Some Thoughts On The Next Couple Months

[OHweather]

Not a "winter forecast" per say, more like a sh*tload of speculation about the pattern through the first ~half of winter...

The Key Points Up Front:

1. The pattern of “cold west, warm east” continues through most of this week
2. Later this week into this weekend, cold spills into the central and eastern United States. The pattern then remains fairly chilly across the Lower 48 for a couple of weeks, with the coldest overall conditions across the northern Rockies and northern Plains
3. Several signs point towards the weather pattern in much of the continental United States trending mild yet again towards the end of November and early December
4. A few analogs and early signs in extended guidance suggest the potential for increased high-latitude blocking and colder weather may return into December. Given the ongoing La Nina and -PDO, confidence in this occurring isn’t high yet. However, the coldest December since at least 2016 is distinctly possible if things align properly

The Details:

After a very chilly first half of October, which was enough to plunge most of the eastern U.S. to below normal values for the entirety of the month, mild weather has dominated the pattern over much of the central and eastern U.S…this pattern continues into this upcoming week, but the GFS and Euro ensembles both indicate below average temperatures over fairly decent stretch for almost the entire CONUS closer to mid-month:

It’s getting to be the time of year where colder anomalies have some more bite and can start bringing snow to more of southern Canada and the Lower 48. This cooldown has trended more and impressive as it moves up in time on the models, evidence by this GFS ensemble trend loop for the same time period:

After such a prolonged mild spell, is this cooldown shown in the medium to long range feasible, and how long may it last? Looking at a few things, including the character of the Pacific jet stream and the MJO, suggests that the projected cooldown on the ensembles has legitimacy. Let’s start with the pattern over the last week leading up to Friday:

The pattern is undoubtedly a warm one for the central and eastern CONUS and into southeastern Canada, with a positive AO (PV generally tight and confined to the high latitudes), a very positive EPO (the trough over Alaska and western Canada), a negative PNA (Aleutian ridge and West Coast trough), and positive NAO (trough over the north Atlantic).

The above pattern correlates very nicely to the expected pattern when the Pacific jet is retracted, as it has been most of late October and very early November per the above chart:

The flat ridge south of the Aleutians, trough over Alaska and western Canada/the western US, and downstream ridge over the eastern US are quite characteristic. There are a couple of ways to analyze how the Pacific jet is progged to behave on current guidance over the next week or so…one is just to throw in a loop of ensemble mean forecast 250mb winds:

We start off in the middle of last week with a “jet retraction” look, with the jet barely extending off of Asia and a ridge over the Aleutians, directing the jet stream towards Alaska and the northwest coast of North America, helping facilitate the current very mild pattern across a good portion of the Lower 48. However, quite a bit of westerly momentum is getting added as I type this and into early this week. Initially, the ridge near the Aleutians just amplifies and disperses a lot of this added momentum around it, but eventually the jet extends and pushes the now-amplified ridge east, facilitating cross-polar flow into North America and really cutting off the Pacific influence by this upcoming weekend. Here is the GEFS forecast Pacific jet character:

A similar trend, from a pronounced jet retraction in late October towards neutral, with perhaps some modest lean towards an equatorward shift or jet extension over the next week or so. Here are what a Pacific jet extension or equatorward shift tend to look like:

Note the trend towards much higher heights into the northern Pacific and Alaska, with resultant troughing and colder weather over a good portion of North America…in particular, over western and central Canada into the northern Rockies and Plains with an equatorward shift, but bleeding towards the East Coast. The equatorward shift looks more like a -EPO but still somewhat negative PNA, while the jet extension looks more like a classic +PNA with a somewhat negative EPO. This generally matches the ensemble’s forecast pattern over the next week or so:

The impetus for this change seems to be a combination of increased east Asian mountain torque and tropical forcing working out of the eastern hemisphere and into the western hemisphere early this month. Initially, the pattern this weekend into the first half of the week simply looks like a significant amplification to the going pattern:

At first, we just see the ridge south of the Aleutians amplify, which amplifies the downstream pattern over North America (western trough and eastern U.S. ridge). However, this very mild look over the eastern U.S. doesn’t last too much longer as the ridge amplifies into Alaska, forcing cold south towards the CONUS, and as an Aleutian low develops. An Aleutian low is a trend towards a more positive PNA.

Note positive MSLP anomalies (high pressure) dropping into eastern Asia right around now, signifying a significant increase in east Asian mountain torque, which results in added westerly momentum to the east Asian-Pacific jet. There may be another push later this upcoming week, before a fairly well agreed upon trend towards a much more negative east Asian mountain torque into mid-November:

Positive East Asian mountain torque tends to result in an extension of the Pacific jet and subsequent rise in the PNA, as the extended jet and associated left-exit region towards the north-central Pacific tends to favor low pressure over the northwest Pacific or Aleutians and subsequent height rises to the east closer to the West Coast of North America.

At the same time, the MJO has come out of the Maritimes and into the western Pacific at a fairly high amplitude, and is now quickly working into the western hemisphere. The satellite/VP anomaly loops over the last two weeks show a similar trend as the above RMM plot, with strong uplift over the western Pacific until the end of October quickly shifting east. Note how areas that had the strongest upward motion (~120E) at the beginning of the loop have strong sinking motion now, and vice versa over portions of the central and eastern Pacific. Clearly, the tropical forcing is changing from the forcing that led into our current very mild pattern.

After a decent Phase 7 passage, an increase in blocking near Alaska in October-December is quite common:

We are not going to get the NAO help in the short term, but blocking located near Alaska/a -EPO is often common during and following a phase 7 MJO this time of year as seen above. The MJO is about to briefly get into Phase 8, which also often leads to a colder outcome into the southern and eastern U.S. than a Phase 6-7 in the fall:

And for what it’s worth, the same October-December lagged composites from the CPC for a phase 8 MJO, which is briefly occurring right now:

The issue with these is that the pattern right now into this week, which would be a “Lag=0” for the current phase 8 RMM indication, is that the NAO is quite positive with a deep trough out west. That said, a phase 8 MJO this time of year often corresponds to immediate and short term blocking, with an Aleutian low/+PNA and colder trend over most of North America. This is then followed by the PNA trending more negative and blocking generally breaking down within a few weeks of the phase 8 MJO occurring.

Despite the phase 8 MJO pointing to a -NAO, I am fairly confident it will remain positive for the next 10-15 days. This is because the stratospheric PV, while getting stretched a bit at times, is going to remain on the stronger side of normal, which argues towards a +NAO for now. In addition, recall back to this EPS mean sea level pressure/anomaly loop:

Note multiple high pressure systems dropping in just east of the Rockies over the next 10 days. The Rockies are not quite as tall as the Himalayas, but they’re still plenty tall enough to produce a mountain torque that requires increased momentum in the jet stream to conserve angular momentum in this equation (the positive mountain torque removes momentum by slowing Earth’s rotation slightly). This speeds up the jet over the eastern U.S. into the North Atlantic, encouraging positive NAO trends. Given that the NAO has been positive since late October, I don’t see it flipping negative in the face of this through at least the middle of November.

Looking Beyond Mid-November:

A dramatic shift to a colder pattern in the CONUS, first into the Pacific Northwest over the next few days and then expanding into the rest of the CONUS through next weekend and through mid-November is agreed upon by the major ensembles and seems very well-supported by various forcing mechanisms…driven by a plunging EPO and rising PNA. But how long will it last, and does it mean shit for the approaching winter season as a whole?

To answer the first part of this question, we will examine things such as mountain torque and tropical forcing yet again. Starting with mountain torque, and picking up closer to mid-November, after our upcoming increase in mountain torque and injection of westerly momentum into the Pacific jet:

Positive east Asian mountain torque is ongoing at the start of the loop, but as low pressure develops over much of southeast Asia, this becomes negative, reducing westerly momentum into the Asian-Pacific jet around mid-November. This suggests the jet will have a tendency to retract again, which would render the upcoming PNA spike brief and could eventually cause the EPO to start trending more positive again.

Remember, we are in a La Nina with a solid -PDO, evidenced by the cool tongue across the equatorial Pacific, the warm waters over the northwest Pacific, and the cool waters south of Alaska:

These both favor a -PNA and often favor a predominantly +EPO as well. We look to buck that over the next week due to tropical forcing progressing through the Pacific and Western Hemisphere and due to a positive east Asian mountain torque, but when those shorter term pattern drivers subside, the lower frequency forcing can often dominate yet again. So, the expected negative east Asian mountain torque towards mid-November is a signal that a more -PNA and more neutral EPO is a distinct risk into the latter portions of November given the background forcing.

Most guidance (the European ensemble shown above) suggests tropical forcing quickly progressing through the western hemisphere over the next week or so, with eastern hemispheric forcing (in particular, over the eastern Indian/western Pacific oceans) becoming dominant once again towards the second half of November. Given the background state, this seems very plausible after the current higher frequency forcing moves through the western hemisphere in the shorter term. RMM forecast plots also indicate similar, with the ongoing Phase 8 MJO not lasting long and then becoming “indeterminant” (which usually means lower frequency forcing can exert more influence again). Thereafter, the MJO may move into phases 5 or 6 after the 15th. Here is the European ensemble forecast MJO progression through November 19th:

Recalling back to the above October-December MJO phase temperature correlation plot above, phase 6 is quite mild in the CONUS. This general evolution (eastern Indian/western Pacific Ocean tropical forcing becoming dominant again into mid-November) is well agreed upon by various medium to long range forecast models/ensembles. In addition, the water temperatures support convection and tropical forcing wanting to favor this general region again, as does where enhanced convection/upward motion has been most persistent in recent months near the equator:

So, the background pattern suggests a risk for a retracted Pacific jet and -PNA/+EPO to return when other shorter-duration forcing weakens. In addition, there’s fairly consistent indication that the shorter-duration forcing (mountain torque, MJO) will weaken and may in fact positively feedback with the “background” La Nina pattern into late November.

There’s enough support for a significant cooldown that it will take some time for milder weather to return, we’ll probably have a full 1-2 weeks of generally cold conditions (for this early) across the CONUS. However, many indications are that milder weather gradually returns from west/southwest to northeast in the second half of November.

In terms of snow potential over the next few weeks, the higher elevations over much of the western U.S. (outside of perhaps the Four Corners and southern California) will remain cold and active through this week with a -PNA and dropping EPO. As the cold ejects east late this week, a lee cyclone may bring snow potential to the northern Plains and Upper Midwest. Thereafter, it looks like a fairly dry EPO-induced cool/cold shot into the central and eastern CONUS. Not all hope is lost, as some snow may occur via lake effect, weak clippers, or perhaps any waves riding along the baroclinic zone if the sub-tropical jet isn’t totally quiet. Likely not a pattern that supports a widespread, major winter weather event (especially in November), but it’s possible some minor or localized snow events occur outside of the mountains starting this upcoming weekend and through roughly Thanksgiving.

Some Fun With ENSO/MJO Analogs:

The rest of the winter is not yet lost though. In fact, the findings discussed below are what prompted me to make this whole thing a post instead of a Tweet thread. I just thought “there’s a lot here, let’s try to tie it together better than intentionally cryptic Tweets would”.

This much MJO activity in the fall leading into a La Nina isn’t too common. Since 1975, only 4 La Nina Novembers saw the MJO move into both phases 7 & 8 at an amplitude of greater than 1. Those are 1996, 2000, 2010 and 2016. Oh, there’s that fabled 2010-11 analog. We also have a very negative IOD and solidly westerly QBO. Let’s see if we can leverage those high-confidence, long-duration pattern drivers. We have a negative IOD this fall and will have a westerly/positive QBO through this winter, full stop.

2010 and 2016 had a westerly QBO

1996, 2010 and 2016 had a negative IOD

How did those 4 years play out during December?

All but 2010 had a solid -EPO, and 2010 still had very pronounced north Pacific ridging along with a a huge -NAO. All but 2016 had a -NAO. All but 2000 had a -PNA. All but 2016 had a -AO. Here is a look at the October-February monthly temperature and precipitation anomalies for these years (weighted slightly based on QBO/IOD matches):

For reference, here are October’s temp/precip anomalies:

Overall, the October pattern this year actually resembles those analogs, though with the pattern seemingly shifted west slightly. The very warm start to November likely dooms the eastern U.S. to finish with a somewhat mild overall month, but the pattern after this week may resemble these years in November fairly well. It’s at least in the ballpark enough that these analogs aren’t immediately invalid.

I believe how the MJO and mountain torque play out during late November and into December will heavily influence if the potential for a very blocky, cold, active December comes to fruition given the risks for a milder pattern (at least temporarily) returning by the end of November. Just looking at some various products, the EPS (already shown), GEFS, and Australian BOM MJO forecasts:

The GFS/Euro both have the MJO strongly and definitively progressing through phase 6 and towards phase 7 into late November. This could be indicative of a similar angular momentum/global wind oscillation orbit to what we are currently seeing, as per this CFS forecast:

An orbit through phases 5-7 (as has recently occurred) supports convection moving east towards the Dateline and eventually the western hemisphere, along with positive mountain torque and troughiness into the mid-latitudes:

With that said, we are fighting the background state and there is some uncertainty to how all of this progresses 10-20+ days out. Getting the tropical forcing to propagate east again (as the GFS/Euro ensembles are suggesting towards late November) and getting another push of increased east Asian mountain torque is likely critical towards the door being open for a very block and cold December with elevated snow potential across a good portion of the CONUS. If not, the chances for a mild start to the winter quickly increase.

[Chambana]

What an absolutely incredible write up, you are one of my favorite posters to read their analysis. Incredible work, OHweather. 

[Terpeast]

Excellent write up, thanks for sharing! These posts are what makes this forum great. 

[BuffaloWeather]

Amazing stuff as always thanks for this write up!

[raindancewx]

My issue with using 1996-97 was how rapidly that year collapsed into the big 1997 El Nino. By early 1997, the subsurface was super warm, and you got some real interesting patterns, since it was developing from east to west. I wanted to use that year. But I don't quite trust how it played out, it's been different enough that I threw it out.

A lot of the cold-ENSO years with similar early November heat waves for the NE US are kind of interesting - 1938, 1948, 1959 were years I saw today for similar Boston heat.

I tried to pick Fall years that had major heat and cold waves. I know 2016/2020 were both very warm early November among my group, and then 1984, 2011, 2020 got pretty cold mid-month. Mid Nov 1984/2011/2020 is actually pretty decent for how mid-month will look as the cold drains into the US.

1984 goes to this, but still manages to be pretty warm in December in the east as an example for how I see it playing out. The purples are -5 (light) and -7 (dark) in degrees Fahrenheit. My gut is once the hurricane hits Florida, you'll see some stuff evolve differently on the models for late month and beyond.

[Eskimo Joe]

Appreciate the write up and the graphical explanation of how the various indexes play out.

[OHweather]

 

On 11/6/2022 at 8:23 PM, raindancewx said:

My issue with using 1996-97 was how rapidly that year collapsed into the big 1997 El Nino. By early 1997, the subsurface was super warm, and you got some real interesting patterns, since it was developing from east to west. I wanted to use that year. But I don't quite trust how it played out, it's been different enough that I threw it out.

A lot of the cold-ENSO years with similar early November heat waves for the NE US are kind of interesting - 1938, 1948, 1959 were years I saw today for similar Boston heat.

I tried to pick Fall years that had major heat and cold waves. I know 2016/2020 were both very warm early November among my group, and then 1984, 2011, 2020 got pretty cold mid-month. Mid Nov 1984/2011/2020 is actually pretty decent for how mid-month will look as the cold drains into the US.

1984 goes to this, but still manages to be pretty warm in December in the east as an example for how I see it playing out. The purples are -5 (light) and -7 (dark) in degrees Fahrenheit. My gut is once the hurricane hits Florida, you'll see some stuff evolve differently on the models for late month and beyond.

Thanks for your insight as always. I do see your point of contention with 1996-97, as this will not be going towards any kind of a strong, east-based El Nino anytime soon. That said, the La Nina is starting to lose its grip, evidenced by the MJO activity we are starting to see, so that's why I think it may be somewhat useful as an analog. 

I am curious to see how this month looks when it's in the books...while the early month heat is indeed very impressive in the east, and will be hard to overcome on the monthly mean, the rest of the month will be much colder in the central and eastern U.S...many of the years you mentioned were chilly/cold in the west and anywhere from mild to very warm over the east in November, with a large +EPO/trough over Alaska. While this month is starting mild, we're really avoiding that ++EPO look, and probably will have a negative EPO for the month of November overall. So, I'm curious to see if that leads to my colder December idea still having a shot when the analogs you mentioned are much bleaker for the east (but are somewhat more interesting for the west). If we see another strong MJO event to end this month and into early December, I'd be rather surprised to see any kind of +EPO stick around for long, even if it does briefly flip positive after Thanksgiving. 

[raindancewx]

I'm pretty convinced the cold dumps are going to continue into the West, or at least the Rockies for the next four months. The mechanism(s) for that of course will vary, since the PNA/AO/NAO/EPO/WPO all are basically irrelevant for temps in a correlation sense where I am until early to mid-January. The years I mentioned with the severe NE US heat in cold-ENSO are actually fairly cold nationally in November on balance, and then typically cold in the West, and warmer East. 1938 in particular interests me since Fiona was not that different from the system in 9/1938.

One thing that would bug me about 2010 is the WPO actually. I'm pretty sure it's consistently negative that Nov-Mar year, and there have been lots of pretty powerful lows in the NW Pacific, I'd imagine it's going to finish positive this November, and that often ties in with stuff that happens in the West, Plains and South pretty directly. It really seems to weaken cold in otherwise cold patterns.

By the way: I saw Weatherworks has a winter outlook up without you. I think you should start a new service and call it..."Weatherjerks"

[40/70 Benchmark]

Awesome stuff. 

[MattHugo81]

Thanks for taking the time to post this information...

The blocking signals for the early part of the winter period have been consistent, not just related to seasonal model data, but with regards to the key drivers and teleconnections as well. However, we have all been here before over the years and I fully believe now that LRF is becoming an even more difficult task due to the influences from climate change. We've seen some 'strange' behaviour of the QBO in recent years, while analogues and composites still provide interest I believe it is these which are becoming increasingly unreliable when looking ahead. Perhaps one could suggest that has always been the case, but I certainly believe their usefulness is being counterbalanced by climate change influences.

From a Europe and British Isles perspective it has been interesting to see how the +AAM spike/high GWO phases now have helped to push back a more anticyclonic trend and aiding to maintain the trough over the N Atlantic. The flatter pattern, which you discuss and of which is highlighted well on some of the plots shows this. It is certainly interesting to see one of the highest AAM spikes in nearly a year within a well entrenched La Nina (oceanic) regime. Clearly, at the moment an atmospheric and oceanic disconnect which is interesting in itself. As you also highlight nicely, it does look as though that Maritime/W Pacific tropical forcing will be a key feature of Nov and Dec, perhaps the winter as a whole as well. Having the MJO in phases 5-6-7, overall, will certainly be interesting for early winter period, clearly phases that often promote amplification to the N Hem pattern (https://www.meteonetwork.it/models/mjo/) but clearly this is one piece of the jigsaw.

While N American can often see cold from more muted signals, unlike the British Isles which often needs a far more robust -ve AO and NAO regime, from my experience over the years it is often the development and interaction of the sPV and the tPV that can 'lead the winter dance'. If the sPV becomes a dominant feature and of which links to the tPV then, "9 times out of 10" it is curtains for any sort of meaningful -ve AO and NAO pattern which has been exampled well in the last couple of winters. Fortunately, at the moment, despite an increasingly organised feature, there remains little evidence for any rapid connection of the two.

Also, we need to keep a close eye on the persistent block that is modelled over Scandinavia and potential wave breaking influences down the line as well. A case of 'steady away' for now, but again as you have highlighted well in the original post, there is a lot of hope and also science being this winter being far different than last year, for example and perhaps especially so over the next 8 weeks. The latter half of the winter period would likely transition to a +ve NAO pattern, IMO, at the moment, but clearly that depends on any SSW risk and potential down the line.

Kind regards.

[griteater]

@MattHugo81 Matt!!

It looks like your thoughts remain on track Jim @OHweather.  The -VP is progressing east into Africa -> Indian Ocean, shown here on the 1-day JMA charts over the past week

 

 

 

Here is the latest MJO Hovmoller

 

A bit surprising to see projections of the -VP not getting bogged down in the Indian Ocean & Maritime Continent given La Nina, but the MJO speed through the Indian Ocean makes some sense given that we have a negative IOD with some cool SST anomalies there.  We'll likely see a slow down in the West Pacific though based on the high octane water there and typical La Nina behavior

 

 

 

 

At any rate, maybe we see something in the ballpark of these images from late Nov to mid-Dec (or at least a few ideas from these images)....6-7-8 MJO circuit

 

Nothing on the forecast charts show a pattern for strong Strat PV weakening, but we also aren't seeing any signs of a strong +AO pattern developing in the troposphere....it's middle of the road between the 2 at the moment

[OHweather]

On 11/8/2022 at 7:47 PM, raindancewx said:

I'm pretty convinced the cold dumps are going to continue into the West, or at least the Rockies for the next four months. The mechanism(s) for that of course will vary, since the PNA/AO/NAO/EPO/WPO all are basically irrelevant for temps in a correlation sense where I am until early to mid-January. The years I mentioned with the severe NE US heat in cold-ENSO are actually fairly cold nationally in November on balance, and then typically cold in the West, and warmer East. 1938 in particular interests me since Fiona was not that different from the system in 9/1938.

One thing that would bug me about 2010 is the WPO actually. I'm pretty sure it's consistently negative that Nov-Mar year, and there have been lots of pretty powerful lows in the NW Pacific, I'd imagine it's going to finish positive this November, and that often ties in with stuff that happens in the West, Plains and South pretty directly. It really seems to weaken cold in otherwise cold patterns.

By the way: I saw Weatherworks has a winter outlook up without you. I think you should start a new service and call it..."Weatherjerks"

You are little more unique in that you're much more dependent on the sub-tropical jet or cut-off lows for temperatures than a lot of the rest of the U.S...but, I'll be curious to see how the pattern evolves into December. I think we're on a similar page for the next couple of weeks, but I'm more bullish on a -EPO (and perhaps a more workable AO and NAO) returning in December. The WPO is probably going to be slightly negative for this month, or at worst near neutral. It was weakly neutral the first week of the month, is briefly positive now, and looks to trend more negative again for the next 10 or so days. I left WeatherWorks on good terms late in 2021 and am not too unhappy about not having to deal with a winter outlook for my job this year, so they can have at it with theirs! 

On 11/10/2022 at 1:31 AM, MattHugo81 said:

Thanks for taking the time to post this information...

The blocking signals for the early part of the winter period have been consistent, not just related to seasonal model data, but with regards to the key drivers and teleconnections as well. However, we have all been here before over the years and I fully believe now that LRF is becoming an even more difficult task due to the influences from climate change. We've seen some 'strange' behaviour of the QBO in recent years, while analogues and composites still provide interest I believe it is these which are becoming increasingly unreliable when looking ahead. Perhaps one could suggest that has always been the case, but I certainly believe their usefulness is being counterbalanced by climate change influences.

From a Europe and British Isles perspective it has been interesting to see how the +AAM spike/high GWO phases now have helped to push back a more anticyclonic trend and aiding to maintain the trough over the N Atlantic. The flatter pattern, which you discuss and of which is highlighted well on some of the plots shows this. It is certainly interesting to see one of the highest AAM spikes in nearly a year within a well entrenched La Nina (oceanic) regime. Clearly, at the moment an atmospheric and oceanic disconnect which is interesting in itself. As you also highlight nicely, it does look as though that Maritime/W Pacific tropical forcing will be a key feature of Nov and Dec, perhaps the winter as a whole as well. Having the MJO in phases 5-6-7, overall, will certainly be interesting for early winter period, clearly phases that often promote amplification to the N Hem pattern (https://www.meteonetwork.it/models/mjo/) but clearly this is one piece of the jigsaw.

While N American can often see cold from more muted signals, unlike the British Isles which often needs a far more robust -ve AO and NAO regime, from my experience over the years it is often the development and interaction of the sPV and the tPV that can 'lead the winter dance'. If the sPV becomes a dominant feature and of which links to the tPV then, "9 times out of 10" it is curtains for any sort of meaningful -ve AO and NAO pattern which has been exampled well in the last couple of winters. Fortunately, at the moment, despite an increasingly organised feature, there remains little evidence for any rapid connection of the two.

Also, we need to keep a close eye on the persistent block that is modelled over Scandinavia and potential wave breaking influences down the line as well. A case of 'steady away' for now, but again as you have highlighted well in the original post, there is a lot of hope and also science being this winter being far different than last year, for example and perhaps especially so over the next 8 weeks. The latter half of the winter period would likely transition to a +ve NAO pattern, IMO, at the moment, but clearly that depends on any SSW risk and potential down the line.

Kind regards.

Thanks for your input, Matt! 

Many interesting points you raise here. I also am unsure of how old teleconnections or rules of thumb hold up given the influence of climate change. I still think analogs and composites have some use when looking ahead, but you need to mentally adjust for the influence of climate change...which I'm personally still not sure what the influence is...I think it adds another difficulty in long range forecasting. We have seen two odd QBO progressions over the last several years after not really seeing anything like that before, so it is curious to see if that continues happening going forward. It's possible the super El Nino in 2015-16 had at least something to do with that.

Good point that in North America we can get cold from a favorable Pacific even with a lackluster AO/NAO, whereas Europe very much needs the AO and NAO to cooperate. The persistent Scandinavian block you mentioned that's modeled over the next couple of weeks is intriguing for a couple of reasons...it may help cool off eastern Asia, allowing for increased mountain torque down the road, and may have a shot at retrograding towards a -NAO as well. If this aligns with the MJO moving back into the western Pacific in late November, perhaps that's the evolution we need to shake the +NAO? I'll believe it when I see it at this point, but there's reason to be hopeful for the NAO dropping around the end of November or early December. 

If we see La Nina and its associated western Pacific uplift last through the winter, I agree that'd point to an increasing risk of a +NAO and mild weather as the winter goes on, especially if we don't see a SSW. I do wonder if the MJO activity we've seen this fall is an indication that La Nina is beginning to lose its grip...if that's the case and we see the MJO occasionally work across the Pacific at a decent amplitude through the winter, perhaps we mitigate any mid-late winter warm spells a bit. I'm not sure yet which way we go with the stratosphere, but as you mentioned it's not coupling to the troposphere for now even though the strat PV is a on the strong side for this early in the season. Perhaps we can see a brief weakening of the stratospheric PV around the end of November/beginning of December if we see a Scandinavian block and Aleutian low at the same time, though the pattern doesn't scream for anything major yet.

3 hours ago, griteater said:

@MattHugo81 Matt!!

It looks like your thoughts remain on track Jim @OHweather.  The -VP is progressing east into Africa -> Indian Ocean, shown here on the 1-day JMA charts over the past week

 

 

 

Here is the latest MJO Hovmoller

 

A bit surprising to see projections of the -VP not getting bogged down in the Indian Ocean & Maritime Continent given La Nina, but the MJO speed through the Indian Ocean makes some sense given that we have a negative IOD with some cool SST anomalies there.  We'll likely see a slow down in the West Pacific though based on the high octane water there and typical La Nina behavior

 

 

 

 

At any rate, maybe we see something in the ballpark of these images from late Nov to mid-Dec (or at least a few ideas from these images)....6-7-8 MJO circuit

 

Nothing on the forecast charts show a pattern for strong Strat PV weakening, but we also aren't seeing any signs of a strong +AO pattern developing in the troposphere....it's middle of the road between the 2 at the moment

Thanks for the added conversation! I remain fairly confident that the general idea for the next few weeks is on track for the reasons you touched on with the MJO. There are also signs that we may see increased mountain torque again later this month, which would support the EPO and PNA improving again and could also help kick the MJO east of the Maritimes if it tries getting stuck there...which would be a similar evolution to what we just saw early this month. 

How the stratosphere plays out may have something to say about the rest of the winter, and may even have something to say about if blocking does return to end this month or into December. I agree with you (and Matt) that right now, it's hard to glean much from the stratosphere...I could see another brief stretching event of the strat PV around the changing of the months, but otherwise the strat PV is fairly strong but isn't yet coupling to the troposphere in a problematic way. 

[MattHugo81]

Hi to all. Hope you don't mind me continuing the discussions on here...

We seem to be seeing some of the above comments from a week or two back playing out now (no surprises guys!) and it'll be an interesting watch. The extreme -EPO doing the early 'winter goods' across the USA of late but that rise and recovery to more neutral levels seems to be on the way. The feature of interest for the UK and the N Hem as well has been the lack of any progression towards a more blocked pattern sooner than was expected. The EC Seasonal, for example flipped the NAO firmly negative to positive in the blink of an eye and the wait for the early blocking signals have been long overdue, but we seem to be getting somewhere now.

A few key features that are standing out are changes in the AAM profile of late, with more E'ly AAM anoms now appearing through the mid-lats, a reversal of recent weeks, while the all important AAM transports plot highlights a clear change as well through the mid-lats. While the sPV continues to 'do its thing' there is clearly no significant connection at all, as you guys have highlighted most recently as well. Clearly, it can be that time of year now through the RI period that a quick downwelling of strong W'lies just over takes anything else and, for the worst case scenario for the UK, the next 4 to 5 weeks simply becomes locked into a +ve NAO regime as the usual deep cold Canada air floods into the W Atlantic and game is over.

Clearly, that isn't the case as the below plots highlight...

 

What interests me moving forward is how the MJO evolution, which looks a solid 4-5-6 progression, perhaps into 7 too, could well have on the pattern deeper into December. This is something I think was originally mentioned in this thread, about the next MJO passage. It is also interesting to note that the IOD seems to be trending more neutral as well, but clearly there is always a lag here. It will be very interesting to see how this next MJO wave progresses. I do have a feeling as well that these are the early signs that La Nina is on the way out and clearly, the more favourable phases of 6-7-8 through late Nov and Dec would be extremely interesting indeed.

While I can't post the images directly (there's too many nosey people on the internet) I've seen a few recent runs of the UKMO GloSea output for 60N 10hPa zonal mean winds and there has been a sudden shift, but with increasing consistency, for zonal winds to quickly drop away through the second half of Dec, with a number of members bringing about a late Dec/early Jan SSW.

The seasonals have all been about early winter blocking and I still fully expect that to come to fruition now and, finally, should hopefully kick this damn N Atlantic trough to touch, for a while, or least help relocate it. Without jumping the gun too quickly though, could it well be a winter season whereby the primary caveat for sig changes to the outlook is heavily reliant on a significant SSW but one we are potentially seeing the building blocks for come into place now and of which could well mean a very different outcome through January/February than what the seasonals have long predicted.

As ever time will tell, but there's definitely "something" about this winter now that is spiking my interest after viewing the blocked signals from the seasonals for the last 3 months or more.

Cheers, Matt.

 

[40/70 Benchmark]

5 hours ago, MattHugo81 said:

Hi to all. Hope you don't mind me continuing the discussions on here...

We seem to be seeing some of the above comments from a week or two back playing out now (no surprises guys!) and it'll be an interesting watch. The extreme -EPO doing the early 'winter goods' across the USA of late but that rise and recovery to more neutral levels seems to be on the way. The feature of interest for the UK and the N Hem as well has been the lack of any progression towards a more blocked pattern sooner than was expected. The EC Seasonal, for example flipped the NAO firmly negative to positive in the blink of an eye and the wait for the early blocking signals have been long overdue, but we seem to be getting somewhere now.

A few key features that are standing out are changes in the AAM profile of late, with more E'ly AAM anoms now appearing through the mid-lats, a reversal of recent weeks, while the all important AAM transports plot highlights a clear change as well through the mid-lats. While the sPV continues to 'do its thing' there is clearly no significant connection at all, as you guys have highlighted most recently as well. Clearly, it can be that time of year now through the RI period that a quick downwelling of strong W'lies just over takes anything else and, for the worst case scenario for the UK, the next 4 to 5 weeks simply becomes locked into a +ve NAO regime as the usual deep cold Canada air floods into the W Atlantic and game is over.

Clearly, that isn't the case as the below plots highlight...

 

What interests me moving forward is how the MJO evolution, which looks a solid 4-5-6 progression, perhaps into 7 too, could well have on the pattern deeper into December. This is something I think was originally mentioned in this thread, about the next MJO passage. It is also interesting to note that the IOD seems to be trending more neutral as well, but clearly there is always a lag here. It will be very interesting to see how this next MJO wave progresses. I do have a feeling as well that these are the early signs that La Nina is on the way out and clearly, the more favourable phases of 6-7-8 through late Nov and Dec would be extremely interesting indeed.

While I can't post the images directly (there's too many nosey people on the internet) I've seen a few recent runs of the UKMO GloSea output for 60N 10hPa zonal mean winds and there has been a sudden shift, but with increasing consistency, for zonal winds to quickly drop away through the second half of Dec, with a number of members bringing about a late Dec/early Jan SSW.

The seasonals have all been about early winter blocking and I still fully expect that to come to fruition now and, finally, should hopefully kick this damn N Atlantic trough to touch, for a while, or least help relocate it. Without jumping the gun too quickly though, could it well be a winter season whereby the primary caveat for sig changes to the outlook is heavily reliant on a significant SSW but one we are potentially seeing the building blocks for come into place now and of which could well mean a very different outcome through January/February than what the seasonals have long predicted.

As ever time will tell, but there's definitely "something" about this winter now that is spiking my interest after viewing the blocked signals from the seasonals for the last 3 months or more.

Cheers, Matt.

 

Thanks for chiming in, Matt...love your stuff.

The neg IOD and la nina should both relinquish their grip relatively early, per my research, since this is a stagnant la nina that has carried over from last year. They have more staying power when the atmospheric dynamics that foster the development of the ENSO-IOD development and coupling are still maturing, as opposed to largely an atmospheric imprint of last year's state.

[raindancewx]

This is why I went warm in November in the Plains/Midwest. Most of the analogs I had flipped warm late month central/east after a big cold snap mid-month. I suspect the greatest extent of the cold by severity and area was on 11/22 this month - but we'll see. GFS has pretty warm temps for the next week in the general area of red below.

The final weeks of Nov 1984, 2011, 2016, 2020 in my analog set are all pretty warm, with 2012/2021 as near opposites, and then the -high ACE years also favoring the look above generally.

 

[OHweather]

Definitely a good call on the late November warm up...suspected we'd get a milder spell, but for a week or so the CONUS will be very mild. Looking into December, I still remain quite intrigued...agree with Matt that I feel like we may be getting somewhere with the pattern pretty soon.

the ensembles are increasingly keying on a pattern featuring a -EPO and -NAO into the first half of December, though with an initially -PNA. This would support colder air pressing back into the CONUS starting early next week out west after a relatively brief hiatus (on the broader, national scale). With an initially -PNA the cold air will first focus out west with mild weather over the eastern U.S., though a persistent -EPO and eventual -NAO could change that. Ok, time for some loops:

So to start, the pattern early in the loop is a mild one across the CONUS. There’s troughing over Alaska (a positive East Pacific Oscillation/EPO) that’s flooding much of the CONUS with milder air after our impressive mid-November chill. With a -PNA (Aleutian ridge/west coast trough) any limited cooler air is going into the western U.S. right now.

But, focus on Scandinavia (northwestern Europe). A persistent Scandinavian block has been ongoing and is progged to amplify this week. First, it sends a blast of cold air into Siberia and the rest of eastern Asia, a key to changing the Pacific pattern. Then, the block is shown on the European ensemble mean to retrograde towards Greenland, causing a negative NAO to develop through early December.

This Scandinavian ridge/block has been persistently modeled for a couple of weeks, which is impressive…and it’s also a pretty important piece to the puzzle. The set-up, as everything is currently modeled, seems to support both a -EPO and -NAO developing through the first half of December.

The blast of cold air into eastern Asia sends strong high pressure down the eastern side of the Himalayas, in contrast to the current low pressure over eastern Asia. Low pressure lowers the resistance against the planet’s rotation east of these tall mountains, allowing the planet’s rotation to speed up ever so slightly. To conserve angular momentum, the Asian-Pacific jet slows down and retracts. This favors anomalous ridging over the northwestern Pacific and low pressure over western North America…not a cold pattern for the Lower 48.

Fast forward to later this week and beyond, when high pressure drops in east of the Himalayas and does the opposite, speeding up and extending the Asian-Pacific jet. This favors lower pressure over the northwest Pacific in the exit region of the jet and pushes the ridge east, while the added momentum into the Pacific jet amplifies that Rossby wave train. Low pressure over western North America is replaced by high pressure descending out of the high latitudes. It’s a much colder pattern for most of the CONUS, though the East Coast will be the last place to consistently get the cold.

Also note how Rocky mountain torque is demonstrably important. Early in the loop, high pressure east of the Rockies is in place, which favors intensifying/extending the jet over eastern North America and into the northern Atlantic. This favors low pressure over the North Atlantic in the left exit region and a +NAO. However, a series of low pressure systems developing east of the Rockies in the middle portion of the loop does the opposite, retracting the jet and giving the Scandinavian block room to retrograde.

To best illustrate, here's the 250mb wind loop:

Early in the loop, the jet streak is breaking near the coast of East Asia and the north Pacific ridge is well to the west. As the jet extends in response to the East Asian Mountain Torque, that ridge is pushed east, a pattern much more conducive for pressing cold air into Canada and towards the continental U.S…also check out the Atlantic. Initially, the jet is roaring off the East Coast, but as low pressures develop east of the Rocky mountains and cause a negative mountain torque, the jet pulls back and allows ridging to retrograde over the North Atlantic. This causes the NAO to trend negatively, and is more conducive to troughing over the eastern U.S.

Another way to visualize this chain reaction…cold dumps into eastern Asia. Alaska then goes from cold to mild. Cold air then begins pressing into the CONUS. As ridging retrogrades over the North Atlantic and cold continues to funnel into the west, increasing pressure is put on the Southeast ridge and the eastern U.S. gradually sees cooldowns. Probably a very up and down pattern in the east, and leaning much colder west. In general, as the highest latitudes warm, the mid latitudes cool.

The MJO is moving into Phase 7 at a high latitude for the second time this month, and it could end up squeaking into 8:

Convection has been favoring the eastern Indian Ocean/western Pacific all summer and fall, a classic more “eastern based” La Nina response:

In the late fall/early winter, a phase 7 MJO is typically followed by ridging near Alaska and Greenland, a -EPO and -NAO respectively, with cold first dropping into the west and then spilling east. We are approaching Lag=0 now and will be Lag=1 and 2 next week into the following week (each lag is 5 days):

Lots of stuff pointing to a -EPO and -NAO and resulting colder pattern over the CONUS and slightly thereafter Europe as well…though don’t overlook the initial -PNA and Southeast Ridge causing cold to go into the western U.S. first.

Can this return to cold through early December bust? As always with a longer range forecast, yes. My main concern is where the tropospheric polar vortex ends up, and if it splits as quickly as modeled over the next 7-10 days:

In particular, my concern is where the lobe over northeast Asia ends up. If it ends up dropping a bit farther east, it could mute any ridging into Alaska. I feel that’s on the less likely side, but it’s slightly precarious. If we see the tropospheric polar vortex split like the ensembles currently show, with one lobe into Siberia and another into northern Canada it bodes towards the colder outcome being favored over North America in December.