Mike Poole

That was a feature of the 2018 BFTE. It was quite surreal to observe snow literally vanishing into thin air. I said last night that I was sceptical about the return to mild end of next week, I wasn’t expecting so much change in the model output as early as this morning’s runs, with the GEM and GCM excellent, and now the GFS 6z.

GFS pub run T192: I’m posting this not because i think it will happen, actually I don't think it will happen. I think something like the blocking into scandi will happen earlier, and scupper the mild spell completely. I think the models on Sunday maybe, will disrupt that T144 bowling ball low and it will slide. We will see...

Yes, that’s my take on this evenings output too, Phil, I wouldn’t have put money on the GFS to lead with this as it is against it’s bias, so I think tomorrow’s runs will be very interesting.

GFS 18z T150 v 12z T156: it is baby steps here, and it might go nowhere, but just a suggestion of the block holding firmer, crack of light blues south Greenland?

No, not make or break, there’s the possibility of a return to cold shown already after the current mild spell which the models are showing end of next week. It is more the question of whether there will be any significant mild spell at all. And the implications of that which would be significant if there wasn’t. No evidence for that on the current output, but as I said, I’d like to see what the models are saying in a day or two once the cold is in place, it might be harder to shift...this has happened in the past. We will see...

ECM clusters T120-T168. The fact that there are 6 of them should emphasise the uncertainty here, about any potential breakdown: The key time is the T144, the middle column. There are differences in the way that Atlantic low is handled, does it disrupt, does it stall in place, or what? I think this in FI for the moment, but will be firmed up in the next day or two, and could have a big impact on the next months weather.

ECM mean and spread T144: The suite now suggesting some trough disruption on the incoming low, with some uncertainty too. Not worth looking beyond T144 for the UK as the behaviour of this low is crucial for the way forward. I’m not expecting any members to undercut this low yet, but they might in a day or two’s updates to the models...

Interesting model output again tonight, I’m interested in what happens at T144, here GEM and ECM: As modelled, no way that weak block will stop the Atlantic low or send it under. But I wonder how much uncertainty there is about that low at this time? I wonder if it might look weaker when it is at T96 in 2 days time? And after the mild interlude if it is an interlude, what next? I think I would like to have the cold air in place, tomorrow or Sunday, before trying to predict nature of the breakdown, and what happens afterwards.

HARMONIE 12z take on Sunday’s snow chances:

Yes, hi @38.7°C, i will try! Streamers are lines of convective snow activity like storms in summer, exactly the same rules apply - a temperature differential , caused by convection, but in winter is convection because of a warm sea under very very cold air ( as will be the case by the weekend). They form lines similar to squall lines in the summer. A slider is an Atlantic low that instead of going across the UK, or Scotland, instead slides under a high pressure cell and goes south of the UK. All these things are in play at the moment.....

Me as well, TEITS ( and have liked your posts ever since i started following this thread in 2011). Given the output now, you would have to say no to the GFS, it is just not consistent with itself or with any other signal. I think you mentioned a couple of days ago that the easterly would be in earlier if it was to happen, well it will happen, and it is in earlier. Saturday is the start...

GFS pub run T162, a possible milder interlude, and we will probably have to take it anyway: But look at the picture NH, here’s the z500 chart with my edits: The block to our north is difficult to see, no yellows, but it is there and is crucial to the ongoing cold - which by the way, I am fully behind, this is the real thing, just not showing on all models yet. Follow the UKMO...

GFS pub run T120: Just wow! Question is, will this run send the big low under - it might!!!!!

Whatever else befalls us on this run, please can we bank this at T84:

ICON 18z at T120 While more spectacular things are happening in the NH, a wedge is all it takes for us.

I wouldn’t be worried, with an easterly like this you’re in the firing line... I’m not expecting much from the 18z tonight, this situation is playing to the worst of the GFS, if the UKMO, GEM and ECM are on the page that they are on today tomorrow, I’ll be happy.

You should get plastered eventually, here the Arpege take on it, and remember it won’t fully account for convective snow: You can really see the easterly take hold on this! Newbies, notice how the precipitation changes from organised areas to linear streamers as the convection starts...

ECM clusters T120-T168 chart: All -NAO (green border). Variations on a theme really, we’ve seen it on the various op runs. What I would say is this is FI for ensembles at the moment, T96 for ops, T168 for ensembles. Ive glanced at the later ones but look besmirched in uncertainty, to be honest.

ECM mean and spread T240: Mean looks conducive to some heights to the north into Scandi, and potential for atlantic lows to go under. Think there is actually a case even on the mean for average easterly winds in the NH bar the top of the chart, and of course the Atlantic! Spread just shows massive uncertainty, reinforces message FI is T96, anything after that you are relying on background signals or tea leaves, in my case background signals though, and they are good, so expect upgrades in the T144-T240 timeframe.

Oooh, that’s naughty @Cold Winter Night! In theory our setup should be better as the polar vortex is towards Russia, rather than E USA. Would be some undercut to bring that down in 1947. Not saying it didn’t happen mind! ECM T240 profile screams reload to me - might not be necessary though because the initial easterly might actually be still going on if my thinking is right, and this model let it go too soon. What is perhaps more in tune with 1947 is the time of year, I don’t know if there was a SSW in 1947, but what happened suggested there might have been. I do see, now, all things put together, a cold spell rather than a cold snap, and one which ‘could’ last the full span of the SSW, i.e. until into march.

Well, I am taking some time to work out what I think from the 12z suite, having looked at all of them. Maybe the following take aways: The start of the cold spell is nailed-on - well we knew that from yesterday. NH profile looks great early on in the runs, and crucially there is a wedge extending from the Greenland height rise towards Scandi that allow the earlier low to go under. T144. Cold air in place to this point. Then, the bigger atlantic low approaches, same time the NH picture starts to get a bit messy. I think this is now well into FI and what should happen is the NH profile doesn’t get messy and the bigger low disrupts and goes under. I’d be astonished if it didn’t, but we can only wait and see...but if that low does go under, the next one will too. This is so tight that I can’t see -8C uppers over the whole country all the time, these lows even if they undercut will pull in warmer air to the SW and maybe further...but this is the high risk high reward spot for snowfall. Interesting times...

Absolutely, Feb, that is a sign of a special spell.

Yes, but it won’t pan out like that will it? I’m suffering from model fatigue now, but we know from experience that when we get cold entrenched - which it will be now for sure - normal lows off the atlantic will correct south as we get closer to T0. That’s not to say something weird won’t change the whole pattern - it did if I recall with the first BFTE in 2018 - but there is nothing like that showing on the models. I think the lows will go under, just maybe not on this run...

A big low to swallow without some battleground snow, I admit.

...and so are the next two looking at that!!!