Winter Outlook 2024-2025

[40/70 Benchmark]

Just realized I never threaded this in the NE subforum, which I usually do....I prefer to update in here, rather than the main forum.

 

https://easternmassweather.blogspot.com/2024/11/using-past-forecasting-difficulty-to.html

 

 

 

 

 

 

[Typhoon Tip]

4 hours ago, 40/70 Benchmark said:

Just realized I never threaded this in the NE subforum, which I usually do....I prefer to update in here, rather than the main forum.

 

https://easternmassweather.blogspot.com/2024/11/using-past-forecasting-difficulty-to.html

 

seems unlikely to me that a wpo/epo mean < 0 ...even if only between 0 and -1, would lend to that temperature distribution, at least along the np-lakes-ne belt but maybe some cc urine in the punch

[40/70 Benchmark]

3 hours ago, Typhoon Tip said:

seems unlikely to me that a wpo/epo mean < 0 ...even if only between 0 and -1, would lend to that temperature distribution, at least along the np-lakes-ne belt but maybe some cc urine in the punch

Just WPO....went +EPO.

[ineedsnow]

hopefully we can cash in here this year.. 

[Jebman]

How do you all do in cold neutral winters? You sure got the MOISTURE this year, you have gotten over 40 inches of rain so far in 2024.

[tamarack]

10 hours ago, Jebman said:

How do you all do in cold neutral winters? You sure got the MOISTURE this year, you have gotten over 40 inches of rain so far in 2024.

But very little since late August - many wildfires in the Northeast above Mason-Dixon.

[Typhoon Tip]

19 hours ago, 40/70 Benchmark said:

Just WPO....went +EPO.

that's fun.   the wpo and epo are  +.2 correlated in dec and jan.  it gets noisier in february, which is rather counter intuitive because that's about the time when the pattern is most seasonally coherent but whatever.  .2 is a fairly high correlation coefficient, meaning that perhaps a 2 in 10 times, the wpo and epo are the same.    

some may read that and think, 'yeah, well then 8 in 10 times they're not'  - but that's not right.  the remaining 8 times are actually no skill. meaning the correlation is all over the place.   the other problem with the correlations is that they are linear.  that doesn't factor in time, that evil actuator of all events.   the natural progress of events in the atmosphere is west --> east, barring any exceptionally rare hyper retrograding things.   index domain spaces will tend to migrate east...  in other words, there's a time lag that 'hides' some of the correlation of the wpo to the epo.   that .2 is likely higher when time lags are applied.   that's probably all i had to say haha

anyway, this does leave room for -wpo/+epo  but that's an unstable scalar state that is proooobably in a state of change whenever it is observed.        

[SJonesWX]

18 hours ago, Jebman said:

How do you all do in cold neutral winters? You sure got the MOISTURE this year, you have gotten over 40 inches of rain so far in 2024.

Beer?

[40/70 Benchmark]

10 hours ago, Typhoon Tip said:

that's fun.   the wpo and epo are  +.2 correlated in dec and jan.  it gets noisier in february, which is rather counter intuitive because that's about the time when the pattern is most seasonally coherent but whatever.  .2 is a fairly high correlation coefficient, meaning that perhaps a 2 in 10 times, the wpo and epo are the same.    

some may read that and think, 'yeah, well then 8 in 10 times they're not'  - but that's not right.  the remaining 8 times are actually no skill. meaning the correlation is all over the place.   the other problem with the correlations is that they are linear.  that doesn't factor in time, that evil actuator of all events.   the natural progress of events in the atmosphere is west --> east, barring any exceptionally rare hyper retrograding things.   index domain spaces will tend to migrate east...  in other words, there's a time lag that 'hides' some of the correlation of the wpo to the epo.   that .2 is likely higher when time lags are applied.   that's probably all i had to say haha

anyway, this does leave room for -wpo/+epo  but that's an unstable scalar state that is proooobably in a state of change whenever it is observed.        

Well, that state was very prevalent in my extra tropical Pacific analogs. Not anything extreme...I think I went .30 to .60 JM WPO.

[40/70 Benchmark]

 

December Appears Poised To Evolve Colder Than Anticipated

"La Niño"Pattern To Drive Cold Regime Into Mid Month

Recent Corrections Amongst Guidance

There has been a major shift amongst seasonal guidance over the course of the past ten days towards a colder month of December than originally anticipated. Here is the CFS forecast monthly 500mb and temperature departure anomalies for the month of December issued on November 16th.

 

This pattern shown is reflective of a -WPO/-PNA configuration given the warmth over the eastern and southwestern US, as outlined in the Eastern Mass Weather Winter Outlook. 

 

 

However, there have been incremental adjustments over the course of the latter half of November that have culminated in this most recent run of the CFS forecast for the month of December.

 

This new forecast is still indicative of a negative phase of the WPO given the continued warmth over the southwestern third of the US in response to the above average heights in the vicinity of the Bering Sea. However, the marked change towards lower heights and colder temperatures over the east and southeastern third of the nation is representative of a +PNA, which is a significant departure from the previously advertised -PNA (RNA).

 

 

This is obviously both unexpected and uncharacteristic of a burgeoning cool ENSO event, and in fact, it is more representative of the type of regime expected during a warm ENSO event.

Growth of La Nina Interrupted by Hostile Zonal Wind Pattern

The anomaly in region 3.4 as of October 23 was -0.5C and all indications were that at least a modest La Niña was developing. However, as of November 20, the anomaly has warmed to -0.1 This is due to the fact that the zonal wind pattern across the tropical Pacific throughout the month of November has been largely devoid of the easterly trade winds necessary to upwell the subsurface cold pool, and thus sustain the growth of La Niña. Note the stark contrast in the zonal wind anomalies during the month of November to the composite of those preceding the past five cool ENSO events.

 

 

Perhaps the most telling sign of the growing tropical discontinuity is the fact that this past month of November featured one of the most powerful westerly wind bursts on record for the month of November.

 

Note that 5/6 seasons in the above annotation are El Niño, and 4/6 are very powerful warm ENSO events at that. Interestingly enough, the sole cool ENSO season of 1998 also took place on the heels of a potent El Niño and on the cusp of a longer term, multi-decadal shift in the PDO. It is no surprise that the 850mb zonal wind composite of these months of November is much more redolent of November 2024 than the recent cool ENSO composite.

 

Both this growing discontinuity throughout the tropics, as well as last year's potent El Niño within the secondary nadir of a prominent Pacific Cold phase are signs that a major shift in the multi-decadal phase of the PDO maybe imminent. 

 

While this is unlikely to have major ramifications for the coming winter, the ongoing tropical deviation from the cool ENSO regime that has been so prevalent for the past decade most certainly will, for at least the first half of the December, anyway.

December 2024 Preview

Perhaps the purest manifestation of this unexpected and historic westerly wind burst during the month of December is with respect to the Global Angular Atmospheric Momentum, which continues to be positive and more indicative of a warm ENSO event than an incipient La Niña. 

 

This is likely the primary reason why this deviation from the Maritime Continent forcing, which was expected to take place in January per the Eastern Mass Weather Winter Outlook, has taken place earlier than expected and appears rather stable. Note the persistence of this -WPO/-EPO/+PNA paradigm throughout the first half of December.

 

 

 

While the MJO has not been a major influence on the pattern of late due to the overwhelming +atmospheric momentum, it may represent a subtle constructive interference with the ongoing regime early on in December with its passage though phase 5.

 

 

Regardless, the early month pattern is of high confidence with multi-ensemble suite consensus.

 

 

There is also strong agreement that this pattern will remain in place until at least the end of the second week of the December.

 

 

 

However, mid month is when the plot thickens, so to speak, as there are mixed signals abound. The trade winds are forecast to reinvigorate, as the atmosphere makes one final attempt to ignite La Niña.

 

 

This late reinvigoration of a modest La Niña is similar to November 2008, when the region 3.4 anomaly warmed from -0.5C on October 1 to -0.1C on November 5th. Note the similarity in the modest subsurface cold pools below region 3.4.

 

 

Concurrent with the expected resurgence of La Niña mid month is the potential propagation of the MJO into phase 6, which features an Aleutian ridge oriented, RNA pattern that is much more reminiscent of cool ENSO.

 

 

The caveat being the issue of whether the MJO wave will make it into phase 6 with a enough amplitude to over power the residual, waning positive atmospheric momentum, as guidance indicates that the MJO impulse may decay before reaching phase 6. 

 

 

 

The early December 2010 is a prime example of a meager Maritime Continent wave being insufficient to de-constructively interfere with ample antecedent positive global angular momentum.

 

 

However, even the latter portion of December 2010 featured a return to an RNA pattern and the ensuing resurgence of the moribund La Niña should ensure a similar occurrence this month before another potential deviation beyond the new year.

 

 

In the mean time, a few higher terrain locales may experience a sneak preview of winter on Thanksgiving day, with perhaps up to 1-3" in the highest terrain of the Worcester hills and up to 2-5" in the Berkshires for a transition to rain. 

 

 

Thereafter, the region awaits the first potential major and widespread wintry threat along or about December 7th.

 

 

[40/70 Benchmark]

Festive Winter Preview on Tap for Some Areas Early Thursday

Plan to Allow Extra Time for Thursday AM Commute

A weak system will provide much of the region with a winter preview on Thursday morning, and while accumulating snowfall will primarily be confined to the higher terrain and deep interior, even the Boston metro area may see some snow flakes mixing in with the rain during the morning commute. Thus while this system is not anticipated to be a major event, it remains worthy of ample consideration due to both the time of impact and the reality that the vast majority of the region has yet to record measurable snowfall this season.

Synoptic Overview:

A weak lobe is poised to separate from the polar vortex during the day today, as a ridge simultaneously begins to amplify along the west coast.

 

 

The ridge out west will continue to amplify as the PV lobe continues its descent SSE into the US.

 

 

The amplification of the upstream ridge will allow the system to continue to grow more cohesive throughout the day on Wednesday as it approaches the Great Lakes.

 

 

And subsequently moves into New York State on Thursday, at which point precipitation will overspread much of New England.

 

 

Although the system will encounter an arctic airmass over the region, its track through northern New England will allow weak southerly inflow to scour out enough of the cold to ensure primarily rainfall over the coastal plain.

 

 

However, the higher terrain is likely to see its first plowable snowfall, while all of the interior records its first measurable snowfall. This evolution is expected to complicate the Thursday morning commute at least to some degree.

 

Anticipated Storm Evolution

Light snow showers over the interior and rain showers near the coast should overspread the region by midnight late Wednesday evening.

 

Precipitation will become steadier during the predawn hours, as rainfall roughly inside of 128 and mixed precipitation within the 128/495 belt. Primarily snowfall will be the rule near I-495 and beyond.

 

Precipitation may end as a brief burst of more moderate snowfall closer to the coast during the Thursday morning commute prior to tapering off an ending by late morning.

 

 

First & Final Call:

[H2Otown_WX]

On 11/15/2024 at 6:56 PM, 40/70 Benchmark said:

Just WPO....went +EPO.

OT but every time I look at your avatar I throw up in my mouth a little. That's Jan 2015 right?

[Go Kart Mozart]

2 hours ago, H2Otown_WX said:

OT but every time I look at your avatar I throw up in my mouth a little. That's Jan 2015 right?

Is it 1969?

[40/70 Benchmark]

2 hours ago, H2Otown_WX said:

OT but every time I look at your avatar I throw up in my mouth a little. That's Jan 2015 right?

Yea

[H2Otown_WX]

1 hour ago, 40/70 Benchmark said:

Yea

That's my all-time melt and the end of my potential forecasting career lol...how much did you get? 28"?

[40/70 Benchmark]

8 hours ago, H2Otown_WX said:

That's my all-time melt and the end of my potential forecasting career lol...how much did you get? 28"?

I think like 25"......jack was like 10mi nw of me, where Lowell and Westford area had like 3'.

I was all over that closing off later than guidance indicated. I remember I went into the NYC thread and said that after that run giving them like 3', but it wasn't well received...go figure.

[40/70 Benchmark]

On 12/3/2024 at 1:47 PM, 40/70 Benchmark said:

 

Festive Winter Preview on Tap for Some Areas Early Thursday

Plan to Allow Extra Time for Thursday AM Commute

A weak system will provide much of the region with a winter preview on Thursday morning, and while accumulating snowfall will primarily be confined to the higher terrain and deep interior, even the Boston metro area may see some snow flakes mixing in with the rain during the morning commute. Thus while this system is not anticipated to be a major event, it remains worthy of ample consideration due to both the time of impact and the reality that the vast majority of the region has yet to record measurable snowfall this season.

Synoptic Overview:

A weak lobe is poised to separate from the polar vortex during the day today, as a ridge simultaneously begins to amplify along the west coast.

 

 

The ridge out west will continue to amplify as the PV lobe continues its descent SSE into the US.

 

 

The amplification of the upstream ridge will allow the system to continue to grow more cohesive throughout the day on Wednesday as it approaches the Great Lakes.

 

 

And subsequently moves into New York State on Thursday, at which point precipitation will overspread much of New England.

 

 

Although the system will encounter an arctic airmass over the region, its track through northern New England will allow weak southerly inflow to scour out enough of the cold to ensure primarily rainfall over the coastal plain.

 

 

However, the higher terrain is likely to see its first plowable snowfall, while all of the interior records its first measurable snowfall. This evolution is expected to complicate the Thursday morning commute at least to some degree.

 

Anticipated Storm Evolution

Light snow showers over the interior and rain showers near the coast should overspread the region by midnight late Wednesday evening.

 

Precipitation will become steadier during the predawn hours, as rainfall roughly inside of 128 and mixed precipitation within the 128/495 belt. Primarily snowfall will be the rule near I-495 and beyond.

 

Precipitation may end as a brief burst of more moderate snowfall closer to the coast during the Thursday morning commute prior to tapering off an ending by late morning.

 

 

First & Final Call:

Gonna update this map slightly tonight because I acidentally omittted the 4"+ area in the NW CT hills and southern Berks.

[40/70 Benchmark]

Poorly Thursday AM Snowfall Over Higher Terrain

Lower Elevations More According to Plan

The forecast for the storm system that concluded late this morning was greatly flawed, as the system amplified slightly more than forecast, which allowed it to dig further to the south. While this did not have drastic implications across the lower terrain and valley floors, it clearly made a significant difference across the higher elevations.

 

 

Note the disparity with respect to the degree of forecast success over the higher terrain versus the lower terrain.

 

 

Given how marginal the thermal field was, a slightly more intense system coupled with a further south track was enough to turn a forecast for a light to moderate snowfall into a moderate to heavy snowfall in the hills. The forecast across the lower terrain, as mentioned, was not impacted and verified well. However, the 3-6" range predicted for the northern Worcester Hills and Berkshires would have been more representative of reality had it been 4-8", and extended southward into the hills of northeastern Connecticut. The forecast also would have been better served to have a 5-10" range over the Berkshires.

 

Final Grade: D

[40/70 Benchmark]

Much Milder Balance of December Before Potential Holiday Week Changes

Winter 2024-2025 Thoughts on Track

Warmer December Transition Marked by Light Weekend Snows

It was conveyed in last month's Winter Outlook that the cold start to the month of December would likely be on borrowed time.

"The colder pattern looks to be fleeting, as the month of December should turn very mild in short order with the passage of the MJO in phase 4. The mild regime should remain in place until at the very least mid month". 

 

While this concept does indeed still look to be valid, it will be a round of light snowfall that will actually herald in this transition to the warmer regime, as an added twist of irony. Snow will be of the nuisance variety with the potential for an inch to two of snowfall in the Worcester hills, and up to perhaps as much as 3" in the Berkshires.

 

Accumulations across the rest of the region should be relegated to an inch or less, and any snow will melt quickly, thereafter given the imminent pattern change. The aforementioned light snowfall is obviously inconsequential as it pertains to longer term ramifications for the month of December and onward towards the New Year.

 

Balance of December Update

Although variability was anticipated to be the theme of December, the magnitude and length of the warmer interlude that will extend well beyond mid month was expected to outweigh the cold start, and that is precisely how the month appears to be evolving. Notice that December 1999, one of the milder members of the December forecast composite, is being reflected in the CPC forecast centered on December 14.

 

 

 

This warmer shift, as earlier implied, is triggered at least in part by the translation of the MJO wave through phase 5 in the Maritime continent.

 

 

These changes are reflected most prominently by the erosion of the North Pacific block, as evidenced by the precipitous and sudden rise in both the West Pacific and East Pacific Oscillation.

 

 

It is also evinced by the recovery of the polar domain.

 

 

As one would expect, this much mass flux will be accompanied by a significant storm system on Tuesday, however, it will be essentially all rainfall throughout southern New England with some snowfall possible across the ski resorts of northern New England.

 

 

 

Thereafter, warmth should continue to prevail across much of the country through the holiday week, as the MJO eventually enters phase 6.

 

 

 

What happens towards the end of the holiday week and in the vicinity of the New Year is what is somewhat more nebulous.

New Pattern for New Year Possible

The GFS suite continues to indicate that the MJO will advance into phase 7 prior to the New Year.

However, other guidance hints of the possible decay of the MJO wave prior to reaching phase 7.

 

 

This is crucial since phase 7 of the MJO in early January would imply a major transition to a colder pattern, marked by the redevelopment of poleward north Pacific ridging.

 

 

Most long range guidance supports the aforementioned redevelopment of poleward ridging over the North Pacific and adjacent west coast, in conjunction with a strong polar vortex that is tilted favorably as to allow for the delivery of cold air over the northeastern US.

 

 

This is a scenario that is very similar to the type of mismatch from the predominate MC forcing that took place in January 2022, which was cited in the Winter Outlook is a strong analog for January 2025. 

 

 

Note the similarity to the forecast progression of the MJO to its behavior from December 2021 into January 2022, implying a generally similar evolution, albeit potentially delayed and somewhat subdued.

 

 

In conclusion, although the progression of the MJO wave into phase 7 for the onset of January may be slightly rushed on the GFS suite of guidance, it is unlikely to stagnate in the MC and should indeed reach the West Pacific and trigger a colder pattern beyond the new year. 

[Prismshine Productions]

+WPO/+EPO/+AO/+NAO...

The Four Horsemen of Shitty Winter at the same time, oof...

Sent from my SM-S146VL using Tapatalk

[40/70 Benchmark]

 

Pre-Christmas Winter Storm Possible Next Weekend 

Holiday Travel Contingencies Should Be Considered 

Warm ENSO Flavor to Month of December Continues

Despite both the Relative Ocean Nino Index (-.80 SON)  and the Multivariate ENSO Index (ON) both being indicative of a meager La Niña event, the month of December has featured a notable departure from the type of pattern normally associated with cold ENSO.  Although inconsistencies of this nature are much more common in weaker ENSO events,  the deviation during this month of December has been much more prominent than one would expect.

Here is the prototypical La Niña pattern:

 

 

  

 

 Note the prevalent ridge south of the Aleutians, which tele connects to the downstream trough over the west in what is known as the RNA (-PNA)  pattern. However, the mean pattern this month has been essentially the opposite, with an Aleutian low that is very redolent of the baseline El Nino pattern.

 

 

 

This type of pattern is much more conductive to east coast winter storms during the winter season, and with winter set to begin this weekend, the atmosphere looks as though it just may oblige during the peak of pre-Christmas roadway roadway congestion.

 

High Volume of Holiday Road Traffic Potentially Impacted by Weather

The combination of the MJO entering phase 6 and the continuation of a surplus of Angular Atmospheric Momentum will ensure that the aforementioned El Niño like deviation to the pattern will continue throughout the upcoming week and into the weekend. 

 

 

 There is now strong cross-ensemble suite support that this will lead to the amplification of a northern stream shortwave courtesy of a deep eastern northeastern trough, at the precise time that pre-holiday roadway congestion is anticipated to peak this weekend.

 

 

While significant snowfall, or even a storm, is far from a certainty, what is a certainty is that area roadways are going to begin to look a lot more like Christmas this weekend. Thus it is advised that travelers have contingencies in place in the event that the weather follows suite.

More to come this week-

 

 

[weatherwiz]

I am hoping to get to read this today. Want to read it on a day when I can read it and digest all of it without distractions. 

[40/70 Benchmark]

Festive Lights Snows Possible Leading into the Holiday

Focus Overnight Friday and Perhaps Christmas Holiday

The prospect for a White Christmas continues to relatively bleak for the majority of the region, however, there is a relatively strong likelihood of some areas receiving a light snowfall over the next several days, This first such opportunity will present itself overnight Friday into early Saturday morning, which is the timeframe that was initially introduced last Saturday. 

The overall long wave pattern, as initially outlined last weekend, is fairly conductive to a significant winter storm along the northeast US coast. In fact, there is a chance that a period of light snow will engulf a portion of the area on Friday evening as the low pressure area is in its incipient stages.

 

 

 

 However, what has become apparent over the course of this week is that there will be a lead piece of energy that will prevent the trailing wave from amplifying fast enough to provide a major storm system for the forecast area.

 

 

This mitigating factor is exacerbated the by fact that the MJO is just now beginning to emerge from phase 5.

This also acts to inhibit trough amplification on the east coast.

 

 

The end result is thus a retardation of the evolution of this system, which does not begin to coalesce with the lead energy until the predawn hours of Saturday, when it is ready to exit area.

 

 

 

This causes the precipitation shield to remain light and recede rapidly towards midnight on Friday and into early Saturday morning, effectively ending the event before it can provide most locales with an appreciable chance of a White Christmas. 

 

 

However, there is a subtle suggestion that all hope may not be lost courtesy of a meager piece of energy on Christmas itself.

 

 

Be that as it may, odds of catching a glimpse off Santa twerking down the chimney maybe slightly more robust than those of a white Christmas for the vast majority of the area.

 

Extended Range Preview for Balance of 2024

Beyond the Christmas holiday and towards the New Year, there are signs that the anticipated warm up will be muted to some extend by the emergent agreement that the apex of the ridge node will maneuver into Canada an the Davis Straight.

 

This would act to trap modified polar air beneath the block and potentially force any storm systems further to the south, which could introduce some wintry precipitation chances across at least a portion of the area.

[40/70 Benchmark]

 

Verification of Friday Snows 

Poorly Prepared Forecast Missed Heavier Coastal Band

The clipper system that moved through during the day on Friday proved to be quite the challenge for forecast guidance, as there were uncharacteristically large shifts until essentially the snow actually began to fall. There were two main aspects that guidance struggled to grasp:

1) Just how close the developing coastal system would track to the coast and just how fast it would develop. This obviously had large ramifications with respect to how far inland the burgeoning precipitation shield would make it and how intense it would be.

2) The precise placement of an ocean enhanced band of snowfall that was triggered by an onshore fetch out ahead of the storm system itself.

Obviously a capricious forecast of this nature with mesoscale features such as ocean enhanced snowfall required immense attention to detail until the final moment, which is a commitment that this writer was ill prepared to make with the holidays fast approaching and the assumed paltry magnitude of the approaching system. Thus there was never a Final update issued as is usually the case, which likely would have at least somewhat reflected of a track slightly closer to the coast, along with the potential for more moderate snowfall within the ocean enhanced snow near the coast. The implication of this is that the issued forecast missed the 1-3" of snowfall that fell over cape cod and the islands, as well as extreme southeastern Massachusetts due to the slightly closer track and faster development of the storm, which maintained enough lift to transition rainfall to snow before exiting. The forecast also failed to account for the 3-6"+ of snowfall that fell within the coastal band, which something that guidance began to signal Thursday night and Friday morning, albeit struggling with its placement. 

 

 

The forecast clearly lacked the nuanced detail that was required given the mesoscale nature of the snowfall near the coast, however, snowfall amounts were fairly well forecast over the majority of the area. The forecast would clearly have been better served to have been updated to reflect a band of 3-6"+ along the immediate north shore and into the Boston area, as well as a 1-3" area over the cape and islands.

 

Final Grade: D

 

 

[40/70 Benchmark]

 

Much Colder Than Forecast December Potential Prelude to Wintry January 

Brief New Year Relaxation Followed by Return of Winter with Vengeance

December 2024 Recap

Snowfall was not expected to be abundant during the month of December, so it comes as no surprise that it was in fact below normal across the vast majority of the region. However, that is about where the similarities between the December forecast and the actual sensible weather end. 

Here is a juxtaposition of the forecast temperature departures across the CONUS in degrees F for the month of December with the actual anomalies.

 

Cleary the forecast for the month of December went awry and any accuracy with respect to regional snowfall was largely a coincidence. The expectation was for a predominately -PNA and a variable to perhaps modestly negative NAO in the mean, but what actually verified was an extremely positive PNA along with a positive NAO.

 

 

AO Has Been Near Neutral

This represents a more protracted early to mid winter deviation from the prominent MC forcing of the modern era along the lines of the 2017 mismatch period considered in the Winter Outlook.

It was intimated that his was likely to occur approximately one month ago, when it became apparent that there would be a delay in the development of La Niña.

 

When La Niña is Away (Delayed) The Aleutian Low Will Play

The seeds of the December forecast demise were indeed planted during the month of November, when a very pronounced westerly wind burst (WWB) throughout the tropical Pacific halted the development of La Niña, and allowed for an episode of Positive Global Absolute Angular Momentum during the month of December that was more protracted than expected. 

 

 

Since positive GLAAM is indicative of an atmosphere that is generally redolent of El Niño, and negative GLAAM La Niña, this likely contributed to the development of an Aleutian low in the December monthly mean as opposed to the Aleutian ridge evident in the forecast composite. 

 

 

This Aleutian low enabled the potent PNA ridge to sustain in the monthly mean, which of course promotes lower heights and thus colder temperatures downstream over the eastern US despite the passage of the MJO through the Maritime Continent. However, the journey of the MJO through phases 5 and 6 for the vast majority of the month of December may have played a role in the maintenance of a predominately positive monthly NAO, which likely limited regional snowfall. 

 

Be that as it may, it appears likely that the MJO will begin to constructively interfere with the prospects for more severe winter weather along the east coast early on in the New Year. Ironically enough, these are prospects that are actually augmented by the much anticipated emergence of La Nina.

 

East Coast Winter Weather Prospects Bolstered by Reemergence of La Niña

Clearly the reports of the failure of La Niña to materialize that ran rampant throughout the forecasting industry were premature, as asserted by Eastern Mass Weather throughout the fall and into the early winter season. 

 

 

Indeed, the parallels drawn between the late-blooming cool ENSO event of 2008 and the current one in terms of both the subsurface, as well as the December easterly trade surge have proven valid. Note the parallels in the late recovery of each event during the month of December.

                            Region

Date                   1.2          3               3.4             4

04DEC2024     0.1     -0.4     -0.3     -0.2
11DEC2024     -0.2    -0.4     -0.6     -0.3
18DEC2024     -0.2    -0.5     -0.8     -0.4

03DEC2008     -0.6    -0.4     -0.6     -0.8
10DEC2008     -0.3    -0.6     -0.8     -0.7
17DEC2008     -0.2    -0.7     -0.8     -0.8
24DEC2008     -0.3    -0.8     -1.0     -0.9

This may lead some forecasters astray in that they are likely to rush the return to an RNA
 style pattern during the month of January, however, this is a case in which the recent strengthening
 of La Niña in conjunction with the passage of the MJO into phases 7, 8 and 1 is likely to constructively
 interfere with its maintenance.  This is congruent with the paradoxical positive correlation between
 the intensity of ENSO and the incidence/extent of deviation from MC forcing detailed in the Winter Outlook.

 

The first significant winter storm threat after the colder transition during the first week of
 the New Year looks to take place on about January 7.

 

This immensely ominous signature during the second week of the month is very well supported by long
 range guidance and is slightly earlier than the January 21-February 4 period identified in the
 seasonal outlook as being conductive to a potential KU event.

       EPS                                                          GEFS                                                    GEPS

 

Confidence is further increased by modularity in the vicinity of said date in a show of tele connector convergence. Note varying degrees of recovery of the -WPO/EPO/NAO/AO, as well as the +PNA that herald in a potentially intense bout of cold beforehand.

 

Thereafter, as intimated by the aforementioned mass fields, the GLAAM is likely to finally respond to the late-developing La Niña mid-month, which should ultimately contribute to the return to an RNA pattern in compunction with the approach of the MJO to phase 3.

The precise timing of this transition will obviously impact monthly verification, but as it stands currently, the only significant potential deviation with respect to January from the seasonal outlook published in November is the NAO domain.
 

This would pose yet another cold risk relative to the forecast, as the intensity of the cold anomalies would be increased, and they would extend further to the south than originally anticipated.

 

However, the January portion of last fall's outlook appears largely on track, as the MJO is indeed progressing into phase 7 by the New Year as advertised, despite conflicting forecast data. More importantly, this progression is very comparable to the primary analog of 2021-2022.

Thus while the mismatch period from the MC forcing that has been so prevalent for the better portion of the last decade has been more protracted than that which occurred during the 2021-2022 analog, the January portion of said period still looks to evolve in a similar manner even if perhaps featuring a greater degree of polar blocking.