chris55

GFS very close to a huge snow event for those in the south, http://www.wetterzentrale.de/pics/Rtavn1442.png http://www.wetterzentrale.de/pics/Rtavn1441.png What happens to this Little cut off Low could be very interesting, We need it to hold and push energy southwards (like GFS) rather than just filling/disrupting (like UKMO) One to watch and the slightly unusual nature of the set up may give the models some headaches.

The ECM00z runs keeps 850s between -2 to -8 throughout the run once the milder blip is through on Monday, and with what looks like quite an unstable flow snow could be a factor for many next week especially on slightly higher ground and further north but not exclusively so. As others have mentioned the shortwave at 144 hold the most potential, Also ends with a nice block to the east, overall a good wintry ECM 00z.

Excellent wintry outlook this morning!! We need to remember that Dec 2010 was a very rare event and using that period as a benchmark for comparison means you're always likely be disappointed GFS ens are good, mean hovering around - 5 util Sunday/Mondays front pushes through, then back down to sustained cold pattern, as GP has said the sustained nature of the below average conditions are noteworthy. And small adjustments could well allow so snow to fall as we get closer to the time. I am sure all those famous cold winters of the past were often cool/cold and what some would perceive as "boring" but for those cold winter CETs we see in the history books sustained cold is a must. The deep cold people are looking for could well materialise as we head through the month and into Jan but for now this is a good winter pattern IMO.

As others have said it's the jet streak pushing through past the tip of southern greenland thats our problem tonight, The chunk of PV over northern Canada is like a breeding ground for bits of energy to be spat out towards us. If we look at how the PV is modelled on the 18z it's interesting Plus 48 split vortex, we've gone cold, but it's just a little bad luck we didn't go really cold. Then at plus 186 the PV is reorganising around northern Canada area (there was talk about where the PV would reform after the split) Then towards the end of the run the PV looks to be moving off to the Eurasian side of the globe (hopefully to be split again soon) Basically whilst the chunk of the split vortx and the reforming of the vortex is taking place over Northern Canada we are always going to be up against it a bit trying to get a high lat block to the North West and a Scandi high could form but will probably be squeezed over by the energy to the north.

Hi Simon there are many weather models and a lot to take in with all the information available, ECM is probably the best model but "a beast from the east" is not showing on it today!! There are many options available and colder weather is probably the more favourable as it stands. Model output does change with each new run so looking to far ahead can be misleading when searching for cold weather. Up to about day 4 (96 hours) is pretty reliable but beyond this it could be open to change. If you stick around on here you will soon pick things up but it is a minefeild out there.

ECM 12z shows intense Lows running to the south AND to the north, it seems rather unusual to me, is it? I would normally expect a zonal pattern with Low pressure rolling in from the west with higher pressure below, or blockig to the north with an undercuttung jet. We seem to have both here with a wedge of high pressure in the middle.

This current cold spell (or failed proper cold spell) is, as I understand it, totally disconnected from the Strat. It does make you wonder about the whole strat theory though, as things in the start do look to be encoureging in the next few weeks, but if our weather at present is not being effected by a very cold strat, are we confident a warmer more favourable strat will actually have an influence on the trop?? (excluding a SSW)

Lots of southerly Lows tracking there, we just need the energy coming off southern Greenland to disipate and we'd be looking good, http://www.wetterzentrale.de/pics/Recm2161.gif

Sandi high coming up? (surface high) http://www.wetterzentrale.de/pics/Recm1921.gif

We need to watch out for the possibility of some wintry ppn to the southwest as the fronts come in on Sunday, positioning looks interesting to me,

GFS looks to slide the Low a little more on the 12z and the very cold surface air to our east just sits there like a stone in a stream deflecting the Low underneath

Yes Steve, i flicked through all the models tonight and got to ECM last. When i saw that 72 hour chart i did think hmmmm.. are we sure this is set in stone yet, even at 72 hours!! Obviously we do get the Atlantic push through from the ECM as expected, but a trip back to 80s style model output may well still throw up a surprise at the shortest of notice, although with the improvements in computing I highly doubt it will. It is ironic that so often we are actually looking for the Atlantic to push under a high and when we do need one (in the right location), they rarely come off. Though generally the overall pattern does support the chances of some decent probabilities of getting proper cold to our shores, and I'm sure we will see such potential in the charts over the next few days.

Messy initial picture this morning, although some cold air getting in from the east is likely at the weekend, http://www.wetterzen...ics/Rukm722.gif Then we have the Atlantic push trying to come in, this might get very interesting IMO and "could" produce a snow event. Steve M yesterday was looking at the 0c isotherm spike seen coming in to the west of Scotland here, http://www.wetterzen...s/Rtavn1322.png http://www.wetterzen...cs/Recm1442.gif The ensemble mean on the ECM 00z shows it further south http://www.meteociel...H0-120.GIF?26-0 http://www.meteociel...H0-144.GIF?26-0 http://www.meteociel...H0-168.GIF?26-0 GFS has it more like the ops, http://modeles.meteo...h-0-0-144.png?0 One to watch.

Brilliant Ian, thanks for that, very clear. Kind of sums up many peoples thoughts on here including mine.

FAX 120, retreating decaying front, 528 over the UK

I disagree, the broad pattern has been forecast well at quite a range from the EC32, high pressure to the north, Low to the south. The anomaly charts have also been very good. Random charts picked out from most of the output will tell you that, here's two from the 18z http://www.wetterzentrale.de/pics/Rtavn721.png http://www.wetterzentrale.de/pics/Rtavn1921.png The problem is we are relying on shortwaves/ridges to fall just right "within" this broad pattern to deliver cold to our "tiny" bit of the world. So in the mid range we CAN rely on the models picking up a general theme but it's all the details (which matter so much for our little island) that can have a real bearing on what we actually experience within that pattern. I would also add that the % of us experiencing cold and snow is highly increased when in this type of disrupted meridional flow than if we are stuck in a flat Zonal pattern. But sadly that doesn't guarantee anything. But back to the hear and now and I am very much of the opinion that things are by no means over WRT all the happenings in the models.

Sensible conclusion Nick. (but come on UKMO and JMA whoop whoop)

UKMO supported by JMA this evening I'm gunning for the underdog, I know we have many signals coming in that the UKMO is missing this Atlantic push, and it may well be, although the consistency is notable, and having another credible model on boards helps! JMA evolves into Snowmagedon for a good chunk of the UK, It's the positioning of the Euro trough that looks to be dictating things tonight, the Canadian Low up to 120 looks pretty consistent between ECM and UKMO but the positioning of the Euro trough/ridging Arctic high is what is holding the Atlantic energy back on the UKMO and JMA. UKMO, trough southerly based, Arctic high further south. ECM, trough much further north, Arctic high much further north. This allows the Atlantic to push underneath resulting in a milder period. But looking beyond this on the ECM the cold returns.

Solid UKMO (again...) and a very cold one to by the looks of it. ECM leaning more towards UKMO with the Canadian Low GFS pushing energy through to the North With UKMOs consistancy and the ECM leaning towards it i'd put my faith there as we stand this morning. Exciting model watching!!!!! Will look forward to the 12zs.

Chinio I do agree over a broader more "normal" synoptic period this is the case, however since the major northern blocking has been showing up in the charts ECM does look to have struggled more than GFS UKMO. It may mean nothing but worth mentioning. Is it the unusual synoptics ECM is having trouble with or is it just a blip regardless? Who knows.

You have hit the nail on the head there Terry "Exeter will make a judgement tomorrow" If you think (and I agree) the pro's will wait for tomorrows runs to make a call, then surely we should be doing the same, and not writing any solution off just yet.

Some interesting info on the (excellent) TWO thread, that I'd thought I'd pop in here. Verification stats are interesting to say the least, ECM verifying on par with NOGAPS at the moment, with GFS leading and UKMO second. Also to note is the 500mb anom charts, big differences between ECM and GFS http://www.meteo.psu.edu/~fxg1/ECMWF_12z/hgtcomp.html

ECM and some of the lesser models throw a spanner into the works on the 12zs!!!!! HOWEVER, the UKMO has been rock solid in it's evolution (the ONLY model to do so on the Det run) and GFS is fine. We will have to wait until the mornings runs to see how this Canadian Low is dealt with across the board on the 00zs, we can't make a judgement on one conflicting set of 12z operationals. My advise would be to come back in the morning and we should have a better idea of which evolution is more likely.

GFS ens have a couple of mighty cold runs after the third, trendsetters for the next phase of the cold spell!! (winking smiley) To be serious though, looking at the mean past December 3rd is pointless the large scatter renders it useless. And overall confidence is low in any outcome beyond this point.

Consistency in the ensembles is just as important as consistency in the Dets, if we see a continued uptick in the scatter ensembles over the next few runs then we need to consider them, but ensembles can flip pretty easily, I've seen it plenty of times before.