Singularity

Yeah okay, GFS is really digging for the spanners now with that vigorous low racing onto the scene from the Eastern Seaboard days 7-10 which leaves us waiting until it's had its fun with the UK before we can start to tap into the cold air again, but the alignment of the flow west of Greenland is great for building a strong ridge from the mid-Atlantic to link with the Greenland block so the rest of this run should be increasingly tasty to look at . Yes... getting there, through shortwaves and everything. Quite a spell for Scotland possible while things arrange themselves, but of course such specifics are not worth much at such range.

Funny how the 06z often seems to be more inclined to sharpen ridge-trough sequences (i.e. planetary waves).

At 6 days range we find that ECM has by far the most mid-Atlantic ridging, and yet as much as UKMO differs to ECM there, it also differs to GFS with respect to the blocking over W. Asia, which is more akin to the ECM run as there is a cut-off low (out of shot in the UKMO chart due to the weird cut-off) with the ridge building around it, rather than a low still attached to the jet stream off the N. Atlantic. As with yesterday, this is heavily dependent on how flat the jet pattern is across the N. Atlantic and into Europe. GFS remains stubbornly flat, ECM stubbornly not so, and UKMO is still lodging at halfway house. This is not helping with predictions for next weekend's weather but of course it tends to become more common during the winter season when the range of possible mobility to the pattern grows much wider.

So the sharper weekend pattern has further knock-on effects in the ECM 12z as a trough is able to drop down across Italy during the same period that the blocking across Asia is becoming very extensive. This has interesting consequences - shame they're way out at 9-10 days range and with the manifestation of the required preceding pattern in a week's time a subject of debate.

The retreat of the Arctic Ocean sea ice margins has certainly hurt the potential depth of cold in direct northerlies over the past couple of decades. Last winter it was the worst situation so far, but different wind patterns have allowed the sea ice to recover closer to what was typical a decade or so ago, which is not a big gain but better than nothing. Still - it seems we must indeed look NE to E for our coldest airmass imports these days. One may wonder about looking NW to Greenland, but unfortunately, descent of even extremely cold airmasses down the eastern slopes of the ice sheet results in a lot of adiabatic warming (the airmasses are usually very dry having lost their moisture while ascending the western slopes), which modifies the depth of cold to the point that it's no longe cold enough to be of much use after traversing the northeastern waters of the N. Atlantic. About a decade ago, I had hopes that disrupted jet stream and polar vortex patterns would increase blocking incidences close to our NE to such an extent that having to look between NE and E would not seem much of a problem, but alas, other forcing has proved sufficient to deny us much access to those bitter airmasses when even just a couple of the many teleconnections are in states that favour more in the way of westerly flows across our lands. It seems unfair until you consider that we are a small island nation on the eastern edge - so downstream based on typical thermal winds which are westerly - of a large body of open water through which flows a current that originates right down in the tropics. Well okay - the fact that we can't look to potent northerlies to interrupt this as much as was once the case, well that's largely humankind's fault anyway based on the majority of scientific literature, and it's true that those born into this already-damaged climate are getting a less than fair deal here... unfortunately, no amount of petition signing for example can rectify this - only mitigate, so that'll have to do I'm afraid.

We have a classic situation on our hands for Fri-Sat next week; GFS flattest with the ridge-trough combination, ECM sharpest, and UKMO at halfway house. The impact on wind direction is not huge; from WSW to WNW, but the difference in airmass across the UK for Saturday daytime is more significant; tropical maritime versus polar maritime. By Sunday the resulting 2-metre temperature differences amplify to some 4-5*C. Essentially it's a quite mild, cloud-laden WSW flow with a bit of rain in the north, or more or less a repeat of this weekend's conditions but without the mass of rain across England during the early hours. Having been out on a nice walk with various convective cloud formations lit very nicely by the low sun, I know which one I'd prefer...!

I can see why you're keen to share that East based does make things nice and interesting

The little low that cuts off Wednesday next week and drops into NW Europe would have had us on the edge of our seats in the depths of winter with colder air in place. First it was there, then it wasn't, then it really wasn't, then it almost was, and now it is again! p.s. I very much support the idea of having a dedicated mid-longer range MOD thread. This one here can become a dedicated shorter-term updates thread where viewers can head for a quick run-down on what the models are showing for the week ahead, say

It's been the biggest question on my mind this past month; what's behind these strong positive NAO projections from GloSea5 and CFSv2? Something must be forcing that. They might be some of the strongest with the La Nina but I didn't think that necessarily corresponded to a +ve NAO-dominated winter. It is most puzzling! May not be worth worrying about though, given poor track records in recent winters, and the volatility of recent NWP output with respect to even the broader-scale patterns (apart from the mangled trop. vortex, which is itself a contributing factor to the variability at hand).

Here we go again eh? Perhaps. Seems the silly season is starting to kick into gear. Prepare to be teased as usual - but it's about time something actually came off so here's hoping. It is best though not to set the bar too high, and just to enjoy the more entertaining charts as and when they come . It is true to say, though, that I have had one eyebrow inching upward at times today.

The models keep on screaming near-average conditions and I can't find consistent enough signals for much to the contrary, so a boring old 7.0*C is my guess for Nov 2017. If it's going to be wide of the mark, let it be a positive error...

Feeling more 'classic' this season with a near-average strength vortex that should resist warming events sufficiently for troposphere-stratosphere transfer to potentially (with enough supply) continue until the warming is large enough to have a more significant impact on the vortex, which is preferable to a dishevelled mess of a vortex that just gets displaced by even minor warming (the situation last Oct-Nov), messing up the troposphere-stratosphere transfer mechanisms, and can happily wait for support from the upper stratosphere to kick off big time (last Dec). Overall this should translate to less of immediate/short-term interest but more during the winter itself. Whether sufficient warming will actually manifest, remains to be seen.

As much as there are some disrupting troughs and blocking to the NE to wonder about, the past few GFS runs would each place UK temps as a whole very close to average as of mid-month, and this doesn't even hide all that much variability within those two weeks; just chilly, then quite mild, then chilly, etc. So nothing obviously exciting on the offering and the lack of any strong storms tracking across our lands is noteworthy. Vortex looking compact but rather weak to our NW (i.e. not very extensive) hence the exploration of trough disruption by some runs, interchanging with the most probable alternative that his an extension of subtropical ridging right across the UK, producing the aforementioned benign run of weather. Oh well - at least we'll have plenty of energy left for the real chases in the actual winter months!

It is interesting how the models seem to have this recurring idea of putting one of those mid-Atlantic ridges up toward Greenland, but with seemingly no real clue when this will actually take place, assuming it even does at all. Then again, I remember far too many of these 'dangling carrot' situations in recent winters. It just seems to be how NWP modelling tends to go.

Not without interest how the trop. vortex falls apart days 8-10 of the ECM 12z. Some very, eh, interesting discoveries while working today have got me paying more attention to this winter season at last. Most long-range models still seeing something different dominating the pattern forcing though, and it remains elusive as to what exactly. Anyway - I'd not worry too much about missing out on a few early northerlies, and in any case, we should after the past few winters be very used to the light being at the end of a tunnel that seems capable of suddenly changing length without any warning . If the vortex can be kept dishevelled in the troposphere and lower levels of the stratosphere, that's as good a place to start as any. IF.

So the first northerly teaser of the season has been adjusted largely or entirely (depending on the model) east of the UK, which I expect comes as little surprise to many who have battled through the last few winters. Good agreement in the EC ens. for settled conditions to predominate early next week, before much uncertainty arises over and a little east of the UK and the mean ridge shifts west, illustrating - as can be seen from other sources - the potential for a trough to drop down closer to our east in the 9-10 day range. Question is - will the same adjustments take place with time as seen with this weekend? This time we have the northerly signal coming forward from the long-range rather than appearing suddenly in the mid-range, so it's not the same situation as such... interesting times, although not very much so (at this stage at least) if you live way down south.

So let's get this straight - with a little assumption regarding the uppers not reducing unusually quickly during next Saturday afternoon, the ECM 12z run has the 15*C 850 hPa isotherm visiting the UK on three days out of the week starting Saturday (or Sunday if you like). We've had a hard time getting that to happen in a number of recent Julys (not this year's though, thankfully) so it seems pretty extraordinary to me.

The anomaly pattern still seems oddly inconsistent across the region. Starting to see some values near -2*C now though and with that trades outlook these should expand. Will it be enough to prevent October from having the warmest troposphere on record for the globally? I was amazed to see that September managed this feat but the negative equatorial anomalies were less intense back then. In our little part of the world, retracing ridge tendencies could make for some interesting weather patterns by late Oct, though this does not necessarily tie in with height rises far N. enough in the Atlantic to deliver much of wintry interest; for that the Arctic profile needs to behave nicely. That detail is still unclear at this range.

A shallow trough dangling down west of ex-Ophelia interacts with it enough to keep its core west of most of the UK on the GFS 12z, but the 12z UKMO sees less interaction with the core moving through Scotland, while ECM has less still and takes it through the heart of the UK. Thankfully, the system is weakening rapidly during this translation across our lands, but it still delivers a heavy blow to Ireland and a strong one to SW UK (ECM) or W. Wales (UKMO), along with some heavy rain. The Euro High soon shrugs this off in the ECM 12z though. What is it with this resilient ridge I wonder - could all that warm air that keeps getting thrown across at the upper levels and then slowing down be tending to sink and support increased SLP over the region? I'm not entirely sure of thermodynamics permits such a mechanism.

A slight reduction in the forward motion of Ophelia allows the plume to stick around a few hours longer on Monday. Optimal setup for maximising temps. In fact, given that back in May this year GFS fell a few degrees short with the highest temps when conditions were warm but very breezy, I'd not rule out a localised 25*C this side of the Channel. Incredible to see France largely in the mid-high 20s, let alone having already spent the weekend hitting the mid-20s widely. This push back of the Euro High on Tuesday seemed to spring up quite suddenly yesterday evening, and while the 12z applies more pressure from the Atlantic troughs than the previous two runs, this only serves to place us under tight pressure gradients for a time before the ridge winds out anyway - albeit with some cooler air cutting in rather than the balmy setup of what was a pretty extraordinary 06z in terms of implications for the month-mean temperatures. Hopefully this sneaky 'attack of the Euro High' is not a trend that will still be with us a month from now (as much as GloSea5 seems to think it will be... how dare it eh?).

If only it was January eh? Bit of a departure from recent det. runs of both this and GFS so just a wildcard at least for the time being. Much more concerning matters to deal with in the nearer-term, first in a positive sense if you like a late burst of warmth, and then negative for western Ireland potentially (and who knows, maybe a bit further east as the path may still shift by up to 100 miles one way or the other - although either westward or little change both seem more likely than eastward due to the Euro ridge looking quite impressive). The tropospheric vortex sure seems to be having a bit of trouble getting its act together this month - but this taking place in October means little of significance for the winter as was made apparent following informative discussions not long ago in the stratosphere thread.

Some quite impressive warmth building across W. and C. France on this run, with support from the preceding 00z plus the 00z ECM. If we could just get a more direct feed from the south on the day... but that's being greedy I know! As far as I'm concerned a late reminder of summer is perfectly fine in October, before my opinion steadily inverts itself as November progresses (early cold in that month rarely cuts the mustard all the way down here).

Interesting to note the weak vortex spell in October that year too. It would take a lot to prevent a recovery to near-average at some point which from the looks of things ought to be enough for a sufficient magnitude of breakdown. Looking for a nice clean split for a change rather than the messy developments of last winter and the unhelpful displacements of the one before that (we sure have been through a lot of frustrating shortfalls in recent winters...).

Another key aspect last winter was long periods of moderate-strength stratospheric warming with positive height anomalies frequently having some but not a lot of influence on tropospheric patterns... yet still enough to - ironically I suppose - interfere with the vertical wave activity needed to produce a bigger, more effective warming event. Or at least, that's what J. Cohen deduced from how things panned out.... he's not had the best track record these past few winters so there's no guarantee that this is an entirely valid theory. What do others make of it? TIA If it does hold truth then I will have some concern if the vortex is consistently very weak from early on as this seemed to be what facilitated the long-duration-yet-weak-magnitude warming tendency of last winter. Just my take on things though!

Very interesting that just as with last year, we're seeing a lot of heat flux into the Arctic troposphere and with subsequent vertical wave activity flux modelled to disrupt the formation of the polar vortex. Under the new 'oceanic Arctic climate' that may well have established, this troubled vortex formation could well become the new 'normal'. Too early to be sure about that climatic shift though; a few years prior to last started off about as balmy in the Arctic but then dropped nearer to typical temperature setups. If the weather patterns continue to bring a lot of heat poleward and then upward through to late autumn then it will be time to start wondering just what might transpire given that last year some promising developments were scuppered primarily by an exceptionally strong westerly QBO (and perhaps a bit of solar forcing) which allowed the vortex to exploit a relatively brief lull in wave activity forcing to spin up furiously and achieve a state capable of taking on a lot of warming events with barely a wobble. Given shortfalls in handling poleward heat flux into the Arctic, I don't expect the models to do very well at spotting whether we will have a disheveled vortex as we start the winter. Lots of waiting and seeing to come. I will occasionally comment but will have to be far more restrained than last winter due to work commitments. 7 winters now without satisfactory duration and/or intensity of cold & snowy weather here in S. England. Here's hoping for an overdue change of fortunes!