Autumn & Winter 2023---2024 Stratospheric Polar Vortex. Events, Analysis, Discussions AND Outlooks

[Andy8472]

55 minutes ago, bluearmy said:

And the 06z op at day 16 showed a surge of strong zonal flow around 70N at 1 hpa so that shows the problem of using operationals at that range 

i agree, the operational is all over the place atm 06 vs 12z, stick with the mean i would say

[bluearmy]

2 hours ago, Andy8472 said:

i agree, the operational is all over the place atm 06 vs 12z, stick with the mean i would say

The 12z (as if to prove a point ) looks very likely upcoming ssw at the top of the strat day 16

i wonder how many ec46 members will show a reversal by new year ? 

[SqueakheartLW]

When seeing lots of individuals over in the mod thread getting annoyed with the potential loss of blocking and cold to end the year need to think that we don't want to see a blocked pattern just prior to and during the potential SSW.

If we have ZONAL BEFORE and DURING the SSW there is a much GREATER chance that the effects of the SSW will FLIP the pattern from ZONAL to BLOCKED.

The reverse also holds true where a BLOCKED pattern BEFORE and DURING the SSW there is a much GREATER chance that the effects of the SSW will FLIP the pattern from BLOCKED to ZONAL.

Example ZONAL to BLOCKED due to SSW

Early 2013 was a perfect example. We went somewhat blocked in early December 2012 before we entered a more zonal period mid December to early January prior to and during the SSW which is exactly what we wanted as we then saw the result with the pattern flipping to generally blocked from mid January 2013 to early April 2013 and generally colder than average with some snow at times.

Example BLOCKED to ZONAL due to SSW

In contrast to this is winter 2001/02. We had a blocked and colder pattern just prior to and during the SSW. The result was that we lost the blocking signal early January 2002 and we FLIPPED back to default ZONAL for the rest of the winter. On this occasion the SSW RUINED the rest of the winter.

[CoventryWeather]

I know it's a model that's not used much, but the CFS is consistently showing a SSW early Jan, and a rather cold easterly. 

It has been consistent with it for the last few days, albeit differing strengths, so it seems the likelihood has perhaps increased compared to last week. Wonder what modelling has picked up? 

[Andy8472]

1 hour ago, bluearmy said:

The 12z (as if to prove a point ) looks very likely upcoming ssw at the top of the strat day 16

i wonder how many ec46 members will show a reversal by new year ? 

Wide spread

Edited December 11, 2023 by Andy8472

[bluearmy]

28 minutes ago, Andy8472 said:

Wide spread

Approx 5% agreement then ! 
gfs likely progressive in that respect then. 

[SqueakheartLW]

GFS 12z best warmings

GEM 12z strange vortex stretching and weakening charts just like yesterday. No idea what is causing this.

[Mike Poole]

ECM 46 is making corrections in the strat at fairly short timescales at the moment:

Notice how the resurgence in zonal winds after the Canadian warming has been wiped from the model output over the last 5 days.  I still have a big question about the lack of horizontal resolution of this model, and would not just assume it is more correct at early timescales compared to GEFS.  Actually, this upcoming SSW (if we have one) will be a very good test of the update to this model.

[summer blizzard]

3 hours ago, bluearmy said:

The 12z (as if to prove a point ) looks very likely upcoming ssw at the top of the strat day 16

i wonder how many ec46 members will show a reversal by new year ? 

About 50% of members go for an SSW with the highest concentration between 1st-12th January.

[Andy8472]

7 hours ago, summer blizzard said:

About 50% of members go for an SSW with the highest concentration between 1st-12th January.

48% on the extended gefs

Edited December 12, 2023 by Andy8472

[feb1991blizzard]

6 hours ago, Andy8472 said:

48% on the extended gefs

I like that footnote - GEFS inhibit a strong vortex bias with increased lead time.

[Andy8472]

Pretty big signal for a wave 2 attack on the core 

Edited December 13, 2023 by Andy8472

[stodge]

The GFS 12Z OP suggests the warming beginning not in Siberia but Europe which is unusual.

I'm not keen on Siberian warmings because that usually sends the PV back over to Greenland/Canada but a European warming would, perhaps, send the PV back over to Siberia or western Canada which would suggest heights over Scandinavia during January.

Just how it looks to my untrained eye...

[Andy8472]

ECM extended

Todays vs 2 days ago, a marked drop in the short range 

[Andy8472]

For what's it worth CFS Jan forecast

[feb1991blizzard]

4 hours ago, Andy8472 said:

For what's it worth CFS Jan forecast

 

4 hours ago, Andy8472 said:

For what's it worth CFS Jan forecast

on that it looks like a displacement SSW is a possibility - would prefer a split.

[bluearmy]

Last few gfs ops have lost the downwelling signal and now have a trop with a stronger zonal flow than the strat above 50 hpa at day 15/16 - hence late week 2 looking more mobile hemispherically 

However, the 00z run looks like a clearer flushing down late on as a reversal takes hold above 100hpa. 

 

 

Probably a little progressive but then if the sceuro trough does really  dig then that should drive an sig russian ridge and in tandem with the persistent Aleutian trough we have quite an attack ongoing. 

Edited December 14, 2023 by bluearmy

[sebastiaan1973]

Cohen:

 And as I discussed two weeks ago (see 27Nov_blog), a Canadian warming almost always transitions to either a stretched PV or an SSW.  This time I am anticipating an SSW to follow. 

It is of my opinion, much of the winter will likely hinge on the nature of this SSW that is predicted to begin the last week of December.  I think the models were slow to appreciate the magnitude of the energy transfer from the troposphere to the stratosphere.  Where the energy leaves or diverges it creates cold, low pressure and the westerly winds increase or in this case in the troposphere.  Where the energy enters or conerges it creates warm, high pressure and the westerly winds decrease or in this case in the stratosphere.  That is why I believe that the weather models both showed a more robust weakening of the PV simultaneously predicting more low pressure and less high latitude blocking in the troposphere and milder temperatures across the continents.

But if the SSW starts to go sideways and has little or limited (in both time and/or space) impact, I see little reason anticipate anything but an overall mild period for a more extended period.  Once an SSW rolls over prematurely it is my experience that it takes many weeks for a chance at another one.

Given so much uncertainty I will refrain to say much more today other than to expect greater than usual model volatility in the lead up to the SSW and even beyond.  But I will leave you with two teasers.  First the quasi-biennial oscillation (QBO) has a long history as an in and out fad and recently it is back in.  This winter it is easterly and according to the most recent research that favors a more robust tropospheric response to an SSW and overall colder temperatures across the NH post the SSW.  Second all the weather models are for now predicting a PV displacement, but this is still an evolving situation.  The weather models are converging on a dominant wave-2 in the troposphere for late December (for example see Figure with ridging centered near the Urals and western North America and troughing in the North Pacific and North Atlantic.  My personal favorite PV disruption, the PV split, is thought to be favored when wave-2 dominates the tropospheric pattern. 

AO/PV Blog Update | Verisk's Atmospheric and Environmental Research (aer.com)

https://www.aer.com/science-research/climate-weather/arctic-oscillation/

[Andy8472]

Op vs control vs mean

[Andy8472]

23 hours ago, Andy8472 said:

ECM extended

Todays vs 2 days ago, a marked drop in the short range 

Another drop

[Catacol]

I think we are seeing the beginnings of a process that will end with an SSW. Statistically these things are almost impossible to forecast until within a 14 day window, and the outer edges of that 14 day window are looking significant.

A stretched vortex impacted by wave 2 forcing looks to me like grounds for optimism for a split. Exciting times. Top down SSW impacts alongside ongoing possible pacific trop led impacts  might serve up a tasty mid winter diet...

Edited December 15, 2023 by Catacol

[Andy8472]

First warm pulse at the end of the 06z op, now more in line with the mean, eventually normally makes it's way into the pole area 

[DavidS]

2 hours ago, Andy8472 said:

First warm pulse at the end of the 06z op, now more in line with the mean, eventually normally makes it's way into the pole area 

Good to see. There are some -12s on that chart, which is toasty. Hopefully we see some consistency in the output and it starts to come into the reliable. End of December is a good time to have a warming.

[rwtwm]

On 11/12/2023 at 19:32, SqueakheartLW said:

When seeing lots of individuals over in the mod thread getting annoyed with the potential loss of blocking and cold to end the year need to think that we don't want to see a blocked pattern just prior to and during the potential SSW.

If we have ZONAL BEFORE and DURING the SSW there is a much GREATER chance that the effects of the SSW will FLIP the pattern from ZONAL to BLOCKED.

The reverse also holds true where a BLOCKED pattern BEFORE and DURING the SSW there is a much GREATER chance that the effects of the SSW will FLIP the pattern from BLOCKED to ZONAL.

Example ZONAL to BLOCKED due to SSW

Early 2013 was a perfect example. We went somewhat blocked in early December 2012 before we entered a more zonal period mid December to early January prior to and during the SSW which is exactly what we wanted as we then saw the result with the pattern flipping to generally blocked from mid January 2013 to early April 2013 and generally colder than average with some snow at times.

Example BLOCKED to ZONAL due to SSW

In contrast to this is winter 2001/02. We had a blocked and colder pattern just prior to and during the SSW. The result was that we lost the blocking signal early January 2002 and we FLIPPED back to default ZONAL for the rest of the winter. On this occasion the SSW RUINED the rest of the winter.

I'm not sure that finding one example of each scenario is sufficient to declare a rule?

Given that the definition of a (major) SSW is a mean reversal of the zonal stratospheric wind, I'd find it unlikely that such an event can lead to increased zonality overall. This is just on a purely academic level.

I'd have some sympathy with the suggestion that we were in a blocking regime conducive to cold, an SSW might encourage the block to migrate elsewhere. That said, I don't have the data to back that up, and this is one of the busiest weekends of the year for me, so I haven't the inclination to check. 

[Mike Poole]

Yesterday I promised to set out some thoughts about how the rest of winter might pan out, so this post is focussed on the period post-Christmas.

To take a step back, it has seemed to me that the patterns in the NH going into winter were unusual, on the back of a year of weird weather, SSTs that are not within past precedence, so I have tried to be open to the unusual, maybe paying more attention to the models, which continue to just simulate the laws of physics regardless if whether the patterns are old or new.  

Much of the expectation around winter has seemed to follow a timetable set out by the MJO, and likely developments in the strat commensurate with El Niño and easterly QBO.  But the early winter cold confounded the first, and the Canadian warming in the strat called into question the second.

So right now we have a weakened strat vortex, and the MJO is moving into Phase 7 with questionable amplitude.  There have been suggestions of a rise in AAM, more consistent with El Niño, but that hasn’t really happened, not yet anyway, it seems to be struggling to get past the half way line!

It would have been nice to have a trop-led amplified pattern deliver cold, then a SSW to come along later and reinforce things when it waned.  Well it might have been nice, but that is now not where we are.  It is looking like the SSW is coming sooner rather than later, but the effects of the Canadian warming are already being felt as the trop vortex relocates away from Greenland/Canada.  I maintain that the NH pattern is still very unusual, so even if mild and rain is what the UK gets (that can occur with many setups!), the NH setup is not normal service.  Why the pattern is so unusual when there hasn’t been much forcing that I can see from the background drivers so far has not been explained to my satisfaction.

An SSW looks most likely to occur last week in Dec or first week or so in Jan:

It is now starting to come within the 16 days range.  Until very recently I would have said this looks more likely to be a displacement, some GFS runs a couple of days ago showed single digit zonal winds, but very little in the way of high temperatures so I was concerned we might get a fairly ‘low energy’ SSW that essentially just means a displaced very weak vortex - although towards Russia which is not a bad place for it to go.  Now there is a more usual pre-SSW signal, I think, from the GEFS:

But there looks to be some uncertainty, today’s GFS 12z showed a possibly more interesting evolution, 14 m/s zonal winds by T384 but it has some way to go, but the idea is:

It is not possible to tell much about the way a SSW will happen from the averaged 100 realisations plots of the ECM 46, but as of right now, I would not rule out the better prospects of a split SSW, I think that signal is in the ascendency.  

If there is no split, we will be relying on a decent trop pattern to take hold while the strat vortex is weak and displaced, with the downwelling of the easterly winds.  That really means Greenland heights if anything is to really deliver.  Given the location of the trop vortex, and the displacement of the strat vortex, I cannot see how a Scandi high establishes itself, it is for a reason that that option has totally vanished from the ECM clusters.  We ideally need some help from this MJO wave (lagged) or rising AAM to aid amplification.  

If there is a split, there is probably greater potential for a UK cold pattern to set up due to the strat driving things after the trop response.

Either way, in my view, with all this going on, the next 4 weeks will decide whether winter 2023/24 is one to remember or not.  If the UK finds a way to stay mild, then that’s it really.  

The next MJO wave (+ lag) could be well into February and is just as likely to disappoint, and by that point the  writing’s probably on the wall (for the south anyway!)  However, the chance of a locked-in really cold spell in the heart of winter is still very much on the table at the moment.

All the best

Mike

 

 

 

Edited December 15, 2023 by Mike Poole
Meant to put this in the MOD, will copy it over, but probably relevant here too.