Cambrian

Changeable with fluctuating temperatures during Christmas week on the 0z ECM operational run. The mildest period is tomorrow, Christmas Eve, good for travelling, the UK and Ireland in the warm sector of a low pressure system between Scotland and Iceland. This moves east to merge with the trough over Scandinavia by day 4, trying to bring down a northerly on its western flank, but this is held off by low pressure heading in on a much more southerly track from the Atlantic. A seesaw in the T850s for a few days thereafter. This low pressure is the main feature of the coming week, passing through the UK and Ireland to the North Sea by day 6. It gets interesting by then, as temperatures have dropped off considerably. The North Atlantic is prone to wedges throughout this period and as a result, the following low pressure is being disrupted and is sliding southeastward to merge with the base of the North Sea low at day 7. The T850s at day 8, New Year’s Eve, show the extent of the cold air in the mix and a long way south too. Mild to begin with, but overall changeable, cyclonic at times and increasingly cold. All in all, a quite seasonal end to the year, with plenty of interest in the models. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982346

Changeable with fluctuating temperatures during Christmas week on the 0z ECM operational run. The mildest period is tomorrow, Christmas Eve, good for travelling, the UK and Ireland in the warm sector of a low pressure system between Scotland and Iceland. This moves east to merge with the trough over Scandinavia by day 4, trying to bring down a northerly on its western flank, but this is held off by low pressure heading in on a much more southerly track from the Atlantic. A seesaw in the T850s for a few days thereafter. This low pressure is the main feature of the coming week, passing through the UK and Ireland to the North Sea by day 6. It gets interesting by then, as temperatures have dropped off considerably. The North Atlantic is prone to wedges throughout this period and as a result, the following low pressure is being disrupted and is sliding southeastward to merge with the base of the North Sea low at day 7. The T850s at day 8, New Year’s Eve, show the extent of the cold air in the mix and a long way south too. Mild to begin with, but overall changeable, cyclonic at times and increasingly cold. All in all, a quite seasonal end to the year, with plenty of interest in the models.

This comes up a lot in the winter and draws excellent discussion, but the reflections surrounding the Hadley Cell often occur as a reaction to a specific phase of “Hadleyesque” heights, an oscillating signature of which the waxing phase has to be progressed through, before we often quite swiftly get to a pattern where the last thing anyone is thinking about is anything close to what concerned George Hadley in 1735. If we take the 18z GEFS at day 5, and compare it with the classic Hadley signature, Azores and eastern Med heights, we have a culprit. Shoot the Hadley. But look at the north-south alignment of the Greenland and Atlantic lows, and the forcing heights through eastern Canada, ready to progress that wall of low heights east into Europe. By day 10, the trough moves east and south, a cold trough with low heights through the Norwegian Sea, UK, Ireland and North Sea down through the continent to Algeria. Irony is of course that the telltale elements are still there, Azores and eastern Med heights, just we’re not thinking about them any more because they have waned and because we’re on the cold side of a sumptuous looking trough that could well bed down as a Euro-low by day 14, a notion reinforced by a look at tonight’s EC46, and the NAO- signal for the first week of January. Are we thinking Hadley and its associated roaring NAO+? Yeah, exactly, not at all, more Hadbeenley than Hadley, and as is so often the case after a milder Christmas, the winter resumes. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981775

This comes up a lot in the winter and draws excellent discussion, but the reflections surrounding the Hadley Cell often occur as a reaction to a specific phase of “Hadleyesque” heights, an oscillating signature of which the waxing phase has to be progressed through, before we often quite swiftly get to a pattern where the last thing anyone is thinking about is anything close to what concerned George Hadley in 1735. If we take the 18z GEFS at day 5, and compare it with the classic Hadley signature, Azores and eastern Med heights, we have a culprit. Shoot the Hadley. But look at the north-south alignment of the Greenland and Atlantic lows, and the forcing heights through eastern Canada, ready to progress that wall of low heights east into Europe. By day 10, the trough moves east and south, a cold trough with low heights through the Norwegian Sea, UK, Ireland and North Sea down through the continent to Algeria. Irony is of course that the telltale elements are still there, Azores and eastern Med heights, just we’re not thinking about them any more because they have waned and because we’re on the cold side of a sumptuous looking trough that could well bed down as a Euro-low by day 14, a notion reinforced by a look at tonight’s EC46, and the NAO- signal for the first week of January. Are we thinking Hadley and its associated roaring NAO+? Yeah, exactly, not at all, more Hadbeenley than Hadley, and as is so often the case after a milder Christmas, the winter resumes.

12z GEFS between days 7 and 10 nicely shows the Atlantic trough moving east, elongating north-south through Western Europe and carving the heights out of Iberia. Aleutian trough linking through the Siberian Arctic down into Europe. Ridge over Pacific Canada, positively anomalous heights to the north, negative to the south over North America, so a weakened Atlantic jet stream, allowing a band of heights to link north-south through the mid Atlantic. Only minor changes from there through to day 14, though by then some hints in the contours of a ridge building north into Greenland. Notably different setup heading into the new year.

Happy (almost) winter solstice! It’s a bit wild here to say the least. Solid indications of a trend back towards more normal temperatures in the 0z ECM ensemble mean T850s and anomalies. Days 1-10 A very changeable Christmas week with fluctuations, but a good, clear overall trend towards more seasonal temperatures, and the core PV on the move to the Siberian and Scandinavian side of the Arctic by the new year, signalling better potential for a more notable cold spell in time.

Some real encouragement for something quite different by the end of the 12z GEFS. The return of the Scandinavia - Europe trough on the ensemble mean, the core of the PV over Barents / Kara nearby to Svalbard, and mean T850s falling away over Northern Europe, cold getting re-established to our northeast over Scandinavia.

6z GEFS was a reasonable run for showing the developments we might expect between Christmas and New Year. Though it’s not looking like a sustained cold spell, there are clearly colder interludes being signalled, which might set up some interesting transitions, and once the temperatures get below average, we can be in the game for all kinds of interesting features. Day 5, Christmas Day, at 132h, the T850 anomalies indicate a mild day in the far south of the UK, supported by those stubborn heights over France, but rather cold in the far north, with most in between close to average. Ireland is largely below average. It gets milder for all by day 8, but the change is underway, with the Greenland trough steadily working east, pushing the heights further east over the Mediterranean. The day 10 / 11 charts caught my eye for their notable difference with day 5. By New Year’s Eve, the heights to the south over Iberia have been removed and the trough is running north-south through the UK, Ireland and the North Sea, through northern France and the Low Countries to the western Mediterranean. The T850s are below average, looking rather cold by then for the UK and Ireland. The 0z EPS show the same broad transition between days 5 and 10 but with more positive heights relative to the mean, both to the south and in the intensity of the trough… but nevertheless sits alongside the GEFS in clearly signalling scope for more seasonal conditions to end the year, with the trough moving through to our east and heights again building strongly north through the Atlantic, west-east alignment of heights anomalies at day 5 being replaced with north-south alignment by day 10.

That is an exceptional build of mid Atlantic heights at the current time that is diverting a potentially potent push of cold air down across Western Europe, here on the 12z ECM ensemble mean for day 1, 1050mb+ high pressure over the middle of the ocean. Unlikely for us to see anything like that again for a fair while. It’s highly anomalous, and had many of us reflecting that if it wasn’t for that reinvigorated hook of PV extending over the northeast Canadian seaboard from Greenland, the heights could well have migrated northwest and landed us the firm northerly that some of the models were promising a couple of weeks ago. The high doesn’t stay there long, slipping southeast towards Iberia by day 6, Christmas Day, Feliz Navidad / Feliz Natal. It’s already weakened a great deal by then, allowing the southward encroachment of a northwesterly flow into the UK and Ireland. Heights rise over northeast Canada, but low heights still lurk over Greenland. The day 10 mean and anomalies charts are very interesting, not just for the further weakening of heights over southern Europe, but also for the rebuilding of heights over the mid Atlantic, and this time in concert with a consolidation of heights over northeast Canada and a removal of low heights from most of Greenland. The PV has moved back just that little bit east and withdrawn from Canada. There are already hints at that stage for the potential establishment of a flow from the north as we approach the end of December and head into the new year. The anomalously strong mid Atlantic high, with its flat west-east orientation has resulted in a surprisingly effective scuppering of the longer term setup we were envisioning for the later part of December, but there are plenty of signs here, taken with their keenness to so quickly re-emerge, that suggest that this might well only be a relatively short delay. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4980430

That is an exceptional build of mid Atlantic heights at the current time that is diverting a potentially potent push of cold air down across Western Europe, here on the 12z ECM ensemble mean for day 1, 1050mb+ high pressure over the middle of the ocean. Unlikely for us to see anything like that again for a fair while. It’s highly anomalous, and had many of us reflecting that if it wasn’t for that reinvigorated hook of PV extending over the northeast Canadian seaboard from Greenland, the heights could well have migrated northwest and landed us the firm northerly that some of the models were promising a couple of weeks ago. The high doesn’t stay there long, slipping southeast towards Iberia by day 6, Christmas Day, Feliz Navidad / Feliz Natal. It’s already weakened a great deal by then, allowing the southward encroachment of a northwesterly flow into the UK and Ireland. Heights rise over northeast Canada, but low heights still lurk over Greenland. The day 10 mean and anomalies charts are very interesting, not just for the further weakening of heights over southern Europe, but also for the rebuilding of heights over the mid Atlantic, and this time in concert with a consolidation of heights over northeast Canada and a removal of low heights from most of Greenland. The PV has moved back just that little bit east and withdrawn from Canada. There are already hints at that stage for the potential establishment of a flow from the north as we approach the end of December and head into the new year. The anomalously strong mid Atlantic high, with its flat west-east orientation has resulted in a surprisingly effective scuppering of the longer term setup we were envisioning for the later part of December, but there are plenty of signs here, taken with their keenness to so quickly re-emerge, that suggest that this might well only be a relatively short delay.

Focusing on the more reliable timeframe, the 0z UKMO gives a balanced take to my eye on the developments over the next week or so in the run-up to Christmas Eve at day 7. High pressure to the west peaks at 1050mb at day 4, a remarkably high surface pressure for an Atlantic cell at any time of the year. By day 7, it’s pushed a long way southeast to the east of the Azores and is much weaker, at 1030mb. This movement is being driven by the same core development that we’ve watched come in from the day 10+ timeframe, now at days 4-7, namely the relocation and reorientation of the PV away from northeast Canada and Greenland to Scandinavia. This north-south orientation of the polar trough is the core development that opens the door to incursions of much colder air from the northwest and north, a good push at day 6 and another looking likely just beyond the run heading into Christmas itself. These feeds from the northwest will be moisture-laden and potentially rich in spawning features. There is one at day 4 / 5 to the southwest of Iceland, that swings southeast, bringing that colder air south at day 6, and another ready in the wings at day 7, looking like it has our name on it, for bringing the colder air wrapped around it our way. These blasts of cold air will find it easier to make southward progress as time goes by, due to the steady encroachment of notably colder air much further south over the western Atlantic later in the week. For the UK and Ireland, precise timings, how cold and how far south will be firmed up over the next few days, which will make for very interesting viewing. Plenty to look out for, slight variations either way on this core theme to keep us on our toes and anything beyond day 7 to be taken with a huge dose of salt. And no doubt about it, with the reorientation of the PV and the steady southward movement of the polar front through the North Atlantic, this is a fascinating approach to Christmas, much more than is so very often the case. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4978551

Focusing on the more reliable timeframe, the 0z UKMO gives a balanced take to my eye on the developments over the next week or so in the run-up to Christmas Eve at day 7. High pressure to the west peaks at 1050mb at day 4, a remarkably high surface pressure for an Atlantic cell at any time of the year. By day 7, it’s pushed a long way southeast to the east of the Azores and is much weaker, at 1030mb. This movement is being driven by the same core development that we’ve watched come in from the day 10+ timeframe, now at days 4-7, namely the relocation and reorientation of the PV away from northeast Canada and Greenland to Scandinavia. This north-south orientation of the polar trough is the core development that opens the door to incursions of much colder air from the northwest and north, a good push at day 6 and another looking likely just beyond the run heading into Christmas itself. These feeds from the northwest will be moisture-laden and potentially rich in spawning features. There is one at day 4 / 5 to the southwest of Iceland, that swings southeast, bringing that colder air south at day 6, and another ready in the wings at day 7, looking like it has our name on it, for bringing the colder air wrapped around it our way. These blasts of cold air will find it easier to make southward progress as time goes by, due to the steady encroachment of notably colder air much further south over the western Atlantic later in the week. For the UK and Ireland, precise timings, how cold and how far south will be firmed up over the next few days, which will make for very interesting viewing. Plenty to look out for, slight variations either way on this core theme to keep us on our toes and anything beyond day 7 to be taken with a huge dose of salt. And no doubt about it, with the reorientation of the PV and the steady southward movement of the polar front through the North Atlantic, this is a fascinating approach to Christmas, much more than is so very often the case.

Some notable differences across the models with regard to the rate of the westward removal of heights from around the UK and Ireland towards day 10. 0z EPS at 240h vs. 6z GEFS at 234h. 0z GEPS was somewhere in the middle. Partly as a result, there’s also differences in the southward extension and shape of the trough around Iceland. GEFS is much keener on dropping a trough with a round base well to the south of Iceland. The EPS trough is much more elongated and remains much further north. There are consequently marked differences for the projected T850s, the GEFS looking quite seasonal. But the contrasts are only so profound at that stage, the differences are much more resolved by day 12, with the trough slowly working its way towards Scandinavia. We see a lot of this, where there is seemingly better agreement on the ultimate destination than the road taken to get there. If this happens, this is a very interesting place to be for Christmas Eve, the tightness of the contours suggests an active jet stream, with the UK and Ireland on the northern, colder side of it. Pacific jet, Atlantic jet, both up for it. Both North American and Siberian heights, pinching a cross-polar trough at the pole. The point is that’s a cold trough, hanging north-south. The mixing air masses underpinning the cyclonic developments that will be heading our way are from a long way further north than for our usual upstream pattern, with plenty of Arctic air mixed in. The EC46 heights anomalies have over recent days slowed down the eastward progression of the trough to our north, but have been settled on the ultimate outcome for the turn of the year for several weeks now, with the polar trough slowly moving east to bring us under the influence of flows more directly from the north. These are yesterday’s charts for 25th-1st and 1st-8th and it’s good to see the NWP outputs falling more in line with these as time goes by. And whatever it’s like on the day, almost two weeks away, it’s the whole feel of the season that matters to me, and that is a long way from a normal Northern Hemisphere profile - the precise timings are not going to be clarified until only a handful of days beforehand - surely why the developments around this core theme are going to keep us especially riveted over the days and weeks to come, for Christmas itself and through the New Year. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4974896

Some notable differences across the models with regard to the rate of the westward removal of heights from around the UK and Ireland towards day 10. 0z EPS at 240h vs. 6z GEFS at 234h. 0z GEPS was somewhere in the middle. Partly as a result, there’s also differences in the southward extension and shape of the trough around Iceland. GEFS is much keener on dropping a trough with a round base well to the south of Iceland. The EPS trough is much more elongated and remains much further north. There are consequently marked differences for the projected T850s, the GEFS looking quite seasonal. But the contrasts are only so profound at that stage, the differences are much more resolved by day 12, with the trough slowly working its way towards Scandinavia. We see a lot of this, where there is seemingly better agreement on the ultimate destination than the road taken to get there. If this happens, this is a very interesting place to be for Christmas Eve, the tightness of the contours suggests an active jet stream, with the UK and Ireland on the northern, colder side of it. Pacific jet, Atlantic jet, both up for it. Both North American and Siberian heights, pinching a cross-polar trough at the pole. The point is that’s a cold trough, hanging north-south. The mixing air masses underpinning the cyclonic developments that will be heading our way are from a long way further north than for our usual upstream pattern, with plenty of Arctic air mixed in. The EC46 heights anomalies have over recent days slowed down the eastward progression of the trough to our north, but have been settled on the ultimate outcome for the turn of the year for several weeks now, with the polar trough slowly moving east to bring us under the influence of flows more directly from the north. These are yesterday’s charts for 25th-1st and 1st-8th and it’s good to see the NWP outputs falling more in line with these as time goes by. And whatever it’s like on the day, almost two weeks away, it’s the whole feel of the season that matters to me, and that is a long way from a normal Northern Hemisphere profile - the precise timings are not going to be clarified until only a handful of days beforehand - surely why the developments around this core theme are going to keep us especially riveted over the days and weeks to come, for Christmas itself and through the New Year.

If we look at the day 15 charts, for 0z Christmas Eve, from 0z EPS, 0z GEPS and 0z GEFS, the GEFS is the flattest, but going even flatter on the 6z run. And perhaps conspicuously so. The heights contours running through the north of Iceland are 522 dam for EPS, 528 dam for GEPS and 519 dam for GEFS on the 0z run, but down to 510 dam on the 6z. It’s also particularly progressive in building heights back in over Europe. EPS, GEPS GEFS 0z, 6z The EC46 weekly anomalies I posted earlier (admittedly generated yesterday) are working off close to 525 dam for the north of Iceland for both the 18th-25th and 25th-1st. This might be the later GFS run picking up on an emerging signal based on newer data or it might be further over-developing the Iceland trough. Either way, the GFS at 0z was at the bottom end and at 6z it’s fair to say is rather out on its own, which is why I’ve been more focused on the northbound waves of amplification prior to that across all the models, where it looks like it’s all clearly all up for grabs for around day 8, let alone day 15, with a very wide range of outcomes possible.

That’s quite a difference at day 11 and 12 between the 0z and 6z GEFS. Much better orientation and build of heights towards Iceland in the latest run, the link-up through eastern Greenland rather than through the Norwegian Sea. Day 11 0z, 6z Day 12 0z, 6z This allows the development of a better defined Scandinavia - Europe trough, around 6 dam lower on the contours at the northernmost part of the Baltic Sea. The trough is further west too. The models seem to be working these run-to-run variations around the core theme of where the EC46 has the weekly means for the 18th to 25th and the following week, between Christmas and the New Year. We could perhaps be looking at more of a northwesterly flow as the Atlantic high draws west, before it then builds heights north as the trough consolidates over Scandinavia, straightening to a flow more directly from the north for the holiday period for the UK and Ireland. With the models consistently toying with these patterns for durations of weeks rather than days ahead, the run-to-run differences should perhaps be taken in the context of there being clearly plenty of scope for a very seasonal end to the year. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972776

That’s quite a difference at day 11 and 12 between the 0z and 6z GEFS. Much better orientation and build of heights towards Iceland in the latest run, the link-up through eastern Greenland rather than through the Norwegian Sea. Day 11 0z, 6z Day 12 0z, 6z This allows the development of a better defined Scandinavia - Europe trough, around 6 dam lower on the contours at the northernmost part of the Baltic Sea. The trough is further west too. The models seem to be working these run-to-run variations around the core theme of where the EC46 has the weekly means for the 18th to 25th and the following week, between Christmas and the New Year. We could perhaps be looking at more of a northwesterly flow as the Atlantic high draws west, before it then builds heights north as the trough consolidates over Scandinavia, straightening to a flow more directly from the north for the holiday period for the UK and Ireland. With the models consistently toying with these patterns for durations of weeks rather than days ahead, the run-to-run differences should perhaps be taken in the context of there being clearly plenty of scope for a very seasonal end to the year.

On the face of it, the 0z ensemble means at day 8 appear to be portraying a similar outcome - a generous looking surface high pressure over France. Nice, quiet period in mid December - could be a lot worse! Except they’re really not that similar at all. There are already profound differences in the Atlantic / Arctic heights profiles. ECM has the heights over the UK and Ireland flirting with a liaison with those further north and east, but just holding back. A more forthright linkage of heights between Greenland and Scandinavia would help seal off the Canadian PV. It’s actually almost there. The GFS is pushing the Atlantic heights further to the northwest, but allows shortwave trough development through the Norwegian Sea, which flattens the pattern considerably. The GEM has cracked it! Building solid heights just that bit further north towards Iceland and the link-up to Svalbard is on. That could easily push on from there to pull a flow down from the Arctic and there’s plenty of trough development over Scandinavia to spawn features in the flow. That’s how finely balanced it all is. I know that many, like me, are vaguely aware of a forthcoming holiday period, but this setup around day 8 has to be resolved before we can begin to arrive at any meaningful expectations regarding the following week. Have a great day.

Any doubts regarding the broad trend being picked up by the models can be allayed by looking at just a couple of pairs of charts - the 0z ECM ensemble mean, comparing day 8 and day 15. Day 8 shows high pressure centred over northern France bringing a quiet spell of weather to Western Europe. The T850s for the UK and Ireland are a couple of degrees above average but with the long nights, conditions at the surface are likely to be on the chilly side particularly further south, and likely get chillier too as the anticyclonic spell progresses. The core of the PV is over Arctic Canada. By day 15, the PV is being stretched out by the rolling pin of Siberian and Arctic heights, lobes becoming established over Alaska and around Svalbard, supporting the Aleutian and Norwegian Sea troughs, the latter extending as an upper trough down into Southern Europe. Now these are simple charts, blunt instruments when considering an averaging out of an ensemble of runs at 15 days away. It is nigh on impossible for them to show a northerly flow through the isobars at day 15, this is about as close as they can get at that range. I have been looking at them for many years, and more to the point, I have never before seen a drop of 5 or more degrees for the UK and Ireland between day 8 and 15. The transformation is stunning. The drop in temperature is not particularly associated with an intensification of cold over Scandinavia, though there is more of a drop for Iceland, so it’s strongly indicative of a northerly flow becoming established just before Christmas. It’s very much in the upper range of the strongest manifestation of a signal that could be expected from these charts. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972067

Any doubts regarding the broad trend being picked up by the models can be allayed by looking at just a couple of pairs of charts - the 0z ECM ensemble mean, comparing day 8 and day 15. Day 8 shows high pressure centred over northern France bringing a quiet spell of weather to Western Europe. The T850s for the UK and Ireland are a couple of degrees above average but with the long nights, conditions at the surface are likely to be on the chilly side particularly further south, and likely get chillier too as the anticyclonic spell progresses. The core of the PV is over Arctic Canada. By day 15, the PV is being stretched out by the rolling pin of Siberian and Arctic heights, lobes becoming established over Alaska and around Svalbard, supporting the Aleutian and Norwegian Sea troughs, the latter extending as an upper trough down into Southern Europe. Now these are simple charts, blunt instruments when considering an averaging out of an ensemble of runs at 15 days away. It is nigh on impossible for them to show a northerly flow through the isobars at day 15, this is about as close as they can get at that range. I have been looking at them for many years, and more to the point, I have never before seen a drop of 5 or more degrees for the UK and Ireland between day 8 and 15. The transformation is stunning. The drop in temperature is not particularly associated with an intensification of cold over Scandinavia, though there is more of a drop for Iceland, so it’s strongly indicative of a northerly flow becoming established just before Christmas. It’s very much in the upper range of the strongest manifestation of a signal that could be expected from these charts.

There’s a lot going on with the 12z ECM op, days 1-10. Not often you get a fierce sub-950mb storm in the western Atlantic at our latitude get squeezed out as proficiently, we’d normally take one look at that and start battening down the hatches. The mollification is undertaken by the same heights that start moving southeast out of Canada and Greenland at day 1, in the mid Atlantic by day 6, then push east to form the Western European high from day 8. These heights are trying throughout to link up with those over the Siberian Arctic and the Urals, but the latter wriggle away, darting over the pole to Canada between days 8-10. Not to be put off, the northwest Europe heights then start following to the northwest to catch them! This game of cat and mouse for the heights over the North Atlantic, Europe and the Arctic not only results in the dissipation of a fearsome looking Atlantic storm, but then just as the Canada-Greenland lobe of the PV is looking to get going, the surge northwest of heights from the UK and Ireland splits the lobe in two. By day 10, there’s a polar wedge, aligned with another one over eastern Siberia, likely to be joined by the heights swiftly departing northwest Europe towards Greenland. And from there, with the Canada lobe isolated and the other lobe moving to Scandinavia, aligned with low PV heights backing up through Siberia, things could get very interesting! Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971896

There’s a lot going on with the 12z ECM op, days 1-10. Not often you get a fierce sub-950mb storm in the western Atlantic at our latitude get squeezed out as proficiently, we’d normally take one look at that and start battening down the hatches. The mollification is undertaken by the same heights that start moving southeast out of Canada and Greenland at day 1, in the mid Atlantic by day 6, then push east to form the Western European high from day 8. These heights are trying throughout to link up with those over the Siberian Arctic and the Urals, but the latter wriggle away, darting over the pole to Canada between days 8-10. Not to be put off, the northwest Europe heights then start following to the northwest to catch them! This game of cat and mouse for the heights over the North Atlantic, Europe and the Arctic not only results in the dissipation of a fearsome looking Atlantic storm, but then just as the Canada-Greenland lobe of the PV is looking to get going, the surge northwest of heights from the UK and Ireland splits the lobe in two. By day 10, there’s a polar wedge, aligned with another one over eastern Siberia, likely to be joined by the heights swiftly departing northwest Europe towards Greenland. And from there, with the Canada lobe isolated and the other lobe moving to Scandinavia, aligned with low PV heights backing up through Siberia, things could get very interesting!

There has been some talk recently of the “blob of death” (I think it’s only on here that I hear that term!). It might be a bit strong a term in this case, in that though the PV clearly is getting its act together over the next week or so, in the context of many recent winters, it is relatively weak, and at the medium to longer ranges, seems keen to withdraw to the Canadian Arctic. A sign of just how weak the influence might be over Atlantic weather is given in the 0z GEM control at day 11 - a 1050mb high pressure over the UK and Ireland. Now that could be very pleasant. And then of course, the high migrates west. In the longer term, there were some useful indicators on today’s runs, across the ensemble means, to support the broad evolution we’ve been talking about over the last few days, but no forward traction in terms of timing as yet. The commonalities are there across the means by the end of week 2 in the form of Aleutian trough, west Canada ridge, Atlantic block, weak PV withdrawn to the Canadian Arctic, trough running down the Norwegian Sea to the UK and Ireland. 0z EFS at day 15 6z GFS at day 16 The 0z GEM ensemble mean is doing something extra with the blob, moving it faster over to Alaska and also donating a chunk of lower core heights to the Svalbard to Norway area at the top of the Norwegian Sea trough, adding to the vorticity there. That would be fascinating if it happened - reduction to a 2-wave pattern, Aleutian and North European troughs, with low heights all the way, straight across the pole. Not just ultimately encouraging a cross-polar flow but making it extremely hard to shift too. Not that it exactly rolls off the tongue, but of what I’ve seen of the modelling of the early part of this winter, I think the term “blob of eventual opportunity” might perhaps be more fitting. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971621

There has been some talk recently of the “blob of death” (I think it’s only on here that I hear that term!). It might be a bit strong a term in this case, in that though the PV clearly is getting its act together over the next week or so, in the context of many recent winters, it is relatively weak, and at the medium to longer ranges, seems keen to withdraw to the Canadian Arctic. A sign of just how weak the influence might be over Atlantic weather is given in the 0z GEM control at day 11 - a 1050mb high pressure over the UK and Ireland. Now that could be very pleasant. And then of course, the high migrates west. In the longer term, there were some useful indicators on today’s runs, across the ensemble means, to support the broad evolution we’ve been talking about over the last few days, but no forward traction in terms of timing as yet. The commonalities are there across the means by the end of week 2 in the form of Aleutian trough, west Canada ridge, Atlantic block, weak PV withdrawn to the Canadian Arctic, trough running down the Norwegian Sea to the UK and Ireland. 0z EFS at day 15 6z GFS at day 16 The 0z GEM ensemble mean is doing something extra with the blob, moving it faster over to Alaska and also donating a chunk of lower core heights to the Svalbard to Norway area at the top of the Norwegian Sea trough, adding to the vorticity there. That would be fascinating if it happened - reduction to a 2-wave pattern, Aleutian and North European troughs, with low heights all the way, straight across the pole. Not just ultimately encouraging a cross-polar flow but making it extremely hard to shift too. Not that it exactly rolls off the tongue, but of what I’ve seen of the modelling of the early part of this winter, I think the term “blob of eventual opportunity” might perhaps be more fitting.

Yes, still a long, long way off for the NWP models to pick up on any impending change back to cold weather, but maybe as an appetiser to the later parts of the 12z’s, here’s more support, this time from our Canadian friends, for a NW-SE aligned jet stream taking low pressure down into Europe in the run-up to Christmas. 0z GEPS heights and jet stream, 0z GEM control for day 16, and for good measure, thrown in by their neighbours across the 49th parallel, there’s a deep Norwegian Sea trough on the 6z GFS control too. Some early but growing signals, well worth keeping an eye on the control runs from here on in, they picked up early on the broad signal of the recent cold spell very well, sporadic at first but then gaining good consistency. Had my first mince pie of the season today, from a local bakery - delicious!