stodge

Evening all Well, having viewed the myriad 12Z output, I expected this place to be in meltdown but it seems the doubters and the cynics are out in full force this evening. I agree it doesn't look like a snow fest initially and I recognise for many on here, snow is all that matters but for fans of cold it's a very strong scenario going forward. For those who are already worrying about the breakdown (yes, I know), the favourite looks to be a shift toward a west-based negative NAO which opens the door for an attack from the SW. http://www.wetterzentrale.de/pics/archive/ra/2011/Rrea00120110103.gif http://www.wetterzentrale.de/pics/archive/ra/2011/Rrea00120110104.gif This is what killed off the late 2010 cold spell and ushered in a benign start to 2011. The much-talked about Greenland High isn't a holy grail or even a help if it is oriented wrongly as these show. http://www.wetterzentrale.de/pics/archive/ra/2011/Rrea00120110106.gif There you are - lovely Greenland High but no help at all. Having the HP to the North (as BOM shows tonight for example) may not bring a lot of snow to the north but it keeps the cold in place for most if not all. The irony of all this is that the south wins from the scenario that keeps the cold while the north is left cold and dry.

Afternoon all A solid opening for those who like their charts with a generous portion of cold. http://www.wetterzentrale.de/pics/Rtavn1441.png Very reasonable for my part of lowland East London. We just need to hope this is a clear, dry HP rather than a cloudy one. http://www.wetterzentrale.de/pics/Rukm1441.gif Some differences and not, I think, quite as "good" as the GFS oddly. The "hope" is that retrogression can occur but I'm not convinced that a T+168 chart would show that. GEM very much at the party too. Possibly the best of the lot so far for my part of the world. Like UKMO, it begins the process of moving the HP out of Scandinavia with the option of retrogression clearly on the table. I suspect ECM 12Z will be similar which will offer the kind of cross-model agreement at T+144 that we've lacked in the two previous colder spells this winter. I remain to be convinced about a real Arctic incursion as some of the ECM output has offered and GFS hasn't bought into it at all thus far.

But instead of that we get people either saying ad nauseam "ECM never delivers an Easterly" or "I don't believe the evolution until it's at T+48 and anyway FI is T+96". If that's all people are willng or able to post, this soon becomes a very dull and quiet forum. We have what the models give us - if people are too scared or unwilling to commit themselves and want to pour cold water on other people's enthausiasm that's their prerogative but again that shouldn't be what this forum's about either. On topic, both ECM and GFS are very good and I don't think anyone was suggesting cold as early as the weekend or early next week. The route to very cold, as I've often said, usually starts from very mild and the first stage is to get the blocking in place which will happen over the weekend and early next. Colder conditions are on the table but not for another week. Forecasts of colder weather were always talking about the last third of February and into March and that still looks plausible tonight.

Unfortunately, we're not soulless robots and by definition it's impossible for every run to be equally credible (or incredible). On that basis, either every run would verify or they'd all be completely wrong in which case there'd be no point discussing them. The analogy I would choose is studying horse racing form. The Models Handicap is open to 3-y-o of all ages and has three main form horses: GFS by American Model out of Big Depression UKMO by British made out of The One We Like ECM by European Model out of What we Want to See The three form horses all have different form on different surfaces and all have their strengths and weakenesses. On a zonality surface, GFS is the favourite but on more testing conditions such as blocking or an SSW downswelling, the formbook may have less value. My point is that studying the models is like studying form - you get to "know" over time which one is reliable and which isn't. Those advocating the binning of the GFS 12Z operational output may be doing so because they don't like what it shows but they also have past form to go on. Now you're more confused than before and my work here is done...

Morning all Some excellent charts about this morning if you're a fan of settled, dry and cold (which I am) but less so if you want snow (not so bothered about that). As always, GFS takes the circuitous route to the Promised Land http://www.wetterzentrale.de/pics/Rtavn1201.png The blocking regime well established on the 00Z Operational output. Continental Europe would be cold under this but of course the established pool of milder air plus the sea keeps UK temperatures at higher values (8c or thereabouts). http://www.wetterzentrale.de/pics/Rtavn1921.png Yep, all pretty blocked and quiet. I wonder if we'll see some fog under this set-up which has been one of those features absent this winter. Under such a foggy regime it could be very cold by day. http://www.wetterzentrale.de/pics/Rtavn2521.png And so it begins... well, cooler at least for the SE with a light continental feed. ECM does things rather differently, thanks oddly enough to a more active Atlantic and at http://www.wetterzentrale.de/pics/Recm1201.gif the orientation of HP and LP systems is very different. The more active Atlantic LP shifts the HP further NE pulling in SSE winds over the UK. http://www.wetterzentrale.de/pics/Recm1921.gif I'll take a chart like that any time in winter. The HP is able to undergo retrogression much earlier and this kind of chart was, I think, the sort of thing proponents of SSW were envisaging right back at New Year so, IF it verifies, huge plaudits to them. http://www.wetterzentrale.de/pics/Recm2401.gif I'm sure there will be plenty of drooling over this as well and I won't add to it. Time also for some perspective - it's mid-late February but that doesn't mean you can't get snow or even near ice days by any stretch. http://www.metoffice.gov.uk/climate/uk/2006/march.html There's a pretty cold March from the recent past as an example of what CAN happen. In my part of lowland East London, I've had four snowfalls this winter but none has lasted longer than 72 hours because I live in an urban heat island but I had snow that year and also in 2009 if memory serves. If you live in the south and want ice days and feet of snow in March, you're going to be out of luck any year and every year. The one thing this morning's charts do NOT offer is raging zonality and nor do they offer an early spring which some people seem to want desperately. Oddly enough, this weekend could be quite pleasant but late Feb-early March has often delivered cold even in the mildest of winters and my money (and very nice money it is too) would be on some form of repetition. How far into March any cold period will go I cannot say. In 2006 it lasted past mid-month in many places and we have perhaps been spoilt by a number of warm March months (often coming off colder early winters).

Snowing here in lowland East London - the fourth fall of the winter so far. Slushy on the pavement thus far but covering other surfaces.

http://www.wetterzentrale.de/pics/Recm1201.gif As I said earlier, the key feature is the Baltic LP. ECM has this less intense and further south than GFS. This enables a more significant block to build over Scandinavia. The impact of this on the rest of the run I don't know. It's not for me to say but I would have thought such a system would be better modelled by the European than by the American models.

http://www.wetterzentrale.de/pics/Rtavn1201.png The problem isn't to our west but to our east in the form of the LP over the Baltic States. As in December, this feature stops the Russian HP ridging strongly into Scandinavia and building up the block. http://www.wetterzentrale.de/pics/Rukm1201.gif UKMO has the feature a shade further south and weaker and that allows a small HP cell to build up over Scandinavia and holds the Atlantic to a more NW/SE trajectory. http://www.wetterzentrale.de/pics/Recm1201.gif The 00Z ECM showed a weaker feature over the Baltic with the main LP further south. I fear IF that Baltic LP is as far north and as strong as modelled by the GFS, any block will be scuppered.

Morning all I have to say a cursory perusal of the main 00Z output has left me none the wiser this morning. I see varying support for a rise in pressure to the NE but with the Atlantic never far away. http://www.wetterzentrale.de/pics/Rtavn1201.png An almost classic "Col" chart and potential perhaps for a little fog and frost down south. http://www.wetterzentrale.de/pics/Rukm1201.gif Very similar. It's worth noting that the LP in the Baltic was a key factor in undermining the potential December cold spell as it prevented ridging from the Russian HP cell into Scandinavia. A feature like that poses a similar threat this time. http://www.wetterzentrale.de/pics/Recm1201.gif The best of the big three for my part of the world. The Baltic LP is less pronounced and the HP is able to develop into Scandinavia. I note the Azores HP is less pronounced here as well. Last decade, one of the "routes to cold" in an otherwise often-miserable synoptic scenario was to get the Azores HP and Scandinavian HP to "link" - that at least advected some colder air into the SE.These were often undone by the lack of low heights on the Continent but at least we have those this time at present. http://www.wetterzentrale.de/pics/Rgem1201.gif This looks uncertain to say the least. Lots of shortwaves and a confused synoptic pattern though the fundamentals are there. http://www.wetterzentrale.de/pics/Rngp1201.gif This is the poorest scenario for cold fans overall. The Azores HP is more pronounced, the Scandinavian HP much less so and the LP over the Baltic more extensive. With no ridging from the east, the Atlantic has no block to overcome. Overall, we can say it's not looking mild. Here in lowland East London, as I've said before, I don't expect snow to stay for long - the fall of two weeks ago was gone in 72 hours - but I certainly don't rule pout snowfall under the right conditions. That said, none of these charts scream snow to me - they do suggest a quiet period of cool/cold weather with frost and fog possible. I think longer-term we may be looking at an anticyclonic spell moving into mid and late February which might well deliver cold but perhaps not snow.

The unpalatable truth for us in lowland East London is that getting snow is far easier than keeping it. Whether from North or East, even late March can deliver snow so there's a huge amount of time left for the white stuff. The fall of Sunday January 20th had mostly gone in 72 hours I know I'm not going to get days of lying snow but no snow at all for the rest of the winter - nowhere near that point yet. The 00z output at T+168 tantalises with a classic North Sea northerly. Not the most unlikely evolution on offer and though I'll get nothing wintry from it, those to higher ground in the Pennines and possibly the Wolds might do quite well.

Afternoon all Went from an almost snow-free lowland East London to South-East London for a funeral this afternoon. Amazed to see how much snow there still was south of the Dartford Crossing and even at Mr Stodge Senior's house in Orpington. The aforementioned progenitor had measured his snowfall on Monday morning at five and a half inches but had retained far more then we had off a similar fall. I suppose altitude plays a part as does the urban heat island but he also told me they had experienced very little wind while we had endured or enjoyed a stiff E'ly breeze on both Tuesday and yesterday which, I think, had caused much of the snow to disappear through evaporation. I doubt any of it will survive the weekend either north or south of the river.

As with any weather, this spell has been fascinating and full of interest. Here in lowland East London, the current near-fortnight of cold temperatures has followed a month-long period of mild and initially very wet conditions. In terms of low temperatures, it's been unremarkable though we had a very cold night Monday-Tuesday and suspect we have another cold night or two to come in the last spasm of the cold spell as is often the case. As others have commented, it's been a very cloudy spell with little or no sunshine an therefore no fog though plenty of low cloud. In terms of snow, this spell has brought three separate falls - an initial dusting on the night Of January 13/14 followed by a more significant fall on Friday 18th which left about an inch and which shifted to a considerable extent on Saturday 19th and a substantial fall on Sunday 20th which topped out at five and a half inches of level snow. This exceeds (and this will surprise some) the fall of December 18th 2010 though that fall was more remarkable in other ways and is surpassed only by the six and a quarter inches recorded on February 1st 2009, a possibly highly-marginal fall but which accumulated wet snow. Sunday's snow has, like the fall of February 2009, not endured and it's a fact of life in the urban heat island that getting snow to endure requires a set of highly-unusual synoptics such as we had in December 2010 when the pool of very vold air displaced from the polar vortex sat over us after the snowfall and meant that on Sunday December 19th 2010, we had an ice day and maintained our snowcover almost intact. This time, a cold and dry E'ly wind has evaporated most of the lying snow and with the return of milder air, this may conceivably be the last snow of the winter though, as recent years have shown, snow can fall and settle as late as the end of March. Overall, a solid 6 out of 10.

Evening all Well, a remarkable day, no question. About five inches of level snow here in lowland East London, about the same as December 2010 and a notch less than February 2009. The snow was relentless but the temprerature remained very close to freezing - just below though did hit zero briefly mid afternoon so not an ice day. A gentle fall off in the past few hours and it does look as though we are moving toward a regime of slightly above freezing maxima and much lower minima over the next three or four days. Surprisingly, pressure is still falling so the possibility of more snow must remain. The other aspect that I've observed is how temperatures are at their lowest immediately prior to a snow fall and then rise once the snow starts falling. Will be interesting to see how London deals with the morning.

Morning all Indeed, a gentle thaw overnight and current temperature +0.9c indicative of that. I was out just before the snow started and it was incredibly cold - I recorded -1.9c and an E'ly wind of 15 mph which provides a pretty significant windchill. Since then, the temperature has risen slowly as it often does with snow and we moved back above freezing in the early hours. I don't know if this is the urban "heat island" effect or whether we have imported some warmer air via mixing. It does look as though we will get a second shot of cold and snow tomorrow and Monday before the gentle thaw resumes on Tuesday.

Afternoon all A modest fall here in lowland East London but, as often the case with snow, fascinating to see the huge variation between locations based on distance and altitude. This seems to have been a much bigger event for the west and south-west of the capital than the north and the east so far and I hear from colleagues that part of Surrey have had a lot of snow but again altitude often plays a role in that. As for Sunday/Monday, the "potential" is there and, as someone said, reminiscent of a summer outbreak of thundery rain in synoptic terms. I appreciate the uncertainty from the forecasters but this looks like the event where those who have done less well today "catch up" though we're a long way off it at the moment.Beyond that, an evolution to something more anticyclonic looks a distinct possibility which would mean some very cold nights but with daytime maxima probably above freezing in the capital.

Put simply, if we knew, without a doubt, what the weather was going to be in ten days, this forum wouldn't exist. The point is that this forum functions on the glorious uncertainty of our weather. It MAY get milder next weekend but it may not. Those who analyse the model output in depth rather than commenting on every frame of the Operational output, will tell you that currently trying to predict what will happen tomorrow is a challenge. The forecast you have picked up uses an extrapolation of data to produce an outcome but the chaos that is the atmosphere defeats most if not all attempts to understand and predict it. Looking back to New Years Day, how many of the models forecast the current scenario? Very few. If you are going to use a single temperature forecast as your basis for predicting the weather, fine. You'll be no more wrong than most other people. All we have to go on is a combination of past evidence and regular updates. Past experience tells us cold blocking systems CAN be very difficult to shift.

Morning all Slightly surprised to see a dusting here in lowland East London. Still cloudy and very cold.

We're drifting off-topic here but I don't agree with you at all. It's perfectly possible to have a very strong HP over southern Scandinavia sending frigid air to the SE of the UK but for that air to be very cold, clear and dry. I do agree there's more than enough to keep us all interested in the next 48-72 hours.

Indeed, but don't assume cold equals snow. It's entirely possible the SSW and a negative NAO will produce a very cold, blocked situation under HP to the NE. Under an ESE'ly flow from a frigid continent, it will be plenty cold enough for most but snow may well be limited.

Evening all The ECM 240 chart tonight suggests the other side of the winter equation - huge potential for cold but little or nothing for snow. A negative NAO scenario would offer this kind of synoptic picture and those who talk about jets and the PV miss the point that the jet doesn't have to be displaced a long way south - sending it a long way north in winter also works for cold. A disrupted PV under an SSW might not lead to a snowy scenario at all but to something like this - blocked and cold. Under clear days, mid-January can deliver some very cold nights and that chart suggests we could be considering a very foggy spell as well.

Evening all I'm in lowland East London and I don't see much in the way of snow until Monday when it does look, at present, extremely interesting. The possibility exists of considerable snow with air temps close to freezing and said snow persisting to Tuesday. Tuesday is my birthday - I'll be fifty-two years young and I've never seen snow falling on my birthday. Most years it's mild and damp though I've also known cold and dry. Never seen snow though - could this be a first?

Afternoon all Apologies if this isn't the right thread for this, but I'm musing on the GFS and the discussions thereof. Correct me if I'm wrong but there are at least 22 versions of the output available on Meteociel (Op, Control and twenty perturbations). Now, these all start from the same point so they would be identical at T0 and there wouldn't be much variation at say T+48. It seems that variations increase (as mathematical theory and probability would suggest) from T+72 onward and by T+144 the 22 versions are starting to vary quite considerably. This is where we begin to talk about "groupings" of cold and mild runs on the Ensembles produced later in the day. By T+240 it seems that the 22 versions are going to diverge even further and while there many be some common features, that commonality will erode further so that by T+384 there are a series of wildly different outcomes on display. Those who think that all 22 versions will all go the same way at even T+240 are not merely barking but well on the way to upminster (a little London Tube humour). In every ensemble set therefore, there will be a minority of versions which differ from the majority let alone the Operational or Control runs. What I don't know is whether this is a complete lottery (in the sense that any one or none of the 22 might verify at that range) or whether there are "form" horses. At T+24 I would expect the vast majority (if not all) the outcomes to verify, at T+72 I would expect a majority to verify but has anyone studied whether at T+240 any version is any more likely to verify than any of the others. Is the Operational considered the most likely followed by the Control or is it even less ordered than that? If you have an Operational run which shows one scenario at T+144 and more than half of the other versions show an opposite scenario, I would be tempted to argue that the opposing scenario is more likely to be correct but if the Operational has more data or more "form" if you like, then we can weight the probability of its verification accordingly. I've "heard" that "more data" is programmed for Op and Control runs but I have no idea whether that is a) true or B) it enhances the verification statistics of those runs. I appreciate that you could argue that tonight's Op will verify at T+6 and probably even at T+24 but those who follow every frame of the Op run as it rolls out are not only deceiving themselves as to comparative analysis but also to ensemble analysis. Looking at the ensembles as a bloc would seem to be the coherent way to analyse the output and ignoring the average (will have outliers) and look primarily at the largest cluster of scenarios as, by definition, the most likely to verify. I suspect somehow it doesn't work like that but I'm a historian not a mathematician or physicist.

Evening all Well, quite an evening after quite an afternoon. I have to say I was unprepared for the forecast longevity of cold into next week. I need more convincing of the likelihood of snow in my part of lowland east London though the probability for eastern higher ground looks quite high. As always, more output is required and I still feel 48 hours away from being able to call this for certain.

Afternoon all It should of course be remembered that to even get 7-10 days of severe cold out of a winter is remarkable and, as last February shows, being "on the edge" doesn't mean that for some it can't produce "the goods". My view last week was that the journey to cold would be a gradual one and that's still my view. Last Saturday we recorded 11c in my part of the world, the GFS 06Z operational output offers 4c for the same time this Saturday so that's a pretty marked decline. The journey to very wintry starts from very mild and then we need to get the cold established before we can worry about snow (the ground is quite warm at present as well). The model dynamic of this remains confused as others have stated and I still think the real time for cold is early Feb rather than now. Past severe spells have often been presaged by one or more shorter colder interludes before the proper onset of something noteworthy - the notion of a switch flipping from mild to very cold isn't for me how it works. Again, and it's only my view, a short-lived colder period this weekend followed perhaps by a return to milder but still broadly anticyclonic conditions by the middle of next week followed by a second more serious cold snap followed by a final brief milder interlude toward the end of the month followed by a 10-day severe spell in early Feb followed then by a return to milder conditions. No more than guess-casting on my part though and I expect to be proved wrong.

Thank you for the kind word, Ian, and, coming from you, much appreciated.