MattH

Morning...Just wanted to jump back to late Nov and a screenshot that I posted, one of the key points back then, which is still relevant is highlighted... It is and has been the amplitude of the MJO event that has been the troublesome aspect of the forecast and this has had some influence on the expected rise in the AAM and the GWO as mid-December approaches. However, there is still expected to be some recovery looking ahead. I have touted the final third of Dec (20th-31st) as the key period of interest for some time and as we are now seeing that period remains of interest looking ahead. The -ve VP200 anom signal is still progressing eastwards and I believe this is something NWP is still yet to properly get a grasp of - Granted the high impact amplitude of a phase 6-7-8 MJO event isn't there, but there are still potential influences here from the upstream developments. There are some very unusual anomalies, in terms of temperatures setting up over in the USA looking ahead, but this, overall, isn't of much relevance to the North Atlantic. The key evolution here is the eastward movement of both the sPV and the tPV off the pole to be more towards the Russian side of the H Hem. Clearly, all details aside, we are seeing a highly cyclonic but increasingly cold polar maritime NW'ly flow develop as we move through the end of next week onwards. We can see this pattern and evolution well on the loop below - What will be key for the British Isles is how far east the main lobe of the tPV gets and just how much ridging takes place over the W and NW of the Atlantic. This is never going to be a significant cold setup, seasonal and wintry yes, but a widespread UK sub -10c 850mb event - no. One of the primary variables to be aware of with this pattern though is the potential for "last minute" rapid cyclogenesis events that could stop the cold air from getting to our shores. Using the 240-hour EC as an example, we can see a weak low or an open wave exiting the NE USA. On face value, it's a cold trend of course. However, the N Atlantic would be a breeding ground for rapid cyclogenesis given the high thermal gradient (baroclinic zone) that would be present. Again, the warmth over the USA has little relevance to our outlook, IMO, as it is the N Atlantic in its own right that'll determine the Christmas outcome. If these small-scale features exit into the N Atlantic and rapidly blow up then you cut off the polar maritime or, perhaps, arctic maritime flow, but these are all details for further down the line. Over the next week, the keyword is 'trend' - If you're looking for a seasonal Christmas week, which I believe is now more likely than not, especially with still some influences from the GSDM, then keep tabs on how far eastwards the main lobe of the tPV gets, while keeping a close eye on the amplification over the W and NW Atlantic and whether any small scale features potential immerge. As things stand, a seasonal Christmas looks a good shout - A significant and widespread UK cold spell is, unlikely, but in this synoptic regime higher ground of the north can do very well, with low tropospheric heights, cold 500mb temperatures and 850mb temperatures of -5C or below can bring wintry precipitation to rather low levels. An upgrade would be a more 'clean' N or N-NW flow, which remains possible, but that final third of December still looks like delivering something far more seasonal/interesting in time for the Christmas week and I feel it's just another starter before the 'main course' through Jan and Feb. With kind regards, Matt. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4975385

Morning...Just wanted to jump back to late Nov and a screenshot that I posted, one of the key points back then, which is still relevant is highlighted... It is and has been the amplitude of the MJO event that has been the troublesome aspect of the forecast and this has had some influence on the expected rise in the AAM and the GWO as mid-December approaches. However, there is still expected to be some recovery looking ahead. I have touted the final third of Dec (20th-31st) as the key period of interest for some time and as we are now seeing that period remains of interest looking ahead. The -ve VP200 anom signal is still progressing eastwards and I believe this is something NWP is still yet to properly get a grasp of - Granted the high impact amplitude of a phase 6-7-8 MJO event isn't there, but there are still potential influences here from the upstream developments. There are some very unusual anomalies, in terms of temperatures setting up over in the USA looking ahead, but this, overall, isn't of much relevance to the North Atlantic. The key evolution here is the eastward movement of both the sPV and the tPV off the pole to be more towards the Russian side of the H Hem. Clearly, all details aside, we are seeing a highly cyclonic but increasingly cold polar maritime NW'ly flow develop as we move through the end of next week onwards. We can see this pattern and evolution well on the loop below - What will be key for the British Isles is how far east the main lobe of the tPV gets and just how much ridging takes place over the W and NW of the Atlantic. This is never going to be a significant cold setup, seasonal and wintry yes, but a widespread UK sub -10c 850mb event - no. One of the primary variables to be aware of with this pattern though is the potential for "last minute" rapid cyclogenesis events that could stop the cold air from getting to our shores. Using the 240-hour EC as an example, we can see a weak low or an open wave exiting the NE USA. On face value, it's a cold trend of course. However, the N Atlantic would be a breeding ground for rapid cyclogenesis given the high thermal gradient (baroclinic zone) that would be present. Again, the warmth over the USA has little relevance to our outlook, IMO, as it is the N Atlantic in its own right that'll determine the Christmas outcome. If these small-scale features exit into the N Atlantic and rapidly blow up then you cut off the polar maritime or, perhaps, arctic maritime flow, but these are all details for further down the line. Over the next week, the keyword is 'trend' - If you're looking for a seasonal Christmas week, which I believe is now more likely than not, especially with still some influences from the GSDM, then keep tabs on how far eastwards the main lobe of the tPV gets, while keeping a close eye on the amplification over the W and NW Atlantic and whether any small scale features potential immerge. As things stand, a seasonal Christmas looks a good shout - A significant and widespread UK cold spell is, unlikely, but in this synoptic regime higher ground of the north can do very well, with low tropospheric heights, cold 500mb temperatures and 850mb temperatures of -5C or below can bring wintry precipitation to rather low levels. An upgrade would be a more 'clean' N or N-NW flow, which remains possible, but that final third of December still looks like delivering something far more seasonal/interesting in time for the Christmas week and I feel it's just another starter before the 'main course' through Jan and Feb. With kind regards, Matt.

As I mentioned in a previous post, with some attachments and slides, the outlook is focused on this next MJO passage. There was some caution here as to whether the signal was being over-amplified by tropical cyclone activity and that may still be the case, but the overall trend in model data, as exampled in the two images here, is for the MJO to quickly progress towards the Maritimes and then the W Pacific. Any amplitude through phases 6-7-8, along with a rise in the GWO to higher Nino phases continues to point towards very interesting synoptics further down the line. Good morning... I start by highlighting the above first - Since the opening few days of December, the above remains a feature that still needs to occur. While not a surprise there are far too many posts in here already, essentially, saying Christmas won't be cold, or the end of December will be x,y and z - Some need to put the breaks on for a little while... The evolution ahead (short term) is not a surprise. The more progressive progression to a more cyclonic spell has been well documented for some time and we are seeing that now, the exact reasons for the build of pressure later this coming week, IMO, can't simply be linked to the teleconnections. The reason for the build of pressure, through a couple of stages, is linked to synoptic developments over the USA and the W Atlantic. What is disappointing mind is it is likely to lead to a very mild spell indeed, given the main CoG of the high. While there remains some room for 'give and take' over the position of the high, the GFS is looking too bullish with this build over the UK and a mild/very tropical maritime W-SW flow is likely to dominate the mid-month period as an active westerly flow dominates over the top. We then look, still, to the period that I've focused on for some time and that being the final third of December - The 20th to the 31st - We continue to see differences in the evolution of the MJO and the associated VP200 signal. As I mentioned back in early December "there was some caution here as to whether the signal was being over-amplified" and we have model differences over this even now. Equally, while this remains a watching brief it is disappointing to see little influence, yet anyway, on the GSDM with the GWO yet to rise, as was suggested, for example. If we don't see the amplified MJO signal, like the BOM model is suggesting, and we end up with a less significant event then I do believe the output for the Christmas period may well actually evolve like is signalled now, with semi-amplified Atlantic highs that bring brief N or NW'lies, but with more cyclonic events flattening the high as they move over the top and I am leaning more that way now after this being a watching brief - The 'holy grail' of a high amplified MJO passage, large GWO rise and significant impacts are becoming less and less likely with reducing risk of "very interesting synoptics" further down the line. It does, however, remain a watching brief and to completely rule out the rest of Dec because of recent model runs is, as ever, just daft. Once again December was never meant to be a 'wintry month' and was often progged to be the most +ve NAO month of the winter. We've just had a noteworthy week of cold weather and the outlook is still nothing like it can be at this time of year when a resolute and strong sPV links to the tPV - Those Decembers really can often be written off, but, again that isn't the case this year. Some adjustments need to be made as the situation continues to evolve - significant or pronounced northern blocking and 'holy grail' winter synoptics through the Christmas period do look less likely, but we still need to see how the current tropical signal evolves and with 2 weeks to go until Christmas, let alone the end of the month, there is still a lot of legs left in this yet. Cheers, Matt. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4973511

As I mentioned in a previous post, with some attachments and slides, the outlook is focused on this next MJO passage. There was some caution here as to whether the signal was being over-amplified by tropical cyclone activity and that may still be the case, but the overall trend in model data, as exampled in the two images here, is for the MJO to quickly progress towards the Maritimes and then the W Pacific. Any amplitude through phases 6-7-8, along with a rise in the GWO to higher Nino phases continues to point towards very interesting synoptics further down the line. Good morning... I start by highlighting the above first - Since the opening few days of December, the above remains a feature that still needs to occur. While not a surprise there are far too many posts in here already, essentially, saying Christmas won't be cold, or the end of December will be x,y and z - Some need to put the breaks on for a little while... The evolution ahead (short term) is not a surprise. The more progressive progression to a more cyclonic spell has been well documented for some time and we are seeing that now, the exact reasons for the build of pressure later this coming week, IMO, can't simply be linked to the teleconnections. The reason for the build of pressure, through a couple of stages, is linked to synoptic developments over the USA and the W Atlantic. What is disappointing mind is it is likely to lead to a very mild spell indeed, given the main CoG of the high. While there remains some room for 'give and take' over the position of the high, the GFS is looking too bullish with this build over the UK and a mild/very tropical maritime W-SW flow is likely to dominate the mid-month period as an active westerly flow dominates over the top. We then look, still, to the period that I've focused on for some time and that being the final third of December - The 20th to the 31st - We continue to see differences in the evolution of the MJO and the associated VP200 signal. As I mentioned back in early December "there was some caution here as to whether the signal was being over-amplified" and we have model differences over this even now. Equally, while this remains a watching brief it is disappointing to see little influence, yet anyway, on the GSDM with the GWO yet to rise, as was suggested, for example. If we don't see the amplified MJO signal, like the BOM model is suggesting, and we end up with a less significant event then I do believe the output for the Christmas period may well actually evolve like is signalled now, with semi-amplified Atlantic highs that bring brief N or NW'lies, but with more cyclonic events flattening the high as they move over the top and I am leaning more that way now after this being a watching brief - The 'holy grail' of a high amplified MJO passage, large GWO rise and significant impacts are becoming less and less likely with reducing risk of "very interesting synoptics" further down the line. It does, however, remain a watching brief and to completely rule out the rest of Dec because of recent model runs is, as ever, just daft. Once again December was never meant to be a 'wintry month' and was often progged to be the most +ve NAO month of the winter. We've just had a noteworthy week of cold weather and the outlook is still nothing like it can be at this time of year when a resolute and strong sPV links to the tPV - Those Decembers really can often be written off, but, again that isn't the case this year. Some adjustments need to be made as the situation continues to evolve - significant or pronounced northern blocking and 'holy grail' winter synoptics through the Christmas period do look less likely, but we still need to see how the current tropical signal evolves and with 2 weeks to go until Christmas, let alone the end of the month, there is still a lot of legs left in this yet. Cheers, Matt.

Yeah, it's certainly possible... As ever we don't want to be assigning a specific synoptic outcome to a specific MJO phase but the idea of a Scandinavian block isn't out of the question, for sure, based on the tropical links and connections. The Scandinavian blocking high though is still one of the "hardest" synoptic features to achieve and produce, at this stage I would simply be looking more for blocking at higher latitudes, in general, in NWP looking ahead and a greater amplification to the pattern over the N Atlantic and European sector - essentially keep an eye out for more unusual/blocked/colder synoptics than would be usually expected. As we have found out just recently, the importance of lower heights into Europe is always key as well - sometimes this can be overlooked, but even in a more zonal pattern, if you've got lower heights into Europe then the UK can still get cold weather, etc, it's the dreaded SW to NE jet axis with building heights into Europe that often dominate our winter, something which isn't likely to do very often this year, IMO. 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 Regards, Matt. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4968713

Yeah, it's certainly possible... As ever we don't want to be assigning a specific synoptic outcome to a specific MJO phase but the idea of a Scandinavian block isn't out of the question, for sure, based on the tropical links and connections. The Scandinavian blocking high though is still one of the "hardest" synoptic features to achieve and produce, at this stage I would simply be looking more for blocking at higher latitudes, in general, in NWP looking ahead and a greater amplification to the pattern over the N Atlantic and European sector - essentially keep an eye out for more unusual/blocked/colder synoptics than would be usually expected. As we have found out just recently, the importance of lower heights into Europe is always key as well - sometimes this can be overlooked, but even in a more zonal pattern, if you've got lower heights into Europe then the UK can still get cold weather, etc, it's the dreaded SW to NE jet axis with building heights into Europe that often dominate our winter, something which isn't likely to do very often this year, IMO. 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 Regards, Matt.

Just flicking through some of the EC46 plots, amongst a busy weekend shift, and I think there is already some evidence for changes in there, for towards and beyond mid-December. As ever the usefulness of the layout of the EC46 images on a day-by-day basis allows you to see clear trends and a few links to some of the more interesting ones are as follows... The regime changes are trending away from a resolute 'blue' or +NAO to now a very uncertain 'no regime' signal in the latest plot. You can see how the predicted +ve NAO has been nibbled away at in recent days to now the most recent one nearly losing that strong signal altogether. The other series of plots which have changed is the VP signal, obviously no surprises on this one after numerous comments and discussions on this thread, but the last few runs highlight that strengthening signal. Lastly, the one that stood out the most to me was the general 500mb height anomalies - We can see how the signal was for -ve 500mb height anoms over NW Europe a week or so ago, with a cyclonic signal through the 18th to the 25th Dec. However, note how that signal has been nibbled away at as well with now the most recent signal showing something far more blocked. Whether this is just run-to-run variability, time will tell, but I don't think it is. Again this is why viewing these plots in this format is better than looking at them individually as you can visually see and extract potential trends and there are certainly trends there in my opinion already. Once this -VP200 signal and associated MJO event pushes further into the W Pacific with a resultant +GLAAM/+GWO rise, it should be a fascinating watch from an NWP perspective in the 10 to 15-day time period, again as I mentioned the other day, covering the final third (20th-31st) or so, or now perhaps even earlier... Cheers, Matt. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4968664

Just flicking through some of the EC46 plots, amongst a busy weekend shift, and I think there is already some evidence for changes in there, for towards and beyond mid-December. As ever the usefulness of the layout of the EC46 images on a day-by-day basis allows you to see clear trends and a few links to some of the more interesting ones are as follows... The regime changes are trending away from a resolute 'blue' or +NAO to now a very uncertain 'no regime' signal in the latest plot. You can see how the predicted +ve NAO has been nibbled away at in recent days to now the most recent one nearly losing that strong signal altogether. The other series of plots which have changed is the VP signal, obviously no surprises on this one after numerous comments and discussions on this thread, but the last few runs highlight that strengthening signal. Lastly, the one that stood out the most to me was the general 500mb height anomalies - We can see how the signal was for -ve 500mb height anoms over NW Europe a week or so ago, with a cyclonic signal through the 18th to the 25th Dec. However, note how that signal has been nibbled away at as well with now the most recent signal showing something far more blocked. Whether this is just run-to-run variability, time will tell, but I don't think it is. Again this is why viewing these plots in this format is better than looking at them individually as you can visually see and extract potential trends and there are certainly trends there in my opinion already. Once this -VP200 signal and associated MJO event pushes further into the W Pacific with a resultant +GLAAM/+GWO rise, it should be a fascinating watch from an NWP perspective in the 10 to 15-day time period, again as I mentioned the other day, covering the final third (20th-31st) or so, or now perhaps even earlier... Cheers, Matt.

Hi. This, essentially, still sums up the outlook period. The current and upcoming evolution, despite run-to-run differences, hasn't changed. There remains strong evidence for the more westerly push through next week, the regime change eventually coming through, but clearly with the cold block in place to the NE, won't be a straightforward transition, but despite what some may think, cold air can get displaced. As I mentioned in a previous post, with some attachments and slides, the outlook is focused on this next MJO passage. There was some caution here as to whether the signal was being over-amplified by tropical cyclone activity and that may still be the case, but the overall trend in model data, as exampled in the two images here, is for the MJO to quickly progress towards the Maritimes and then the W Pacific. Any sort of amplitude through phases 6-7-8, along with a rise in the GWO to higher Nino phases continues to point towards very interesting synoptics further down the line. It should also be noted that for months seasonal forecasts have often signaled key areas of tropical forcing (-VP200 anoms) to be over MJO phases 6-7-8 this winter, which links in with the El Nino. December, as a month, was always meant to be the most +ve NAO of the winter, often unsettled, often mild and wet. This current cold spell is aided by the entrenched cold air that has been in place over Scandinavia in recent weeks as well and, without question, has been a major bonus to start winter. What we aren't likely to see is a pattern that becomes 'locked in' - This isn't a La Nina/wQBO December, nor is the sPV well organised and strongly connected to the tPV. If we can manage to see these synoptic changes through the final third of the month (approx 20-30th) with colder synoptics and especially if these influence the Christmas period then this December will end up far more noteworthy, in terms of cold synoptics, than was originally expected. Without question too, the CW and the weakening of the sPV is just waiting for a follow-up "punch" and a phase 7-8 MJO, with amplitude in December, has a well-known link to 'down the line' SSW's. I still fully expect an SSW to take place at some point in January. Enjoy the cold and winter synoptics that are here, now, let the medium term come and go and then keep firm eyes on the second half of December... Regards, Matt. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4965581

Hi. This, essentially, still sums up the outlook period. The current and upcoming evolution, despite run-to-run differences, hasn't changed. There remains strong evidence for the more westerly push through next week, the regime change eventually coming through, but clearly with the cold block in place to the NE, won't be a straightforward transition, but despite what some may think, cold air can get displaced. As I mentioned in a previous post, with some attachments and slides, the outlook is focused on this next MJO passage. There was some caution here as to whether the signal was being over-amplified by tropical cyclone activity and that may still be the case, but the overall trend in model data, as exampled in the two images here, is for the MJO to quickly progress towards the Maritimes and then the W Pacific. Any sort of amplitude through phases 6-7-8, along with a rise in the GWO to higher Nino phases continues to point towards very interesting synoptics further down the line. It should also be noted that for months seasonal forecasts have often signaled key areas of tropical forcing (-VP200 anoms) to be over MJO phases 6-7-8 this winter, which links in with the El Nino. December, as a month, was always meant to be the most +ve NAO of the winter, often unsettled, often mild and wet. This current cold spell is aided by the entrenched cold air that has been in place over Scandinavia in recent weeks as well and, without question, has been a major bonus to start winter. What we aren't likely to see is a pattern that becomes 'locked in' - This isn't a La Nina/wQBO December, nor is the sPV well organised and strongly connected to the tPV. If we can manage to see these synoptic changes through the final third of the month (approx 20-30th) with colder synoptics and especially if these influence the Christmas period then this December will end up far more noteworthy, in terms of cold synoptics, than was originally expected. Without question too, the CW and the weakening of the sPV is just waiting for a follow-up "punch" and a phase 7-8 MJO, with amplitude in December, has a well-known link to 'down the line' SSW's. I still fully expect an SSW to take place at some point in January. Enjoy the cold and winter synoptics that are here, now, let the medium term come and go and then keep firm eyes on the second half of December... Regards, Matt.

The dominance of the blocking patterns is quite impressive, in the short-term, reinforced by a number of wave breaks over the N Atlantic, but the 'writing is on the wall' for a breakdown further into December, but probably not before the first week of December is done with, so a cold start to winter it is. Anyway, a few slides and thoughts below as part of a wider document/analysis of mine... Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4962051

The dominance of the blocking patterns is quite impressive, in the short-term, reinforced by a number of wave breaks over the N Atlantic, but the 'writing is on the wall' for a breakdown further into December, but probably not before the first week of December is done with, so a cold start to winter it is. Anyway, a few slides and thoughts below as part of a wider document/analysis of mine...

The Canadian Warming is gathering pace for early December now. The drop in ZW at 10hPa has increased significantly as well over the last few days. CW's rarely lead to an SSW, often pushing the main vortex towards the Russian side of the pole. How this will influence the coming weeks is very uncertain as clearly there remains little strat and trop connection as it is, despite a recent downwelling of westerlies, but that event has come to an end. At a minimum, a displaced vortex towards Russia can mean that it reduces the risk of the main tPV setting up over Greenland, while, importantly, this weakening of the vortex is likely to aid, to an extent, in reducing the chances of the sPV influencing the tPV anyway. It also brings about the threat of the sPV being properly 'taken down' deeper into winter, now it's been knocked about at this (very) early stage in the season. Fascinating winter synoptics already and it's not even winter yet!

This exactly... There is so much conjecture to that post, unfortunately, it makes little sense at all. While the overall post explains what would happen if the MJO did evolve like that, the timing and correlation to the current and upcoming evolution couldn't be any further from the truth. There is simply too much of a jump in evolution here. A correct discussion and piece of information on showing what could happen under those circumstances, but once again this is another A+B=C outcome using the MJO, it doesn't work like that and with little relevance dropping it onto current and upcoming time frames, unfortunately. Matt.

Afternoon. Just some thoughts and a point of reference (let's see how this ages) with regards to December. To summarise the short-term, after weeks of being stagnant through phases 8-1 the MJO is on the move back to the Western Hem and this does continue to support a more dominant Westerly pattern to return into December, in some shape or form. However, jumping ahead of that and it is the next eastward movement of the MJO that is of significance and importance as we look through December. The latest data is now showing some weakening of the IOD as well, which is what was expected to occur by the end of the year anyway. For the last several weeks there has been a very slow-moving tropical pattern in terms of forcing, with key areas of subsidence over the Maritimes, while forcing and uplift (convection) have dominated near the dateline (MJO phases 8-1). Finally, however, things are on the move. There is evidence for the -ve 850mb ZWA's over the I/O to weaken, while the latest EPS plot, in particular, shows a far more active west-to-east movement of the key VP200 anoms looking ahead, with strong surface convergence and upper-level divergence over the W Hem and the I/O over the remainder of November. With evidence for the long-standing easterly to be waning over the I/O then all eyes will be on how the MJO and the -ve VP200 signature evolves through December. Primarily how far east does it progress and with what potency, in terms of the amplitude, etc. A few extra plots which are based on the CFSv2 looking ahead highlight what may happen in terms of this next MJO event. Indeed, the signal on the Real Time CFS plot is thickening up with another significant WWB set to propagate into the west and then central Pacific through Dec. The result is, therefore, a resultant signal for AAM to rise, along with the GWO as well. It should be noted not to take the AAM and the GWO plots literally, but to use them as a guide as to the overall evolution looking ahead, especially if it's a consistent signal. Lastly, the ever-useful EWP Zonal Harmonics plot also highlights this evolution too... As we found out last December, any significant eastward progression of the MJO in Dec, especially through phases 6-7-8 with amplitude could be significant, not just from a trop perspective but also the strat as well. Therefore, this signal needs to be monitored closely in the next 2 to 4 weeks, as another WWB with a GWO rise and if there is a reasonably high amplitude MJO event too, again through phases 6-7-8, then all eyes would be on some potentially very interesting synoptics (amplification/blocking/colder weather potential) from approx mid-December onwards. With regards, Matt.

Let's strip this all back shall we and highlight the key points; Will it turn colder end of the week onwards? - Yes for many areas, the exception perhaps being far W and SW of the British Isles Is this a resolute, text-book Greenland block? - No, it isn't, it is an amplification of the N Atlantic pattern (Atlantic Ridge regime) as expected for several days Did the GFS 'win this one'? - Yes, IMO, it did. The consistency over the colder flow from the N, has been consistent from the GFS in some shape or form, EC poorest with the handling of this. Is widespread snow likely by the weekend? - No, the pattern is likely to be more anticyclonic than cyclonic, but still some 'give and take' in that Which areas could see snow? - Scotland and E England, primarily over higher ground, with little or no snow elsewhere Is this the first 'noteworthy' cold spell of the season for many? - Yes, it is likely to be so Without dredging up individual model runs and details, there is now high confidence for this cold spell to arrive as a cold front moves southwards on Thu into Fri. Logic dictates it will be in the N and E where the coldest air will be, less cold in the S and W. The 06Z GEFS highlights this now almost 'clean' transition and change in air mass, also worth noting that the 06z GFS and Control on the milder side into next week too. The long-term still carries a trend for a return to more Atlantic-driven weather, but the signal for the eastward propagation of the tropical signal and MJO is gaining traction for December and a potentially very interesting second half of December may still be on the cards. Despite some evidence for a strat and trop connection as well, there remains little evidence in NWP for an organised vortex either with certainly some 'unusual' goings on at the moment, in keeping with recent global extremes/variations/unknowns in past seasons too. Regards, Matt. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4954700

Let's strip this all back shall we and highlight the key points; Will it turn colder end of the week onwards? - Yes for many areas, the exception perhaps being far W and SW of the British Isles Is this a resolute, text-book Greenland block? - No, it isn't, it is an amplification of the N Atlantic pattern (Atlantic Ridge regime) as expected for several days Did the GFS 'win this one'? - Yes, IMO, it did. The consistency over the colder flow from the N, has been consistent from the GFS in some shape or form, EC poorest with the handling of this. Is widespread snow likely by the weekend? - No, the pattern is likely to be more anticyclonic than cyclonic, but still some 'give and take' in that Which areas could see snow? - Scotland and E England, primarily over higher ground, with little or no snow elsewhere Is this the first 'noteworthy' cold spell of the season for many? - Yes, it is likely to be so Without dredging up individual model runs and details, there is now high confidence for this cold spell to arrive as a cold front moves southwards on Thu into Fri. Logic dictates it will be in the N and E where the coldest air will be, less cold in the S and W. The 06Z GEFS highlights this now almost 'clean' transition and change in air mass, also worth noting that the 06z GFS and Control on the milder side into next week too. The long-term still carries a trend for a return to more Atlantic-driven weather, but the signal for the eastward propagation of the tropical signal and MJO is gaining traction for December and a potentially very interesting second half of December may still be on the cards. Despite some evidence for a strat and trop connection as well, there remains little evidence in NWP for an organised vortex either with certainly some 'unusual' goings on at the moment, in keeping with recent global extremes/variations/unknowns in past seasons too. Regards, Matt.

An interesting one this but the key development here as perfectly highlighted by @WeatherArc is the upstream pattern which influences the downstream pattern. There is a preference from the UKMO for their own model to be a good half way house solution at the moment, but a lot of uncertainty. The reasons for this amplification (or not) has been discussed before but we are getting down to short term here (forget teleconnections etc for this now) and it's the first standoff between the EC and the GFS of th season. I keep trying to analyse the N American trough and cold plunge but the intricacies of the short waves over the W Atlantic doesn't mean this will not be resolved until at least Monday IMO. Matt.

Morning. It isn't surprising to see the end of next week slowly arrive with the amplification being watered down. As was discussed the other day, the only link I could see was about the continued -ve VP200 anom near the dateline and the associated eastward push of another WWB which has, of course, created some rise in AAM and the GWO. However, if you remove that aspect from the equation, everything else doesn't point towards the amplification that the GFS et al. have indicated. While some sort of N or NW'ly is still possible, leading to seasonal late November conditions, a 'full on' N Atlantic/Greenland block remains highly unlikely. Using the below, we can see the impacts and influence over the last week if we re-cap this. It remains interesting to note, however, that the key areas of +ve W'ly AAM anoms are running at more southerly latitudes, circa 40-50N. Clearly, this continues to be played out by the ongoing synoptic patterns of developing lows approaching the UK from the SW, with the more usual jet stream pattern for the time of year yet to arrive. This is another great example of how you can visually "see" the influence of the AAM on observed atmospheric patterns too, by the clear and +ve zonal wind anoms at more southerly latitudes than would otherwise be expected. One chart that I take a lot of notice of is the following CDAS GPH anom plot. Sometimes it isn't about looking at forecast models to see what may arrive, it is looking at what is happening now. While there is always a delay of 2 or 3 days with this plot, the stand-out feature here is the downward progression of the -ve GPH anoms now into the top of the trop, with the long-running +ve GPH anomalies essentially coming to an end. If you do then tie this in with model data, the teleconnections (El Nino/+IOD) then the long-standing predictions for a more dominant westerly regime to dominate the coming weeks is, obviously, the form horse. Don't forget as well that it is often "easier" to forecast the weather at this time of the year when the key early winter building blocks fall into place which continues to happen. Looking ahead and with the return of any MJO signal to the W Hem, most likely into phases 1-2-3, coupled with everything else then, again there remains only one primary and most likely outcome and that is for a very unsettled/potentially stormy end of Nov and first half of Dec. Clearly, this doesn't preclude colder intervals, especially as the N Hem continues to cool, but those looking for early winter synoptics to bring more significant winter weather are likely going to need to wait. We can see this, as a guide on the below plots using the GEFS VP200 anom coupled with the ever-useful RMM regression plots from Paul Roundy, which IMO are better as a guide than the MJO composites as well... As I mentioned the other day as well, we then start talking about a time frame that is beyond weeks 3 and 4, sub-seasonal, and the only thing that needs to be watched, again, is the next eastward progression of the convective signal through the tropics, as Tamara mentioned too. However, the key issue and question here is still; Will the +IOD event stop this from occurring or complicate this progression? At the moment there is no answer to that question, given the lead time. I would, personally, be writing off the first half of Dec, in terms of any significant winter cold (the opposite of what happened last Dec), but provide some possibilities for the second half or the final third of the month IF the MJO does return and especially ends up traversing phases 6-7-8 with another associated WWB, this, again, perhaps timing for Christmas and New Year. Someone was asking for this plot the other day, sorry can't remember who, but it is from Karl MacRitchies site ( https://www.kylemacritchie.com/ ), which does contain some other interesting charts and charts you make yourself. The signal from the ever useful and, IMO, reliable EWP zonal harmonics plot is thickening up for an eastward movement of the -ve VP200 anoms, but, again not before mid-December, while Karl's plot continues to highlight this as well using the CFSv2. So, in summary, there are no changes to all the long-standing thoughts as we move towards the end of the year. Surprises could arrive, but if we take all of the data and analysis together, again, the long-standing predictions are for a more +ve NAO start to winter are falling into place as we speak. Regards, Matt. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4952428

Morning. It isn't surprising to see the end of next week slowly arrive with the amplification being watered down. As was discussed the other day, the only link I could see was about the continued -ve VP200 anom near the dateline and the associated eastward push of another WWB which has, of course, created some rise in AAM and the GWO. However, if you remove that aspect from the equation, everything else doesn't point towards the amplification that the GFS et al. have indicated. While some sort of N or NW'ly is still possible, leading to seasonal late November conditions, a 'full on' N Atlantic/Greenland block remains highly unlikely. Using the below, we can see the impacts and influence over the last week if we re-cap this. It remains interesting to note, however, that the key areas of +ve W'ly AAM anoms are running at more southerly latitudes, circa 40-50N. Clearly, this continues to be played out by the ongoing synoptic patterns of developing lows approaching the UK from the SW, with the more usual jet stream pattern for the time of year yet to arrive. This is another great example of how you can visually "see" the influence of the AAM on observed atmospheric patterns too, by the clear and +ve zonal wind anoms at more southerly latitudes than would otherwise be expected. One chart that I take a lot of notice of is the following CDAS GPH anom plot. Sometimes it isn't about looking at forecast models to see what may arrive, it is looking at what is happening now. While there is always a delay of 2 or 3 days with this plot, the stand-out feature here is the downward progression of the -ve GPH anoms now into the top of the trop, with the long-running +ve GPH anomalies essentially coming to an end. If you do then tie this in with model data, the teleconnections (El Nino/+IOD) then the long-standing predictions for a more dominant westerly regime to dominate the coming weeks is, obviously, the form horse. Don't forget as well that it is often "easier" to forecast the weather at this time of the year when the key early winter building blocks fall into place which continues to happen. Looking ahead and with the return of any MJO signal to the W Hem, most likely into phases 1-2-3, coupled with everything else then, again there remains only one primary and most likely outcome and that is for a very unsettled/potentially stormy end of Nov and first half of Dec. Clearly, this doesn't preclude colder intervals, especially as the N Hem continues to cool, but those looking for early winter synoptics to bring more significant winter weather are likely going to need to wait. We can see this, as a guide on the below plots using the GEFS VP200 anom coupled with the ever-useful RMM regression plots from Paul Roundy, which IMO are better as a guide than the MJO composites as well... As I mentioned the other day as well, we then start talking about a time frame that is beyond weeks 3 and 4, sub-seasonal, and the only thing that needs to be watched, again, is the next eastward progression of the convective signal through the tropics, as Tamara mentioned too. However, the key issue and question here is still; Will the +IOD event stop this from occurring or complicate this progression? At the moment there is no answer to that question, given the lead time. I would, personally, be writing off the first half of Dec, in terms of any significant winter cold (the opposite of what happened last Dec), but provide some possibilities for the second half or the final third of the month IF the MJO does return and especially ends up traversing phases 6-7-8 with another associated WWB, this, again, perhaps timing for Christmas and New Year. Someone was asking for this plot the other day, sorry can't remember who, but it is from Karl MacRitchies site ( https://www.kylemacritchie.com/ ), which does contain some other interesting charts and charts you make yourself. The signal from the ever useful and, IMO, reliable EWP zonal harmonics plot is thickening up for an eastward movement of the -ve VP200 anoms, but, again not before mid-December, while Karl's plot continues to highlight this as well using the CFSv2. So, in summary, there are no changes to all the long-standing thoughts as we move towards the end of the year. Surprises could arrive, but if we take all of the data and analysis together, again, the long-standing predictions are for a more +ve NAO start to winter are falling into place as we speak. Regards, Matt.

Just a quick addition to this one, as there is model data at hand which highlights these discussions well looking ahead...The main caveat is that this is model data and for weeks down the line, so take on that on board first. However, the CFSv2 plot highlights this next tropical convection wave well, which is mentioned by Tamara here, through December, with an associated signal for a WWB (yellow and orange colours) The other plot I always note is the EWP zonal harmonics plot for CHI as well. We can see the expected evolution through the short-medium and long-term here, with the initial -ve VP200 anomalies through the Pacific, continuing eastwards into the E Pacific and the W Hem by the end of November. This is what will likely signal another temporary fall in AAM, with the GWO returning to a potential phase 8 or 1, it is through this period, during the end of Nov and into Dec that if coupling of the strat and trop does takes place, then a very unsettled/stormy spell may well evolve as we move into December. However, notice the signal for the -ve VP200 anoms to return eastwards, in the time, through December. This is the key watch because as we found out last year, any noteworthy MJO event will be important from a strat perspective and perhaps aiding to bring amplification again deeper into December. All are highly subjective, but if the timing is as such, then a Christmas/New Year cold spell *could* evolve. Cheers, Matt. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4952039

Just a quick addition to this one, as there is model data at hand which highlights these discussions well looking ahead...The main caveat is that this is model data and for weeks down the line, so take on that on board first. However, the CFSv2 plot highlights this next tropical convection wave well, which is mentioned by Tamara here, through December, with an associated signal for a WWB (yellow and orange colours) The other plot I always note is the EWP zonal harmonics plot for CHI as well. We can see the expected evolution through the short-medium and long-term here, with the initial -ve VP200 anomalies through the Pacific, continuing eastwards into the E Pacific and the W Hem by the end of November. This is what will likely signal another temporary fall in AAM, with the GWO returning to a potential phase 8 or 1, it is through this period, during the end of Nov and into Dec that if coupling of the strat and trop does takes place, then a very unsettled/stormy spell may well evolve as we move into December. However, notice the signal for the -ve VP200 anoms to return eastwards, in the time, through December. This is the key watch because as we found out last year, any noteworthy MJO event will be important from a strat perspective and perhaps aiding to bring amplification again deeper into December. All are highly subjective, but if the timing is as such, then a Christmas/New Year cold spell *could* evolve. Cheers, Matt.

As ever need some caution of taking the MJO phases and multiplying them forward to get an amplified ridge in 10 to 14 days, or potential blocking in December, when that simply isn't the expected route of travel in terms of the N Hem pattern and particularly the N Atlantic. This signal for amplification within the week of the 20th to the 24th has, essentially 'come from nowhere'. One could argue that the trop remains disconnected from the strat, but for how long and if you do use the MJO and VP200 anomalies as a forecasting tool, within a Nino November, with the key areas of forcing within phases 8-1, the outcome is far from amplification in the N Atlantic. The only data I can see, to hand, that connects these uncertain dots is a rise in the GWO, in November, which given the current and significant WWB through the dateline could well be driving this amplification but, again, I wouldn't want to put money on it. Nov GWO phase 5 leads to this anom pattern... Could this be one of "those" scenarios whereby we are seeing influences from the unknown brought about the wild SST anomalies, globally? It is very difficult to tell. The weather will do whatever it wants but as usual, following the medium and long-term almost daily, but particularly weekly, this signal for an amplified N Atlantic goes against the grain for all forecasts for the second half of November in recent weeks. An interesting one but I wouldn't hold your hopes up for charts like the GFS is currently showing with heights right up into Greenland and a proper -ve NAO trend, I have a feeling this signal will be watered down but we watch with interest... Matt. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4951711

As ever need some caution of taking the MJO phases and multiplying them forward to get an amplified ridge in 10 to 14 days, or potential blocking in December, when that simply isn't the expected route of travel in terms of the N Hem pattern and particularly the N Atlantic. This signal for amplification within the week of the 20th to the 24th has, essentially 'come from nowhere'. One could argue that the trop remains disconnected from the strat, but for how long and if you do use the MJO and VP200 anomalies as a forecasting tool, within a Nino November, with the key areas of forcing within phases 8-1, the outcome is far from amplification in the N Atlantic. The only data I can see, to hand, that connects these uncertain dots is a rise in the GWO, in November, which given the current and significant WWB through the dateline could well be driving this amplification but, again, I wouldn't want to put money on it. Nov GWO phase 5 leads to this anom pattern... Could this be one of "those" scenarios whereby we are seeing influences from the unknown brought about the wild SST anomalies, globally? It is very difficult to tell. The weather will do whatever it wants but as usual, following the medium and long-term almost daily, but particularly weekly, this signal for an amplified N Atlantic goes against the grain for all forecasts for the second half of November in recent weeks. An interesting one but I wouldn't hold your hopes up for charts like the GFS is currently showing with heights right up into Greenland and a proper -ve NAO trend, I have a feeling this signal will be watered down but we watch with interest... Matt.