BlueHedgehog074

Does look as though that moody Low South-West of the UK on that FAX chart could slip through to our South. Not too round that Low, has look that it could very well slide (Edit: although did just notice a post above that the Low is quite powerful, so guess we’ll see how things continue to go regarding that cyclone). Hopefully a lot of us cold weather fans can squeeze something white out of it, but can be fine balance these things. Also had my first proper frost this morning (still lingering in parts). So the colder weather from the North that’s been modelled fairly well in advance has definitely arrived now

The upper Vortex above getting squashed like a pillow.

Looks like that Low on the GFS heard @northwestsnow’s concerns (at least for now)

I do believe so too. Best model there is the NAVGEM…

Just a comparison from numerous operational models below at 168 hours with respect to the tropical Low. All from 12Z runs. GFS ECMWF UKMO GEM ICON JMA NAVGEM Main thing to note first is that, as was to be expected, there is noticeable variation as to how they program that stressed-out Low out West/South-West. GEM and ICON have it just to our South-West, and rather stretched with the Lows on both ready to slide to the South of the UK. GEM does have stronger heights around the Central and Western Greenland area with 2 Low Pressure centres with that Low. The ICON, on the other hand, has some much lower heights over Greenland. Some of the ridging and pockets of higher heights the ICON has surrounding Greenland are still just enough to suppress the Atlantic Low to the South/South-West of the UK. Even though it does feel a bit on edge. UKMO, while it did feel even more on edge as to how far North that Low could have gone, manages to just about push the Azores/Atlantic Low through the Channel. Despite it having an area of lower heights just South of Greenland, the higher heights over Greenland extending East-South-East towards Scandinavia seemed to be enough get that Low to go over to the far South of the UK. Running back through the last few frames of the UKMO on Wetterzentrale, you can see that the Low does try to push slowly North-East against the ridging to the North of the UK (perhaps partly thanks to that Low Pressure area over Iceland that would probably try to swing the Southern UK Low, North). Nevertheless a great run at 168 hours for bringing a big fall of snow to Southern/Central parts of the UK. You could also argue on the UKMO that it’s not one strong, organised, big, stormy Low that many of the other operational models have above to our West/South-East. The GFS was rather slow with the Atlantic/Azores Low progression South-East to the South of the UK in its later frames. But you can see at the timeframe above, it holds that annoyed Low quite far West towards the Western Atlantic compared to many other models. There is a shortwave that develops on the Low’s Southern flank which would swing East through the South of the UK against the strip of reasonably high heights to the North of the UK extending Esstwards through Scandinavia. Again, while the UKMO did feel quite nerve-racking with how it handled those Low(s) out in the Atlantic, these 4 models I’ve talked about are ones, despite varied timings, pushed Low Pressure through to the South of the UK. Questionable whether the UKMO would keep the cold going (at least probably for Southern UK), the ICON, and especially the GFS and GEM which built a ridge in the Atlantic behind the sliding Low, would prolong the cold further. The other 3 models from the ECMWF, JMA and particularly… the NAVGEM, have the Atlantic Low at more of a Northerly latitude more directly to the West of the UK (the Low wound up and bloaty on NAVGEM and JMA). The shape and latitude of the Low on the ECMWF makes it look unfavourable to slide East through the South of the UK. Patchy low heights to the North-West - one area over Greenland, and a couple of areas South of Iceland - doesn’t help. Even with the ribbon of higher heights stretching West to East (in some form) to the North of the UK, the Low swings North-East. But did lose a lot of energy as it crossed the UK in later frames. Low still struggled a bit against the modest Northern/North-Eastern UK blocking at that time. Behaviour of the upstream pattern to the West of that Low, where a ridge behind that Low was forced to head East into South-Western Europe, encouraged the Jetstream to lift further North. JMA keeps the Low blown up on approach to the UK bringing blustery South-Easterly winds ahead of it. A lack of high heights directly to the North of the UK, so not much in the way of forcing from the Greenland and Iceland area to push the Low through to the South of the UK. Plus, the Low is contending with a build of higher heights across South-Western Europe. Low is not disrupted and squashed - can’t slide properly. In spite of that, you’ll notice the Low is sorta sandwiched between a ridge of High Pressure in the Western mid-Atlantic and a South to North aligned ridge over Scandinavia. The role of these 2 ridges I think contributed to the Low not just quickly smashing North-East through and to the East of the UK, but it rolling over the top of the South-Western European ridge through the UK and then back South-East into the Northern tip of France (just a bit of a one-off example below. Pulls in a North-Easterly flow over whole UK). Fair to say as well that, mostly, Northern UK areas retained a flow between the South-East and East as the Low pushed directly through the UK. Despite a narrow strip of a ridge/wedge to the East of the UK on the NAVGEM, it is probably the least favourite of the lot regarding the chances of the Low being able to slip to the South of the UK. A lot of bluey low heights ganging up to the North of the UK across the Greenland area. For the cold weather fans, it makes the upstream pattern close to our West unappealing. There is a developing little Low to the North-East of that main Low also on the NAVGEM. These Western Scandinavian shortwaves/Lows can cause extra complications and issues for getting stronger cold South-West through the UK sometimes. Can weaken some of the blocking to the North/North-East of the UK and at times pull Atlantic Lows in more of a Northerly direction. Is hard to be fully sure, since NAVGEM only goes to 180 hours (maybe a good thing), whether the narrow, modest, ridging across Scandinavia would help still put pressure on that Low out West making it disrupt at all. Having said that, I think GFS, GEM and ICON look to be the most preferable options for their handling of the Low. (Especially if you’re after further cold without much in the way of milder interruptions). Interestingly, the GEM is the one that looks the best in terms of high heights to the North-West of the UK. UKMO is certainly passable I feel despite the wonky(ish) pattern upstream. Plus would provide a great snow event for some. In some ways, that Low, depending on its specific track and behaviour has a real possibility of delivering white surprises for quite a number, even if transient (which I appreciate a lot of us would just love an all snow event). Some people though would feel it would be better if that Low never saw the face of Earth! I do definitely feel this proves that the models haven’t got this Low nailed down yet. Liable to many more adjustments. It could reach the UK, it might not. It could unleash milder conditions, particularly across Southern UK. But could just get colder again later. I also admit to getting carried away analysing the above operationals, especially the day chosen being outside the reliable timeframe currently. Additionally, it becomes more about the details at that range. It is going to be a fascinating next few days to come at least.

Models do feel as though they really struggle in these situations, particularly with blocking outlooks and especially Lows that try to sneak in from the South-West of the UK. Certainly a fair bit for the models to sort out. Before the bother of the Low, still wouldn’t rule out any snowy surprises within the next few or so days (except for the likely coastal and Northern UK areas). This Thursday for example could, while probably unlikely, still produce something a bit more widespread, even though it might just be Northern and some Western parts of the UK that see some sleet and snow. I guess we’ll have to see. Quite a nice area of snow there for Wales and many Central parts of the UK extending into Southern parts of Northern England. Likely to change again, but a little boot Southwards could nonetheless discharge the M4 snow shield.

The operational models do love to keep many on their toes

I see what you mean Am still admittedly becoming more familiar with Cold Air Advection (still learning, so could be incorrect with how I’ve done the above), but have tried to illustrate the processes with the arrows In the closer period, it looks like a cold Northerly will be setting in from the North today with some very cold nights with a chance of thick frosts. Chances of snow probably increasing further into this week, particularly this weekend, as the pressure pattern over the UK looks to become more cyclonic. Though most of the wintry precipitation for the next few days probably mostly reserved for Northern UK areas and down some Western and Eastern coasts. I suspect this will still change (snow chances can even rock about at very short notice), most particularly later into this week. There is always the prospect of models under-estimating wintry precipitation in some of these setups. And a bit of a snowy tease for Central/Eastern Central areas later on Sunday: But… to be honest, this amazing invention below will give 100% accuracy whether white stuff will fall from the sky:

Having gone through the whole run, the GFS 18Z could fool you into thinking that this is a Winter that never dies! For a bit of fun too, the GEFS 18Z ensemble mean (few examples from 144 hours up to 282 hours), generally keeps the blue and purple beast caged up on the other side of the Northern Hemisphere North of Greenland. It expands a bit, but it looks like the Vortex just doesn’t want to chill out in Greenland and North-Eastern Canada.

It is amazing that in relation to this morning’s 00Z run… …the GFS 18Z Pub run now goes for an Easterly/North-Easterly setting in during Saturday… Examples from both during mid day this Saturday. Does show that even within a few days (excluding the general pattern they’re showing), the models are making quite a few changes.

Not been through the ensembles myself, but that’s good to see that many of them make the Low less strong, even though a stronger Low could heighten the chances of blizzards. But likely more of a riskier scenario as an angrier Low could go further North bringing milder air with it, unless maybe there’s enough forcing from ridging to our North-West and/or North/North-East to prevent that happening. Also know what you mean regarding the worries of the operational runs’ modelling of that Low as, sometimes, they can lead the way or pick out trends the ensembles are slow to catch up on. Mind you, that’s not to dismiss the idea that it can be the other way round too. Hopefully will get some better clarity in next few days what that fella will do. Personally, should it reach the UK, I feel, like a few others, it’ll take Southerly latitude with the cold air staying in place. Will be interesting to see what further runs and ensemble charts churns out. Looks like at least the next few days will be getting colder with some wintry opportunities at times. While some parts may not see much sleet or snow (and this can still change), the rest of this week does provide something for many to look forward to

Indeed. In fact, compared to even the GFS 00Z ensemble mean, the -5*C 850 hPa temperature line is a fair bit further South-West over the UK. And the mean Low to the South West has quite a squashed, slidey look to it: The above from the 12Z GFS mean compared to both the 00Z and 06Z GFS means below: GFS 06Z mean 00Z GFS mean All for Tuesday lunch time next week.

With the scenario of that approaching Atlantic Low from the South-West being a fair while away on the ICON, the models still won’t quite have a definite handle on that Low yet. If the run went out further, the Low would probably at least produce snow as it runs into the chilly air over the UK, particularly in inland areas, before the possibility of milder air winning out. Maybe staying colder further North perhaps (but hard to be totally sure). In these sort of frontal battleground situations, too, -5*C or colder 850hPa temperatures won’t always be needed for snow. Known times from these setups before, to have falling sleet or snow with even just -1/-2*C 850 hPa temperatures. (There’s more than the 850 hPa temperatures when it comes to determining if sleet and snow will reach low levels).

Looking at various operational models at 96 hours, and they all showing well the blocking High over the Greenland/Western Iceland area combined with the Scandinavian trough to the North East of the UK. With some of that troughing reaching South-West towards the UK. Shows well the established cold conditions that will have invaded the UK from the North earlier this week. GFS 00Z ECMWF 00Z UKMO 00Z GEM 00Z Considering the timeframe we’re dealing with, wasn’t expecting much differences between the models at that time. You could argue, such as is the case of the Scandinavian troughing, that it’s a touch deeper (slightly darker blues) on the GFS, ECMWF and GEM compared to the UKMO. GEM is perhaps the furthest West with the light Northerly over the UK on Friday, but all essentially show some very cold weather. Cold weather enthusiasts really are in an interesting place. And while the details are still likely to change, nice to see the operational models make that mad Low to our far South-West less of a trouble maker. Many either significantly squashing and sliding the Low towards/through to the South of the UK, or some just keeping it just slow moving to our South-West. The Icelandic ridge (or wedge I suppose) seems to help put pressure on that Low and make it squashed and pancake-y on some of the models, such as in the example below: One way that can help keep the cold weather going through the UK (even though that Low could provide some snow chances for the UK at some point, so not a totally enemy for cold weather fans). This might have already been posted below, so apologies if so, but the 00Z ECMWF ensemble mean at 192 and 216 hours shows that bad boy (stormy Western Atlantic Low) staying squashed keeping the UK in an Easterly to North-Easterly flow. A slidey look it has about it, although with the mean of the lowest pressure out to our South West. In regards to extending this cold spell, the models overall are in a good mood this Monday morning. I think that is the thing, to be fair, as longs as their is some kind of High Pressure somewhere between the North-West and North-East, possibilities of cold weather can continue to pop about.

May not yet be Christmas, but Santa sure loves to deliver a lot of cold and snowy goodies for the cold weather enthusiasts on these GFS pub runs. Interesting watching the excitability that unravels on here as some of these runs provide the dreams many want. Some of these dreams very well coming true with the cold and, at times, wintry weather that this week, and perhaps even the one after, could easily offer.

Though I’m guilty of using this model quite a bit lately (mostly for fun), to prove your point regarding the swings that occur at timeframes beyond 96 to 120 hours, the 12Z NAVGEM goes a much different route to how it handles that tropical grumpy spinner later this week in relation to models such as the 12Z ECMWF: The Greenland ridge dangles quite far South occupying the Northern mid-Atlantic. This keeps the angry spiral (storm) locked up near the coast of Eastern Canada on the South-Western side of the Greenland ridge. At best, it makes little shifts Eastwards. Due to what happens upstream, and probably due to some of the high heights South-East of the Scandinavian Low, the UK stays under the chilly Scandinavian trough for a while. Very wintry looking for the UK it looks. Compared to the 12Z ECMWF below for a similar time period, that stormy Low to the South-West of the UK doesn’t get trapped that easily, though just slowly makes it’s way East/North-East towards the UK. Except at the start, the Greenland ridging is less influential. The Southern flank of the High isn’t as amplified not dangling down as far South through the Northern mid-Atlantic. The angry Low has an easier time escaping further East. That angry Low could clearly be a friend of snowy weather for the UK, at least some areas of it, if it behaves itself and not go too far North. But not certain enough yet as to how exactly it behaves. Despite the model we’re dealing with, it can be hard to admittedly place much faith in the NAVGEM. It’s solution kinda feels like the odd one out of the operational models, so probably unlikely (confidence would increase a bit should GFS 18Z become manipulated by the NAVGEM. And then have other models following along with growing ensemble support). But I think it’s trapped stormy Low idea could be considered an option. Just like how the GFS in the last few runs has been powering up Low Pressure around the Iceland area. The above comparison, however, is just a way to prove that operational models can vary wildly beyond certain timeframes - at least sometimes. Depending also on the pattern the models are dealing with. I guess we all all have our own instincts and desires as to how we feel things evolve. Plus we can all see things in different ways when looking and summarising model output, which can then lead to some highly varied analysis.

Even the 00Z NAVGEM wants to provide Incredible Hulk powers to the tropical Low to the far South-West of the UK later into next week. Just how many Domino’s pizzas has that Low had? Appears to bottom out around 955mb. I do personally think as well that the models at the moment are overdoing the moodiness of that frustrated Low. Suppose will have to see how it continues to be handled on the models. Perhaps to something else to mention is if you play back the animation of the track and travel of that storm, it looks as though of the run went out further than 180 hours, it would quite likely head East through to the South of the UK. In the nearer time frame, nevertheless, looks as though the chilly Easterly flow in the next couple of days (perhaps still bringing a few showers over Eastern UK), will become terminated by a Northerly flow during Tuesday with colder conditions descending upon the UK from the North along with an upper trough (blue-y areas) around the Arctic/Scandinavian area dropping South and South-West towards the UK. The Northerly nearer the beginning of the week at first likely just bringing wintry showers to some Northern areas such as Northern Scotland and down some Eastern and Western Coasts (possibility of the Pembrokeshire Shower dangler). As the heights look to lower further into the week with the flow quite likely turning more to the North of West (exact positioning of the surface features into late this week may not still be fully decided), then there is a prospect of more widespread wintry showers and longer spells of rain, sleet and snow. Northern areas - not exclusively so - probably seeing the best of the snowy conditions, but again a chance for anywhere to catch some white stuff. Where skies clear at night, could lead to some fairly thick frosts in many parts of the UK. Especially where winds become slack, which looks very possible this week with shallow-looking surface Lows around/near the UK later into the week.

A little focus on the current chart from the 12Z GFS at 00 hours, it is quite incredible the ribbon of High Pressure that is occurring to the North-West, North and North-East of the UK. A lot of blocking. Not bad going at all for the beginning part of December. Don’t see this sort of thing often!

Getting around to having a quick peep of the GFS 06Z, while it may be kinda disappointing that the Low/Through dropping down from the North later next week circulates back further North with the pattern becoming Western based for a time (latter of which still can’t be ruled out), acquiring a buggy and teddies from the pram store wasn’t really worth it. Plus, the 6Z run did renew ridging of High Pressure out West in the Atlantic forcing Atlantic Low Pressure South-East into the nearby continent with a chilly flow establishing from the North-East (despite 850 hPa temperatures being underwhelming). General pattern seems to be set with blocking to our North-West (length perhaps uncertain), and a chance of Lows dropping down from the North. Without worrying too much how Low Pressure might affect things later into next week and into the week after, there is at least a fairly good possibility of some widespread wintry weather (snow-wise) around the mid part of next week. That seems a little more certain at the moment, though not 100% definite. As has also been spoke of before, it’s not impossible for cold and/or snowy spells to become stamped-out on the models even as close as 48 to 96 hour mark. Which would then mean the cold spell would have never really existed in the first place (bearing in mind we’re in a chilly period currently), particularly since it’s only the weather that can decide what it wants to do, whereas the models just predict what could happen.

Although there’s still some details to resolve for next week, next few days from the models shows the UK continuing to being influenced by a chilly Easterly flow with blocking to our North. As with this setup, Western and North-Western areas, especially, seeing the best of brighter, drier, spells. The Easterly flow bringing some showers at times over Eastern/North-Eastern areas (few could reach Central areas too), some of which, particularly in heavier showers, being wintry over the hills. And maybe, especially on Sunday morning/early afternoon with some patchy -5/-6*C 850 hPa temperatures over a wider part of the UK… any showers around that time could be a little sleety to some lower levels too, with hilly areas over Wales and some higher Northern England peaks probably seeing the best of sleet and snow from the showers. Does then look to be the case of High Pressure shifting into the Greenland/Iceland area with the possibility of even colder weather coming down from the North and North-East. Though how cold and the amount sleety and snowy weather there could be depending how the trough of Low heights over and to the North of the UK behaves. But even if it does get stuck to the North for a time (and not too far West to the North), there still looks as though there could be enough cold air wrapped around it to provide sleet and snow to numerous places. Probably would say, though, the further North in the UK you are, the higher the margin for error there could likely to be. Still does all depend how the models continue to handle the behaviour of both the Greenland/Iceland High and the troughing coming down from the North later next week. All set! And hopefully won’t need it, but just in case:

https://community.netweather.tv/topic/98032-model-output-discussion-moving-into-winter/?do=findComment&comment=4749524 Managed to find your original post (from page 160). I understand the 12Z ECMWF caused quite a scare for a few, particularly as there’s no guarantee how very cold and/or snowy things could become. But unless its outlook of more Northerly tracking Lows and milder Southerly flow in FI starts being picked up by other models and it becomes more of a trend, then would just leave the toys and prams untouched for now. There’s always going to be some up and down emotions on here, but if we can please all, let’s keep it friendly in here. Thanks. After all, there has been a lot of great, informative posts in this thread (room for fun posts here, too, as longs they’re not rude and are mostly on topic). It would be a shame to ruin that.

If not already posted then I thought you really needed to know what the noble NAVGEM was up to this morning. Just for fun at both 144 and 180 hours below. Really do love this model… While it might not sit directly over the heart of Greenland, the block is nicely positioned and orientated with the upper trough dropping South/South-West through the UK. End up with a a high quality unstable cyclonic North-Easterly flow - that very cold 850 hPa to our very nearby North-East over the North Sea and Scandinavia looking ready to swamp the UK. I imagine some heavy snow showers pushing South-West through the UK from the North-East.

Probably not much more to contribute (and sorry if this has been posted), but the 6 to 10 day 500mb NOAA/CPC anomaly chart just reinforcing the good chances of seeing the current North-Eastern UK blocking become a king High over Greenland. Upper flow originating from the North (Greenland/Arctic area) down towards the UK with the lowest of the upper heights to the South of us. While surface-wise, this won’t reveal the fine details, there really is a lot to get the cold weather fans flying around like buzzing bees Climate Prediction Center - 6-10 Day 500mb Outlook WWW.CPC.NCEP.NOAA.GOV Will, though, take a few more days before the certainties of where and how widespread any wintry precipitation will be into and during next week (depending also where the Lows are likely to end up). But as many say, it feels like a festive start to December Plus, I sneaked into Terrier’s house, swiped all 3 sledges and his receipt, and took them back to the shop for a refund. So there’s no reason to be worried. Anymore

You know things are interesting for the cold weather enthusiasts on the models when the number of members viewing the thread reaches 3 digits!

Will probably find, as is the case sometimes with these things, some kind of half way solution between what the ECMWF/GEM shows and what the GFS shows. Nice to see the GFS showing a bit more of a cleaner evolution to Greenland heights though.