particular situation. Here’s why:

 

Solar DJF 135+/west QBO:

57-8: SSW 1/31/58 about right at peak

59-60: SSW 1/17/60 descending 

69-70: SSW 1/2/70 descending

78-9: SSW 2/22/79 ascending

80-1: SSW 2/6/81 descending

90-1: no SSW descending

99-00: SSW 3/20/00 ascending

01-02: SSW  12/31/01, 2/18/02 descending

 

 So, these +QBO major SSWs that occurred during high solar were as follows:

- two ascending

- one near peak

- six descending

- So, three times as many during descending as ascending

- So, I don’t think that if 2024-5 winter turns out to be descending (but still 135+) that that itself would necessarily reduce the chance for a major SSW

- However, the criteria requires DJF SSN to exceed 135. If it falls to below that, then winter 24-5 wouldn’t even qualify as high solar (135+) and thus the correlation of high solar/W QBO to SSW frequency would no longer be relevant.

https://www.sidc.be/SILSO/DATA/SN_m_tot_V2.0.txt

Not what I am saying...talking about max vs ascending...the hostility towards blocking due to solar wind dispersed electrogeomagnetic particles isn't much of a factor for a couple of years post max.

[40/70 Benchmark]

39 minutes ago, donsutherland1 said:

I think that's a fair point. Were the general public more information literate, my point would have less relevance. But issues exist. There is the public perception that even short-range forecasts are wrong. And one also sees such sentiments in news coverage of events i.e., recent claims that the devastating floods from Helene were "unexpected", comments that forecasters didn't provide sufficient warning that led to tremendous traffic jams in parts of PA, NY, and Ontario from the recent lake effect storm, etc. In such cases, the forecasts were on the mark. People had ample warning and ample time to avoid some of what took place. They chose not to respond appropriately. In cases, people don't respond, because of perceptions that forecasters exaggerate the threats or had been wrong previously.

Indeed, the NWS is struggling to grapple with such matters. That's part of the reason they keep refining and revising the kinds of advisories, watches, warnings, and other products they put out. The NWS is not solely concerned with forecasting accuracy. It is also concerned with how people perceive and respond to their forecasts.

The map in question was posted later in the day on X. When I came across it, I posted it here, as it provided a good example of my concerns.

IMO, there is no credible basis that a map showing unprecedented cold more than 5 weeks in advance should be posted (the same would apply for extreme rainfall, snowfall, heat, etc., at such a timeframe). Posting that map was unprofessional. It provided zero public or commercial benefit.

Even worse, should the map not verify--which is very likely given the extreme nature of what was depicted and low probability associated with such an extreme event--I fully expect only silence on that matter from BAMWX. BAMWX won't revisit the map, much less highlight what could be an enormous forecasting error. The average error for the four cities will likely be much larger than if one simply chose climatology for that period. 

Further, to show the absurdity of the map, I asked AI (GPT-4o) to generate a random anomaly at tenths of degree fahrenheit using the following prompt: "Generate a random one-week temperature anomaly in tenths of a degree Fahrenheit. The mean long-term anomaly is 0. Assume daily anomalies could range from -50 to +50. The deviations are normally distributed." The random 7-day mean output: -1.7°.  I suspect what amounts to a simple guess will also do better.

It may well be colder than normal in some or even all of the highlighted cities (though a warmer outcome can't be dismissed either right now). But an entire week of 20F-30F or more below normal over a large part of the northern U.S. is extremely unlikely (historic climate, warmer climate, inherent error of the guidance at 5 week or longer timeframes). Thus, even a large error will be only part of the problem. The avoidable nature of that error will also be important.

As noted previously, I will post the verification here and on X. 

Yea, fair enough...social media oriented communicative patterns and decreasing reading comprehension aren't a great combination. 

[GaWx]

7 minutes ago, 40/70 Benchmark said:

Not what I am saying...talking about max vs acending...the hostility towards blocking due to solar wind dispersed elctrogeomagnatic paericles isn't much of a factor for a couple of years post max.

I thought that when you said, “I think being near solar max as opposed to ascending 2 years ago is somewhat less favorable” that you were impying the chance for an SSW this winter being lower than that of two winters ago because it’s no longer ascending. So, you’re not saying that?

[snowman19]

I am quite confident that we well given my research using [mention=564]bluewave[/mention]'s data regarding usage of the MJO behavior to diagnose periods of deviation from said MC forcing. This is especailly true since La Nina is finally getting the jolt that you and I have been calling for.

We are very clearly in a La Niña state. @Bluewave likes to use these VP/OLR plots

[40/70 Benchmark]

20 minutes ago, GaWx said:

I thought that when you said, “I think being near solar max as opposed to ascending 2 years ago is somewhat less favorable” that you were impying the chance for an SSW this winter being lower than that of two winters ago because it’s no longer ascending. So, you’re not saying that?

Yes, I am saying ascending is better than solar max.

[GaWx]

37 minutes ago, 40/70 Benchmark said:

Yes, I am saying ascending is better than solar max.

 Based on the +QBO/high solar analogs (thank you Dr. Dewpoint (Joe D’Aleo) for inspiring me to check):

 If it looks like DJF SSN is going to be 135+ (don’t know yet as Dec has started out lower), I’m going to increase the chance in my mind for a major SSW to likely this winter/early spring from the moderate chance I previously felt was the case.

[40/70 Benchmark]

3 minutes ago, GaWx said:

 Based on the +QBO/high solar analogs (thank you Dr. Dewpoint (Joe D’Aleo) for inspiring me to check):

 If it looks like DJF SSN is going to be 135+ (don’t know yet as Dec has started out lower), I’m going to increase the chance in my mind for a major SSW to likely this winter/early spring from the moderate chance I previously felt was the case.

I certainly woudn't be suprised if one took place, as you could probably gather from my write up...but I'm just saying its not as glaring a signal as 2022. I agree conditions aren't as hostile as some are implying.

[Snowstorms]

4 hours ago, Terpeast said:

We did get the coldest first week of december in 14 years. All other first-week decembers colder than this one are between 2002 and 2010.

The first week of Dec 2008 was pretty cold too. So definitely been a long time since we've seen a cold start to December, so it's nice. Although, at least locally, 2010, 2008, and 2002 were more colder. 

[40/70 Benchmark]

@GaWxJust for clarity as to where I stand on this, here is the appropriate section from my November release.

The Polar Domain 

Primary Modern Polar Domain Analogs: 2022-2023, 2016-2017

Secondary Archaic Polar Domain Analogs: 2007-2008, 1999-2000, 1975-1976, 1970-1971

Influence of ENSO on the Extra Tropical Atmosphere

It is evident in the graphic below that Modoki, or basin-wide La Nina events, such as this one is likely to be, often feature the seasonal nadir for the NAO near the bookends of the season in December and March. In contrast, east-based events are more likely to feature mid season NAO blocking and accompanying cold.

 

The behavior of the NAO is the reason why December is the coldest month of the CP la Nina composite, as the NAO is only moderately positive in the composite, while it is highly positive in January and February. The NAO averages slightly negative in November and March. Contrary to the CP la Nina years, the month of December is the most mild month of the EP composite because the NAO is neutral-negative, and is very negative the rest of the winter before ascending slightly in March. Thus the orientation of La Nina can play a vital role in not only the aggregate NAO value of the winter season, but also the overall progression. This is due both the aforementioned modulation of the Hadley Cell via convective forcing patterns and the oceanic circulation patterns that feedback into the Atlantic via subtropical jet bridges to sustain said forcing patterns. Zhang et al 2014 verify through several atmospheric simulations that CP la Nina favors an extratropical response redolent of a positive NAO configuration across north America and the north Atlantic. And EP La Nina favors negative NAO during the winter season due to a diametrically opposing atmospheric and oceanic circulation pattern. It is suggested that the subtropical jet bridges the connection between ENSO and the NAO. Essentially, the circulation pattern of the CP la Nina strengthens the Pacific subtropical jet, which augments the Atlantic jet and creates an anticyclonic circulation. This circulation configures SSTs in such a manner as to reinforce positive NAO through a wind-evaporation-SST feedback. 

 

The EP event has a diametrically opposed circulation pattern that weakens said subtropical Pacific jet, which in turn diminishes the Atlantic jet and fosters the development of an cyclonic circulation that sustains negative NAO via said wind-evaporation-SST feedback. This likely played a role in why the more eastern biased, strong hybrid la Nina season of 1955-1956 featured both high latitude blocking and poleward Aleutian ridging, while other years within the dataset, such as 1999-2000 and 1975-1976 were so much milder with a notable dearth of blocking. In fact, Zhang even referred to basin-wide events as "hybrid" or "mixed" events, since they often display characteristics of both east-based and Modoki events. Due to the fact that this season is likely to feature a central-based, hybrid event of weak intensity with a moderate ocean-atmosphere interface, odds favor a +AO and NAO consistent with a fairly strong polar vortex in the mean. The months of December and March may be most prone to an episode(s) of -AO/NAO. However, variance in this data set is high, thus it is imperative to consider alternative outcomes. Obviously, weaker SST anomalies present within more marginal La Nina events have a reduced ability to couple with the atmosphere, thus other extra tropical factors play a more prominent role. This means that the correlation of the NAO to the structure of La Nina is reduced in weaker ENSO events. This is also why some weaker CP events, such as the 2008-2009 and 2000-2001 events, did not feature a very prominent positive NAO signal and were thus more prone to episodes of blocking. 

 

 

Likewise, the minor EP event of 2005-2006 was relatively mild, despite some blocking episodes. Note that the extremely positive NAO value reflected during the moderate Modoki season of 2011-2012, which in conjunction with a very consolidated polar vortex and cold phase of the Pacific undoubtedly played a role in the very mild character of that winter. Clearly there are other factors at play with respect to the modulation of the polar domain that are independent of ENSO and are very worthy of consideration in their own right. One such consideration. Quasi Biennial Oscillation (QBO).

 

Role of the Tropical Stratosphere on the Polar Domain

The system of cycles and oscillations that occur throughout the tropical atmosphere extends high above the waters of the ENSO region. And all of it plays an integral role in modulating the atmosphere across the entire span of the globe. The Quasi Biennial Oscillation (QBO) is an atmospheric phenomenon marked by a circuit of zonal winds measured at 30mb and 50mb, which run in dual bands throughout the equatorial stratosphere. Each band oscillates from an east to west direction with height, while propagating downwards until its dissipation at the top of the tropical tropopause. Currently the QBO is ascending and is nearing its westerly peak at both the 30MB and 50MB levels. This past summer, Eastern Mass Weather identified the year 2016, 2020 and 2022 as three primary QBO analogs when considering both the 50MB and 30MB levels and this preliminary analysis remains valid.

 

October 2024 50MB QBO: 9.54 & rising

2022: 5.13 & rising

2020: 6.94 & rising

2016: 4.53 & rising

 

October 2024 30MB QBO: 11.64 & rising 

2020: 10.80 & rising

2016: 12.83 & rising

2022: 10.93 & rising

 

Given that the QBO will be westerly both the 30 and 50mb levels during the 2024-2025 winter season, the state of the tropical stratosphere dictates that blocking is more likely to occur earlier in the season before dissipating by mid season, which is congruent with history concerning hybrid, or "mixed-type" La Niña seasons.

This is evidenced by the December-January 500mb composite for all cool ENSO seasons with a westerly (positive) QBO, similar to this season. Note the slight blocking signature in the vicinity of Greenland, as well as the pronounced poleward ridging near Alaska. This aligns with earlier analysis of the West Pacific.

W QBO/Cool ENSO DJ H5

 

Thereafter, any semblance of blocking vanishes later in the season, like the other composites, which supports the notion of a Pacific driven mid-season MC mismatch period akin to January 2022.

 

W QBO/Cool ENSO FM H5

 

This is why most of the eastern US warms appreciably during the second half of winter in the general W QBO/cool ENSO dataset.

 

W QBO/Cool ENSO FM Temp Anomalies

This same trend for early season blocking is noted with respect to the primary QBO analog composite of 2016, 2020 and 2022.

 

2016-2017, 2020-2021, 2022-2023 DJ H5

Interestingly enough, in the analog composite, while certainly decreased in the aggregate relative to the December-January period, blocking appears to reassert itself late. However, it seems to be largely negated by the very deep Western CONUS troughing that is related to the Western Pacific Warm pool, which doomed last season's outlook. This was alluded to in the extra tropical Pacific analysis, and was wonderfully illustrated during the 2022-2023 season. This more recent tendency for southeast ridging to adjoin NAO blocking is predominately why the aged polar analogs are considered secondary to the more modern day analogs.

 

2016-2017, 2020-2021, 2022-2023 FM H5

 

The subtle trend for the polar vortex to become at least somewhat disturbed once again later in the season is confirmed through a consideration of solar data in conjunction with the aforementioned QBO analysis.

Influences of the Solar Cycle on the Polar Fields

 

The impact of the solar cycle and the stratosphere on the earth's atmosphere continues to be a work in progress and much like seasonal forecasting in general, it is still very much a frontier science. Traditionally, research correlated high levels of solar activity near solar max, such as will be the case for winter 2024-2025, to a stronger polar vortex and thus milder winters for much of North America and Europe. There are a multitude of theories as to why this is the case, however, most of these theories cite drivers such as UV radiation and total solar radiation (TSI), which closely mirror sunspot activity, as responsible for increasing ozone levels and temperature in the equatorial stratosphere. This warmer tropical stratosphere then results in a stronger latitudinal gradient and a cooler polar stratosphere (stronger polar vortex) via a modulated Brewer-Dobson cycle. The issue with these theories is that the peak levels of the aforementioned potential drivers of the solar-stratosphere connection coincide with solar max. And most recent research cites stronger drivers that do not coincide with solar max, such as geomagnetic energy and solar winds, which peak during solar flux or, about one year after solar max in terms of peak UV and TSI . (Maliniemi et al, 2014). Malimiemi et al theorize that geomagnetic energy makes its way into the polar region via the process of energetic particle precipitation, which then produces nitrogen oxides in the the upper atmosphere that have a protracted period of time to descend downward and increase ozone during the polar winter in the absence of any sunlight, which cools the stratosphere and strengthens the PV. This more closely corroborates both with other recent research, which cites drivers that do not peak at solar max as defined by UV and TSI (geomagnetic energy peaks approximately one year after solar max), as well as the research of Malimiemi et al (2014), which found that the declining phase of the sunspot cycle remarkably consistently produces the spacial pattern of surface temperature anomalies related to the positive NAO during the last 13 solar cycles" (Maliniemi et al, 2014). This makes sense since the geomagnetic energy peak that Maliniemi et al cite as the main driver behind the connection between the solar cycle and polar domain lags solar max as defined by UV, TSI and sunspots by approximately one year, which is during the declining phase that so strongly correlates with the +NAO response in their research.

 

 

 This implies that winter 2025-2026 and 2026-2027 will be more favorable for a stronger polar vortex than the impending winter season, which is also consistent with other recent studies of seal level pressure patterns that revealed a +NAO pattern lagging solar max by approximately 2-4 years. The work of Maliniemi et al also showed that this relationship is not at all dependent on overall sunspot activity due to intra-cycle variability. 

 

Mean winter NAO index values for the four cycle phases, averaged over cycles 11 to 23. The red line represents the overall mean value of wintertime NAO (0.05). Bars represent the 95% confidence intervals.

 

Perhaps more germane within the context of the coming winter is that the study found that both the solar max and the ascending portion of the solar cycle are weakly correlated to a colder pattern redolent of the -NAO, although this is more dependent on intra-cycle variability of activity. There is a modest negative correlation with solar minimum, which was the case in the QBO analog year of 2020-2021.

 

 

These relationships between solar behavior and the NAO are evident in the graph above, with reds, denoting +NAO, very evident in the declining phase of the last several solar cycles. And Blue, indicative of -NAO, prevalent in the ascending portion of the cycles. What can also be deduced from the graphic above is that while solar max seasons are not as favorable as the ascending phase of the cycle for incidences of high latitude blocking, nor are they as hostile as the descending seasons. Thus winter seasons such as 2024-2025, which are near solar max, are not entirely devoid of blocking, however, nor is this season as prone to an intense round of late season blocking the magnitude of March 2023 given that the solar cycle was still ascending at that point. Be that as it may, solar max seasons are not entirely hostile to incidences of a disturbed polar vortex and this is evident when considering the best solar analogs of 1970 and 1999.

 

There was a split of the polar vortex on January 17, 1971, a displacement on March 20, 1971 and a displacement on March 20, 2000. While there was an easterly QBO evident during the 1970-1971 winter, the polar vortex displacement that took place in March of 2000 occurred during a westerly QBO, as will be the case this season. Thus the latter displacement seems worthy of more consideration for the coming season. When considering the three primary QBO analogs of 2016, 2020 and 2022 within a solar context, although none took place during solar max, 2022 was the closest, followed by 2016 and 2020, the latter of which is a poor solar match having taken place near solar minimum.

 

Given that the QBO analog of 2020-2021 took place near solar minimum, the early January 2021 SSW  is of least relevance as a viable analog occurrence this season. However, the February 2023 SSW, which is a better solar analog, lends more support to a later season potential polar vortex disruption along the lines of March 1971 and 2000. This notion is supported by research on high solar, westerly QBO seasons, which lends credence to the late winter/early spring displacement scenario.

 

 

 

 

The postulation of a modestly disturbed polar vortex during the month of December, followed by a recovery during the middle portion of the winter, prior to a more substantial displacement of the polar vortex during either February or March is well supported by research on moderate, basin-wide La Niña events taking place near a solar maximum with a westerly QBO. Such an evolution would also be consistent with the 2022 type of preferred mismatch during January 2025, which would be Pacific driven (-WPO/-EPO and/or +PNA and accompanied by a fairly strong polar vortex (+AO/NAO). This preliminary conclusion is based upon a constellation of historic data can be checked against observed, concurrent data in real time.

Observations During 2024 That Inform Behavior of the Polar Fields During Winter 2024-2025

The Role of Atlantic Accumulated Cyclone Energy

 

The primary reason why the tropics are so crucial to what ultimately transpires here in the mid latitudes is because it is here that the earth's energy budget is set, and it is the subsequent redistribution of said energy from the tropics, throughout the mid latitudes and all the way to the poles that is the very essence of weather. All types of weather and everything involving the atmosphere, from storms to oscillations, and ocean currents play a role in the redistribution of said heat in an effort to achieve an illusory balance that will never be reached. Aside from ENSO, perhaps the most prolific re-distributors of this heat are topical cyclones. Given that heat transported poleward can also increase atmospheric heights, it stands to reason that the amount of energy transported poleward by tropical cyclones during the summer and into the fall can have some baring on what transpires at the higher latitudes during the ensuing cold season. A graphic configured by @RaindanceWX, who is a highly recommended follow:

 

 

 

Note the tendency for the delivery of cold to the northern tier via a fairly cold source region in the absence of NAO blocking. This lends credence to the concept gleaned from the solar data that early NAO blocking may be more ephemeral in nature, with consolidation of the polar vortex thereafter across the mid Atlantic and southeast. Although the season is still in progress, the final Accumulated Cyclone Energy (ACE) value is already above average at 159.8 with more activity potentially on the horizon. The poleward redistribution of heat that this entails is more likely to foster the development of the higher latitude ridges that can contribute to deviation from the MC like regime, as was the case in January of 2022. While this certainly does not ensure ample AO/NAO blocking, it does provide more reason to doubt an excessively strong polar vortex in the DM seasonal mean, which is supported by additional events from around the globe during 2024. In fact, most skilled seasonal forecasters are those that devise methods that incorporate both an exhaustive analysis of what has happened throughout history under fairly similar conditions with what is actually happening in reality, and how the hemisphere evolved following similar occurrences in the past.  Forecast confidence can be increased when the results are congruent. 

 

Major Disruption of Antarctic Polar Vortex Lends Support to Polar Analog

 

This past summer featured a major SSW occurring over Antarctica, as evidenced by the extremely negative Antarctic Oscillation (AAO) that was observed, which is the southern hemispheric cousin of the Arctic Oscillation here in the northern hemisphere.

 

Looking back at similarly extreme -AOO episodes during fairly comparable La Niña events, the year 2007 stands out as a stronger, basin-wide La Niña that featured a -2.63 AOO value during the month of July. The behavior of the polar domain during the ensuing winter of 2007-2008 is interesting in that it behaved fairly similarly to the progression of the solar/stratosphere composite. While the season finished with a fairly robust polar vortex in the mean (+.79 DM AO/+.51 DM NAO), the month of December featured an elongated polar vortex that kept the northeast cooler, while deep western CONUS troughing kept a southeast ridge fixed in place. 

 

 

Deep western CONUS troughing became the predominate driver of the pattern mid season, as the PV lifted northward and heights rose through the eastern US, which is expected early and late in the season this year.

 

The season drew to a close with a textbook high solar/westerly QBO SSW on February 22, 2008, which led to considerable warming throughout the polar stratosphere during the month of March, which is congruent with the theme of other polar analogs. 

 

It is noteworthy that the 2007-2008 season is both a poor solar and QBO analog, however, this does not entirely negate the value of what is a strong ENSO match working in conjunction with similar behavior of the southern hemisphere during the northern hemisphere summer to potentially yield a result similar to the solar max/W QBO dataset. 

Note the support for the +EPO/-WPO configuration that was strongly emphasized in the analysis of the extra tropical Pacific, however, for adjustments for the modern tendency of the southeast ridge to be more prevalent would need to made assumed.

 

 

It is prudent to consider each individual season of this six year composite as an individual ensemble member with slightly perturbed initial conditions in one manner or another.

The mean aggregate DM AO of the dataset is +.41 & DM NAO is +.54. This is remarkably consistent with the subsurface formula derived by @stormchaserchuck1 at Americanwx.com weather forum.

The index is a measurement of May 1 - Sept 30 SSTs in the North Atlantic. It's correlated to following November-March NAO/AO (+6 month lag). The index is a composite of 2 areas in the

  North Atlantic (blue box - red box). Because the northern area has more volatility, the total dataset, SSTs and NAO were normalized by multiplying the total historical absolute number of both, and dividing it by each other. 

When blue box is cold SSTs, a negative NAO is implied for Winter.

 When red box in warm SSTs, a negative NAO Winter. For comparison, and red box is 65%

 value of blue box anomaly (so -1 blue +0.65 red is same thing). Visa versa.

 The index this year from May 1 - Sept 30  is +0.52, making it a 50% chance of having the DJFM NAO -0.04 to +1.04.

 

 This compared to the mean DM NAO value (.54) of the Eastern Mass Weather polar analog composite, which is also in alignment with the rather unremarkable signal from the both the Eurasian Snowcover Advance Index (SAI) and the Snowcover Extent Index (SCE) vourtesy of Dr. Judah Cohen.

 The Eastern Mass Weather 2024-2025 forecast for the AO is between .26 and .56 and the NAO between .38 to .68, with the most favorable period for a modestly disturbed polar vortex being in December (albeit largely negated by a MC driven Pacific), and the greatest likelihood for a major disruption in February or March.

[GaWx]

Latest available CFS ens based AAM: still positive but not as strongly positive in late Dec and early Jan as prior runs (these often jump around and aren’t reliable):

 

Prior run:

[GaWx]

Latest EPS (0Z) based HDD: that second spike centered on Dec 12th had increased the last couple of days (though 12Z backed off some I think) but otherwise week two is mainly mild: