Cambrian

6z GFS op at day 10 shows the freezing level at 0m and sub-528 dam thickness throughout the UK and Ireland. A rare sight. Parts of Scotland are at sub-510 dam. Looks a bit nippy.

Yes, January 1987 was a good one, but strictly model chat in here please folks or the posts may well magically disappear… …in any case the current models are exciting enough, like 12z EPS for day 10. From there, the Atlantic showing a few more signs of wanting to force the issue perhaps make things really interesting!

There has understandably been a lot of focus on the initial setting up and location of the high pressure and the extent of northwestward retrogression. The role of specific low pressure systems and the forcing of the lobes of the PV is as vital to the evolution though. The 15 day animation of the 12z ECM ensemble mean shows the spawning of a series of lows during the next week, from the eastern North America trough, a southward extension of the Canadian lobe of the PV. The first two contribute to the formation of a deep system to the south of Greenland around day 4, which helps pump up the heights for the high pressure over the UK and Ireland. The trough moves east with these developments by day 6, and elongates southwards into the Atlantic, squeezed around the western flank of the fully developed, strong high, 1040mb+ now centred just to the northeast of the UK. Around day 7-8 (180h) is a critical juncture, as the high pressure intensifies further and begins to move northwestward, and in tandem with the rise in heights up into Newfoundland, breaches the trough, sending the cut-off low southeast towards the Azores, looking to phase with low heights over Iberia, and also bumping the high into further northward migration. The low pressure at the base of the residual Greenland trough rides up and over the Atlantic ridge, then down into the Norwegian Sea by day 9, sealing off any potential eastward movement of the high, and on into Scandinavia by day 10, reinforcing the base of the Siberian trough and aligning the PV southwestward towards Northern Europe by day 12, which by then has grown bitterly cold. In this modelling of the evolution, these ripples of energy, provided by the Canadian lobe of the PV, taking form in North American cyclogenesis, sent up and over the ridge, serve to fortify the forcing of a formidably cold European pattern via the Siberian PV, in one of the most compelling runs of the ECM ensemble mean that we are ever likely to see. Awesome. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4994145

There has understandably been a lot of focus on the initial setting up and location of the high pressure and the extent of northwestward retrogression. The role of specific low pressure systems and the forcing of the lobes of the PV is as vital to the evolution though. The 15 day animation of the 12z ECM ensemble mean shows the spawning of a series of lows during the next week, from the eastern North America trough, a southward extension of the Canadian lobe of the PV. The first two contribute to the formation of a deep system to the south of Greenland around day 4, which helps pump up the heights for the high pressure over the UK and Ireland. The trough moves east with these developments by day 6, and elongates southwards into the Atlantic, squeezed around the western flank of the fully developed, strong high, 1040mb+ now centred just to the northeast of the UK. Around day 7-8 (180h) is a critical juncture, as the high pressure intensifies further and begins to move northwestward, and in tandem with the rise in heights up into Newfoundland, breaches the trough, sending the cut-off low southeast towards the Azores, looking to phase with low heights over Iberia, and also bumping the high into further northward migration. The low pressure at the base of the residual Greenland trough rides up and over the Atlantic ridge, then down into the Norwegian Sea by day 9, sealing off any potential eastward movement of the high, and on into Scandinavia by day 10, reinforcing the base of the Siberian trough and aligning the PV southwestward towards Northern Europe by day 12, which by then has grown bitterly cold. In this modelling of the evolution, these ripples of energy, provided by the Canadian lobe of the PV, taking form in North American cyclogenesis, sent up and over the ridge, serve to fortify the forcing of a formidably cold European pattern via the Siberian PV, in one of the most compelling runs of the ECM ensemble mean that we are ever likely to see. Awesome.

A week ago, this is what the 0z ECM ensemble mean modelled for the 4th of January at day 10… …compared with what it’s modelling for the same date today at day 3. The comparable GFS means we’re similar. We can forgive the models for not modelling the wedges, although the ECM did a great job of indicating the polar high. The greatest difference lies with the PV, in that the Barents / Kara lobe is missing altogether and also that the heights to the south of Greenland were underestimated. So where would we put the jet stream on today’s chart? Somewhere in the belt of greens heading into France? Mais oui, bonne année. This compares with the modelling of it a week ago further north over the UK and Ireland. The models have been underestimating the Siberian lobe of the PV and the high Atlantic heights, slightly overestimating the strength of the Canadian lobe, all resulting in the jet stream being modelled for us, quite significantly further north than later transpires. Interestingly, looking ahead into week 2 from here, there are some signs that the same trend isn’t on the cards. The 0z ECM ensemble mean for week 2 (day 8-15) hands the dominance to the Siberian lobe, introducing a surface northerly flow into the UK and Ireland as heights lower from the northeast over Scandinavia. This is a very positive sign for cold in northwest Europe. The last few runs of the GEM have also been very supportive of this trend in week 2, nice because we also have the anomalies to show the westward then northward migration of the heights from the UK and Ireland, and the low pressure working southwestwards through Scandinavia in our direction. And if we have learned anything from the above, the Siberian lobe may be even stronger and the pattern may be even further south than currently modelled. I can not recall a New Year with such firm indications for a forthcoming cold spell. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4990389

A week ago, this is what the 0z ECM ensemble mean modelled for the 4th of January at day 10… …compared with what it’s modelling for the same date today at day 3. The comparable GFS means we’re similar. We can forgive the models for not modelling the wedges, although the ECM did a great job of indicating the polar high. The greatest difference lies with the PV, in that the Barents / Kara lobe is missing altogether and also that the heights to the south of Greenland were underestimated. So where would we put the jet stream on today’s chart? Somewhere in the belt of greens heading into France? Mais oui, bonne année. This compares with the modelling of it a week ago further north over the UK and Ireland. The models have been underestimating the Siberian lobe of the PV and the high Atlantic heights, slightly overestimating the strength of the Canadian lobe, all resulting in the jet stream being modelled for us, quite significantly further north than later transpires. Interestingly, looking ahead into week 2 from here, there are some signs that the same trend isn’t on the cards. The 0z ECM ensemble mean for week 2 (day 8-15) hands the dominance to the Siberian lobe, introducing a surface northerly flow into the UK and Ireland as heights lower from the northeast over Scandinavia. This is a very positive sign for cold in northwest Europe. The last few runs of the GEM have also been very supportive of this trend in week 2, nice because we also have the anomalies to show the westward then northward migration of the heights from the UK and Ireland, and the low pressure working southwestwards through Scandinavia in our direction. And if we have learned anything from the above, the Siberian lobe may be even stronger and the pattern may be even further south than currently modelled. I can not recall a New Year with such firm indications for a forthcoming cold spell.

12z ECM ensemble mean days 5-10. Yes. Good, clean separation of the two lobes of the PV, the Canadian lobe moves off west, the Siberian lobe holds its ground. A build in heights to establish the high pressure over the UK and Ireland, the heights subsequently extending north through Greenland to join with the Arctic high. Plenty of scope for the northwestward retrogression being scoped in the clusters. Little point looking beyond this timeframe at the moment. Very interesting developments for early January.

Another fascinating year of studying the models comes to an end with another complete turnabout on the cards, but to be fair, a step forward from the usual “will it turn cold?” to “just how cold will it turn?”, which all in all, is not a bad place to be if you like that kind of thing Here on the 0z ECM ensemble mean, the transformation between day 4 and day 7, the second half of the coming week is astounding. How far north the high will ultimately sit by next weekend is still to be resolved. If this is right, it will be cold enough, but mainly dry, a very welcome anticyclonic period. Thereafter, it’s best just to look at the overall evolution at this stage. For hints about that, the 0z ECM control closely shadows the mean for pressure, a rise to 1030mb+ by around day 9, followed by a fall as the high sinks southeast, but doing so only to make way for a good chunk of the Siberian lobe of the PV to drop into Northern Europe. Day 8-15 Notably, not once in the T850 animation is there any flow from the west, Arctic air from the northwest at times, but no Atlantic sourced air. The core evolution surrounds a generally cold outlook with a trend towards even colder as January progresses. (If I may: It’s not anything I ever expected but I proudly accepted the offer of a role with the forum team as despite one or two rough edges that we all know we collectively have, I genuinely believe in the forum, its purpose, uniqueness and integrity. Already I see the challenge. Please help by staying on topic. Please try and avoid too many one liners, try and post a chart or at least refer to one, be as clear as you can in specifying details of model runs that you’re speaking of, avoid knee jerk posts that you just know afterwards you should have thought about a bit more before clicking submit. Don’t get wound up, report nonsense. If you have any questions or concerns, approach the team. I never realised how much work is done. Most of all, on a human level, please be kind. There is so much crap going on in the world, and we in our common interest, friendship and care are such a hell of a lot better than all of that. In addition to helping with the tremendous team effort of moderation, I will endeavour to maintain the same posting and reaction “presence” and try and make a good contribution to what we collectively enjoy so much.) Blwyddyn Newydd Dda i bawb, Happy New Year to everyone. Have a brilliant 2024.

All these machinations of the various ops are playing out front stage before a consolidating backdrop, such as that seen with the generous firming up of the colder pattern in the 12z EPS at day 9, here compared with 12z yesterday at day 10. 12z yesterday @ 240h 12z today @ 216h Look at the bend in the contours straight north in today’s chart heading up into the Icelandic ridge and the greater heights, now further north, supporting it, as well as the stronger linkage of Atlantic to Arctic heights through Greenland. This brings the UK and Ireland into a longer fetch northerly flow at 500mb. The low heights associated with the Siberian lobe of the PV are further southwest, the European trough is further consolidated and also further west, an extension of low heights bending southwest through Western Europe, including the south of the UK. With all this, the T850s respond accordingly. The overall trend is not flinching, indeed it’s sticking to schedule and even more clearly pointing at a cold spell.

Once more I find myself thoroughly captivated by forthcoming developments with the Atlantic jet stream, here the next 10 days on the 0z ECM operational run - good viewing before the 12z’s. If ever we want to look at a wave break delivering cold, shown by the T850s. This run was even better - the jet stream sinking south, followed by a double wave break, the second wave with markedly greater amplitude than the first, delivering a progressively colder setup to the UK, Ireland and Europe.

Looking at the broader picture, it’s fair to say we’re seeing a decisive pattern change in the nearer range than can currently be as decisively developed in the longer range. It’s fascinating how these pattern changes appear a long way off, then seem to so often get submerged only to re-emerge in around the day 7 mark. This change manifests as a classic jet stream split off the eastern seaboard between day 6 and day 8. 12z GEM op 12z GFS op Weakened by the split, the northern arm undulates north and then south in tandem with the amplification of the Atlantic ridge. The southern arm remains flat and diverges even further south. From there, it’s a weaker but still significant northern arm capable of downstream trough development over Europe and a more dominant southern arm ultimately pointed at North Africa. At some point, some very cold air will spill south into the trough. The 12z ECM mean brings the cold a good way south around the base of the Scandinavian trough, with a slack northerly flow down into Western Europe. Where exactly the ridge and trough set up will determine will where and how cold the conditions will get over the different parts of Northern Europe, but with the consistently modelled build in heights well north in the Atlantic by day 8, continuing to build through day 10, it’s clearly looking to get generally much colder at some point, at the T850 level and / or (especially) at the surface, and when it does, there appears to be very little upstream in the Atlantic to shift what might very well become an extensive cold pool. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4986434

Looking at the broader picture, it’s fair to say we’re seeing a decisive pattern change in the nearer range than can currently be as decisively developed in the longer range. It’s fascinating how these pattern changes appear a long way off, then seem to so often get submerged only to re-emerge in around the day 7 mark. This change manifests as a classic jet stream split off the eastern seaboard between day 6 and day 8. 12z GEM op 12z GFS op Weakened by the split, the northern arm undulates north and then south in tandem with the amplification of the Atlantic ridge. The southern arm remains flat and diverges even further south. From there, it’s a weaker but still significant northern arm capable of downstream trough development over Europe and a more dominant southern arm ultimately pointed at North Africa. At some point, some very cold air will spill south into the trough. The 12z ECM mean brings the cold a good way south around the base of the Scandinavian trough, with a slack northerly flow down into Western Europe. Where exactly the ridge and trough set up will determine where and how cold the conditions will get over the different parts of Northern Europe, but with the consistently modelled build in heights well north in the Atlantic by day 8, continuing to build through day 10, it’s clearly looking to get generally much colder at some point, at the T850 level and / or (especially) at the surface, and when it does, there appears to be very little upstream in the Atlantic to shift what might very well become an extensive cold pool.

You pays your money and takes your choice, but thankfully all the main models essentially offer consistently good value at day 10 on the 12z EPS, GEPS and GEFS… …courtesy of Iceland / Greenland / polar heights, and a Scandinavia / Europe trough, ultimately leading to variations on the single emerging theme of European cold. All wondrously impressive stuff for just a couple of days after Christmas, which I’m far from having finished celebrating Have a great evening.

A very interesting period underway with the NWP models, that are in the process of very actively modifying the near-reliable as well as the longer ranges. There’s quite a stark difference between yesterday’s 0z EPS for day 7 and today’s day 6. The upper trough heading south from Scandinavia into Italy and the stronger heights to the northwest of Iberia have both been moved northwest to the order of a thousand miles or so, bringing the trough through the UK and Ireland, at the western end of what is now actually a deeper trough running through the Baltic Sea. This has the effect down the line of setting up low European heights by day 10 (right), compared here with yesterday’s day 11 (left). There is a polar high anomaly too, bringing cold air westward through the Siberian Arctic towards Northern Europe. It’s this combination of developments that ultimately digs out the Iberian heights and makes the difference between the continuation of average to slightly above temperatures across the continent and the beginning of a European cold spell. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984089

A very interesting period underway with the NWP models, that are in the process of very actively modifying the near-reliable as well as the longer ranges. There’s quite a stark difference between yesterday’s 0z EPS for day 7 and today’s day 6. The upper trough heading south from Scandinavia into Italy and the stronger heights to the northwest of Iberia have both been moved northwest to the order of a thousand miles or so, bringing the trough through the UK and Ireland, at the western end of what is now actually a deeper trough running through the Baltic Sea. This has the effect down the line of setting up low European heights by day 10 (right), compared here with yesterday’s day 11 (left). There is a polar high anomaly too, bringing cold air westward through the Siberian Arctic towards Northern Europe. It’s this combination of developments that ultimately digs out the Iberian heights and makes the difference between the continuation of average to slightly above temperatures across the continent and the beginning of a European cold spell.

The colder local pattern is established as early as day 10 on the 12z GEFS, that’s the 4th of January as the trough gets through to our east with a strong build in heights to the northwest, the 12z Christmas Day offering for day 10 much more clearly developed in this regard than the 12z Christmas Eve for day 11. Heights and T850s anomalies, yesterday… vs today… The hemispheric pattern consolidates further thereafter. By day 14, there’s a pronounced Siberia - Scandinavia trough, low heights throughout Europe, and the whole continent is in the fridge. Worth noting that going by today’s GEFS, these changes to a cold pattern are being described by a better defined setup - in that regard more clearly signalled to happen - and also to happen sooner. It’s looking like the next few weeks will be compelling model viewing!

First signs on the GEFS of a surface northerly flow incoming for the UK and Ireland by the end of the first week of the new year, here at day 11 on the 6z GEFS, with a Norwegian Sea trough. Atlantic ridge a bit sharper and a bit further west than on earlier runs, Iberian heights less of an issue… …and certainly by day 15… A marked impact on the temperatures by then too. A long way off, but notably closer than in previous runs, perhaps one of those situations where the models are finding more definite traction in a specific (potential) outcome at the same time as detecting a gaining momentum for its earlier arrival, bringing it forward in time. It will be good to see what the 12z’s show, and whether EPS and GEPS will again follow, but very interesting signs at this stage from the extremely keen GEFS.

I wasn’t going to post today, but this is exceptional. 0z GFS ensemble mean, days 8-16. The core evolution - heights from western Canada and Alaska join with heights from Central Asia over the Siberian Arctic and then move southwest to Iceland, Greenland and eastern Canada. Then we get the Eurasian trough and the door is opened to the east. Northern blocking, mid-latitude trough. Comparing with the 0z ECM ensemble mean at day 10, both largely on the same sheet, ECM / GFS and 0z GEM ensemble mean very similar to GFS by day 16. GEM / GFS The word fascinating doesn’t do it justice. Nadolig llawen, Merry Christmas. Have a brilliant day

Nadolig llawen i chi gyd. A Merry Christmas to you all. The week 2 trend in the 0z ECM ensemble mean / EPS provides a very clear signal for the first week of the new year, charts for day 8 vs day 15. The lobe of the PV over Greenland at day 8 withdraws westward into the Canadian Arctic, squeezing the west Canadian ridge up through Alaska to between the Bering Sea and the pole, which helps Siberian lobe also move west towards the Barents and Kara Seas and Svalbard by day 15. The Pacific jet stream intensifies south of Japan, while the Atlantic jet stream weakens notably, the chart for day 15 showing it being split into northern and southern arms, blocked off by the Azores-Iceland ridge, the northern arm ultimately feeding a Scandinavia / Russia trough, the southern arm some low pressure development to the west of the Azores. There is a significant rise in heights in the gap through Iceland towards Greenland, which links through the pole to the Bering Sea heights. The pattern looks a bit too far east for the UK and Ireland to be availed of a direct hit from the north, but ripe perhaps for meaningful cold air advection from the east or northeast. Notice the loss of heights through the Caucuses and the low heights over Eastern Europe. Back to the PV - if the split happens in early January in any way that perpetuates or reinforces that axis of the cross-polar heights as it is shown for around day 15, the UK and Ireland will be much more open to being influenced by the Eurasian trough than the southerly displaced Atlantic trough, which looks like it will be having a very lean time of it by then in any case. But it’s that reversal of heights around the Caucuses that looks particularly telling to me in putting us in with a very good chance of being in the right place for a long cold spell if and when the roulette wheel slows to a stop, by ushering cold air around into Western Europe from the northeast. That’s a fascinating thing to be looking at on Christmas Eve and it’s developments around this theme that I’ll be looking forward to seeing being firmed up over the coming days. Thank you for all the support and camaraderie, and for all the learning I have been afforded again this year. It’s a great community. I hope that the beautiful time that is Christmas will ease any troubles that people have. Have a good one

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.