stodge

This was, as I recall, one of the possibilities from the SSW and something mentioned by Judah Cohen as a possible outcome. If you get a strong anticyclone over the Pole the possibilities for cold at lower latitudes increase considerably because, as you rightly say, the cold gets chased south. One evolution touted last week on a number of GFS OP and Parallel runs was dropping the trough into NW Europe or Scandinavia with a mid Atlantic ridge behind it - the 12Z Parallel ends with a sharp N'ly. Other evolutions today have returned to the possibility of the mid-latitude block creeping into southern Scandinavia. - you can see the kick of WAA between T+288 and T+300 over eastern Greenland on the 12Z GFS OP that allows an HP to build over Scandinavia and re-enforce the mid-latitude block. Developments in the stratosphere continue to intrigue and perplex in equal measure and as others have said may constitute to make the model output even less unreliable than usual. We seem to have stepped back from an Atlantic breakdown in the New Year to a continuation of the quiet anticyclonic theme but it's by no means assured and a number of the GEFS keep the signal of a revived stronger jet. Oddly enough, as the cold does draw out of the Polar region I could see a brief return of a more active regime before more amplification takes hold. The onset of much colder conditions took two and a half weeks in February from the initial PV split so if the split is due Jan 1 that takes us to Jan 18-19 or thereabouts and as I recall there was plenty of wailing and gnashing of teeth earlier tin the year when some output seemed to suggest the SSW having no real effect in our area.

From this night 12 months ago, this was the projected state of the PV on 11th January 2018: Tonight's 12Z Parallel offers us this: Quite a difference.

We have seen a shift in emphasis in the past 48 hours. The Scandinavian HP has been off the table for some time and we are now looking to the north and north west. OP. Control and Parallel (I think) are surprisingly similar - all flatten the second HP but shift it west in the week after New Year before bringing the trough SE into NW Europe with mid-Atlantic pressure rises behind so quite a potent shot of PM air followed by (hopefully) a mid Atlantic block. As to the strat, certainly plenty of signs of the PV coming under serious strain and fragmenting rather than splitting and is there another minor warming coming in the New Year?

Afternoon all Sometimes the new day makes things clearer but more often it only makes it all murkier. Those who were hoping for an early New Year present from the stratosphere look to be out of luck - whether we get a split or a displacement the initial impact of the ongoing warming seems to be, as we often see, to re-group the focus on the Canadian side so the second burst of HP which sits over the British Isles as a mid latitude around New Year is flattened as the jet powers up at the end of the first week of January. There is then the usual 7-10 day period of renewed Atlantic conditions as the PV sits over Canada/Greenland before the amplification or the downwelling takes over and it shifts either westward or over to Siberia with the latter looking the favoured option which opens the door to the trough dropping down into NW Europe (suggested by both 06Z OP and Parallel). Whether we can see mid Atlantic height rises behind that is the next question. The option of a Scandinavian HP seems off the table. Plenty of the 06Z GEFS favour an anticyclonic FI but where the HP ends up still seems open to question. P11 would be ideal for the cold fans (PV over the Pole and heading for Siberia). A lot will depend on how quickly residual PV energy can be washed out of the Canada/Greenland region - it may be we will have to wait until mid January for the process to complete and the way to be clear for high latitude blocking in our part of the world.

Morning all First, Christmas greetings to all fans of cold and snow (and presumably frost as well). It looks very anticyclonic to end 2018 and start 2019 - the first push of HP will retreat slightly but the second push from Iberia looks much stronger and will create an MLB centred over or perhaps just to the west of the UK at New Year and just after. We could hopefully see some nice inversion under the anticyclone so some cold for many. It does look as though (and the MetO forecast suggests this) we'll get another short-lived Atlantic push after that before (hopefully) we start seeing something more interesting. so yes, we might have to wait three weeks before we get the wintry nirvana for which we are all hoping (in this thread at any rate). One route might be for the HP to pull far enough west to allow the Arctic trough to drop down over north west Europe - shades of December 2010. The GFS continues to frustrate with its strat forecast but we are seeing a significant warming event now and what comes out the other side will be a much warmer and weakened PV which can only bode well.

As an aside I'm also struck by the difference in 10HPA temperatures between the stratosphere this time last year and now. By early 2018 it was still showing values of -84c and below at its core - the early 2019 value is scheduled to be -68c which is quite a difference, much warmer and much weaker.

Evening all Onwards with the roller coaster it seems. The main model output still not yet factoring the stratospheric events but it's not surprising with the warming barely underway and still a couple of days off its peak. I get the sense however there is some movement - the option of building a Scandinavian HP seems to be receding in favour of keeping the HP to the west or north west and allowing Arctic incursions as the main trough (and a lobe of the weakened vortex) to drop into Scandinavia. I imagine heights to the North West and a raging northerly in January will probably be cold enough for most. If the HP is kept well out to the west we might see the trough drop down right over us (shades of December 2010) and I imagine most people on here would be happy with that. Watching the stratospheric modelling is fascinating - GFS seems to go less for a split than a shearing of the PV and what comes out at T+384 is a smaller, warmer and weakened PV (no -90c raging PV to start 2019). Looking at the 12Z Parallel and OP (which look very similar) the forecast sees this shredding of the PV rather than a full split so instead of two distinct intact PV segments you get a single weaker vortex - I don't know how that will play out and clearly the EC isn't seeing that. For now, the immediate outlook looks benign for most with the weather not seemingly getting in the way of Christmas and New Year events.

First, it isn't flat but yes, the first build of HP is declining SE and the second, more substantial build is coming NE from the Azores and Iberia. There's also a good sign the Atlantic is slowing and weakening on the UKMO as well which we also need to see.

Afternoon all As usual, those wanting snow, ice and -20 uppers are complaining because there's nothing showing in the next 7-10 days. True and it looks a remarkably benign Christmas and New Year period for most which is no bad thing for those having to travel and visit their families and/or loved ones. The signals for something of more interest in the early to middle part of January remain there - the 06Z Parallel was a thing of beauty in far FI and interesting to see both Control and OP toying with slowing the Atlantic to a crawl and rising pressure over to the NE of the British Isles. GEM 00Z looks more like an inflated ridge from the UK and that's ten days out. The first HP for Christmas won't be strong enough to ridge NE combined with too much residual energy in the jet so it slides ESE but a second burst of HP at New Year looks more promising but nothing is settled. The 06Z GEFS does indicate more members taking the core of the HP to the north which may be good for cold fans but there's no snow in many of the members at this time. It's a three phase process I think - the HP moves up from the south, transfers north or north east and later retrogresses. Ideally, we'd need a nice cool down before we get the easterly and then the northerly and then back to an ESE as the Atlantic tries to come back in from the SW. That's a 7-14 day severe cold spell for mid January (or maybe later). The split PV continues to be modelled on the Parallel if not the OP with the split coming on January 2nd and indeed the 06Z Parallel initiates another burst of warming on the shattered PV which would pretty much finish it off. Even the OP weakens the PV significantly from what we would expect in January but it is a displacement not a full split. That said, even a displaced vortex offers opportunities for cold.

Afternoon all Well, the ship has sailed for Christmas cold but the New Year, well, we'll see. The Parallel has been consistent in splitting the PV on or about 3rd Jan and the GFS 12Z OP looks like ushering s second warming to split the PV soon after 6th Jan. We'll also see if Amy Butler's tweet is a sign of a backtrack or just some modelling inconsistencies over the next few days. The substantial pressure rise from the south and the subsequent transfer to Scandinavia followed by retrogression to the NW provides a typical 10-14 day severe spell as we have seen before. The risks remain substantial - in splitting or displacing the PV may have enough energy to sink the initial HP into Europe before it goes wandering and the amount of energy in the northern arm of the split jet remains troubling. I'm still of the view we are looking at more severe conditions from mid January (halfway through winter for those who are worried or counting) rather than earlier.

Afternoon all I suspected this morning's output would restore some colour to people's cheeks and get the curtains a-twitchin'. For those of us who love cold without the snow, GFS FI is delightful with both OP and Parallel showing substantial mid-latitude blocking and as I constantly have to remind people, it's perfectly possible to get an ice day in London without a flake of snow on the ground if you get a serious inversion and both OP and Parallel - I know the 2m temperatures aren't suggesting that at the moment but I'm absolutely convinced IF we got a set up like: We would have fog and frost as long as (and it's a big proviso) we can avoid embedding cloud in the circulation. This is why I quite like an HP forming from the south over land as they have less cloud in the embedded circulation than an HP coming in from the east or west. Anyway, all a long way off and of course the big positive is the split PV now showing on both OP and Parallel which is significant IF it plays out. All this will be too late for Christmas and New Year celebrations I suspect but promises a lot for January if the cards drop right.

Morning all :) 10c here in lowland East London but no rain as yet. Breezy with a SSE wind and cloudy but with variable cloud levels. Looking at the wonderful NW radar, the main pulse of rain for SE England is still over North West France so we may get a few dry hours yet this afternoon but I think we will have a wet night. Looking elsewhere, the rain band looks particularly heavy and slow moving over western areas and especially the Lake District - I hope we won't get a repetition of past flooding spells around Christmas in these areas.

Morning all It's worth emphasising we remember certain cold spells (December 2010, March 2013, March 2018) because they are so infrequent and unusual. The synoptics we saw in March 2013 and 2018 would have produced much more severe conditions had they occurred in a January or February but they were pretty severe in their own right. It doesn't snow that often in Cornwall for example and for it to snow in March. Most of the time we forget the mundane, the normal, the mild, wet mush except of course when it's stormy or persistent so we remember the big storms (1987, 1990, 2013 etc) rather than the weeks of zonal weather. As we celebrate the rare and the exceptional we look for it but would we be happy if it were somehow to become "normal"? No, because it would lose its quintessential nature. In a 90 day winter, a 7-10 day severe cold spell becomes memorable even if the other 80 days weren't. We talk about December 2010 but who remembers January and February 2011? A cold month is even more pronounced and rare yet somehow you'd think we were entitled to 90 days of freezing temperatures and snow. MY personal preference would be 10 days of anticyclonic inversion with fogs and frosts but I recognise that would be life-threatening for many people while for others snow id the beginning and end. A week of snow makes up for a month of dull drab drizzle. The very fact winters such as 62-63 and 46-47 are placed on such a pedestal is testament to how unusual they were but the world was a different place then. There may not be snow at Christmas again this year - there may be none at all this winter for me in lowland East London and be assured millions of our fellow residents would be delighted at such a prospect. We always, it seems, need a lot of luck to get the white stuff especially at lower levels but we're once again in the game, we've placed our bets and the wheel is spinning. Will we get lucky or will the Mild House win as it so often does?

We know vortex displacement doesn't work in our favour in western Europe if the displacement comes from the Siberian side and sends the PV back to Canada/Greenland. Indeed, we can probably assume 7-10 days of mild positive NAO and AO conditions from any such displacement. Yet the displacement does weaken the PV and renders it susceptible to further Wave 1 and Wave 2 assaults and getting the PV pushed further west opens the door to Scandinavian HP. The question for this winter is how long is it going to take before the PV is so sufficiently disorganised as to allow for blocking to develop - those who advocate a middle to back loaded winter probably have made a sensible call irrespective of whether we get any northerly outbreaks in the interim.

Yes but the longer the ridge persists over Scandinavia the more the energy off the Atlantic will be drawn SE through the British Isles into Europe which keeps us in colder PM air and offers some snow possibilities for Scotland as LP swing SE through central Britain and into the Low Countries.

You or the Bearded One noted the negative tilt on the trough this morning and it's still there this evening on the 12Z at T+216. There's enough residual heights in northern Scandinavia to send the LP SE into Europe. Similar to the GFS OP at the same time: http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=216&mode=0&carte=1

Morning all Plenty of deflated individuals this morning but to try to be analytical it's worth looking at a single run and a single timeframe to see how the modelling has developed. On Tuesday 4th, the GFS 00Z OP at T+174 A strong ridge moving north and NE across the British Isles with a large Atlantic LP retreating westwards. Wednesday December 5th, GFS00Z OP at T+150: The ridge is weaker, the LP over Eastern Europe deeper and the Atlantic model is different. Now, this morning and the 00Z at T+126: If this cold spell next week has failed, it's because the original ridging from the south has ended up weaker than originally modelled which makes the block over Scandinavia weaker and less able to withstand a vigorous Atlantic but I'd also note the modelling of the LP over the Baltic which is deeper again this morning and also inhibits the development of a suitably robust block. The Atlantic LP was at the start moving west to the south of Greenland but the new LP coming up from the SW invigorates the energy and aids the LP in punching through the weaker block.

Afternoon all I think what strikes me about the 06Z OP, Parallel and Control is how they are all very differently modelling the NH profile in FI. OP tries to restore the PV in its usual place but both Parallel and Control displace the PV away from the Canadian side. As we know, a displaced vortex isn't a guarantee of cold but it's a good start. I don't think anyone thought the colder outbreak was going to last a length of time and to be fair cold spells lasting more than 7-10 days are unusual. Looking at the GEFS I'm struck again by the weakness of the PV in mid December - again, as you might expect from the synoptic evolution, the Parallel makes much more of a second assault on the PV in far FI - the OP is quite muted.

First, thank you very much for the detailed forecast, Ian. It sounds like a typical back-loaded British winter - those wanting snow and cold at Christmas are going to be disappointed but those wanting snow and cold for late February may be in luck. I suspect it's going to be a long and slow pull into spring next year. The indications of early pressure on the PV perhaps offer more hope for a chillier January but as I've mentioned here before, my birthday is exactly midwinter, January 15th, and the number of occasions it's been cold and snowy have been few while more have been dry and cold but the majority have been mild.

I think our first "hope" (and the 12Z Parallel at the very end of FI suggests this) is to get the trough negatively tilted and send the LP SE into Europe. That will need either the Arctic HP to build SW or the Eurasian HP to build WNW and it's the latter which occurs at the very end of 12Z Para FI.

It is modelled a notch stronger on the 12Z than it was on the 00Z - it is now 1030MB for example. As a result, the jet is further north and the LP is tracking further north as well.

Afternoon all Having stepped away from the models for a couple of days, a shade disappointing to see the earlier promise of a blocked situation in early December not quite happening. As I suspected, we are looking at a 7-10 day period minimum of Atlantic-influenced weather and that now looks to be 14 days as it's around T+288 on the GFS 06Z suite we see the next attempt at amplification. In truth, it's not wholly successful as the jet remains too powerful and the block in most instances gets blasted away but there are members where that doesn't happen and the Bearded One's call from the ECM ensembles looks about right at this time. I thought the signal for blocking a little stronger earlier in the week - I do wonder if the pressure on the PV from the Eurasian side is causing the classic response of a re-location to the Canadian/Greenland side so you can add a further 7-10 days while that happens.

The 12Z Parallel hasn't finished rolling out so let's reserve judgement on that. The difference between OP and Control is simply the rifdge coming SE from Greenland is able to hold back the Atlantic LP and indeed push them back westward allowing the much colder air to come in from the east. Oddly enough, the NH profile for the OP gets more interesting at the very end of FI with the PV displaced over the Pole so it may just be a matter of timing.

I suspect while most on here will be hoping for high-level blocking over Scandinavia I suspect we may finish up with the HP right over the British Isles so cold, frosty and foggy conditions under a mid-winter inversion but no snow.

As did I and I think the question about the mid-latitude block is whether it will end up right over the British isles or perhaps just to the west which wouldn't be ideal for cold weather fans. By mid December inversion will be a powerful weapon for those wanting fog or frost and ice days are entirely possible.