Uncertainty

Good evening everyone. The middle weeks of December have shown potential for interesting and atypical UK winter weather and today’s model trends do little to dispel that hypothesis. First of all the latest EC46 is a significant upgrade certainly on last weeks nadir but also on Monday’s iteration. Week 2 presents a strong Euro low anomaly not far off a centre in the favourable Genoa region. Anomalous heights are present in the mid Atlantic, but not quite a Greenland high. The corresponding surface temps are cold, but they don’t scream snow. I think given the op runs shown today we’d be fortunate to get a nationwide lowland snow event next week but clearly, given the anomaly above, its within the envelope of possibilities. Week 3 shows a similar pattern with weaker anomalies I have posted the charts for the same time last year in a previous post, suffice to say these are much, much better. Week 4, which includes the Christmas period, also shows some interest, better illustrated using 500mb heights Heights over Scandi and perhaps into Greenland, hints of low pressure heading towards Iberia? Certainly one for the The very silly range CFS has been like a dog with a bone for a cold Xmas week and it has to be right one day. And here’s the global view for week 5, taking us out of this dreadful year. More northern blocking. The far reaches of the GEFS and GEM ensembles are interesting too Crucially, they fit the narrative shown by the ECM above. Surprising consistency at that range it must be said. I’m not sure about you guys but this feels a bit more than a pipe dream from the models for this period. These charts are unusual for December but we do have some teleconnections on side: - Toned down moderate La Niña, showing a mixed profile perhaps not as central based as first feared. - A potentially favourable pattern to perturb the stratosphere with persistent Ural heights. The latest EC46 has a minority cluster which go for a reversal, plenty of strong ones too mind showing it’s all to play for, mean below average. @Met4Casthas posted the chart above. -Evidence for the MJO to traverse the maritimes towards the Western Pacific, is this more favourable in a WQBO? compared with last week GEFS similar, though a little less bullish than recent days Overall an Atmospheric set up that was conspicuous by its absence last year. The dream of an early winter cold shot with the main course of a favourable mid winter SSW is indeed possible this year and thus the hunt, as it were, is well and truly on.

The latest GEFS edging towards the scenario highlighted by the GEM and ECM ensembles for a good few days now. Back this pattern further East we’re in business, further West you’d be wet and wondering what could have been. Also good too see some heights over the Urals and and Aleutian troughing. Perhaps that’s why the EC46 toned down the strong vortex signal into mid December? Below average from the 16th ish. Remember that singularity wise, this upcoming period is usually a dreadful barrage of south westerlies and storms. The ‘early December storms’ occur very frequently so even if we end up seasonal with North westerlies or better yet a cold UK high then we’ve done great in my book.

Last Wednesday, I posted the GEM ensemble at 340, shown here: Next, today’s 12z at 216. The ECM mean for comparison. Commendable, if it verifies. Weeks 3 and 4 also significantly improved vs last week in the EC 46. In some ways it has returned to what it had been showing a couple of weeks ago for this same time period. Precipitation anomalies for week 3 suggesting higher pressure to the North West and the SLP anomaly backing this up We’d need a favourable orientation of the Atlantic ridge for snow but it’s an interesting and unusual pattern for this time of year. Week 4 is a bit more vague but still some blocking at higher latitudes and no slug. Week 5 is horrendous but a long way off thankfully. In all fairness, the multi-model mean for December from the Copernicus suite was suggesting this kind of pattern so it would be a good forecast if it came off. Thanks to Simon Lee for these charts. Recent history is against us on the potent Northerly front but I don’t actually remember seeing such an intriguing mean Atlantic ridge setup over the last few winters. The fact that it’s forecast quite significantly by a good proportion of the NWP means it’s an option we have to consider. The GFS, in typical panto villain style, presents the grim alternative.

Good evening everyone. Lots of early winter obituaries in the last few days, and for good reason, but are we absolutely sure there isn’t a twist in the tale? A closer inspection suggests that a long locked in zonal spell Isn’t quite nailed on yet. The models have yet to fully resolve the deconstruction of Tuesday’s trough and the angle of the jet crossing the Atlantic behind it. ECM control, op and mean + the latest GFS look a lot like the Nina phase 2 mjo composite. Even the Iberian low also present The GEM too with a similar theme So we wake up tomorrow and a) All the energy goes North East, we curse the models and hours tick by on this forum without posts or b) see a) Seriously though , a much better evening since that ECM op. We’ll all by back tomorrow to check, that’s for sure

Has anyone seen the GEM ensemble mean at 340? Didn’t think so! They’ve been very flat for quite some time so just thought apropos of absolutely nothing to put that one out there. The GEM itself post upgrade is worth a look sometimes so I wonder if the ensembles had the same retrofit? It does also show the potential validity in @Allseasons-si’s excellent analysis above. The EPS at the same range are roughly 60% zonal, 40% varying degrees of blocking. Not a mean like the above however. I’m still too cross with the GEFS for its Urals high fiasco to post it at the moment And yes @Daniel*I’m a new poster / old lurker. I realise the NWP aren’t hopeless especially when zonality is forecast. The ECM for example is formidable and even in FI it can spot trends very well. It certainly backed off Monday’s amplification a good few days ago after that one run Scandi high wonder. I was as you say referring to the amplification busts (I can think of 10+ in the last year or so) and perhaps the lack of flight data does have something to do with it. The thing is, why doesn’t it happen the other way round e.g. a zonal setup is forecast up to 6-7 days ahead and then a blocked / -NAO setup verifies? I’m sure that happens on occasions but it’s so rare compared to the usual way that I’m convinced most medium term models have an amplification bias.

Good evening all It seems evident (and has been for many days - apart from the GFS) that the first attempt (Monday) at building a significant ridge is going to fail. However, the Icon, UKMO and ECM have dangled a fresh carrot in front of us. The UKMO perhaps the most amplified in the Atlantic, so would presumably go on to emulate the other two models to some degree. It is very difficult however to give these ridges any credence given the persistent flattening trends we are seeing in the models as they approach T = 0z. I’m sure, as @Steve Murr points out there is an underestimation in FI in the models of the strength and flatness of the jet stream in the Atlantic sector but this phenomena has been happening for so long regardless of the season. The MO clearly have the same issue we do as they consistently prog higher pressure / drier weather in the medium term and it consistently gets pushed back. The EC used to be the main culprit but ever since it gave the GFS a brain transplant the latter has been doing the same thing! Does anyone know why this is? Surely the modellers can just add 25% more Westerly momentum into the jet, a bit like adding RAM to an old desktop? The seasonals don’t seem to suffer from the same issue. In fact, I’d trust a 3monthly winter Glosea mean over a 144 chart anytime! I know they smooth out a big mean over a long time but it’s months away not a blinking week! Favourable ridges, even mid latitude UK highs need X model agreement down to T96 to verify. We all know that really. BUT I ask myself, would I rather they were accurate and thusly would barely ever show meaningful ridging and even the BOOM charts that send this forum wild? Of course I wouldn’t. And neither (I think) would you! So let’s bring out the random perturbations, the 2 week later stratospheric meltdowns and day 10 ECMs because... one of these days... you never know... it might just happen.

Yep and this is the bifurcation point now. The cold spell Saturday went kaput days ago now but the path of the next low is up for grabs. Less spacing between the two lows on the GFS 6z and the amplification is weaker and too far East. There were certainly more 6z GEFS members which went for this but it’s 50/50. Similar on the EPS clusters. On the other hand there are plenty of runs which have barely any spacing and thus there is minimal amplification. The 0z GFS para highlights this: With the result being Long fetch southwesterlies. The pest from the West. As long as that’s on the table It’ll be an anxious watching brief over the coming days...

I think this forum would self destruct if that happened!

Yes Nick, yesterday’s 12z GEFS were particularly keen. It’s just that there have been so many amplification busts in the 8+ day range in recent months that I’m highly sceptical until proven otherwise! (Unless the amplification is mid Atlantic based in summer then it’s a given, of course!)

The wait is over Zac! 2 outta 3 ain’t bad! @Mike Poole we really could do with verifying that Scandi / Urals high to perturb this burgeoning vortex. Otherwise as you say it’s only a matter of time until... Just for once in our lives could we have that chart inverted!!!

Evening all I think we’ve got good agreement on the Synoptics up to around day 6 or 7. A node of heights amplifying around Greenland and then tumbling down through the U.K. All models then have another low approaching and possibly disrupting against that little wedge, but the nature of this interaction and the subsequent amplification (or lack of) is presently unclear. The GEM for example, does disrupt the low under the wedge to some extent but then it sort of hangs around near the UK and the next low follows quickly from the Eastern Seaboard with little amplification in between. Agree with the comments above vis the ECM, nice evolution but it’s got serious history of day 9-10 garden path highs. Still, it’s not completely unsupported by the 240 mean from earlier on and perhaps more so on the latest mean. The GFS at a similar time frame also toys with a Scandi high. As Nick rightfully points out, it’s a precarious evolution to get there and thus, unlikely to be there tomorrow morning. I think the form horse this evening is a cooler, unsettled outlook with systems perhaps taking a more negative tilt. There is certainly scope for amplification after that, but it’s been so long since a chart like the day 10 ECM actually happened during late autumn / early winter that I struggle to put any faith into it! The MJO’s expected evolution from phase 1 to 2 and then into the COD also supports these ideas to some extent. One thing does seem clear though is a disconnect between the borderline rampant upper strat and the troposphere, as long as this continues, the game remains on.

Good afternoon all I’ve enjoyed this thread this year and I feel it’s been a useful addition. It’s brought an eclectic mix of musings and models and, without a whole heap of rules or protocols to follow has managed to strike a nice balance between one line speculations and detailed synoptic analysis. I’m going to throw my ten pence in here with a focus on the run up to Christmas. First of all, the early-mid December period is now within the crystal ball of the EC46, which for all its failings is still imho (and presumably given their implicit references to it the writers of the 16-30 day METO?) the best medium range forecasting product presently available. So where are we now? I’m using the Icelandic charts to give a clearer comparison with last years situation. Weeks 4 and 5 from 12.11.2020 Mid Atlantic ridge, cooler, maybe colder. As BA suggests, lack of a Eurolow perhaps precluding a jackpot scenario but still, very acceptable for early December and within expectations for the canonical Nina winter. Weeks 4 and 5 from 14.11.19 Bleak. No hope there. Only for ducks. Simon Lee has tweeted the December round up of the Copernicus affiliated seasonals and they’re very much along these lines. And yes the NOAA contribution is flat but I would take All earthly models versus the CFS every single time. Cansips and BCC for in particular are not without interest for December. The former progs a UK high (which personally I would bank in December, especially being a Cumbrian river valley dweller...). The latter a little outlandish but still another string to our increasingly interesting bow. Week 4 CFS anomalies are also promising Also some very interesting ruminations on Twitter vis a drop in the anomalous high AAM state that has set up our present situation to something a little more accommodating to the early winter mid Atlantic Nina ridge... too early to be sure perhaps and certainly beyond my pay grade! So enough evidence then to suggest that the early - mid part of December holds some seasonal promise. Not a 2010 redux but hopefully not relentless long fetch South westerlies. Finally, to answer SqueakheartLW’s pertinent question regarding the classification of this Nina event, I would say it still looks basinwide, certainly not CP and as you say the sub surface anomalies don’t support it either.

Good evening! 1st ever post! 1st of many I hope. Love this forum. ECM: Tonight Matthew, I’m going to be... The GFS from yesterday! A real tease, shame the OP only goes out to 240... but flicking through the EPS from this morning revealed a considerable minority building significant heights into Greenland. On the other hand, the latest GEFS has trended flatter from this mornings runs. The GEPS, for what it’s worth, are rubbish. So who knows where we’re headed but it is 2020 after all and I’m sure the weather has some surprises left for us yet! Thanks to all for the great contributions. Josh