Tamara

Ed Berry, previously an NOAA affiliate who designed the GSDM wind-flow diagnostic product, passed away a few months and he held the primary authority for the use of the product and which David Gold inherited rights to its use. There may be something in this that is stalling processes of fixing & updating the site - but a degree of speculative reasoning in that admittedly. For those in the UK and NW Europe generally, there shouldn't be too much concern at this time about summer. In fact with the tropics & extra tropics continuing to amass truly substantial surpluses of +AAM westerly inertia, this is set to drive highly anomalous anticyclonic wave trains across mid latitudes as the effects of an unstable tropospheric boundary to the polar field at higher latitudes continues to lose residual influence. With summer wavelengths approaching there could well be a seismic shift towards northwards advection of heat as the Hadley cell expansion from Africa into southern European is producing staggering record breaking heat down here. Records broken here in Portugal during April that go back 78 years. A flick of a switch could mean quite a dramatic change in weather moving northwards across greater and greater parts of Europe - as this heat can only keep building through May and into June. So much so, that summer down here is a subject of quite some apprehension in contrast to the wait for heat to arrive in the UK. Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4848987

Ed Berry, previously an NOAA affiliate who designed the GSDM wind-flow diagnostic product, passed away a few months and he held the primary authority for the use of the product and which David Gold inherited rights to its use. There may be something in this that is stalling processes of fixing & updating the site - but a degree of speculative reasoning in that admittedly. For those in the UK and NW Europe generally, there shouldn't be too much concern at this time about summer. In fact with the tropics & extra tropics continuing to amass truly substantial surpluses of +AAM westerly inertia, this is set to drive highly anomalous anticyclonic wave trains across mid latitudes as the effects of an unstable tropospheric boundary to the polar field at higher latitudes continues to lose residual influence. With summer wavelengths approaching there could well be a seismic shift towards northwards advection of heat as the Hadley cell expansion from Africa into southern European is producing staggering record breaking heat down here. Records broken here in Portugal during April that go back 78 years. A flick of a switch could mean quite a dramatic change in weather moving northwards across greater and greater parts of Europe - as this heat can only keep building through May and into June. So much so, that summer down here is a subject of quite some apprehension in contrast to the wait for heat to arrive in the UK.

Boa tarde e todos Since the middle of last month the GSDM site has not been working, so without wind-flow & torque budget data to hand this makes diagnostic analysis less straightforward - but there is clear evidence of quite a seismic shift in the core ocean>atmosphere dynamic and low frequency standing wave shift of tropical convection rossby wave trains into the Pacific. A late Spring and Summer dominated by westerly wind bursts across the tropics lies ahead. The impact this has on frictional torque inertia and associated upstream wind shear heading downstream from the Equatorial Pacific into the Equatorial Atlantic (supressed trade winds) suggests intermittent ebbing and flowing of this feedback (enhanced by periodic MJO cycling) and a consequent series of weakenings of the strength of the Azores high pressure likely. This implies phases of cut-off low pressure across the Atlantic and downstream response anticyclones across much of mainland Europe (including also UK) and Scandinavia. This looks increasingly like the default pattern for the coming months - with relatively short interruptions as torque mechanisms reverse temporarily according to cyclical lulls in the MJO "mini cycle" The legacy of the late winter SSW is the obstacle to a warm air advection pattern,associated with this trough>ridge sequencing setting up sustainably across NW Europe, but already the Hadley cell is exerting strength on the downstream ridging pattern across Portugal & Spain 8 into the Western Mediterranean with true summer-like conditions and values in excess of 32C already (including locally in my part of Portugal) - way above average for the middle period of April. This type of pattern taking hold ahead of summer has quite worrying implications for potential heat intensity in the coming months as the rossby wave sequences keep amplifying the trough>ridge pattern with repeated plumes building from higher and higher temperature bases across southern Europe and with time also advecting north through France towards UK & NW Europe as the default Atlantic trough in the Atlantic forges instability from the west - with thundery breakdowns before re-setting. Hopefully at some stage the GSDM site will be operating up to date once again and some more cohesive analysis might be possible. Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4844071

Boa tarde e todos Since the middle of last month the GSDM site has not been working, so without wind-flow & torque budget data to hand this makes diagnostic analysis less straightforward - but there is clear evidence of quite a seismic shift in the core ocean>atmosphere dynamic and low frequency standing wave shift of tropical convection rossby wave trains into the Pacific. A late Spring and Summer dominated by westerly wind bursts across the tropics lies ahead. The impact this has on frictional torque inertia and associated upstream wind shear heading downstream from the Equatorial Pacific into the Equatorial Atlantic (supressed trade winds) suggests intermittent ebbing and flowing of this feedback (enhanced by periodic MJO cycling) and a consequent series of weakenings of the strength of the Azores high pressure likely. This implies phases of cut-off low pressure across the Atlantic and downstream response anticyclones across much of mainland Europe (including also UK) and Scandinavia. This looks increasingly like the default pattern for the coming months - with relatively short interruptions as torque mechanisms reverse temporarily according to cyclical lulls in the MJO "mini cycle" The legacy of the late winter SSW is the obstacle to a warm air advection pattern,associated with this trough>ridge sequencing setting up sustainably across NW Europe, but already the Hadley cell is exerting strength on the downstream ridging pattern across Portugal & Spain 8 into the Western Mediterranean with true summer-like conditions and values in excess of 32C already (including locally in my part of Portugal) - way above average for the middle period of April. This type of pattern taking hold ahead of summer has quite worrying implications for potential heat intensity in the coming months as the rossby wave sequences keep amplifying the trough>ridge pattern with repeated plumes building from higher and higher temperature bases across southern Europe and with time also advecting north through France towards UK & NW Europe as the default Atlantic trough in the Atlantic forges instability from the west - with thundery breakdowns before re-setting. Hopefully at some stage the GSDM site will be operating up to date once again and some more cohesive analysis might be possible.

From the point of view of those of you in NW Europe, I wouldn't worry. Next week still looks due for potential high impact weather events and snowfalls. From my point of view though, it also looks better with a sub tropical jet stream returning to end to this anomalously very below average spell of weather which is no fun down here for flora and fauna. Quite a big jump in values to the high teens next week and very much warmer nights than the close to freezing nights of this week. Just taken at face value for what it is worth, tonight's ECM operational for my part of the world would be a thing of beauty

This is probably one of the highest quality assessments of the GSDM diagnostic working in real time that I have read and with well explained and argued prospects ahead (at least for NW Europe). Very much a bookended season. This winter has seen the Hadley/polar cell dual that I talked about coming into winter back in November. December saw poleward momentum under a destabilised tropospheric lead into the lower stratosphere and thereafter equatorward fluxing took over as angular momentum fell in tandem with the westerly gyre of the upper stratosphere descending into the troposphere. This has largely prevailed through to the end of winter. Now we see the reverse back in AAM fluxing at the same time as instability in the form of -ve zonal winds descends from the upper levels of the stratosphere c/o SSW into the troposphere- but this time creating a coupled relationship which will enable a more sustained phase of poleward momentum than the early winter with, as @Met4Cast points out (with no further embellishment required) angular momentum tendency surging very high. Make no mistake, when tropics (MJO) and extra tropics (GWO) phase in a harmonious momentum transport wind-flow signal such as at present, in tandem with a highly unstable trop/strat combination than a sustained phase of high impact weather conditions are in the offing. For my part of southern Europe this significant pattern change will ironically bring to a (welcome) end to anomalously very below average temperatures which have been a nuisance at night for the Mediterranean planting garden. Both late January and now the end of February have seen repeated cold air advection patterns coming around the eastern and southern flanks of high pressure stuck over the UK/eastern Atlantic. With the return of the -ve NAO from the end of the coming weekend and through next week, sub tropical air will bring a quite noteworthy jump in temperatures into the upper teens and potentially low 20s in places - but also with bands of rain bringing wet conditions. So Spring begins much as to how the winter began. As for the UK there is a similar parallel to how winter came in (nut with reverse trends in weather). Increasingly set to be on the polar side of the jet stream and depending precisely where the boundary of southerly tracking low pressure is, high impact weather events look odds on with significant snow events. Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4813471

This is probably one of the highest quality assessments of the GSDM diagnostic working in real time that I have read and with well explained and argued prospects ahead (at least for NW Europe). Very much a bookended season. This winter has seen the Hadley/polar cell dual that I talked about coming into winter back in November. December saw poleward momentum under a destabilised tropospheric lead into the lower stratosphere and thereafter equatorward fluxing took over as angular momentum fell in tandem with the westerly gyre of the upper stratosphere descending into the troposphere. This has largely prevailed through to the end of winter. Now we see the reverse back in AAM fluxing at the same time as instability in the form of -ve zonal winds descends from the upper levels of the stratosphere c/o SSW into the troposphere- but this time creating a coupled relationship which will enable a more sustained phase of poleward momentum than the early winter with, as @Met4Cast points out (with no further embellishment required) angular momentum tendency surging very high. Make no mistake, when tropics (MJO) and extra tropics (GWO) phase in a harmonious momentum transport wind-flow signal such as at present, in tandem with a highly unstable trop/strat combination than a sustained phase of high impact weather conditions are in the offing. For my part of southern Europe this significant pattern change will ironically bring to a (welcome) end to anomalously very below average temperatures which have been a nuisance at night for the Mediterranean planting garden. Both late January and now the end of February have seen repeated cold air advection patterns coming around the eastern and southern flanks of high pressure stuck over the UK/eastern Atlantic. With the return of the -ve NAO from the end of the coming weekend and through next week, sub tropical air will bring a quite noteworthy jump in temperatures into the upper teens and potentially low 20s in places - but also with bands of rain bringing wet conditions. So Spring begins much as to how the winter began. As for the UK there is a similar parallel to how winter came in (nut with reverse trends in weather). Increasingly set to be on the polar side of the jet stream and depending precisely where the boundary of southerly tracking low pressure is, high impact weather events look odds on with significant snow events.

You are following the right guidance with the GSDM/GWO and your analysis of how it was possible to pinpoint toppling Atlantic ridging is sound. enough The whole purpose of the GSDM is proactive, not reactive - and objective correct use of it would bear it out There is nothing to apologise for

There remains all kinds of potential outcomes from the stratospheric diminution. This winter has seen a complex relationship between the troposphere and the stratosphere - I made some posts in late November foreseeing such complexities between the tropics and the pole. It has indeed panned out that way in respect of the differences between the earliest part of winter, and the countervailing forces which then flipped to a lot of equatorward fluxing of momentum. This has meant that active tropical forcing has manifested anomalous sub tropical anticyclones across the extra tropics rather than blocking at higher latitudes that *may* have continued to result from poleward fluxing of momentum transport. This is a truncated background context, at least as I continue to see it, which frames the balance of events for the upcoming SSW period which is occurring as tropical convection propagates eastwards across the tropics. Some comparisons have been made with February 2018. It is certainly true that the 2023 SSW is timed to occur close to when the 2018 event did - but the background relationships within the troposphere and the stratosphere are not the same as I see it. Winter 17/18, as a whole, saw an unstable wind-flow propagation coupled relationship between the tropics & extra tropics. Equally, an equally unstable partitioning of zonal wind anomalies existed across the polar field which seemed primed to detonate as far back as mid January 2018.. In that sense the tropospheric synoptic patterns moved in symmetry with the machinations within the stratosphere. That is not the case this winter - there has been a stand-off between the two with the troposphere lead of early winter, overtaken by a more stable stratospheric lead. Poleward momentum was very extreme ahead of the 2018 event with a massive surge of angular momentum tendency that led to a temporary reversal of the La Nina walker cell. Broadscale extra tropical mountain torque deflection of wind eddies from the troposphere c/o wholesale meltdown within the atmospheric circulation created the means for a quick tropospheric response from the SSW and -ve zonal winds at higher latitudes manifesting robust blocking structures. The background this winter has differences - the Global Synoptic Dynamical modelling (GSDM) (which essentially is a diagnostic of the wind-flow budget through frictional & mountain torque mechanisms in the tropics & extra tropics) has been more stable than during the 17/18 winter. In simple terms, other than the very early part of winter, there has been equatorward rather than poleward fluxing of AAM anomalies - as outlined at the beginning of the post. Whilst tropical forcing is active, the same as was the case in 17/18 - the different pattern of directional fluxing alongside a more stable stratospheric profile, overall, has dampened the amplification profile within the extra tropics. Hence limited poleward amplification of anticyclones that have been produced by the wave-breaking transferring from tropics > extra tropics. These differences make predicting the outcomes this year ever more complex and uncertain. Much more so in my opinion that in February 2018 when probabilistic outcomes were more clear cut and loaded emphatically towards a QTR and anomalous polar blocking. Following the huge +ve AAM rally of early February 2018, momentum collapsed in tandem with the timing of the SSW and this actually helped to augment the tropospheric reaction as attempts to switch jet stream inertia into the polar stream were utterly nullified by the wall of -ve zonal winds at the tropospheric boundary and this road blocking enhanced the cross polar ridging response and cold air advection processes. This year, as stated, the lack of relative strength of momentum transport (more stable GSDM within the troposphere) means that there is less latent inertia to enhance/superimpose on any downwell of zonal winds into the troposphere that may occur. Indeed it is conceivable that equatorward flux could hinder processes and lead to either a supressed response, or a diffused response. Such a diffused response (if it was to occur) could also on the other hand be an extended one if seasonal wavelength changes into Spring re-configure synoptic responses with the troposphere (wavelengths evolve to enhance cold air advection processes more easily than during winter). A 'warm' polar stratosphere and 'cold' tropical stratosphere suggests enhanced Brewer Dobson circulation of ozone & continued promotion of active tropical convection - and this could play its part in how amplification processes within the extra tropics behave. Quite possibly, very differently to winter wavelengths based on evolvement finally to a coupled unstable tropospheric> stratospheric state. The difference being this occurs after the SSW rather than priming the atmosphere before it as occurred in 2018. In summary, a lot of complexities & uncertainties and an open mind is required in the days (and weeks) ahead. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804685

There remains all kinds of potential outcomes from the stratospheric diminution. This winter has seen a complex relationship between the troposphere and the stratosphere - I made some posts in late November foreseeing such complexities between the tropics and the pole. It has indeed panned out that way in respect of the differences between the earliest part of winter, and the countervailing forces which then flipped to a lot of equatorward fluxing of momentum. This has meant that active tropical forcing has manifested anomalous sub tropical anticyclones across the extra tropics rather than blocking at higher latitudes that *may* have continued to result from poleward fluxing of momentum transport. This is a truncated background context, at least as I continue to see it, which frames the balance of events for the upcoming SSW period which is occurring as tropical convection propagates eastwards across the tropics. Some comparisons have been made with February 2018. It is certainly true that the 2023 SSW is timed to occur close to when the 2018 event did - but the background relationships within the troposphere and the stratosphere are not the same as I see it. Winter 17/18, as a whole, saw an unstable wind-flow propagation coupled relationship between the tropics & extra tropics. Equally, an equally unstable partitioning of zonal wind anomalies existed across the polar field which seemed primed to detonate as far back as mid January 2018.. In that sense the tropospheric synoptic patterns moved in symmetry with the machinations within the stratosphere. That is not the case this winter - there has been a stand-off between the two with the troposphere lead of early winter, overtaken by a more stable stratospheric lead. Poleward momentum was very extreme ahead of the 2018 event with a massive surge of angular momentum tendency that led to a temporary reversal of the La Nina walker cell. Broadscale extra tropical mountain torque deflection of wind eddies from the troposphere c/o wholesale meltdown within the atmospheric circulation created the means for a quick tropospheric response from the SSW and -ve zonal winds at higher latitudes manifesting robust blocking structures. The background this winter has differences - the Global Synoptic Dynamical modelling (GSDM) (which essentially is a diagnostic of the wind-flow budget through frictional & mountain torque mechanisms in the tropics & extra tropics) has been more stable than during the 17/18 winter. In simple terms, other than the very early part of winter, there has been equatorward rather than poleward fluxing of AAM anomalies - as outlined at the beginning of the post. Whilst tropical forcing is active, the same as was the case in 17/18 - the different pattern of directional fluxing alongside a more stable stratospheric profile, overall, has dampened the amplification profile within the extra tropics. Hence limited poleward amplification of anticyclones that have been produced by the wave-breaking transferring from tropics > extra tropics. These differences make predicting the outcomes this year ever more complex and uncertain. Much more so in my opinion that in February 2018 when probabilistic outcomes were more clear cut and loaded emphatically towards a QTR and anomalous polar blocking. Following the huge +ve AAM rally of early February 2018, momentum collapsed in tandem with the timing of the SSW and this actually helped to augment the tropospheric reaction as attempts to switch jet stream inertia into the polar stream were utterly nullified by the wall of -ve zonal winds at the tropospheric boundary and this road blocking enhanced the cross polar ridging response and cold air advection processes. This year, as stated, the lack of relative strength of momentum transport (more stable GSDM within the troposphere) means that there is less latent inertia to enhance/superimpose on any downwell of zonal winds into the troposphere that may occur. Indeed it is conceivable that equatorward flux could hinder processes and lead to either a supressed response, or a diffused response. Such a diffused response (if it was to occur) could also on the other hand be an extended one if seasonal wavelength changes into Spring re-configure synoptic responses with the troposphere (wavelengths evolve to enhance cold air advection processes more easily than during winter). A 'warm' polar stratosphere and 'cold' tropical stratosphere suggests enhanced Brewer Dobson circulation of ozone & continued promotion of active tropical convection - and this could play its part in how amplification processes within the extra tropics behave. Quite possibly, very differently to winter wavelengths based on evolvement finally to a coupled unstable tropospheric> stratospheric state. The difference being this occurs after the SSW rather than priming the atmosphere before it as occurred in 2018. In summary, a lot of complexities & uncertainties and an open mind is required in the days (and weeks) ahead.

I have taken these two posts purely as snapshots of two sides of the same thing in respect of context for use of teleconnections and stratospheric phenomenon and in respect of having altered quite appreciably my approach to them as more experience of them has been gained. The more understanding one gets, the more realisation there is that there is no room for bias confirmation in their use. Which admittedly makes it hard to provide worthwhile contributions into this thread that do not fit in with that purpose. Apologies for repetition - but as I have commented many times the total atmospheric wind-flow budget, incorporating the extra tropics has to additionally be considered and then a further diagnostic of directional flux of momentum transport identified to get a reflection of a probabilistic ranges of synoptic responses. There is no x+y= equation with these composites, ever more skewed by increasing numbers of extra variables (including climatic forcing). Gauging the extra tropical synoptic response based on the tropics as a stand alone is prone to error as these can and do sometimes work in disconnect. Much as they have done through sections of this winter. The Global Wind Oscillation (GWO) incorporates both tropical & extra tropical wind-flow and using this in tandem with tropical convection forecast expectations gives a fuller and more reliable indication. That is, if they are used objectively and not to fit a desired pattern. Equatorward fluxing of AAM anomalies continues as a consideration in this last section of winter heading into Spring helping to consolidate the mid latitude blocking patterns and distinct polar jet - much as was seen in February 2019 when an earlier and stronger warming across the polar field was evident and there was no cold air advection response. Of course currently proceedings are ahead of such developments and it could indeed be the case that seasonal wavelength changes are ultimately an extra catalyst for the weakening of the polar vortex to switch fluxing of momentum poleward and change the blocking pattern and alter the Northern Annular Mode state - but too many uncertainties remain about this. Those in more northern parts of Europe wanting Spring proper will be hoping that such a switch is not the case.. Some down here after an anomalously cold few weeks (on the southern flank of the mid latitude blocking) look for more seasonally normal temperatures and would welcome some extra rain (not a monsoon!) ahead of the scorching summer to top up from the very wet December c/o the -ve NAO state back then. So mixed feeling exist in different ways. But irrespective of preferences (whatever they may be), it is wholly a large part of following the subject of meteorology to point to pattern changes ahead - as interactions stemming from the tropics into the extra tropics are a bellweather indicator for changes ahead within the troposphere at the same time as zonal wind anomalies drop sharply across the polar field c/o substantive warming of the stratosphere occur. However, equally prudent to be open minded to precisely what synoptic outcomes might be across a wide expanse of the Northern Hemisphere. When expectations are geared so strongly in one direction in this thread at this time of year, the latter part is clearly a struggle to achieve. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804320

I have taken these two posts purely as snapshots of two sides of the same thing in respect of context for use of teleconnections and stratospheric phenomenon and in respect of having altered quite appreciably my approach to them as more experience of them has been gained. The more understanding one gets, the more realisation there is that there is no room for bias confirmation in their use. Which admittedly makes it hard to provide worthwhile contributions into this thread that do not fit in with that purpose. Apologies for repetition - but as I have commented many times the total atmospheric wind-flow budget, incorporating the extra tropics has to additionally be considered and then a further diagnostic of directional flux of momentum transport identified to get a reflection of a probabilistic ranges of synoptic responses. There is no x+y= equation with these composites, ever more skewed by increasing numbers of extra variables (including climatic forcing). Gauging the extra tropical synoptic response based on the tropics as a stand alone is prone to error as these can and do sometimes work in disconnect. Much as they have done through sections of this winter. The Global Wind Oscillation (GWO) incorporates both tropical & extra tropical wind-flow and using this in tandem with tropical convection forecast expectations gives a fuller and more reliable indication. That is, if they are used objectively and not to fit a desired pattern. Equatorward fluxing of AAM anomalies continues as a consideration in this last section of winter heading into Spring helping to consolidate the mid latitude blocking patterns and distinct polar jet - much as was seen in February 2019 when an earlier and stronger warming across the polar field was evident and there was no cold air advection response. Of course currently proceedings are ahead of such developments and it could indeed be the case that seasonal wavelength changes are ultimately an extra catalyst for the weakening of the polar vortex to switch fluxing of momentum poleward and change the blocking pattern and alter the Northern Annular Mode state - but too many uncertainties remain about this. Those in more northern parts of Europe wanting Spring proper will be hoping that such a switch is not the case.. Some down here after an anomalously cold few weeks (on the southern flank of the mid latitude blocking) look for more seasonally normal temperatures and would welcome some extra rain (not a monsoon!) ahead of the scorching summer to top up from the very wet December c/o the -ve NAO state back then. So mixed feeling exist in different ways. But irrespective of preferences (whatever they may be), it is wholly a large part of following the subject of meteorology to point to pattern changes ahead - as interactions stemming from the tropics into the extra tropics are a bellweather indicator for changes ahead within the troposphere at the same time as zonal wind anomalies drop sharply across the polar field c/o substantive warming of the stratosphere occur. However, equally prudent to be open minded to precisely what synoptic outcomes might be across a wide expanse of the Northern Hemisphere. When expectations are geared so strongly in one direction in this thread at this time of year, the latter part is clearly a struggle to achieve.

I live in Portugal, and am therefore detached from the interest in this thread, but you are correct in respect of the over "magic bullet" association to cold weather with SSW's. As interesting a phenomenon they are in themselves, the associated cold weather hype rather detracts from that appreciation. Similarly with the MJO - this is not the stand alone phenomenon it is treated as in this thread and equally as such not a magic bullet to cold weather preferences. It is just one part of the atmospheric circulation total wind-flow budget, and while clearly an important catalyst for changes in weather pattern, it has to be taken in association with the rest of the wind-flow budget which comprises the extra-tropics. The relationship between the tropical & extra tropical wind-flow circulation does not work on a linear x+y = equation (in the same way as the troposphere and stratosphere can have both a connected & equally often quite disconnected relationship). With this in mind the frequent use of MJO composites on this thread is not going to lead to accuracy, especially when attempted to be fitted to weather bias patterns, without considering the extra-tropical Global Wind Oscillation (GWO). The GWO incorporates analysis of the total circulation budget and gives analysis of each flux and torque component within the total atmospheric circulation and is therefore a much more accurate guide. That is, again, if one is willing to suspend skewing.such a diagnostic to try to fit to a desired outcome. This will also lead to inevitable error (and disappointment) So to put some of this background rationale into practice: The GWO, a plot depiction of total wind-flow, is firmly in a -ve inertia state taking both the tropics and extra tropics as a whole. A disconnect is evident between both components - with westerly wind additions (orange shaded) in the tropics across the Indian ocean as measured by inflection of wind-flow frictional torque at the same time as being over compensated by anomalous -ve inertia across mid latitudes and a large vacuum evident as a result of this c/o -ve mountain torques across both Americas. This vacuum, in order to be filled, has been driving an extended period of mid latitude retrogressive sequences of anticyclonic wave breaking (blue shading on MT plots) and hence the sustained elongated blocked pattern across the mid hemisphere. At the same time the polar jet is energised across the northern perimeter of these blocking structures in association with added assistance of downwelling of +ve zonal winds from the stratosphere into the tropospheric boundary layers. The MJO tropical component continues to operate at amplitude (in accordance with a prediction of recurrence periodicity cycle made back in early December). The complex relationship this winter between the stratosphere & troposphere makes it problematic ascertaining how eastward movement of amplitude tropical convection through the tropics propagates into the extra tropics and then how directional flux of AAM anomalies routes the amplifying wind eddies either poleward in association with weakening stratospheric vortex, or continued equatorward ( as in Feb 2019 following vortex destabilisation) Rising AAM under equatorward flux would give rise to anomalous blocking structures across mainland Europe set against a highly amplified recurving jet stream around a deep upper trough in the Atlantic. In such a situation continued disconnect between the troposphere (equatorward flux) and an unstable stratosphere would lead to the negating of potential outcomes of cold air advection. The Hadley/ferrel cell fuelling a strong +ve NAO signature disconnect to a likely displaced -ve AO vortex, as mused about in the post under response. At present, it is still early in February of course, I agree that there is no real evidence to suggest that a poleward stratospheric pathway to work in tandem with a weakened vortex will inevitably occur & give the QTR that the UK members of this thread hope for to fulfill cold weather & snow aspirations.. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4802091

I live in Portugal, and am therefore detached from the interest in this thread, but you are correct in respect of the over "magic bullet" association to cold weather with SSW's. As interesting a phenomenon they are in themselves, the associated cold weather hype rather detracts from that appreciation. Similarly with the MJO - this is not the stand alone phenomenon it is treated as in this thread and equally as such not a magic bullet to cold weather preferences. It is just one part of the atmospheric circulation total wind-flow budget, and while clearly an important catalyst for changes in weather pattern, it has to be taken in association with the rest of the wind-flow budget which comprises the extra-tropics. The relationship between the tropical & extra tropical wind-flow circulation does not work on a linear x+y = equation (in the same way as the troposphere and stratosphere can have both a connected & equally often quite disconnected relationship). With this in mind the frequent use of MJO composites on this thread is not going to lead to accuracy, especially when attempted to be fitted to weather bias patterns, without considering the extra-tropical Global Wind Oscillation (GWO). The GWO incorporates analysis of the total circulation budget and gives analysis of each flux and torque component within the total atmospheric circulation and is therefore a much more accurate guide. That is, again, if one is willing to suspend skewing.such a diagnostic to try to fit to a desired outcome. This will also lead to inevitable error (and disappointment) So to put some of this background rationale into practice: The GWO, a plot depiction of total wind-flow, is firmly in a -ve inertia state taking both the tropics and extra tropics as a whole. A disconnect is evident between both components - with westerly wind additions (orange shaded) in the tropics across the Indian ocean as measured by inflection of wind-flow frictional torque at the same time as being over compensated by anomalous -ve inertia across mid latitudes and a large vacuum evident as a result of this c/o -ve mountain torques across both Americas. This vacuum, in order to be filled, has been driving an extended period of mid latitude retrogressive sequences of anticyclonic wave breaking (blue shading on MT plots) and hence the sustained elongated blocked pattern across the mid hemisphere. At the same time the polar jet is energised across the northern perimeter of these blocking structures in association with added assistance of downwelling of +ve zonal winds from the stratosphere into the tropospheric boundary layers. The MJO tropical component continues to operate at amplitude (in accordance with a prediction of recurrence periodicity cycle made back in early December). The complex relationship this winter between the stratosphere & troposphere makes it problematic ascertaining how eastward movement of amplitude tropical convection through the tropics propagates into the extra tropics and then how directional flux of AAM anomalies routes the amplifying wind eddies either poleward in association with weakening stratospheric vortex, or continued equatorward ( as in Feb 2019 following vortex destabilisation) Rising AAM under equatorward flux would give rise to anomalous blocking structures across mainland Europe set against a highly amplified recurving jet stream around a deep upper trough in the Atlantic. In such a situation continued disconnect between the troposphere (equatorward flux) and an unstable stratosphere would lead to the negating of potential outcomes of cold air advection. The Hadley/ferrel cell fuelling a strong +ve NAO signature disconnect to a likely displaced -ve AO vortex, as mused about in the post under response. At present, it is still early in February of course, I agree that there is no real evidence to suggest that a poleward stratospheric pathway to work in tandem with a weakened vortex will inevitably occur & give the QTR that the UK members of this thread hope for to fulfill cold weather & snow aspirations..

It is certainly true that rising angular momentum tendency c/o westerly wind inertia generated in the tropics through eastward propagating convection convergence and heading poleward into the extra tropics is a classic recipe for 'blocking'. However, what the overwhelming audience of this thread defines as blocking (in the acceptable sense) is the high latitude variety and this is where the difficulties arise because it is not always the case. Fluxing wind-flow eddies can be diverted back equatorward as much as torque mechanisms can also further diverted them poleward to high latitudes and augment instability at the tropospheric boundary. These contrasts have been precisely seen so far this winter with poleward, and now equatorward fluxing of wind-flow eddy anomalies and the resultant switches in the Annular Mode The Portuguese Institute for Sea (aka Maritime) and Atmosphere (IPMA) who are the equivalent of the UK Met Office have released their January to March seasonal update and predict the high rainfall totals so far this winter reducing heading through later January and especially during February. March close to average. Temperature anomalies slightly above the seasonal average overall throughout each month. Synoptically the thinking reflects the rainfall and temperatures anomalies with further ascendency of the 'local' Azores high and ridging extending across the Iberian continent and the rain bearing fronts further north than the early part of the winter when the -ve NAO prevailed and went a long way to reversing the national drought. Clearly it is also possible to extrapolate what that might mean for NW Europe and it infers not the blocking UK members are looking for - even if it would suit me from a local perspective.. But time will tell. The IPMA are excellent. The detail & explanations of local weather events & types and also synoptic patterns are very good quality and clearly set out. Their website provides English translation but it is a good source also for trying to learn the Portuguese language! Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4783571

It is certainly true that rising angular momentum tendency c/o westerly wind inertia generated in the tropics through eastward propagating convection convergence and heading poleward into the extra tropics is a classic recipe for 'blocking'. However, what the overwhelming audience of this thread defines as blocking (in the acceptable sense) is the high latitude variety and this is where the difficulties arise because it is not always the case. Fluxing wind-flow eddies can be diverted back equatorward as much as torque mechanisms can also further diverted them poleward to high latitudes and augment instability at the tropospheric boundary. These contrasts have been precisely seen so far this winter with poleward, and now equatorward fluxing of wind-flow eddy anomalies and the resultant switches in the Annular Mode The Portuguese Institute for Sea (aka Maritime) and Atmosphere (IPMA) who are the equivalent of the UK Met Office have released their January to March seasonal update and predict the high rainfall totals so far this winter reducing heading through later January and especially during February. March close to average. Temperature anomalies slightly above the seasonal average overall throughout each month. Synoptically the thinking reflects the rainfall and temperatures anomalies with further ascendency of the 'local' Azores high and ridging extending across the Iberian continent and the rain bearing fronts further north than the early part of the winter when the -ve NAO prevailed and went a long way to reversing the national drought. Clearly it is also possible to extrapolate what that might mean for NW Europe and it infers not the blocking UK members are looking for - even if it would suit me from a local perspective.. But time will tell. The IPMA are excellent. The detail & explanations of local weather events & types and also synoptic patterns are very good quality and clearly set out. Their website provides English translation but it is a good source also for trying to learn the Portuguese language!

This cues up quite appropriately a review of extracts from a post made back in November which touched on such interactions and how they have to be kept in objective context if they are to used for the purpose intended. Posted November 16 2022: This, as far as I am concerned at least, sets up an interesting duel between the Ferrel & Polar cells. ... there are longer term superimposed effects of warming that are intensifying sub-tropical ridging responses year on year and in winter it is requiring ever stronger stratospheric instability to create deep cold air advection across larger hemispheric areas of mid latitudes. Modelled stratospheric forecasts are a tombola at distances of two weeks and more and too much can be read into them in my opinion. ...the macro global set-up in respect of this tropics/polar duel is the fascination going forward. Attempting to fit tropical & extra tropical forcing diagnostics and resultant wind-flow patterns into a desired pattern (whatever the time of year) will more often than not result in error and human frustration. ........................................................................................................................................................ The winter so far has certainly seen quite a duel, as suggested in that post, between the opposing cells - Equatorward at the tropics and then at the other end of the scale at the tropopause/lower stratospheric layers disconnected from the middle/upper gyre of the vortex. The latter dictated the opening period of the winter, the former has now taken control of the proceedings with the tropospheric/stratospheric disconnect now neutralised and reversed. Rising AAM associated with tropical convection propagating eastwards through the tropics into and through the Pacific, as gets repeated endlessly in these posts, are not magic bullets each and every time to high latitude blocking. As reasoned in some subsequent posts to the quoted extract during the early part of December, there was never any taken for granted confidence that the follow up MJO cycle to the robust forcing of late autumn would produce the same repeated result heading from the festive period into the New Year, Equally, reasoning was given to explain why. In circumstances of more organised gyre taking over at the troposphere/stratosphere boundary and with the Ferrel/Hadley cell further beefed up with help from solar uptick and consolidating a switch to a much more +ve Northern Annular Mode signature, then poleward momentum transport of +AAM anomalies are by contrast deflected equatorward and reinforce the blocking patterns in the sub tropics heading into mid latitudes. In this equatorward fluxing context, any upstream mid latitude +ve mountain torque is an ally to Iberian/European ridging and amplification to any Scandinavian higher latitude ridging inhibited by increased polar jet flow in absence of instability within the polar field.. Therefore this is the case, rather than poleward momentum that is aided and abetted as unencumbered by an unstable and disconnected polar field that promotes easterly inertia (or -ve zonal wind anomalies) at the boundary between the troposphere and stratosphere. Hence the higher latitude blocking patterns in this instance. I agree with some objective sentiments expressed on these pages that current weaker tropical forcing (as anticipated) further giving impetus to falling angular momentum and in turn energised polar jet energy looks set to sustain the westerly pattern at mid latitudes for some time to come at least. Many of the previous summaries discussed the periodicity (recurrence timeline) of MJO cycles and active intraseasonal patterns often recurring on a 60 to 90 day basis. With the previous active cycle having occurred in late autumn as curtain raiser to the winter, then one could make a reasonable extrapolation of another intraseasonally active cycle heading into February onwards from that time. Again though, how this impacts the tropospheric/stratospheric pathway has to be taken in context of the interactions as discussed in these analyses with the omission of the x+y= assumptions that are repeated so often in this thread. Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782658

This cues up quite appropriately a review of extracts from a post made back in November which touched on such interactions and how they have to be kept in objective context if they are to used for the purpose intended. Posted November 16 2022: This, as far as I am concerned at least, sets up an interesting duel between the Ferrel & Polar cells. ... there are longer term superimposed effects of warming that are intensifying sub-tropical ridging responses year on year and in winter it is requiring ever stronger stratospheric instability to create deep cold air advection across larger hemispheric areas of mid latitudes. Modelled stratospheric forecasts are a tombola at distances of two weeks and more and too much can be read into them in my opinion. ...the macro global set-up in respect of this tropics/polar duel is the fascination going forward. Attempting to fit tropical & extra tropical forcing diagnostics and resultant wind-flow patterns into a desired pattern (whatever the time of year) will more often than not result in error and human frustration. ........................................................................................................................................................ The winter so far has certainly seen quite a duel, as suggested in that post, between the opposing cells - Equatorward at the tropics and then at the other end of the scale at the tropopause/lower stratospheric layers disconnected from the middle/upper gyre of the vortex. The latter dictated the opening period of the winter, the former has now taken control of the proceedings with the tropospheric/stratospheric disconnect now neutralised and reversed. Rising AAM associated with tropical convection propagating eastwards through the tropics into and through the Pacific, as gets repeated endlessly in these posts, are not magic bullets each and every time to high latitude blocking. As reasoned in some subsequent posts to the quoted extract during the early part of December, there was never any taken for granted confidence that the follow up MJO cycle to the robust forcing of late autumn would produce the same repeated result heading from the festive period into the New Year, Equally, reasoning was given to explain why. In circumstances of more organised gyre taking over at the troposphere/stratosphere boundary and with the Ferrel/Hadley cell further beefed up with help from solar uptick and consolidating a switch to a much more +ve Northern Annular Mode signature, then poleward momentum transport of +AAM anomalies are by contrast deflected equatorward and reinforce the blocking patterns in the sub tropics heading into mid latitudes. In this equatorward fluxing context, any upstream mid latitude +ve mountain torque is an ally to Iberian/European ridging and amplification to any Scandinavian higher latitude ridging inhibited by increased polar jet flow in absence of instability within the polar field.. Therefore this is the case, rather than poleward momentum that is aided and abetted as unencumbered by an unstable and disconnected polar field that promotes easterly inertia (or -ve zonal wind anomalies) at the boundary between the troposphere and stratosphere. Hence the higher latitude blocking patterns in this instance. I agree with some objective sentiments expressed on these pages that current weaker tropical forcing (as anticipated) further giving impetus to falling angular momentum and in turn energised polar jet energy looks set to sustain the westerly pattern at mid latitudes for some time to come at least. Many of the previous summaries discussed the periodicity (recurrence timeline) of MJO cycles and active intraseasonal patterns often recurring on a 60 to 90 day basis. With the previous active cycle having occurred in late autumn as curtain raiser to the winter, then one could make a reasonable extrapolation of another intraseasonally active cycle heading into February onwards from that time. Again though, how this impacts the tropospheric/stratospheric pathway has to be taken in context of the interactions as discussed in these analyses with the omission of the x+y= assumptions that are repeated so often in this thread.

Another brief one-off interjection to the thread as means to measure context of how things have evolved and try and offer some insight to the present: Posted 29 November: An attempted musing sees me point to the remaining pockets of -ve zonal winds in the troposphere/stratosphere layer orchestrate with rarified retrogression of the substantial blocking structure to Greenland as inertia across the Pacific weakens (becomes more coupled to base state). Highly likely that this retrogression will eventually edge further east towards Canada (and try and evolve the pattern more -NAO west based) Further out, an attempt at reload is conceivable with the GWO en route back to Phase 4 and renewed rises in angular momentum tendency. However, heading back to the starting discussion of this post, there is great uncertainty about this - based on the said reasoning for tropical correction to re-assert a further active cycle. The chances are equal that this might not materialise/be delayed. So to reiterate, at least from my viewpoint, a lot of caution and restraint in over expectations of wholesale stratospheric destabilisation around the end of the year. At this stage, if it is to happen at all, closer to the mid-winter period seems more feasible. However, there are plenty of advanced pitfalls that can be foreseen, notwithstanding it is a ridiculous time period ahead to try to speculate. .................................................................. Posted early December: The question remains long term how far the retrograde evolves and how the -ve NAO behaves accordingly. The intuitive reasoning remains that attritional battle ground towards NW Europe culminates in an attempted breakdown - which tries to re-set to another Atlantic trough and amplifying downstream ridge. Does the Eurasian feedback reload this as another Scandinavian block, or, does the polar jet then prevail and create a more traditional zonal pattern with heights across mainland Europe? Finely balanced in my neutrally objective opinion as much more work will be required from the tropics next time round to assist, with angular momentum at a lower base level than it has been up to this -VE EAMT. Reasoning behind that has been given fully already this week. I don't personally, at this time, believe the Eurasian feedback signal on its own is enough. However, all of that is some way ahead. From my own point of view though, the evolution of the diagnostic remains the focal interest. ........................... In short and as simplified as possible : 1) Tropical convection patterns should be looked at in respect of their periodicity timeline (recurrence) when attempting to look in extended periods. Bias confirmation (weather preference influenced) processes attached to this can skew expectations. 2) Renewed orbit of tropical convection to Pacific is verifying but less coherent as per the caution previously exercised and in tandem with organisational/coupling of polar vortex & troposphere. Neither, genuinely intended in the nicest way, should have been a surprise. 3) According with renewed eastward propagating tropical convection, relative atmospheric angular momentum has seen a rebound and GWO Phase 4 verified as estimated in above summary. This has reloaded the Atlantic trough and downstream ridge scenario as led up to higher latitude scenario of early to mid December when AAM was previously at elevated levels (higher than currently) 4) BUT: Factors discussed in quoted summaries and in points 1) and 2) are meaning that, as suggested previously, that emerging mid latitude blocking scenarios look set to prevail rather than evolution to higher latitude blocking. A case where applying x+y= equations in respect of rising AAM & eastward propagating tropical convection through phases 6/7 etc are not inextricably magic bullets to high latitude blocking & weather preference gratification. It is very difficult to communicate realities onto ideals in this internet format without sounding like an annoying preacher. I/we all have ideals. However analysis is truthfully not worth the time and effort if it does not suspend preferences & hopes. Looking ahead: Clearly two months left for UK weather watchers to keep looking for the cold weather patterns they hope for. As muted in those early summaries, it could be that another active intra-seasonal cycle of tropical>extra tropical momentum transport re-visits heading into the second half of winter and in tandem with traditional passing of peak upper vortex intensity create another period of instability within the polar field which in turn creates a re-configuration at mid latitudes and implications for polar advection such as seen at the beginning of winter - but this clearly cannot be fleshed out coherently and speculated further about at this time. Melhores desejos para 2023 Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778436

Another brief one-off interjection to the thread as means to measure context of how things have evolved and try and offer some insight to the present: Posted 29 November: An attempted musing sees me point to the remaining pockets of -ve zonal winds in the troposphere/stratosphere layer orchestrate with rarified retrogression of the substantial blocking structure to Greenland as inertia across the Pacific weakens (becomes more coupled to base state). Highly likely that this retrogression will eventually edge further east towards Canada (and try and evolve the pattern more -NAO west based) Further out, an attempt at reload is conceivable with the GWO en route back to Phase 4 and renewed rises in angular momentum tendency. However, heading back to the starting discussion of this post, there is great uncertainty about this - based on the said reasoning for tropical correction to re-assert a further active cycle. The chances are equal that this might not materialise/be delayed. So to reiterate, at least from my viewpoint, a lot of caution and restraint in over expectations of wholesale stratospheric destabilisation around the end of the year. At this stage, if it is to happen at all, closer to the mid-winter period seems more feasible. However, there are plenty of advanced pitfalls that can be foreseen, notwithstanding it is a ridiculous time period ahead to try to speculate. .................................................................. Posted early December: The question remains long term how far the retrograde evolves and how the -ve NAO behaves accordingly. The intuitive reasoning remains that attritional battle ground towards NW Europe culminates in an attempted breakdown - which tries to re-set to another Atlantic trough and amplifying downstream ridge. Does the Eurasian feedback reload this as another Scandinavian block, or, does the polar jet then prevail and create a more traditional zonal pattern with heights across mainland Europe? Finely balanced in my neutrally objective opinion as much more work will be required from the tropics next time round to assist, with angular momentum at a lower base level than it has been up to this -VE EAMT. Reasoning behind that has been given fully already this week. I don't personally, at this time, believe the Eurasian feedback signal on its own is enough. However, all of that is some way ahead. From my own point of view though, the evolution of the diagnostic remains the focal interest. ........................... In short and as simplified as possible : 1) Tropical convection patterns should be looked at in respect of their periodicity timeline (recurrence) when attempting to look in extended periods. Bias confirmation (weather preference influenced) processes attached to this can skew expectations. 2) Renewed orbit of tropical convection to Pacific is verifying but less coherent as per the caution previously exercised and in tandem with organisational/coupling of polar vortex & troposphere. Neither, genuinely intended in the nicest way, should have been a surprise. 3) According with renewed eastward propagating tropical convection, relative atmospheric angular momentum has seen a rebound and GWO Phase 4 verified as estimated in above summary. This has reloaded the Atlantic trough and downstream ridge scenario as led up to higher latitude scenario of early to mid December when AAM was previously at elevated levels (higher than currently) 4) BUT: Factors discussed in quoted summaries and in points 1) and 2) are meaning that, as suggested previously, that emerging mid latitude blocking scenarios look set to prevail rather than evolution to higher latitude blocking. A case where applying x+y= equations in respect of rising AAM & eastward propagating tropical convection through phases 6/7 etc are not inextricably magic bullets to high latitude blocking & weather preference gratification. It is very difficult to communicate realities onto ideals in this internet format without sounding like an annoying preacher. I/we all have ideals. However analysis is truthfully not worth the time and effort if it does not suspend preferences & hopes. Looking ahead: Clearly two months left for UK weather watchers to keep looking for the cold weather patterns they hope for. As muted in those early summaries, it could be that another active intra-seasonal cycle of tropical>extra tropical momentum transport re-visits heading into the second half of winter and in tandem with traditional passing of peak upper vortex intensity create another period of instability within the polar field which in turn creates a re-configuration at mid latitudes and implications for polar advection such as seen at the beginning of winter - but this clearly cannot be fleshed out coherently and speculated further about at this time. Melhores desejos para 2023

Just wanted to wrap up some recent analysis by way of conclusion: This was posted a week back in the old thread: ................................. I continue to think that ultimately following attritional battleground forcing (and a very wet and muggy period of weather in my SW Europe locality) there will be something of a lifting of the cold air from the south for parts of NW Europe, including obviously the UK. Clearly the further south one is most likely to see this. A downstream ridge building from the sub tropics into Iberia (following the low-pressure sequence) could well then build northwards. Much a similar sequence as occurred from last weekend and early last week. As stated in the last post - it is a case of how any energy put back from the sub-tropical -ve NAO jet regime into the polar jet then interacts with this process and how much unstable-ve zonal wind inertia remains at higher latitudes. This sensitive balance of opposite forcing, meaning the difference between a European mid latitude ridge and Atlantic trough, or a re-connection of a northward building ridge to arctic high pressure and cold pooling. How far this cold pooling is dislodged through attrition is finely balanced. ........................... The ultimate attritional nature of the breakdown is set to be rather less than perhaps anticipated, but the broad thrust of that analysis looks set to verify closely for the coming weekend with the suggested return of an Iberian ridge now clearly modelled. With that in mind the 'fork in the road' discussed in a few other posts also comes clearly and precisely into view. The re-building downstream Iberian/Euro mid latitude ridge interestingly has been poorly modelled in extended modelling (e.g the ECM monthly modelling) but a rinse and repeat of the last week of November heading into December modelling (which commenced with a building Iberian ridge that moved poleward to connect with heights to the north east_ was a self-evidently sound pitch based on tropical>extra tropical forcing and how much +ve AAM inertia had accumulated in the atmospheric circulation. This next time around, with the next building sub tropical ridging, continues to look much more problematic to call than the poleward ridge that built to Scandinavia the first time around. On the one hand, and unlike last time much more cold air has amassed close to NW Europe to re-advect, (should there be a reloaded -ve AO/NAO pattern) but this time with angular momentum now at a lower base state (one has to consider wind-flow in the extra tropics as well as just the MJO) and (personally) still not sold on the next round of propagating tropical convection through the Pacific having the same 'teeth' as the previous mini ENSO cycle, there is more work to do to reload the pattern sustainably. Much was spoken about MJO periodicity (timeline re-cycling of amplitude tropical convection waves) if anyone wanted to look. Commitments and other matters here in Portugal mean no further updates but a close watch from afar when time allows will be interesting to see how things pan out. Enjoy the rest of the winter whatever the weather patterns evolve. Best wishes to all for Christmas and into 2023. Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764784

Just wanted to wrap up some recent analysis by way of conclusion: This was posted a week back in the old thread: ................................. I continue to think that ultimately following attritional battleground forcing (and a very wet and muggy period of weather in my SW Europe locality) there will be something of a lifting of the cold air from the south for parts of NW Europe, including obviously the UK. Clearly the further south one is most likely to see this. A downstream ridge building from the sub tropics into Iberia (following the low-pressure sequence) could well then build northwards. Much a similar sequence as occurred from last weekend and early last week. As stated in the last post - it is a case of how any energy put back from the sub-tropical -ve NAO jet regime into the polar jet then interacts with this process and how much unstable-ve zonal wind inertia remains at higher latitudes. This sensitive balance of opposite forcing, meaning the difference between a European mid latitude ridge and Atlantic trough, or a re-connection of a northward building ridge to arctic high pressure and cold pooling. How far this cold pooling is dislodged through attrition is finely balanced. ........................... The ultimate attritional nature of the breakdown is set to be rather less than perhaps anticipated, but the broad thrust of that analysis looks set to verify closely for the coming weekend with the suggested return of an Iberian ridge now clearly modelled. With that in mind the 'fork in the road' discussed in a few other posts also comes clearly and precisely into view. The re-building downstream Iberian/Euro mid latitude ridge interestingly has been poorly modelled in extended modelling (e.g the ECM monthly modelling) but a rinse and repeat of the last week of November heading into December modelling (which commenced with a building Iberian ridge that moved poleward to connect with heights to the north east_ was a self-evidently sound pitch based on tropical>extra tropical forcing and how much +ve AAM inertia had accumulated in the atmospheric circulation. This next time around, with the next building sub tropical ridging, continues to look much more problematic to call than the poleward ridge that built to Scandinavia the first time around. On the one hand, and unlike last time much more cold air has amassed close to NW Europe to re-advect, (should there be a reloaded -ve AO/NAO pattern) but this time with angular momentum now at a lower base state (one has to consider wind-flow in the extra tropics as well as just the MJO) and (personally) still not sold on the next round of propagating tropical convection through the Pacific having the same 'teeth' as the previous mini ENSO cycle, there is more work to do to reload the pattern sustainably. Much was spoken about MJO periodicity (timeline re-cycling of amplitude tropical convection waves) if anyone wanted to look. Commitments and other matters here in Portugal mean no further updates but a close watch from afar when time allows will be interesting to see how things pan out. Enjoy the rest of the winter whatever the weather patterns evolve. Best wishes to all for Christmas and into 2023.

And so the same prognosis moves into another day and starts to firm up the timetable for the first half of December. The short to medium term consolidating the cold theme for NW Europe (and very wet but equally at least very mild/quite warm down here) The interest beyond that remains how long the weakness at the tropopause/stratospheric boundary can sustain the -ve AO/NAO pattern. Most all of this has been driven through the remarkable longevity of tropical forcing during the second half of autumn and programme of poleward +ve AAM anomaly eddies propagating from the tropics into the extra tropics and creating the highly amplified tropospheric pattern to forge the weakness at the boundary to the lower stratosphere. As stated previously, tropical forcing is now heading into a periodicity timeline cyclical lull - which in simple terms means that the poleward forcing ammunition within the troposphere is being withdrawn and it is the built-up momentum unstable inertia lag at higher latitudes that is driving the -ve Annular Mode pattern into the medium term. This, to stress again, is not sustainable indefinitely. While a trickling seeping away of angular momentum and consequential attempts to inject renewed polar jet energy downstream will initially interact with the upper tropospheric weakness and 'roadblock it - as time goes on in the absence of renewed poleward momentum c/o tropical>extra tropical forcing, then the upper tropospheric levels will stabilise, and more organised vortex layers higher up should descend and turn the Arctic Oscillation increasingly less negative. This implies the polar jet being less and less disrupted and 'roadblocked' and returning on a flatter downstream path and with the jet stream returning incrementally northwards - through the attritional processes discussed in many previous posts. It underpins my own scepticism expressed a few times about SSW potential. There is no top-down mechanism whatsoever here and, at present, there is no tangible sign or route to one. Falling angular momentum persisting well into December and towards New Year most probably wholly focussed on a slow but sure battleground focus heading from south to north over time. It all becomes highly speculative beyond that and with a lot of winter remaining and renewed westerly winds stirring in the Indian ocean perhaps attempting another poleward tropospheric lead on the atmospheric circulation. Before that though, while finely balanced, it could be that the coming couple of week sees peaking coldest and potentially snowiest peak for NW Europe before the last third of the month and into the New Year sees a relaxation from the south and milder air making inroads from the SW. For my part of southwest Europe, a distinctly wet period looks to remove further the severe drought issues of over 12 months - before with luck a more settled period arrives as pressure rises with the jet stream heading northwards, bit by bit.

A re-quote I know, but none of the latest NWP should be a surprise at all. For the latter period, the key to watch is how the pattern might re-load. A potential sub-tropical ridge amplification is all part of that. Watch for a rinse and repeat of another possible poleward sequence of events with interest in the UK based on the remaining instability within the polar field and how further poleward amplification might interact with it. I would welcome the sub-tropical high down here, if it does transpire, and those of you in the UK may reap some rewards of what then evolves. But as repeated so many times already the evolution is very finely balanced one way or the other and extra uncertainty even than is usual exists from the end of the coming week. Boa sorte e boa noite. Edit: Not much is going to be gained on looking at latest ensemble data. The trend of a re-set pattern has to be gauged over the coming days and the lead that they take,

Talking about the tropics vs polar cell duel as I have previously - at the other end of the scale (just for fun) in my location it would be lovely sitting outside in this during December On the objective theme however, and with quite deep cold air poised across NE Europe looking for a chance to advect south westwards towards the UK, it all sums up the contrasting fascinations of a pattern evolution like this.