Uncertainty

Regardless of the short term conundrum the improvement in the day 10-15 EPS is significant as @mulzyhas highlighted. The long fetch SW feed runs are now in the minority and there is a bit more blocking showing up to our NW and to an extent N. Here’s last night’s clusters at day 15 with 40% going for a long fetch SWer The 0z for the same timestamp The signal for NW heights now stronger. Cluster 2 looks most like cluster one from the 12z but it’s further south with the low anomaly and the GH heights look more influential. Cluster 3 looks excellent with w/ a Euro low / Gricelandic high similar to recently and the 1st cluster shows a general area of heights to the N but probably non-descript weather for us at the surface. I continue to see a short milder spell day 8-9 to day 12-14 but evidence is building that it looks brief. No need to berate the models if this shows up as the signal has been there for about a week. If however we end up with a UK high in the holding pattern then it could well feel cold at the surface throughout... GFS on its own in the mid term unfortunately but we’ll give it till tonight to make the call. If it was the one going flatter on its own we’d be discounting it. Hard to bet against the Euros here unfortunately Would love to be wrong!

Would feel better if some more EPS members went for it SK, they’re just too generally flat at the minute to truly back the early downwelling wave evolution. But as you say, it’s there in the envelope and great to see... And plenty of time for the EPS to flip. Saying that... You can add the JMA to our growing evening Motley Crew!

Hypothesis A: Pub run codswallop Hypothesis B: See Hypothesis A Except... There’s been a stonking SSW and the 18z *could* be picking the first real sign of a QTR. ECM ens might look poor on the heights but the anomalies suggest the above is within the envelope...

You’ve been Bob on so far Scott, unlike the supercomputers you’ve never let us down Honestly pal at this point I’m more interested in human input and reasoning inc this forum and Wxtwitter + MO as the supercomputers flounder in this setup and as I’ve been suggesting it *loooks* like they’ve got this whole winter wrong too... Amy Butler, @chionomaniac and others called this SSW almost to the day with no fuss almost a month ago and the models lagged them well behind.

It’s been there for days Feb MJO headed to phase 2 and corresponding Nina Jan composite... Also CP Nina going forward looking likely and SSW interference might make a passage to the WP with good amplitude really tough... So yes there’s evidence for a westerly spell in the medium term, but most suites go for a later split so I’m going for a week tops of SW guff then lift off. Something like this perhaps?

Agreed Scott but the day 11-15 signal *taken at face value* shows westerlies returning backed up by BBC/METO musings. For 4 days now the FI signal has been weakly flat so we can’t ignore it...The EPS were all over the present pattern and most of them are poor in the 15 day time period. Thankfully we have a 2 week + reversal so even if we did revert to type it would be hard pushed to establish. But as you say it’s so chaotic, going through the ens at day 8+ shows just about every pattern and wind direction you can think of, don’t even now if/how/what angle that trough is going to drop at day 6 so until that happens it’s a case of wait and see. Really buoyed by the end of the 30dayer from Exeter vis increased chance of snow that to me says downwelling expected. Also CANSIPS first seasonal to drop. The first passing bells are a ringing... Last months run for Jan: This months run: Oops!

As @CreweColdsaid pal we want the ridging up to Greenland to be as strong as possible to avoid the low dropping down through the U.K. phasing (joining) with the low on the US side of the Greenland ridge. This will ‘blow up’ the low over the U.K. and mix up the 850’s thus less snow, more windy and the low won’t sink SE into Europe to set up the snowy easterly... Even at 168 on the ECM the ridge is weaker and the writing’s on the wall.... The latest GFS brothers avoid this phasing and thus produce snowy day 8-10s. ECM has just flipped to the other side of the pack, the 0z represented the favourable outcome for cold seekers. Might be Saturday till we get more clarity on this one... FWIW this pattern keeps repeating this winter and so far we haven’t been able to fully link up heights over the top of the diving low and it’s tended to blow up. Hopefully 2021 brings us a change of fortunes in that regard....

Well what a year it’s been... Horrendous for the most part, but early 2021 brings with it possibilities for snow lovers that have been wholly absent in recent years. This was not looking the case in mid November, at that point in time the ‘factors’ that guide seasonal forecasters and lowly musers such as myself were ominous, we had - Strong La Nina Forecasts - Weird but mostly west QBO - Some evidence the above 2 factors could weaken the MJO signal especially towards the western Pacific - Strengthening Stratospheric PV with v low polar cap heights - No Urals blocking to speak of - Unfavourable N Atlantic / N Pacific SSTs - An unspeakably horrendous met office 3 month contingency planner for cold in November that gave a colder than average DJF CET <5% Add this to the generally flat westerly seasonal mode output generated in late November and based on the above factors... In short, it was bleak. And yet... We are now at the point when we can confidently reason that those Seasonal forecasts were broadly wrong, perhaps fundamentally so. The weakening of the SPV, precipitated by the dominance of the Urals high in late November / December has exposed these forecasts as fantasy. With the fuse lit by record breaking pressure differentials from Mongolia to Kamacha the reversal of the zonal winds is now assured. This now looks like a long-lasting event, and present forecasts from the GEFS/EPS have for some time been indicating a second warming later in January that would surely toast and split last year’s nemesis into oblivion for the best part of the winter That is a serious reversal. Let’s be clear about that, not a quick dip into negative territory before a quick VI and game over for February. The longer lasting the better to ensure long lasting tropospheric effects and present evidence suggests that is likely. The present cold spell we find ourselves in is causally connected to this weakening, as we would not be afforded the moribund Atlantic jet were have now were we in the canonical VI period we usually endure in this period. However, the full effects of the warming are still to be determined, but my educated guess is the SLP anomaly for JFM will not look like this, heights to the south, low to the NW: On the contrary, for the NA sector it might even be reversed! The latest EC46 thinks so...Here’s week 4 which is fairly representative... Hmm - Heights to the NW, lows to the south! Maybe the seasonals got their colours wrong. Better luck next time Now before we get to excited, the above is not a forecast for a very cold and snowy UK for the next 2 months, indeed, the extended range of the big three (11-15 days from now) have for many days been indicating an Iberian high and swerly string out between that and the Northern blocking. This would be unfortunate but it may only be temporary before the full effects of the start warming leak down to the troposphere and fully reverse the flow. Regardless, the anomaly chart for the same date is still not reconcilable with the seasonal means Mu point is, it really looks like a bust for the seasonals this winter and a huge boon for the human intuition and gut instinct that questioned them. Happy new year and take care everyone. This forum is what it is because of all of you, the one liners and moans, the ramps and the out of the prams. The detailed analysis and the professional input. I’m sure, like me, it’s helped keep lots of people sane during a very trying and desperately sad year. Roll on 2020.

Jackpot! No easy Atlantic comeback here. One of the best 8-12 day runs I’ve seen. Obviously it’s total twaddle, but it’s beautiful nonetheless! The evolution of the trough dropping down from the North has been the theme of the day. Personally I would take GFS18z >Para12z>ECM12z>Para18z (urgh)>GFS12z>GEM12z. Seeing how different the above evolutions are we still haven’t got a scooby what the trough will do but having it dropping down is more likely than before...

Btw you snow starved south easterners after clipping the south coast inc Kent the GEM pivots the snow back into you guys late Thursday night... Matt H is very fond of the GEM for short term precip and I’ve followed it recently and he’s right it’s often excellent. Far from a done deal!

Yes Seb if the research is correct then bizarrely we should really be wanting to avoid a Greenland high... which for most on this forum I imagine almost impossible...Jam tomorrow and all that... However, does a well supported evolution such as the GFS para not already have a good amount of NW Euro blocking? A 1030mb Scandi ridge at around the time of peak onset? This, along with the Icelandic block leaves a large high covering, at least initially, both sectors? Surely that would make it hard to classify either way? I realise this is about timing but as you know every event is different and we could get a perfect trop anomaly and no significant downwelling, we’ll just have to wait and see...

A simply stunning chart from the UKMO which has been all over this evolution. The Europe view shows the high getting ‘sucked’ up towards central Greenland and a polar trough about to come down from the North. GFS is very different and has the high to the North weaker, still cold medium term and snow showers NE coasts moving inland. GFS para is further North with the block and also looks to be heading for retrogression. Given ICONs Nward adjustment expect ECM to be closer to UKMO than its 0z. A great start to the 12z runs!

Yes Scott as you said UK high evolving to Greeny with time. Fill in an application form at Exeter ASAP The EC46 members have put their order In at the Winter hotel and they’d like a stonking -NAO for starter, main and dessert! The GEFS, sitting at the far table, take a whiff and say “We want what they’re avin!”

It’s no coincidence pal. The vertical heat energy spilling into the strat via Wave 1 through this event is gigantic. If it splits down the line as even the reluctant GEFS are suggesting then it could be effectively done for during the heart of winter. This surely is the foundation of the 6 week block fest on the EC46.

Listening in to Eric Webb on Twitter and the it Looks like the world record for hPa is going to go in Mongolia - a station ‘Tsetsen Uul’ reporting 1093.5mb. We could also have a record breaking low in the Pacific in the mid 920s. No wonder the fire is about to start in the Strat. Huge hemispheric happenings leading up to the Atlantic shake down. There’s serious forcing, and thus confidence, for a serious -NAO here...

Just goes to show Zac if you baselessly predict 12 inches of snow every week for 7 months of the year you’re bound to be right sometime!

Some people are running on to the pitch they think it’s all over... @CreweColdcould teach those seasonal models a thing or two! He called this winter in August! The signs have been loud and clear in the modelling since late November, you can thank the Urals high for that. If anything like the EC46 comes off then the seasonals are toast. If they were right every winter it would be boring. And we know weather forecasting is anything but boring. A huge victory this would be for human reasoning, interpretation and experience. Only downside I see in the medium term is GEFS/ GEPS go west based -NAO right at the end: It’s always going to be a risk but if the strat splits later which it *looks* as if it will do then such a scenario would be but a blip in our best chance for deep, perhaps infamous cold for 10 years. PS this chart is bonkers and incomparable with any synoptic in the NH DJF for a decade...

I’ve been thinking this for a while BA we would dismiss it (the present gfs) in the trop if it was up against ECM/JMA and an apparently better version of itself. Though as @SqueakheartLWpoints out, many GEFS have a warming rebound anyway. Would much rather the Split now though personally. The GFS also lacks the amplification In the trop over the exact area (Greenland corridor) that the other models have. Coincidental? I’m not so sure... Anyone know if the GEPS are still in for the split?

My pseudonym was never more appropriate... JMA 192 GFS parallel GEFS mean at 192 Regardless of the disruption type, huge differences in the level of warming at day 8. Many of the finest on Twitter are favouring an initial displacement so it remains a watching brief. Hopefully some clarity on this asap. Down below the shenanigans, EC continuing the trend I have been seeing over the last few days, heights transferring towards the E/NE over the top of the U.K, a ‘toppler’ @IDO yes, but a very nice one. The full GH by end of December was never consistently progged by the models, but significant Atlantic height rises certainly were and these look like verifying nicely. Back to the present and the pivoting band of sleet and snow tomorrow is predictably proving unpredictable. There are two primary uncertainties: 1) The initial track of the surface low overnight Sunday as it tracks SSEward towards the Irish Sea. The Euro 4 and UKV are taking it through the Eastern Irish Sea, with the snow band through NW England Alternatively, the Arpege takes the low through Northern Ireland southwards, with the snow avoiding mainland England altogether Other models are somewhere between the two tracks. The MO warning update tomorrow morning will be revealing. 2) The low then continues SE, perhaps pivoting as it does so. The Euro 4 brings the SE into play, as does the GEM Many other models have the track further west, the SW could be in the firing line here Added to this is the marginality debate that has been one of the many ‘themes’ of this thread over the last few weeks (and indeed, ‘‘twas always thus”). Either way, it’s nice to be viewing Hires models outside of the summer thunderstorm window. The only reason I’m used to viewing them in Winter is for rainfall accumulation forecasts, a lonely and miserable activity that sadly is necessity in a canonical Cumbrian winter. But this is proving so far not to be a canonical winter at all. Which is brilliant. So here’s to the, ahem, uncertainty!

Such differences in the strat at such a short lead time Mike! Old GFS not interested even though the para splits consistently around day 9. Either a) The extra resolution has allowed it to ‘see’ the enhanced warming and subsequent split or b) It’s rubbish. It has however also been consistent, along with the GEM, with a wedge of heights forming over Scandi following on from the initial amplification in the Atlantic. Leading to an easterly a day or two later Though the GEM goes all In tonight with a conduit of heights linking up to a monster Siberian high. Stunning. The EPS mean also has a broad region of higher heights North of the UK Fair play to the GFS for consistently spotting Bella and the Atlantic ridging but right now it seems up to its usual tricks of being unable to resolve split energy nearer to the UK. If the Para verifies (in both atmospheric levels) we really ought to be giving it just as much, if not more credence than it’s incumbent older brother.

GFS para going down the Scandi wedge route that GEM has been hinting at in recent days. The 12z did the same. Won’t be long until this model is the GFS so we can’t discount it. Jma, an excellent run, also leaves a wedge of heights over Scandi which in turn adverts much colder air in from the North East That trend for a wedge of heights to transfer East to the North of the British Isles is one to watch going forward. Both above models split the strat vortex in under 10 days time. JMA first. GEFS still not so keen. I think a split vs displacement is still 50/50, but a reversal looks odds on, which is marvellous for early January. The propensity towards blocking patterns and amplification in FI is sensational. GEFS already more amplified than the 12z. Merry Christmas to all on this fantastic forum.

Btw That would be a beautiful chart for any operational run in the winter... But it’s the mean! Aaand it had a wobble at the key time frame! Surely the other big models don’t back it up... Not so fast! Eps shows a mean Icelandic high too! The best month of model watching since Feb 2018, can we top it?

Here you go fellas GEPS going for the split... Only 3 EPS members don’t reverse... GFS op flips back to a split... The seasonals are on the ropes...

I think they’ve taken the poss SSW into account NWS, they’ve referenced a possible weaker SPV in the outlook and weighed it up against the moderate late winter Nina background (weaker MJO?) and unfavourable Atlantic SSTs. The latter did us no favours in Jan 2019... In all fairness it’s a lot better than the last update which was horrific for cold or dry conditions. They do mention an increased chance of a colder Jan vs the last few years. Still a low chance mind. The latest seasonal output for JFM won’t be available to them yet, they can’t ignore the westerly dominance the seasonals currently show based solely on the hypothetical effects of a downwelling SSW that doesn’t exist yet. But we can

Morning all! Still uncertainty over the precise track, shape and precip distribution of tomorrow’s low. Snow looks limited to the tops of the Cumbrian fells and Pennines so rain is the main focus. Icon has the heaviest rainfall focused through the Bristol Channel into Southern East Anglia. Arpege is pretty similar Euro4 has the main band slightly further North highlighting the continued uncertainty. Now, back to the future... What a chart from the GFSp. Cut off block forming over Greenland, a developing NErly, troughing all over Europe, the slack flow and building snow cover on the ground would enhance the snow risk. And still the Russian high promoting +EAMT to toast the SPV. Blizzard incoming for the SW? ECM op is just the better side of marginal this morning and has lots and lots of snow for lots and lots of people. Would please a lot of members on here. A lot of tricky micro scale synoptic reasoning ahead for the pros, that’s for sure! Support in the EPS for the blocking to the NW and NE of the UK to continue, if not strengthen after day 10 With the continuing developments in both the troposphere and the stratosphere there will be plenty of model output for us to discuss going forward...