Uncertainty

Cherrypicked and apropos of not very much, this GEPS mean chart for the 11th of January shows quite a bit of support for split flow, low euro heights and some level of Ural blocking. It looks like the big pacific ridge is toast too. The EPS aren’t really as convinced and are either cold or mild zonal. Interesting how muddled the models have been recently, we’ve had 3 main fails: a) The longevity of the U.K. high over the Xmas period was severely overestimated, with a cyclonic period verifying b)Next, The sub seasonal and medium range predictions of an extended period of an East Based -NAO were incorrect c) Finally, The short lived Northerly spell next week was not strongly indicated 2 days ago The above shows that we are in a period of model volatility (some would say we are ever thus but the initial mid December amplification was very, very well signposted from over 330 hours on all 3 main models) Because of this volatility any predictions (even next weeks northern blast) are highly questionable and changes can and will crop up.

The 12z GFS op broadly in line with the last few sets of ens which suggests troughs diving SE eventually Resulting in the possible development of Ural blocking. The lack of Ural blocking is for me the primary reason the Strat vortex has remained imperious thus far this winter. The 2019/2020 winter inhibited this blocking completely and feedback mechanisms from the strong Strat led to that horrific storm laden spell in February that year. IMHO we really need a spell of Ural blocking to cause a meaningful, absorbative disruption to the SPV. The current reflective event, along with the mjo’s slow progression to phase 8, generally sends the core of the cold stateside. As can be seen on on the GFS here… This temperature contrast will fuel lows developing on the eastern seaboard. Having them dive southeastward around the U.K. is the ‘best we can hope for’ at present and does form the main theme of recent GEFS runs, including the 12z Notice the potential retrogression of the Pacific ridge to E Siberia. There is a resemblance to the January phase 8 composite here, albeit the Alaskan ridge is further east on the composite (perhaps due to the reluctance of the MJO to progress fully into phase 8?)

You can’t infer that level of detail from that chart alone at that range. That mean is a blend of stormy SWerlies, Cold Easterlies and the scenario you mention. Tbh the former still looks most likely. However, I wasn’t trying to forecast a weather regime from the chart I posted I was merely commenting on the anomalous low euro heights which are generally a prerequisite to achieve the stated goal of this thread.

That’s quite the signal for low euro heights. And there’s a decent cluster that supports the op evolution of Scandi heights above them.

Caution: Cherrypickers spotted in the area ahead… GEFS 348 GEPS at day or so before EPS clusters Cluster 2 is indeed very blocked, good to see these options have returned as they were mostly absent for a few runs. The very +NAO option is there as a strong minority. Overall there is a weak signal for higher heights to the W/NW around day 12-15. Not unrealistic given the next bout of tropical forcing. We have another +EAMT event occurring and that should propel the GWO into the higher AAM phases. It should also at least delay any return to the low frequency forcing state. I’m also a bit surprised that we’re not seeing more of an impact on the upper strat, especially given the considerable wave 2 pressure coming into the reliable time frame Athough today’s GEFS are considerably toastier than for the last few days, though very ‘displacementy’? Opinion alert: We really need this warming signal to increase sharpish. Should this effort fail I personally believe the SPV will recover big time and couple with the lower levels. Similar thing happened in v early 2020 and we know how that ended up! Just a bit of cope/hope then for coldies whose hopes were so cruelly dashed over the past few weeks. Not that I trust it in the slightest, but it will be interesting to see what the EC46 does with this signal in weeks 3 and 4. Hopefully it builds upon it rather than squashing it.

One list one from me before I sign off. GEFS for the last few runs has had this little signal if the outermost reaches… I’m not sure what the extended EPS anomaly would look like, there are certainly some pretty stormy members but there’s 20 or so really quite interesting ones too. Bizarrely, the cluster algorithm has assigned a non +NAO regime to every cluster. Not sure a human would arrange them like that but hopeful nonetheless! This was the same clusters for the same time stamp in 2017 3 blues and a raging strat with ++NAO all other the seasonal / subseasonal dashboard. Hopeless you say? Heres what we ended up with This unforecasted ridge went on to produce a short but critical period of the Scandi-Greenland (high-low respectively) dipole pattern which provider the heat flux to destroy what had been a very very strong strat. The models can be wrong. At 72 (which we’ve just experienced) at 144, at 240 and certainly beyond. But we do need to hope they’re wrong about the strat this winter. All the best for tomorrow and beyond ! Josh

Noticed that too James, the wave breaking on that ridge recently and going forward has been quite the sight to behold. GFS 12z is a total outlier tonight but looks too early for me, however come the turn of new year when the AAM cycle starts to cycle up again I can see a scenario like that gaining support. In 17/18 a poorly forecasted wave breaking event in the Atlantic spawned a similarly unlikely Scandi ridge and ultimately led to the events that gave the strat vortex the knockout punch needed for the BFTE. I do think we’ve entered that territory now, where we need to get that knockout punch in before mid/late Jan as otherwise it will surely take over affairs until the best part of winter is done. Merry Christmas to all. Except the sun that is…As much as we love and need you, you’re definitely on the naughty list this year for spoiling our Christmas cold spell!

It only we had slightly less vigour in the jet… Need at least a 25% cluster to go with this otherwise it’s back to dreamin…

Extended EPS Slightly less +NAO options on the clusters. Though cluster 2 probably leans that way too. Looking through the members, about half have interesting, often highly blocked patterns. (No BFTE signal). The other half are varying degrees of unsettled westerlies. In the extended, there’s no clear signal on the GEM or GEFS either. Very hard to see where we’re headed, one of these not completely uncommon situations where the short term and extended ranges are elusive, but the warm up in the medium range days 6-10 is very clearly signposted. If there is to be a scandi high and ensuing cold easterly days 10 to 15 we need to see signs of it in the anomalies ASAP as they very rarely just ‘pop’ up, especially with us getting little help from the strat any time soon… Not seeing it just yet personally… One bit of good news mind, this protracted spell the MJO has spent in the west pacific probably spells the beginning of the end of this La Niña event. The low frequency tropical forcing, which the seasonal models were predicated on, is now less likely going forward. So every chance we could see a back end of winter that doesn’t follow the canonical +NAO pattern in NW Europe. Providing that is, that the strat helps us out and doesn’t go into PV of doom Mode. Looks pretty strong for the time being… There is a consistent signal for a minor warming to develop from the Euro side on the GEFS but it’s all rather unconvincing. Overall I’m stumped. Though I do agree with Tamara in the sense that despite all the recent trauma there’s plenty this winter has to offer just yet. As Marco P has stated, the drivers couldn’t be better for a cold U.K. winter. Hopefully they’ll be enough for something that will satiate the snowy desires of this thread!

We still need to discuss it though swfc, it’s the model output discussion and sooner or later we need to move onto the next question and it does look as if that’s going to be how much amplification can we squeeze out at day 8/9 and can the Arctic high for once come to our aid and link up with the ridging iberian heights?? The 0z EPS only had about 5 members really going for that so we’d need to see that trend grow and grow. If you’ll allow me to borrow a slightly edited quote from Star Trek 6… ‘I don’t trust Arctic highs. And I never will. I’ll never forgive them for the death of my Winter 2019 failed easterly.’

Mogreps: Much colder than 0z set and most members broadly back the op. 12z 0z Until we get x model agreement, which we never have had, we can only agonise over this traumatic period of model watching!

We’re all going to have to do this all again next week aren’t we! Cold air in place this time so we do want a bit of that energy to slide across, would be very snowy if it did…

Yep. Definitely not awful And COLD FOR ALL Seen as what we’re meant to be hunting for, it’s closer to awesome than awful!

I’ve seen a lot of awful charts in my life Feb. And this ain’t one of them.

Pretty sure that’s why there’s significant strat warmings on many of the GEFS members now. Too early to call it, but these slow moving west pacific MJO events during La Niña are strongly correlated to strat disruption. And this is turning out to be an exceptionally slow event. I won’t post individual perturbations (not my thing) but I’ve been following it, there’s a small but growing signal and it’s also in the GEPS too. The CFS members (including the BC) are torn between PV of doom V2: The PV strikes back) and a significant weakening. Nothing drastic either way from the 0z GEFS members but the 6z enhanced the warming signal late on 6z mean Not bad for a mean chart, surf zone for now but given the warmings on some members I think some serious heat would be about to enter the pole from there. Early days this and not a forecast hence why it’s in the hunt thread and not the strat one. But a few more days of this and confirmation of the protracted stay in P7 and I imagine many more folk will be paying attention… Im seeing this day 10 Iberian ridge too but personally I’m not seeing it there for the whole of the winter!

It’s still the best verifying model suite as a whole. I (and I imagine most others) still respect it more than the others. Though gfs and gem have improved noticeably imho in the last year or so. It’s more, As I and many others have pointed out, that the ecm (op especially but not exclusively) have scored a few ‘own goals’ recently. This and the weight of evidence elsewhere suggests we are right to question its veracity this time. You never know, it might still win the champions league should the EC46 be right about the scandi blocking in week 3/4!

Regarding the cold air moving south Xmas day/Boxing day… And Bearing in mind it’s clear outlier status it’s now ecm and Icon Ops vs EPS/GFS/GEFS/GEM/GEPS/UKMO/MOGREPS There’s people on the pitch. They think it’s all over…

Outer reaches of the extended EPS and still lots of blocking kicking about but a signal for the low to our SW to remain the talking point for quite a while yet… Perhaps the deep cold Over nw US is fuelling the jet. I don’t think we’ve seen the last slider gate, even the main trough at day 9 looks to eject some energy through/SE of the U.K. before becoming the dominant player!

Not in the last year or so Georgina. The ECM folk helped upgrade the GFS with the advent of the FV3 core and it has trumped it’s ‘master’ on a few key occasions recently. Last two runs the ECM has slowly trended towards the UKMO/GFS/GEM solution (e.g cold air moving south through Xmas day - Boxing Day with associated snow risk). The others have broadly ‘held the line’ for the last two runs. ECM is still doubtless the best model and I won’t fully ‘buy’ this spell until Itfalls into line however if I was to forecast it I would go with the southerly solution posited above

Bog standard cold spell? perhaps but We haven’t had a shot at a true white crimbo since 2000/2001! The latest GFS has a channel runner not long after! Not at 300+! Yes there’s huge uncertainty and absolutely you could be right but you know better than most Dan that so many options are on the table right now… The mjo orbit has to wane eventually, it doesn’t mean winters dead! Only the last frame of the EC46 is flattish but it’s hardly Feb 2020! Anything could happen in Feb. (For the record I too see a milder /wetter spell late jan early Feb but I still feel we’ll get a big enough SPV disruption to bring the cold back later…) You know the drivers this winter you can’t just write it off like that! Would you say July / August were done for in late June? When the drivers and long term teleconnections were ON side not off? The ECM has been poor imho since the upgrade and one mild set of EPS isn’t going to sell me this time. I won’t be convinced till /if it flips, but they’ve hardly led the way in this forecast… Save that last red flag for now mate. We’ll all know when the time to really throw the towel in comes, and it ain’t tonight!

I didn’t throw the towel in! Though after the ECM this morning it was holding on by a thread on my pinky! Seriously this could flip back both ways twice. But again the trend broadly today has flipped to a colder outcome from Xmas day. There are so many tiny minutiae that make so much difference that it’s almost impossible to forecast in detail. Central U.K. still looks favoured but even that could get squeezed out if the ridge gets to strong. Im now starting to become interested in what happens towards new year and personally I would like the Greenland wedge to descend well to the W of us (via the Atlantic lows disconnecting from the main trough.) There seems to be quite a lot of momentum in the Atlantic jet going forward so if the ridge collapses over or to the east of us it will simply become the next euro high. If it falls well to the west of us we might get a quick shot at a convective NErly. Right now at 240 that Atlantic low looks big and bowling ball shaped but at 240’s week ago we had an eternal U.K. high and look what happened to that. Finally I’m fully expecting the EC46 to back down on the blocking but hopefully not a total Sign flip. More importantly I’d like to see a cluster decelerate the zonal winds significantly to give us more clues as to whether the recent musings of the GFS are gaining momentum. (Note Judah Cohen’s respectable AER model supports a weaker vortex in Jan also).

GEM, at it again?? The only thing we should be binning is the ECM

Maybe being in phase 7 for nearly two weeks? Plenty of research to support a role for slow mjo waves through P7 triggering an ssw…

Note the 6z JMA also sends the first low under the block comfortably and with a stronger block than the 0z… Thats GEM/UKMO/ECM/JMA vs GFS If you’re new to this… don’t throw in the towel yet.

It would be rare for the GEM/ECM and UKMO, and their associated ensemble suites, the worlds 3 top verifying models, to be wrong over the 4th best at 72-96 hours. All the GEFS has done is double down on its 0z suite. It did the opposite on the 12/18z yesterday. Part of me wishes it didn’t exist, especially the 6 and 18z for the extra torture they bring! Tonights 12z will be key for me. But were it the other way round you would be expecting the gfs to flip back to the solution shown by the other 3...