fergieweather

Indeed, and rapidly-growing spread remains evident post-Tuesday. Inspection of postage stamps shows a veritable raft of possible outcomes by Weds onwards (one member even with a deep low barelling-into the UK... just to keep us entertained!). However, both Op & experimental runs of 00z EC do jointly lean to a muted recovery in temperatures after midweek, peaking to average for a period towards end of the week/into mid-month. Tail-end of experimental run then suggests these start falling-away. Nonetheless, given ongoing spread and varied to-and-fro between models and inter-run within their respective suites, it's inescapable that confidence into the 10-15 & 15-30d periods remains very low.

Yes, intriguing. Next week remains tricky: as of last night, a switch to a more mobile, milder W'ly pattern was slightly more favoured to emerge onwards into mid-month (60% prob), albeit the opposite scenario (retention of cold blocked set-up) had fairly sizeable minority backing (40%). The 00z EC ENS are awaited, of course, to assess level of support for the deterministic run. In many respects, recent GFS runs towards mid-month seem over-cooked (re scope of more vigorous westerly patterns) and are viewed with suspicion. The more favoured outcome at present remains a slightly higher chance of a transient westerly phase into mid-month (coupled to a bounce-back in temps), but a likely resumption of cold, blocked scenarios later in Nov (postage stamps from GloSea showing a variety of these). As we've seen in previous winters, expect operational models to struggle/take a few bites to adequately synthesise the route ahead, set against emergent influences (MJO expected into phase 7/8; and ongoing stratospheric shenanigans).

The tipping-point of key uncertainty emerges next week. Will the westerly pattern come blowing-through, heralding a steady return to average temperatures on towards mid-month (as now strongly indicated by sizeable majority of EC 12Z ENS)... and if so, will longevity of that phase prove rather transient further into the month? Imponderables, for now...

Yup. Abnormally weakened stratospheric PV 1st half winter, says GloSea, before flipping other way to much stronger into Feb. But there's much water (or zonal winds) to pass under the bridge before we get too clever into that period.

Correct. GloSea5 points to a weakened PV throughout the period. Note the markedly low probability for +ve avg temperatures overall (compare to last year's prognosis!). Anyway, it's all for a different thread: Apols mods. :-)

Can now let this cat out of bag. http://www.metoffice.gov.uk/services/public-sector/contingency-planners Sorry had to sit on this until formally released in last few minutes!

Note I mentioned *probabilistic* output (you'll see more on that later today). However, spread in plumes next week onwards is very marked. There's a growing but presently 20% assessed chance of Atlantic mobility/zonality appearing later this month and the upturn in temp anomalies appearing towards end of Nov, whilst tentative in latest 30-d suites, may be instructive in this respect. What longevity any such phase yields (should it indeed verify) is another matter, set against the background probabilistic tone as we switch into winter. Current view is it may prove temporary....

It may not (in any pronounced sense)... a very different probabilistic look to the coming weeks ahead ;-)

... just FYI, that's essentially based on GloSea rather than MOGREPS. As I mentioned in an earlier post, the favoured outcome by UKMO remains -ve AO/NAO (due to combination of stratospheric state; sea ice & Eurasian snow cover) through the next 30d period. The 3-monthly probabilistic outlook (N-D-J) will be made available next week.

I subscribe to Bluearmy's cautionary note. Whilst 00z EC EPS agreement is fairly good on a cyclonic NW'ly regime into the 7-10d period, spread has increased (cf 24hrs ago) onwards into d11-15, including the proportion of members exhibiting a leaning towards an increased westerly component. However, it's still a shifting signal, with only a low level of agreement. So, as before, forecast confidence remains effectively low beyond next weekend, albeit continuation of an amplified pattern remains favoured through the 1st half of Nov.

....but do bear in mind the inevitably low confidence at that sort of lead time. There's enough 'issues' to unravel in the nearer-term medium range... albeit the broad sort of blocky/slowly-progressive pattern anticipated through first 2 weeks of November is favoured to *probably* persist thereafter. Key word 'probably'.... :-)

Yes, quite so - we were just discussing that at work. It'll be interesting to see if that tentative signal and associated 'dip' in 850 temps late month is bolstered in further output.

Just a note about interpretation of the anomaly fields in EC Monthly. When these (eg 2m temp fields) resort to nil/clear areal signal, this should be taken to mean there's 'no useful signal' that departs from the model climatology. It does *not* mean, de facto, that a signal reflects no potential for milder/colder than average conditions; merely that we should read it as the signals having weakened to such an extent as to no longer offer any useful steer away from climatology. Some people seem to read these 'nil' signals - such as when emerging after an earlier phase showing -ve temp anomalies - as thus meaning it turning 'milder'. Whilst that could of course be the ultimate outcome (especially if other model parameters are suggestive of that), it does not mean that result is being actually shown by the anomaly itself.

You'll have seen the 2m temp and PPN anomalies from EC Monthly posted above (via Hungarian Met Service). The temperature anomalies weaken substantially after week 2 and are thus of limited significance thereafter, whilst conversely, 500hPa GPH anomalies continue leaning towards +ve heights to the NW of the UK throughout November. However, bear in mind that nearer-term, forecast confidence is low on outcomes beyond circa 4th November, with a widening synoptic spread having emerged in the 00z EC ENS beyond 1st week or so of the month (albeit underpinning a continued theme of temperatures a bit below normal). Glosea favours those -ve temp anomalies to generally remain this month, with -ve AO/NAO considered by UKMO the more likely outcome onwards into early winter. But as repeatedly stressed, respective high-low centre(s) positioning remains very low confidence (& ditto re possible strat-related matters late Nov and/or early Dec) and consequently so do the weather outcomes for the UK. So in short, no confidence can really be expressed for now beyond week 1 of November.

No, not much to add other than I'm trying to recall the last time we saw output (irrespective of ultimate veracity) appear like this in early Nov. I'm sure someone keen on archive-fishing can tell us. Either way, as you rightly note the paucity of unambiguously zonal signals into medium range lately is all the more noteworthy, given typical model tendency to ultimately lean or revert towards climatology (ie a more energetic W'ly). In all honesty, it's all very extraordinary stuff (as per Lorenzo post), but we were anticipating an extended period of 'curiosities' to characterise NWP watching over coming days (weeks??).

18z GFS going off on a November journey into a coldie's Nirvana. Did one of you lot hack into NCEP's dynamical core coding? ;-)

Not at all. 12z EC EPS continues to show a conspicuous descent to (possibly fairly marked) below average temperatures 1st week of Nov. Extended EPS clusters beyond T+240 offer various colder (mostly cyclonic) possibilities in the mix. Nothing can yet be discounted.

Ops Centre don't buy the way the UKMO-GM disrupts the trough earlier (versus other operational centres) across the mid-Atlantic, thereby amplifying the pattern in such a pronounced fashion as suggested by the 12z run. Perhaps instructively, the majority of MOGREPS members - at least for now - don't support it, either. Time will tell.

UKMO indicate that the ongoing model turmoil for Atlantic developments/major trough disruption into medium range can be traced back to key analysis differences emerging in western-central Pacific. In other words, we're seeing the back-end of modelling issues harking from other side of the globe. I doubt this will resolve any time soon...!

The EC monthly run looks unconvincing when set against 00z EC ENS. Herein lies the cautionary note regarding lagged models for extended range. They can quickly fall behind the curve...!

EC Monthly has large above average 500hPa GPH & MSLP anomalies to NW of UK into early Nov (the +ve GPH signal then remains to end of run), with low pressure over Scandinavia 1st week of the month. GloSea5 is in agreement with this for 1st week of Nov. Into 2nd week onward, GloSea maintains a weaker +ve MSLP signal over and to NW of the UK. Bias between anticyclonic v cyclonic signature is indistinct by then. So in summary: a leaning towards N/NW'ly mean flow early Nov. Neither model suggests anything other than modest progression, with likelihood of any vigorous westerly regime continuing to look much lower than normal.

Pattern remains prone to amplification through the 1st half of Nov (at least), with currently scant sign in either ECMWF or GloSea of pronounced zonality/deep lows/strong westerly flow, at least for now (EC's monthly suite runs again this evening). As previously discussed, where we ultimately see respective high/low centres positioned remains open to considerable uncertainty (eg as per model flux last 24hrs) but given the amplified tendency, will continue to offer potential for northerly outbreaks. I wouldn't be at all surprised to see this sort of muddle repeating on through the next fortnight (or more).

I don't see any major change of emphasis for the week ahead...albeit boundary layer detail will be the main day-to-day headache. If, however, you refer to extended medium range wax and wane lately... that's why we use ensembles/clusters at that range, not deterministic runs!

....and some very interesting ongoing signals for rest of Nov and 1st half of winter. Rest assured we have some very interesting model-watching coming our way :-) Enjoy.

Yes, GloSea5 performance has been good thus far (including stratospheric modelling for this period from runs even output back in mid-Sept), but ECMWF Monthly model was equally very keen on picking-out the potential (as now reflected by operational models, albeit devil will be in detail) for +ve MSLP building to NW and resultant cooler/colder flow into early Nov (refer to my earlier posts re this expectation). How much this emergent pattern will then sustain through November is quite another matter, but for now at least, there remains scant sign of 'mild 'n wild' Atlantic-borne weather within the latest (12z) ECMWF ensembles across the 15d period. With the GloSea prognosis equally considered, such a pattern still remains less likely than average during the early to 1st half of next month.