How accurate are these charts? Snow to cross the country during tomorrow afternoon. Looking good for a covering in the west mids and wales particular.

Almost enough elongation of the low SE into Europe for the UKMO 144 hour chart to at least mitigate the low-level maritime influence and hence the effect of the warm sector on the far S and SW. Perhaps sufficient for the SE for reasons covered by Retron.

I suppose there's still room for a less rounded feature to develop given that this is a day 6 chart we're talking about. Never mind the sausage highs, how about a sausage low?

As for that sneaky GFS 12z, it plays trickster - the slow slides SE more quickly and cleanly, but this is part of a whole host of changes to previous runs, generally more progressive overall, particularly across the U.S., and these lead to energy firing over the top of the high about a day sooner than previous runs and with more vigour.

The trough hangs on enough to keep us in a cold easterly for numerous days, with uppers not bad at all, but I've seen these Euro troughs overdone and/or maintained too long on enough occasions to know that this is a riskier way of going about things.

Also, it still brings me cold rain for the majority of the time. So you can imagine how furrowed by brow became when watching that run unfold!

The sheer number of changes to the previous three runs calls for a skeptical eye, hopefully just a strange fling from the model, otherwise the risk of that easterly potential for later int he week falling short of desired results will have stepped up a notch.

Quite large differences on the GFS and UKMO at +144, GFS much more amplified

GFS wants to give up to 8 inches of snow here at least. But it's all rather messy and uncertain ATM

 Agree. I've got it down as 0.87 rather than 0.8, not that it makes much difference if one can't read the colour scale. 

12zs so far have shown nothing to make me ease off on my pessimism.

But as a rider to that, as I said earlier, there are always potential reloads in situations like this (or indeed upgrades).

There are also regular "wobbles" that go on prior to a cold spell, so that's what I'm pinning my hopes on.

What I meant by my earlier comments was (and no I was not forgetting February), is that normally, the chances are reloads of cold are possible, but a late February/March bitter spell like was experienced in 2013 are as rare as hen's teeth, hence running out of time for anything substantial this winter.

That's not to say it won't, or can't happen though.

But as it stands at the moment, nothing jumps out as exceptional here - just a bog standard cooler than average winter period with a bit of frost.

Doesn't float my boat - but I guess as long as there are blue skies, it will at least feel better than relentless wind and rain.

You can't beat cold rain whilst (it feels like) everybody else is getting snow to furrow your brow.  Hopefully, as you say this is a extreme solution within the range of possibilities.  The ensemble and ECM runs will help to put it in context.

Predicting precipitation, let alone snow, accumulations at this distance is almost pointless... It's only 24 hours prior to an event before there's any confidence on location of snowfall even to the nearest 50-100 miles or so, and that's on a good day.... I've lost count of the number of times people have been dissapointed or pleasantly surprised at last minute twist and turns, especially in marginal situations, which this spell is likely to be for many.  As has been said ad nauseam, get the cold in first.... the instability caused by that cold will more often than not cause all sorts of features to crop up at short notice..... January 2010 is a good example - 48 hours prior to the main snow event, people were bemoaning a 'dry' cold spell... In the event many southerners had over a foot of snow.

I agree that those looking at specifics are wasting their time. PPN amounts are not worth too much attention beyond a day or two.

I didn't see the 06z GEFS but as far as the GFS 12z op goes, it was an upgrade for me  Scandi Highs, though very cold, quickly become boring

Given the GFS 12z op has swung the other way and soon brings much lower northern heights and some good old scandi troughing, I eagerly await the ensembles... just to see the trend and as James indicated, to see if the pendulum has just started to swing the other way.

Regardless of what the extended GEFS may show, I'm sure if you'd posted these charts a month ago people would have been all over them!

http://www.meteociel.fr/cartes_obs/gens_display.php?x=306&y=141&run=12&ville=Londres&runpara=0&type=3&ext=0

http://www.meteociel.fr/cartes_obs/gens_display.php?x=306&y=141&run=12&ville=Londres&runpara=0&type=0&ext=0

(Short ensembles, the coldest set this winter!)

This message has been quite consistent.  The only significant feature that looks to be arriving with a sustained snowfall within - would be the slider low on Tuesday.  The forecast made so far has been consistent in saying it will be a decaying feature with little punch in it.  The GEFS has also been consistent with this.  This is not data in isolation.

Usually with any system given a few days you can see how much impact it will make in a rough manner.

Im just not seeing any significant features either way.

I do often wonder how exactly GFS calculates it's precipitation type output, and whether it is actually much use at handling the parameters resolved even when you're getting within 24 hours of the event.

It seemed to miss the southward extent of snowfall yesterday morning, but that could have been more down to resolution - from the pixels seen on screen it seems that a single grid point is still enough to encompass everything from Bournemouth Beach to Salisbury Plain, and in the observation data I have often seen a difference in temperature and dew point of two or three degrees across that space.

What I do know is that warm sectors running into an established cold pool are great ways to bring a brief period of heavy snow just ahead of them, but unless they rapidly occlude out before arriving at your location, a transition to rain is pretty much inevitable.

There is a way around that issue of course - have the warm sector pass just to the south of your location, preferably with as much east-west elongation as possible. You never lose the cold air and get absolutely pasted. Somewhere or other will get to experience that so long as the warm sector doesn't head SW of the UK or (somehow) track across the far north.

I came very close to experiencing it in December 2010, when hour after hour of heavy snow had me grinning like a chimp in a warehouse full of bananas, only for the warm sector to make a brief visit, the half hour of heavy rain compacting the snow into what then became a hard, icy substance during the following night (temperatures did fall to around -10*C though, which was impressive).

Starting to drift off topic there so will cut reminiscence short here, this is the model output discussion thread after all    

I can vouch for that. Even Penzance gets heavier snowfalls than Portsmouth. It is without doubt, the worst location in Britain for snow (IMO).

Regarding the ensembles Darren posted:

Agree it is looking cold next week but there are just a few signs of things returning closer to average at the start of next weekend. I really think Scotland and the N of England really look like doing well and the Scottish ski industry will be rubbing their hands.

I know Fergie over on NW has mentioned that they're not to be trusted! That said, a certain Euro4 over-egged the extent of snow and precipitation yesterday morning, as it was bone dry here despite a few runs in a row showing snow here. Again, Fergie mentioned that Euro4 was overdoing things in the preceding couple of days, imploring folks on NW to not take the scale too literally!

I know the models are generally better at handling frontal precipitation and that's been the case for many a year now. I guess part of the problem with convection is the modelling of the individual shower cells - there's no way on earth you can accurately model exactly where a specific cell will be and of course that means there's no accurate way of predicting how much will fall, or even if there'll be anything falling at all. I don't suppose we'll ever be able to model convection properly, as to do so you'd have to cater for every square centimetre of atmposhere from ground level up to thousands of feet about ground. The amount of data and processing required for that is mind-boggling!

What is with all this depression, its a fascinating model watching period, or is everyone still comparing it to 2010 and will never be satisfied unless it tops that? If it helps then feel free to use me in jest be it about the lake effect, or the hope index, that might distract and cheer you up! 

I have to ask, what were people expecting? The trend for a long time now (ever since it became visible around the 4th) was for a Pm based cold spell, the fact we actually have some easterly component is a bonus, and was not the most likely option.

"But Q, you live in the north and might actually get snow"

Well deal with it! I have had to put up with so many sliders trending from Scotland, to N england, to end up in the North Midlands, or conversely to have stuff coming up from the SW only to peter out in S yorkshire. And anyway, you still have a very good chance of seeing at least some local significant snow, maybe even some lake if we get the easterly which is suggested for a couple of days at least.

Makes you wonder why we ever get excited - it all looks pretty standard winter fare - for lowland areas of England at least.

At least we are not getting the relentless zonality of last winter however.

As posted by Richard Dixon on USW - a new way of looking at the GEFS ensembles. I think I'll be using this a lot in the days to come!

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefsts&MODELLTYP=2&BASE=-&VAR=tmp2&HH=&ZOOM=0&ARCHIV=0&RES=0&WMO=03772&TABLE=2

Other places are available.

EDIT: And here are the T850s. Only snag is - it seems to be slow at updating compared to other sites.

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefsts&MODELLTYP=2&BASE=-&VAR=t850&HH=&ZOOM=0&ARCHIV=0&RES=0&WMO=03772&TABLE=2

Absolutely squat on the Euro 4 though

The Euro 4 was pants with its ppn forecast on Tuesday night / Wednesday morning IMBY .

http://www.meteociel.fr/modeles/ecmwf/runs/2015011512/ECH1-72.GIF?15-0

http://www.meteociel.fr/modeles/ecmwf/runs/2015011512/ECH1-96.GIF?15-0

ECM so far