ITSY

Aye. We’re drifting a bit from the thread but it was the same here - in NW London we had about 7-9cms of level snow, our heaviest since 2013. So no, you can’t take precip charts at face value and no, Dec 22 wasn’t a busted flush. It certainly delivered for many. The value in this thread is both its intrinsic face value reactions on a run to run basis AND the skilled interpretation offered by many. I suggest everyone thinks about what bucket each reply falls into before calling it out. That makes life and reading the thread a lot easier.

Spot the outlier. An excellent set there for the week ahead - remember when people kept shouting about day 10? - and a reminder that the disruptive snowfall may be good for some but for the vast majority, the prolongation of the cold could bring far greater opportunities and interests down the track.

I'm not the first to say or think this but worth noting that in these potential battleground scenarios, usually if the cold wins out it means the initial low has moved south towards the Channel Islands and France - not always, but usually. That would remove the risk of disruptive snowfall for most but would conversely deepen and prolong the cold therefore hightening the risk of further snowfalls occurring down the track. So long as you're not the bill payer the latter option is the safer bet for the vast, vast majority. That's where the GEFS and GFS have taken us this morning - and it tallies much more closely with what Exeter has been saying...(who have to mention the risk of disruptive snowfall since, well, it is by its definition disruptive and requires some warning).

This is hugely entertaining and interesting. If UKMO verifies as shown, any eventual encroachment from the West will produce significant snow for somewhere in central or southern England, even if transitory. If the GFS verifies as shown - well, the less said the better there for anyone who's virtually not on a Scottish mountaintop. GEM continues to paint a positive picture closer to UKMO and with a bit of consistency too. GEFS, ECM and EPS will be interesting now... PS. I think someone else has just said this but you cannot just 'bin' a model output because you don't like it. If we think a model is handling a feature wrongly that is fine - but it's not to be dismissed. It's a possibility, especially for our Isles where if things can go wrong they usually do in the hunt for cold.

People need their heads testing if they think this is a bad run. It's basically identical to the former. The only challenge that both runs show is the lack of low heights over Europe. Ideally we want the low over the Azores to move westward a bit more quickly. But come on team, this is what we dream of. Isn't it?!

The stronger (potentially undercutting) low in the Mid Atlantic, and the lower heights over Iberia, are also noteworthy. Together these two things should lead to somewhere positive.

Some interesting observations here regarding the specific route, extent and nature of any blocking on the ECM. Looks like either a classic but more pronounced pre blocking hiccup or an unexpected new trend. Too early to tell.

Good god I can’t actually believe I’m saying the words “West-Based” but this is the actual first run where I’ve seen it threatening to make an appearance, owing to the additional 3rd wave of High Pressure out of Canada, which subsequently drags the Greenland block slightly westward and forces a couple of lows to behave very weirdly over Greenland. This is then followed by a vintage GFS dartboard low - almost by default - so may not be a trend. But it is worth watching out for, however marginal the chances. Even then, this run, with its weird dartboard low, potentially ends up with a NWly snow maker so it may still be a case of reaching Rome via another route, which bodes well. As Catacol posted earlier, GFS is currently the 4th best performing model though at long range so let’s see where this route features in the pack before getting too bogged down in the mud. EDIT: the fact that after all of that we still end up here, speaks volumes about where we are. Happy hunting all - good night!

This is precisely the opposite of what took place this morning when the reverse trend emerged - excellent news and a definite upgrade across GEFS. I'm torn - between participating in the sheer enjoyment of these insane charts and the digital delusional atmosphere in here OR Nick's more pragmatic sanguine approach of 'wait and see'. We should wait and see really and the oldies in here know it. However, the thing is, the term 'we've been here before' isn't quite right. We haven't had this kind of consistent, prolonged, cross-model, cross-suite output before, complemented by loads of affirming background factors, only to see it go totally wrong. If it does go wrong...then it does and we'll remember it as the absolute mother of all let downs. Fair enough. But my god, if you can't enjoy this then why bother?! Incredible synoptic output. Just incredible.

Just to back up what I said earlier about the mean, here's the GEFS stamps for London. It follows on from the 00Z with a number of milder runs (albeit still in the minority and at long range) - this doesn't mean the cold spell won't happen but it does mean that there are upstream factors that could make the transition either messier than forecast currently or leave us on the wrong end of the high. The point being, we really do need to look at what's happening in the mid and western atlantic sectors, as well as what happens to our low around Iberia, to get an accurate grip on how our high will behave and where it will go. Clearly, and unusually, the cold horse is favoured as of now but there are still wrinkles to be ironed out - as in all future spells. It's important people acknowledge that to avoid desk thumping disappointment if the worst materialises. Those of us who have been on here since the mid 00s have learned from experience to proceed with caution, even in the face of amazing charts. It's excellent viewing right now but we need to be steady with the ship...

Just a word of warning to keep people grounded - unusual from me I know. Yes the charts this morning are jaw-dropping, by and large. But there are variations and nothing is banked just yet. The GEFS mean at day 10 is slightly less confident on Greenland compared to the 00Z (see below). At this range interrun variability is to be expected and the broad pattern is almost identical so it may not be much to worry about. But we do need to pay close attention to what is happening all around us - in Canada, Alaska and Scandi - not just in our corner of NW Europe

Back to the realm of reality, it’s the heights out of Canada we need to be watching. That’s the sliding doors moment for us. The Control at +186 is making heavy weather of holding the Low back. If it rolls over the top of the high it Will be much harder to retrogress our high into Greenland. The GEFS mean suggests the low is slightly intensified and the high slightly slightly weaker by comparison to the 12Z. That’s what I mentioned earlier as the key thing to look out for. Given the amount of HP around and WAA into the pole, it’s possible this won’t matter in the scheme of things but it’s an opening trigger moment for us. Keep watching… Edit: look at the comparative inroad of high pressure into Greenland on the control to demonstrate my point. This is the key area for us for sustained cold, not the relatively dry Easterly this weekend - whether it’s -6 or -9 uppers won’t cause fundamental differences to the main event… 18Z 12Z

Forget whether it comes off or not for a second, this is one of the most monstrous cut off Greenland Highs I think I’ve ever seen! What mad Synoptics. Reinforcement of the block from all directions (Atlantic, Canada, Alaska). And you couldn’t position the evermore elongated Iberian low more perfectly if you imagined it (although I too would rather it elongated a tad more quickly but no one could seriously complain). Madness! Visual porn jokes aside, heavenly viewing. edit: the western hemisphere called and asked for its polar vortex back

I’m travelling on the tube at the moment so can’t post effectively well but a huge decision-maker is the second wave of heights and lows coming out of the American seaboard around 168-192. If the low topples over the top of the secondary high in NE Canada, the high downstream around the UK gets isolated and the pattern sinks a bit. If the same low gets blocked off by the secondary high however, as per this afternoons ECM, we get powerful advection into Greenland and an Atlantic shut down. This is one of the key tropospheric determinants to look out for in the ens, GEFS and future det runs! Internet about to go… Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4993832

I’m travelling on the tube at the moment so can’t post effectively well but a huge decision-maker is the second wave of heights and lows coming out of the American seaboard around 168-192. If the low topples over the top of the secondary high in NE Canada, the high downstream around the UK gets isolated and the pattern sinks a bit. If the same low gets blocked off by the secondary high however, as per this afternoons ECM, we get powerful advection into Greenland and an Atlantic shut down. This is one of the key tropospheric determinants to look out for in the ens, GEFS and future det runs! Internet about to go…

My god that end of low res is incredible Synoptics. meanwhile the control does its best ECM impression in high res. such fascinating watching!

The GEFS mean is also substantially more amplified over Iceland than the 12Z by +216hrs. Bodes well. Seen enough! Onto tomorrow folks. A good, bankable day. More of the same please!

Really great trend line. And I wonder if the true pros have any insight into why the GFS ops are so relentlessly mild? The short answer of course is they could be right but I’d be interested in both the meteorological factors they pick up that the pack don’t, or the mechanical factors that programme the det a bit differently…

I wonder if there should be a ban on all posts until the high res part of a run has finished Anyway, it’s positive. Forget the specifics at this point - it’s too far out. The main thing is that GEM, ICON, UKMO and even the notorious loner itself, the GFS Det, are showing amplification toward the Griceland region. let’s await GEFS and then the ECM. Once we’ve got the the same broad scale pattern sorted we can start worrying about cold depth and snow potential as things move towards high res. good set so far edit: GEM kind of flirts with it then backs down. Pot kettle black!

The oldies on here might remember the term "Murr Sausage". Well I present to you this, a sausage in its early evolution:

Oh stop it GEFS, that is naughty Mean: Control:

core blimey. Merry Xmas chaps and chapettes!

I’ve got to say I’m a bit bemused by this talk of -7/-6 being necessary upper air temps for southerners. I’ve had inches of snow in Greater London and indeed Cambridge with -2/-3 uppers before. When you throw in late December sun, relatively low dew points and extremely low thickness values, temps of -3/-4 could readily suffice for surprise snowfalls in heavier bouts of precipitation. The reverse is also true of course and I’ve had rain in -4 uppers because the other factors have been out. -4 (certainly not -7) is the general line we should look for as a max upper air temp but it’s quite possible, in given circs with the right other factors, for snow to fall at higher temperatures than these even in southern areas without altitude.

Hmm. It's an interesting pattern we're in, here. What's currently being projected by GEFS and others is no 'normal' northerly incursion - it's a quite unusual European displacement of the TPV, something I can't recall seeing for some years. The current angle of the TPV's descent into Europe isn't the best for widespread snow in the UK as the uppers (largely introduced from WNWlies rather than NNWlies) are broadly pegged to be too marginal but, as we recently saw in Cumbria, it won't take many tweaks to give some folks in here a pleasant seasonal surprise. There are far more disturbances typically associated to Nlies and NWlies than there are with, say, the longed-for Easterly setup where it's often boom or bust. Unquestionably though, for many in the south these disturbances (on the current output) would bring cold rain for the festive period. It's up for grabs though and therefore worth watching the charts to see how they evolve in the lead up to the Xmas period, especially if you have latitude and altitude on your side. Thereafter, I'm drawn to the unusual bullishness of the UKMO's long-ranger, together with Stratospheric and MJO developments that Catacol has expertly outlined, which suggest further reason to stay tuned into January. This is, in other words, an unusual set up. It's not spectacular for us snow hunters but it's a long way from what we could be faced with. Take the point and stay tuned.

Sorry one more thing - argh how on earth does one concentrate amidst a cold weather chase! - look at the time stamp on the GFS Op 06z evolution. The set up that we're looking for arrives at +300hrs - not +384hrs as per the last 3 days. Slowly does it. Let's keep the pattern right and reel this one in. Patience is a virtue!