Cambrian

Little point ducking the issue. A quacking weekend in store… 0z ECM op for day 4, as another low pressure system finds us with impressive timing! Further ahead, some more positive signs - once we start seeing this type of “super-meridional” pattern - ambitious building of heights up through the Atlantic and more spectacularly, through all the S’s - Sahara-Sweden-Svalbard-Siberia-Seguam like here at day 6 on the 0z ECM op… …it’s only a matter of time before we start seeing the trough becoming over-extended with the cutting off of the low at the base of the trough, it sinking south, the heights linking up through the UK and Ireland like here at day 8… Yes, add Skegness and Sandymount to your list, spectacular super-meridional S thing! After that, a weaker version of the trough tries to reassert itself from the northwest, which the GFS op has been keenest on, though looking at the 0z ensemble mean, the pressure never really falls away again, a steady rise to a respectable 1020mb for Birmingham by the end of week 2… …which is consistent with the ECM charts and the pincer movement of heights weakening the polar trough at its stem - so though nothing wall to wall by any means, the chance of a somewhat more promising setup emerging into early May. I’ll post again around then. All the best. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5060751

Little point ducking the issue. A quacking weekend in store… 0z ECM op for day 4, as another low pressure system finds us with impressive timing! Further ahead, some more positive signs - once we start seeing this type of “super-meridional” pattern - ambitious building of heights up through the Atlantic and more spectacularly, through all the S’s - Sahara-Sweden-Svalbard-Siberia-Seguam like here at day 6 on the 0z ECM op… …it’s only a matter of time before we start seeing the trough becoming over-extended with the cutting off of the low at the base of the trough, it sinking south, the heights linking up through the UK and Ireland like here at day 8… Yes, add Skegness and Sandymount to your list, spectacular super-meridional S thing! After that, a weaker version of the trough tries to reassert itself from the northwest, which the GFS op has been keenest on, though looking at the 0z ensemble mean, the pressure never really falls away again, a steady rise to a respectable 1020mb for Birmingham by the end of week 2… …which is consistent with the ECM charts and the pincer movement of heights weakening the polar trough at its stem - so though nothing wall to wall by any means, the chance of a somewhat more promising setup emerging into early May. I’ll post again around then. All the best.

Not very often we see a low pressure system romp so triumphantly west from Scandinavia through the UK and Ireland to the Atlantic, as here on the 12z UKMO but there are some very intricate handovers of pockets of low heights that drive the whole process and give it some considerable elegance. The first pocket drops south to join the Scandinavian low at day 2, deepening it. The second drops out of the trough at the tip of Greenland at day 3, joining the melee at day 4 and drawing the system west over the UK and Ireland for the weekend. Thanks A third pocket drops southeast via the same route at day 6, pulling the system west out over the Atlantic. Looks like an “atmospheric” weekend awaits to round off this very mixed April, ripe for savoury evening treats washed down with a sumptuous glass or three of your favourite ale or wine. The late spring fitness effort can wait until some suitable conditions are laid on. And from there, let’s grab all the potential silver linings. Though not seemingly immediately on offer, there are at least some emerging signs that this remarkable retrogression, as a part of wider adjustments occurring within the generally very static hemispheric pattern, might eventually lead to sufficiently consistent heights building over the near continent to bring us a better chance of some warmer interludes as May progresses.

@Josh Cool Stundon Hi Josh, I think that we have to look at each event on its own rather than necessarily seeking a sub-classification of the classic Spanish plume. I have looked at the archive charts for June 28th 2012. What is striking about that event is the dramatic west-east temperature gradient that developed that day and how the contrasting air masses interacted in the circulation of the developing low pressure system. I have examined the pressure charts and the T850 charts, relevant here because the 850 hPa temperature, at altitude about 1.5 km, is above the atmospheric boundary layer and so is a very good measure of the relative temperatures of the air masses. At 0z that day, the low pressure at around 1000mb, was centred about 800 km to the southwest of Ireland. The pressure was around 1005mb over southwest Ireland. The T850 was around 11 degrees over Limerick and around 14 degrees over southeast England, though the 16 degree isotherm of the plume was over the English Channel coast. The surface circulation over Ireland was a southeasterly, drawing in warm, humid air from that region. By 6z, the low pressure had extended northeast, and the pressure over southwest Ireland had fallen to 1000mb. The centre of the low was by then around 400 km to the west of Kerry. The T850 over Limerick was around 9 degrees, and the 16 degree isotherm had arrived in southeast England. The surface flow into southwest Ireland was still from the southeast, continuing to feed in warm, humid and unstable air. By 12z, the deepening of the low pressure, to around 995mb had pulled in colder air from the northwest, so that the T850 over Kerry and West Cork was only 6 degrees and this knuckle of much cooler air was pushing in from the southwest behind a developing front, into the very warm humid air to the east of it. The T850 over Kent was around 17 degrees, so two things had happened. Firstly, over 12 hours, the difference in T850 between southwest Ireland and southeast England had risen from 3 degrees to an 11 degree difference, so the temperature gradient had become extremely steep. The atmospheric instability through that zone would have become profound. Secondly, the centre of the approaching low pressure had more or less stalled, still several hundred kilometres to the southwest of Ireland but the low was deepening in situ, so all of Ireland was by then below 1000mb as the system grew. The winds would have been slight and variable within this cyclonic circulation but with the dramatic west-east temperature contrasts within the system, and the peak convection of the afternoon, severe thunderstorms would have formed through the frontal zone, fed by the growing instability and making only very slow eastward progress. As the front approached, the wind would have backed southerly running along the front, so a local effect of air getting lifted over the Cork and Kerry mountains, enhancing the updrafts, might have been an additional factor for the Limerick area. Limerick was in effect stuck in the trigger zone for several hours with the growing temperature contrast of the air masses and increasing convection of the day feeding a growing instability that resulted in the severe thunderstorms. I hope this helps look at the question in another way. The precise setup for each instance of this type of event is naturally different, but I was hoping that by looking at the dynamics of this particular event, the requisites might be identified.

Keeping abreast of the models, here’s a notable pair of ECM means, in near perfect hemispheric symmetry around day 9 / 10, persistent heights reinforcing the cleavage. The sheer indecision of it all - sure to be amongst the abiding mam…oops, memories of spring 2024.

We’ve been quite lucky this morning, it has been absolutely beautiful, steadily warming up from a -1.2 degrees frost around dawn, 1026mb and no wind. April mornings don’t come much better. A very reasonable looking few days ahead, through the weekend and into early next week, the 0z EPS chart for next Monday morning at day 4 is a cracker. The MSLP chart shows a high pressure of 1036mb over the UK and Ireland, part of a “bar” of higher pressure extending through to the Siberian Arctic. But make the most of it! Even with this setup, though it is nigh impossible for our high to be shifted east by anything off the Atlantic, it instead gets undermined by trough development to the east. There were good hints of this in the models yesterday, and though still a fair way off, the subtle hints of yesterday for day 10 have grown into clear suggestions today for day 9, the trough notably deeper and further west. This is the kind of evolution I love to see, not necessarily for the weather it will bring, but for the phenomenon itself. The 0z ECM op at days 6-10 shows the potential, the Scandinavian trough spawning a little low pressure system running down through the Norwegian Sea, joining with another more active one coming out of Greenland and sweeping down through Iceland… …the two merging and swivelling down into the UK and Ireland, with the cold air reasserting itself in the process. With the seasonal timing, probably not at all welcome, though I keep the faith that one of these years we’ll get this kind of thing a couple of months earlier and enjoy it a lot more. As it stands in the current modelling, it’s a spring ambush!

This appears to be quite a telling moment in the development of this spring. The Atlantic jet stream is heading very decisively north before fragmenting, here on the 0z ECM op for the next 10 days. The 0z ECM mean anomaly shows an impressive build in heights not only north through the Atlantic but also west into Greenland. The low pressure over the pole is lost as heights link up through the Arctic to the Siberian side. So the pattern is getting locked down. From the meridional 5-wave hemispheric pattern we’ve been looking at recently, we might have seen the next stage involving injection of some energy to incorporate a couple more waves, reduce the amplification and introduce a more mobile setup, but instead we’re seeing the opposite happen - the Atlantic build is so substantial that it serves to carve out one of the waves altogether. This is shown nicely by the 0z GEFS jet stream charts, the 5-wave starfish at day 5 being replaced by a 4-wave cross at day 10, the jet stream actually bending back on itself with a northeasterly component as it dives south towards the UK and Ireland. The surface flow will be very much in the northeast for several days, following the contour lines in the mean heights charts (below) from around day 5 onwards. So we’re moving towards a more static setup towards the end of the month, drier than it has been, but with suppressed temperatures. The stronger sunshine when on offer could make for some pleasant weather all the same, especially further west with shelter, though as discussed, the onshore breeze could be quite the dampener in eastern parts at times. One more thing, looking through to day 10, the upper trough remains uncomfortably close by to the east, even steadily working its way further west - so small systems beginning to run down the western flank of the trough, picking up moisture through the Norwegian Sea, might well become an added complication later on next week. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5058638

This appears to be quite a telling moment in the development of this spring. The Atlantic jet stream is heading very decisively north before fragmenting, here on the 0z ECM op for the next 10 days. The 0z ECM mean anomaly shows an impressive build in heights not only north through the Atlantic but also west into Greenland. The low pressure over the pole is lost as heights link up through the Arctic to the Siberian side. So the pattern is getting locked down. From the meridional 5-wave hemispheric pattern we’ve been looking at recently, we might have seen the next stage involving injection of some energy to incorporate a couple more waves, reduce the amplification and introduce a more mobile setup, but instead we’re seeing the opposite happen - the Atlantic build is so substantial that it serves to carve out one of the waves altogether. This is shown nicely by the 0z GEFS jet stream charts, the 5-wave starfish at day 5 being replaced by a 4-wave cross at day 10, the jet stream actually bending back on itself with a northeasterly component as it dives south towards the UK and Ireland. The surface flow will be very much in the northeast for several days, following the contour lines in the mean heights charts (below) from around day 5 onwards. So we’re moving towards a more static setup towards the end of the month, drier than it has been, but with suppressed temperatures. The stronger sunshine when on offer could make for some pleasant weather all the same, especially further west with shelter, though as discussed, the onshore breeze could be quite the dampener in eastern parts at times. One more thing, looking through to day 10, the upper trough remains uncomfortably close by to the east, even steadily working its way further west - so small systems beginning to run down the western flank of the trough, picking up moisture through the Norwegian Sea, might well become an added complication later on next week.

Please continue to use the reporting facility in the usual way. If you have a specific issue regarding moderation, or in general, that you would like to raise with the team, then please do so via here: https://www.netweather.tv/other/contact-us We greatly appreciate this feedback. Please remember that the moderators are keeping an eye on the shape of the forum across many threads. If you have reported a post and no action has been taken, it’s invariably because it has been reviewed and the decision was to leave the post as it is. For instance, at quieter times, when there is little possibility of the thread becoming derailed by a marginal post, some leeway is sometimes given in order to keep the threads moving along and as engaging as possible. A blustery and chilly morning here, showery with plenty of hail. Not great, but a 1030mb+ high building through the UK and Ireland by day 6 on the 0z ECM op, day 0-6 here, the rise in pressure and its convenient location now well inside the reliable and for once, coinciding with the weekend! Many a lawn will get mowed…. An impressive build in heights to the west and north. No doubt some fresh and chilly nights and mornings as it works its way in and settles down. Consistent signs of the high pulling back west thereafter, but for a fair few days, this is going to feel much, much better!

Shiver me timbers! Looks like we have a retrogressing high before our very eyes, ha ha haar (and other pirate noises) - even before it’s properly arrived. Whether ‘twill be as shivery as 6z GFS op at day 9, where it withdraws far enough to the northwest to allow a proper cold blast down the frontage with some snow a fair way south, and settling on the hills… or holds close enough nearby to keep the old lunger a bit further east like on the 0z GEM op at day 10 (beware that sea serpent beyond the pole, haar)… the retrogression and European trough are definitely looking to be features of week 2 - ‘tis here too on the 0z EPS at day 11. Aar. The CFS weeklies (weeks 1-3) show the Euro trough by week 3 being reinforced by its maritime buddy that’s come romping through the Azores in weeks 1 and 2, while to the north, the Atlantic heights hint at wobbling back east, a tad back our way again… …the big concern for us island landlubbers looking for something to warm our jellies is that rather than a generally quiet but cool outlook, the pattern in the event all heads just that bit further north bringing us back into chilly cyclonic influences that just judder your rafters. More pirate noises…. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057987

Shiver me timbers! Looks like we have a retrogressing high before our very eyes, ha ha haar (and other pirate noises) - even before it’s properly arrived. Whether ‘twill be as shivery as 6z GFS op at day 9, where it withdraws far enough to the northwest to allow a proper cold blast down the frontage with some snow a fair way south, and settling on the hills… or holds close enough nearby to keep the old lunger a bit further east like on the 0z GEM op at day 10 (beware that sea serpent beyond the pole, haar)… the retrogression and European trough are definitely looking to be features of week 2 - ‘tis here too on the 0z EPS at day 11. Aar. The CFS weeklies (weeks 1-3) show the Euro trough by week 3 being reinforced by its maritime buddy that’s come romping through the Azores in weeks 1 and 2, while to the north, the Atlantic heights hint at wobbling back east, a tad back our way again… …the big concern for us island landlubbers looking for something to warm our jellies is that rather than a generally quiet but cool outlook, the pattern in the event all heads just that bit further north bringing us back into chilly cyclonic influences that just judder your rafters. More pirate noises….

The end of the coming week looking settled sooner and for longer now on the models. We’ve been watching this change develop for several days now, but it’s always good to see a signal: a) firm up b) come forward in time And this one’s really beginning to look very good. 0z EPS for next Thursday (18th) from last Monday for day 10, and today at day 5, showing the two sides of the coin becoming more clearly imprinted - the bubble to the west of the UK and Ireland gaining in modelled heights and steadily being modelled further north, and the low heights earlier focused over Scandinavia, now modelled as a deeper trough extending down into southeast Europe. Typical of how these models often work as they firm up, we can see the uncommitted, white gaps and softer shades getting gradually taken up by stronger signals, Atlantic heights growing stronger and more expansive, while a fully-fledged polar trough becomes marked out running down into Europe, the most notable synoptic difference being the development of the small low pressure to the east of Greenland that aids the link-up of low heights. Though some colder, less settled conditions are slowly departing to the east, for the UK and Ireland, the more relevant feature is the decisive edging east of the modelled ridge, and more noticeably into southern Greenland and Iceland too, which sets up the prospect of an earlier arrival of a much quieter end to next week, and combined with the better build, dare we say it (!), hints at this being followed up by several back-to-back usable days… ….this positively illustrated by the EPS MSLP charts for day 7, with the high pressure edging in from the west at day 7, gradually establishing itself slap bang over the UK and Ireland by day 10. Rightly being picked up on is the Atlantic becoming sealed off, but this looks a more substantial block than just that, with high pressure extending from the Azores through our stretch of Western Europe to Siberia, so by that stage it’s not only a block to weather off the Atlantic but also a block to further troughs running down through Scandinavia - with the added benefit that with the removal of the threat of the colder air to the east, in the gentle and variable circulation of the high pressure, daytime temperatures should be building to much more encouraging levels into the last week of the month - drier and warmer - good news for those yearning to give their spring freckles an airing. Have a great weekend.

Historybuff They appear to be the old Beaufort letters, used up until around that time, but replaced very swiftly thereafter. e.g. ogm at Lerwick is o = overcast, m = mist and g = gale (mean speed 34-47 knots over a period of 10 minutes or more). cq at Stornaway : c = cloud covering 6 to 7 oktas (eighths of the sky); q = recent squall They are listed in this document here: https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/library-and-archive/library/publications/factsheets/factsheet_11-interpreting-weather-charts.pdf The really useful bit for these Beaufort letters gets going around page 29-30. There are some others relating to cloud cover on page 18. It looks like you have many happy hours of meteorological detective work ahead! Best of luck.

Blimey. Outstanding choreography from the ridge dance troupe, lining up to really sock it to the PV on the NH dance floor over the next 10 days on the 12z ECM operational run. Let’s watch the elaborate performance as successive waves of heights push north. Starting from where we are today, PV centre stage, coordinating Atlantic, Scrussian and Bering Sea troughs in a whole hemisphere twirl. Keep an eye on that little pocket of heights over the Canadian seaboard with the hook north, because…. …first up is the Atlantic ridge by day 3, still with the northward extension of heights, now extending well up through Baffin. By day 5, the PV still holding centre stage, but the Atlantic ridge has been joined by the Alaska ridge, a sweet little link-up of heights pushing the lower heights east. But about to join in is a nascent ridge pushing up the east of Japan towards eastern Russia, and there are hints of a naughty little squeeze from Kazakhstan. By day 9 / 10, the Kazakh squeeze is maintained, well and truly heating up that floor, while the Japan surge goes all-out Siberian, joining their friends from the west in a hemispheric Cha Cha that ultimately congas its way right through the heart of the Arctic. PV exit stage left, arrivederci. A good few days respite for the UK and Ireland. Yeah, sign up everyone (if you’re not totally exhausted), the moves are awesome. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057123

Blimey. Outstanding choreography from the ridge dance troupe, lining up to really sock it to the PV on the NH dance floor over the next 10 days on the 12z ECM operational run. Let’s watch the elaborate performance as successive waves of heights push north. Starting from where we are today, PV centre stage, coordinating Atlantic, Scrussian and Bering Sea troughs in a whole hemisphere twirl. Keep an eye on that little pocket of heights over the Canadian seaboard with the hook north, because…. …first up is the Atlantic ridge by day 3, still with the northward extension of heights, now extending well up through Baffin. By day 5, the PV still holding centre stage, but the Atlantic ridge has been joined by the Alaska ridge, a sweet little link-up of heights pushing the lower heights east. But about to join in is a nascent ridge pushing up the east of Japan towards eastern Russia, and there are hints of a naughty little squeeze from Kazakhstan. By day 9 / 10, the Kazakh squeeze is maintained, well and truly heating up that floor, while the Japan surge goes all-out Siberian, joining their friends from the west in a hemispheric Cha Cha that ultimately congas its way right through the heart of the Arctic. PV exit stage left, arrivederci. A good few days respite for the UK and Ireland. Yeah, sign up everyone (if you’re not totally exhausted), the moves are awesome.

A good indication of how far the models have come since the weekend in terms of bringing some anticyclonic promise to the UK and Ireland is provided by the MSLP charts of the 12z EPS and GEFS, and comparing today’s day 9 charts with the day 12 charts from Sunday. EPS for the 19th, 7th + 12 days / 10th + 9 days GEFS for the 19th, 7th + 12 days / 10th + 9 days Both EPS and GEFS now picking up on a signal for high pressure over or near the UK and Ireland, for a few days at least. Looking a lot better. Much more positive signs as we approach the middle of April, and high time for the models to be finally picking up on a more solid drier spell.

Looking at the next ten days, which cover the middle third of April, t’s good to see the relevant part of the annual cycle, in the form of the springtime waning of the PV, well underway. It is happening a bit later than the last couple of years, but is striking nonetheless, here on both the 0z ECM operational run and ensemble mean, day 1 - 10 animations, the PV very much on the wane, being nibbled away by evolving mid-latitude ridges, with the core PV diminished and returning from the Siberian Arctic to the pole. This leaves us with a solidly meridional 5-wave hemispheric pattern by day 10, shown nicely on the op and mean anomalies, ridges by then through western North America, up through the eastern seaboard, Western Europe, Kazakhstan up into Siberia, and the far east of Russia. The picture for the UK and Ireland alternates from seeing a shallow ridge over the next few days, to being under the influence of an active low pressure system passing through with the trough around days 5-6, before the arrival of a better amplified ridge by day 9-10 as the more meridional pattern firms up. Day 10 provides a convenient juncture for the UK and Ireland for showing the potential for something more settled getting a bit further north to be more widely shared, op and mean again. However, it looks very much like it’s a snapshot in a slow but steady revolution of the 5-wave ridge / trough pattern around the pole, with approximately 4 days appearing to be the current phase for the ridge to trough transition, hinting at a period of drier, brighter spells of 3-4 days alternating with more changeable spells of 3-4 days. A much more normal and much more pleasant a pattern on view as spring more clearly shows its hand. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5056678

Looking at the next ten days, which cover the middle third of April, t’s good to see the relevant part of the annual cycle, in the form of the springtime waning of the PV, well underway. It is happening a bit later than the last couple of years, but is striking nonetheless, here on both the 0z ECM operational run and ensemble mean, day 1 - 10 animations, the PV very much on the wane, being nibbled away by evolving mid-latitude ridges, with the core PV diminished and returning from the Siberian Arctic to the pole. This leaves us with a solidly meridional 5-wave hemispheric pattern by day 10, shown nicely on the op and mean anomalies, ridges by then through western North America, up through the eastern seaboard, Western Europe, Kazakhstan up into Siberia, and the far east of Russia. The picture for the UK and Ireland alternates from seeing a shallow ridge over the next few days, to being under the influence of an active low pressure system passing through with the trough around days 5-6, before the arrival of a better amplified ridge by day 9-10 as the more meridional pattern firms up. Day 10 provides a convenient juncture for the UK and Ireland for showing the potential for something more settled getting a bit further north to be more widely shared, op and mean again. However, it looks very much like it’s a snapshot in a slow but steady revolution of the 5-wave ridge / trough pattern around the pole, with approximately 4 days appearing to be the current phase for the ridge to trough transition, hinting at a period of drier, brighter spells of 3-4 days alternating with more changeable spells of 3-4 days. A much more normal and much more pleasant a pattern on view as spring more clearly shows its hand.

As the great man himself promised, Kathleen is being taken back home again, to be reabsorbed within the PV by day 5, here on the 0z ECM operational run. As a result, for the UK and Ireland, a vastly improving picture over the coming week as heights build northeast from the Azores, temperatures picking up by the end of the week for a while too if the T850s are anything to go by. Before exiting east, Kathleen ejects some energy westward to help the next system along, this one passing east further north through Iceland, to set up over Scandinavia from day 6 through to day 10. The bulk of Kathleen has by then rejoined the PV from the Siberian side, helping it pivot to be elongated down towards the Norwegian Sea, fuelling the dropping of the trough down through Scandinavia, bringing the UK and Ireland into a cold northerly flow for several days. After this rather dramatic phase (following three inches of snow in west Wales last week and three days of gales in the west of Ireland this week!), Kathleen looking to help ultimately deliver something for everyone - a storm, briefly something a bit warmer, followed by some clear Arctic air and the possibility of a quieter, more standard meridional pattern as we head into the second half of April. So I guess it’s only fair to leave the man have the last words: “And when the fields are soft and green I will take you to your home Kathleen”

Attempting to piece together (as we are inclined to do!), emerging trends of the outputs from different models, here the 12z GEFS and UKMO at day 4: And then, taking it through to day 7: That is one very welcome surge in heights from the southwest early next week, resulting in a 1030mb+ high pressure cell making a visit on the UKMO. A tad optimistic perhaps and probably not that long-lasting in the event, but the contrast is striking and very good to start seeing all the same. Have a good one.

Hope you all had a great Easter and that the beginning of April finds you in good health. Looking at the models over the last couple of weeks it’s easy to perceive little or no change to the pattern and no respite from low pressure for the UK and Ireland. However, there are slow but important changes consistently creeping in to the Northern Hemisphere profile in the longer ranges. They’ve been in recentruns of the EPS / ECM too, but here we’re looking at the 12z GEFS. At day 5, not much change from the here and now, PV elongated in our direction, with the trough dropping down to our west, and anchored there due to an attractive bump of unseasonably warm heights along with a surface high pressure over the central Mediterranean. Another notable bump of heights up through central North America too, into Hudson Bay, maintaining the tight Bering Sea to eastern Atlantic alignment of the PV. By day 10, we’ve lost the heights heading up through the American Midwest into central Canada, replaced by an upper level trough, allowing the PV to fill out west, so we get low heights working down into Hudson Bay. As a result the Atlantic jet stream and trough begins to relax north, so though we still have low pressure anchored to our west, it’s further northwest and nowhere near as deep, central pressure about 20mb higher. At the same time, the loss of heights over the Mediterranean should allow easier eastern transfer of frontal systems through Northern Europe, so the setup not near as stuck. The same process continues through to day 16, so much indeed that the PV is now orientated Siberia to Labrador, with a fully fledged trough pointed down into eastern Canada. A good build in heights from Eastern Europe up into northern Scandinavia puts a roof over our heads so that the draught can only get in through the window. The gradual warming out of the Atlantic trough continues with the 1015mb isobar clipping the far south of the UK, high pressure relocating to the Azores, bringing the foundation for a greater chance of some more substantial ridging northeast in time, the models at least now showing signs of beginning to search out a route out of the rut towards a slow but steady improvement by, and more especially after, mid month. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5053938

Hope you all had a great Easter and that the beginning of April finds you in good health. Looking at the models over the last couple of weeks it’s easy to perceive little or no change to the pattern and no respite from low pressure for the UK and Ireland. However, there are slow but important changes consistently creeping in to the Northern Hemisphere profile in the longer ranges. They’ve been in recentruns of the EPS / ECM too, but here we’re looking at the 12z GEFS. At day 5, not much change from the here and now, PV elongated in our direction, with the trough dropping down to our west, and anchored there due to an attractive bump of unseasonably warm heights along with a surface high pressure over the central Mediterranean. Another notable bump of heights up through central North America too, into Hudson Bay, maintaining the tight Bering Sea to eastern Atlantic alignment of the PV. By day 10, we’ve lost the heights heading up through the American Midwest into central Canada, replaced by an upper level trough, allowing the PV to fill out west, so we get low heights working down into Hudson Bay. As a result the Atlantic jet stream and trough begins to relax north, so though we still have low pressure anchored to our west, it’s further northwest and nowhere near as deep, central pressure about 20mb higher. At the same time, the loss of heights over the Mediterranean should allow easier eastern transfer of frontal systems through Northern Europe, so the setup not near as stuck. The same process continues through to day 16, so much indeed that the PV is now orientated Siberia to Labrador, with a fully fledged trough pointed down into eastern Canada. A good build in heights from Eastern Europe up into northern Scandinavia puts a roof over our heads so that the draught can only get in through the window. The gradual warming out of the Atlantic trough continues with the 1015mb isobar clipping the far south of the UK, high pressure relocating to the Azores, bringing the foundation for a greater chance of some more substantial ridging northeast in time, the models at least now showing signs of beginning to search out a route out of the rut towards a slow but steady improvement by, and more especially after, mid month.

Hats off to the models. They had picked up on the deepening trough in the nearby Atlantic on the run-up to Easter about a week ago. Not a great outcome in terms of the weather, but the UK and Ireland in the box seat for observing some industrious cyclogenesis over the next 4 days, here on the 0z ECM op. Interesting to see the two packets of low heights dropping out of northeast Canada, the second one really packing a punch and deepening the low pressure to around 965mb, as it spins around nearby giving us all a good wallop, centred to the northwest of Ireland by Thursday. The 0z ECM mean anomaly chart for day 5, Good Friday, shows the problem for the Easter holiday in the form of the trapped trough, held firmly in place for several days by a bank of heights pushing up over the western half of the Atlantic and the other bank stubbornly holding on over the eastern half of Europe. The western Atlantic heights look to ultimately prove the stronger, migrating north to Greenland by day 10, squeezing the trough to the north through the Norwegian Sea as the eastern European heights get slowly nudged into Russia, allowing the surface low to move through to Germany, bringing the UK and Ireland into a northeasterly flow. So looking like we’ll eventually get rid of the poorly timed unsettled spell for something a bit drier and chillier. Yes, hats off to the models but I’ll definitely be keeping my hat on. At this time of the year in particular, with the full range of weather that the spring can offer, the choice of hat is indeed a valuable indicator of how it’s going. Clearly far too early for the time being to venture to the apparel shown on the left, looks like I’ll be sticking with my reliably functional fisherman’s beanie for now. Have a great day. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5050682

Hats off to the models. They had picked up on the deepening trough in the nearby Atlantic on the run-up to Easter about a week ago. Not a great outcome in terms of the weather, but the UK and Ireland in the box seat for observing some industrious cyclogenesis over the next 4 days, here on the 0z ECM op. Interesting to see the two packets of low heights dropping out of northeast Canada, the second one really packing a punch and deepening the low pressure to around 965mb, as it spins around nearby giving us all a good wallop, centred to the northwest of Ireland by Thursday. The 0z ECM mean anomaly chart for day 5, Good Friday, shows the problem for the Easter holiday in the form of the trapped trough, held firmly in place for several days by a bank of heights pushing up over the western half of the Atlantic and the other bank stubbornly holding on over the eastern half of Europe. The western Atlantic heights look to ultimately prove the stronger, migrating north to Greenland by day 10, squeezing the trough to the north through the Norwegian Sea as the eastern European heights get slowly nudged into Russia, allowing the surface low to move through to Germany, bringing the UK and Ireland into a northeasterly flow. So looking like we’ll eventually get rid of the poorly timed unsettled spell for something a bit drier and chillier. Yes, hats off to the models but I’ll definitely be keeping my hat on. At this time of the year in particular, with the full range of weather that the spring can offer, the choice of hat is indeed a valuable indicator of how it’s going. Clearly far too early for the time being to venture to the apparel shown on the left, looks like I’ll be sticking with my reliably functional fisherman’s beanie for now. Have a great day.

There’s often comment on here regarding the reduced reliability of the models past a given timeframe. 5 days is often stated as the point at which models become unreliable. Studying the ECMWF web pages, it would appear to be a good deal more nuanced than this. They publish charts showing the “Continuous ranked probability skill scores (CRPSS) of forecasts of upper-air parameters by TIGGE centres”, with the following notes about the score being used: The Continuous Ranked Probability Skill Score (CRPSS) is a measure of how good forecasts are in matching observed outcomes. Where: CRPSS = 1 the forecast has perfect skill compared to climatology - forecast beneficial; CRPSS = 0 the forecast has no skill compared to climatology) - forecast has no benefit over climatology; CRPSS = a negative value the forecast is less accurate than climatology - forecast misleading. CRPSS is evaluated by calculating the function CRPSS = 1 − CRPSforecast / CRPSclimat where: Continuous Ranked Probability Score for the forecast (CRPSforecast) is calculated comparing the Cumulative Distribution Functions (CDF) for the forecast against observations (or analyses) over a given period. Continuous Ranked Probability Score for climatology (CRPSclimat) is calculated comparing the Cumulative Distribution Functions (CDF) for the forecast against climatology over the same period. Hersbach, H., 2000: Decomposition of the continuous ranked probability score for ensemble prediction systems. Wea. Forecasting, 15, 559-570. Here’s the link to the paper that ECMWF cite: https://journals.ametsoc.org/view/journals/wefo/15/5/1520-0434_2000_015_0559_dotcrp_2_0_co_2.xml From the cited paper, excerpted: Instead of two options (event occurs or does not occur), the range of the parameter of interest is divided into more classes. In addition, the RPS contains a sense of distance of how far the forecast was found from reality. For a deterministic forecast for instance, the RPS is proportional to the number of classes by which the forecast missed the verifying analysis. Although the choice and number of classes may be prescribed by the specific application, the exact value of RPS will depend on this choice. It is possible to take the limit of an infinite number of classes, each with zero width. This leads to the concept of the continuous ranked probability score (CRPS)…This CRPS has several appealing properties. First of all, it is sensitive to the entire permissible range of the parameter of interest. Second, its definition does not require…the introduction of a number of predefined classes, on which results may depend….Finally, for a deterministic forecast, the CRPS is equal to the mean absolute error (MAE) and, therefore, has a clear interpretation. This is useful because: 1. Rather than the (subjective) right or wrong, we have a graded measure of the extent of deviation from the realised outcome. 2. Any score above zero demonstrates some forecast skill over the assumption of climatology. Here are the CRPSS charts for T850 and 500hPa height for the Northern Hemisphere incorporating data for the winter just ended. At day 5, ECM attains a score of 0.62 for T850 and a score of 0.72 for 500hPa geopotential. The score for heights is higher at day 6 than that for T850s at day 5. The timeframe above the 0.5 CRPSS level (where the forecast matches the observed outcome in more instances than it doesn’t, compared to climatology) corresponds to between day 6 and 7 for T850 and between day 7 and 8 for heights. At day 10, the score is 0.28 for T850 and 0.33 for 500hPa height. Both those scores continue to offer reasonable “value” at day 10, though to be fair, at a level less than half the value offered at day 5. By day 15, the score is around 0.12 for T850 and near 0.15 for 500hPa height, much lower, but still above zero so exhibiting some skill when compared to just assuming climatological norms. The ECMWF appears to put some store in the 0.25 or 25% level, as this is what they use to illustrate the improvement in skill over the last 25 years. This graph is great. It shows the lead time in days before the score drops to 25% and is for T850. The model has the same level of skill at day 10 in 2024 than it did at 5.5 days in 1998. Noticeable too that winter T850s appear to be handled better than summer ones, probably due to the winter PV, with typically fewer meridional episodes and less dramatic fluctuations in the winter as a result. In summary, in our parlance, the models are more “reliable” for longer for predicting heights than they are T850s. For heights, these are typically of sound merit all the way out towards forecast day 8. The reliability drops off steadily from day 0, there is no sudden drop at any point and the forecasts maintain some predictive value when compared with climatological expectations all the way through to day 15, which is presumably why this timeframe is catered for in the outputs. Lastly, and perhaps most excitingly, the models appear to be better now at day 10 than they were 25 years ago at day 6. This all fits very nicely with the general narrative surrounding their use here in the model thread. Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5049286