Winter 2025-2026 Offers Return to Normalcy

[40/70 Benchmark]

Verification of High Impact & Long-Duration Sunday-Monday Winter Storm

Strong Forecast Leaves Room For Improvement

Overall the Eastern Mass Weather Final Call for the major winter storm that impacted the forecast area from Sunday through Monday verified quite well.

 

However, the coastal front enhancement was somewhat misdiagnosed, as the front itself was pinned slightly closer to the coast than anticipated. The forecast for the front to penetrate into roughly the  I 495 corridor was predicated up global guidance.

 

But as it turned out, mesoscale guidance, which pinned the front closer to the coast, or along rt 128 and near I 95 on the north shore, proved to be more accurate. This is why highest amounts 

 ended up along the coast (Gloucester, MA, 27"), (Ipswich,  MA, 26"), rather than near the I 495 belt. Be that as it may, amounts of two feet, and event slightly more, were reported throughout much of northeastern Massachusetts, with a secondary on the east slope of the Worcester hills (Sterling, MA, 25.2"), as forecast.

Final Grade: A

[40/70 Benchmark]

Remarkably Well Forecast January Poised To Deliver Wintry February

Stratospheric Reflection Event To Deal Major Blow To Polar Vortex

Recent Stratospheric Reflection Event Key To Potentially Bitter Latter January

 The recent polar vortex infiltration and onslaught of severe winter weather throughout the second half of January should sound familiar to those of you who took the time to read the Eastern Mass Weather Winter Outlook last fall, which advertised that the mild, mid-month Pacific Trough Regime responsible for our January thaw would also serve as the precursor pattern to the development of what is referred to as a stratospheric reflection event. Indeed, society's understanding of the stratosphere and the role that it plays in modulating our weather is very rudimentary to say the least. The basic conceptualization is that a weak polar polar vortex makes the mid latitudes more prone to cold outbreaks, and while that is true, the method of delivery for cold to North America is multifarious in that it is not relegated to a weak polar vortex/-NAO pattern. In fact, the coldest outbreaks in the CONUS are actually triggered by a strong polar vortex and +NAO regime in what is referred to as a "stratospheric reflection event". During these stratospheric reflection events, heat is transferred upward by a Rosby wave (kink in the jet stream) over Siberia and reflects back downward of off the PV into Canada via the reflective surface posed by negative vertical wind shear in the stratosphere. ( Lee et al 2019). The study notes that these reflection events are most common during the month of January.

 

There is one reflection event on average each season, so they are by no means rare events. Reflective events are declared when the reflection index (RI), which denotes the difference in anomalous poleward eddy heat fluxes in the lower stratosphere between Siberia and Canada, exceeds 1 for 10 or more consecutive days (Lee et al 2019). Reflective events are unique occurrences in that the PV is undisturbed and initially remains strong, before being stretched by the development of Alaskan and Aleutian ridging and returning to normal strength.

 

 

 It is the stretching that delivers the cold south and eastward into the CONUS, as depicted in the "end of event" graphic above. This type of stratospheric phenomenon differs from the SSW events, in which heat propagates upward in waves that converge in the stratosphere, thus weakening the PV by decelerating and even reversing the zonal westerly winds that are ordinarily prevalent in the polar stratosphere. Reflection events also differ from SSW in that they are more favored during the westerly phase of the QBO, with 30/44 events since 1980 having occurred during a +QBO. While this ostensibly rendered such an occurrence unlikely this winter given the very strong easterly QBO that is nearing peak, the analog events of January 16, 2001 through February 18, 2001, and January 13, 2018 through February 2, 2018 were weighted heavily in the seasonal forecast given their strength as general analog seasons due to considerations discussed last fall, such as polar, ENSO  and solar implications. This is also why these two seasons are considered superior SSW analogs during the month of February.  Here is a list provided by Lee at al (2019) of the most prominent reflection events of the past 45 years, including the primary analogs of 2001 and 2018.

 

 

Courtesy Lee et al 2019

 

Note that the mean length of the process is 20 days, with 10 days being the minimum, and 60 days the maximum, per Lee et al (2019). The length of the 2001 (33 days) and 2018 (20) events were considered in the forecast for a reflection event to begin between approximately January 13th and 16th 2026, and end between about February 2 and 18th, which is consistent with the climatologically favored time frame per the research that was referenced previously. It is clear that this has indeed taken place given the latest feed back from Judah Cohen.

 "And as I have been routinely doing, looking at the wave diagnostics in Figure iv continues to display wave reflection over the weekend and into late January. For both periods shown, wave energy goes up and east over Asia, reflects off the stratospheric PV and then heads down and east over North America where the energy is re-absorbed and could potentially amplify the standing wave over North America and deliver cold air from the Arctic south, east of the Rockies. There is westward wave tilt with height over Asia and an eastward wave tilt with height over North America that is a classic signature of wave reflection. Though the eastward tilt is more pronounced in the first period compared to the second period".

 In order to better understand how the PV interacts with North American weather,  Lee at al identified four distinct weather regimes and listed their respective frequency of occurrence between the months of November and March, from 1979 through 2017, since they last longer than synoptic scale patterns and thus provide an opportunity for longer range prediction. 

Pacific Trough Pattern Precursor for Reflection Events

 Pattern recognition is paramount in the analysis and diagnosis of reflection events because the behavior of the polar vortex has predictive value on each of these regimes at both seasonal, and sub-seasonal leads, which is roughly 15-60 day in advance. "The PV strength significantly affects the occurrence and persistence of each regime and transition between regimes" (Lee at al 2019). Research by Kretschmer et al (2018) illustrated the importance of planetary wave reflection for anomalous cold across North America. This expounded on earlier work by Kordera et al (2016) that found that wave reflection born of Pacific blocking tele-connected to a down stream trough over North America. Thus the implication here is that the Alaskan ridge pattern, which is not at all connected to the PV and is actually accompanied by a +NAO, as alluded to earlier, is most conducive to reflection events and is this correlated to the most severe arctic outbreaks in the US. Lee et al (2019) refers to this type of pattern as the "Alaskan Ridge Regime" , which is similar to the  positive phase of the Tropical/Hemisphere Pattern (+TNH). The +TNH pattern is marked by higher heights over the Gulf of Alaska, the Gulf of Mexico and over the southeastern US and into the western Atlantic. 

 

 

 

Below average heights are normally anchored over southeastern Canada in association with a vortex buoyed between the Great Lakes and Hudson Bay, which is precisely what has taken place during the latter portion of January.

 

 

This particular pattern was cited last fall as the most common vehicle for cold delivery over the past decade given the increased tendency for +NAO during the winter season, which underscores the fact that climate change is certainly not prohibitive to severe cold outbreaks. That disclaimer certainly seems to have been validated based on the current arctic outbreak.

 

This is not at all surprising based on past +TNH episodes. 

Here is a composite of seasons that fit this +TNH description over the past decade or so.

 

 

Note the similarity to the -EPO predominate extra tropical Pacific pattern that was favored this winter season.

 

 

The implication here is that there was an increased likelihood for both anomalous cold outbreaks, and deviation from the predominate MC regime of the past decade during winter 2025-2026, which was also outlined last fall. Here are the four regimes as defined by Lee, accompanied by the spacial pattern of the temperature anomalies that accompany them.

 

 

The Pacific trough regime (31.6%) is the most frequent, followed by the Alaskan ridge pattern (25.1%). Note the strong resemblance between the Alaskan ridge pattern and the -EPO style extra tropical Pacific pattern expected to be predominate this winter season.

 

Below is the composite for the Pacific trough regime, which is akin to the extra tropical Pacific +EPO regime that was previously discussed.

 

This composite contains the Eastern Mass Weather extra tropical Pacific analogs of 1950-1951 and 2001-2002, as well as the La Nina analog of 2005-2006. Note the similarity to the mild interval during the middle portion of the month that was initially poorly modeled.

 

This portion of the seasonal forecast evolution was predicated upon research by Lee et al (2019), which identified the transition from this Pacific trough regime to the Alaskan ridge regime as most conducive to the type of wave propagation needed to trigger a reflection event. This is what renders the Pacific trough regime the precursor to the stratospheric reflection necessary to trigger the +TNH pattern that is now delivering an absolutely brutal stretch of winter to the region. This proved to be a remarkable extended forecasting tool given the expectation for a mid January onset of a reflection event that coincided with an influx of mild Pacific air.

 

 

Note that the pattern begins to reverse in earnest approximately 5 days after the event onset, which is precisely what has taken place.

 

Simultaneously, the anonymously strong PV reverts to normal strength, and begins to stretch due to the building Alaskan and Aleutian ridging that retrogrades from North America. 

 

In addition to the return to climo strength and above, the stretching of the PV during this reflection event has also been evident.

 

 

Although the pattern progression since the new year has evolved largely as expected, it is not without some unexpected twists. One notable deviation from the forecast was a return of -NAO blocking in conjunction with the development of this +TNH pattern, which occurred on the heels of the mid-month interval of +NAO that accompanied the Pacific trough-fueled thaw.

-NAO Flavored +TNH Pattern Will Bias Month Cold

It is evident in the annotation below that rather strong NAO blocking rematerialized after the milder period centered mid-month.

This is also on full-display in the monthly 500mb pattern to date, which has far more blocking within the NAO domain than expected.

 

 

This has consequently resulted in the PV being displaced slightly lower in latitude relative to the forecast, which is in large part why the month will end up somewhat colder than expected throughout the northeast (-1 to -3F Instead of +1 to +3 Forecast), despite a superb overall pattern diagnosis.

 

 

This also helped to ensure the deeply -AO that was perhaps even kore prominent in the monthly mean relative to the forecast.

 

 

Another unique flavor to this particular +TNH episode that was better foreseen in last fall's winter outlook was it's co-occurrence with predominately +PNA, which would ultimately bias the month in this fashion.

Emergence of Western CONUS Ridging Key In More Active Pattern

Guidance was originally insistent that the RNA pattern from the month of December would persist throughout the vast majority of the month of January, with the exception of a brief interval of PNA flex the second week of the month (10th-15th).

 

The above annotation ultimately proved correct in asserting that the forecast return of RNA after mid-month, as suggested by guidance, was in fact erroneous.

 

Eastern Mass Weather used history as a guide last fall in positing that the consistently negative PNA values from December would give way to a mean positive PNA in the mean during the month of January, as per the expected deviation from the cool ENSO oriented Maritime continent forcing.

December 2024-January 2025:

 

This notion was recently buttressed by data provided by Don Sutherland of Americanwx forums, which indicated that 10/10 -PNA streaks of 35 days or greater during the months of November-December since 1980, have averaged positive over the subsequent 30 day period.

 

Data Courtesy of Don Sutherland

It was posited that this represented an integral part of the forecast for the +TNH pattern that would become established during the latter half of January because the addition of a +PNA in this type of pattern would increase the likelihood of significant, and perhaps even major east coast storm, as opposed to the traditional overrunning type of precipitation events that typically rule these sort of regimes. This was evident last week, when the intense +PNA ridging was instrumental in the development of a major snowstorm across much of the northeast, despite the fact that southeast heights remained somewhat elevated.

 

The influence of the southeast heights were insufficient to preclude a major northeast snow event due to the influence of the western ridging in conjunction with the southward displaced PV, and western-biased negative NAO block acting to suppress the system enough to remain offshore. It was also suggested that the approach of the MJO to phase 7 at a relatively high amplitude It was also correctly anticipated that the trend for a more protracted period of PNA would constructively interfere and subsequently maintain a +PNA value for the duration of the month.

 

This particular convective forcing regime across the tropical Pacific indeed did indeed have this impact, despite what guidance at the time implied.

 

 

This is largely why the month ultimately ended up even wetter than forecast, despite the very dry first half.

 

 

 

Conclusions Regarding January

This behavior of the stratospheric vortex is precisely why it is very mild at the onset of these reflection events, during the antecedent Pacific trough pattern, but by ten days post reflection the pattern has reversed and is characteristic of an Alaskan ridge regime (bottom right above). Winter 2025-2026 represents a splendid illustration of why seasonal forecasting is a much more feasible endeavor when a proper diagnosis of the stratosphere is made given it's tendency to lead the configuration of the pattern on a hemispheric scale. Accordingly, it was posited just beyond mid-month that the general public was poised to learn just how costly that January thaw would be, as not only were our heating costs going to rise precipitously for the balance of January, but there also existed the potential for heavy snows. This lesson is now complete, as the region is mired in the midst of a historic and downright brutal stretch of winter that was set in motion by a sequence of events over 30 miles above the earth's surface, in the stratosphere. Indeed, this lesson can be carried forward;  as not only can an exhaustive assessment of the QBO (stratosphere) overlaid on the solar cycle yield insight as to how a mild, seemingly innocuous mid-month pattern can trigger a relentlessly punishing onslaught of winter. It was also elucidated how the current +TNH pattern punishing the eastern US is simultaneously planting the seeds to destruction for the polar vortex in February.

February 2026 Preview

Nuances Of Polar Domain Dictate Cold, Active Month On Tap

The largest threat to the February forecast issued last fall is a colder threat, due to a continued uncoupling of the troposphere from a strong stratospheric PV. 

 

This is why the -NAO was so much more prevalent during the month of January than forecast, which caused the month to verify colder in the mean, despite an otherwise accurate forecast. However, this variation did not materialize until the latter portion of January, specifically during the +TNH interval, so this has the potential to bias the month of February even colder relative to forecast than January should this persist as appears as though it may.

 

Note how large of a role this could potentially play in the month verifying colder than the forecast composite per the latest guidance, initialized very recently on January 25th.

 

Although the mean of all seasonal guidance is much more congruent with the forecast composite, the January 1 initialization of this seasonal data is unlikely to have incorporated the ongoing -NAO blocking, so it is also likely be in error for the precisely same reason.

 

This colder pattern may very well yield an active month in terms of snowfall across much of the northeast considering that the busy northern stream portrayed in the analog composite from the winter outlook does seem to maintain support from latest guidance.

 

In fact, a busy start to the month is already explicitly implied.

This is crucial because there is little doubt on the part of Eastern Mass Weather that the aforementioned colder risk to the forecast is very real given the expectation that the NAO is likely to remain negative for the vast majority of the month. This is due in large part to the continued expectation of a major polar vortex disruption by way of a split, and this is a conclusion that is only growing in confidence.

Imminent Polar Vortex Split To Protract NAO Blocking

The inference from the winter outlook last fall was that the easterly QBO would constructively interfere with the tendency for the modest, eastern biased La Niña to predispose the PV to major disruption(s) given that solar geomagnetic peak, which provides the most resistance to PV disruptions, will not be reached until roughly this summer. 

 

 

The Holton-Tan relationship, which dictates that an easterly QBO is correlated with both a greater incidence of, and an earlier development of SSW, reaffirms this conclusion 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 and 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 12, 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, which proved a valid analog for the first SSW, 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. The primary analog event of February 12, 2018 also ultimately culminated in a split of the PV, and is a member of the QBO and ENSO composite. This 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 17 to February 17 timeframe, with an increased emphasis on the latter portion of this window, which normally favors late season NAO blocking to commence roughly in early March. However, it is feasible that there may not be any lag time at all given that the antecedent conditions are consistent with both strong -AO/NAO, thus it may not need to propagate. The implication being that it may simply act to prolong the current blocking regime through the balance of February. 

Here is a look at latest guidance.

 

 

 

Note that the favored window is between February 10th and 17th, which is confident with the latter portion of the January 17th tp February 17th window emphasized last fall. Although an official SSW via zonal wind reversal is not yet indicated, guidance is still likely adjusting, as both the behavior of the stratosphere , as well as the struggle that modeling would have with it were anticipated. The fact that a strong PV was modeled through February as recently as January 8th is illustrative of this.

 

In addition to the decided trends amongst current guidance, both the development of the forecast +TNH interval, as well as the recent behavior of the MJO also act to bolster confidence. 

Precursor Patterns Bolster Confidence in Major February PV Disruption

The recent high amplitude of the phase MJO wave in phase 7 was cited earlier as a harbinger of the +PNA interval that ensured earlier this month, despite guidance to the contrary. This behavior of the MJO is also predictive with respect to the stratosphere. According to recent research, amplified activity in the MJO in phase 7 has been linked to the occurrence of a SSW during the 12 days later (Garfinakel et al 2012). Garfinkel et al elucidate that "the MJO can affect the stratospheric polar vortex by modulating the vertical coupling of the mid-latitude planetary waves". 

 

Note that the modeled behavior of the MJO has it exiting phase 7 today, which corresponds to a SSW approximately February 9th, also with the the latter portion of the 1/17 to 2/17 timeframe and just one day prior to the window reflected on the previously referenced European ensemble plot. Furthermore, Baldwin er al 2020 found that there two precursor patterns that precede the wave absorption needed to trigger a SSW approximately 12 days later. it just so happens that the current +TNH pattern bares a an absolutely uncanny resemblance the wave 2 pattern identified by Baldwin, et al.

 

 

This would also imply a SSW on or around February 9th given that pattern remains in place. The operational European and GFS guidance support a split slightly earlier than this, by the 5th and 7th, respectively, thus it is prudent to assume that a SSW and accompanying split of the PV will ensue between February 5th and 17th.

 

This is likely will protract the high latitude blocking into at least the early portion of March. This implies an active fish to winter, however, this is conditional on the persistence of the blocking pattern within the polar domain because contrary to what some within the weather circles are intimating, the influence of La Niña is alive and well, albeit waning.

Extratropical Pacific To End Up Redolent Of Canonical La Nina

La Niña is undoubtedly weakening, as ENSO is climatologically predisposition to do at this juncture of the season. The lates weekly reading within region 3.4 is up to -0.3 as of January 24th. 

 

 

The ONI was a marginal -0.5 as of the OND tri-monthly reading and may very well fall below the La Niña threshold when the DJF value is released. This is evident by the infiltration of warmth within the ENSO subsurface.

 

However, there is a reason that the ONI value is calculated on a tri-monthly basis, as there is a lag due to the fact that there is no metaphorical "switch" in the atmosphere. It is a deliberate process for these changes to couple with the atmosphere and manifest throughout the hemisphere, especially given the perpetual state of cool ENSO that has been so prevalent of the better part of a decade.

 

This point is underscored by the fact that the Angular Atmospheric Momentum, which is a measure of the earth's circulation patterns, is modeled to remain indicative of La Niña into the month March.

 

Additionally, the -.92 RONI value as of the OND try-monthl period was still dropping and while that may be unlikely to continue, it does reaffirm that the fact that La Niña is still very evident when normalizing for climate change. The is supported by the fact that the MEI remained -0.8 as of the ND bi-monthly period, and while it is weakening, it is likely to remain in at least marginally indicative of La Niña through February. The point is that there is absolutely no indication that a decade's worth of angular momentum throughout the hemisphere is going to abate simply because the weekly value of region 3.4 is dropped below the -0.5 threshold. Why this concept is lost on so many skilled hobbyists and professionals alike is a question only those individuals can answer. That being said, here is a composite of the month of February for the weak La Niña dataset.

 

What is apparent is that the Pacific grows more hostile to winter enthusiasts, while the opportunity for high latitude blocking remains given the right circumstances, which seem to be in place this year as elucidated. Current guidance also is consistent with the development of a -PNA pattern, as the poleward Aleutian ridging wanes, as indicated last fall.

 

 

 

Needless to say, blocking within the polar domain will need to persist as is expected, or else an early spring may very well ensue.