Uncertainty

Check out this monster ridge on the ECM! Would be a seriously anticyclonic northerly! Could we have a 2nd decent July in a row? The first half is certainly looking that way…

You’re not wrong Blue CFS presently keen on a warm / dry August too Early days, but it’s hardly setting up as a 2007 redux, notwithstanding this week in the NW! FWIW, the latest contingency planner is veering towards hotter rather than cooler. I’ve felt all along the seasonals were going warm and dry in the south this season and no reason to change that supposition for the time being.

The Long awaited early July improvement is finally being signalled, perhaps from as early as next weekend as the stubborn trough that will be plaguing the NW this week gets replaced by a ridge from the Azores GEFS 174 EC op 168 Followed by a renewed surge of heights towards day 10 Still a long way off mind, the GEM not interested. The trough never clears out and the Atlantic heights build over the top. Broadly though even the GEM ensembles clear the trough eventually and build the hp back in from the SW Given the entrenched La Niña base state, what could be behind this +NAO suggestion? Surely this big push into the maritimes, aided and abetted by the rather negative IOD is the big shaker. I think this is a pivotal point in the summer, a bit like the Christmas Easterly Disaster (remember that ) and it could go a long way in determining how the season develops. If we do get the momentum push, then a period of warm/hot HP could well dominate early July. If we don’t then expect the base state to revert, Atlantic heights to blossom once again and the green snot magnet to activate once more.

Laughable consistency from the GFS UKMO, which has been so solid on a strong ridge building over the SW low from Thursday, has decided to throw a wobbler. Latest run for Friday AM Last night’s effort, more representative of recent days runs Nevertheless, a flimsy consensus is merging for late next week and weekend and the U.K. high option is emerging as favourite. ECM Saturday GEM I think the GEM sums up the situation. - HP looks to build but it’s strength is uncertain and modelling is not fully decided on it. Even if it did it wouldn’t be particularly warm, especially further SE - There are two interloper lows, one to the SSW and one to the NW that could easily spoil the jubilee celebrations for many - The previous scenario, where the low to the SW fully phased with the U.K. low and troughing to the NE looks less likely now Were the Hp to materialise there looks to be more pressure on it from the W from next Sunday night onwards, the ECM has been consistent on this in recent days There could well then be a thundery breakdown, followed by westerlies, more HP or who knows what. You get the feeling there’s another twist in this jubilee saga yet. Things do look better than a few days ago though.

3rd time lucky? ECM day 9 GEM day 10 GFS day 11 All 3 models build HP to the NW of Ireland, as the models generally have for about 11 months now. It has often materialised too, but the last few times it’s been modelled it’s trended S and E hence the frustration on here. NOAA has it too, as do the EPS But it’s not a strong signal. And recent history tells you not to book the bbq just yet.

Early thoughts on summer modelling… Headline: Could be worse, better in the south perhaps? Not much evidence of N blocking… With lots of 2007 talk kicking about, I’ve been following the seasonal modelling and expecting to see a trough parked over the U.K. and Greenland doing it’s best Dec 2010 rendition… but this just isn’t what I’m seeing. If anything, it’s the opposite, with an unusually strong +NAO setup seemingly the favoured option. Caveat: We’re looking now at smoothed out 3-monthly mean SLP charts. Interpreting these is of course fraught with uncertainty and only the most general gleans can be made and only if there is a consistent trend can a reasonable supposition be made. We’re going to be looking at the June - August period. CMCC A strong signal for LP over the pole, westerly HP? Cansips Lots of LP around the NH but just a hint of average SCeuro heights? ECM Again, a really strong signal for below average pressure over Greenland. A ridging AH with occasional incursions from the strong Atlantic. A horrid winter setup, but definitely a good setup for the southern half of the U.K. if you like dry summer weather. This heavily supported by the precip charts Meteofrance A weak signal for HP over Denmark on the significant anomaly (no signal on the standard anomaly). Less of a Greenland low but not dissimilar to the others. So what can we surmise? Not a 2007 redux anyhow, and little sign of LP hanging around S U.K. The signal for HP isn’t as strong as it was last year, when a definite trend for above average heights over NW U.K. was becoming apparent (and manifested). However the signal for a +NAO is very strong. So strong I face that we could foreseeably end up with flat unsettled westerlies , but even these don’t take much of an amplitude shake up to bring the odd hot few days and a TS (think July 2019…). The other possibility from the above is the euro high repeatedly repels the Icelandic low, thus allowing a very pleasant summer indeed to come to pass. We await the UKMO and the other Copernicus models to come out later in the week. But there’s enough hints in the modelling to hang fire on writing off summer before it’s even began. My punt is that it’ll be better in the SE than last year (not difficult). The NW is trickier and last year was unusual, but we could get in on the Azores action. Of course this could all be wrong, momentum could collapse and the Nina / -IOD combo could pin the tail on the U.K. trough and we could have a year W/O a summer. But that’s not what the modelling presently prefers.

I think you’re absolutely right Don. It now only seems to take a day or two to convert from a showery westerly to a ‘quick plume’ and end up with a very hot few days. 2019 was a classic for this phenomenon… And just a few days later… The drivers certainly don’t look great for warm and dry weather this summer, but using drivers alone would have told you last winter would have been cold… which of course it wasn’t. The CFS, cansips and to an extent a few of the Copernicus group models, give some hope to a better affair… I’m not seeing a 2018 affair (nor did the modelling in April 2018) but I’m not seeing the locked in washout many are anticipating. There’s enough heights to the south ok the modelling to indicate to me that some hot spells are likely this year, as long as we get an occasional bit of activity in the pacific. A 2018 redux does seem highly improbable though; as the Nina base state will tend to force lower AAM and that pesky Atlantic ridge will rear it’s head. As to the here and now, it’s the old winter classic. Where for art thou, Greenland high? Latest ec I do find it bizarre that such a climb down would cause consternation (not least from me) amongst the community during winter, but this latest flip is met with silence and shrugs. For most however, a collapsing high would be preferable than a cold northerly. Always the chance that you could stretch a further dry spell out of it should a U.K. high persist. I think the chances of a memorable early may cold spell have started to drift. Still time for the old counter flip though. Let’s check in midweek. Josh

Once again, the EPS have bowed to GEFS pressure… Yesterday’s 0z EPS day 8 mean Today’s mean for the same timeframe Much more HP influence and it’s westerly has become an easterly. I have said this countless times over the past year since it’s FV3 upgrade… the GFS and in particular the GEFS have improved drastically and are now to be taken in the same seriousness as the EPS. I’m talking about days 7-10, earlier than that I would still rank the ECM number 1 and the day 6 stats usually support that. So as @Mike Pooleconfidently bet the house on it now looks highly likely that this HP will be very influential late next week. It looks like sticking around until towards the end of the Easter weekend. Which would be nice

The Easter weekend now coming into view on the models and with rising AAM pressure looks like rising too. GEFS day 9 EPS The gfs suite has always been more bullish with this pressure rise and the EPS are still reluctant. Confidence is therefore highest in the SE for fine conditions with the NW most vulnerable to Atlantic incursions but it is an optimistic outlook overall. Both Ops generally align with their respective means. Beyond this, there are tentative signs the HP may focus more the the NW GFS MJO April P7 composite The EPS generally support this west pacific activity, but the clusters aren’t really interested in the GFS solution at present, though cluster 1 does have blocking to the NW but it’s too far away and leaves us with a west based -NAO So an increasingly blocked outlook to the North looks likely, where it places itself after it’s short U.K. stay is the next question…

Absolutely. In fact the 6z and 0z show the two extreme ends of the spectrum vis the developing low and associated front… On the 6z, the low barely develops… the energy simply feeding into the euro low leaving a cold NErlly in its wake. The front is thus pushed well southwards and by late Wednesday it has turned mostly to snow even over the SE On the 0z, the low develops quickly before it even reaches the U.K., washing out the cold uppers The ECM has found the middle ground this morning, developing the low but later than the gfs/icon 0z, leaving a band of heavy snow over the borders Whilst snow showers would quickly melt under the late March sun, a band of heavy precip with -8 uppers would easily suffice for settling snow and it is this scenario which could prove disruptive were it to occur. As we saw in late 2021, these disruption events under a weakish Greenland ridge are ferociously difficult to forecast. They are highly sensitive to tiny perturbations in jet amplitude and short term factors such as solar activity can make big differences even down to T48. Recently these events have trended NORTH in the days before leaving only central Scotland north in the snow zone. The 6z gfs still plonks the low over the N of the U.K. leaving a cold wet mess and this option is very much on the table still. If by Monday morning all models converge on an ecm/Icon style solution then expect warnings etc but until then I imagine it will chop and change a few times yet… Another interesting development is the change in emphasis post the above low. A strong westerly spell was very strongly forecast, but recent op runs have backed off and some now forecast heights to the N and W to be resilient, leaving a colder northerly regime rather than southerly tracking zonality as was previously indicated. GEM day 10 ECM day 10 If it weren’t for the strat reversal I would be highly dubious of the above but the switch in regime on these op runs needs close attention. Certainly an interesting period of model watching ahead…

Indeed Sleety, but this run shows how many pieces need to fall in place. We eventually get a cold pool transported around the high and then fired in on a developing trough as the high reorientates ECM is simpler and pretty cold but not particularly snowy at this stage. On both models the scandi high is 1050mb not often you see that, at any time of year. It does all feel a bit ‘what you could have won’ if the strat vortex had been taken out in mid December. There’s also a long way to go and these charts are day 10+ though you do feel quite that with the split and a more active mjo that a big block is plausible.

Some fascinating atmospheric goings on over the coming weeks, a dynamic final warming looks increasingly likely… The GFS op has done extremely well predicting last weeks shard shear event and it has also consistently forecast a much stronger warming and subsequent split this time round. Well supported now by its ensemble, the cfs, the GEPS and the ecm. The driver for this could well be the strong scandi / greenland dipole we currently have in the trop. This pattern, so notable by its absence in winter ( and most crucially, November) is optimal for disrupting the SPV and you would imagine there will be significant and long lasting tropospheric effects should we get a major split type final warming. In the medium term, the EPS is suggesting an easterly wind is possible around day 9 - 11. Garden path perhaps, but this is a really significant signal, not just an anomaly but a mean easterly. It should however be noted that there are very few very cold members, and the pattern required to achieve a true cold or even snowy easterly in mid / late March is not favoured on this or any other ens set at present. The alignment required for a NS snow machine event is highly improbable. What is clear is that blocking is forecast to become increasingly prevalent and that a cool/cold outcome can’t be discounted. The GEFS and GEPS are more conservative and opt for a warmer south easterly. NOAA perhaps closer to the more easterly eps prediction Beyond this, and into the back end of week 2, retrogression of the high and / or a merger with a new lobe of heights from the west looks possible and the strat split might allow this outcome quite easily. In short it looks like a ‘blocking - but where’ scenario is ahead. How much the events in the strat alter the course of the spring season as a whole remains to be seen but the odds of a cooler or even colder early part of spring have increased significantly over the last few days.

What a chart that is. We need many more of these over the coming days to have confidence but that folks is a beast and it’s only a week or so after 2018. Would pack quite a wallop. So different from the 12z and it’s the first real BFTE op we’ve seen. So low confidence and an extreme solution, but not implausible with the split in the strat and a QTR Classic streamer set up.

Now then…

2nd split showing again on GFS. Would surely finish the vortex and herald big blocking in the weeks ahead… Back to the easterly saga… The EPS strengthen the ridge slightly leading to quite a cold mean next Thursday . Remember this is from bifurcated outcomes so there will be some bitter members Temp spreads indicate too that a good cluster of members go ‘all the way’ with the cold Still, there’s not many op runs I’ve seen that go full on BFTE. If it’s going to happen, expect to some major model op runs really going for it tomorrow. There are more, like the UKMO, who don’t advert the cold anywhere near and begin queuing lows up in the Atlantic early next week I think there’s now high confidence that the scandi high will exist and that it will pack some serious cold on its southern flank. The key variable is now it a position and the ability of any Atlantic lows to ‘guzunder’. Ideally we would see some retrogression but that doesn’t seem likely at present. This ecm pert shows the way, but the fact I really had to hunt for it tells you it is not the sensible forecast tonight Nevertheless, and given the continued theme of this thread, the possibility of a spell of snow showers in the east and / or a stalling front from the west clashing with cold air is perfectly plausible and I’m sure Exeter are watching these developments as keenly as I am.

ECM entering at least mini beast mode That would be Not a great deal of snow though even with that set up. There isn’t really time to get the right orientation before the breakdown. The cold easterly has really gained traction this morning, but not a full on North Sea snow machine one. But this saga has been going on for 8 days now and the shape, size, strength, position and orientation of this scandi high are still shrouded in mystery. At the very least however, it’s existence does look likely now meaning an Atlantic attack is most likely delayed till at least Tuesday, or perhaps anywhere up to Friday. As mentioned by the MO, it is the breakdown which could be snowy. By the following weekend, there is a consistent signal for the westerlies to return

The fact is we still don’t know what’s going to happen vis the potential easterly. There’s as much uncertainty as there has been for a week now and it reminds me of the Xmas debacle. 6z icon and JMA both have stronger ridges than their 0z runs. Without the wildcard of the ‘shard split’ event in the strat you’d say the big easterly was nonsense but it remains possible. What a bizarre chart this is at the back end of the GFS And there’s not one, but two splits in the strat during the period on this run. Remarkable.

Wow! The game’s afoot!

GEM rolling out. Looks frost and chilly, but no snowy easterly. Nevertheless, The HP influence in the medium range has gained massive traction this evening. Don’t let us down ECM!

It gets extremely close at 156 pal Bit of shortwave bother after that so maybe not as clean as gfs but the icon has a big N Scandi blocking feature too A huge flip from these models vs last night. Look through the eps though a good many of them did go for this this morning and the scandi ridge option has remained at 50/50 throughout the last few days. Still time for one last flip you feel (in terms of establishing the block) but even if it does develop there’s still plenty of barriers to cross before the e coast snow machine powers up. Fascinating stuff mind.

Hahaha Are we sleepwalking into a day 8 cold easterly? I’m glad I’m not doing the medium ranger in Exeter tonight!

Marco’s saying it’s a split and it looks like it just about makes it to me. Surely this isn’t a coincidence Heights building to the NW of the U.K. splitting the PV into two vortices at both levels. Can anyone add anything to this? There is very little fanfare about this online. Presumably because a reversal seems unlikely and the temps don’t warm up enough to be a major ssw??? I can’t access the ECM strat charts, is it still going for a split? I’m guessing it isn’t given the op. Alternative explanation if the ecm strat profile is similar is it’s the stronger tropical signal on the GFS is driving the ridge. Maybe it’s both.

Next week starting to look a bit messy now, the low disrupting on Weds/Thurs gets trapped, slowly filling across the U.K. leading to a potentially quite unsettled 2nd half of the week After that at 168, we have almost full model agreement on high pressure building in strongly over the top. If you’ve been following my posts, or indeed the models, there’s no prizes for guessing which model objects to this scenario. ECM booo GEM High building strongly, easterly winds incoming. ICON Note that the limpet low stays over S U.K. here, but the high still builds strongly over the top. Wet, but hard to know what would happen next here, with another trough waiting to disrupt out west. JMA Again, the strong pressure build goes on to produce a significant Scandi high GFS The low sticks around close to the SE, but doesn’t stop the high building. GEM ensembles A mean high over Norway, though not a cold snowy easterly progged GEFS Still a strong pressure build, but the high more over the U.K. EPS Has the weakest pressure build, but still far stronger than the westerly op. The uncertainty over the existence and possible persistence of the scandi high only increases as the forecast period evolves. Still that 50:50 split with 2/4 clusters going for heights to the NE and two that don’t. By day 10, The uncertainty is most apparent on the spreads, which indicate large discrepancies in the scandi area. If it was anything other than the ECM you would dismiss it and forecast the high building over the top option, despite the uncertainty around the midweek low. But because of its status, the flipper can’t be discounted. I think this is a big test for this iteration of the ecm op. Should it get this right and the high fail to materialise then I shall once more bow to its omniscience. Should it not however, then my suspicions that it is presently not to be trusted beyond 120 will be confirmed. We await the judgment of the weather gods.

It was this morning and for 4 days straight. I’m getting really tired of it’s flopping about. I still regard it as the best model overall but imho the gfs and gem are catching up fast and the former finally has an ensemble set worth paying attention to after the FV3 upgrade last year. If it only ran twice a day and only went to 240 its rep would probably be better but there’s no doubting it’s improved day 8+ and the EPS has gone backwards. All the other big 5 Ops have an easterly at day 8 and the European centre for medium range flipcasting picks just about the most unsettled member as it’s op and then to make matters worse it brings back the flooding spectre for most of the U.K. As expected this is proving an immensely difficult outcome to forecast. Clearly the strat is involved as at same time as the high/no high shenanigans are occurring the 10hpa vortex is *just about managing to technically split Most forecasts have it very quickly reorganising and at this rate it’ll still be pumping iron come the solstice! The GEFS on the other hand are slowly but surely coming round to the idea of HP winning out over scandi, but not really in such an orientation to give us a cold snowy easterly, more of a layers of stratus affair but still preferably to the ecm option (though there is a chance a front could get ‘stuck’ straddled N/S over the country sometime between Thursday and Saturday before the Ne heights assert themselves and squeeze it out.) An anomalously positioned 1030mb high is often the sign of growing confidence in a forecast. The GEM goes one step further Regardless, the models do agree on a westerly flow returning towards week 3. But that’s a long way off. Still time for at least 3 more ECM flips until we know what next Monday will bring.

It does Nick but I agree that a return to a flat outlook next weekend as per some of tonight’s eps members is equally unlikely. The latest GEFS is actually firmer with the blocking trend and just about manages a mean light easterly The GEPS even more so It is the ECM which has flipped embarrassingly again, this time to a mean sw flow So the half way house between cyclonic and cold easterly is often a UK high. As @Cambrianpoints out, this has been the pattern of this winter period. There are 2 particularly complex factors that make the forecast for this time next week challenging. a) The behaviour of this low: On this latest gfs it just about cuts off from the larger parent trough in the Atlantic and undercuts. This allows another ridge to build over it keeping it at least drier for a while longer. The 12z kept the two lows in phase, leading to a flatter solution These lows are very difficult to pin down and essentially reflect the amount of jet energy that is able to split off SE (or not). 18z 12z B) The movement of an Arctic high These dastardly features have done us no favours at all in recent years and SO rarely fall right for us. But They are critical in providing a link to ridging from the South. 63, 47, 2018 all famous examples of a successful link up kicking off a cold spell. Here is the Arctic lobe on the 18z, looking like it might descend promisingly… But the link to our ridge next week never fully establishes, and the zonal train starts up again. Pert 1 for example here shows how a disrupting low, upstream ridging and a perfectly positioned Arctic high can work in tandem to open the gates to cold from the east. The latter sucking up the scandi ridge with lows forced into Europe. So the halfway house might be something like the GEM 12z Which whilst not snowy, would be very pleasant for most, much like much of the next week. Taking the modelling together at the moment, and especially if the ecm reverts closer to the GEFS / GePs tomorrow, then I would say the above is the most likely option for next weekend. But a simple forecast it ain’t.