fergieweather

I don't think GFS has, but I haven't checked ENS. EC toyed with it; e.g. as per the low probs shown in the 00z tropical cyclone activity prognosis further into the month:

Doesn't look 'mild' to me from those Theta-W's and an inevitably quite chilly E/SE boundary layer flow...?

Totally agree. Models have been playing with the Caribbean TD potential in latest runs and as you note, any such feature (should it become reality) then getting entrained into the pattern - with downstream effects - will cast major doubts over operational model handling of medium range, plus how the lagged 30-d models resolve it. We saw this sort of emergent saga with Nicole.

...and - as over successive runs across many days - GloSea remains keen on a blocked story emerging into December. It'll be interesting to see how ECMWF Monthly handles things later this evening.

It has been thus for many days. Tricky.

Ah, but other blocked solutions remain too. All to play for. :-)

If anything, the proportion of members showing deep cyclonic NW-W-SW'ly solutions in vicinity of the UK have markedly increased in 12z EC-ENS as we start the last calendar week of the month (some of these clusters look especially sporting). Fascinating and highly uncertain times ahead to keep us engaged.

With both long range suites (ECMWF and GloSea) still agreed on a zonal and/or cyclonic bias remaining into late November - and % likelihood of a blocked set-up emerging at some point from mid-month until then remaining very tricky to quantify - it's unsurprising we see operational models churning-out their present fare. It'll take a while for response to predicted MJO phase (to 7/8) in next week and half to be adequately resolved, with the favoured effect of these phases still apparently in conflict to the more mobile EC/GloSea signals we see at present. Indeed, it's only at the turn of the month when we see EC and GloSea both switch to a signal indicative of a more blocked regime (EC's Monday run developing heights to our NW, whilst GloSea evolves a broad +ve MSLP signal in vicinity of the UK). So there's still great cause for uncertainty and ditto, much room for suspicion about how models are handing the route ahead. As I mentioned yesterday, the ENS members going more blocked set-up mid-late Nov remain a sizeable minority... but ones that may yet prove prophetic.

...albeit equally interesting how we now have an emergent if presently minority cluster (circa 10% in 12z ENS) from the 19th, which - rather than raise heights over Greenland - instead do so markedly above Scandinavia and the White Sea, with a cut-off vortex to our south and a resultant net easterly flow. Varied medium-range shenanigans loom (persist!?), me thinks.

Yup. Very similar (for once) composite signal to both November's ECMWF and latest GloSea.

Sorry, let me just add meat to bones: above statement pertinent for DJF (early winter) whereas +ve MSLP anomalies drift to W/SW for JFM. Thus indicative of higher chance colder 1st half winter, with change into 2nd half, in keeping with UKMO assessment. A winter of 2 halves...

ECMWF Seasonal just released: extensive +ve GPH/MSLP to N/NW/NE of UK through its D-J-F suite. Consistent signal with last run.

...as may yet happen. Models remain in a fair degree of flux further into medium range. Lagged 32d runs may prove equally prone.

Worth adding that today's ECMWF Monthly lends some credence to the idea of a changeable NW'ly/broad W'ly theme dominated by low GPH always close at hand, with (like GloSea5) the next concerted build of 500mb heights (once again our to W/NW) holding-off until very end of Nov and on into early Dec.

Yes, by late in the month/into next.... but the mid-November period has retained lately a broad signal for NW'ly flow (including in GloSea) albeit this can mask anything ranging from a fair element of westerly mobility to something more northerly. EC12z EPS highlight well the varied spread into that period (and indeed on to the end of it's current run), albeit with 15d ensembles *broadly* favouring temperatures close to average from later this week onwards (with some inevitable oscillation). Whether this signal is wholly trustworthy is another matter, given marked spread and various colder options therein.

Normally around the 10th of each month. Like the Contingency Planner document, there's no 'set' date as such.

Indeed. It'll be interesting seeing how ECMWF Seasonal output tomorrow (and for that matter, EC Monthly this evening) handle prospects as we crossover into December, versus CFS (albeit that product doesn't receive the same weighting in UKMO seasonal assessment as GloSea, ECMWF and MeteoFrance-Climate) and what sort of parallel exists with them all, or not. GloSea continues it's path to resurrect the blocked theme later November and on through December... whilst the signal for an extraordinarily weak stratospheric PV remains an underpinning and noteworthy theme. Given how well the model has synthesised developments 'up aloft' since September, it does lean to fair confidence in how this now unfolds, at least in the broadest sense. 2nd half of winter could well be in a different 'mode' to the 1st, but let's see how Part 1 gets on.

Until the models (= all of them!) adequately resolve how the ridge out west (tied to low Rossby wave pattern) flexes in terms of weakening/strengthening, they will continue to flip dramatically as they try to synthesise what degree of propagation unfolds with the strong jet emerging from the US. We can see lately how both deterministic models and their ensembles are leaping around from one solution to another. This situation isn't some simplistic GFS v ECMWF v UKMO issue. The overriding fact is that limited confidence exists in ANY output beyond around d4. Moreover, ensemble means are viewed with caution: eg an ostensibly NW pattern may mask possible outcomes ranging from full westerly mobility to a less progressive/blocky northerly....

Hmmm. A brave shout... if based on ensembles post-Weds, albeit admittedly 'mild' shouldn't be confused with 'average'. The uncertainty remains stark, based on 12z output: the last few days have merely moved our confidence levels along one day at a time. And this incremental improvement in medium range reliability may continue for a while...

UKMO-GM 12z accepted only to T+108. But net result for Weds remains (as per last 24hr forecast cycle) the risk of snow from Pennines northwards, with much lower risk for uplands further south, such as Chilterns.

Yes, and it's conspicuous rebuild of +ve GPH to N of UK into tail-end of Nov/opening days of Dec has GloSea5 support, so even allowing for model lag I'm not convinced the entire run is without merit.

Hmmmm.... don't discount it! Snow showers possible down to circa 300m on Monday (in eastern areas) and dropping further down to 200m on Tuesday (probably focused in the SE corner of England), based on latest UKMO-GM, as the flow drops-away and picks-up an ever more maritime fetch, and the convective depth starts to increase . Never say never...

No, 8th (Tues).

It'll be fascinating to see if this ultimately goes the recent GloSea route (slack low established across UK into mid-month)...

Ah, caution here: whilst assessment from the 00z suites suggested a 60% favour for the westerly pattern, it is by no means clear-cut and this is exemplified by EC individual members for the period post-Tuesday. Moreover, even if such a pattern is indeed the outcome, it's longevity is questionable (e.g. GloSea indicative of blocking returning later in the month). The key point here is that in such a period of clear model volatility, with a bit of a knife-edge between the westerly/mobile solutions versus the more blocky ones, it's not sufficient to simply rely on ENS means. They will be skewed (in any model - not just GFS) by the more 'energetic' members (=the westerly ones) and may not offer reliable route ahead *if used or cited in isolation*. Inspection of individual stamps is essential and I'd be surprised if no GFS stamps offer a notion of either a much slower / less vigorous return to mobility (colder, slack conditions here holding on for longer) and / or something de facto blocked (as per 40% of EC 00z members, but we wait to see how this shifts in the 12z).