stodge

Evening all It seems any lingering hopes of a chilly PM outbreak over Christmas are becoming restricted to the most northern hills and mountains. Twas ever thus... The post-Christmas evolution remains far from clear - the straightforward sine wave of ridges and troughs is one option but signs also of other possibilities and options. I continue to note the strong 10 HPA warming signal from the GFS 12Z OP and arguably 12Z Control might be where many would like us to go into 2024.

Evening all ECM at T+240 does throw the live grenade into the sack of presents but as others have opined it's hard to take seriously until and unless we see some support. It's always looked like a milder interlude through Christmas and New Year especially for the south but perhaps wetter than I had first thought with a succession of shallow LP moving through the British Isles. As to the start of 2024, no real clues - glancing at the 10HPA on GFS still piques the interest for a strong warming but I doubt we'll see any benefit as all it will do initially is knock the PV back over to our side of the northern hemisphere so if I had to hazard a forecast for the first part of January, I'd go with unsettled, possibly stormy at times and mild.

In all fairness, they rarely do. We know a lot of pieces need to fall just right for a prolonged and memorable cold spell (as distinct from brief transient cold with snow on hills). The models are suggesting a cold or at least chilly spell close to Christmas as the trough drops into Scandinavia (945MB over Sweden anyone?) and you'd think any north or north westerly in December is going to deliver to high ground and at times lower ground in the north. The brief period of negative alignment caused by the trough dropping SE looks set to be brief as the HP builds back into Iberia and re-setting the alignment to positive. There are some "interesting" signs in the background signals and a number of LRF suggested a backloaded winter so we could be looking well into January or even February but we're barely one third of the way into the game - a long way to go.

The GFS 12Z OP suggests the warming beginning not in Siberia but Europe which is unusual. I'm not keen on Siberian warmings because that usually sends the PV back over to Greenland/Canada but a European warming would, perhaps, send the PV back over to Siberia or western Canada which would suggest heights over Scandinavia during January. Just how it looks to my untrained eye...

Evening all The key seems to be how the push of heights from the south west is going to play out. It could migrate right through to Scandinavia and set up a cold block - it could sit just to the west or south west and offer the possibility of transient cold as LP systems move NW-SE across the British Isles or it could establish a mid-latitiude block over the British Isles. A mid-latitude block in mid-December isn't going to be "mild" - temperature inversion under clear skies would lead to very cold night time minima and low daytime maxima as the days are at their shortest. It's the route to ice days without snow.

I'm going to disagree with you here, Nick, but purely because the main ECM run is shown at 24 hour increments. As we know from the song what a difference a day can make to a developing or evolving scenario. The 0.4 ECM run which shows the evolution at 6 hour increments is much more helpful. The HP begins as an Azores ridge, becomes a cut off HP close to the SW approaches and then ridges north as a small LP heads into BIscay. That latter feature is, I think, crucial in stopping the ridge moving into Europe. As to whether any of this will verify, I've no clue.

Evening all Saturday's LP passes over London at lunchtime at 962MB - I think the winds could be more of a feature both before and after the rather complex LP has passed. In my neck of the woods, quite a strong SSE'ly in the morning and a strong N'ly in the afternoon. After that, perhaps a more "traditional" Autumn set up with LP further north and transient ridges but little sign of anything settled at this time. There seems to be a persistence of heights to the north which keeps forcing a negative tilt to LP as they approach the British Isles sending the core either over England or just to the north accnetuating both wind and rain.

Evening all Here in East London, my thought is also we've had a narrow escape. I was worried the storm would shift NE to the NW of London and we would be on the windiest side but as @Blessed Weather has pointed out above, the forecast track was further south and east than many models had suggested. I don't have a barometer an would love to know the MSLP as it passed over London this morning - forecast to be 953MB but I suspect a notch less intense. The wind here has been stronger this afternoon and evening from the north west and now west - plenty of rain once again. I know Lingfield Racecourse had 34 mm of rain but I've not seen the 24 hour cumulations for London.

Evening all The track seems to be settling on a straight run up the A30/A303 from Cornwall to London and I'm wondering if on 10am on Thursday the centre will be more or less over my head at 953 MB. I'm concerned about the S'ly gales preceding and the NW'ly gales following - I also have some concerns about water piling up in the Thames Estuary so I suspect the flood barrier will have to be raised.

Evening all Slightly apprehensive here in East London - I really don't want bits of West London flying past my window. I'm far from convinced the track of this storm has been resolved even at 72 hours out. UKM takes it north - ECM puts the centre of the LP pretty much over my head while GFS 12Z OP toys with the 1987-type SW to NE move (hopefully, as others have said, without the sting jet). GFS 12Z OP forecasting 7 inches of rain in the next 10 days for parts of South Wales.

Evening all A prolonged and wet spell for southern Britain is knocking on the door - 4-5 inches for London over the next 10 days and I suspect we're going to see some flooding issues. Planty of rain for eastern Scotland and parts of Ireland as well. After a dry early autumn, the second half of the season looks set to give the south in particular a real soaking.

Evening all As is often the case at this time of year, tropical developments are keeping us all on our toes. The remains of Lee won't be an issue and neither will Margot but TD15 (presumably to become Nigel in all good time) could be a big player in our part of the world. 12Z GEM has its remnants hitting us as a 975 MB LP in ten days while ECM keeps it to the south west but it remains a potent feature. The initial NHC guidance taking it close to Bermuda has already markedly shifted east so who knows if it will recurve early and keep its strength longer in the warm mid-Atlantic. I'll get this in first - we should be making plans for Nigel.....

From what little I understand, the key is the trough over the eastern part of the US. I'm not quite sure how it would interact with Lee but presumably if it is ejected east, Lee would be caught up in the circulation and recurve further out to sea. A slightly more westerly track might spare the continental US but presuambly places like Nova Scotia and Newfoundland might see a landfall and I would imagine Lee would still be a powerful system.

Evening all An unusually warm start to September being proposed by the models with the peak of the heat (so far) on Wednesday with 32-33c quite likely around London. That puts the London temperature record for September of 32.8c under threat and I could easily see that going on Wednesday. I also suspect the night time records will be under threat as well. From there, the heat does slacken to a degree and it looks a 7-8 day affair which is noteworthy. Not "undeserved" after a disappointing (for fans of heat) July and August. The only note of caution remains the tropical or ex-tropical features. The forecasting of Frankin, Idalia and Gert has each in their own way shown how difficult it remains to get these features right.

Evening all As it now seems likely Franklin, albeit as a major storm, will head to SE Greenland rather than re-curving fully into the Atlantic, we can see the impacts. One is to raise heights over Scandinavia - there seems to be residual heights in the area and it's possible the British Isles will sit between heights to the NE and SW and lower pressure to the NW and SE or south. This means another spell of E'ly winds and thundery conditions can't be ruled out for the south as we move into September but the emphasis tonight is on a restoration of "normality" with low heights over Greenland and heights over the Azores trying to ridge in. GFS remains unconvincing and wants to bring heights back into Greenland so those calling a warm, settled September are, I think, premature. If the core of heights is too far NE or SW, the British Isles ends up in a col or coming under the influence of either the European trough or a negatively aligned trough running NW-SE and it's much less settled. Original post: https://community.netweather.tv/topic/99056-model-output-discussion-mid-summer-onwards/?do=findComment&comment=4912857

Evening all As it now seems likely Franklin, albeit as a major storm, will head to SE Greenland rather than re-curving fully into the Atlantic, we can see the impacts. One is to raise heights over Scandinavia - there seems to be residual heights in the area and it's possible the British Isles will sit between heights to the NE and SW and lower pressure to the NW and SE or south. This means another spell of E'ly winds and thundery conditions can't be ruled out for the south as we move into September but the emphasis tonight is on a restoration of "normality" with low heights over Greenland and heights over the Azores trying to ridge in. GFS remains unconvincing and wants to bring heights back into Greenland so those calling a warm, settled September are, I think, premature. If the core of heights is too far NE or SW, the British Isles ends up in a col or coming under the influence of either the European trough or a negatively aligned trough running NW-SE and it's much less settled.

Indeed and quite often ex-tropical systems work in our favour giving the jet a nudge and pushing the Azores HP over us. The problem is their unpredictabilty - as an example, GFS, GEM and ECM all have different evolutions for Franklin. The idea of the storm as a cut off dying on the approach to the UK just doesn't sit well - I think the idea of Frankin being absorbed into another trough and intensifying that feature is more credible but that in turn helps as described above.

All optimism aside, given the models haven't got a coherent line on Hurricane Franklin, I think making assumptions about September may be a shade premature. Will it be a "busy" season in the tropical atlantic and what kind of tracks will be favoured?

Indeed - my point is the models may well struggle with this unusual combination of factors in trying to come up with plausible evolutions. If we aren't certain about how Franklin is going to play at T+168 we can't take too much notice of the rest of the output. My personal view is the warmer SSTs may well encourage tropical development further north and east from what we might expect - we have seen, for instance, tropical features move to the Azores or even the Canaries and these serve to displace the usual HP systems further north but these in turn become more elongated as they interact with the jet stream. I'm NOT suggesting we'll see hurricanes - we know of Medicanes for example - but what I am suggesting is tropical characteristics surviving longer over the warmer waters and the transitioning to more standard LP features happening later and nearer to our shores.

Evening all Once again we move into that time of year when ex-tropical features can play their part (often indirectly) in our weather. Frankin will become a Major Hurricane when it passes west of Bermuda and hile it's basically a fish storm it will get close to Newfoundland after the weekend and then head into the Atlantic as an extra-tropical LP putting some energy into the jet, lowering heights over Greenland and allowing the Azores HP to finally get its act together and ridge across us later next week. From there, who knows? GFS 12Z OP transfers the Azores HP quickly into Scandinavia and then further east and the trough fills the gap. GEM, on the other hand, brings the remnants of Frankin for a visit.

I have to say, contrary to some, I found today "pleasantly warm" but not unbearablly so. Some very warm air is close - just the other side of the Channel - but while the +16 850 might flirt briefly with the south coast, tonight's charts certainly make me think by the end of the week into the weekend and beyond we'll have seen the end of any serious warmth. Huge caveat - as we all know, tropical features can change the picture. Franklin, currently a tropical storm , is set to be a hurricane by the weekend and could, if GFS OP is to be believed, move north and then east and inject some energy into the jet - now, the real path could be very different but it's one to watch and with a possibly active season ahead, we have to see how these ex-hurricanes and ex-tropical features interact with the other synoptics.

My only observation so far would be if we were to have above normal SSTs going into winter, we would expect storms to be more intense as they could draw warmer air and moisture from the sea. In particular, I think we could be looking at a scenario of rapid if not explosive cyclogenesis of secondary LP features along slow-moving frontal systems bringing enhanced wind and rain. These phenomena tend to affect southern and central parts thought can also accentuate orographic rainfall in the Lakes and other areas. It wouldn't surprise me to see a spell of such strong secondary LP features moving rapidly ENE in a strong jet stream deepending rapidly across the warmer water and bringing a lot of wind and rain. We may get a hint of this if ex-tropical features coming off North America or recurving from the central Atlantic reach our shores with more potent wind and rain than has been the case.

It's a part of the world I've visited on two or three occasions and have spent Christmas and New Year in Rancho Mirage. It's extraordinary to see the volumes of water off what for us would be a lot of rain but of course for them it's months of rain falling in hours. American roads aren't well equipped to deal with the water and break up quickly and many American drivers, especially in desert southern California, have no clue how to drive in even light rain which always causes a spte of accidents. I've not heard of any fatalities mercifully and it looks as though "normal" service will be resumed from midweek with temperatures back over 100F. Whether this phenomenon will occur more regularly is impossible to know at this time - it's rare to have the synoptic set up of an upper LP in the Pacific and an extended HP to the east - it's usually the other way round - but as we've seen, the NH summer patterns have been disrupted widely this season.

Evening all Before looking at our impending predicament, it's worth noting the Hawaii fires were the product of classic LP (hurricane) to the south and a strong ridge to the north. The question for me is whether the synoptic set up is atypical as in whether a fish hurricane would be getting to this part of the Pacific as such a powerful feature at this time of year. In our neck of the planet, it's looking more and more like we will have some form of very warm to hot spell at the end of next week with ECM putting the +20 850 over southern England while GFS keeps it to the south - both evolutions would bring very warm to hot conditions but ECM would be severe but brief while GFS would be less severe and longer lasting with both likely to have a thundery breakdown from the west. The overall flow remains slack on GFS OP - Control is more progressive in replacing the heights over southern and central Scandinavia with a shallow trough.

Evening all Certainly a deal warmer today - a long way from really uncomfortable in truth but it looks as though any thoughts of high 20s will be of short duration and we'll be back to our much more tolerable 22-24c. Signs of another brief warm up at the end of next week but far from clear and already looking like a short duration event. GFS has the +20 850 air fringing the south flettingly before cooler air returns - oddly enough as the Azores HP re-asserts and this is when the Azores HP can be our friend. A strong ridge holds the heat to the south and prevents any LP dropping to the west and advecting heat from the south. I do wonder if we might end up in the trough between heights to the south west and north east - looks less likely noe but still possible.