BTW, its still very active per ACE...bit of a misconception in relation to that.

2024 Accumulated Cyclone Energy [ACE]

*Yearly climatology from historical 1991-2020 Tropical cyclone best track datasets

2 minutes ago, LibertyBell said:

hmm I wonder if that means that if we see a lot of tropical activity in October that's a good sign for winter?

I think a big ACE value correlated to more poleward Aleutian ridging.

Just now, LibertyBell said:

bookend winter perhaps Ray?

I think the only wild card for mid season is Bluewave's October MJO rule...if the MJO isn't amplifed in October, then we roast mid winter.

3 minutes ago, LibertyBell said:

Early winter might be cold (it's already turning cooler and feels like Fall), but it will also probably end after Mid January.  Most of our snow will likely be in December and part of January

Looks like the tropical season won't live up to expectations-- I never thought this was going to be some historic 2005/2020 repeat.

 

I think the early season will be more Pacfic driven..ie Aleutian ridging and -EPO/WPO, though the PV shouldn't be too stout....then mid season it goes very warm with less of an RNA before perhaps blocking/big RNA late season.

11 minutes ago, Damage In Tolland said:

I envision a weenie like object this fall but right into my tukis instead of my mouth

Shake it up

7 minutes ago, GaWx said:

What do you mean by “a bit more aggressive”?

Colder relative to what many susepect.

I feel like there have been some low key hints that raindance is going to be a bit more aggressive for the east than some may suspect.

1 hour ago, CoastalWx said:

Maybe we can get some late season home brew in October/early November. That would be fun with the timing of troughs getting deeper as we head into the cold season.

I feel like we could see a Michael redux this fall.

Preliminary Assessment of the Extra Tropical Pacific for Winter 2024-2025

Mutually Reenforcing Cool ENSO & Pacific Cold Phase

ENSO & North Pacific are In Sync

 

 

In fact, the statistical guidance continues to suggest an ENSO neutral season with a forecast peak DJF peak of -.29  DJF. This is likely to a large degree a reflection of the of the fact that the current 0.2 MJJ ONI value would mark the second greatest of any developing La Nina on record. Only the 1983 La Nina was preceded by a greater MJJ ONI value of 0.7 and that particular La Nina event peaked at -1.0. While this renders a peak ONI value of anything lower than approximately -1.0 exceedingly unlikely given that such an occurrence following a MJJ ONI this high is unprecedented, a weak event is still very feasible. In fact, given the state of the Pacific basin, La Niña is still expected to materialize and couple with the atmosphere to a degree commensurate with a moderate event. This is evinced by a JJ MEI value that is already nearing moderate La Nina intensity at -.07 and is comparable to other moderate to strong La Nina events at this time of the year, such as 1999, 2011 and 2022. 

 

Note that the aforementioned seasons reached peak MEI values of -1.4, -1.3 and -1.7 respectively and are reasonable analogs with regard to the ultimate peak MEI value of this particular La Niña event. The peak Relative Ocean Nino Index (RONI) of the three seasons was comparable, having reached -1.67 in 1999, 1.05 in 2011 and -1.08 in 2022. Thus the 2008 analog represents a viable floor for the peak intensity of this particular La Niña episode in that it remained weak per ONI (-0.8) and near the threshold of weak-moderate in terms of its imprint on the hemisphere, as depicted by the -1.1 peak MEI value and -.90 RONI. The year 1996 and its -0.8 JJ MEI value from the above analog graphic is a sound illustration of the scenario favored by statistical guidance in that it remained a cool ENSO neutral season as opposed to a full-fledged La Niña event. However, this is not considered to be viable a possibility because it occurred during a time when the extra tropical Pacific was incongruent with the tropical Pacific and this is something that statistical guidance does not consider. The contrast is evident with even a cursory analysis of the subsurface plots.

Here is a plot from August 1996, which featured roughly -1C anomalies beneath the surface:

 

 

Versus anomalies of around -3C and -2C in August 2022 and 2008:

 

 

The current subsurface plot represents a compromise between the more robust 2022 La Niña and the more modest 2008 event:

 

 

 

 

 Having the ENSO regions in conflict with the north Pacific acts to impede the ability of ENSO to impress on the hemisphere, whereas this year the opposite is the case.

 

Extra Tropical Pacific will Enhance La Niña During 2024-2025

The behavior of the extra tropical pacific is usually relatively predictable during a well coupled cool ENSO event such as the present one and vice versa. Intense negative PDO episodes are usually accompanied by La Nina because the two share a symbiotic, mutually reenforcing and sustaining relationship. La Nina represents the cold phase of ENSO and cooler waters present during episodes of La Nina such as the one observed this season tend to be generally supportive of a negative phase of the Pacific Decadal Oscillation (PDO), which are marked by cooler waters along the west coast of the US.This is because la Nina favors Aleutian ridging, as identified in the la Nina composite below:

 

This season will be no different in that respect, as the PDO value for the month of July was -2.97 and it will once again average decidedly negative for the DM period. In fact, July 1894 (-2.98) is the only year in recorded history with a lower PDO value for the month of July. This immensely intense cold phase of the extra tropical Pacific will accentuate the relatively modest developing cold phase ENSO, as they are harmonious.This is very evident when considering the resultant 500mb pattern this past summer. The ONI has been reflective of ENSO neutral conditions, yet the pattern was reminiscent of a robust la Nina season with powerful ridges near Japan, south of the Aleutians and east of New England.

 

 

This is a very stable pattern that is likely to persist into and through much of the winter season given the ongoing near record intense cold phase of the extra tropical Pacific.

Potential Implications for the Extra Tropical Pacific in Winter 2024-2025

 

Below is a generic plot of the potent La Nina 500mb pattern that has been prevalent throughout this summer season extrapolated into the cold season.

 

There exists striking similarities to the aforementioned MEI analog composite.

This is further proof of the notion that the unremarkable MJJ ONI value belies the magnitude of the formidable cool ENSO regime that has and will continue to be well entrenched throughout the northern hemisphere as we progress through the fall and into boreal winter 2024-2025. The flat nature of the Aleutian ridge is very evident in this composite, which is unsurprising given that 3/4 four seasons in the composite are characterized as Modoki La Nina events (right). 

 

Some Tendency for Poleward Aleutian Ridging and High Latitude Blocking in Basin-Wide Composite (center)

 

The flatter ridge in these type of La Niña episodes have a reduced ability to deliver cold south and eastward, which results in a more composite across the southern and eastern US (left) relative to the more eastern composites.

 

 

East-Based, Basin-Wide, Modoki La Niña

However, the developing La Niña event is currently central-based, or basin-wide (middle) and is forecast to continue to remain as such.

 

 

 

 

Thus if is fair to conclude that while the overall DM period should undoubtedly be rather mild throughout at least the eastern third of the US and most especially the southeast, there may very well be significant period(s) of poleward Aleutian ridging and/or high latitude blocking. This is a concept that is also bolstered by a north Atlantic Accumulated Cyclone Energy that is currently well above average, which will be discussed at greater length this fall. It should be more of an either/or proposition in terms of amplified Aleutian ridging versus NAO blocking, as they are unlikely to occur simultaneously using recent history as a guide, which would render the northeast far more favorable to intervals of wintry weather versus the mid Atlantic and southeast. December 2008 is one such example, whereas poleward Aleutian ridging was present in the absence of AO/NAO style blocking.

 

 

 

 

 

December 2022 and March 2023 are illustrations of the other likely scenario in which a pronounced RNA pattern coincides with NAO blocking.

 

 

December 2022

 

 

 

March 2023

 

 

The type of patten being envisioned clearly fits one of three prominent types of extra-tropical Pacific regimes during cool ENSO winter seasons, which of course all exert themselves upon the weather pattern over N America in various ways.

 

RNA Style Winter Likely

The first pattern is associated with a distinct -EPO appeal in which high latitude ridging is concentrated in the general vicinity of Alaska and the Gulf of Alaska.

 

Here is the DM 500mb composite of these la Nina seasons:

 

 

Note that the giant EPO style ridging delivers cold...this composite contains the 2008-2009 analog and
31% of these seasons averaged a negative NAO for the DM period, which is a bit less than the next dataset due to the fact that lower heights are displaced to the east due to the large EPO ridge in the vicinity of Alaska.

DM temp anomaly composite:

 

 

Said EPO block also inhibits Pacific moisture inflow in the absence of a split flow, which limits precipitation across most of the nation
DM Precip anomaly composite:

 

 

The most likely extra tropical Pacific pattern for winter 2024-2025, as alluded to, will feature a -PNA as the most prominent characteristic.:

40% of these seasons averaged a DM -NAO, which is the most of the 3 datasets, due to the fact that lower heights to the north, which is typical of la Nina, are displaced to the west and away from the Davis Strait and Greenland.

DM H5:

 

 

This pattern also allows for the delivery of cold, albeit spilling west first, before bleeding east-southeastward...note 1973 and 2022 are each members of this composite, which lends credence to the idea of perhaps one winter month  averaging a - NAO in the mean or at least an extensive episode(s) of blocking. 
DM Temp anomaly:

 

 

 

This is a pattern that allows for a great influx of Pacific moisture with a slightly less prominent EPO ridging a bit further off of the west coast.
DM Precip anomaly:

 

 

 

 

 

This solution offers the greatest blend of cold and snow for the eastern US on average due to blend of ample cold and available moisture, however, the final composite, which is the mildest for the east coast, is also well represented.

The +EPO composite, which contains the MEI analog seasons of 1999 and 2011, features a more defined Pacific jet and thus a milder overall appeal. The presence of two of the analogs form the MEI data set is consistent with the notion of an overall mild DM period in the mean:

 

Only 28% of winter seasons averaged a -NAO for the DM period, which coupled with lower heights in the vicinity of Alaska, spells a very mild winter for the east in the DM aggregate mean.

DM H5:

 

 

 

DM Temp anomaly:

 

 

 

DM Precip Anomaly:

 

 

In Summary, the general implication of each of the data sets for the east coast winter season are as follows:

1) -EPO composite=cold and dry

2) -PNA composite=cold and wet (snowy)

3) Mild with moderate moisture influx biased north.

 

Here is a composite of all RNA composite members that are classified as basin-wide La Niña events given that this is the expectation for the coming season.

 

The general theme of deep RNA with occasional bouts of poleward Aleutian ridging and high latitude blocking continues.

 

Early Conclusions to be Drawn

The ongoing near record Pacific cold phase will continue to enhance the seemingly modest La Niña event per ONI, which will result in a very potent cool ENSO Walker cell throughout the coming winter. The fact that La Niña is expected to be central-based, as opposed to Modoki in conjunction with a prevalent  RNA pattern makes episode(s) of NAO blocking and poleward Aleutian ridging fairly likely. The latter is also supported by a very active north Atlantic Accumulated Cyclone Energy to date. However, the ability for cold air to reach the east coast will be limited and the milder periods will be far more frequent and intense than the wintry periods. 

 

Potential Analogs: 

Pacific Decadal Oscillation (PDO) Analogs: 1955, 1964, 1973, *1975, 1998, *1999, 2011, 2021, *2022 PDO Analogs

Pacific-North American  pattern (PNA) Analogs: 1964, 1973, 1998, *2007, *2022 

East Pacific Oscillation (EPO) Analogs: 1974, 1995, *2016 

West Pacific Oscillation (WPO) Analogs: 1954, 1973, 1988, *1999

Denotes strongest extra tropical pacific analog

Denotes strong extra tropical Pacific analog

* Denotes years that are also polar analogs

 

Preliminary Extra Tropical Pacific Analog Composite

Although there is a rather flat Aleutian ridge in the DM mean composite, it is expected that there will be intervals of such occurences that will coincide with episdes of +NAO and arctic intrusions focused over the west and midwest. The key for the mid Atlantic or the southeast to be more involved in said cold delivery will be to time an Aleutian ridge flex with a period of -NAO, which should be a fleeting occurence if at all. The season should average decidedly -PNA in the mean, however, some more extensive intervals of +PNA are possible mid season given what has been ascertained about the polar domain wth respect to NAO blocking being favored late in the season.

 

More updates to come-

Here is my early stab at the extra tropical Pacific....will be expanded upon in a more exhaustive segment this fall as part of the whole outlook.

https://easternmassweather.blogspot.com/2024/08/preliminary-assessment-of-extra.html

@bluewave or anyone....Do you have the piece on the new Pacific pattern designations...ie. Alaskan trough, etc...?

11 hours ago, raindancewx said:

I think we're moving into the cold AMO transition. If you subtract out the cold AMO years from the warm AMO years in La Nina, the three areas of biggest change are very warm/very cold east of Japan, very warm/very cool by West Africa, very warm/very cold by NE North America.

The cold AMO La Ninas tend to be snowier with severe (albeit brief) cold dumps into the SW US and Southern Plains. 

-PDO was roughly 1947-1976

-AMO was roughly 1964-1994

Some pretty severe and unusual cold-ENSO winters in the brief -PDO/-AMO period - ala 1964-65, 1966-67, 1967-68, 1970-71, 1971-72, 1973-74, 1974-75, 1975-76. La Nina has a reputation for dryness out here. That's largely true, but if the tropical Atlantic and tropical Pacific remain cold, I'd imagine the air over the deserts would get exceptionally dry to the point that someone out here would see a winter with sporadic near to record cold lows. January 1971 got to -17F ln Albuquerque in a January that isn't even that cold if you look at the records - that month was nuts.

I have really been warming up to the 1973-1974 analog..especially with respect to the Pacific.

16 minutes ago, bluewave said:

The Euro seasonal had a good summer forecast. The smaller cool spot was centered further north over the Midwest rather than down near Texas. This cooler in the middle and warmer near the coasts has been the summer temperature pattern since the 15-16 super El Niño.

 

I thought last summer was rather cool around here....

On 8/21/2024 at 6:47 AM, bluewave said:

This was one of the strongest La Niña 500 mb summer patterns that we have ever experienced. In our older climate, a La Niña summer 500 mb pattern featured a ridge near Japan and south of the Aleutians. The Atlantic usually had a ridge east of New England. These 3 ridges this summer were some of the strongest we have observed. If this had been the winter with such a strong ridge near the Aleutians and near the East Coast, then it would have been among the warmest on record. So this is telling is that unless we can get some version of mismatch like in January 2022, the winter is going to be very mild again. Probably have to wait until October for some clues to see how the October early MJO indicator evolves. 
 

 
If the winter ridges turn out as exaggerated as the summer, then it will be a very mild winter again. So we need a mismatch along the lines of Jan 2022 with the MJO 8 and more +PNA to counter it. Without pushback we end up with 22-23 warmth again.

This is an absolutely lethal match to the MEI analogs....uncoincidentally.

11 minutes ago, PhiEaglesfan712 said:

If we're talking about 2013-14, then that one tipped its hand in July with the ridge building in the PNW. I mean, we got a big flip in the temperature pattern midway through the summer. The change in PDO pretty much sealed the deal.

If we're talking about 2014-15, well that was just a continuation of the +PDO/PNW ridge. JFM 2014 and 2015 were the coldest this side of 1980. Even the summer of 2014 was cooler than average (the coldest since 2010, though some places were cooler last summer). The PNW ridge finally subsided in spring 2015 (which is why we got a very warm May here, and a cold May in most of the West).

I didn't really look at all of that back in 2013....I would just watch the models for snow in season and measure when it fell.

On 8/21/2024 at 6:47 AM, bluewave said:

This was one of the strongest La Niña 500 mb summer patterns that we have ever experienced. In our older climate, a La Niña summer 500 mb pattern featured a ridge near Japan and south of the Aleutians. The Atlantic usually had a ridge east of New England. These 3 ridges this summer were some of the strongest we have observed. If this had been the winter with such a strong ridge near the Aleutians and near the East Coast, then it would have been among the warmest on record. So this is telling is that unless we can get some version of mismatch like in January 2022, the winter is going to be very mild again. Probably have to wait until October for some clues to see how the October early MJO indicator evolves. 
 

 
If the winter ridges turn out as exaggerated as the summer, then it will be a very mild winter again. So we need a mismatch along the lines of Jan 2022 with the MJO 8 and more +PNA to counter it. Without pushback we end up with 22-23 warmth again.

Full disclosure.....gonna use this in my current blog piece.

Thanks.

2 minutes ago, snowman19 said:

2014 was obvious once the PDO went ++. You knew the +PNA/-EPO/-WPO was coming. 13-14, though technically -PDO, the configuration resembled +PDO and it was as textbook a +TNH pattern as you will ever see

Not sure how early it was "obvious", but admittedly I only knew a fraction of the little that I know now, so....that was my first outlook attempt.

21 hours ago, 40/70 Benchmark said:

Often the most difficult ones to predict end up being the ones perceived as being easy leading in because we are usually missing something. I think 2007-2008 and 2008-2009 are the pathways to better winter outcomes.

16 minutes ago, snowman19 said:

IMO the forecasts for 25-30 named storms are probably in peril

Any time you feel highly confident in racing to your laptop to convey seasonal throughts...pause, reflect and reconsider.

17 hours ago, bluewave said:

The La Niña background state is so strong that it’s actually creating easterly shear in the Atlantic. This is why the models are quiet for late August instead of very active which we usually see during La Ninas. So we’ll have to wait until September for our next period of tropical development.

https://michaelrlowry.substack.com/p/the-bell-has-rung-so-why-are-forecast

Too much of a good thing?

 

As regular readers of this newsletter know, wind shear – the change in wind direction or speed with altitude – is one of the big hurdles to tropical development. Typically it’s the strong winds at upper levels (30,000-40,000 feet) which blow from west to east (known as upper-level westerlies) through the deep tropical Atlantic and the Main Development Region or MDR that create most of the wind shear issues.

So when upper-level winds in the tropical Atlantic turn more east-to-west (easterly winds) and against the west-to-east grain, it usually helps to reduce wind shear, which in turn favors hurricane development. This is especially true during La Niña years like we’re experiencing and when rising air settles in over Africa and the North Indian Ocean as it has recently – a big upper-level disturbance we track across the tropics called the Madden Julian Oscillation or MJO.

The combination of La Niña with the part of the MJO that usually reduces wind shear would normally suggest a conducive period for development. However, the upper-level winds have switched so far out of the east that they’re creating easterly wind shear issues across the Atlantic, an unusual problem not often seen in the basin.

 

It means that the MJO will need to move to a less conducive phase to bring back the seasonal upper-level westerlies and tamp down on easterly shear issues plaguing the basin right now. The easterly shear is also worsened by the low-level westerly winds from the northward displaced ITCZ we discussed earlier.

The MJO naturally propagates eastward across the globe and extended range models are already showing the easterly shear issues abating toward the end of the month.

So when will activity pick back up?

 

Putting all the pieces together, it should be another week or two before the current impediments clear out.

 

It’s possible our next spurt of activity is delayed until the beginning of September, but we should see the transition as August comes to a close late next week.

Traditionally 70% of tropical activity, including most hurricane formations, happens from September onward. Still a long way to go in the game, but for now we’ll soak up the unforeseen late August lull.

Yea, this is why I didn't entirely agree with notion that ENSO will not be a large factor this year....the entire hemisphere has been in a cold ENSO state for several years, which will allow it to be more influencial than implied by the ONI. We saw this in 2022. I feel like the point regarding less emphasis on ENSO was very valid last season with respect to the El Nino and certainly ENSO in general is not as prevalent a driver as it was 10-20 years ago.

13 hours ago, PhiEaglesfan712 said:

13-14 and 14-15 were more straightforward to me than 17-18. In 17-18, the record warm October threw me off. That one and a record warm February really skewed things.

 

Agree on 2017-2018, but 2014 was a bit more tricky in that it was entirely Pacific driven.....and I am willing to bet that most folks who went big expected a lot of NAO blocking, which includes myself.

13 minutes ago, 40/70 Benchmark said:

Its definitely not going to be a picturesque H5 plot for NE winter aifionados...I think that is a given. ...but that doesn't mean we can't get some more unconventional means of winter weather delivery. Key will be poleward ridging and shape/orientation of PV, etc.

Obviously this will be easier to pull off with latitude. If you didn't go well in 2007 or 2008, then you can probably pack it in save for maybe a fluke event.

5 minutes ago, snowman19 said:

IMO 17-18 was another easy one. It already tipped its hand by this point in time and very little changed that fall. The overall synoptic picture never stopped being a very favorable one from August on….

Its definitely not going to be a picturesque H5 plot for NE winter aifionados...I think that is a given. ...but that doesn't mean we can't get some more unconventional means of winter weather delivery. Key will be poleward ridging and shape/orientation of PV, etc.

19 hours ago, snowman19 said:

Honestly, I think this winter is going to be a relatively easy one to predict, in fact, I think this is going to be one of the few easy ones, (i.e. 02-03) we’ve seen, without many question marks. The people on twitter who are saying that it’s “going to be a very hard one to predict” are the same people who look for excuses to predict a very cold and very snowy winter for the east coast every year. I’m reserving my final judgment for November because things can change of course and it’s foolish to make a winter forecast right now IMO. That said, I don’t expect very much at all in terms of the main global ‘players’ to change between now and November. I think this winter is already showing its hand pretty clearly

Often the most difficult ones to predict end up being the ones perceived as being easy leading in because we are usually missing something. I think 2007-2008 and 2008-2009 are the pathways to better winter outcomes.

20 hours ago, Stormchaserchuck1 said:

We had a RNA block make it past +600dm in Dec 2021! Because of how we started seeing big RNA anomalies in Feb-March 2009, then it picked up over time in the same months, I'm thinking RNA-December is a new trend that is also picking up.. 

Would go along with the idea of a slightly distubred PV early on before it really consolidates.

Just now, Typhoon Tip said:

it's the other way around most likely.  but .. like i said, chicken or egg.   i suggest the egg is CC ... and just like the gom and adjacent sw atl basin is also an inferno, so to has this accumulated in the sw-w Pac.   it's just that the west pac is larger unobstructed expanse so is larger and more looming, but in either case...

Fair enough....we generally agree.