kold weather

Sadly we aren't probably going to have any real clue until its basically on top of us (if it gets that far!) these things tend to shift around. I mean take that US storm, the low was still shifting about quite a lot within 36hrs, to the extent that the snow line moved about 100 miles north in that time. For our ize country, thats quite a sizeable adjustment within 36hrs. As you say, it is cool to look at but it probably only informs us of the range of options out there until closer to the time. Sundays slider does still look subtly interesting, there is a slight consensus on the GFS ensembles of the cold air digging down quickly enough to turn the back edge at least snowy...but at this range we just won't be sure.

I'd take the cockles Kentspur, but not so keen on the jellied eels! Though my Dad being a proper born and bred E.Londoner is always game for some (I mean, technically I am since I was born in Newham, but realistically I'm an Essex lad at heart!) Clouding over here now in advance of the warm front pushing in from the west that should make things far milder than they have been lately.

The general pattern is certainly interesting, despite some very odd pressure distrubtions over our neck of the woods between 144-216hrs (I'd be stunned if it all remains that flabby!) however the trend upstream is good and we finally relocate that PV. Also yes the models did show that beasterly for now pretty much, I suppose in a funny sort of way we have still ended up in a broadly cool/cold pattern, despite the models originally resetting into an Azores led pattern that hasn't really proved to be the case. Also the big difference is we have realistic snowfall opportunities before 144hrs...and we have near total model agreement on at least something being close to the mark, we couldn't even get run-run consistency from any model with that easterly, it always was 50-50 more or less (bar maybe the 12z suite on Thursday?)

Yeah, definitely a cold run, just doesn't look quite right to me with these flabby lows, especially with the jet still being quite strong, I'd be stunned if we didn't form a decent low on either of those LP circulations that work down SE over the UK on that run. Equally, those ensemble members that go down to like 960mbs for that low also look overblown. EDIT- para has a complete 180 on the global pressure distrubtion by 300hrs as well over E.Canada!

Well the para is certainly throwing out some odd looking solutions and is kinda out of sync with the GFS suite in some ways in that it brings down several very flabby area of LP with no frontal activity on any of them (which in itself seems very improbable?!) but it remains nice and cold and the flow turns NE effortlessly on this run. Seems highly unrealistic to me though in how it handles that LP, surely you'd get at least one active front come down? A good run though for sure... EDIT- even in America it looks unrealistic with its LP pattern. Think unfortunately that maybe for the bin this run...highly unrealistic pressure distribution!

Ah yes, its not being pedant because that extra difference above or below say 15mbs from 1000mbs probably does add up a fair amount! I think my 1mbs was just a lazy guide I used back in the day, but 0.87 is correct. With my grounded (critical?!) hat on, even the milder less enticing ensemble runs still have a pretty solid snow-rain event for all areas bar maybe for the far SW. So that is positive. Still a small chance of something on the backedge of the low on Sunday, but that seems small right now away from Scotland, where odds look decent enough.

There are some legitimate Channel low set-ups on a couple of those GFS runs, with some very tight gradients (5-6C within 30 miles). Control run is also better for our region for sure. Long to go yet though everyone, a REALLY long way!

I'd also say the control run looks more realistic for that PV over E.Canada, maybe a touch underdone but much more realistic IMO. PS, there are some extreme snowfall solutions in the ensembles, with a VERY tight gradient between the snow-rain. Still, a heck of a lot of disagreement on that track of the low, and don't expect any real clarity for some time yet, for good or ill.

Control run is a edge bit further south on this run, which brings more of the south into a pure snow set-up rather than snow-rain like the operational run. We probably won't have a more solid grip on that low track though until 96hrs out, and even then could be quite sizeable differences right down to 12hrs out...so we have an awful long way to watch it and it could still very easily trend way too far north...or much further south.

I suppose I should be glad I've had nothing, at least can't be disappointed with nothing. Anyway a very good 06z for our area, always more marginal further south but there is still plenty of good stuff to look forward to on this run. Also think the snow would hold for longer in the south than the operational is suggesting in the set-ups it shows

That's a foot type of snowfall on the 06z GFS fwiw! I think this is the first time I've visited this thread in years!

As always getting snow from these set-ups is a mighty tough ask. How many times has a LP that starts by getting a frontal system into Scotland only for them to push further and further south to the point where it barely reaches S.england. Don't think it would be that unrealistic for that trend to happen. 06z is a fair compromise for a fair chunk of the country, any further north and it'd be mainly rain event for the south, much further south and it'd only be the S.midlands/South that gets anything at all. Anyway very good 06z GFS and one that is loaded with potential throughout the run, starting on Saturday night.

Take a look another 24hrs onwards, even the south coast gets abit of a dumping on this run in the end! Snow-rain-snow would be the theme of this run for us lot in the south, certainly not the worst solution and the snow would probably hold longer than the models initially show.

252hrs is a classic example of where having a cold pool established makes a big difference. It looks like a sleety mess on 850hps, however the boundary/surface level is so cold that I'm fairly confident any precip would snow. Loving this run, despite the super strong PV doing its best to blast it all away, this is what things can be like IF the first low ends up staying far enough south!

Very cold day there Frosty, not surprising given the low thicknesses and also the probable fairly widespread snow cover by that point which will help hold back temperatures. Indeed the wrap around low drops quite a lot of snow, sweet spot would be S.Midlands/ Home counties on this run.

Yeah we may see that LP move SE, but the whole pattern to our north is towards lower pressures/thicknesses as that PV lobe to our NE is also starting to strengthen again. May not end badly but much will depend in how the LP moves and phases with the PV lobe to our north. With cold in place, does give us some leeway. With that being said, the likelihood of a 950mbs PV is exceptionally low, probably on the lower edge of what is likely, so it is highly probable the GFS is just overblowing it a fair whack which may make the GFS pump things up a little too much.

Wow, that PV lobe develops a central pressure of 950mbs, that's VERY low for the core of the PV, I'd imagine the thicknesses there must be truly insane! Azores high won't last long against that sort of pressure but we already are on the right side of the cold so that may not be a total disaster, but we will see. That 2nd lobe to our north will probably induce a +ve NAO type pattern eventually given the strength of that PV/jet combo to our east.

I've been hearing some US mets say that is one of the most intense PV they have seen, the cold is also very impressive for sure!

Also worth noting that 8 out of 10 times these sorts of LPs adjust southwards, that is where the likely margin of error will be, especially if the models are a little too strong with this feature (though well within the range of what is possible).

Good 06z run, we could do with that LP being a solid 10mbs weaker BUT the trend for a possible snow event is still there for Jan 29-31st period. The ECM ensembles have been onboard this for the last 3 days now, so worth watching. Given the low is still shifting from run to run, we still have plenty of time for adjustments. On this run verbatim, N.Midlands is probably the snow line, though just about everywhere would get leading edge snow at least. On that snow line you'd be looking at 6-9 inches probably.

Looks quite similar to the ECM in the way its handling that LP coming out of the states between 120-144hrs. Probably a snow-rain for the south on this run, but how far that line extends will be interesting to see, especially if the LP shifts its center.

Yeah. For those who don't know, to work out thicknesses you need to find out the geopotenial heights (that would be the colours on the meteociel charts for example, same with wetterentrale), lets say 528 for example here of the top of my head. Then for you either add or subtract from that based on the pressure above or below 1000mbs. So for example, with a low pressure of 970mbs, that actual thickness is 558, which would actually be high. In contrast if the surface pressure is 1020, the thickness would be 508, which would actually be very cold. Broadly anything below 520 is going to be snow in all but the most exceptional chances. 533 will be rain, except again in exceptional circumstances.

I think that is going to be key, the Canadian PV lobe isn't the worst thing in the world if we can keep the cold air either within a 12-24hrs fetch of the UK, or preferably over the UK. Unfortunately seems like we are going to be very susceptible to what is quite small adjustments on a global scale, but for us that makes the difference between cold and snow, and mild and wet. It is about time I feel this winter we had a stroke of luck work in our direction, given there has been very little of it so far this winter with how the pattern has evolved. Whitefox, I seem to recall there are some SSW that don't have any impact on the troposphere, especially with where we are in the QBO cycle, I think they more often than not don't impact (though this is a more severe SSW than normal which may balance that out.) I think that figures were something like 2 out of 11 had an impact?

There is also quite a,ot of snow for NE Scotland in particular from the ICON. I know the eCM also has been showing quite large falls tin the Ne of Scotland. The whole lot then starts to shift southwards bringing more of Scotland intbo play.

Depends on how quickly the westerly winds downwell, and also to a certain extent how early/late the final warming of the PV is. For example the Jan 2013 SSW didn't really mix down until late Feb and the effects lasted through March and early April. This one may not hold as long but its certainly a possibility that we keep this wonky mix for a while yet.