Uncertainty

Quite a few GEPS members looking pretty stretched up top as well late on, though obviously the 0z gfs is a huge outlier. I know there’s been some heat flux and wave 2 into the strat recently but not enough to trigger an SSW? MP first mentioned this around a week ago? I haven’t heard many of the strat gurus mention much? My concern would be some sort of stretching towards the NA side giving them a cold January and us a rampant jet… Tell me I needn’t worry blue!

This is so 1978-1979 (Heavy rain across N England turned to heavy snow and moved south, channel blizzard eventually). There’s been a general shift towards disruption this morning and a slightly stronger GH. The matter of Who gets the snow is going to have to wait… FWIW those Mogreps stamps show a small but noticeable cluster where the south gets the snow so all tracks remain on the table…

Major headaches… perfectly put knocker. But were you referring to the models or the mood on this forum? @Kasim Awancheck the extended eps before writing off further easterly chances later in the period. It’s one of the most blocked sets I’ve seen for any post in winter, it’s as if there’s been a split up top! The clusters just don’t do it justice. There’s no way there’s 33 members with a full blown W based NAO and Swerlies for us. (Although it doubtless is a risk). I’ve been through them, they’re pretty incredible for both potential for us and the -AO signature. @CreweCold, that Siberian ridge could be our ‘have cake and eat it’ card that I’ve been mentioning since early autumn. Although if we did get an ssw, presumably we’d get a spell of flushed down westerlies, and it’s not like we don’t have blocking in the forecast for the next 15-20 days at least! I’ll say it again I think an extended, good amplitude spell In phase 7 is optimal for us as a quick progression to 8-1-2 would drop AAM and favour the east US for the cold eventually. The longer it stays in 7 the bigger the likely hood of perturbing the SPV. It will also continue to encourage blocking to our North. No concrete signs of an ssw yet though. I said last night I feel the track of this low is the beginning of a cold saga not the endpoint and I’ve no reason to abandon that prognosis this morning. Here’s New Year’s Eve… GEPS GEFS

Extended EPS at 360 are better than the clusters suggest, and the clusters suggest they’re pretty good I went through the members. The control for example is 2010 esque. There’s Scandi and Greenland highs, many of which are intense. The signal for hig lat blocking is huge. Cluster 2 I did see, but the vast majority still had big time northern blocking but as you can see the blasted euro heights got in the way. Clearing those euro heights is going to be the key as there will be more chances whilst the mjo stays in 7. Plenty of Strat perturbing patterns too as we’re only in week 3/12 of winter don’t forget.

U.K. = Still In the game. I know the feeling when the hope collapses and you know it’s ‘done’ and I just haven’t got that yet. Moreover, it looks like somewhere in the U.K. is getting a heavy band of snow on Christmas Eve. ECM had it, at Amber warning intensity, right over me (N Cumbria) and 4-5 million others in N England and S Scotland and no, @northwestsnowI wouldn’t trade it with the south! (and neither would you!) Though I’d rather they had it than the sea south of Iceland!

JMA slides…

Yes Dan it certainly is! Are we the only ones pleased with the 12zs so far! UKMO is much improved and easterly by 168 GEM almost a stonker Arpege solid and would slide Icon pattern further south One predictably duff run from the 4th best global model known to suck in these situations and… Toys… out of the pram!

This is by no means ‘done’ The trendsetting GEM, first to highlight the more cyclonic outlook, is now sending more energy SE into Iberia 12z first 0z So the low heights in the Atlantic are disrupted rather than a bowling bowl type Great to hear you back in here again Scott. I was literally typing about the energy disruption being so difficult to model. It’s the beginning of a saga this, not the end.

I’m not sure on its global verification but the key developments are now within its timescale - we need as much of the ridge to be split to the Greenland lobe early on - even if only some energy slides towards the Med we’re in business.

12z Arpege lowers heights over Iberia - that would slide if it went on. Cold air already moving in. This is absolutely on the edge. Icon is at least further south and stronger with the greenly heights. A good start I’d say. An improvement from the UKMO and especially the GEM and the game is very much ‘on’…

Just to illustrate the size of the shift on the 18z mean. It’s so much better. Mean easterly on Xmas eve for most of the country vs mean westerly 12z 18z The Heights are Griceland and significantly stronger. We could have a slider then a few days of ice days and snow showers then repeat. Or the high could dissolve away NW and it’s mild and wet. Wouldn’t want to call For the big day but the long long stay in P7 rather than racing to 8 is better imho You can see on the P8 Nina composite that the GH is west based, the east coast of the states would be cold and the Iberian ridge is in play But staying in 7 has twofold benefits. a)Encourage the heights not to drift to far NW b) Continue to, at the very least, put pressure on the SPV from undergoing VI and killing our potential January blocking from the top down. Plenty of 46 members kept it in 7 for over 15 days. AAM is correspondingly high and very Nino esque. Blocking and -NAO thus the theme expected, perhaps even throughout Jan. What a stunning plot that is. the EPS follow the GEFS tomorrow.

I’m not ready for the b word but the 18z op’s an absolute stunner. Good spot, black hole anomaly now on the mean and a tad further south Incredible to see these charts w/o an SSW.

Worth a fanfare in 90% of winters @bluearmy and @knocker Regardless of your regime preference! Looks like less of a risk of a Wbased -NAO? I’m more worried about it simply being too small and weak, 1020mb even if its over E Greenland might not be enough to put the U.K. on the fun side… The DJF seasonals would be in serious trouble though if those anoms above came off… 12z EPS flip back like yesterday but I think I echo @Ed Stone’s sentiment that historically either the Atlantic barrels though and the block is weaker and too high NW (please no) or the low disrupts underneath the block leaving a weak slider trending ever further south. Ec 0z and GFS 12z found the sweet spot snow wise. The sinking high option seems to have faded though… Also the back end of the NAEFS, GEFS and GEPS signals are really quite striking Key difference is the enhanced Siberian high on the GEPS and perhaps GEFS. Vortex pressure for later in Jan perhaps? Regardless, the blocking/Wedge over Greenland still looks pretty strong even this far out. No reason to think there won’t be more cold chances after we sort out the angle of attack from the Christmas low…

Worth the wait Kasim! FI is a world away from this morning! It looks the the 0z set over compensated. Let’s hope today’s trends are maintained.

The block is stronger blue… On face value, it’s a very exciting mean… Beyond that the clusters at least don’t go +NAO but I’ll bet quite a few of the members will feel that way. Would still produce a tasty looking mean anomaly I imagine.

The GEFS often over react to a newish signal and they can be tempremental. That said there is a clear movement across the suites over the past 24 hours towards a more LP dominated outlook, bringing rain or snow from The west into play when they really weren’t before. As BA said, high risk high reward. The one consolation if it all collapses is (as @CreweCold has frequently alluded to) we never really had a particular clear cut snowy pattern evolution to look forward to. Just weeks of high pressure. I personally love the latter so am really quite annoyed but in a way the actual chances of a snowy outcome have increased. There’s a reason why UK highs are rare at Christmas . It’ll be a nervy run in now. So this mornings bad news for cold/snow lovers and SWerly haters is the flip on the GEFS, the GEM and Icon ops The better news can be found on the GfS op, EC op, JMA op Its still 50:50 like I said a few days ago it’s now just 50:50 Between cool and wet and cold and snowy whereas before it was the latter and and cold and dry. Hoping for the block to be more resilient..

Good consistency from the GEM, it’s really flown the flag for the colder evolutions. At day 10, the E Greenland high is in an excellent position to Marshall lows below it, you would imagine a significant battleground snow event incoming for SW areas very shortly after as the Atlantic low drifts towards the cold block. Also, a quite stunning NH chart, especially given the strong SPV well above. The GFS has upgraded and the UKMO is a little bit 6/10 but now we just need to get an ec op that doesn’t sink. 3 in a row and I’m always concerned. EPS mean would suggest it won’t but we’ll soon see…

Note the Arctic high lobe sucking the U.K. high towards it. Some of the big time cold spells of yesteryear have started this way. It helps pull the high N on this run, not quite enough on this run perhaps. But it’s irrelevant at this range. Plenty of time for a couple of 100 miles N to unleash the… (I’m not saying it yet in case I get accused of hyperbole again) Regardless it didn’t flop like the Ec op. One word of caution these Artic highs are notoriously difficult to model and have done us in the past (think Jan 19) but I think we’re going to need it if the models do go the ‘Scandi’ route rather than the Greenland one.

Basically the EC46 goes for an East based -NAO (ideal for U.K. cold) persisting throughout Xmas —> Mid Jan whereas the last run (Thursday) had a Northerly mid lat high then westerlies. The difference is so stark. W3 latest W3 last run Notice the low heights surrounding the base off the Icelandic heights connecting with those over SE euro W4 latest W4 last run The anomaly sinking slowly on the last run, not so on the latest W5 latest W5 last run Wow! phase space reversed. + to - NAO Agree with this also note the sheer duration and unusual amplitude spent in the the WP phases. This regime chart sums up the shift clearly Last run Latest Of Particular note is the tiny fraction of +NAO runs even as far out as the first week of the new year! The ecm op (which as I’ve mentioned repeatedly has been highly volatile beyond day 7 recently) is the flat out worst case scenario. If it’s repeated in both runs tomorrow then it might be on to something but there’s little in the rest of the global output or forecasting to support it at present. It’s still just one single run remember and I’m confident in the coming days it’ll pick some other extreme scenarios out from the other end of the envelope. The latest extended EPS clusters aren’t quite as mouthwatering as the 0z, but of note is the 50/50 split between a stonking -NAO and a weaker blocking signal that briefly lets the Atlantic back in then sees the a blocking resurgence. What this shows is that a very snowy synoptic over Xmas / New Year is maybe 50/50 and given our myriad previous disappointments I would say that’s probably fair. As I’ve mentioned previously the last decade has been 0% so a huge chance in relative terms. Also the GEPS are pretty telling, notice how, even at the 300+ range, the high anomaly extends Nwards with time! I can’t remember seeing that on this model very much. Certainly adds credence to the EC46 outlook that’s for sure. The strat still looks strong on this run though, though much more spread than the previous run and a perhaps half the members go slightly weaker than the climatological mean. Latest Also note the deceleration next week is sharper than previously expected. Last run Aside from one fruitloop, mostly a very strong signal for a strong vortex last time but the trend is getting weaker. GEFS perhaps starting to have other ideas, with perhaps even a weaker than average trend later in the month Certainly no imminent SSW sign then, but an unexpectedly weaker one perhaps allowing us our big shot over the coming weeks. (N.B a cheeky split is possible around New Year but still unlikely at present). Overall, aside from one dodgy back end of an op run aside, it’s a really rather exciting outlook for cold fans. Finally, Don’t take any individual day 7+ op runs seriously at present. Especially if the outcome is extreme at one end (sinking ala 12z EC op) or the other (rush to monster GH/BFTE ala GEM 0z). Take a nice look at this NOAA 8-14 And smile

Omg EC46

The Seasonals this year are zonal… predictated on a strong, coupled SPV which *potentially* could be nuked in the next three weeks via difficult to predict at short timescale tropospheric processes. If one such event occurs combined with the already anomalous December height anomaly then the maps for DJF are going to look upside down again

You certainly do Aaron and the means are indicating exactly that: a U.K. high, then huge uncertainty. History is with you and there is so much time for this to go wrong as it so often does. Difference for me this time is the conviction that many of the states Twitter mets have for a significant -NAO should the MJO eventually track into P8. Strat is a bit of a wildcard as yes it’s strong up top but presently it’s decoupled and then there’s this potential warming (surf or poleward) to deal with. The seasonals can’t pick out these nuanced details and they have missed SSWs before. All To play for but you’re well within your rights to be cautious / pessimistic.

3 serious questions warrant exploration based upon recent output: 1.)is the upcoming U.K. high unusual at this time of year? 2.) Are we sleepwalking into a genuine cold spell? 3.) Are we seeing the genesis of an SSW with ensuing implications for the heart of winter? For the first question, the short answer is: Very. What is for sure is we are about to enter a highly anomalous HP dominated spell, the likes of which have been utterly absent for the past decade. Excuse the amount of charts, but here are the last 10 years worth of 21st December charts, spot the centre of the high… 2011 - Azores - Portugal. Home sweet home. 2012 - N Africa, (the W Russian high didn’t last long…) 2013 - Powerslug 2014 - Azores / W France 2015 - Revenge of the Powerslug 2016 - Azores 2017 - Biscay of a bad bunch (best yet?) 2018 - Iberian holiday 2019 Squashed under the PV of dooom 2020 Home sweet home. Day 10 EPS mean - North West England!?! I think we can safely say it’s a rare event in modern times to have such a positioning, note also the phenomenal agreement between the big 3 ensembles all the way at day 10. Good consistently from the 0zs too and the trend, as we will get onto soon, is N and not SE… GEPS GEFS So now for Q2 and the difficulty level increases. Today has seen a significant trend towards a colder outcome in the extended. Last night, the EPS clusters contained only a minority of very cold members. The same number were zonal and others were drier than most Decembers but with little chance of snow. Tonight we have 3 clusters. No +NAO in sight All have a significant cold pool waiting to the East and there are hints of lower pressure over Iberia. A big shift towards cold though over the past 24hrs as the mean ridge shifts ever further N and W with time. The GEFS have some outrageous members, many of whom have been posted, but the mean is very intriguing Hints of a mean cold Easterly there, even at that range? (Boxing Day) No such mean flow on the GEPS, but the anomaly will do just fine thanks Consistent Support too from the CFS weeklies (must be a strong signal then!) NOAA ‘on board’, but we await the human input tomorrow for more support MJO doing exactly what we want it to do and loitering around phase 7 (The curve back is related to the potential WP typhoon, which could well serve to boost the signal). No surprise then to view the phase 7 Nina composite which I’m sure we’re all familiar with now Latest Pacific SST’s still look basin wide to me but the very coldest anoms are EP, perhaps this is helping our tropical signal to propagate further into the WP. Phase 8 seems likely to me and the twitteratti but it’s not a given yet. Plenty of research to support the hypothesis that a slow, high amp phase 7/8 orbit is conducive to a -NAO. In short again the answer to this question looks to be yes for a cold spell but a big fat maybe for snow. Presently the high looks quite close but it’s only one more trend north and the North Sea snow machine is back open for business. Finally q3 is above mine (and the seasonal models haha) pay grade but @Catacol’s +EAMT is looking good and these correlate well with SSWs (especially over the Tibetan Plateau, fingers crossed that’s the case this time) A protected, slow stay in phase 7 is equally important, especially in an EP Nina winter… Hopefully @jules216 doesn’t mind me using his ideas but essentially research suggests that during Nina winters P7 is associated with activating vertical heat flux into the strat, weakening it and thus teleconnecting with a -NAO. Combined with the +EAMT and it’s no surprise to start seeing a reasonable warming signal emerging So For our final question. It’s a humdinger and one to watch very closely. Even the likes of Marco and Judah and Simon Lee are beginning to mention the possibility (nothing more than that at present). But it sure would put the cat amongst the seasonal pidgeons! So there you have it, it’s a yes, probably and maybe but boy is it more exciting than the last decade of tripe! Huge EC46 tomorrow, for the trop and the strat. let’s see where we’re at then. Adios for now. Josh

Not sure you can dismiss it that easily Aaron. The mlb is favoured yes but if the mjo goes strongly to 8 the US Twitter mets favour a strong -NAO. Last 10 late Decembers have had no chances, this time there is a small but non negligible chance. These are not typical day 9/10 run up to Xmas charts, as shown by the anomaly shadings GFS 18z GEM 12z Hardly disappointing charts for snow lovers??? It’s supposed to be prime time Xmas storm singularity time, these charts are very very rare for this time of year! Also the seasonals were wrong last year, wrong in Jan 2018 and they’ll be wrong again. If they’re that bad this year, what will they be like next year with a nino/Wqbo/increased solar background? I dread to think. Finally, what have the past 3 SSWs really brought us? 1 beast mostly in Spring, one fail and one big tease. 95/96 managed cold with a strong SPV why not this one? If we get the trop pattern right (a few rogue ops have last few days) we could end up with an SSW in 2-3 weeks which would trash the seasonals. For anyone thinking the forecast pattern is ‘poor’ have a look through the run up to crimbo on reanalysis over the last 10 years. It’s a horror show. This year is a highly anomalous and interesting pattern that needs careful watching for big implications in Jan and snow, whilst not favoured, is certainly plausible between xmas and new year this year so keep watching.

Not sure what to make of the clusters late on, I’ve been through all the members and there’s at least 15 which are zonal or stormy and 15 very very blocked and the rest are non descript! Not much of guide for the direction of travel! @Mike Poole Atlantic very strong on a good few of them. It’s not off the table just yet sadly, but still a minority option (as is the big GH!)