Cambrian

The end to another week marked by another cold trough dropping down from the north over the UK and Ireland, 12z GFS op, 0-78h. These are the 500mb temperature and heights charts. Nice to look at. Last week’s colder snap flattered to deceive in many ways. The impressive looking 528 dam thicknesses only delivered for the tops. I must admit that I saw more scope in it for snow than transpired. This one will perhaps prove more interesting in the event as there is a low pressure system with its own circulation that forms at the base of the trough. The trajectory of arrival is more sharply NW-SE so there is slightly colder air wrapped up in it, with heights as low as 512-520 gpm, and there is also more organised precipitation. This time there is a keen ridge building behind the low, which serves to cut it off from the trough at least for a while, until it merges west with the base of the next incarnation of the Greenland longwave. The models have struggled all week with the rate at which the low gets warmed out, with a trend over the last few days toward keeping it that bit colder for longer. @Ali1977 has been picking up on this firming up over the last few days. In any case, there’s certainly plenty of weather around on Friday into Saturday in particular, at 36-78h, as the low pivots its way through Ireland and the UK and spins out a secondary system to France. It’s made more interesting by the system arriving during nighttime hours and the relatively slack circulation as it grinds to a halt possibly aiding some evaporative cooling at times with the heavy and sustained precipitation, so maybe the first couple of days of spring this year might well have a decidedly wintry feel. Very likely my last post of the winter! I have greatly enjoyed it, though it seems that the models we study are possibly on as steep a learning curve as we are.

Much cleaner evolution to an easterly flow on the 0z ECM op, which adeptly delivers an unorthodox 1-2-3 left jab / right jab / uppercut combo to put paid to the trough. In slow motion, first the jabs, at days 4-6, the left jab from the Atlantic heights heading north, in tandem with the right jab from the heights over Eastern Europe also pushing through to north of Iceland. Then the upper cut, days 7-10, delivered by a quick hit of Iberian heights, pushing up to reinforce the pressure being exerted to the north - indeed unlike other recent challengers, critically getting sufficient heights far enough north - and resulting in the isolation of the cut-off low at the base of the upper trough, now much weakened and pushed west, but not before some energy ejects southeast from the trough into southeast Europe at day 7… …the upshot of all this being the establishment of an easterly flow through Europe, extending the continental feed into the UK and Ireland. Even some support from the ensemble mean old judges at day 10, with the surface high holding over Scandinavia and a southeasterly flow. At this stage, looking increasingly like a points decision for a very welcome drier spell.

A slow pattern as we enter meteorological spring, as low heights on the western side of the Arctic vie with positive heights on the eastern side - the tropospheric PV, that never really got going this winter, withdrawn to northeast Canada, but extending a cold trough through Greenland and Iceland, down into the UK and Ireland, here at day 5 on the 0z GEFS. There is a decent Atlantic ridge, and as this topples, it links up with heights over NE Europe and western Russia at day 7, allowing for development of a cut-off low over the UK and Ireland, maintaining its own pool of cold air, in this evolution, likely this year for meteorological spring to kick off with a distinctly chilly feel, mean T850s at day 6. Thereafter, another trough drops through Greenland by day 10, this time to the west of us over the Atlantic. This looks to be followed by another bisection of the trough, forming another cut-off at the base, which again slowly migrates southeast over Western Europe by day 15. A big difference at this stage though, is that the PV has moved northeast over the pole, all the troughing is removed from Greenland, allowing heights to build through the North Atlantic to Scandinavia, the pattern by then looking to be even slower, very typical of recent springs with a slow, chilly start to the season. Have a great day.

0z ECM ensemble mean is useful for “removing the noise” and showing the core pattern for the next 10 days. It’s a recurring one, the PV over Arctic Canada spawning a succession of low pressure systems that move southeast towards the base of the trough over Western Europe. Two systems push their way through a gap between Atlantic and Scandinavia / Russia heights, with a third one ready to drop out of Greenland by day 10, shown more clearly on the anomaly chart. Also nicely shown on the anomaly charts are the episodes of heights building over eastern North America, that then run in pulses along the ribbon of heights through the Atlantic. These pulses are helping to push the systems down from Greenland but are struggling to establish a base into Iberia, with the jet stream diving so sharply southeast over the eastern Atlantic, keeping it changeable with temperatures close to average overall. On a closer look, milder for a few days in the middle of the spell as winds turn into the west riding over the top of the Atlantic ridge, 0z EPS jet stream at day 6… …before turning colder again around day 8/9 as the next system drops down from Greenland, reinforcing the trough over Western Europe, the UK and Ireland by then back on the cold side of the jet stream.

The Iberian heights taking a bit of a late season pasting at the hands of the polar trough during the next few days (these are all for 0-84h) on 0z GFS op… …in more ways than one. With the 528 thickness line briefly grazing the north of Spain and the freezing level at 800 - 1200 metres, heavy falls of snow for the Cantabrian Mountains, which reach up to over 2000 metres. Closer to home, with those kinds of thicknesses that far south, falling snow is a very reasonable possibility anywhere in the UK and Ireland. Freezing levels often near 400 metres, sometimes a tad lower in the colder pockets of polar maritime air bustling through, so upland Scotland doing very well for settling snow, and scope there for slight accumulations at times for parts of Central Wales and Central England too, as well as local accumulations more widely no doubt. The GFS has been consistent with the modelling of these thicknesses, freezing levels and precipitation for several days now, as it has been with this morning’s deluge! Whatever falls out of the sky and whether it sticks, for everywhere in Western Europe a very different feel to the end of the week. Have a great day.

12z GFS op is a good workout. Day 1-3 : Lateral lunge Day 3-7 : Dumbbell curtsey Then rest. Then repeat. Day 9-10 Day 10-12 Then lie down flat and think of spring. *No gym enthusiasts were harmed in the writing of this post.

6z GFS op shows how we just might have a bit of a surprise with this low pressure at the end of the week. At day 4, it’s landed in where it’s been modelled for several days now, to the north of the UK and Ireland, with its core of low heights over where Iceland used to be. It’s a complex low, with secondary centres continually forming around and becoming engulfed within the primary low, this process serving to drag the main core further south, dragging pockets of colder air south with it. Day 4-8 animation. This sets up some heavy snow next Saturday night on the northern edge of one of these secondary lows. Just one model, so a low chance of it happening like this, but a timely reminder that once we get a complex low, developing and spinning features around in decently cold air, with heavy precipitation at night - the 6z GFS is a great run for showing that while the overall setup is perhaps just a bit too mild, events can crop up that demonstrate that marginality is a two-way street. At the very least, worth keeping an eye on - it’ll be interesting to see if anything similar crops up in the next few runs and days.

It’s looking like the UK and Ireland will be under the influence of a particularly slow moving trough from around day 6 through to the end of the month and into March. 0z GEFS at day 6, 10 and 16. I like seeing this in the models, as it moves us on from the mild, incessantly damp theme of the last several and immediate next few days, and is more believable than being teased with a straight as a dart northerly or a pretend Scandinavian high. It’s actually a reinforcing pattern, cyclonic becoming northwesterly for a good few days before relaxing into a westerly around day 12. Hints then though of another injection of some more serious polar maritime air as another low pressure moves southeast out of Greenland, cyclonic and more northwesterly again, shown here in the day 8-16 animations. Notice that the PV is gravitating once more towards the centre, extending back over the pole. Although very much at the low end of the ensemble for temperature, something like the 0z GFS op is not out of the question, with a cold polar maritime theme being maintained throughout, not much difference between day 9 and 14, T850 chart for day 13 as a taster. Bursts of poleward amplification up through Greenland, but nothing major or sustained, northwest Europe too messily cyclonic to get a clean draw south off the Arctic. A long way off but looks like the kind of period where the hills might see plenty of snow coming and going - changeable and rather cold fits the bill, definitely more seasonal for the end of winter. Have a great day.

12z UKMO neatly captures the change over the next week, as a chunk of the PV circulation swings around through northeast Canada, through the south of Greenland to the Norwegian Sea. The 500mb temperature charts that we don’t often use, nicely show the replacement of the tropical maritime air over the UK and Ireland with a polar maritime air mass, that has followed the same path out of the Arctic through Canada and Greenland to get here, with some reasonable T850s to show for it. Should get rid of all this claggy stuff and eventually into some clearer air with decent lapse rates. Getting through to some proper cold sectors and seeing the tops of some beefy shower clouds, maybe the odd anvil, in a chilly northwesterly, bringing cold stuff down in the downdraughts sounds like a really good option right now.

Both the EPS and GEFS have moved away from the idea of a strong Scandinavian / NW Russian trough being established at around day 8. Comparing charts for the 22nd, at day 10 from Monday and day 8 from today’s 0z runs. EPS GEFS Both suites appear to have underplayed the Atlantic troughing, both immediately to our northwest and upstream towards NE Canada. GEFS has been overplaying heights rises at day 10 further north in the Atlantic and through Greenland. EPS did a better job of those at day 10, but overplayed the heights through Western Europe. Inter-model convergence, along with loss of wide ensemble spread, is a good indicator of the point at which these models become more reliable. This appears to be at around day 8 for this particular period. Both models have adjusted upward the activity of the Atlantic jet stream, and both would now seem to be indicating a spell of a NW-SE aligned jet stream running south of the UK and Ireland and down into Europe, around the base of a trough around Iceland. Day 8 GEFS. The overall take on looking forward from there at day 8 through to the last week of the month fits nicely with the ideas on the strat and the clusters. For me, possibly a bit more to play for in the event than looks firmly on the cards at the moment. Rather cold and changeable for northwest Europe, scope for systems that develop over Greenland wrapped up in cold air, to run down the western flank of the trough. These feeds typically contain pockets of colder and less cold air, as systems pass through. It’s not a bad time of the year for some wintry episodes from that quarter. I’ll be keeping an eye on how cold the lows heading out of Greenland will be, some wintry weather at times from this setup looks a fair possibility, and definitely more so than for the month up until now! Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5037414

Both the EPS and GEFS have moved away from the idea of a strong Scandinavian / NW Russian trough being established at around day 8. Comparing charts for the 22nd, at day 10 from Monday and day 8 from today’s 0z runs. EPS GEFS Both suites appear to have underplayed the Atlantic troughing, both immediately to our northwest and upstream towards NE Canada. GEFS has been overplaying heights rises at day 10 further north in the Atlantic and through Greenland. EPS did a better job of those at day 10, but overplayed the heights through Western Europe. Inter-model convergence, along with loss of wide ensemble spread, is a good indicator of the point at which these models become more reliable. This appears to be at around day 8 for this particular period. Both models have adjusted upward the activity of the Atlantic jet stream, and both would now seem to be indicating a spell of a NW-SE aligned jet stream running south of the UK and Ireland and down into Europe, around the base of a trough around Iceland. Day 8 GEFS. The overall take on looking forward from there at day 8 through to the last week of the month fits nicely with the ideas on the strat and the clusters. For me, possibly a bit more to play for in the event than looks firmly on the cards at the moment. Rather cold and changeable for northwest Europe, scope for systems that develop over Greenland wrapped up in cold air, to run down the western flank of the trough. These feeds typically contain pockets of colder and less cold air, as systems pass through. It’s not a bad time of the year for some wintry episodes from that quarter. I’ll be keeping an eye on how cold the lows heading out of Greenland will be, some wintry weather at times from this setup looks a fair possibility, and definitely more so than for the month up until now!

Variations on a theme from the last couple of runs from the ECM op between days 6 and 8, yesterday’s 12z on the right, with a welcome high pressure building in the vicinity of the UK and Ireland. The variation is toward the north of that in how cleanly the linkup with the polar high separates the Canadian and Eurasian lobes of the PV. It’s supported by the 0z ECM ensemble mean as a stepping stone between where we are over the next few days and the setup for the end of the month, day 4, 8 and 14. It’s a nice evolution. Something like this happening is clearly on the cards, to get from here at day 4 on the 0z GEFS to where we are at day 12 (a couple of days quicker than ECM). The extent and nature of the split of the tPV is clearly still to be pinned down, but strong indications that its machinations will switch the Northern Hemisphere profile from lateral to longitudinal. Reversal of the Barents / Kara ridge to a trough, ridging up through Greenland all the way up through the pole so that the Arctic cold is split, cold air sweeping south over both North America and northwest Europe… …plenty of interesting variations on this theme likely to become available as the season has finally managed a 3 lobe PV pattern with a favourable 2-way split of the cold air, with the strong Greenland ridge, and the East Asian and North American lobes showing signs of linking up. The interest for me is not all about hanging on in there for at least some prospect of seeing some wintry weather to round off the winter. The end of February, beginning of March is often cold, even in years with a strongly coupled PV, so I’m really interested in how the troposphere plays out the final throes of this season characterised by a phenomenally weak stratospheric PV. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5036584

Variations on a theme from the last couple of runs from the ECM op between days 6 and 8, yesterday’s 12z on the right, with a welcome high pressure building in the vicinity of the UK and Ireland. The variation is toward the north of that in how cleanly the linkup with the polar high separates the Canadian and Eurasian lobes of the PV. It’s supported by the 0z ECM ensemble mean as a stepping stone between where we are over the next few days and the setup for the end of the month, day 4, 8 and 14. It’s a nice evolution. Something like this happening is clearly on the cards, to get from here at day 4 on the 0z GEFS to where we are at day 12 (a couple of days quicker than ECM). The extent and nature of the split of the tPV is clearly still to be pinned down, but strong indications that its machinations will switch the Northern Hemisphere profile from lateral to longitudinal. Reversal of the Barents / Kara ridge to a trough, ridging up through Greenland all the way up through the pole so that the Arctic cold is split, cold air sweeping south over both North America and northwest Europe… …plenty of interesting variations on this theme likely to become available as the season has finally managed a 3 lobe PV pattern with a favourable 2-way split of the cold air, with the strong Greenland ridge, and the East Asian and North American lobes showing signs of linking up. The interest for me is not all about hanging on in there for at least some prospect of seeing some wintry weather to round off the winter. The end of February, beginning of March is often cold, even in years with a strongly coupled PV, so I’m really interested in how the troposphere plays out the final throes of this season characterised by a phenomenally weak stratospheric PV.

There are two ways of looking at this at a time like this. We either beat ourselves and the models up over how the winter hasn’t ended up like it was often modelled to, particularly at the longer ranges, or we accept the models for what they are - mathematical predictions that can be right or wrong to a range of extents, only ever a snapshot representation of some brilliant mathematical simulations, and that what we do in analysing them at any one time is part of a long term learning process as to the strengths and weaknesses of these approaches. For looking after my head and maintaining my enjoyment of such a great interest, there can, for me, only be one way forward. So we have another tease on the means for day 10 and after, this time offering the model punch-drunk hardcore some potential for a cold end to official winter. The beginning of it is around day 10 but is being consistently modelled, the extension of a trough into northwest Russia, here on the 0z EPS and GEFS. It’s interesting to note that at that stage, the EPS is firmer, more advanced on the development. The progression from there towards the 0z GEFS at day 15 is at the raunchier end of the winter 23/24 cold tease spectrum… …the heights contours running down almost true north, a flow from the middle of Greenland, through Iceland to the middle of the UK and Ireland, the MSLP charts showing the computing of a low pressure system by then over the North Sea, the UK and Ireland under a cold, cyclonic regime, some proper cold showing in the T850 charts now. Will it verify? Not exactly like that, that’s for sure, but it is what it is, a growing signal for a notably cold end to February. I’m pleased to see it - we’ll get the weather we’ll get, but in quite openly being interested in seeing a good fall of snow before winter’s end, I’m happier looking at this than at a continuation of the charts we’re looking at for the coming week. Have a great end to the weekend.

12z GFS op and mean very much in kilter between days 8 and 16 in terms of Northern Hemisphere profile with the separation of the lobes of the PV being orchestrated by northwest European and Alaskan ridges interacting through the pole. That means there’s arguably reasonable support there for a PV split on the mean too, which is interesting to observe. Both ultimately bring the Scandinavian trough southwest through the UK and Ireland, with a handsome trend in the mean T850s. A crisp evolution towards a cold end to February.

Difficult to pretend that the models are playing ball in terms of anything decisive. But what is going on is definitely fascinating. I’m taking the 0z GEFS because it’s been great value this winter, and using the mean MSLP charts because we don’t show them enough. We’ve well and truly learned how to practice the virtue of patience, so let’s look at the next couple of weeks. Day 7 shows a long fetch southwesterly from the Azores, riding along the northern flank of the high pressure to the south, likely mild and very moist, the jet stream continues to water the meadows. Let’s move on. But before we do - ironically, it’s that high pressure, another wave of Iberian heights, that begins the transition to another pattern. By day 10, it’s working north towards the UK and Ireland. Like over recent days, the highs modelled to be aligning during this period from Western Europe through the pole to the Bering Sea. It’s that “super-ridge” of high pressure that both holds the Atlantic at bay and as it moves west, makes room for the developing Scandinavian trough, and the establishment of a cold northerly sourced pattern by day 14. Fascinating pattern towards the end of the month, low pressure anomalies to the south, high pressure anomalies to the north, consistent with a mollified jet stream, weak and running far to the south, heading into North Africa, Western Saraha, Tropic of Cancer, around 23 degrees North. No great heights to the south at that stage and the entire pattern north of the jet stream is profoundly slack, it looks particularly challenging to model, and is very open to a much higher potential for surprise than normal. It’s at that stage that any modest bit of circulation out of the Arctic, that won’t even have started to develop yet, may well turn out to be more decisive in terms of the weather for northwest Europe. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5035424

Difficult to pretend that the models are playing ball in terms of anything decisive. But what is going on is definitely fascinating. I’m taking the 0z GEFS because it’s been great value this winter, and using the mean MSLP charts because we don’t show them enough. We’ve well and truly learned how to practice the virtue of patience, so let’s look at the next couple of weeks. Day 7 shows a long fetch southwesterly from the Azores, riding along the northern flank of the high pressure to the south, likely mild and very moist, the jet stream continues to water the meadows. Let’s move on. But before we do - ironically, it’s that high pressure, another wave of Iberian heights, that begins the transition to another pattern. By day 10, it’s working north towards the UK and Ireland. Like over recent days, the highs modelled to be aligning during this period from Western Europe through the pole to the Bering Sea. It’s that “super-ridge” of high pressure that both holds the Atlantic at bay and as it moves west, makes room for the developing Scandinavian trough, and the establishment of a cold northerly sourced pattern by day 14. Fascinating pattern towards the end of the month, low pressure anomalies to the south, high pressure anomalies to the north, consistent with a mollified jet stream, weak and running far to the south, heading into North Africa, Western Saraha, Tropic of Cancer, around 23 degrees North. No great heights to the south at that stage and the entire pattern north of the jet stream is profoundly slack, it looks particularly challenging to model, and is very open to a much higher potential for surprise than normal. It’s at that stage that any modest bit of circulation out of the Arctic, that won’t even have started to develop yet, may well turn out to be more decisive in terms of the weather for northwest Europe.

This has been the feature of the winter for me - the recurring Scandinavian trough. It hasn’t delivered wintry weather for all parts of the UK and Ireland equally, far from it, but it alone has been conspicuous in consistently delivering the right kind of air mass to our shores. It’s been a winter where the modelling of heights into Scandinavia / easterly tease, though not transpiring, has proven to be a frequent prelude to the reassertion of the trough from the PV as it shuffles each time over from Canada to settle for lengthy periods on the Siberian side of the Arctic. If we look at the NH profile, we can see that it’s at it again! The signs were there last night on the GEFS, but now indeed, its arrival is being smartly expedited in the 0z ECM models. Yesterday’s 12z mean at 252h versus today’s 0z at 240h. All hail the arty rabbit looking thing - may your front legs grow long and maintain that southwestward orientation trend. Atlantic ridging and western Atlantic trough also a good deal further west, that push of heights into Greenland is outstanding for a day 10 mean, driving amplification for the trough but also serving to push the southwesterly flow well away and opening us up to the north. This is reflected in the mean T850’s too. A big change in the models over just 12 hours. There’s evidently still plenty of time for a meaningful cold spell. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5034848

This has been the feature of the winter for me - the recurring Scandinavian trough. It hasn’t delivered wintry weather for all parts of the UK and Ireland equally, far from it, but it alone has been conspicuous in consistently delivering the right kind of air mass to our shores. It’s been a winter where the modelling of heights into Scandinavia / easterly tease, though not transpiring, has proven to be a frequent prelude to the reassertion of the trough from the PV as it shuffles each time over from Canada to settle for lengthy periods on the Siberian side of the Arctic. If we look at the NH profile, we can see that it’s at it again! The signs were there last night on the GEFS, but now indeed, its arrival is being smartly expedited in the 0z ECM models. Yesterday’s 12z mean at 252h versus today’s 0z at 240h. All hail the arty rabbit looking thing - may your front legs grow long and maintain that southwestward orientation trend. Atlantic ridging and western Atlantic trough also a good deal further west, that push of heights into Greenland is outstanding for a day 10 mean, driving amplification for the trough but also serving to push the southwesterly flow well away and opening us up to the north. This is reflected in the mean T850’s too. A big change in the models over just 12 hours. There’s evidently still plenty of time for a meaningful cold spell.

If the 12z ECM’s nod towards a split PV at day 7/8 is taken at face value, the evolution from around that time shown in the 12z GEFS could well be of interest. It’s much more definite in bringing the main PV action back to the Eurasian side from around mid month, here at days 8-14, developing a fresh Scandinavian trough that quite speedily reintroduces cold air, feeding steadily southwestwards through Northern Europe. That’s a very decent signal for a mean, even better if taken on the back of a prospective split. Looking forward to seeing the EPS later. The models are definitely picking up on new signals today. Mid to late February still more than early enough to pack a punch in terms of winter interest, and for a good few weeks, before we properly turn the corner toward spring.

Day 4 / 5 looking a bit chilly on the 0z ECM ensemble but otherwise above average temperatures for the foreseeable. However, the very definite southerly track of the jet stream on the 0z ECM op - often heading into Iberia - would suggest that the mild outlook is a fairly precarious one. The day 10 mean anomaly gives the impression of being very blocked through the eastern Atlantic, good heights to the north and south but the heights through Western Europe are only marginally positive. The Atlantic trough will eventually try to head for the gap, but ironically looks that it will be blocked by the heights to the south. 0z EPS shows that the low is no longer being directed from Greenland, rather from a centre over Newfoundland, where the heights are lowest, all the while pumping heights north into Greenland and Iceland. 0z GEPS sends a ridge up through Iceland into Greenland at day 12, with a surface high over the Greenland plateau and a notable polar high. Along with low pressure over the Barents Sea, this is feeding a cold northerly flow down into the Norwegian Sea. That is how we can get cold air back into Europe. The 0z ECM control is at something similar. Don’t worry about modelled uppers at this range, a path to insanity. The Atlantic low can’t go north and is being blocked from disrupting southeast into Spain, so just stalls over the Atlantic, leaving the UK and Ireland at the southern edge of an Arctic block with easterlies or northerlies an option from there. The resilience of the southerly running jet stream and looking out for the Atlantic low to eventually pump enough heights north are the main aspects to watch here. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5033825

Day 4 / 5 looking a bit chilly on the 0z ECM ensemble but otherwise above average temperatures for the foreseeable. However, the very definite southerly track of the jet stream on the 0z ECM op - often heading into Iberia - would suggest that the mild outlook is a fairly precarious one. The day 10 mean anomaly gives the impression of being very blocked through the eastern Atlantic, good heights to the north and south but the heights through Western Europe are only marginally positive. The Atlantic trough will eventually try to head for the gap, but ironically looks that it will be blocked by the heights to the south. 0z EPS shows that the low is no longer being directed from Greenland, rather from a centre over Newfoundland, where the heights are lowest, all the while pumping heights north into Greenland and Iceland. 0z GEPS sends a ridge up through Iceland into Greenland at day 12, with a surface high over the Greenland plateau and a notable polar high. Along with low pressure over the Barents Sea, this is feeding a cold northerly flow down into the Norwegian Sea. That is how we can get cold air back into Europe. The 0z ECM control is at something similar. Don’t worry about modelled uppers at this range, a path to insanity. The Atlantic low can’t go north and is being blocked from disrupting southeast into Spain, so just stalls over the Atlantic, leaving the UK and Ireland at the southern edge of an Arctic block with easterlies or northerlies an option from there. The resilience of the southerly running jet stream and looking out for the Atlantic low to eventually pump enough heights north are the main aspects to watch here.

If not so much the charts themselves, I’ve been enjoying the discussion about the heights being too far north. However, looking at the EPS charts for a week ago for day 9, and comparing with today’s 0z for day 2, particularly focusing on western Greenland, it’s more of a case of a complete reversal of predicted positive height anomalies to negative ones in that part of the world that is critical to the prospects for northwest Europe, contours of 520’s dam incrementally replaced during the last week by lower and lower heights, now 492 dam. It’s the unexpected depth of those low heights in that position around Greenland that has allowed the low to the south to be recruited and orientated north by the Greenland low - it’s not the heights anomaly that matters here, it’s the heights themselves. A few days ago, I wrote that it looked like around 3 days in the cold air before the Atlantic had another go. That was based in part on having seen a succession of charts showing 501 dam heights up around Greenland, low heights and a trough through the UK and Ireland, like here from a week ago at day 12. Interestingly, when compared with today’s 0z chart for day 5, it’s still only around 501 dam, but is further east so has been able to link up with the UK / Ireland low. Notice as well though that the heights to our north, over the Norwegian Sea, are being underestimated. Looking ahead to day 8, there is ridging north through the UK and Ireland up into that region, the jet stream is strong only over the western Atlantic, and is on a southern track before splitting mid-ocean. No Atlantic onslaught in the offing and there is notable spread at day 8 over the Norwegian Sea so the build in heights there might be even more substantial. The pressure anomalies show it nicely - it’s only going to take a bit more of a build into that zone to our north, the northwest Russia high drifts west and that Atlantic low is likely going under, with the low pressure over the eastern Mediterranean to help pull it through. Writing off the rest of a month in any particular direction before we’re out of the first week of it is not sensible when the balance is so fine and the scope so plausible. I’m actually looking forward to the next few weeks.

Here’s the ECM Thursday snow chance demise in all its gory detail, for all to see. Yesterday’s 12z ensemble mean at 96h vs. today’s at 72h, heights / pressure and T850s. Exactly, neither can I - unless it’s that version of the demise where the colder T850s are now modelled further south in what is turning into one heck of a battle zone, with much of the detail far from being resolved.

What a great Sunday morning to be up early looking at the charts! Especially when there’s such interesting ones on show, even now for the end of the same week. 0z EPS day 6 is a cracker of a surprise with the low pressure tracking to the south of Ireland through Wales and southern England, many of us kept on the cold side, or quickly brought back into it in the wrap. Just a point about how low the heights are - this is a mean, probably the best mean we have, showing 525 dam heights to the southwest and through southeast England at day 6. There could well be a lot of surprises in store with this one. Thereafter, by day 8, we have the centre of the low heading into Europe but with a meaty bit of troughing hanging back through the southern UK, with some properly cold air entrained in the northeasterly flow of the departing low. The icing on the breakfast cake for me this morning though is how quickly and solidly the high pressure builds in from the west by day 10, a surface high extending from the UK and Ireland northeast to Scandinavia. This puts one of the best types of prospect on the table - some snow on the ground, with a high pressure quickly established to trap in the surface cold over the snow. Potential for a good winter spell. At this stage, we’re still very much defining and re-measuring the envelope. But it’s actually now surprisingly a bigger envelope than yesterday, with many more of our addresses being considered for being written on the front. Mornings like this are what makes this hobby so enjoyable. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5029260