Focussed Model Discussion

[ICE COLD]

13 minutes ago, ICE COLD said:

This looks interesting. Would the strat boffins like to comment??? 

Edited January 22, 2019 by ICE COLD

[Man With Beard]

Right, I'm ready to face the ECM clusters again this morning. I think I need to change my approach slightly - rather than focusing on individual days, it would be more helpful to look at evolutions over time, as there's a danger of common pattern progressions being missed if timing differences lead to mean signals being muted.

So looking at the past three clusters for 31st Jan, 2nd Feb and 5th Feb

31st Jan

    

The Euro trough remains the form horse, and the current op run looks a little out of kilter at T216 in keeping the trough slightly more towards the UK than across the channel. Given the fact this is D9, and that modelling tends to push troughs a little east at around D4/D5 when there's no strong blocking ahead (I forgot this last week, to my cost!), I'm prepared to back the general ensemble picture over the op at the present time, and expect the trough to be in the SE position, which should be slightly colder for the UK, though, without significant cold ahead, snow chances would remain up in the air especially further south, so don't tell the neighbours yet. 

Strong signal for Atlantic ridging too, but alas! the past few days have shown us you need a really strong anomaly on the southern tip of Greenland to be confident that low pressure activity will be curtailed completely in that area. Therefore, it's handy to see what the clusters are showing a couple of days later to judge how successful a block we can expect. Having a quick glance at the clusters below for 2nd Feb... 

    

it is clear that a block is a possible result (i.e. clusters still maintaining red patches to our NW), but in general the positive anomalies near Iceland / Greenland have weakened. Therefore, the best forecast right now is that end of January ridging will lead to an extended PM (rather than arctic) event, which might mean the window for northern snow / southern wintry mix might be limited to 2-3 days, with a collapse of Atlantic ridging to some degree. Unless ...

5th Feb

     

... unless some of those anomalies to our north by 5th Feb continue to develop from what is shown here. It looks a close call in the days between 3rd February and 5th February between a. an Atlantic recovery (still on the cooler side of average), and b. enough of a ridge to the north to punch a hole in the Atlantic train and send us into an easterly. Today's control run would be a clear example. It smacks a little of the same conundrum we saw on the models last week. I would suggest the positive anomalies to our north do look a little better for the start of February than they ever did for the coming week. However, I can't see enough on these clusters to even suggest northern blocking is the front-runner, let alone a strong possibility. 

So all in all, I think we've got pretty good continuity up to 2nd February, and I'd suggest some sort of cold shot coming up around the turn of the month with - in keeping with cold NWlies at this time of year - good snow chances for the north and minor snow chances for the south. I don't think the ensembles are telling us the full story beyond this timeframe, even if a few northern blocking hints are there.

Edited January 22, 2019 by Man With Beard

[IDO]

The subtleties of the upcoming pattern, I expect is not lost on anyone, with the GEFS at T180 giving us 21 different solutions within the bigger picture for this low and accompanying mini-ridge episode:

T180  D10 

No doubt there are some cold and snowy ensembles along with less cold ones. As a whole pretty good.

It is a good trend from the 0z at D10 with pretty much universal support for the upcoming NH pattern***

The short ens. are similar to the 0z with the mean uppers -5 below climate in the latter stages. I suspect from this pattern, this being London uppers, that is a reasonable outcome:

Noticed the warm sector less warm at D3-4.

Just need to tighten up on the snow chances at D7, but assuming status quo, a locked in pattern for the next 10 days with mesoscale details determining if we can get something wintry along with the relative cold?

[kold weather]

There is an awful lot of uncertainties within the ensembles and giving the set-up we are in a small shift here and there will make quite a large difference to our actual weather.

As has been said there are basically 21 different solutions from the GFS ensembles, though two generally broadly differening views of how things evolve to our north past day-8:

1: pressure generally rises along with a more southerly jet.

2: PV strengthens and shifts towards Greenland and jet lifts north.

As can be seen, some rather big differences to our weather would be expected. The 06z GFS op run more or less fell into the 2nd camp, though it does give a cold spell beforehand. My guess though is the idea of a re-strengthening PV is unlikely at this point, we'd be badly unlucky to get that to shift have not had any real impact from the SSW.

What is interesting is there is more than a hint again of possible snow event around the 29-31st. This was also highlighted yesterday on the 12z ECM ensembles, though I've not seen the 00z ECM ensembles to see whether that has held.

So as you can see, a rather 180 contrast from the GFS ensembles

Edited January 22, 2019 by kold weather

[Singularity]

I'm keeping an eye on signs of deep cold pools being closer-by to the east than was generally predicted the past few days. Needs a number more days to confirm if it's a genuine trend though. It's a tough one to track using EPS too, as the deep cold doesn't necessarily come alongside much of a positive height anomaly to be seen in the clusters, instead it can be a surface-based high with us looking more to the circulation around the Euro trough to draw the cold across the UK.

Essentially, it's the wildcard in the pattern that could suddenly turn a typical wintry pattern into a severely one. Feels like Russian roulette but where the bullet is made of compacted snow. It could really sting .

[Singularity]

 

The shift closer of the continental cold happened even sooner than I first observed in the 06z run; I was guilty of skipping straight to the weekend. 

The reason is a tiny weak low splitting away from the parent trough. Hopefully this solution at least holds steady now, as it helps put across just how close we come to the regional strat-trop imprint delivering a cold easterly flow and that it was only a very poorly timed unhelpful U.S. storm system that prevented it (assuming we don't now see an extraordinary turnaround for the weekend).

[alexisj9]

17 minutes ago, Singularity said:

 

The shift closer of the continental cold happened even sooner than I first observed in the 06z run; I was guilty of skipping straight to the weekend. 

The reason is a tiny weak low splitting away from the parent trough. Hopefully this solution at least holds steady now, as it helps put across just how close we come to the regional strat-trop imprint delivering a cold easterly flow and that it was only a very poorly timed unhelpful U.S. storm system that prevented it (assuming we don't now see an extraordinary turnaround for the weekend).

Wow you surprise me, we've been talking about that little low in the south east thread since the 6z yesterday. I've been wondering why everyone in both model threads was ignoring it. Mind you, it was only picked up by the gfs first, and then the euro 4, and arpage and arome followed. Not sure it's in every model, even now. If gfs is making more of it, I think it's on to something this time. I think the reliable in the models, is t12 at the min.

[Singularity]

I mainly focus mid-long term so with no clear representation beyond the surface wind charts it was slipping under the radar, to to speak. Interesting that it’s been represented in some form beforehand but has only now become better defined in a few model runs.

[knocker]

Worth noting the new thinking for Friday midday this morning

And the high res sat image at 1115

Edited January 22, 2019 by knocker

[southbank]

seems a fair bit different in a rather short period of time (6 hrs ) from T96  to T 84 . And theres people looking at T240 charts in MOD ?

[knocker]

And the next question is what is the score over he weekend? Somewhat above my pay grade but in theory the high pressure should ridge in the Atlantic with the upper trough pushed south east and thus the waving front will do the same. We shall see

[winterof79]

3 hours ago, knocker said:

Worth noting the new thinking for Friday midday this morning

And the high res sat image at 1115

Icon 72z looking like it fits better than GFS with Fax

Edited January 22, 2019 by winterof79

[knocker]

The main batch of showers on the trough will continue to move across eastern England this evening, clearing quite quickly whilst the wintry mix will continue down western regions. So a clear night and winds abating equates to a cold and frosty one, particularly in Scotland,  with ice a problem in the morning (note the temps are not 2m)

Edited January 22, 2019 by knocker

[knocker]

21 minutes ago, winterof79 said:

Icon 72z looking like it fits better than GFS with Fax

And this is the conundrum as the gfs continues to form a wave on the front to the west and track it across the UK on Saturday. This evening's fax charts are not without interest

[knocker]

Without attempting detail it's probably as well to keep in mind, vis the phasing of the warm and cold and as the energy distribution gets sorted, that there is a lot of cold air upstream. All of which tends towards wintry conditions

Edited January 22, 2019 by knocker

[knocker]

The latest fax and gfs for midday Friday. No further comment required

Edited January 22, 2019 by knocker

[kold weather]

Good luck trying to pick a pattern out of the GFS 12z ensembles, all over the shop!

Some develop strong northern blocking, some are redeveloping quite a potent looking PV. Some have a cracking southerly jet (indeed maybe abut too much even for us) whilst some create some impressive ridging into Europe.

Even from 120hrs there is considerable volatility, with everything from a Azores ridge, a weak easterly, a COL, powerful northerly or gentle NW showing.

Generally I'd say a lot more of the Azores ridge on this suite of the 12z GFS ensemble, quite noticeable at times, though most runs do scoop it up eventually still (only for some to spit it back out again!) 

[bluearmy]

25 minutes ago, kold weather said:

Good luck trying to pick a pattern out of the GFS 12z ensembles, all over the shop!

Some develop strong northern blocking, some are redeveloping quite a potent looking PV. Some have a cracking southerly jet (indeed maybe abut too much even for us) whilst some create some impressive ridging into Europe.

Even from 120hrs there is considerable volatility, with everything from a Azores ridge, a weak easterly, a COL, powerful northerly or gentle NW showing.

Generally I'd say a lot more of the Azores ridge on this suite of the 12z GFS ensemble, quite noticeable at times, though most runs do scoop it up eventually still (only for some to spit it back out again!) 

from almost 100% agreement a couple days ago on the dropping trough in week 2, we have a complete dogs dinner now. looking at the NH profiles, it must be the downwelling wave playing havoc with differential timings

[kold weather]

Yep, we are going to hold off getting to excited over the operational runs because there is so much variability. Same goes for any bad runs that come out.

Of course I think all are assuming this must mean things are going to go badly, but it is equally possible for things to go explosively well...in truth there is just no way to really know at the moment.

The only thing I would say is this is the 2nd time the models have drawn back from a Euro trough idea (the failed easterly being the first).

[knocker]

50 minutes ago, knocker said:

The latest fax and gfs for midday Friday. No further comment required

The ecm

[knocker]

Taking the ecm from t120.  A strong upper flow around the Atlantic ridge plunging the upper trough down the North Sea resulting in a fresh cold northerly on the surface. Twenty four hours later the now quite intense trough is over southern Europe as the next trough has swung into the Denmark  Straits and the ridge is under pressure with a weak front approaching north west Scotland. The trough then moves east over Iceland more fronts track south east across the country giving a wet and windy day on Tuesday

[IDO]

The ECM 12z op run is more of the same, treat as another ensemble helping within the 51 members and if anything like the GEFS then not a lot of help. 

The means are similar for the GFS and ECM and they follow the 0z line.

Until we get the phasing of the lows in the SE flow along with the correct vorticity of them we are really just hoping for the best when that eureka model moment happens! There are four GEFS that are similar to the ECM with that blown up low though timings and tracks are all different and they lead to different journeys. From my experience, it is unlikely that the low will blow up at T168 as ECM models, and in fact, the mean has it as 1010 rather than 980 depth, the GFS at 995! So possibly the ECM op is the extreme scenario? ECM is at its worst in nascent blocked patterns, so best to ignore as per previous few runs.

So really a day of holding patterns for us as we await clarity as to how the D7+ pattern will evolve for cold and snow within a reasonably confident long-wave NH profile to around D11. After that even more entropy with floating wedges and the ebb and flow of those blocks and troughs. As always, we need to get a bit of luck to draw that cold to our small island, but chances will be a lot better than normal so quietly optimistic...

ECM & GFS means at D10:

Edited January 22, 2019 by IDO

[Paul]

Just copying a few recent posts in here.

32 minutes ago, ANYWEATHER said:

Evening All is, Tuesdays Checklist ....

1/  Jet stream way south of UK in the days ahead...Yes!

2/ Cold becoming insitu,,,,Yes!

3/ Deep Cold ...No!

4/ Cold enough for snow for the south....Yes!

5/ Expect many Wintry surprises folks thanks to that ever growing block of Ice and winds from ....Greenland!!!

 

21 minutes ago, kold weather said:

Well only one word I can use for the ECM ensembles:

Stonker!

Seriously that is amazing set of ensembles, just for reference just 6 out of 50 do not create a decent Azores ridge into the Greenland area by the 31st Jan. Several of those end up with decent northern blocking a few days later. I think there maybe some outrageous looking charts for the UK in this set of ensembles.

 

19 minutes ago, bluearmy said:

Yes Kold, the control evolves like the operational was was expected to days 9/10. 

Very strange how some seem to take enjoyment in posting nonsense. ..... anyway, the spreads reveal that there is a risk that the trough could drop due south or even ssw a little to our west and risk pulling in a southerly as opposed to a sou’easter .........all in all, trends are execellent for cold and wintry and I also expect there is a fair chance that things could accelerate into colder. However, the Canadian lobe will keep us on our toes for the next week or so at least. 

 

[The Enforcer]

Meanwhile, who wants to join us in time for Sunday lunch?

T+144: T+120:T+96: ?

[Man With Beard]

Clusters tonight again have the ecm op as a clear outlier against most ensemble members by D8

Given the models are likely to be faster through the pattern than slower once in the D5 zone, I'm still inclined to go with the ensembles on this one. We will have a better idea in 24 hours.