chris55

The big three at 144, broadly similar but ECM still want's the Euro trough further north. As we move forward, the possibilities are open, but slider type Lows moving off southern Greenland and being ejected S.E towards the UK could be very snowy on their Eastern edge if the air embedded over the UK is cold enough. If the high Lat blocking holds this is a real possibility.

An Artic high, is just that, a high pressure cell that forms over the Arctic regions. It is a rare beast in winter, as usually you would have the Polar Vortex (Low pressure) in that area. It will by it's nature, allow the cold air from the Arctic to spill out clockwise around it as it ridges and interacts with other features. The famous cold spell of 1987 is probably the best example of an Arctic high delivering extreme cold to the UK, Although our current projected set up certainly is evolving around an Arctic high, the 850s are not as cold as that famous event. As for 850s, well, anything from 0/-1c or below, but there is a whole host of other factors to consider, one is how dry the air is, a dry airmass with low dewpoints needs less cold 850s to produce snow. But to be honest you could write a 50 page essay on the in's and outs of conditions for snowfall!!

P13 is pretty much identical to UKMO at 144

Coldest De blit ensembles so far, looking good.

Much better WAA heading up the Western side of Greenland on the 12z http://www.wetterzen...cs/Recm1442.gif Overall a much cleaner, and better run so far. Now we just need the Euro trough to be corrected south and were all in lol.

A deeper Low exiting Labrador at 120 should help support the Greeny ridge compared to the 00z.

Yes, I was thinking this "could" happen on yesterdays runs, so much up in the air at the moment it's pointless looking at such details, but from an IMBY perspective a "clipper" shortwave would be great!!

This has been a theme of the ECM in recent runs, to me it looks unlikely, but we'll just have to wait and see.

Solid UKMO, three very consistent runs now, As others have said it will be interesting to see where the BOM goes this evening as if it follows UKMO it could gives us an idea of what may evolve from 144 if the UKMO was to verify.. GFS seems to be quite volatile between runs, however it can by no means be discounted. ECM will throw some more uncertainties into the mix, but a follow on from UKMO would be nice!

From the MET UK Outlook for Wednesday 28 Nov 2012 to Friday 7 Dec 2012: Outbreaks of rain will continue to affect the far southeast Wednesday, clearing away by Thursday. Elsewhere, a mixture of sunshine and showers throughout the rest of next week, with the heaviest showers towards the northeast, wintry over high ground with hill snow in the north. Windy at times, with the risk of gales in the southeast at first. It will be rather cold with a risk of overnight frost and icy patches. Becoming cold into the start of December with widespread overnight frosts. More settled than of late with sunny spells, but also wintry showers, especially in the north and east where accumulations over high ground are likely with snow perhaps falling at low levels. UK Outlook for Saturday 8 Dec 2012 to Saturday 22 Dec 2012: As is usual, there are uncertainties in the forecast for this period. However, there are signs that northerly winds may be quite frequent across the UK. So, on balance, colder than average conditions are likely to continue, with a risk of frost and fog, and an increased risk of some snow. Issued at: 0238 on Sat 24 Nov 2012

P20 on the GFS ens looks to have the day 10 pattern spot on :winky:

Stunning UKMO and BOM this morning and both very similar, so some consistency between these two models at least GFS not to far of either, The evolution of the little SW "slider Low needs watching as rather than spoiling the party it "could" if things fall right, produce some snow on it's eastern edge if the interaction with the colder uppers and positioning is just right. Although at present the influence of the block holds it to far West, ECM still has the trough to the east to far North IMO.

Out of all the charts today I think the UKMO 144 has it right, http://www.meteociel...44-21.GIF?23-18 I know it also happens to be the best for getting the coldest 850s to the UK but both ECM and GFS look to have the trough to far north, I can't seem to find anything like it in the archives. And ECM is especially odd with this boomerang high idea. http://www.meteociel...H1-168.GIF?23-0 Of course UKMO may well join the ECMs ideas tomorrow but it wouldn't surprise me if the trough was corrected southwards over the next few runs. And instead of this "strange" northerly type set up we see more of an easterly influence again.

Yep, look how the Azores high ridges northwards and allows the trough to duck underneath, this is going to be an important evolution IMO. UKMO would follow a similar path ECM fails due to the Low off southern Greenland All to play for though!!!!

Oddly it seems to me that it's the Azores high that we need for all this to come off. If it can ridge freely north/north east and link with the encroaching Arctic high then we are away, however it looks as though the shortwave moving off the tip of southern Greenland is just enough to stop this, and in turn the Azores high sitting in residence actually holds back the CAA from the north east!

You gotta laugh at this, now ECM wants to drag up a toasty easterly due to the cut of high forming to the far north east!!!! http://www.wetterzentrale.de/pics/Recm2162.gif What the final outcome will be I have no idea, and neither do the models.

ECM had this slightly odd pattern the other day on one of the Det runs with the trough quite far north. http://www.wetterzentrale.de/pics/Recm1921.gif I say the models have no idea at the moment? More runs needed.

Just to reiterate, take the UKMO 144 (amazing) and the GFS 12z ens and IMO nothing has really changed tonight except that the GFS was a bit of an outlier in the mid range, over doing the power of the shortwave exiting Greenland. http://www.wetterzen...cs/Rukm1441.gif http://www.wetterzen..._London_ens.png If the Op had been perb 6 (which is as plausible as the Op IMO) there would be many more excited posts on here although that would have no bearing on the end result. http://modeles.meteo...-6-1-180.png?12

Check out the GEMs evolution, it has the 120-144 part in more detail and similar to UKMO. The Low your talking about is a separate thing.

Seeing UKMO from the NH view, it's a stonker of a run. Though at range this range, in this situation, all options open.

Yes something wrong there for sure.

GFS 12z just another option in the grand scheme, this wont be decided for a while yet. UKMO better as things stand, wonder what ECM will throw into the mix.

The Met are doing a kind of "mean" forecast. It could well be much colder if the synoptics set up right, but it could also be less cold if the synoptics are less favourable. We know some major high lat blocking is in the offering, but as the Deterministic and ensemble data shows from run to run small changes in the grand shceme could have significant impact on just how cold it will be. So the Met can't really give any other forecast until things firm up closer to the time. From my perspective we look to be leaning towards the cold/snowy option, rather than the damp and cold/snow on hills in the last few runs. So will await the 12Zs with interest to see where we are later today and into the weekend.

Yes Nick averaging close to the -5 line (around London) http://modeles.meteociel.fr/modeles/gens/naefs/graphe_ens3.php?mode=0&x=311&y=143&run=0&runpara=

p18 has got the pattern nailed. http://modeles.meteo...18-1-174.png?18 http://modeles.meteo...18-0-174.png?18