2025 ENSO/Winter Speculation

[Typhoon Tip]

On 4/21/2025 at 10:54 PM, bristolri_wx said:

The CFS thinks the earth is on fire all the time.  CANSIPS DJF 25/26:

 

Considering what it’s doing to the polar Arctic region up there… I don’t think it’s a hell of a lot better

[40/70 Benchmark]

14 hours ago, 512high said:

was it 2011-12? (I think!) Hope you and the family are well!

2011-2012 was awful.

[wxsniss]

Let’s hope this isn’t true…

https://studyfinds.org/winter-weather-moving-west-how-the-polar-vortex-rewriting-americas-cold-map/

“LOWELL, Mass. — Americans expecting the worst winter weather to slam the East Coast might need to look northwest instead. A major study spanning four decades reveals that severe winter storms are shifting away from traditional snow belt regions toward the Pacific Northwest and northern Rockies, potentially changing where Americans should brace for brutal cold and heavy snow…”

”According to the study, published in Science Advances, the first pattern “features an upper-level vortex displaced toward western Canada and linked to northwestern U.S. severe winter weather.” The second “features a weakened upper-level vortex displaced toward the North Atlantic and linked to central-eastern U.S. severe winter weather.”

[Go Kart Mozart]

 

So, for the last four decades winter storms have shifted away from the east coast?  How much of our taxpayer funded grant money went into this load of shit?

Don't get me twisted, I am not denying that the earth is warming....different issue....but WTF is this?

[40/70 Benchmark]

On 7/13/2025 at 10:14 AM, wxsniss said:

Let’s hope this isn’t true…

https://studyfinds.org/winter-weather-moving-west-how-the-polar-vortex-rewriting-americas-cold-map/

“LOWELL, Mass. — Americans expecting the worst winter weather to slam the East Coast might need to look northwest instead. A major study spanning four decades reveals that severe winter storms are shifting away from traditional snow belt regions toward the Pacific Northwest and northern Rockies, potentially changing where Americans should brace for brutal cold and heavy snow…”

”According to the study, published in Science Advances, the first pattern “features an upper-level vortex displaced toward western Canada and linked to northwestern U.S. severe winter weather.” The second “features a weakened upper-level vortex displaced toward the North Atlantic and linked to central-eastern U.S. severe winter weather.”

It would make sense if this were focused on the last 7-10 years or so....but four decades? the 90s, 00s and 10s were great for NE coastal snowfall. I haven't read it over, but it seems like they are exagerating the sample size to prematurely launch a west warm pool derived CC theory because they know there isn't enough data yet.

[Prismshine Productions]

I know, bigger payoff that way, but I’m just so sick of dealing with marginal air masses.

Yeah, same, hence my projection

Sent from my SM-S166V using Tapatalk

[Typhoon Tip]

On 7/13/2025 at 7:14 AM, wxsniss said:

Let’s hope this isn’t true…

https://studyfinds.org/winter-weather-moving-west-how-the-polar-vortex-rewriting-americas-cold-map/

“LOWELL, Mass. — Americans expecting the worst winter weather to slam the East Coast might need to look northwest instead. A major study spanning four decades reveals that severe winter storms are shifting away from traditional snow belt regions toward the Pacific Northwest and northern Rockies, potentially changing where Americans should brace for brutal cold and heavy snow…”

”According to the study, published in Science Advances, the first pattern “features an upper-level vortex displaced toward western Canada and linked to northwestern U.S. severe winter weather.” The second “features a weakened upper-level vortex displaced toward the North Atlantic and linked to central-eastern U.S. severe winter weather.”

I suggest it is true ... 

At least intuitively so - a more advancing/sophisticated corroborative science not withstanding. It aligns well with faster hemispheres that occur as a result of increased gradient associated with CC.

More over, this is reproducible observation, folks.   I mean we spend all this time with deep statistical comparisons with mid last century longer termed teleconnectors .. trying to find secrets that no one has. Yet from what I'm reading ... no one considers CC enough and or blinking light limits that are materializing now.  Can't build expectations based upon the former - not nearly as much so.   

I've been snarky - admittedly - in recent post with drive-by pot shots ... more for funniness that those who engage in the practice of course don't see the humor.  HAHAHA.  Seriously though, when joked to just take the last 10 years, average them, and call it a day for temp and precip bias expectation... mm, unfortunately there's more than a mere modicum truth to it.  And the why is rooted in the gradient soaked hemisphere. When there's more non-hydrostatic lines demarcating the polar field from the subtropical field, that physically/deterministically speeds up the flow.  That does a few things.. But the mains are: faster flow  alters the wave frequency;  telecon reliance takes a hit because though the correlations are clad, they change faster than the correlation can be realized. This casts an illusion of chaos but's really that the patterns are changing almost as fast as a cold wave synopsis gets underway ( for example), and vice versa.   

This is why part of the climate reporting, globally, is complaining  about dramatic short term changes.  It's because the increased speed of wave propagation at planetary scales.  This then causes non-linear and linear resonance break down.  Think of it as less positive interference.   

As an aside/anecdotally ( so taken with a grain - ), this is causing a gutting of the "middle class"   Less standard model cyclones in lieu of weird events that gets us more or less in the range of seasonal snow - which is also a delta climate metric, so it's silly to think of seasonality if based upon 1980 ...  We seem to get more 20 to 30" events making up seasonal totals though.  We get nickle dimes by accident, or the big historic wild bombs, otherwise, we're yawing between deep cold and balmy thaws in less time.  This' phenotype' winter has been reproducible regardless of PDO this, or ENSO that, are AMO(AO/NAO/EPO) derivatives, solar belches or opposite house birth signs.  The variant behavior is dominating despite all those.

[40/70 Benchmark]

https://easternmassweather.blogspot.com/2025/07/la-neutral-enso-conditions-will.html

[Snowcrazed71]

20 hours ago, 40/70 Benchmark said:

https://easternmassweather.blogspot.com/2025/07/la-neutral-enso-conditions-will.html

Of course, you're getting those saying a weak La Nina is going to develop going into the Winter, but I suspect even if that happens, it won't really make much of difference ( like a typical La Nina ).

Thanks for your blog/insight on what you are seeing for this upcoming Winter.

[40/70 Benchmark]

15 hours ago, Snowcrazed71 said:

Of course, you're getting those saying a weak La Nina is going to develop going into the Winter, but I suspect even if that happens, it won't really make much of difference ( like a typical La Nina ).

Thanks for your blog/insight on what you are seeing for this upcoming Winter.

Define "difference"......will it mean a below average temperature season with above average snowfall? Probably not....but will it prevent a wall-to-wall disaster with some periods of poleward Aleutian ridging and some blocking...probably.

[Prismshine Productions]

Define "difference"......will it mean a below average temperature season with above average snowfall? Probably not....but will it prevent a wall-to-wall disaster with some periods of poleward Aleutian ridging and some blocking...probably.

So warmer and drier than last winter but not as touchy as 2023/4 correct?

Sent from my SM-S166V using Tapatalk

[40/70 Benchmark]

3 minutes ago, Prismshine Productions said:

So warmer and drier than last winter but not as touchy as 2023/4 correct?

Sent from my SM-S166V using Tapatalk
 

No, warmer and wetter than last winter is my guess.

[Prismshine Productions]

No, warmer and wetter than last winter is my guess.

My preliminary guess is +2-3C, 75-80% of normal snowfall

Sent from my SM-S166V using Tapatalk

[512high]

7 hours ago, 40/70 Benchmark said:

No, warmer and wetter than last winter is my guess.

Well was hoping for more "cold" then warm, however, will take my chances, what choice do we have? I understand its still early, hopefully things improve.

[forkyfork]

this is all i need to see

[GaWx]

1 hour ago, forkyfork said:

this is all i need to see

It’s surprising that the Arctic is blue. Do you know why?

[Typhoon Tip]

1 hour ago, GaWx said:

It’s surprising that the Arctic is blue. Do you know why?

Not in the conversation but ... when was the last time the 30-year climate intervals were re-applied?

It could be a cooler AO domain relative to a "new" data set/means therefrom.   Just a plausibility

[GaWx]

1 minute ago, Typhoon Tip said:

Not in the conversation but ... when was the last time the 30-year climate intervals were re-applied?

It could be a cooler AO domain relative to the "new" data set/means therefrom.   Just a plausibility

 Thanks. In case you didn’t see it, the map says it is vs 1991-2020 climatology.

[Typhoon Tip]

3 hours ago, GaWx said:

 Thanks. In case you didn’t see it, the map says it is vs 1991-2020 climatology.

Ha... I did not - 

Well in that case ... the model product is a piece of shit because there's no way the whole AO domain does that.  nope -

[forkyfork]

17 hours ago, Typhoon Tip said:

Ha... I did not - 

Well in that case ... the model product is a piece of shit because there's no way the whole AO domain does that.  nope -

probably erroneous because of ice cover

[MJO812]

[40/70 Benchmark]

On 8/1/2025 at 12:09 PM, forkyfork said:

this is all i need to see

Any interest in this?

22 hours ago, mitchnick said:

Looking at the 30 day change, you may be stuck with cool piss if you don't hurry.

 

[cleetussnow]

Does that mean we revert to colder anomaly or does it mean less hot anomaly but still hot anomaly?  We need the northpac to cool off obviously but until I see the blues of its hues in current pac ssts anomaly, don’t know if that map means much.    

[40/70 Benchmark]

12 hours ago, cleetussnow said:

Does that mean we revert to colder anomaly or does it mean less hot anomaly but still hot anomaly?  We need the northpac to cool off obviously but until I see the blues of its hues in current pac ssts anomaly, don’t know if that map means much.    

Its a start-

[40/70 Benchmark]

 

Preview of the Polar Domain for Winter 2025-2026

Preview of the Polar Domain for Winter 2025-2026

Solar & Stratospheric Influences on the Arctic 

Ramifications of the Peak of Solar Cycle 25 on the Higher Latitudes

 

Perhaps the most inconspicuously integral driver of the earth's atmosphere, and thus the most logical starting point for any sound analysis there of is the sun. Indeed, our weather is driven by the inexorable and constant quest of the earth to achieve balance via the poleward redistribution of this immense amount of solar heat that is concentrated near the equator. Needless to say, the behavior of the sun of kind of a big deal, which makes the waxing and waning of sunspots known as the solar cycle a prudent place to start when examining the potential behavior of the higher latitudes for the coming winter. Although not an absolute certainty, NASA has determined that there is approximately a 90% chance that the peak of solar cycle 25 has already occurred, during October 2024.

 

 

There admittedly remains more questions than definitive answers regarding the impact of the solar cycle on the behavior of the polar domain, which means that much like the frontier science of seasonal forecasting in general, it is still very much a work in progress. The central question that continues to elude modern research is the precise mechanism by which the solar cycle affects the polar fields, which also renders the exact lag time between altered levels of UV radiation and the sensitivity of the polar vortex there of nebulous.

Identification of Solar Driver is Key

Traditionally, research has correlated high levels of solar activity near or shortly beyond solar max, such as will be the case for winter 2025-2026, to a stronger polar vortex and thus milder winters for much of North America and Europe. There have been studies that have cited sensitivity to solar influence among many different polar elements, including polar temperatures and Geopotential heights in the stratosphere (Labitzek, 2005), as well as in the troposphere (Van Loon and Labitzek, 1988) and the NAO via Atlantic and European sea level pressure patterns (Korea, 2002). However, while there seems to a consensus around the concept of some type of solar modulation of the polar domain via altered stratospheric and tropospheric circulations, there exists a multitude of theories as to the solar driver of said relationship. Many theories cite factors 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. The "top-down" theory argues that enhanced ozone levels and warmer temperatures resulting from increased solar UV warm the tropical stratosphere and produce a stronger latitudinal gradient and a modulated Brewer-Dobson Cycle, which is transferred downward in the atmosphere and poleward at the surface to result in a cooler polar stratosphere (stronger polar vortex) (McCormack and Hood, 1996). Conversely, the more dubious and so-called "bottom-up" theory posits that the enhanced solar heating of the equatorial ocean surface during solar max results in the transfer of latent heat to the upper levels of the atmosphere through increased evaporation. This heat is then carried to a convergence zone by the trade winds, which triggers a positive feedback that ultimately impacts the North Pacific and Arctic. Both of the aforementioned theories would entail that the greatest propensity for +NAO due to this solar-stratosphere connection would coincide with solar max. However, more recent research cites stronger drivers that do not coincide with solar max, such as geomagnetic energy and solar winds, which peak about two to fours 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 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. This consequently cools the stratosphere and strengthens the PV, which more closely corroborates with other recent research citing drivers that do not peak at solar max, as defined by UV and TSI. 

 

 The implication of this is that the +NAO response peaks during the descending portion of the solar cycle between approximately 2-4 years after solar max (presumably October 2024) and in the vicinity of Geomagnetic peak, which is depicted in the forecast graphic above as roughly summer 2026. This implies that while winter 2025-2026 is certainly predisposed to averaging a +NAO in the seasonal mean, perhaps the subsequent seasons of 2026-2027 and 2027-2028 will feature an even stronger bias towards an more stout polar vortex. The inference here is that although winter 2025-2026 is highly likely to feature a +NAO in the seasonal mean, solar implications are certainly not prohibitive to spacmodic warming of the polar stratosphere during favored intervals. 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. Malimiemi 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).

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.

 

Incidentally, the study also 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 weaker correlation is more dependent on intra-cycle variability of activity and potentially discrepancies in the calculation of the NAO domain. There is also a modest negative correlation between the NAO and the solar minimum. These relationships between solar behavior and the NAO are also illustrated in the graph below, 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 is clear from the research is that there exists a lag of approximately 1-4 years for the maximum impacts of variation in solar irradiance to manifest by way of polar modulation. This lag has been attributed to discrepancies with respect to the solar driver. Early research cited peak UV in the vicinity of solar max as the main driver with a lag of approximately 1 year, with more recent research settling on a 2-4 year lag centered on the geomagnetic peak during the descending phase of the solar cycle. The Eastern Mass Weather critique of many of these theories is that they largely neglect the role of the Atlantic in the modulation of the NAO, which is undoubtedly involved in an solar sensitivity of given that the index is derived from Atlantic and European sea level pressure patterns. 

 

Lagged North Atlantic Climate Response to Solar Variability

The atmosphere in its truest essence is the oft delayed feedback between the land, sea and air that serves to budget the immense degree of solar energy that is concentrated around the equator by redistributing it upward. First in altitude via the convergence and upward ascent of air due to convection, which is a term referring to concentrated areas of showers and thunderstorms. Then eventually poleward by both major storms such as hurricanes, which are essentially spinning gyres of convection, as well as ocean currents and oscillations. This epitomizes how the cycle of ocean and air processes act to budget heat around the globe, which was touched upon in an oblique manner when referencing the interplay between the sun and the poles at work in the "bottom-up" theory. The work of Sciafe et al, 2013 is revolutionary in that it ostensibly bridges the previously discussed works concerning polar sensitivity to the solar cycle with prior research (Czaja, 2002) positing a 6 month lag between the leading of the NAO by the 500mb pattern over the Atlantic. The work posits the Atlantic has a sensitivity to solar UV variability that triggers an immediate atmospheric signature that takes several years to accumulate in the subsurface of the ocean, during which time the atmospheric response progressively increases as part of a coupled feedback between the ocean and atmosphere. The response continuously projects onto the winter North Atlantic Oscillation and the familiar tripole pattern in North Atlantic sea surface temperature as referenced by Cjaza et al (2002), with a lag time of 2-4 years (Sciafe et al 2013). Thus is it is reasonable to conclude from the preponderance of evidence owed to a multitude of varied research efforts that changes in solar irradiance along the progression of the solar cycle trigger instant surface responses that progress through the subsurface and then ultimately resurface through a process of meridional overturning. This reemergence fosters a delayed feedback (6 months) between the sea and air that can be self-sustaining. Member stormchaserchuck1 at Americanwx.com weather forum has put this theory into practice. His index consists of 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 through early August (61% of the way through) is about +0.20, making it a 50% chance of having the DJFM NAO -0.34 to +.74

 

This slight hedge towards a positive NAO in the DM mean seasonal calculation is consistent with the nascent portion of the descending phase of solar cycle 25 within two years of solar max, which presumably occurred this past October (2024). Given that there is no overwhelmingly strong solar signal concerning the polar domain for winter 2025-2026 it will be crucial to explore the stratosphere concerning potential periods of vulnerability for the polar vortex.

Diagnosing the State of the Polar Vortex for Winter 2025-2026

The system of cycles and oscillations that occurs 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 descending after recently having entered its easterly phase at both the 50mb (May) and 30mb (July) levels.

 

It is an absolute certainty that it will remain in the easterly phase at both levels throughout the impending winter given that it takes several months to bottom out before recovering towards a new westerly phase. Considering the expectation for a modest cool ENSO event for winter 2025-2026, here are the best match QBO analogs as per the July values.

July 2024 50MB QBO: -2.06 & descending

2021: 2.82 & descending

2017: 5.08 & descending

2012: -8.10 & descending

2007: -8.75 & descending

2005: -8.13 & descending

2000: 3.25 & descending

1974: -3.42 & descending

1970: -8.05 & descending

1962: -3.08 & descending

 

July 2024 30MB QBO: -19.19 & descending

2021: -13.17 & descending

2017: -10.48 & descending

2012: -27.82 & descending

2007: -24.92 & descending

2005: -24.20 & descending

2000: -13.13 & descending

1974: -19.58 & descending

1970: -18.62 & descending

1962: -15.49 & peaking

A composite of these analogs provides an early conceptualization of the state of the higher latitudes for this winter season.

Note the marked tendency for both poleward Aleutian ridging and NAO style blocking in the DM seasonal composite. Given that the QBO will be in its Easterly phase this season, the above composite is consistent with research that concluded that the polar vortex is more prone to disruption from Sudden Stratospheric Warmings (SSWs) earlier in the season per what is referred to as the Holton-Tan relationship. This is due to the fact that the default direction of the zonal winds in the polar region is from the west, thus an easterly QBO is more likely to lead to disruption, or even a reversal of these winds in the case of a technical SSW (Holton, Tan 1980). Additionally, it is also theorized that easterlies in the stratosphere more foster the development of a stronger Aleutian high, which is more conducive to the development of said SSWs. The full reversal of zonal winds that constitutes a technical SSW subsequently leads to either a splitting or displacement of the PV. The inference here is that although a positive NAO is favored in the DM seasonal mean per previously referenced research on years descending from solar max, the easterly QBO is likely to be the catalyst for significant period(s) of high latitude blocking given that solar geomagnetic peak, which provides the most resistance to PV disruptions, will not be reached until roughly next summer. Research by Gray et al, 2004 elaborates on the complex relationship between the solar cycle and the QBO phase.

Integrating Solar & QBO Research for a Comprehensive Polar Forecast

The aforementioned Holton-Tan relationship, which dictates that an easterly QBO is correlated with both a greater incidence of, and an earlier development of SSW, becomes more complicated when considering the solar cycle. In some cases, when the QBO and solar cycle are in conflict, they can either over ride one another or even cancel each other out (Gray et al 2004). Here is a list of combinations and the theorized relationships for clarity.

Solar min/W QBO: This is entirely consistent with the Holton-Tan relationship in that the westerly QBO essentially "wins". The PV is likely to be stronger than average until the final warming in spring.

Solar max/W QBO: In this case, the Holton-Tan relationship is applicable early on in the season, as major warmings are unlikely. However, the Holton-Tan relationship reverses mid winter and the latter portion of the season from February onward is susceptible to warmings and major PV disruption. Winter 2024-2025 was a textbook example of this.

Solar Min/E QBO: There are no inconsistencies here, as the entire season is more prone to polar vortex disruptions and SSW as per the Holton-Tan relationship.

Solar Max/E QBO (2025-2026): The Holton-Tan relationship applies early on given that PV disruptions are likely in December, before the relationship reverses and they are less likely later in the season. The final warming is of course the exception to this rule, while it is usually more relevant for spring, it can and does sometimes occur early enough to have an impact for the major population centers in terms of late season cold and/or snowfall.

Below are a couple of annotations to aide in the simplification and visualization of these relationships.

 

Interestingly enough, although statistically speaking early and late season disruptions are favored, there is a an outlier set of major PV disruptions noted in the solar max/E QBO quadrant of the chart above. This also becomes a theme when comparing the solar QBO analog composites. 

Here is a list of cool ENSO/ solar analogs for the winter 2025-2026 season.

 

Here is a DM composite of these seasons.

 

 

There are obvious similarities between the Solar composite (right) and the QBO composite (left) given that they both feature high latitude blocking and poleward Aleutian ridging.

 

 

The primary difference is that the QBO analog composite is biased more towards early and late season NAO blocking, whereas the solar composite focuses the NAO blocking more in the early portion of the season.

 

 

The discrepancy is primarily with respect to late season owed to the aforementioned outlier set of mid winter PV disruptions, which is evident in the list of SSW analogs compiled from the solar and QBO composites, respectively.

January 17, 1971: PV Split

December 4, 1981: PV Displacement

February 11, 2001: PV Split

January 2, 2002: PV Displacement

February 22, 2008: PV Displacement

January 7, 2013: PV Split

February 14, 2018: PV Split

March 20, 2025: PV Displacement

The majority of the SSW events are split between the mid winter months of January and February with three events per month. There is also an outlier event in December, 1981 and March 2025.  The primary analog events of January 17, 1971 and February 11, 2001 were both accompanied by PV splits and are the only two members to appear in both of the QBO and solar analog composites, which lends more credence to the mid winter outlier scenario that contains 6/8 the analogs. Thus the favored timeframe for a SSW and subsequent split of the polar vortex is during the January 14 to February 14 timeframe, which favors late season NAO blocking to commence roughly between February 8 through March 6. 

 Now that an a reasonable consensus for the evolution of the polar domain during boreal winter 2025-2026 has been reached through a thorough examination of the relationship between the solar cycle and the QBO state, a more thorough consideration of ENSO is the final step before a preliminary winter composite can be made.

How La Nina Intensity & Orientation can Impact the Polar Fields

Below is a juxtaposition of all weak (left), moderate (center) and strong (right) La Nina events dating back to 1950 in which intensity has been assigned via a personalized assessment of ONI, MEI and Relative Ocean Nino Index. There are some subtle differences between the weak and moderate composites that grow more pronounced in the strong composite that can have important ramifications with respect to the seasonal polar fields.

 

When viewing the 500mb composites above, it is evident that there is significant poleward Aleutian ridging in the weaker La Nina composite, as well as a greater susceptibility to higher latitude blocking in general. It's these greater heights at higher latitudes that aid in the delivery of colder air across North America. The strong composite is much more subdued with these higher latitude heights and instead more pronounced with southeastern ridging. These differences are illustrated well in the temperature composites below.  

 

The primary reason why the weaker La Nina composite is significantly cooler across the eastern US is because the distribution of the SST anomalies is biased to the east, which has a significant impact on the placement of the Hadley Cell, and thus the orientation and placement of the Aleutian ridge that either augments or inhibits the delivery of cold air south and eastward.

 

Note the disparities in forcing that are evident in the velocity potential composites below.

It is apparent that the eastern-based La Nina SST anomaly composite on the left is the weakest of the three composites. This is due to the fact that a weaker cool ENSO Walker Cycle inherently means weaker easterly trade winds, which are responsible for fostering both the development of La Nina, as well as the progression of cooler waters westward.

Thus diminished trade winds entail a weaker cool ENSO event that is more relegated to the eastern zones.
 

This means that generally speaking, not always, weaker events are more east-based and stronger events tend to fall more on the Modoki end of the spectrum since they are the most mature. The implication of this is that the same contrasts noted previously between weak events and strong events also exists between east-based La Nina events and Modoki episodes, which has a similar effect on the respective temperature composites.

 

 

This is very similar to the intensity composites in that it is the tropical SST orientation that largely dictates the placement of the convection that is so crucial to the configuration of the Hadley Cell, which ultimately determines the weather pattern in the mid latitudes.

It is evident in the composites below that descending air is aligned with the core of La Nina, and convection inducing ascent is focused over the Maritime continent that aligns with MJO regions 4-6, which is usually more unfavorable for high latitude blocking.

Clearly strong and Modoki La Nina composites have a much larger degree of subsidence in the general vicinity of the dateline, which inhibits variation from these phases. This is why this particular forcing regime is fairly hostile to high latitude blocking and creates such a great variation in regional climate relative to its more eastern biased and weaker cool ENSO counterparts. The distinction coupled with a proper diagnosis is an integral part of the seasonal forecast since the difference between La Nina winters that have a -AO vs a +AO is significant. Here are -AO La Nina winters in the CONUS (leaving out cool neutral years) vs the +AO La Ninas.

 

 

These key differences have implications with respect to not only informing the degree of high latitude blocking that may or may not materialize over the course of the ensuing winter season, but also the timing of any such occurrence. Additionally, these SST anomaly patterns result in large differences with respect to the extratropical oceanic circulation over the Pacific and Atlantic, which acts to feedback on and sustain the resultant pattern over the polar domain.

Disparate Seasonal Evolutions & Oceanic Circulation Patterns of La Niña Types

It is evident in the graphic below that Modoki and basin-wide events 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 in the middle portion of the season, which is important to note considering that the developing cool ENSO event is expected to remain both weak and east to central-based, in addition to the fact that easterly QBO-SSW analogs seemed to flag the potential for a mid-season SSW.

 

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 while the easterly QBO data set seemed to imply some PV dysregulation in December, that does not have to mean that it will be particularly cold. It would appear that 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, as was the case with respect to the interaction between the QBO state and the solar cycle. This sensitivity of the NAO progression to the El Niño Modoki Index (EMI) is due to the aforementioned modulation of the Hadley Cell via convective forcing patterns and the oceanic circulation patterns that feedsback 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. 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 an east to central-based event of weak intensity, odds favor a -AO with polar vortex disruption(s), however, the NAO is more nebulous and may very well average positive in the DM seasonal mean, which would be consistent with a freshly descending portion of the solar cycle within two years of solar max. The period from December into early January, as well mid February into mid March (1/14 to 2/14 favored SSW window) 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. This is why it is absolutely imperative to view each season within the polar composite as an individual ensemble member, and the composite as an ensemble mean. Each season represents a  plausible solution within the range of mathematically plausible outcomes, and to view any seasonal composite as a deterministic tool is pure folly.

Winter 2025-2025 Preliminary Polar Analog Composite

Primary Polar Analogs: 1970-1971, 2000-2001

 

The DM mean AO value for the 13 seasons within the composite is -.30 and the mean NAO value is +.13, the latter of which matches stormchaserchuck1 's +.20 value to within .07. This clearly increases confidence relative to such an extended lead time, as does the remarkable consistency that the polar composite has with other the weak La Niña, east-based La Niña, QBO, solar and EMI composites.

 

These preliminary composites also share a consensus with some of the early seasonal guidance.

 

Conclusions to Drawn Regarding Winter 2025-2025

The fact that the weak and east-based/basin-wide La Niña composites match the preliminary Eastern Mass Weather Polar Composite belies the fact that they have a great deal of variability. This does not mean that  a weaker cool ENSO event  necessarily favors a colder pattern with more high latitude blocking, however, it does mean that they are much less prohibitive to said regime than are strong La Niña events. Weaker La Niña events are more prone to higher latitude influences, which in this case will be a negative QBO/near max descending solar cycle. This latter combination is why winter 2025-2026 will likely feature some blocking and colder intervals, as a weak La Niña event in and of itself does not necessarily ensure that particular outcome. The easterly QBO and high solar conditions should largely cancel one another out, with a slight nod in the direction of the easterly QBO relative to the AO (modestly negative), and the solar max with respect to the NAO (modestly positive). That being said, there are likely to be periods of significant negative NAO possible during the month of December into early January before the polar vortex recovers, and then again between mid February and mid March in response to a potential mid season SSW between approximately January 14 and February 14. Although snowfall may be more plentiful than it has in recent seasons, the interior of the northeast is still likely to be favored given the likelihood of a variable storm track and a substantial mid season thaw period.

 

Eastern Mass Weather will have a preliminary assessment of the extra tropical Pacific for winter 2025-2026 within the next few weeks-