Catacol

The heaviest snow is forecast for 0000 to 1200 across the region, and Wiltshire looks set to receive most of what it will get between 0000 and 0600. I am still assuming it will be a very borderline event though - whether it sticks is open to question. Only time will tell.

Sigh.... they were/are not. Go look at the NAE high res model over on Weatheronline. You will clearly see that the event is panning out exactly as forecast and people on here are about 12 - 18 hours ahead of themselves. The problem for us Somerset/Devon folk is that the 06z NAE had most of the precipitation for tomorrow morning falling as snow, but the 12z updated to rain. We need the 18z which comes out soon to switch it back to snow - I think it will be a very close thing down here but further North and East over towards Gloucs and Wilts and the Bristol region it looks very likely it will be snow. Whether it will be heavy enough to lie on wet ground remains to be seen.

Already? That's good news. Going by the NAE it looked as though it would stay as rain a fair bit longer. Here's hoping then that the NAE has underestimated the snow potential and it all goes in our favour.

You'll make no friends down here saying things like that... Any snow of substance will be after midnight anyway.

Latest NAE has it as rain for most of the SW... big change from the 06z. I hope its wrong - I've told everyone here that snow is on its way in the morning...

All rain here down by the Devon border. As expected - 40 - 50 miles too far south and west. However what is interesting is that the surface temperatures are only 1.6 degrees. I have big hopes for the coming week: if surface cold can hang on and the east wind bring back cold uppers we could do well out of events on the horizon mid week.

Somerset / Devon border. Snow grains... but this will be rain before very long. Our interest in this event will wane fast, but maybe mid week can bring something more useful for us.

GP - for a man whose winter forecast is just about to become the stuff of legends you are very quiet. From a technical angle, now that the cold is on our doorstep and it looks as though the high may retrogress ala GWO phase 8 as you stated - where are we sat for more specific details through February, or is it just a case of sitting back and watching weeks of cold? I read the article from Lorenzo's post above on WX the other night which, apart from having my head spinning, suggested and phase 8 -1 - 2- 3 shift perhaps mid month. In a more simplistic way than that post what are the signals going through later Feb and on towards March? Apologies for asking you to do more work. :-)

Sorry to sound confused... but if the Strat forecasts are looking good for HLB then why is it the models are defaulting to sinking high and zonal winds over the top. Do the strat forecasts not feed into the models, and if so what could be causing them to ignore the background data? I know the 12z are only 5 - 7 hours away, and maybe they will swing back, but the overall trend to blocking in this part of the globe is not as swift as I had expected it to be (even taking into account the fact the years of model watching has taught me that high pressure cells always seem to react more slowly than the models think they will...) and the last 2 runs of GFS and ECM have fallen in line with the sinker. The MetO themselves have been very twitchy about getting on board the easterly idea... they must obviously read the strat forecasts - so what extra input is there that is causing them to see a 1 in 3 chance of a sinker and a return to zonal?

Knowing how organisations work, and the need always to release information to Joe Bloogs rather carefully (in any business) I disagree with this. I suspect that a 30/70 split was probably their verdict when using the previous forecast; this new forecast smacks, to me, of a decision that the balance of probability has actually slid above the 50%, and probably up towards a 60/70% certainty of cold. As a result the language changes to a possibility, but they will continue to state that it is less than 50% to prevent any egg left on face afterwards, even though their reading of it is that cold is likely. It's all about perception and the need to be in control of information

... thought it is important to point out that the big 2 winter forecasts (GP and RJS) both pointed to little at all up until mid January and then winter arriving. RJS hasnt quite got his timing right - no NE direction yet, but GP was very clear that the timing of the change was hard to pinpoint. Here we are on Jan 17 and that is exactly what is happening. Plenty of time yet. I have faith in both these guys, and GP in particular. If he says a change is on its way - and last night he mentioned a 10 day time frame approx - then let's not throw all hopes into the bin yet.

Not much comment on GP's earlier thoughts? If he thinks the Azores High is going to be dragged westwards around day 10 - 15 that's good enough for me. Angular momentum low so overall tendency for the pattern to back west and the Russian High exert an ever greater influence. Could we have a mega block develop with the azores high sucked to Iceland by that growing Russian High? I think it's on... I've seen enough in the models in the last week, plus that comment from Stewart, to go dust off my sled and find the gloves from last year. This is the week of transition with the vortex wobbling and breaking up. Next week blocking to the north and low pressure to the south. Looks about as nailed on as the northerly of Dec 2010 to me - just a bit less certain on timing.

ECM continues to model a trough into the UK at the end of next week. Many of its ensemble members model a colder evolution while some see it milder - so it is not a colder run. It continues to model a more amplified pattern, and UKMO maintains its agreement. GFS continues to be on its own in the war of the big three. NOAA continue to support the ECM evolution.

Currently nothing is nailed on, but there are growing numbers of respected posters and analysts who are seeing an amplified pattern backing west as we approach February.

I thought, according to Steve M, that the 00 GFS verification stats were running in 5th behind the GEM?

I agree that we deal in probabilities - of course. How can weather forecasting really be anything else? I doubt the science will ever be there to predict more than a few days ahead the specific synoptic setup because there are too many variables that contribute to a system of chaos. However I'll still stick to my guns here and suggest that you are being rather one sided. For as long as the vortex remained strong and undisrupted the probability of sustained cold weather for the whole UK was very slim indeed. Now that we have a vortex on the wobble, and possibly about to be splintered by warming, the probability of cold weather increases substantially. An arctic high is a by-product of a a vortex under pressure, and it cannot be right to move from a position of arguing (correctly) that cold weather is unlikely in a westerly scenario, to then stating that now the westerlies are likely to fade and higher latitude blocking is likely to emerge somewhere that cold is still not going to happen and that Jan 87 was an exception. Smacks of wanting to have your cake and eat it. On topic - and the ECM shows greater amplification at T144, an attempt at high pressure to our NE at T216 and a trough sinking south at T240. To me it looks like a computer struggling to cope with mixed signals and an uncertain calculation as to what the final product will be from next weekend onwards. Cold weather not probable? Looks a darned sight more probable than 3 weeks ago.

eh? I know we cant disagree with your face value interpretations of the models at present - it is the model thread after all - but this I dont understand. How can an arctic high, which is characteristic of the vortex on the move, be a foe? Always the chance of ending up on the warm side of the amplified pattern as a result, but also a chance of being on the cold side? And are the models not hinting at such a shift to an amplified pattern? I note that you do not want to acknowledge that at all.

The poppy cock lies in this statement above. At what point when the forecast was put together was a storm "in a few days" predicted? Do you mean "in a few weeks" and if so you are right - a prediction of 2 weeks of stormy weather was put together and it duly arrived 4 weeks after the prediction, followed by a prediction of several days of cold air - which also arrrived - and finally a remark about a possible storm early next week... and guess what? - that looks possible at this stage too, though maybe 24 hours later than predicted weeks and weeks ago. Going back to last year Dec was accurate in my book, and if you actually look at the January charts from 2011 you will see accuracy there too. The transitional energy peak that was forecast for 17-20 Jan arrived on about the 18 and from there the forecast did go awry... but Roger himself hinted a couple of times that he was not totally happy with his Feb forecast and that he had not listened to his gut instincts about it: and these were comments made before Feb got close, not after. So 1/3 of last winter spot on, 1/3 close, 1/3 off target (but suspected so beforehand). I rate that as not bad... for poppy cock that is. I mark academic scripts on a regular basis at work, and the kind of vague, baseless argument put together here by you CC is a head shaker at the best of times. If you want to suggest that someone else's forecast technique is off target you need to do a whole lot better than this. Some evidence would be a good start; you wont find any for this year yet that you can make use of, but come the end of Feb perhaps you could revisit this thread and put together something constructive. If I am an reader of personality Roger will be the first to hold his hands up if the forecast goes wrong (unlike many others around in the media at present) but let's not forget that he is currently targetting 60 - 70% accuracy across the season so any criticism will need to be on the basis of a failure to meet this. And let's be fair: 60 - 70% accuracy across a season is damned good (if it comes off) and it makes me wonder why the likes of Maddon and Corbyn get a ton of publicity for putting out an awful lot of rubbish, and yet someone with a track record of reasonable accuracy gets ignored. Perhaps you need your own website Roger??

I dont think this gentle criticism stacks up. Are you suggesting that FI model runs in mid november that had started to show a northerly plunge was the basis for this forecast last year? The deep cold of 4 weeks later would have been a majorly risky call to make based on model runs that at FI range are almost always wrong. No - it was done using Roger's methods that I dont understand but am increasingly wishing that I did. Roger: as a long time lurker and reasonably able researcher and computer user, if you ever want someone to assist or work with you to help improve things then I would be very willing. I would need to start reading up on your methods from scratch, but I am impressed enough by my gut-feeling accuracy of your forecasts that I would like to know more.

But surely that's the point? RJS put a 5 day bracket on the coldest spell which materialised, put 2 weeks on zonal stormy stuff which materialised beforehand, and now may have pinpointed the storm on 26/27 Dec. I am staggered - for all the talk of no SSW and strong vortex and amplitutde or non amplitude of the pattern etc etc Roger put a 4 week spell of UK weather together 4 weeks before it started and has got it right. Is that just luck? Could be I suppose, but he got much of last year right (the first year I read NetW) apart from Feb where his instincts were to go mild but bowed to BFTP's feelings that his data suggested possible cold. Had he stuck to his instincts then last year's forecast would also have been very close. I am not trying to start an argument - just wondering aloud really whether the rather "odd" methods that he bases his forecasts on may actually have real substance. Chicken and Egg? Which is which?

Hmmm - i put a post in the model thread about the accuracy of RJS's forecast, come back to my puter and find my post mysteriously gone and people talking about some rubbishing of RJS. Did I provoke something? Just to say again - staggering accuracy for me of RJS's forecast. Pattern correct, dates correct. Astonishing.

So far RJS's forecast of strong winds and depressions for the first 2 weeks of Dec is spot on. Models arent yet picking up on the cold arctic air he forecast in the run up to Christmas from the 15th onwards - wonder whether they will start to turn his way...

Hi Chio - I understand the anomaly as compared to average, but when I look at the charts for Jan 2007 they dont seem to fit at all in terms of creating that deviation from average. By Jan 20 there is a deep low off the north of Scotland which would have helped reduce the average pressure, but for the rest of the month it is distinctly ordinary looking, and pressure over Greenland which shows up on the composite as likely to be lots above average looks nothing like. My point is that GP's chart suggests winds from the NE with pressure deviations encouraging that flow, but if you look at a chart on almost any date in Jan 2007 you dont see a NE wind. The wind was predominantly westerly for most of the month aside from a short easterly flow from around Jan 22 to 25. So are these composite charts actually not potentially very misleading? I'll say again that I understand they are deviations from average, and not 500Pa charts themselves, but as deviations they imply a particular flow and that flow doesnt match up with the reality of the Jan 2007 charts. Am I missing something? GP's chart makes me excited for cold; but then a look at Jan 07 makes me wonder why I bothered to think something might happen...

Ah - apologies; I was being dull. Thanks... And yet I still cant see the warm stratosphere in autumn last year that is supposed to have caused the vortex to destabilise and allow that chunk of very cold air to dive over us in late December. Am I remembering that wrong? Was there not a warm stratosphere last autumn?

I am still learning - forgive me - but looking back through the archives of Jan 10 (one of the analogues listed on the January composite chart above) the pattern was not exactly as set here. At the start of the month Jan 10 the match is good, but as the month progressed it is less convincing. Looking then at Jan 07 I find a similar reality: the match is really not good, with a massive European high in play for a fair amount of the month and active low pressure south of iceland. I am using the archive at Wetter to look at these. So just how are these matches worked out? Who decides that Jan 10 and Jan 07 were matches for this MJO event, and just how close a match does it have to be? I cant really see how an anomaly chart is much use if it doesnt actually match the synoptics of the years it claims to mirror.