[Model Output Discussion - Colder but how cold and for how long?]

Bom dia e todos

I make no apologies for yet again re-pasting this sequence originally posted just prior to New Year, because it has become an even more focused roadmap. Not just for the upcoming 10 day period, but indeed confidence increasing as a blue-print for well into the second half of the winter:

....................................................................................................................................................................................

With the Nino attractor phases fully engaged, the amount of westerlies propagated into the atmospheric circulation between tropics & extra tropics do, as you suggest, indicate a higher floor to the angular momentum budget in the 'lull' ahead of the next upswing as the MJO traverses the tropics during January. GWO Phase 4 is a good medium base floor level I would think.

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream.

Muito obrigada. Melhores Cumprimentos

......................................................................................

To update the template of this analysis:

A very starkly high octane angular momentum budget is emerging and prolific within the global-wind-flow budgets. This translates to stockpile ammunition supply levels for deeply sustained poleward amplification eddies taking on veritable tanker sized reserves.

Based on how much tropospheric led influence there has been on the NH pattern in recent weeks since the starting pistol was fired to destabilise the polar profile, these further poleward swathes of +ve momentum transport take on especially egregiously gargantuan proportions for future wholesale instability and implosion across the polar field. In this respect it is not hard to comprehend the latest sentiments of Amy Butler and how she sees the synoptic pattern imprinted

The copied post referred to a baseline phase landing place for the Global Wind Oscillation. This baseline, ahead of the strongest wind-additions yet c/o eastward progressing high amplitude MJO wave back to the Pacific has remained higher than intermediate phase 4 (as discussed in the copied post)

The latest GWO phasing, even under present lull stopgap at very low amplitude 5/6, reflects the remaining considerably high levels of +AAM anomalies within the atmospheric circulation as aggregate total AAM. (Phase 4 GWO would be more suggestive of flatter return of the jet and greater attrition from the Atlantic against blocking. (Though even this sharpens somewhat against late Jan/early Feb wavelengths)

This GSDM wind flow budget situation is significant. More on this shortly.

The GWO is a phase plot depiction of aggregate wind-flow within both the tropics (MJO related) and the extra tropics as a measure of how efficiently propagation of wind-flow is proceeding between the tropics & extra tropics. This matters, because it is a barometer for synoptic pattern (poleward) amplification potential and provides a diagnostic towards directional flux of wind-flow eddies.

Poleward flux has now become quite supercharged

What of the significance of this?

As the intraseasonally driven MJO crosses the Maritimes at high amplitude, then very strong +ve torque mechanisms will be re-engaged to over top a system already awash with +AAM anomalies. The GWO likely to drill upwards into very high amplitude Phase 5/6. Taking into account maximum winter wavelengths, then this teleconnects ever more strongly to entrenched -ve NAO (under chaotic stratospheric diminution to spotweld a deeply -ve Annular Mode).

How can this be visualised?

The upcoming next cascade of westerly wind burst propagation into the extra tropics creates white water rafting within the sub tropical jet from the Equatorial Pacific downstream to the Atlantic -at the same time as the polar profile becomes riven with -ve mean zonal -ve wind anomalies. Defining solid roadblocks for southward directive of a deeply unstable thermal boundary.

How can this in turn be visualised?

With deeper upper cold air ensconced north of the polar boundary, this leads to feedbacks of entrenched surface cold with time to feed an ever starker thermal boundary, This encourages and emboldens larger progressions of numbers of kayaks slipstreaming below it. This translates to trains of low pressure undercuts - and it is not difficult to envisage the potential for high impact weather events to unfold in such a scenario. 

The kayak posse delivers an "atmospheric river" of saturated sub tropical air and a large jump of temperature into the upper teens for my part of the world well below the thermal boundary at the same time as in contrast...

.... that is better left to the mercurial imaginations of any members who might be looking in from NW Europe.

Putting all this diagnostic analysis together, it is hard to see anything other than a tanked -ve Annular Mode relationship dominating much of the rest of the winter. However, and as ever, further analysis is wholly prudent to document how proceedings unfold.

Muito obrigada. Feliz quarta-feira

 

 

 

[Model discussion highlights]

Posted extract from 30 December:

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream

................................................................................................

 Cutting through the frenzy of  intense reactive posting to NWP output, next to nothing has changed in the suggested outlook since this summary last weekend.

In simple terms, NWP is teeing up the scenario of cold arctic air coming south through N Europe at the same time as momentum starts to return from the west c/o the sub tropical jet stream from next weekend. Based purely on attempted objectivity and looking at probabilistic solutions, rather than being wired to a desired outcome, the bold captions in the posted extract hold very true.

This macro scale diagnostic is not a substitute for micro scale pinning down of thermal boundaries across a given part of the UK or any locality elsewhere in NW Europe, but clearly quite an envelope exists in respect of potential high impact winter weather outcomes where precisely this boundary sets up. For my own part of SW Europe, once the chilly static pattern of the coming week is dislodged from the end of the week, the envelope of probability is smaller in respect of the warmer moister sub tropical jet flow well south of the likely thermal boundary. That will be much welcomed in respect of turning down heating and removing the need for protecting tender plants & farm produce from any night time frosts.

Longer term NWP means are next to worthless in the present scenario - the attritional boundary of the dense cold air advecting south and where it sets up against the returning jet stream cannot be pinned down at this stage and there is so much "noise" within the envelope that nothing can be discerned from such a wide blend.. But quite likely that any returning axis of vorticity to the Canadian side of the arctic will engage the sub tropical jet in such a way as to create an easterly vector above where the polar front eventually lies, and this as such define the high impact weather zone in itself. In this way, it might be worth watching how pressure orientates itself to the NE at such a time. But that is where a next updated analysis may be prescient.

At times like these with seemingly complex factors at play, it helps to return to previous analysis and have confirmation that the main ingredients are panning out as anticipated.

Boa tarde

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4999362

[Model Output Discussion - Into 2024]

Posted extract from 30 December:

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream

................................................................................................

 Cutting through the frenzy of  intense reactive posting to NWP output, next to nothing has changed in the suggested outlook since this summary last weekend.

In simple terms, NWP is teeing up the scenario of cold arctic air coming south through N Europe at the same time as momentum starts to return from the west c/o the sub tropical jet stream from next weekend. Based purely on attempted objectivity and looking at probabilistic solutions, rather than being wired to a desired outcome, the bold captions in the posted extract hold very true.

This macro scale diagnostic is not a substitute for micro scale pinning down of thermal boundaries across a given part of the UK or any locality elsewhere in NW Europe, but clearly quite an envelope exists in respect of potential high impact winter weather outcomes where precisely this boundary sets up. For my own part of SW Europe, once the chilly static pattern of the coming week is dislodged from the end of the week, the envelope of probability is smaller in respect of the warmer moister sub tropical jet flow well south of the likely thermal boundary. That will be much welcomed in respect of turning down heating and removing the need for protecting tender plants & farm produce from any night time frosts.

Longer term NWP means are next to worthless in the present scenario - the attritional boundary of the dense cold air advecting south and where it sets up against the returning jet stream cannot be pinned down at this stage and there is so much "noise" within the envelope that nothing can be discerned from such a wide blend.. But quite likely that any returning axis of vorticity to the Canadian side of the arctic will engage the sub tropical jet in such a way as to create an easterly vector above where the polar front eventually lies, and this as such define the high impact weather zone in itself. In this way, it might be worth watching how pressure orientates itself to the NE at such a time. But that is where a next updated analysis may be prescient.

At times like these with seemingly complex factors at play, it helps to return to previous analysis and have confirmation that the main ingredients are panning out as anticipated.

Boa tarde

[Model discussion highlights]

1 hour ago, Met4Cast said:

Fantastic post & echos much of what I’ve been saying in the last week or so re: EPS/GEPS broadly leading the way on the expected evolution ahead of the GEFS, though put much more concisely than I! 

Do you see the blocking pattern waning as we progress through mid month on the back of falling AAM triggered by a strengthening of easterly trade winds in the Pacific c/o the MJO returning to the I/O for the next cycle? 

It’ll be interesting to see how far total AAM falls & I suspect much dependent on how quickly this next MJO wave progresses eastwards to restart the +FT > +MT > +AAM tendency cycle all over again, likely this time from a higher total AAM base state than this current cycle had to contend with! 

I don’t see any reason to think a zonal, flat Atlantic regime will take over for any extended period (if indeed at all) with tropical/sub tropical forcing likely to become supportive of higher latitude blocking again later into January/early February (assuming a more progressive MJO, a slower progression still a possibility based on current modelling). 

The westerly wind anomalies which developed over the Equator early December onwards that have been fluxed poleward over the last three weeks c/o zonal mean transports cater for the upward spike in angular momentum. (This also paves the way for a cold pattern to return to N Europe later January into February - see further down). 

Relative angular momentum is up c/o fluxing of westerlies from the tropics into the sub-tropic. This, as we know, can be seen as a +ve angular momentum anomaly on the calculated aggregate tendency plot (shaded red) from 30N

.

Uniform extra tropical +ve mountain torque has driven tendency in relative angular momentum and the GWO well into phases 5/6

With the Nino attractor phases fully engaged, the amount of westerlies propagated into the atmospheric circulation between tropics & extra tropics do, as you suggest, indicate a higher floor to the angular momentum budget in the 'lull' ahead of the next upswing as the MJO traverses the tropics during January. GWO Phase 4 is a good medium base floor level I would think.

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream.

Muito obrigada. Melhores Cumprimentos

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4988037

[Model Output Discussion - Into Winter]

1 hour ago, Met4Cast said:

Fantastic post & echos much of what I’ve been saying in the last week or so re: EPS/GEPS broadly leading the way on the expected evolution ahead of the GEFS, though put much more concisely than I! 

Do you see the blocking pattern waning as we progress through mid month on the back of falling AAM triggered by a strengthening of easterly trade winds in the Pacific c/o the MJO returning to the I/O for the next cycle? 

It’ll be interesting to see how far total AAM falls & I suspect much dependent on how quickly this next MJO wave progresses eastwards to restart the +FT > +MT > +AAM tendency cycle all over again, likely this time from a higher total AAM base state than this current cycle had to contend with! 

I don’t see any reason to think a zonal, flat Atlantic regime will take over for any extended period (if indeed at all) with tropical/sub tropical forcing likely to become supportive of higher latitude blocking again later into January/early February (assuming a more progressive MJO, a slower progression still a possibility based on current modelling). 

The westerly wind anomalies which developed over the Equator early December onwards that have been fluxed poleward over the last three weeks c/o zonal mean transports cater for the upward spike in angular momentum. (This also paves the way for a cold pattern to return to N Europe later January into February - see further down). 

Relative angular momentum is up c/o fluxing of westerlies from the tropics into the sub-tropic. This, as we know, can be seen as a +ve angular momentum anomaly on the calculated aggregate tendency plot (shaded red) from 30N

.

Uniform extra tropical +ve mountain torque has driven tendency in relative angular momentum and the GWO well into phases 5/6

With the Nino attractor phases fully engaged, the amount of westerlies propagated into the atmospheric circulation between tropics & extra tropics do, as you suggest, indicate a higher floor to the angular momentum budget in the 'lull' ahead of the next upswing as the MJO traverses the tropics during January. GWO Phase 4 is a good medium base floor level I would think.

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream.

Muito obrigada. Melhores Cumprimentos

[Model discussion highlights]

11 hours ago, Cheshire Freeze said:

There have been changes in the modelling. Look at the NH set up. We’ve gone from initial tpv in tatters type charts to a healthy looking tpv atop some modest Atlantic amplification.

Emphasis currently focusses on tropospheric led diagnostics and the significant switch to poleward momentum of +AAM anomalies. The starting pistol for this was well advertised & discussed over the past 10 days. Such a process weakening the strength of +ve NAO sub tropical ridging, and slowly but steadily increasing westerly sub tropical jet stream momentum from the Equatorial Pacific downstream across S US and into the Atlantic.

NWP has been erratically attritional with this evolution, and it is still unfolding within the 8 to 15 day period but current EPS and GEPS members seem to be handling this better at present than the GEFS which is not seeing the undercutting processes quite as clearly.

Signs of warmer sub tropical influences across south western European c/o clustering ensemble readings point to slightly better support today for lows tracking well under the developing blocking across Northern Europe and into southern Greenland and a more coherent -ve NAO to come. This signal is still a little disjointed but it has gained further traction in the overnight output suites. My own watch has been on this, rather than SSW-gate. The EC det today is a good example of the type of evolution being looked for.

This tropospheric momentum led transport shows that a classic SSW reversal is not required for this type of synoptic set-up when there is instability supplied from the bottom upwards. On the very large scale, December to January 2009/10 proved a case in point with GSDM led poleward momentum providing the tropopause instability. An SSW did follow that winter, heading between January/February 2010 but by this time much of NW & N Europe had been very wintry already for a considerable time.

And, not to forget that broadscale eddying poleward of +AAM anomalies is a key element of stratospheric pathway diminution itself - looking ahead.

From mine & Portuguese perspective and interest, some sub tropical jet induced rainfall would be appreciated ahead of another Iberian summer.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4987895

[Model Output Discussion - Into Winter]

11 hours ago, Cheshire Freeze said:

There have been changes in the modelling. Look at the NH set up. We’ve gone from initial tpv in tatters type charts to a healthy looking tpv atop some modest Atlantic amplification.

Emphasis currently focusses on tropospheric led diagnostics and the significant switch to poleward momentum of +AAM anomalies. The starting pistol for this was well advertised & discussed over the past 10 days. Such a process weakening the strength of +ve NAO sub tropical ridging, and slowly but steadily increasing westerly sub tropical jet stream momentum from the Equatorial Pacific downstream across S US and into the Atlantic.

NWP has been erratically attritional with this evolution, and it is still unfolding within the 8 to 15 day period but current EPS and GEPS members seem to be handling this better at present than the GEFS which is not seeing the undercutting processes quite as clearly.

Signs of warmer sub tropical influences across south western European c/o clustering ensemble readings point to slightly better support today for lows tracking well under the developing blocking across Northern Europe and into southern Greenland and a more coherent -ve NAO to come. This signal is still a little disjointed but it has gained further traction in the overnight output suites. My own watch has been on this, rather than SSW-gate. The EC det today is a good example of the type of evolution being looked for.

This tropospheric momentum led transport shows that a classic SSW reversal is not required for this type of synoptic set-up when there is instability supplied from the bottom upwards. On the very large scale, December to January 2009/10 proved a case in point with GSDM led poleward momentum providing the tropopause instability. An SSW did follow that winter, heading between January/February 2010 but by this time much of NW & N Europe had been very wintry already for a considerable time.

And, not to forget that broadscale eddying poleward of +AAM anomalies is a key element of stratospheric pathway diminution itself - looking ahead.

From mine & Portuguese perspective and interest, some sub tropical jet induced rainfall would be appreciated ahead of another Iberian summer.

[Model Output Discussion - Into Winter]

On 19/12/2023 at 16:03, Tamara said:

Analysis of Azores ridging finds that this ridge is strongest under subdued frictional torque wavelengths across the tropics (stronger easterly trade wind inertia) and weakest when a switch to a +ve frictional torque has propagated +AAM anomalies into the extra tropics and in association therefore suppress the NAO (North Atlantic Oscillation). The ongoing -ve torque wavelength began (very strongly) in last third of November,  and has now reversed. Hence why in recent and ongoing modelling the Azores High has/is being dominant, reflecting the strength of that original signal, based on the lag times.

With directional flux now shifting, though not so apparent yet currently in 10 day modelling, over the festive period itself it is quite likely that there will be gradual signs modelled of the Azores High losing some of its grip & a look out for some sub tropical flow returning. Much then depends on how the polar cell responds and in respect of the movements of the polar vortex which continue to show disorganisation heading into the New Year - and when, perhaps, some more significant disruption occurs during January.

Boa tarde e boas festas

A brief update to simply confirm progress of the jet stream switch as was suggested was coming. The initial starting pistol fired for the +ve FT wavelength to mature within the extra tropics is now well advertised within NWP and southward displacement of the jet evident.

The final sentence of the second paragraph holds true to observe. For one who is more interested in the diagnosis vs the actual outcome, rather than any desired outcome, this is the essence of interest as to how the relationship between  now poleward fluxing extra tropical momentum & a fickle stratospheric environment jives together.

 
In Portugal:

From above the anticyclonic inversion (which ends today)

Favaois (elevation 498 metres) :

 

Muas, Vila Real:

 

Below the inversion:

 

 

Melhores Cumprimentos.  Feliz Ano Novo com saúde 

 

[Model Output Discussion - Into Winter]

Feliz Natal e todos

The strong Iberian heights have created a persistent inversion that has led to some very cold nights in parts of inland NE Portugal. Municipio de Bragança has seen some consecutive sub zero nights and freezing fog leading to rime deposits & Christmas card appearances. By contrast parts of the Algarve have seen maximum day values close to 18C. Locally to me the nights have been down to about 4C and daytimes around 14C.

Seeing festive pictures like this is quite the contrast to the 35C to 40C heat under similar pressure patterns in summer!

Much documented on this thread obviously but January is shaping up to do the opposite of how Dec/Jan 22/23 panned out. Quite a growing signal for a southerly tracking jet replacing eventually the anticyclonic inversion conditions in Iberia and blocking to the north of Europe. Not a day for any analysis, but hope all have a lovely day and best wishes for 2024

[Model discussion highlights]

3 hours ago, Penguin16 said:

Are background signals on a par with fortune telling by this stage? 

The term" background signals" rather grates with its overuse, dumbing down of its actual diagnostic purpose, & its incorrect use in adherence to bias synoptic outcomes - which is largely why so many are left scratching their heads when too often they don't appear "to work".

This is the aggregate global wind-flow fluxing budget plot - in simple terms, a cross section of direction & strength of wind-flow eddy anomalies across the  Equator, Tropics & Extra Tropics (emphasis on the NH section)

This reveals the off Equator fluxing (shaded red close to the Equator) that is a good part of total directional flux and why inflated sub tropical ridging is so evident across Iberia. When looking at angular momentum budgets themselves, this equatorial portion of +ve momentum indicates that it has been offsetting the rest of the +ve torque processes attempting to propagate from the tropics, c/o MJO related activity, into the extra tropics.

If one thinks of an inflection point where either -ve forcing exceeds +ve forcing (-ve frictional torque) or vice versa  (+ve frictional torque) then this is simply the turning force (a torque) exhibited on the jet stream - to deflect & alter its strength & direction whether it is decelerating or accelerating. Expressed as a change, downwards or upwards, in angular momentum tendency.

The recent state of equatorial fluxing has to be taken into account when looking at the MJO component of the wind-flow budget and the fact that it continues (for the time being & read below) not to be optimally conducive to poleward propagation of +AAM anomalies. It is just not always as simple as MJO phase x = outcome y as gets posted so many times, each day, at this time of the year - in search of a desired outcome. Tropical forcing is just part of global wind flow forcing. I think I could maybe put this disclaimer in my profile/signature

The same principle applies at any time of year in respect of weather pattern diagnosis. 

However, also on that GSDM plot, there is now evidence of +ve momentum (red shading at 30N) now propagating from the tropics & heading towards the extra tropics (above 30N) as a starting pistol towards poleward momentum setting off. The wavelength for frictional torque fluxes is lagged some 14 to 20 days to impact from source of origin to final destination (according to direction of fluxing).

Analysis of Azores ridging finds that this ridge is strongest under subdued frictional torque wavelengths across the tropics (stronger easterly trade wind inertia) and weakest when a switch to a +ve frictional torque has propagated +AAM anomalies into the extra tropics and in association therefore suppress the NAO (North Atlantic Oscillation). The ongoing -ve torque wavelength began (very strongly) in last third of November,  and has now reversed. Hence why in recent and ongoing modelling the Azores High has/is being dominant, reflecting the strength of that original signal, based on the lag times.

With directional flux now shifting, though not so apparent yet currently in 10 day modelling, over the festive period itself it is quite likely that there will be gradual signs modelled of the Azores High losing some of its grip & a look out for some sub tropical flow returning. Much then depends on how the polar cell responds and in respect of the movements of the polar vortex which continue to show disorganisation heading into the New Year - and when, perhaps, some more significant disruption occurs during January.

So it could be that the static pattern with chilly nights & sunny days down here in SW Europe starts to eventually become more warmer Atlantic influenced and at the same time, signs that associated Atlantic low pressure systems also start to undercut blocking structures across mid to higher latitudes. A trend to build ridging through Europe towards Iceland & Scandinavia - which retrogresses -ve inertia towards Greenland heading through January as the NAO turns more negative and there is a shift in the polar front southwards

In this sense, the extended January monthly modelling does have some credence. Time as always will tell.

41 minutes ago, MattH said:

The key feature here is the -ve FT tendencies at circa 50-60N, this is what you want to see if you wish to see a more amplified jet stream pattern. This is all linked to the Rossby wave packets and how they propagate northwards and eastwards from the tropics. The significant region of +ve Frictional Torque at 30-40N is linked to the MJO event and the associated -VP200 anomalies and associated Westerly Wind Burst near the Central Pacific that remains ongoing. If this were the opposite where frictional torque tendency is negative towards 30N it creates a negative inflexion point in the Equatorial Pacific and adds momentum to the jet stream downstream in the extratropics. A -ve FT regime at circa 30N, from my understanding, is what can 'prop up' sub-tropical anticyclones and it is the compensating momentum that increases the polar jet through the mid-lats.

This is just one piece of the puzzle, but what we are seeing now is what the likes of myself, Tamara, Catacol etc, touted as would arrive through Dec, but it has been delayed given the MJO evolution.

How about that?  Completed my post and poised to send, and then saw this. Which uncannily discusses the very same elements and to to look out for the same things...and even talks of "inflection points". Spooky. But no genuine collaboration between the two posts.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4980207

[Model Output Discussion - Into Winter]

3 hours ago, Penguin16 said:

Are background signals on a par with fortune telling by this stage? 

The term" background signals" rather grates with its overuse, dumbing down of its actual diagnostic purpose, & its incorrect use in adherence to bias synoptic outcomes - which is largely why so many are left scratching their heads when too often they don't appear "to work".

This is the aggregate global wind-flow fluxing budget plot - in simple terms, a cross section of direction & strength of wind-flow eddy anomalies across the  Equator, Tropics & Extra Tropics (emphasis on the NH section)

This reveals the off Equator fluxing (shaded red close to the Equator) that is a good part of total directional flux and why inflated sub tropical ridging is so evident across Iberia. When looking at angular momentum budgets themselves, this equatorial portion of +ve momentum indicates that it has been offsetting the rest of the +ve torque processes attempting to propagate from the tropics, c/o MJO related activity, into the extra tropics.

If one thinks of an inflection point where either -ve forcing exceeds +ve forcing (-ve frictional torque) or vice versa  (+ve frictional torque) then this is simply the turning force (a torque) exhibited on the jet stream - to deflect & alter its strength & direction whether it is decelerating or accelerating. Expressed as a change, downwards or upwards, in angular momentum tendency.

The recent state of equatorial fluxing has to be taken into account when looking at the MJO component of the wind-flow budget and the fact that it continues (for the time being & read below) not to be optimally conducive to poleward propagation of +AAM anomalies. It is just not always as simple as MJO phase x = outcome y as gets posted so many times, each day, at this time of the year - in search of a desired outcome. Tropical forcing is just part of global wind flow forcing. I think I could maybe put this disclaimer in my profile/signature

The same principle applies at any time of year in respect of weather pattern diagnosis. 

However, also on that GSDM plot, there is now evidence of +ve momentum (red shading at 30N) now propagating from the tropics & heading towards the extra tropics (above 30N) as a starting pistol towards poleward momentum setting off. The wavelength for frictional torque fluxes is lagged some 14 to 20 days to impact from source of origin to final destination (according to direction of fluxing).

Analysis of Azores ridging finds that this ridge is strongest under subdued frictional torque wavelengths across the tropics (stronger easterly trade wind inertia) and weakest when a switch to a +ve frictional torque has propagated +AAM anomalies into the extra tropics and in association therefore suppress the NAO (North Atlantic Oscillation). The ongoing -ve torque wavelength began (very strongly) in last third of November,  and has now reversed. Hence why in recent and ongoing modelling the Azores High has/is being dominant, reflecting the strength of that original signal, based on the lag times.

With directional flux now shifting, though not so apparent yet currently in 10 day modelling, over the festive period itself it is quite likely that there will be gradual signs modelled of the Azores High losing some of its grip & a look out for some sub tropical flow returning. Much then depends on how the polar cell responds and in respect of the movements of the polar vortex which continue to show disorganisation heading into the New Year - and when, perhaps, some more significant disruption occurs during January.

So it could be that the static pattern with chilly nights & sunny days down here in SW Europe starts to eventually become more warmer Atlantic influenced and at the same time, signs that associated Atlantic low pressure systems also start to undercut blocking structures across mid to higher latitudes. A trend to build ridging through Europe towards Iceland & Scandinavia - which retrogresses -ve inertia towards Greenland heading through January as the NAO turns more negative and there is a shift in the polar front southwards

In this sense, the extended January monthly modelling does have some credence. Time as always will tell.

41 minutes ago, MattH said:

The key feature here is the -ve FT tendencies at circa 50-60N, this is what you want to see if you wish to see a more amplified jet stream pattern. This is all linked to the Rossby wave packets and how they propagate northwards and eastwards from the tropics. The significant region of +ve Frictional Torque at 30-40N is linked to the MJO event and the associated -VP200 anomalies and associated Westerly Wind Burst near the Central Pacific that remains ongoing. If this were the opposite where frictional torque tendency is negative towards 30N it creates a negative inflexion point in the Equatorial Pacific and adds momentum to the jet stream downstream in the extratropics. A -ve FT regime at circa 30N, from my understanding, is what can 'prop up' sub-tropical anticyclones and it is the compensating momentum that increases the polar jet through the mid-lats.

This is just one piece of the puzzle, but what we are seeing now is what the likes of myself, Tamara, Catacol etc, touted as would arrive through Dec, but it has been delayed given the MJO evolution.

How about that?  Completed my post and poised to send, and then saw this. Which uncannily discusses the very same elements and to to look out for the same things...and even talks of "inflection points". Spooky. But no genuine collaboration between the two posts.

[Model discussion highlights]

On 05/12/2023 at 11:02, Tamara said:

Unless something rather unexpected happens across the tropics to derail the wavetrain and the angular momentum response, again, somehow falls short..

Always expect the unexpected.  What doesn't make sense, usually gets supplied with an answer why if one waits for it.  

Equatorial fluxing between the tropics & extra tropics has created intense sub tropical ridging and a vastly inflated Azores/Atlantic ridge. That does, contrary to prior expectations in absence of it, make complete intuitive sense. With this, and stubborn legacy of -ve inertia within the extra tropics on the back of two large -ve MT events across both Asia & NA in mid late November and again in the early part of this month, then angular momentum falls shorter than it otherwise would and much greater polar jet energy is present as a consequence - in tandem with the strong sub tropical ridging.

In the absence, at this time, of any switch in fluxing between the tropics & extra tropics to boost amplification in the extra tropics than a continued mid latitude ebb & flow of ridges is well modelled by NWP and the polar front restricted with its inroads in longevity towards NW Europe. SW Europe stays under the influence of the resident anticyclone.

On 15/12/2023 at 12:31, northwestsnow said:

Your post the other day was so so true with reference to teleconnections ,they have limitations insofar as our tiny island is concerned

.The biggest elephant in the room is GW ,and the Hadley cell, its a winter killer for Europe..

Looking at the MJO in isolation is not a magic bullet, especially to try to fit to idealised synoptics. As seen in the ongoing scenario where the tropics & extra tropics are so out of kilter and producing a-typical Nina-esque patterns in what is an El Nino background. Any fluxing from tropical eddies into the extra tropics is muted and rather than eddy waves propagating poleward, they serve instead to boost the Hadley cell and bottle up the pole. In this context also, any displacement of the polar vortex is equally subdued by the ferrel cell asserting itself over the polar cell.

Macro-scale meteorological tools are not intended to micro scale forecast for a very small geographical area in the first place. They assist a framework for the larger hemisphere scale pattern to be evaluated within which that micro scale area exists. But more than anything else, as is always on auto-repeat - no diagnostic approach is intended to be skewed into fitting an idealised weather preference & outcome. Which is why so much mood driven emotion consumes this thread between about November and March.

11 minutes ago, Kasim Awan said:

Often happens in El Nino years, warm September was a giveaway aswell. EQBO + El Nino combination works in our favour a little though.

x+y= theory does not work in straight equations like this. The precise atmospheric circulation in existence at a given time has to be taken on its own merits - there is no given linear response. This post detail, again, tries to illustrate that. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4978487

[Model Output Discussion - Into Winter]

On 05/12/2023 at 11:02, Tamara said:

Unless something rather unexpected happens across the tropics to derail the wavetrain and the angular momentum response, again, somehow falls short..

Always expect the unexpected.  What doesn't make sense, usually gets supplied with an answer why if one waits for it.  

Equatorial fluxing between the tropics & extra tropics has created intense sub tropical ridging and a vastly inflated Azores/Atlantic ridge. That does, contrary to prior expectations in absence of it, make complete intuitive sense. With this, and stubborn legacy of -ve inertia within the extra tropics on the back of two large -ve MT events across both Asia & NA in mid late November and again in the early part of this month, then angular momentum falls shorter than it otherwise would and much greater polar jet energy is present as a consequence - in tandem with the strong sub tropical ridging.

In the absence, at this time, of any switch in fluxing between the tropics & extra tropics to boost amplification in the extra tropics than a continued mid latitude ebb & flow of ridges is well modelled by NWP and the polar front restricted with its inroads in longevity towards NW Europe. SW Europe stays under the influence of the resident anticyclone.

On 15/12/2023 at 12:31, northwestsnow said:

Your post the other day was so so true with reference to teleconnections ,they have limitations insofar as our tiny island is concerned

.The biggest elephant in the room is GW ,and the Hadley cell, its a winter killer for Europe..

Looking at the MJO in isolation is not a magic bullet, especially to try to fit to idealised synoptics. As seen in the ongoing scenario where the tropics & extra tropics are so out of kilter and producing a-typical Nina-esque patterns in what is an El Nino background. Any fluxing from tropical eddies into the extra tropics is muted and rather than eddy waves propagating poleward, they serve instead to boost the Hadley cell and bottle up the pole. In this context also, any displacement of the polar vortex is equally subdued by the ferrel cell asserting itself over the polar cell.

Macro-scale meteorological tools are not intended to micro scale forecast for a very small geographical area in the first place. They assist a framework for the larger hemisphere scale pattern to be evaluated within which that micro scale area exists. But more than anything else, as is always on auto-repeat - no diagnostic approach is intended to be skewed into fitting an idealised weather preference & outcome. Which is why so much mood driven emotion consumes this thread between about November and March.

11 minutes ago, Kasim Awan said:

Often happens in El Nino years, warm September was a giveaway aswell. EQBO + El Nino combination works in our favour a little though.

x+y= theory does not work in straight equations like this. The precise atmospheric circulation in existence at a given time has to be taken on its own merits - there is no given linear response. This post detail, again, tries to illustrate that. 

[Model discussion highlights]

1 hour ago, Singularity said:

Overall the modelling has drifted from a Nino like MJO phase 4-5-6 response (ridging W Europe to Siberia) toward a neutral ENSO one (Atlantic ridge, attempts to dig a trough into Scandi), but GFS more so than GEFS and still more so than ECM & it’s ensemble. A key matter that needs resolving.

That is to be permed with the GWO to provide the full wind-flow budget response from both tropics & extra tropics.

The GWO is struggling with amplitude in Phase 4 but surely a matter of time before a kick to the Nino attractor phases occurs. The extra tropical responses to the Pacific wavetrain continue to be modelled by NWP less buoyantly than expected. The current modelling wants to try to repeat the sequence of a few weeks back of Atlantic ridging replacing the trough A low angular momentum signature.. Based on the progression of tropical forcing through the Pacific & associated rise in momentum tendency, this more Nina-esque synoptical response seems counter intuitive on any sustainable basis.

So this mornings ECM makes more sense than the US modelling - retaining an element of height rises across mainland and NE Europe & the trough resetting to the NW. This would be a precursor to split flow/sub tropical flow returning and attempting to send the jet stream south of the UK and a thermal gradient setting up. Anomalously warm, moist & humid for my part of the world, cold dense air making inroads from NE Europe towards UK and the rest of NW Europe.

With that in mind I remain sceptical about the lack of sub tropical forcing which has flirted with thinking about interacting more with the blocking this past week. This momentum response cannot remain AWOL too long based on the upcoming tropical > extra tropical forcing. So a large mid Atlantic/mid latitude ridge and heights falling over Scandinavia is not intuitive to stick around like the GFS is modelling. Unless something rather unexpected happens across the tropics to derail the wavetrain and the angular momentum response, again, somehow falls short..

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4970436

[Model Output Discussion - Into Winter]

1 hour ago, Singularity said:

Overall the modelling has drifted from a Nino like MJO phase 4-5-6 response (ridging W Europe to Siberia) toward a neutral ENSO one (Atlantic ridge, attempts to dig a trough into Scandi), but GFS more so than GEFS and still more so than ECM & it’s ensemble. A key matter that needs resolving.

That is to be permed with the GWO to provide the full wind-flow budget response from both tropics & extra tropics.

The GWO is struggling with amplitude in Phase 4 but surely a matter of time before a kick to the Nino attractor phases occurs. The extra tropical responses to the Pacific wavetrain continue to be modelled by NWP less buoyantly than expected. The current modelling wants to try to repeat the sequence of a few weeks back of Atlantic ridging replacing the trough A low angular momentum signature.. Based on the progression of tropical forcing through the Pacific & associated rise in momentum tendency, this more Nina-esque synoptical response seems counter intuitive on any sustainable basis.

So this mornings ECM makes more sense than the US modelling - retaining an element of height rises across mainland and NE Europe & the trough resetting to the NW. This would be a precursor to split flow/sub tropical flow returning and attempting to send the jet stream south of the UK and a thermal gradient setting up. Anomalously warm, moist & humid for my part of the world, cold dense air making inroads from NE Europe towards UK and the rest of NW Europe.

With that in mind I remain sceptical about the lack of sub tropical forcing which has flirted with thinking about interacting more with the blocking this past week. This momentum response cannot remain AWOL too long based on the upcoming tropical > extra tropical forcing. So a large mid Atlantic/mid latitude ridge and heights falling over Scandinavia is not intuitive to stick around like the GFS is modelling. Unless something rather unexpected happens across the tropics to derail the wavetrain and the angular momentum response, again, somehow falls short..

[Model discussion highlights]

3 hours ago, MattH said:

So, yeah, coming full circle, that is certainly possible and if you link that into the GWO as well then you end up with the following for higher phases 5-6-7 which I think could be achievable this time around

My expectations follow this. You are correct again, to perm the tropical & extra tropical signals together c/o the Global Wind Oscillation to get the complete picture of the macro scale wind-flow budget & not the MJO in isolation.

The evolution to stronger sub tropical flow against burgeoning blocking over NE Europe, discussed in previous posts, has been panning out on the longer timescale as anticipated - but it is coming. Very classic Nino-esque Pacific>Atlantic wave train 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4968930

[Model Output Discussion - Into Winter]

3 hours ago, MattH said:

So, yeah, coming full circle, that is certainly possible and if you link that into the GWO as well then you end up with the following for higher phases 5-6-7 which I think could be achievable this time around

My expectations follow this. You are correct again, to perm the tropical & extra tropical signals together c/o the Global Wind Oscillation to get the complete picture of the macro scale wind-flow budget & not the MJO in isolation.

The evolution to stronger sub tropical flow against burgeoning blocking over NE Europe, discussed in previous posts, has been panning out on the longer timescale as anticipated - but it is coming. Very classic Nino-esque Pacific>Atlantic wave train 

[Model discussion highlights]

29 minutes ago, Met4Cast said:

Looks like my expectation for an unsettled start to December is going to come to fruition after all, just with a bonus cold spell before hand. 

Quite a few turn their noses up at background drivers/teleconnections in this thread, I suspect due to a lack of understanding them but I think that’s a shame, they are an incredibly useful tool and add a lot of context to NWP outputs. 

 

The MJO continues it’s progression eastwards is a rather amplified state, this wave has been a little faster than modelled and is expected to reach the central Pacific sometime around mid December, meanwhile we should see overall GLAAM rising via frictional & mountain torque processes thanks to this MJO wave with WWB’s returning. 

i.e I don’t expect we’ll see an Atlantic onslaught for weeks on end, it’s very possible we see a switch to more blocked/colder conditions over the Christmas period > into early January. 

As you might expect, I agree completely with the sentiments you make. Irrespective of my own weather preferences, the diagnostic processes are simply used to try to identify the most likely pattern probabilities. It is self defeating to to try to fit the data provided to a desired outcome though that will inevitably conflict in a thread like this which is heavily skewed in the peak seasons of summer, and most particularly winter, to a definitive weather type.

As per recent posts, I would only add to your analysis that considerable doubts continue about the return of the upstream momentum in respect of distribution into the sub tropical jet & how much energy, possibly, finds its way under the cold blocking over NE Europe. Across all main models in NWP there are a plethora of different solutions, some of which try to undercut the blocking.

For my own locality in Portugal, the watch is for a possible atmospheric river situation from midweek next week as warm moist sub tropical air arrives as part of the upstream momentum heading downstream. There is a lot of doubt about how the boundary of this returning tropical maritime airmass interplays with polar air at latitudes further north in Europe and high impact weather event potential clearly exists.

The situation is a little more nuanced than the return of the MJO into the Pacific. The existing complex inertia differential between the polar field and the mid latitudes here in the Atlantic & Europe is set to create some roadblocks a little before then. The question is where, and what then happens afterwards as jet eddies propagate through the extra tropics and poleward to a polar vortex which has already started its traditional seasonal stay in a weakened state.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4963155

[Model Output Discussion - Into Winter]

29 minutes ago, Met4Cast said:

Looks like my expectation for an unsettled start to December is going to come to fruition after all, just with a bonus cold spell before hand. 

Quite a few turn their noses up at background drivers/teleconnections in this thread, I suspect due to a lack of understanding them but I think that’s a shame, they are an incredibly useful tool and add a lot of context to NWP outputs. 

 

The MJO continues it’s progression eastwards is a rather amplified state, this wave has been a little faster than modelled and is expected to reach the central Pacific sometime around mid December, meanwhile we should see overall GLAAM rising via frictional & mountain torque processes thanks to this MJO wave with WWB’s returning. 

i.e I don’t expect we’ll see an Atlantic onslaught for weeks on end, it’s very possible we see a switch to more blocked/colder conditions over the Christmas period > into early January. 

As you might expect, I agree completely with the sentiments you make. Irrespective of my own weather preferences, the diagnostic processes are simply used to try to identify the most likely pattern probabilities. It is self defeating to to try to fit the data provided to a desired outcome though that will inevitably conflict in a thread like this which is heavily skewed in the peak seasons of summer, and most particularly winter, to a definitive weather type.

As per recent posts, I would only add to your analysis that considerable doubts continue about the return of the upstream momentum in respect of distribution into the sub tropical jet & how much energy, possibly, finds its way under the cold blocking over NE Europe. Across all main models in NWP there are a plethora of different solutions, some of which try to undercut the blocking.

For my own locality in Portugal, the watch is for a possible atmospheric river situation from midweek next week as warm moist sub tropical air arrives as part of the upstream momentum heading downstream. There is a lot of doubt about how the boundary of this returning tropical maritime airmass interplays with polar air at latitudes further north in Europe and high impact weather event potential clearly exists.

The situation is a little more nuanced than the return of the MJO into the Pacific. The existing complex inertia differential between the polar field and the mid latitudes here in the Atlantic & Europe is set to create some roadblocks a little before then. The question is where, and what then happens afterwards as jet eddies propagate through the extra tropics and poleward to a polar vortex which has already started its traditional seasonal stay in a weakened state.

[Model discussion highlights]

Posted last week:

Tropical forcing now shows clearly increasing amplitude heading eastwards across I/O and renewed WWB's reversing the lull in momentum this week which led to the mid Atlantic ridge. This is important, because angular momentum tendency soaring heading into December, tied into seasonal wavelength changes and increasingly unstable tropopause boundary is ripe for high impact weather across Europe into December.That mid latitude ridging is set to become a road block to the polar jet as it becomes a higher latitude feature with undercutting jet flow.

---------------------------

This theme continues - sensitivities abound as to how the returning momentum interacts with increasingly cold, dense air across Northern, NW'ern & central Europe.

The recent steep drop in angular momentum significantly sharpened the Atlantic ridging with both Asian & N American torques joining in the act within the extra tropics to scrub westerly inertia from the atmospheric circulation and a sudden void in the vacuum needing to be filled. But as anticipated, the route for the polar jet has become problematic with a weaker than average polar vortex, and a conundrum exists for for the fish in midstream as to which way they shoal and at what depth.

Don't expect quick answers to this question. The return of the jet from upstream makes complete sense in the medium term, but my suspicion continues that the sub tropical jet is being underplayed and something akin to last December evolving heading towards mid month remains quite possible. This implies low pressure tracking rather south of where presently indicated with still the prospect of a fairly steep thermal boundary with very cold air always lurking very close the north east of the UK and at the other end of the spectrum a recovery of temperatures heading towards SW Europe and my locale from the slack pattern at the end of this week in the shorter term.  Attritional processes of these two very different airmasses taking place thereafter. But exactly where this happens across mainland more north-western parts of Europe is something to keep watching.

With all this mind, the final paragraph of Matt H model analysis here reflects my own thinking about the jet stream conundrum

 

 

Equally, take note of his other GSDM analysis and refer to this beyond any MJO data used in isolation - because the latter, as I am fond of repeating, tells only part of the story of the AAM budget & atmospheric circulation wind-flow and will not give the most accurate synoptic interpretation within NWP.

A very unstable GSDM profile to start winter for sure with widely oscillating GWO orbit.

 

The rollercoaster is on the bottom of the ride, and is about to start pointing the rider back up towards the sky. Watch where that return of momentum takes the ride...

Boa tarde e todos.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4962152

[Model Output Discussion - Into Winter]

Posted last week:

Tropical forcing now shows clearly increasing amplitude heading eastwards across I/O and renewed WWB's reversing the lull in momentum this week which led to the mid Atlantic ridge. This is important, because angular momentum tendency soaring heading into December, tied into seasonal wavelength changes and increasingly unstable tropopause boundary is ripe for high impact weather across Europe into December.That mid latitude ridging is set to become a road block to the polar jet as it becomes a higher latitude feature with undercutting jet flow.

---------------------------

This theme continues - sensitivities abound as to how the returning momentum interacts with increasingly cold, dense air across Northern, NW'ern & central Europe.

The recent steep drop in angular momentum significantly sharpened the Atlantic ridging with both Asian & N American torques joining in the act within the extra tropics to scrub westerly inertia from the atmospheric circulation and a sudden void in the vacuum needing to be filled. But as anticipated, the route for the polar jet has become problematic with a weaker than average polar vortex, and a conundrum exists for for the fish in midstream as to which way they shoal and at what depth.

Don't expect quick answers to this question. The return of the jet from upstream makes complete sense in the medium term, but my suspicion continues that the sub tropical jet is being underplayed and something akin to last December evolving heading towards mid month remains quite possible. This implies low pressure tracking rather south of where presently indicated with still the prospect of a fairly steep thermal boundary with very cold air always lurking very close the north east of the UK and at the other end of the spectrum a recovery of temperatures heading towards SW Europe and my locale from the slack pattern at the end of this week in the shorter term.  Attritional processes of these two very different airmasses taking place thereafter. But exactly where this happens across mainland more north-western parts of Europe is something to keep watching.

With all this mind, the final paragraph of Matt H model analysis here reflects my own thinking about the jet stream conundrum

 

 

Equally, take note of his other GSDM analysis and refer to this beyond any MJO data used in isolation - because the latter, as I am fond of repeating, tells only part of the story of the AAM budget & atmospheric circulation wind-flow and will not give the most accurate synoptic interpretation within NWP.

A very unstable GSDM profile to start winter for sure with widely oscillating GWO orbit.

 

The rollercoaster is on the bottom of the ride, and is about to start pointing the rider back up towards the sky. Watch where that return of momentum takes the ride...

Boa tarde e todos.

[Model discussion highlights]

2 minutes ago, Battleground Snow said:

Flicking through the EPS at day 10 and I've picked out the best ones, but most of the suite is solidly blocked and cold

There is your NW Europe *high impact weather* Good examples of what I was describing & suggesting possible earlier. 

At range the modelling will not pick up on features developing along the thermal boundary. Ensemble product means will look 'clean'. Expect changes to be likely over coming days as the sub tropical jet spawns low pressure areas across the evolving -ve NAO region

Similarities with Dec 22 that is for sure the way this is shaping up. Some interesting weather down here too then of a different kind to the UK.

Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4956617

[Model discussion highlights]

2 hours ago, Nick F said:

An interesting thread by Eric Webb on x / twitter explaining the unusual and unexpected developments over Europe next week, especially the -NAO. He suggests recent tropical forcing and strong strat PV would normally be unfavourable for the -NAO pattern we are seeing evolve and that it is more 'local' in situ forces that are shaping it rather than teleconnections to what's going on further afield. Reflects what I mentioned earlier but he has far more knowledge on such matters.

 

Yes. its a technical US twitter style description of what I said earlier in simple terms of the Atlantic ridge roadblock of the returning polar jet as momentum falls this week - but ahead of a much bigger surge of momentum that is set to return as we head to the curtain raiser to winter. The effect is that the residual northern arm of the jet this week becomes strangled just at the time that the sub tropical jet starts to also return. and undercut the block.

To repeat that narrative in the same words but in a different order for extra clarity:

The recent tropical forcing  ()mentioned in that tweet) lead to the mid Atlantic ridge (falling AAM momentum) but it is precise timing of the return of momentum upstream from the Equatorial Pacific > Atlantic and associated STJ heading back downstream that meets the existing mid Atlantic blocking at what looks like 'impressive' timing to send residual polar jet energy looped around that ridging into the polar field and accentuates instability there. At the same time STJ energy returns under the block to underpin it and make it more of a higher latitude feature as the polar field destabilises further.

Yesterdays GSDM plots were posted to depicted the GWO evolution to Phase 8 that evidentially underpinned the predicted Atlantic ridge evolution this week.. The coming days should equally match the GSDM diagnosis as set out since yesterday to equate to the NWP evolution over the coming end period of November into December and a rapid return into December of the GWO towards the Nino attractor phases. Higher orbit that seen for some time -and significant as Winter arrives in respect of propagation of wind eddies from the tropics > extra tropics and then poleward +ve mountain torque transport to sustain disruption of the lower stratosphere...

We need to be careful with how macro atmospheric wind-flow diagnosis jives with the micro effects that flesh out the detail of 'weather' itself. Especially on this site which deals intensively with what is a very small area of the UK in respect of the bigger picture.

To finish: @Met4Cast has been on the right lines of late. The truth is that the current curveballs in modelling will rarely be admitted on global twitter until hindsight makes them big news...My own red flag ( quietly on here and )not on twitter) to a forwarding of pattern change potential to earlier than anticipated came yesterday. Hence the update and explanation then. The truth is that the best knowledge in the world cannot predict such exact timing of dynamics - even if the diagnostic is highly useful in giving a heads-up to inform you of change on the way.

Boa noite e todos.

 

Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4956794

[Model Output Discussion - mid Autumn]

2 hours ago, Nick F said:

An interesting thread by Eric Webb on x / twitter explaining the unusual and unexpected developments over Europe next week, especially the -NAO. He suggests recent tropical forcing and strong strat PV would normally be unfavourable for the -NAO pattern we are seeing evolve and that it is more 'local' in situ forces that are shaping it rather than teleconnections to what's going on further afield. Reflects what I mentioned earlier but he has far more knowledge on such matters.

 

Yes. its a technical US twitter style description of what I said earlier in simple terms of the Atlantic ridge roadblock of the returning polar jet as momentum falls this week - but ahead of a much bigger surge of momentum that is set to return as we head to the curtain raiser to winter. The effect is that the residual northern arm of the jet this week becomes strangled just at the time that the sub tropical jet starts to also return. and undercut the block.

To repeat that narrative in the same words but in a different order for extra clarity:

The recent tropical forcing  ()mentioned in that tweet) lead to the mid Atlantic ridge (falling AAM momentum) but it is precise timing of the return of momentum upstream from the Equatorial Pacific > Atlantic and associated STJ heading back downstream that meets the existing mid Atlantic blocking at what looks like 'impressive' timing to send residual polar jet energy looped around that ridging into the polar field and accentuates instability there. At the same time STJ energy returns under the block to underpin it and make it more of a higher latitude feature as the polar field destabilises further.

Yesterdays GSDM plots were posted to depicted the GWO evolution to Phase 8 that evidentially underpinned the predicted Atlantic ridge evolution this week.. The coming days should equally match the GSDM diagnosis as set out since yesterday to equate to the NWP evolution over the coming end period of November into December and a rapid return into December of the GWO towards the Nino attractor phases. Higher orbit that seen for some time -and significant as Winter arrives in respect of propagation of wind eddies from the tropics > extra tropics and then poleward +ve mountain torque transport to sustain disruption of the lower stratosphere...

We need to be careful with how macro atmospheric wind-flow diagnosis jives with the micro effects that flesh out the detail of 'weather' itself. Especially on this site which deals intensively with what is a very small area of the UK in respect of the bigger picture.

To finish: @Met4Cast has been on the right lines of late. The truth is that the current curveballs in modelling will rarely be admitted on global twitter until hindsight makes them big news...My own red flag ( quietly on here and )not on twitter) to a forwarding of pattern change potential to earlier than anticipated came yesterday. Hence the update and explanation then. The truth is that the best knowledge in the world cannot predict such exact timing of dynamics - even if the diagnostic is highly useful in giving a heads-up to inform you of change on the way.

Boa noite e todos.

 

[Model Output Discussion - mid Autumn]

2 minutes ago, Battleground Snow said:

Flicking through the EPS at day 10 and I've picked out the best ones, but most of the suite is solidly blocked and cold

There is your NW Europe *high impact weather* Good examples of what I was describing & suggesting possible earlier. 

At range the modelling will not pick up on features developing along the thermal boundary. Ensemble product means will look 'clean'. Expect changes to be likely over coming days as the sub tropical jet spawns low pressure areas across the evolving -ve NAO region

Similarities with Dec 22 that is for sure the way this is shaping up. Some interesting weather down here too then of a different kind to the UK.