kold weather

Yes but that only forms because the deeper vortex comes down and forces pressure to rise further south as a consequence of it, if you run P4 on the ensembles between 240-300hrs you'll see that action in progress.

I do think the models are starting to come a little closer mind you BA. The models are probably now within about 100 miles of each other, though with a ESE moving system, even 30-40 miles further north/south means the difference between several million seeing snow, and several million seeing cloud to the south! I do think the chances are there though for a snow event in the south, though again with the caveat that these systems have a nasty habit of adjusting south at short notice so we will need some luck here.

By the way, just to note that if we see an extreme burst of cold coming through the Greenland/Iceland area, it runs a very high risk of developing an area of LP in a place that may very rapidly help us to switch back into a SW pattern, especially should the upper high migrate westwards. For example: You can very easily end up on the wrong side of that sort of pattern and default back into an Atlantic set-up even if the AO remains negative. Just a word of cuation for those that see deep cold coming out of that area and think we are in the money, its REALLY rare for that cold to make it down to our neck of the woods, I've seen it literally a handful of times looking back at the last 100 years of charts on the archives.

I'm not overly concerned in this set-up with regards to deep cold. I think the surface is cooling off nicely and I'd b very surprised if we do end up with the type of evolution currently being pegged if we don't at some point end up with a proper shot of arctic air. Now whether it sustains for long, I've not got a clue. Besides, we have several marginal evolution that will give snow for some over the next few days in a ever slightly cooling pattern at the surface. That ever so slightly cooling set-up makes the world of difference in marginal events.

Yeah, some of the runs on the ECM ensembles are going super low, of course going that low doesn't automatically mean we are cold, especially if we end up with a really overly rampant southern arm of the jet, could end up in a very wet wave train. However, thinking positively for the moment. If things pull off for us, this could well be a very memorable spell. Any ease up will allow an attempt at a SW attack some point between the 5-10th Jan which could end up with a battleground somewhere near our shores. Any re-strengthening of the blocking leads us fairly close to the holy grail of snow set-ups with a 10 day colder spell to prime the situation. However that really is a rare beast and would need alot of things to come together neatly. But the fact its even on the table as an option says we are in a good place for the first half of Jan.

So looking at everything so far here are a few thoughts: 1: There will be disturbances running across the UK this week. I'd imagine as the week goes by things will gradually swing colder simply through dint of continued surface cold pulling down SST's and soil temperatures. It won't be drastic, but in very borderline snow events it can be what swings it. Night time snow events = accumulations. Day time snow = wintry mixes, less accumulations. 2: It stays cold for at least the next 10 days. Probably no mega cold but a sustained spell several C below normal is nailed on now - this ain't going above average before the 15th Jan IMO unless we end up with a very west based -ve NAO. 3: There will be some attempt at a northern block. I have concerns of whether it gets quite as strong as some models are trying to go, but we will see. It remains cold regardless of whether it goes gang busters or not. 4: A slower set-up MAYBE better - if it evolves too fast with too much energy we run a risk of ending up rapidly evolving into a west based -ve NAO and the flow switching SW. We really come close to that on the 12z GFS but we have some mega impressive blocking on that run which saves it. I'd be surprised if it ends up quite that impressive. A slower set-up allows a stronger cold pool which then allows us to tap into it. 5: There maybe little deep cold, but you keep cooling the surface down across the whole of Europe, and keep northern blocking, its eventually going to pay off, especially with an active southerly jet. Remember, get the cold in and time will do the rest.

This is a pretty risky evolution at this point here: We've seen many a time the models try to develop a northerly flow but then a shortwave comes across that isn't forecasted till 96hrs and cuts the upper high off from ever forming in the first place. So caution very much needed on that type of set-up. Not saying it won't happen just we should as of yet get carried away. Alot of old timers will no doubt be urging caution on this. ICON 12z shows what happens if that shortwave behaves differently: Still cold, but very much more bland by 180hrs.

Agreed with all of this, I'm really not comfortable until I see a consistent evolution, nearly every 2-3 suites we are seeing a different type of evolution crop up, with the 12z suite now showing a mid-Atlantic high that morphs into a Greenland high eventually. I'd put FI quite close in at the moment, and that is for both for things to look better or worse. The only thing I will say is back in the great winters of 09/10 and Dec 10 models often started bringing in set-ups faster and faster, this maybe a portent for a similar sustained spell of cold/very cold spell coming up.

I saw my first snow in about 2 years from this event! Granted it literally last 5 minutes, but I'm so desperate I'll take just about anything!

Had some brief wet snow just now in the heaviest of the precipitation. So finally saw some local snow for the first time in nearly 2 years! Now reverted back to rain again . I'd imagine the downs may have had a longer spell on snow, though not sure whether its settled up there or not.

Certainly possible, but that tends to be a bigger risk when you already have a fairly west based -ve NAO. Ironically the current evolution with the HP semi-toppling but failing towards N.Europe buts it in a really strong position for a -ve AO to properly develop and sync up with a strengthening -ve NAO and develop a really textbook looking Greenland high. Still a few hurdles to get over yet but looking promising.

To be fair though there was a trend to flatten out the pattern yesterday, every single model moved quite alot from the previously very amplified pattern to a much flatter pattern. not all were bad per say, but there is a big difference between raging upper high seen on the ECM on the 24/25th December, to the much weaker and more Atlantic based feature seen yesterday. Since then the models have all again shifted back towards that original setup, though it is actually quite different in how it gets there. Caution is defintely advised, I've been here 16 years and seen such features shift around before at far shorter notice. *However* I've not often seen such good global set-up go wrong from this point very often, just a couple of times from my memory. I just feel caution is probably still wise at this point until we have a longer period of consistency. it is GOOD news though to see several models have a very similar patrern from 120hrs onwards.

Yeah I was surprised yesterday when the models totally backed off, these runs have somewhat moved back to where the base background factors would suggest we should be. I'm always very wary when I see models flip flop around with drastically different solutions, in my experience it doesn't tend to bode well. However you are right that this time there are alot of factors out there which auger well for our current cold spell to intensify further. Could end up becoming the longest cold spell since Mar 2013.

Depends on he EXACT wind direction, ENE typically need lower than -5c because the water temperatures tend to warm up the surface flow somewhat and this makes things increasingly marginal the warmer the air is in the lower atmosphere to begin with. Of course the colder the SSTs the less modification there is, but also tends to lead to weaker precipitation. Now if you can get more of an ESE then typically the air travels less time over water and typically will be colder at the surface, therefore you get away with having higher temperatures at 850hpa, in exceptional circumstance over snow fields right upto 0c in theory.

The models really are being very inconsistent at the moment, which would suggest to me that caution is needed, they could very easily swing back again tomorrow to what they showed yesterday. With that being said I was a little suspect that the models were way over-correcting yesterday, and they often do that only to have to row back to a less extreme version of the previous pattern. Either way the models today have locked back onto a cold pattern and long may it stay that way. As for tomorrow 's possible snow, its going to be a nowcast, even at this point there are considerable differences. Could well be some surprises as well as little trough/frontal features can pop up at very short notices in these sorts of set-ups. With a reasonably cold surface from now on, our range of options for snow should increase, especially the longer it holds and the more it drags surface/sea temps down.

Interestingly I'm a decent way south of the M4 yet also got snow on that event, I was quite surprised as well, though not in the same quantities mind you! I do have a modest elevation mind you thanks to the downs. I suspect 28th may well be a wintry slop down my way if it comes off as planned, but the downs maybe worthy a little trip being reasonably local (thus not breaking rules lol!)

Its interesting to see the models shift north it has to be said, it probably only happens on the models 1/2 out of 10, but the models are coming towards agreement so that does strengthen the case that this is what will now happen, and it was within the range of possibilities that both the ECM/GFS ensembles had in their respective suites even yesterday. However it is also true there is time for it to shift around further.

One other thing to note Steve is to watch to see if we end up getting a cyclonic loop out of this low pressure as a secondary low tries to form around it. The models won't clock this till late in the day but such evolution have led to some really big snowfalls in the past. Bit of a lottery as to where the pivot point would be mind you!

Very interesting and somewhat rare to see the models shift back northwards are flirting taking it further south, definitely a better evolution though for a bigger chunk of the country. The evolution for the south is something of a knife edge in particular, timing really will be vital. IMO if it arrives in the south before say 10am, snow is likely, if it arrives to co-incide with peak heating, then ot my end up just as a wintry mess. Further north looks increqasingly less marginal as you'd expect.

Another cold run from the GFS again. Also, reasonably snowy with several bands beyond the 28th. The ECM gas hinted at other bands recently as well so something to have a watching brief with I think.

Yeah an adjustment towards the euro. The GFS 12z ensembles did suggest there was scope for the op to move a little north, and indeed that is still the case. It feels like the impact area is starting to just zero in a little. Still scope for it to miss completely, indeed historically that is what happens but every model run inches the confidence up further...

Still as per most of my updates looking at the 28-29th period as the best shot for snow. The ECM still remains the most bullish of the models, it maybe a little overdoing it but the possibility is there for sure. The GFS and its ensembles are still shifting around but this 12z suite is probably the best agreement seen so far with a path broadly similar to the 12z ECM, though some are too far south and a few are definitely still further north, but not drastically so. I'd guess we are zeroing in on an area within a 100 miles either side of where the ECM is, so still scope for change, but maybe not huge change from here.

Very similar to the 00z ECM operational as well. Still I can't help but shake the GFS maybe closer to the mark, these things do usually shift south closer to the time and broadly they have been already shifting southwards in the last 4-8 suites. Hope I'm wrong with that as IMBY thats a pretty tasty chart, whilst not huge snow here it'd give a nice dusting.

Merry xmas Steve. Regardless of no snow here, its nice to finally have a proper seasonal feeling day with cold in the air and a morning frost. Oh and sunny as well. Makes a huge difference as this had the potential to be a very bleak xmas with the restrictions. The light really does make a difference.

Also just to add to the above, several cold spells that sustained in the past often saw the GEFS suite being very overly keen to reduce heights across the Arctic/to our north too quickly. Indeed in some of those cases there was a reshot of cold that ended up being more intense than the first (Dec-Jan 09 and Dec 10 both spring to mind immediately, to a lesser extent Feb and Mar 2018 as well, though that time seasonal warming ensured the 2nd shot wasn't quite as severe).