Uncertainty

It’s still fun to get excited about it though pal. Make your own judgement regarding whether it’s actually going to happen. Those excited posts are part of the lifeblood of this forum, just as the ‘winters over’ memoirs after the Inevitable 0z backtracks appear are! This pattern is more than just a one-run GFS wonder though. But, as you say, it’s a long way off being ‘in the bag’. And any exact details regarding surface temps, precipitation types and amounts are moot as this stage.

Yes GEM trending more amplified after a soggy Wednesday, even though it develops the mid week low it’s the upstream amplification a few days later that’s key to the post Xmas day pattern. Regardless of Uppers, PPN etc, the fact that 3 successive GFS, the GEM and to a lesser extent ECM op and control get to this point is significant. Given the strat support for a Scandi trough we can now say that some manifestation of this broad pattern is probable. The question is how high can we get this ridge to go? In other news... Positive temperatures in the strat alert! That is less than two weeks away and a consistent signal (of course not always to this extent...) Ahead of schedule surely? No complaints from here though if this run verifies, at either atmospheric level!

GFS Looks really, really good on the anomalies Day 8... Day 10! “It’ll never happen” They said Leicester would never win the league...

Trop and Strat jets mirroring each other in the Atlantic sector on the back end of the 18z Polar Northwesterlies it is then! Plenty of warming too. It’s hard not to get excited by the output at present. @Catacolnailed it and as I’ve said before. If the good weather folk beat the Scroogey seasonals with a split SSW for Jan it’ll be a real coup. But don’t forget, each synapse is effectively a quantum bit. They’ve got a way to go before they can outthink the peoples lol. If we do get this SSW, surely the big +EAMT is playing a big part. Finally, this our bog standard Christmas week singularity anomaly Except, the colours seem to have swopped

Yep but need it south on ALL major models tomorrow to be safe, especially and obviously the ECM. Bear in mind GEM also has the secondary low and lots and lots of rain. These two models together represent a significant element of NOAA and, presumably, Exeter’s musings...

Glad you think that Ed, do you think that that low that got sucked to the to the SW, rather than sent through the UK, is propping up the high? E.G do you feel that trapping it to the SW is necessary for the ridge to gain enough amplification to produce 18z esque outcomes? You can see the same low pressure has become rather convoluted over the Azores, right where the high normally resides. All the good ens I’ve seen have the ridge riding over that low and allow it to build well Northwards, resulting in a sort of super-topler. Those that send the low through the UK as a well developed system never seem to have enough amplitude in the long wave pattern to sustain the following ridge to anything more than ECM’s damp WNW squib.

Could we even link up with @Griff’s ‘old friend’ the Arctic high? It sure feels old given how long it’s final destination has been shrouded in mystery. That’d be a cold lock in all right. A rather large part of me feels like the above chart verifying is impossible, but I’ll enjoy it all the same

EC clusters actually quite revealing tonight. after days of too many or too little to make sense of. The headline is: a big fat euro trough. Or at least, for those feeing pedantic, a lack of persistent euro heights. This straight away tells you there is interest in the charts for those of a cold loving disposition. A slug is a hopeless, persistent winter waster and flood maker. It’s absence paves the way for low pressure to dive into Europe, the angle of which determining the surface weather we receive. On the latest GFS iteration, given the better amplitude, we are surely expecting an even bigger and straighter drop of the low into Europe day 9 and 10? Sure looks that way! PS this is becoming a real saga... if the ECM doesn’t drop that SW low and associated lower amplitude ridge in the morning then surely it has this nailed. If it does finally give it up then charts such as those above become eminently possible!

It’s still there pal, this Late December cold pattern has been progged for months by the seasonals, for weeks and weeks by the EC46 and for 4/5 days on the ENS/EPS. It’s hardly an aberration. It’s still not in the bag though so don’t pop champagne just yet! Don’t want a Jan 19 rerun!

This really has been a tricky pattern for the det runs to nail down. There is as much spread in the strength and amplitude of the incoming Atlantic ridge tonight as there was 3-4 days ago. Some GFS ensembles have prize winning blocks, representative example perturbation 9 Which isn’t dissimilar to the Icon which has been separating and cutting off the low to the south west consistently for days now... A good size cluster of the GEFS resemble the mean, which in itself is more amplified than the 6z Recent ECM ops resemble this mean but beforehand they have powered the low to the SW through the UK bringing heavy rain and, presumably, local flooding This unpalatable scenario is also linked to a weaker upstream ridge and less amplification of the Eastern Seaboard. This could lead to a toppler and west north westerlies behind at best. The good news is the UKMO says absolutely not to this scenario, tracks the first low to the south of the UK, doesn’t really develop it and cuts off the second low, here at 120 The low to the southwest gets trapped under the building ridge to the west, I think the 168 would lead to a cold UK high and a frosty, seasonal Xmas day many on this forum and beyond would happily settle for. With potential for this to move NE with time and keep things interesting. As noted by @Allseasons-siThe GEM after some fodder has produced an interesting outcome at day 10, deja vu to the evolution at the start of this amplification journey we are on, back in V late November, a ridge building through the UK to form a wedgey Scandi high. Another positive solution, if not well supported as yet. So lots to like for cold seekers out there so far this evening. Let’s hope the ECM sacks off this nasty second low and gives its best GFS perturbation 9 impression. We all know that if it does it’ll kick off in here and, before Christmas in this vile year, what a tonic that would be.

Feb I’d wait until the monthly outlook comes out tomorrow, they’ve been hinting at a cold snap in some regard back end of the month for the last few updates. Hopefully they’ll reinforce that tomorrow. Vis the 18z ensembles... Not far off a mean North Easterly there. Good concordance with the EPS at the same timeframe Noaa also ‘on board’ with the blocking signal. We’re 3 for 3! Gonna need more than a sofa to hide behind in the morning to watch the 0z come out though... there’s more twists to come I’m sure...

I think you’re both right here. The dream scenario this winter always was the blocked December predicted by the seasonals verifying then we get the big mid Jan SSW with correct split location etc and a Feb91/10/18 redux. The fact this scenario remains possible is wonderful in itself. In my view if we don’t get the SSW we get VI which means zonal winds get flushed down followed by zonal winds getting flushed down. So a Feb2020 redux. No thanks. I’d take a short period of zonal flushing (?!?) to get two genuine cold spells this year. Hell most years I’d take a frost and no red rain warnings thank you very much!

@Zak MInteresting to see the JMA evolve like that, I had only looked at the 192 I have seen countless charts like that topple and given the WAA wasn’t massively vertical I thought this one would too, but then we end up with a beautiful chart Not quite as beautiful as the latter stages of the Siberian high show on the GFS though! Its amazing how the snow cover advancement through November has finally, after such a sweltering year, cooled the Siberian land mass. According to the good Dr Cohen this has given the Siberian high more vigour this year and indeed, it’s already perturbed the SPV enough to allow us this chance. Even on the 18z you can see how it has linked with the building UK high to form an Uber block. You can see the link/up around Finland there at day 10. The Arctic high hops in there too. This evolution is perfect for the long game because... As @CreweCold rightfully asserts, this is critical to pump big problems into the stratospheric PV. Will the Siberian high gather itself once more to strike the fatal blow? The seasonals say no but the weather folk’s hearts and knowledge say yes! It’s human vs algorithm for the fate of mid winter!

Took your advice Scott and took a few days off the models due to the inevitable fluctuations in the modelling in resolving the Arctic high, extent of Atlantic ridging and the size and shape of the trough exiting the UK - the latter of which gave NW England 80, yes 80 hours of continuous rain on the 13.12.20 GFS 18z The present GFS iteration looks like an Xmas day UK high which again would be a fine call Scott. I’ve learnt loads from your input recently mate so keep it up! None of the above model tribulations have actually been fully resolved but this evening’s trends look good, we have: - A stronger Atlantic ridge on the ECM mean at days 8-10 vs this morning, with a better trend for Euro troughing in the extended as BA alluded to - apparent on the GEPS too. - A glorious ECM op which, despite @Steve Murr’s long shot can’t be discounted. PS Steve whilst I totally understand your family/work based reasoning (am a working single dad myself) to post less, the knowledge, passions and enthusiasm for weather that you and others on this forum share has helped inspire me to learn about Meterology. Any and all input you are able to continue to give, however infrequent, is very gratefully recieved! - An improved GFS on the 12z, with these improvements showing up early in the run serving to squash the troublemaker low southwards and build better heights in behind. The southeast almost hits the Jackpot at day 9! Finally a note on the EC 46, the surface temp anomaly was quite striking for weeks 3 and 4 Week 3 Week 4 Cold becoming quite extensive over NW Europe. Adds credence to the ‘the best is yet to come’ from this fascinating festive setup we have.

Yes @Allseasons-siStrongest signal yet for Atlantic amplification from the GEFS. But can we trust it? Not yet, if this is to come off we at least need a string of EC ops to go with it soon. Last night’s effort wasn’t bad but this morning’s is ugly and has weak, transient amplification and a continuation of the wet and mild pattern we have now, perhaps focused a little further north with weak ridging over the south. A representative example of this solution from the GEFS Notice how the next low Leaving the states is already toppling the ridge ahead of it The jet doesn’t even amplify to southern Greenland and hence the low simply powers through the Atlantic with our name now Stamped firmly on it. What those of a cold persuasion want of course is for the Northern stream jet to amplify sufficiently to allow a more significant high to develop to the NW. Here you can see the jet has moved Northwards up the southwestern coast of Greenland, allowing cold air to flood south. Despite the improved signal on the 6z there are very few that build a long lasting ridge to the NW so a severe, long lasting cold spell is not signposted at present. As BA has rightfully mentioned, there’s more than just the MJO at play here, the Atlantic SSTs don’t fill me with confidence vis the strong Atlantic ridge and there are countless examples of the GEFS at day 9 overplaying Atlantic ridging, the 18z from last Thursday a case in point. Indeed looking at the EPS/GEPS the ridging looks transient, but a 2-3 day cold ‘snap’, especially for Northern areas is very much in the possibility space around the 23rd, so plenty to keep coldies (or ‘not southwesterlies’ like me!) interested over the festive period.

Yes clearly not BA but I’d still rather have the pattern they broadly suggest and be in with a chance. Perhaps I should have suggested said White Xmas for ‘a few’ not ‘many’!

Good evening all Now that the dust has settled on our latest disappointment, it’s now a question of whether our long hoped for December cold spell has been dashed or delayed. I am going to present some evidence for the latter, with the firm caveat that anything interesting to those of a cold persuasion remains at least 10 days away, and given recent history remains hard to put any ‘real’ faith in. Nevertheless, with the AO and NAO set negative for the next few weeks at least, we only need one burst of Atlantic amplification to tap into the cold air waiting to the North (it sounds so simple doesn’t it). The first factor to consider is the movement of the MJO. After meandering weakly between phases 4 and 5 for what seems like an eternity, the GFS suite today finally takes the signal towards phase 6 at reasonable amplitude. No surprise then to see this manifesting in more colder solutions appearing at day 11+. The CFS too with a push across the West Pacific The ECM, unfortunately is much less keen and kills the signal off. So, supposing the American models have got this sussed, where does that leave us with our North Atlantic amplification push? GEM and GFS on Christmas morning: Notably good agreement at 300 hours out, a nice pattern then with good heights to the North West and lower, but not especially low heights over the Low Countries. Still no firm evidence of a big block in the Atlantic and associated WAA, so no Omega style Greenland block on the menu at present, but higher, stronger heights than usual seems likely. This is evident by viewing the pressure and heights at 500mb, rather than using anomalies. This paints a somewhat less exciting picture. Still a mean westerly flow but weak. There are some good members in there though, the control being a prime example. But if the above MJO argument holds, then the ECM should be flattest, right? Well the ECM was the pick of the day 10 op for me and has been discussed above. It wouldn’t take much for it to turn cold if that low to the south west stayed elongated and rolled under the the developing high to the NW. If we are to get a memorable cold spell, this is one of the ways it might manifest itself. But Was the op a flash in the pan? An ECM op day 10 garden path special that we’ve been conned by so many times in the past? Not according to the EPS, I’ve delved through those individual EPS again for the big day and wow, still genuine signs for high pressure to the Northwest, low pressure to the East. Dan and Nick have generously posted the day 15 temperature and height anomalies above but they mask some phenomenal members roughly one sixth of which produce a stonking Greenland high with associated euro trough and thus a white Christmas for many parts of the UK. Another 15 or so members have high pressure to the west and a cool, seasonal NNW flow. It remains the case as I’ve said before that the traditional flat zonal Xmas pattern is not well supported at present. The cause of the ECM’s amplification signal in spite of its weak MJO signal could be more +EAMT or perhaps the effects of the stronger signal for a weaker vortex but it’s not clear to me. I’d love to hear anyone’s thoughts on that as my personal view here is that getting the MJO into phase 6 with good amplitude is the crucial variable here. The future of the strat is highly uncertain, but for our period of interest it doesn’t seem to be strengthening in time to kill a potential cold spell, it’s still reeling from the moderate wave 2 hit it’s presently receiving. Those bias corrected CFS member which do go strong do so in January. We may well see VI in early January, the seasonals seem to be seeing it too but that’s for another day. In summary like it or lump it there’s another chase/opportunity/pipe dream on and it might be our last/best chance for the winter.

I get this Mike and the latest Seasonals are a kick in the teeth and likely to be correct but they absolutely can’t discount a shorter cold spell within the broader westerly pattern. Moreover, Glosea didn’t get the Feb 2018 BFTE event and ensuing blocked early Spring right.... **Disclaimer - it has sadly got most things right since, including this summer gone... However, there is no chance in the next decade that seasonal forecasting will be able to definitively tell you the weather on a particular day. Hell, the ECM can’t get day 9 right most of the time and how often is the 144 UKMO wrong? Seasonal forecasting is powerful in Winter and I imagine very useful for planners, government departments and gas distribution managers but they can’t and won’t be putting the remit of this thread out of business any time soon pal. That said the picture for Jan / Feb has been grim on the seasonals since August hence mine and other hope to cash in on the blocked December. All eyes then on that MJO passage later this month, should that fail... there may be dragons ahead

Whilst I understand the frustration of many forum members tonight, especially after the promise of yesterday evenings GFS suite, it must be stressed that the end of December is not certain to be a zonal washout with a slug and straight line southwesterlies. This in itself is a bonus for the Christmas holiday. Even those far removed from the weather obsessed folk know the singularity for the Christmas period: stormy, wet, mild and miserable. Here in the valley of the Cumbrian hills I’m more likely to be nervously checking river levels than sculpting snowmen. Whilst, at present, it seems unlikely based on the latest high res charts that we can force enough amplification to connect to those Arctic heights, there is a genuine possibility that we will be able to in the Christmas period. First, the GEFS for Christmas Eve, er, Eve: Blocking over Greenland and low pressure south of the UK? Are you telling me you wouldn’t take that in an average year without knowing the context? Next, Christmas Eve itself, this time from the GEPS mean: Stronger heights over Greenland and a trough in the channel? Yes I know many of the perturbations would be mild but come on, you’d take that anomaly any day of the week. Thirdly, the ECM. The day 10 mean on the 12z was a step back from the 0z with the low closer to the UK, stronger and further North too. This led me to believe the blocking in the EPS would collapse, so did it? No sir it didn’t. @Daniel*has kindly posted the longer term EPS and what do we have from the world’s leading medium range prediction tool? A euro low, Greenland heights and colder than average temps. I’ve been through all the members - 10 or so have a genuine GH, some have Scuero blocking, a few a UK high and others have the low over the UK. But crucially, barely any have purple over Iceland, red over Europe and diagonal lines over the UK. The ‘usual fayre’ conspicuous by its absence. As for the 46? It’s rubbish from week 4 onwards yes, but wouldn’t you not rather it was good in weeks two and three, which might actually happen? Week 2: How is that not good? A strong high anomaly over Griceland and a southerly tracking jet. Gorgeous. Week 3: Residual heights to the North and the jet into Iberia. Yes please. What about the MJO, this is where it gets complicated. Some evidence that the Westerly qbo is finally descending to the higher end of the troposphere, which could scupper the progression of the wave into phases 7, 8 and 1. You can see the gold coloured WQBO leaking into the lower levels of the atmosphere which could act as a barrier to the mjo... but in the latest day or two that seems to have backed off. Regardless, the 46 actually progresses the MJO deep into phase 8/1 More amplitude in phase 6/7 would be nice but it’s hardly the worst place to be for favourable tropical forcing with a weakened stratosphere ripe to be knocked down now is it? And what of the mighty stratospheric polar vortex, so often the destroyer of (cold mid latitude) worlds? A small cluster reverse but many are weak and few are strong. Again, in climatological VI, an excellent projection. So there you have it. Narnia? Nope, Interesting? Yes. Potential? Loads. Don’t give up on the second half of December yet...

Indeed Steve and flicking through the ens at day 9 a good many of them are going down similar routes to the op... there’s gonna be some stunners in there. An excellent trend 0z vs 6z The centre of the blocking now well west of the meridian and lower heights moving south east towards Iberia. As to the Eps I flicked through them all there’s so many options in there that you can understand why the cluster algorithm went for one cluster when, in reality, there’s almost every hemispheric permutation you can think of! There are many which end up slightly blocked but still have south westerlies for the UK but there are many that don’t and go onto to signpost easterlies. The GEM ensembles near to Christmas have a very unusual anomaly indeed. I really hope the latest Glosea seasonal gives some credence to this potential January SSW, it’s so frustratingly accurate these days in Winter. It would be brilliant to have it on board for the mid winter period. Genuinely fascinating model watching at present.

Fair play to the GFS if it nails this evolution Steve. Ever since the ECM guys gave it a few pearls of wisdom, added to the extra strat resolution, it’s been a little better. The EC clusters did slightly favour this solution this morning though. Hopefully once the models polish their crystal balls it should become clearer tomorrow.

Absolutely it was Feb. There was even the obligatory GFS wobble Mike if you remember... I think there was a run slightly earlier in the month, but well after the warming, that didn’t even build the initial UK high at all and just steamrolled the westerlies through - all adding to the fun.

Nowhere, lol. Even Glosea had us for a cold one that year didn’t it. This time it doesn’t. But it did get precede an SSW that year, albeit one that favoured us little. But I agree that we’re always at the risk of vortex intensification at any point, and a half hearted reflection event can make it even worse -last year’s intense negative heat flux fiasco after the botched warming being a case in point). But seen as the Atlantic SSTs clearly don’t match 2010s I figure the only way we’re getting serious cold this year is a split ssw therefore a strong scandi-Greenland dipole for as long as possible is our best trop-based hope.

Is it fair to say it’s now the UKMO that’s out on its own this evening? The 12z big 3 ECM, GEM, and GFS all have very interesting NH profiles at day 10. This particular ECM frame has an Arctic high, amplification off the Eastern seaboard, a Euro trough and a huge retrogressing Urals high. Not what you would normally associate with mid December in recent years. A presumption here, but I imagine the vast majority of viewers/posters on this forum would ‘take that’ if you were offered this chart for mid December. If you wouldn’t, would you rather have this vile offering? Or this despicable effort? I thought so! Finally, another nugget from the treasure trove that is the freely available EC46 data. The lime green dots represent the predicted position of the MJO at around day 20, many members reach phase 6, some return to the centre. Here’s the Nina-composite for phase 6 And the Week 4 anomaly A continued signal for a Scandi-Greenland dipole. And finally, fwiw, model watching has actually been ‘enjoyable’ in the last few weeks. It’s been great hearing so many posters, new and old, share their views, analysis and banter and it feels like many of us are “on board” for the prospect (and it is only a prospect at present, with the seasonal models still generally against the idea) of an exciting winter.

Good afternoon everyone. Just a snapshot from the GEM Not dissimilar from the GFS Icon also looked to be trending in a similar direction Wet for the south yes but still seasonal with slider potential. If it wasn’t for the UKMO then we’d have had a reasonable set of medium term charts this afternoon although as @CreweCold and @Catacol point out, if we do get the Atlantic tilting positively against the trough to the east of the UK (which would of course manifest in a wet and windy pattern here at the surface) that may well intensify the pressure on the SPV which, clearly, is under some pressure already from that monster Urals high. We can see this from the Strat projections. (Though notice a couple of bias corrected CFS members go AWOL later on and enter apocalypse mode, which shows the importance of the following...) For me, the longer that Urals high sticks around the better, the more wave breaks we see against it the better. We don’t want a half baked reflective event / displacement spilling over the cold into the US, we want a full on absorbtion event leading to a favourable split down the line. It looks right now to be 50/50 which makes sense in a WQBO/moderate Nina winter. If it fails then Glosea will be right as it usually is and we’re looking at Feb 2020 pt2. If it lands then we’re in the game.