Winter 2023/24 Medium/Long Range Discussion

[DocATL]

The Euro not very enthusiastic about snow.


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[Chicago Storm]

The gyre of a storm system moving across the country the next few days is pretty much the lead-in to the new pattern.

Going to end up with a solid snowstorm (Blizzard?) across portions of the Northern/Central Plains, something that has been lacking out there this season so far.

[OHweather]

21 hours ago, Chicago Storm said:

As has been mentioned, we are heading into a significant pattern change. Changes on the large scale really start to appear this weekend and into the beginning of this upcoming week. This new pattern, which may very well evolve over time, will extend through the first 1/3rd of January, and quite possibly the first 1/2 of January.

Two big changes that we are seeing right off the bat and that have already begun are a progression of the MJO into the colder phases and a stratospheric warming event. The MJO recently entered the COD, after being in low-amplitude warmer phases from the very end of November through the first 2/3rds of December. The trip through those warmer phases is one of several reasons (Raging Pac Jet is another) that we have been stuck in a consistently mild (Sometimes very mild) regime. The MJO has now entered a colder phase, low amplitude phase 8, and is expected to make a trip at lower amplitude roughly through colder phases 1-2 over the next 1-2 weeks. Another thing that we will be watching unfold is stratospheric warming. This event is expected to disrupt the main SPV placement and strength during the potentially 1-3 week event. As is usually the case, any effects of the SSWE will not be seen right away; that is something to keep an eye on from around week 2 in January through early February.

As mentioned above, there are a few reasons we have been seeing consistently mild (Sometimes very mild) conditions over the past several weeks. The raging Pacific jet is one of those bigger reasons. The Pacific jet is expected to break down soon, with increased troughy-ness (Wave breaks) developing. Canadian ridging, which will retrograde from Central to Western Canada and eventually Alaska, will also tend to lower Pacific influence as well.

Getting beyond the MJO, SSW and Pac jet... We are likely to see a fairly consistent flow of waves/disturbances/troughs enter the CONUS along the West Coast, originating from the deep/mean trough from the Aleutians down into the Northeast Pacific. This is characterized by the lower-height anomalies from the Northeast Pacific and then across the southern 2/3rds or so of the CONUS. Additionally, with the Pacific jet breaking down and the retrograding ridging in Canada, this will lead to generally cooler/colder conditions overall than have been seen, with an airmass origin more often than not from the Northeast Pacific to Pole regions.

All in all, with this pattern change...
-While it may not be super/hyper active, there will be a steady stream of disturbances that traverse the CONUS. Will they all turn into something interesting? No. But having a feed is a start.
-It is very clearly not going to be as significantly/consistently as mild as it has been. That's not to say there won't be any bouts of mild temperatures, but what we have been seeing will be in the past for now.
-The chances for wintry storm potential are not amazing, but definitely an improvement compared to much of the past 1-2 months.

Couldn't have said it better myself. Great post!! Pretty much in agreement with you.

This type of evolution, with multiple troughs ejecting out of the west as the PNA trends negative...but with some sort of a PV over eastern Canada and a bit of downstream blocking, keeping things from cutting/amplifying too much...would bring at least some snow potential to the region January 4-10th or so...maybe lingering longer if the blocking can persist. 

I feel like the change to more polar influence and some blocking (both in the northern Pacific and Atlantic IMO) are strongly supported by the larger-scale drivers (tropical forcing, mountain torque, stratosphere) as @Chicago Stormlaid out. I don't think we'll get a great clipper pattern or persistent arctic air, which are the bread and butter of upper Midwest and Great Lakes snow climo, but some colder air and southern stream influence should bring trackable potentials at least. 

[DocATL]

Couldn't have said it better myself. Great post!! Pretty much in agreement with you.

This type of evolution, with multiple troughs ejecting out of the west as the PNA trends negative...but with some sort of a PV over eastern Canada and a bit of downstream blocking, keeping things from cutting/amplifying too much...would bring at least some snow potential to the region January 4-10th or so...maybe lingering longer if the blocking can persist. 
I feel like the change to more polar influence and some blocking (both in the northern Pacific and Atlantic IMO) are strongly supported by the larger-scale drivers (tropical forcing, mountain torque, stratosphere) as [mention=147]Chicago Storm[/mention]laid out. I don't think we'll get a great clipper pattern or persistent arctic air, which are the bread and butter of upper Midwest and Great Lakes snow climo, but some colder air and southern stream influence should bring trackable potentials at least. 

Will be interesting for sure. It seems like Nina or Nino, the pacific jet continues to be the biggest influence on our weather. PV splits seem to not deliver up to the hype. But literally anything beats the current pattern. 52° right now in western suburbs of Chicago. Got to be a record high low.


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[Powerball]

1 hour ago, DocATL said:

Will be interesting for sure. It seems like Nina or Nino, the pacific jet continues to be the biggest influence on our weather. PV splits seem to not deliver up to the hype. But literally anything beats the current pattern. 52° right now in western suburbs of Chicago. Got to be a record high low.


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Surprisingly, the current record high minimum for today at ORD is 37*F (set in 2019). And I say surprisingly because 37*F does feel low (but that's just a hunch, I have nothing empirical to back that up with).

I doubt 52*F (or more specifically, 50*F at ORD) holds, but even several degrees lower than that would still shatter the record.

[DocATL]

Surprisingly, the current record high minimum for today at ORD is 37*F (set in 2019). And I say surprisingly because 37*F does feel low (but that's just a hunch, I have nothing empirical to back that up with).
I doubt 52*F (or more specifically, 50*F at ORD) holds, but even several degrees lower than that would still shatter the record.

Record high minimum for Chicago was 46° and looks like we beat that barring a significant drop before midnight! We won’t beat the all time high of 64° unfortunately. What a time to be alive! Tempted to check if the hydrangeas are budding. Looks like I brought the south with me when I moved north!

[Powerball]

28 minutes ago, DocATL said:

Record high minimum for Chicago was 46° and looks like we beat that barring a significant drop before midnight! We won’t beat the all time high of 64° unfortunately. What a time to be alive! Tempted to check if the hydrangeas are budding. Looks like I brought the south with me when I moved north!

I'm guessing that 46*F is from when the University of Chicago was the main order station (so a stronger UHI influence) as that particular record is from 1936.

[CorePunch]

DTX giving some insight into the upcoming pattern. Optimistic for winter fans. 
 

A quick perusal of recent GEFS/EPS/CMCE runs suggest this may very
well be the beginning of more notable overall winter season pattern
change after starting off with such a mild December as a much larger
reservoir of polar-arctic air is forecast to become established
from the arctic region on south through much of Canada in the early
to mid January time frame. While details are elusive at this time
frame to say the least, it does seem unlikely that the very mild
December pattern will hold through January.
 

[OHweather]

4 hours ago, DocATL said:

Will be interesting for sure. It seems like Nina or Nino, the pacific jet continues to be the biggest influence on our weather. PV splits seem to not deliver up to the hype. But literally anything beats the current pattern. 52° right now in western suburbs of Chicago. Got to be a record high low.


.

Assuming I have time tonight I'll try to put together a post laying out my thoughts a little bit more...I'd agree that the Pacific jet drove things last winter and has largely driven things this winter. Any PV split probably won't happen until about January 5-10th, and if that does couple to the troposphere and lead to persistent high-latitude blocking that blocking likely wouldn't establish itself until the second half of January. These things just don't happen on timescales that are as quick as everyone wants...you can see the early signs of a pattern that may lead to an SSW two full months before it leads to blocking, which is an eternity when the pattern sucks and you want it to change. And unfortunately many people just use those early signs as something to hype without throwing in a line about how long it would take to get results. For the time being, the Pacific jet will continue to dictate things...we'll have a period of more seasonal weather to start the New Year. It does look like there will be at least a transient period of western US troughing and eastern North American ridging in the middle 1/3rd of January, but I am leaning towards a more prolonged pattern change after that. 

[OHweather]

Wanted to lay out some things happening with some larger scale pattern drivers now and over the next few weeks and look at how they may impact chances for cold and snow potential. Chicago Storm's post on the prior page touched on most of these things. Behavior of the Pacific jet and potential for high latitude blocking will determine much of how this goes...something that can probably be said most of the time in the winter months. 

Not to be a wet blanket here but I don't want to get expectations unrealistically high at this point. Much of the subforum is going to be in a rather substantial seasonal snowfall hole before any sort of sustained colder pattern develops. In a strong El Nino it's inherently harder to get into a polar jet dominated pattern with lots of cold, clippers, and lake effect snow...those are patterns that are productive for much of the Midwest and Great Lakes. The mid-Mississippi and Ohio Valley portion of this subforum has lower annual snowfall and may get lucky with an active subtropical jet in an El Nino, so on that I would say that region has the greatest potential to rally and finish near or somewhat above average snowfall at this point...if anyone can. For the rest of the sub a below average seasonal snowfall is by far the more likely outcome at this point, but the pattern will be colder and more conducive to snow at times so I don't think we're looking at another year without a winter. We should see some windows of more wintry conditions. 

A significant influence on the Pacific jet stream is East Asian Mountain Torque (EAMT). Remember that big cold blast in Siberia earlier this month? The Arctic high associated with that dropped across eastern Asia (and is still doing so early in the above loop). This denser airmass and higher pressure east of the Himalayas puts a torque against the planet's rotation, slowing it down an imperceptible amount. To conserve momentum, this is compensated for by speeding up the jet stream over the Pacific...promoting stormier conditions over the northern Pacific. The Rockies can have a similar affect on the jet stream over the north Atlantic.

Note how a strong positive EAMT event occurred over the last week or so as the Siberian high dropped into eastern Asia. EAMT will generally trend more negative over the next 2-3 weeks, though I'd say it's possible we see one last little push of +EAMT in the first few days of January which may be important to determining how quickly the Pacific jet retracts in the coming weeks. 

The strong +EAMT led to the dramatic intensification of the north Pacific jet ongoing now, though the jet will begin retracting over the coming days and continue retracting/weakening into early January as EAMT trends more negative (and as tropical forcing changes, will get into that below). The stronger jet leads to stronger ageostrophic flow within its embedded jet streaks, encouraging a stormier (and amplified) pattern, especially near the eastern edge of the jet where the upper-level flow is most diffluent. 

As the jet reached its easternmost extension over the last few days the stormy pattern was over the southwestern US with ridging amplifying northeast of that. As the jet begins retracting over the next several days the stormy pattern will shift west into the Pacific, allowing ridging to shift west towards the west coast and Alaska while continuing to amplify. This jet evolution has strongly contributed to our ongoing mild pattern and the change will contribute to a period of cooler conditions to start January. 

https://www.atmos.albany.edu/facstaff/awinters/realtime/Deterministic_NPJPD.php

Wanted to demonstrate how important the Pacific jet has been on the pattern we are seeing. Per the analysis, we went from a jet retraction in mid December to a recent poleward shift of the jet. The jet is expected to be more characteristic of the "jet extension" phase the rest of this month, before briefly moving through an Equatorward Shift space back towards jet retraction (due to the negative trend in the East Asian Mountain Torque). 

Poleward shift heights and resultant temperatures:

A very Pacific-dominated pattern with minimal polar/arctic influence and very mild conditions across a good portion of Canada and the northern CONUS. Very similar to what we're currently seeing. 

How about a jet extension, which is what we'll see over the coming days?

Supports increasing heights along the West Coast and into Alaska, less Pacific influence, and at least some polar and arctic influence into North America, with cooler anomalies over parts of the eastern U.S. Looks a bit like the pattern showing up on the models and ensembles over the next week.

An equatorward shift is inherently hard to sustain in an El Nino but is most conducive to EPO-induced cold shots into southern Canada and the CONUS:

Jet retractions favor flatting ridging farther west over the North Pacific...a -PNA pattern, which is showing up in the extended ensembles...

 

Tropical forcing is also influencing the pattern...the MJO is making a fairly amplified pass through phases 1-2 through early January:

This supports amplification of western North American ridging and at least some semblance of a -NAO (Phase 1 top, Phase 2 bottom):

https://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html

So far the East Asian Mountain torque and tropical forcing do a good job of explaining the evolution of the Pacific jet and the recent/upcoming North American pattern. The troposphere and stratosphere have seemed to be relatively well-coupled so far this season, with an amplified pattern in the troposphere in late November and early December leading to increased upward heat and wave fluxes into the stratosphere. This has led to an ongoing stratospheric warming event that appears poised to downwell into the troposphere. 

https://stratobserve.com/anom_ts_diags

Not only do the mountain torque and tropical forcing support amplified ridging on the west coast into Alaska the rest of this month into early January, along with perhaps a -NAO, but the downwelling negative AO out of the stratosphere supports high-latitude blocking. Lots of factors supporting the pattern change that will be getting underway very soon. 

Here's a look at the EPS mean 500mb and surface temperature forecasts through the upcoming pattern change:

The 500mb evolution shown on the ensemble seems strongly supported by the various forcings described above over the next 10 days. The ongoing storm over the central U.S. starts carving out a trough over the eastern US over the next several days, with amplifying ridging on the west coast deepening the trough over the next 10 days as energy ejects out of the southwest U.S. in the subtropical jet. This leads to increased polar influence into Canada and the U.S., but the source region is currently very mild which will take quite a while to completely overcome. 

 

The result is a cooler trend over the CONUS, especially over the southern U.S. where the active subtropical jet keeps conditions more active. Over Canada it remains generally mild for the foreseeable future but certainly trends much less mild than recent conditions. It's worth noting that this is a change from temperatures well above freezing all the way to Hudson Bay to sub-zero temperatures (on the ensemble mean) down to at least that latitude:

The tug of colder air behind the current Plains storm is very meager but the colder air becomes much more "tappable" by the beginning of January, so any storms that develop will be able to pull in seasonally cold air. Nothing crazy but certainly much more wintry feeling that at the moment. Note those frames are all 12z which catches something close to the daily lows.

While the tropical forcing, mountain torque/Pacific jet, and stratospheric influence support upcoming amplification of ridging along the West Coast into Alaska and perhaps a -NAO, there are certainly hints at a more -PNA pattern taking hold in two weeks. Is that legit? 

Recall back to the SLP loop and the mountain torque discussion:

A sustained negative EAMT event appears likely in early January, supporting retraction of the Pacific jet (and a -PNA). Note how a similar evolution (about a week later) of Rocky Mountain Torque supports ridging over the North Atlantic, as a +RMT and strong North Atlantic jet to start January gives way to a -RMT and weakened North Atlantic jet by the second week of the month. 

https://charts.ecmwf.int/?facets={"Product type"%3A[]%2C"Parameters"%3A[]%2C"Type"%3A[]%2C"Range"%3A["Extended (42 days)"]}

There is some uncertainty regarding how the MJO evolves beyond the next 10 days. Many ensemble members have the wave weakening and moving into the "circle" in the day 15-20 range (blue and green dots, valid the 2nd week of January). A number of members maintain amplitude into phase 3 and some into phase 4 and 5. That seems unlikely but the ongoing stratospheric warming event may support a stronger and more amplified MJO moving across the Indian Ocean and into the western Pacific mid-late January...a trend worth monitoring. Even a phase 3 MJO in early January suggests a trend to a more -PNA/west coast trough:

To sum up where things are so far:

Tropical forcing, mountain torque/the Pacific jet and stratosphere support a pattern change over the next week. This will increase polar influence into Canada and the U.S. and favor development of an eastern U.S. trough during the first week of January. Mountain torque and tropical forcing suggest continued Pacific jet retraction in early to mid-January, which will encourage ridging to retrograde across Alaska as troughing over the eastern CONUS also retrogrades/shifts west. This will lead to conditions initially supporting any southern stream systems bringing a wintry threat to the interior Southeast/Mid Atlantic the first few days of January, but with wintry potential shifting west across this subforum in the January 4-10 range...perhaps lingering through the middle of January if ridging doesn't shift west towards the west coast too quickly. With generally mild conditions persisting over Canada the pattern won't favor strong clippers or huge arctic outbreaks that can set off days-long lake effect snow storms, but southern stream storms may be able to bring swaths of snow if they phase enough with the polar jet. And, a modest clipper and some lake effect could still be possible with Canada trending more seasonal. 

Looking further ahead, a number of EPS members have a significant stratospheric warming event (SSW) between January 5-15. If this occurred it would lead to greatly increased potential for sustained high-latitude blocking beginning in late January and persisting well into (and perhaps through) February. It is very common for a warm-up to occur over the central and eastern U.S. as a stratospheric warming event is ongoing, before any blocking it sets off can establish. This would line up with hints of a -PNA and +EPO towards the middle of January. 

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml 

Looking at tropical forcing, the forcing has generally been amplified over the central Pacific (near 180 longitude) and over the western Indian Ocean (near 25E), roughly outlined by the green boxes. Tropical forcing has generally been suppressed between these two areas. The tropical forcing has moved through the western hemisphere (phase 1 MJO and favorable for colder weather) every 3-4 weeks.

If this continued it would move back through the western hemisphere by the middle of January. However, it seems like the tropical forcing was more driven by faster-moving Kelvin Waves until the two most-recent orbits, which featured stronger and slower-moving anomalies more typical of the MJO. This most recent pass remained strong through the eastern Indian Ocean subsidence zone but also took closer to 4-5 weeks to return to the western hemisphere. If this more recent trend continues it will return to the western hemisphere in the ~3rd week of January and support a more favorable Pacific influence on the pattern, along with a -NAO. However, the stratospheric warming event over the pole leads to a colder lower stratosphere over the tropics, which may amplify and slow down the progression of the tropical forcing. I would say smart money is on tropical forcing becoming favorable for a western North America ridge to return during the last week of January. Potential exists for prolonged -NAO blocking by then if we do in fact see a major stratospheric warming event (which appears likely during the first half of January). 

After the cool down into early January, leading to a favorable pattern for any amplified southern stream system to bring snow potential to the region in the January 4-10th timeframe, along with perhaps a modest clipper and some lake effect, a trend towards a trough with colder air over the western U.S. and ridging farther east is supported for the middle portion of January. By the end of January potential appears to be there for impacts from a stratospheric warming event and tropical forcing to support a western North American ridge, eastern trough, and high-latitude blocking with an active southern stream. This would lead to a few week period of more wintry weather, and while unlikely to make up for seasonal snowfall deficits completely could salvage a semblance of a winter in the region. 

[A-L-E-K]

Zzzzzz 

On to February 

[MJO812]

3 hours ago, A-L-E-K said:

Zzzzzz 

On to February 

We are all suffering 

[Dabuckeyes]

5 hours ago, A-L-E-K said:

Zzzzzz 

On to February 

Fantastic analysis. Where did you go to school for meteorology?

[CheeselandSkies]

5 hours ago, A-L-E-K said:

Zzzzzz 

On to February 

Hey, at least the GFS is giving us fantasy range crush jobs now (for southern WI, still rain for Chicago).

[Stevo6899]

5 hours ago, A-L-E-K said:

Zzzzzz 

On to February 

In other words, alek appreciates and thanks you for taking the time to post your analysis ohweather. I echo his sentiments.

[Chicago Storm]

Zzzzzz 
On to February 

lol.


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[Chambana]

7 hours ago, A-L-E-K said:

Zzzzzz 

On to February 

Not ready 2 b buried? 

[Chicago Storm]

15 hours ago, OHweather said:

Wanted to lay out some things happening with some larger scale pattern drivers now and over the next few weeks and look at how they may impact chances for cold and snow potential. Chicago Storm's post on the prior page touched on most of these things. Behavior of the Pacific jet and potential for high latitude blocking will determine much of how this goes...something that can probably be said most of the time in the winter months. 

Solid stuff.

I forgot to mention anything regarding the mountain torque evolution, so it's good you had a big mention of that.

[michsnowfreak]

FANTASTIC analysis @OHweather! I'm not worried about finishing with a below average snow season, I would just love some bouts of wintry weather with some sustainability. Ironically last year, though many areas outside MSP considered it a year without a winter, we actually finished with near normal snowfall in the Detroit area (slightly below average in the southern burbs and slightly above average in the northern burbs). This was due to multiple juicy winter storms that were fun to experience but did not last on the ground long. If we flip the script and get some smaller snowfall that actually stay awhile, given it's a strong nino I won't complain.

[RCNYILWX]

Wanted to lay out some things happening with some larger scale pattern drivers now and over the next few weeks and look at how they may impact chances for cold and snow potential. Chicago Storm's post on the prior page touched on most of these things. Behavior of the Pacific jet and potential for high latitude blocking will determine much of how this goes...something that can probably be said most of the time in the winter months. 
Not to be a wet blanket here but I don't want to get expectations unrealistically high at this point. Much of the subforum is going to be in a rather substantial seasonal snowfall hole before any sort of sustained colder pattern develops. In a strong El Nino it's inherently harder to get into a polar jet dominated pattern with lots of cold, clippers, and lake effect snow...those are patterns that are productive for much of the Midwest and Great Lakes. The mid-Mississippi and Ohio Valley portion of this subforum has lower annual snowfall and may get lucky with an active subtropical jet in an El Nino, so on that I would say that region has the greatest potential to rally and finish near or somewhat above average snowfall at this point...if anyone can. For the rest of the sub a below average seasonal snowfall is by far the more likely outcome at this point, but the pattern will be colder and more conducive to snow at times so I don't think we're looking at another year without a winter. We should see some windows of more wintry conditions. 

A significant influence on the Pacific jet stream is East Asian Mountain Torque (EAMT). Remember that big cold blast in Siberia earlier this month? The Arctic high associated with that dropped across eastern Asia (and is still doing so early in the above loop). This denser airmass and higher pressure east of the Himalayas puts a torque against the planet's rotation, slowing it down an imperceptible amount. To conserve momentum, this is compensated for by speeding up the jet stream over the Pacific...promoting stormier conditions over the northern Pacific. The Rockies can have a similar affect on the jet stream over the north Atlantic.

Note how a strong positive EAMT event occurred over the last week or so as the Siberian high dropped into eastern Asia. EAMT will generally trend more negative over the next 2-3 weeks, though I'd say it's possible we see one last little push of +EAMT in the first few days of January which may be important to determining how quickly the Pacific jet retracts in the coming weeks. 
The strong +EAMT led to the dramatic intensification of the north Pacific jet ongoing now, though the jet will begin retracting over the coming days and continue retracting/weakening into early January as EAMT trends more negative (and as tropical forcing changes, will get into that below). The stronger jet leads to stronger ageostrophic flow within its embedded jet streaks, encouraging a stormier (and amplified) pattern, especially near the eastern edge of the jet where the upper-level flow is most diffluent. 
As the jet reached its easternmost extension over the last few days the stormy pattern was over the southwestern US with ridging amplifying northeast of that. As the jet begins retracting over the next several days the stormy pattern will shift west into the Pacific, allowing ridging to shift west towards the west coast and Alaska while continuing to amplify. This jet evolution has strongly contributed to our ongoing mild pattern and the change will contribute to a period of cooler conditions to start January. 

https://www.atmos.albany.edu/facstaff/awinters/realtime/Deterministic_NPJPD.php
Wanted to demonstrate how important the Pacific jet has been on the pattern we are seeing. Per the analysis, we went from a jet retraction in mid December to a recent poleward shift of the jet. The jet is expected to be more characteristic of the "jet extension" phase the rest of this month, before briefly moving through an Equatorward Shift space back towards jet retraction (due to the negative trend in the East Asian Mountain Torque). 
Poleward shift heights and resultant temperatures:


A very Pacific-dominated pattern with minimal polar/arctic influence and very mild conditions across a good portion of Canada and the northern CONUS. Very similar to what we're currently seeing. 
How about a jet extension, which is what we'll see over the coming days?


Supports increasing heights along the West Coast and into Alaska, less Pacific influence, and at least some polar and arctic influence into North America, with cooler anomalies over parts of the eastern U.S. Looks a bit like the pattern showing up on the models and ensembles over the next week.
An equatorward shift is inherently hard to sustain in an El Nino but is most conducive to EPO-induced cold shots into southern Canada and the CONUS:


Jet retractions favor flatting ridging farther west over the North Pacific...a -PNA pattern, which is showing up in the extended ensembles...


 
Tropical forcing is also influencing the pattern...the MJO is making a fairly amplified pass through phases 1-2 through early January:

This supports amplification of western North American ridging and at least some semblance of a -NAO (Phase 1 top, Phase 2 bottom):

https://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html
So far the East Asian Mountain torque and tropical forcing do a good job of explaining the evolution of the Pacific jet and the recent/upcoming North American pattern. The troposphere and stratosphere have seemed to be relatively well-coupled so far this season, with an amplified pattern in the troposphere in late November and early December leading to increased upward heat and wave fluxes into the stratosphere. This has led to an ongoing stratospheric warming event that appears poised to downwell into the troposphere. 

https://stratobserve.com/anom_ts_diags
Not only do the mountain torque and tropical forcing support amplified ridging on the west coast into Alaska the rest of this month into early January, along with perhaps a -NAO, but the downwelling negative AO out of the stratosphere supports high-latitude blocking. Lots of factors supporting the pattern change that will be getting underway very soon. 
Here's a look at the EPS mean 500mb and surface temperature forecasts through the upcoming pattern change:

The 500mb evolution shown on the ensemble seems strongly supported by the various forcings described above over the next 10 days. The ongoing storm over the central U.S. starts carving out a trough over the eastern US over the next several days, with amplifying ridging on the west coast deepening the trough over the next 10 days as energy ejects out of the southwest U.S. in the subtropical jet. This leads to increased polar influence into Canada and the U.S., but the source region is currently very mild which will take quite a while to completely overcome. 
 

The result is a cooler trend over the CONUS, especially over the southern U.S. where the active subtropical jet keeps conditions more active. Over Canada it remains generally mild for the foreseeable future but certainly trends much less mild than recent conditions. It's worth noting that this is a change from temperatures well above freezing all the way to Hudson Bay to sub-zero temperatures (on the ensemble mean) down to at least that latitude:

The tug of colder air behind the current Plains storm is very meager but the colder air becomes much more "tappable" by the beginning of January, so any storms that develop will be able to pull in seasonally cold air. Nothing crazy but certainly much more wintry feeling that at the moment. Note those frames are all 12z which catches something close to the daily lows.
While the tropical forcing, mountain torque/Pacific jet, and stratospheric influence support upcoming amplification of ridging along the West Coast into Alaska and perhaps a -NAO, there are certainly hints at a more -PNA pattern taking hold in two weeks. Is that legit? 
Recall back to the SLP loop and the mountain torque discussion:

A sustained negative EAMT event appears likely in early January, supporting retraction of the Pacific jet (and a -PNA). Note how a similar evolution (about a week later) of Rocky Mountain Torque supports ridging over the North Atlantic, as a +RMT and strong North Atlantic jet to start January gives way to a -RMT and weakened North Atlantic jet by the second week of the month. 

https://charts.ecmwf.int/?facets={"Product type"%3A[]%2C"Parameters"%3A[]%2C"Type"%3A[]%2C"Range"%3A["Extended (42 days)"]}
There is some uncertainty regarding how the MJO evolves beyond the next 10 days. Many ensemble members have the wave weakening and moving into the "circle" in the day 15-20 range (blue and green dots, valid the 2nd week of January). A number of members maintain amplitude into phase 3 and some into phase 4 and 5. That seems unlikely but the ongoing stratospheric warming event may support a stronger and more amplified MJO moving across the Indian Ocean and into the western Pacific mid-late January...a trend worth monitoring. Even a phase 3 MJO in early January suggests a trend to a more -PNA/west coast trough:

To sum up where things are so far:
Tropical forcing, mountain torque/the Pacific jet and stratosphere support a pattern change over the next week. This will increase polar influence into Canada and the U.S. and favor development of an eastern U.S. trough during the first week of January. Mountain torque and tropical forcing suggest continued Pacific jet retraction in early to mid-January, which will encourage ridging to retrograde across Alaska as troughing over the eastern CONUS also retrogrades/shifts west. This will lead to conditions initially supporting any southern stream systems bringing a wintry threat to the interior Southeast/Mid Atlantic the first few days of January, but with wintry potential shifting west across this subforum in the January 4-10 range...perhaps lingering through the middle of January if ridging doesn't shift west towards the west coast too quickly. With generally mild conditions persisting over Canada the pattern won't favor strong clippers or huge arctic outbreaks that can set off days-long lake effect snow storms, but southern stream storms may be able to bring swaths of snow if they phase enough with the polar jet. And, a modest clipper and some lake effect could still be possible with Canada trending more seasonal. 

Looking further ahead, a number of EPS members have a significant stratospheric warming event (SSW) between January 5-15. If this occurred it would lead to greatly increased potential for sustained high-latitude blocking beginning in late January and persisting well into (and perhaps through) February. It is very common for a warm-up to occur over the central and eastern U.S. as a stratospheric warming event is ongoing, before any blocking it sets off can establish. This would line up with hints of a -PNA and +EPO towards the middle of January. 

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml 
Looking at tropical forcing, the forcing has generally been amplified over the central Pacific (near 180 longitude) and over the western Indian Ocean (near 25E), roughly outlined by the green boxes. Tropical forcing has generally been suppressed between these two areas. The tropical forcing has moved through the western hemisphere (phase 1 MJO and favorable for colder weather) every 3-4 weeks.
If this continued it would move back through the western hemisphere by the middle of January. However, it seems like the tropical forcing was more driven by faster-moving Kelvin Waves until the two most-recent orbits, which featured stronger and slower-moving anomalies more typical of the MJO. This most recent pass remained strong through the eastern Indian Ocean subsidence zone but also took closer to 4-5 weeks to return to the western hemisphere. If this more recent trend continues it will return to the western hemisphere in the ~3rd week of January and support a more favorable Pacific influence on the pattern, along with a -NAO. However, the stratospheric warming event over the pole leads to a colder lower stratosphere over the tropics, which may amplify and slow down the progression of the tropical forcing. I would say smart money is on tropical forcing becoming favorable for a western North America ridge to return during the last week of January. Potential exists for prolonged -NAO blocking by then if we do in fact see a major stratospheric warming event (which appears likely during the first half of January). 
After the cool down into early January, leading to a favorable pattern for any amplified southern stream system to bring snow potential to the region in the January 4-10th timeframe, along with perhaps a modest clipper and some lake effect, a trend towards a trough with colder air over the western U.S. and ridging farther east is supported for the middle portion of January. By the end of January potential appears to be there for impacts from a stratospheric warming event and tropical forcing to support a western North American ridge, eastern trough, and high-latitude blocking with an active southern stream. This would lead to a few week period of more wintry weather, and while unlikely to make up for seasonal snowfall deficits completely could salvage a semblance of a winter in the region. 

Fantastic read - do you post this on a vLab forum in the NWS? If not, you should! We could all learn from analysis like this. I certainly am versed in some of the teleconnection stuff but not nearly to this level, and then you bring it together on the planetary wave scale, which is impressive.

We haven't been optimistic locally about snow prospects this winter based off the moderate to strong Niño climo, but felt that the wild card for a time could be temps. Of the 10 mod-strong episodes, 4 or 5 had near to below normal temps, but of those, only 2009-10 had above normal snow. Since this month has been such a torch though, going to be tough to finish at or below normal for DJF temps.

I'm intrigued by the temporary -PNA that looks to occur toward mid month before potentially more pronounced pattern change. If there's enough blocking, the storm track could be modulated to support a colder/snowier outcome. We tend to do pretty well out here with a -PNA/-NAO/-AO, a recent example being late January-mid to late February 2021.

Interestingly, the 2015-16 super Niño narrowly missed out on above normal snow at ORD with the Feb 24th event *just* missing to the southeast. It certainly helped to have a big late November snowstorm, but I'd say that after the December torch, that winter was relatively wintry vs. expectations going in.

[pondo1000]

20 hours ago, OHweather said:

Wanted to lay out some things happening with some larger scale pattern drivers now and over the next few weeks and look at how they may impact chances for cold and snow potential. Chicago Storm's post on the prior page touched on most of these things. Behavior of the Pacific jet and potential for high latitude blocking will determine much of how this goes...something that can probably be said most of the time in the winter months. 

Not to be a wet blanket here but I don't want to get expectations unrealistically high at this point. Much of the subforum is going to be in a rather substantial seasonal snowfall hole before any sort of sustained colder pattern develops. In a strong El Nino it's inherently harder to get into a polar jet dominated pattern with lots of cold, clippers, and lake effect snow...those are patterns that are productive for much of the Midwest and Great Lakes. The mid-Mississippi and Ohio Valley portion of this subforum has lower annual snowfall and may get lucky with an active subtropical jet in an El Nino, so on that I would say that region has the greatest potential to rally and finish near or somewhat above average snowfall at this point...if anyone can. For the rest of the sub a below average seasonal snowfall is by far the more likely outcome at this point, but the pattern will be colder and more conducive to snow at times so I don't think we're looking at another year without a winter. We should see some windows of more wintry conditions. 

A significant influence on the Pacific jet stream is East Asian Mountain Torque (EAMT). Remember that big cold blast in Siberia earlier this month? The Arctic high associated with that dropped across eastern Asia (and is still doing so early in the above loop). This denser airmass and higher pressure east of the Himalayas puts a torque against the planet's rotation, slowing it down an imperceptible amount. To conserve momentum, this is compensated for by speeding up the jet stream over the Pacific...promoting stormier conditions over the northern Pacific. The Rockies can have a similar affect on the jet stream over the north Atlantic.

Note how a strong positive EAMT event occurred over the last week or so as the Siberian high dropped into eastern Asia. EAMT will generally trend more negative over the next 2-3 weeks, though I'd say it's possible we see one last little push of +EAMT in the first few days of January which may be important to determining how quickly the Pacific jet retracts in the coming weeks. 

The strong +EAMT led to the dramatic intensification of the north Pacific jet ongoing now, though the jet will begin retracting over the coming days and continue retracting/weakening into early January as EAMT trends more negative (and as tropical forcing changes, will get into that below). The stronger jet leads to stronger ageostrophic flow within its embedded jet streaks, encouraging a stormier (and amplified) pattern, especially near the eastern edge of the jet where the upper-level flow is most diffluent. 

As the jet reached its easternmost extension over the last few days the stormy pattern was over the southwestern US with ridging amplifying northeast of that. As the jet begins retracting over the next several days the stormy pattern will shift west into the Pacific, allowing ridging to shift west towards the west coast and Alaska while continuing to amplify. This jet evolution has strongly contributed to our ongoing mild pattern and the change will contribute to a period of cooler conditions to start January. 

https://www.atmos.albany.edu/facstaff/awinters/realtime/Deterministic_NPJPD.php

Wanted to demonstrate how important the Pacific jet has been on the pattern we are seeing. Per the analysis, we went from a jet retraction in mid December to a recent poleward shift of the jet. The jet is expected to be more characteristic of the "jet extension" phase the rest of this month, before briefly moving through an Equatorward Shift space back towards jet retraction (due to the negative trend in the East Asian Mountain Torque). 

Poleward shift heights and resultant temperatures:

A very Pacific-dominated pattern with minimal polar/arctic influence and very mild conditions across a good portion of Canada and the northern CONUS. Very similar to what we're currently seeing. 

How about a jet extension, which is what we'll see over the coming days?

Supports increasing heights along the West Coast and into Alaska, less Pacific influence, and at least some polar and arctic influence into North America, with cooler anomalies over parts of the eastern U.S. Looks a bit like the pattern showing up on the models and ensembles over the next week.

An equatorward shift is inherently hard to sustain in an El Nino but is most conducive to EPO-induced cold shots into southern Canada and the CONUS:

Jet retractions favor flatting ridging farther west over the North Pacific...a -PNA pattern, which is showing up in the extended ensembles...

 

Tropical forcing is also influencing the pattern...the MJO is making a fairly amplified pass through phases 1-2 through early January:

This supports amplification of western North American ridging and at least some semblance of a -NAO (Phase 1 top, Phase 2 bottom):

https://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html

So far the East Asian Mountain torque and tropical forcing do a good job of explaining the evolution of the Pacific jet and the recent/upcoming North American pattern. The troposphere and stratosphere have seemed to be relatively well-coupled so far this season, with an amplified pattern in the troposphere in late November and early December leading to increased upward heat and wave fluxes into the stratosphere. This has led to an ongoing stratospheric warming event that appears poised to downwell into the troposphere. 

https://stratobserve.com/anom_ts_diags

Not only do the mountain torque and tropical forcing support amplified ridging on the west coast into Alaska the rest of this month into early January, along with perhaps a -NAO, but the downwelling negative AO out of the stratosphere supports high-latitude blocking. Lots of factors supporting the pattern change that will be getting underway very soon. 

Here's a look at the EPS mean 500mb and surface temperature forecasts through the upcoming pattern change:

The 500mb evolution shown on the ensemble seems strongly supported by the various forcings described above over the next 10 days. The ongoing storm over the central U.S. starts carving out a trough over the eastern US over the next several days, with amplifying ridging on the west coast deepening the trough over the next 10 days as energy ejects out of the southwest U.S. in the subtropical jet. This leads to increased polar influence into Canada and the U.S., but the source region is currently very mild which will take quite a while to completely overcome. 

 

The result is a cooler trend over the CONUS, especially over the southern U.S. where the active subtropical jet keeps conditions more active. Over Canada it remains generally mild for the foreseeable future but certainly trends much less mild than recent conditions. It's worth noting that this is a change from temperatures well above freezing all the way to Hudson Bay to sub-zero temperatures (on the ensemble mean) down to at least that latitude:

The tug of colder air behind the current Plains storm is very meager but the colder air becomes much more "tappable" by the beginning of January, so any storms that develop will be able to pull in seasonally cold air. Nothing crazy but certainly much more wintry feeling that at the moment. Note those frames are all 12z which catches something close to the daily lows.

While the tropical forcing, mountain torque/Pacific jet, and stratospheric influence support upcoming amplification of ridging along the West Coast into Alaska and perhaps a -NAO, there are certainly hints at a more -PNA pattern taking hold in two weeks. Is that legit? 

Recall back to the SLP loop and the mountain torque discussion:

A sustained negative EAMT event appears likely in early January, supporting retraction of the Pacific jet (and a -PNA). Note how a similar evolution (about a week later) of Rocky Mountain Torque supports ridging over the North Atlantic, as a +RMT and strong North Atlantic jet to start January gives way to a -RMT and weakened North Atlantic jet by the second week of the month. 

https://charts.ecmwf.int/?facets={"Product type"%3A[]%2C"Parameters"%3A[]%2C"Type"%3A[]%2C"Range"%3A["Extended (42 days)"]}

There is some uncertainty regarding how the MJO evolves beyond the next 10 days. Many ensemble members have the wave weakening and moving into the "circle" in the day 15-20 range (blue and green dots, valid the 2nd week of January). A number of members maintain amplitude into phase 3 and some into phase 4 and 5. That seems unlikely but the ongoing stratospheric warming event may support a stronger and more amplified MJO moving across the Indian Ocean and into the western Pacific mid-late January...a trend worth monitoring. Even a phase 3 MJO in early January suggests a trend to a more -PNA/west coast trough:

To sum up where things are so far:

Tropical forcing, mountain torque/the Pacific jet and stratosphere support a pattern change over the next week. This will increase polar influence into Canada and the U.S. and favor development of an eastern U.S. trough during the first week of January. Mountain torque and tropical forcing suggest continued Pacific jet retraction in early to mid-January, which will encourage ridging to retrograde across Alaska as troughing over the eastern CONUS also retrogrades/shifts west. This will lead to conditions initially supporting any southern stream systems bringing a wintry threat to the interior Southeast/Mid Atlantic the first few days of January, but with wintry potential shifting west across this subforum in the January 4-10 range...perhaps lingering through the middle of January if ridging doesn't shift west towards the west coast too quickly. With generally mild conditions persisting over Canada the pattern won't favor strong clippers or huge arctic outbreaks that can set off days-long lake effect snow storms, but southern stream storms may be able to bring swaths of snow if they phase enough with the polar jet. And, a modest clipper and some lake effect could still be possible with Canada trending more seasonal. 

Looking further ahead, a number of EPS members have a significant stratospheric warming event (SSW) between January 5-15. If this occurred it would lead to greatly increased potential for sustained high-latitude blocking beginning in late January and persisting well into (and perhaps through) February. It is very common for a warm-up to occur over the central and eastern U.S. as a stratospheric warming event is ongoing, before any blocking it sets off can establish. This would line up with hints of a -PNA and +EPO towards the middle of January. 

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml 

Looking at tropical forcing, the forcing has generally been amplified over the central Pacific (near 180 longitude) and over the western Indian Ocean (near 25E), roughly outlined by the green boxes. Tropical forcing has generally been suppressed between these two areas. The tropical forcing has moved through the western hemisphere (phase 1 MJO and favorable for colder weather) every 3-4 weeks.

If this continued it would move back through the western hemisphere by the middle of January. However, it seems like the tropical forcing was more driven by faster-moving Kelvin Waves until the two most-recent orbits, which featured stronger and slower-moving anomalies more typical of the MJO. This most recent pass remained strong through the eastern Indian Ocean subsidence zone but also took closer to 4-5 weeks to return to the western hemisphere. If this more recent trend continues it will return to the western hemisphere in the ~3rd week of January and support a more favorable Pacific influence on the pattern, along with a -NAO. However, the stratospheric warming event over the pole leads to a colder lower stratosphere over the tropics, which may amplify and slow down the progression of the tropical forcing. I would say smart money is on tropical forcing becoming favorable for a western North America ridge to return during the last week of January. Potential exists for prolonged -NAO blocking by then if we do in fact see a major stratospheric warming event (which appears likely during the first half of January). 

After the cool down into early January, leading to a favorable pattern for any amplified southern stream system to bring snow potential to the region in the January 4-10th timeframe, along with perhaps a modest clipper and some lake effect, a trend towards a trough with colder air over the western U.S. and ridging farther east is supported for the middle portion of January. By the end of January potential appears to be there for impacts from a stratospheric warming event and tropical forcing to support a western North American ridge, eastern trough, and high-latitude blocking with an active southern stream. This would lead to a few week period of more wintry weather, and while unlikely to make up for seasonal snowfall deficits completely could salvage a semblance of a winter in the region. 

Solid stuff as usual!!!

[OHweather]

4 hours ago, michsnowfreak said:

FANTASTIC analysis @OHweather! I'm not worried about finishing with a below average snow season, I would just love some bouts of wintry weather with some sustainability. Ironically last year, though many areas outside MSP considered it a year without a winter, we actually finished with near normal snowfall in the Detroit area (slightly below average in the southern burbs and slightly above average in the northern burbs). This was due to multiple juicy winter storms that were fun to experience but did not last on the ground long. If we flip the script and get some smaller snowfall that actually stay awhile, given it's a strong nino I won't complain.

Those winter storms you saw the second half of last winter were impressive, and if they were shifted a couple hundred miles southeast I probably would've had a more positive impression of last winter. Hopefully we get a few weeks of sustained wintry conditions later January into February that allows any snow that falls to stick around a bit. I enjoy snow...falling, on the ground, whatever it's doing. I certainly enjoy the "chase" (forecasting, communicating it, etc.) and watching it play out the most, so while I appreciate deep winter periods with persistent snow packs I very much enjoy events like Michigan had last winter.

 

2 hours ago, RCNYILWX said:

Fantastic read - do you post this on a vLab forum in the NWS? If not, you should! We could all learn from analysis like this. I certainly am versed in some of the teleconnection stuff but not nearly to this level, and then you bring it together on the planetary wave scale, which is impressive.

We haven't been optimistic locally about snow prospects this winter based off the moderate to strong Niño climo, but felt that the wild card for a time could be temps. Of the 10 mod-strong episodes, 4 or 5 had near to below normal temps, but of those, only 2009-10 had above normal snow. Since this month has been such a torch though, going to be tough to finish at or below normal for DJF temps.

I'm intrigued by the temporary -PNA that looks to occur toward mid month before potentially more pronounced pattern change. If there's enough blocking, the storm track could be modulated to support a colder/snowier outcome. We tend to do pretty well out here with a -PNA/-NAO/-AO, a recent example being late January-mid to late February 2021.

Interestingly, the 2015-16 super Niño narrowly missed out on above normal snow at ORD with the Feb 24th event *just* missing to the southeast. It certainly helped to have a big late November snowstorm, but I'd say that after the December torch, that winter was relatively wintry vs. expectations going in.

 

I haven't posted on the vLab forum yet (actually haven't looked at it much), I will check it out!

I find it kind of surprising that almost half of moderate to strong El Ninos finished colder than average there but I'd agree that the chances for this winter to are already very slim because of this month. However, I'm not surprised by how poor snowfall climo is in moderate to strong El Ninos there (and it's not any better for CLE...09-10 finished a bit below average snowfall at CLE, though our southern CWA got crushed in February that year and finished well above average, with 3 of our climate sites seeing their snowiest February on record with one of those being their snowiest month on record). 2015-16 did have a period of wintry conditions in the heart of winter which took the edge off the torch for sure...I was in SE Ohio at school for that one and they saw something close to an average winter as they got clipped by the massive January Mid Atl storm with a few other light to moderate events, which isn't too shabby for Athens, OH. It was a pretty slow winter in northern OH but still not nearly as slow as last winter was here. 

And I'd agree that the -PNA could offer potential for parts of this subforum...I think if there's something decent in the Ohio Valley it's more likely early on before the -PNA begins getting established during the second week of January. The -PNA should shift the storm track farther northwest, though as you alluded to the amount of blocking may determine if we can see a snowier outcome from the mid-upper Mississippi Valley into the Great Lakes. If there is enough blocking, the -PNA could actually end up yielded a pretty interesting mid-January to the northwestern half of this sub-forum. 

[Spartman]

7 hours ago, Chambana said:

Not ready 2 b buried? 

[Chicago Storm]

7 minutes ago, Spartman said:

Some of you need to lay off of the trash sources.

[OHweather]

Worth also saying that the 10mb zonal mean wind anomaly only getting down to like 3 m/s (not quite a SSW) instead of -2 m/s (a SSW) doesn't make a huge difference, as long as it significantly weakens and stays relatively weak for a while it'll support increased high latitude blocking. That's also an extremely impressive SSW signal on the weeklies still...not common to get what appears to be something like 65-70% of members agreeing on a SSW over 10 days out. 

[michsnowfreak]

4 hours ago, OHweather said:

Those winter storms you saw the second half of last winter were impressive, and if they were shifted a couple hundred miles southeast I probably would've had a more positive impression of last winter. Hopefully we get a few weeks of sustained wintry conditions later January into February that allows any snow that falls to stick around a bit. I enjoy snow...falling, on the ground, whatever it's doing. I certainly enjoy the "chase" (forecasting, communicating it, etc.) and watching it play out the most, so while I appreciate deep winter periods with persistent snow packs I very much enjoy events like Michigan had last winter.

Oh, don't get me wrong, I definitely enjoyed the storms. The March 3rd snowstorm in particular was like something you read out of one of those old 1800s books the way they would describe a storm blowing in out of nowhere. Usually they're described in a sort of unrealistic way but that's exactly what happened on Mar 3. Plus we also the worst ice storm in years. And the wet nature of most snowfalls was a photography dream. So definitely some positives last winter, it's just that I've always been a snowcover guy so hoping we get a few stretches this winter. 

 

Regardless what happens, your analysis is appreciated and I look forward to more of it!

[buckeye]

Tons of talk about an SSWE...

...never a good sign

[Stebo]

On 12/26/2023 at 6:41 AM, A-L-E-K said:

Zzzzzz 

On to February 

Could you be any lazier? Like if you don't care about someone spending time making a good post, don't reply.

[Stebo]

As for the rest here from the last few days, good stuff and you can already see some hints of the change in the longer range. I still worry about going warm and dry to cold and dry but beyond that it does look colder about a week out from now.

[dmc76]

Ll