Model Output Discussion 01/09/17

[nick sussex]

9 minutes ago, karlos1983 said:

Massive improvement on the Pub run from the GFS 12z. 

Certainly starting to get that feeling of momentum! 

Nail biter tomorrow, although doesn’t seem to be to many dramas/spoilers this time.

@nick sussex have we moved from Amber yet...

Lol! It’s an Amber Green combo ! The committee meets tomorrow morning to discuss going to green! 

[bluearmy]

Only two eps clusters days 7/10 which are pretty well 50/50 with the more amplified op run and the slightly flatter mean. Thereafter we have three clusters, two which are cold troughy for nw Europe and one which is fairly westerly closer to the GEFS mean. The flatter solution is around 50% with the other two 30 and 20. 

[Allseasons-Si]

1 minute ago, nick sussex said:

Lol! It’s an Amber Green combo ! The committee meets tomorrow morning to discuss going to green! 

Looking foreward to it

Edited November 21, 2017 by Allseasons-si

[snowice]

3 minutes ago, nick sussex said:

Lol! It’s an Amber Green combo ! The committee meets tomorrow morning to discuss going to green! 

Greenland Hp

[feb1991blizzard]

Here are the aforementioned clusters.

 

Such a long way out, surely they are stonkers (the last 2)

or am I missing something?  I hate those charts - I wished they were on meteociel, I'm used to the angle now, I view everything hemispherically on meteociel.

Edited November 21, 2017 by feb1991blizzard

[Jonan92]

This run doesn't show an organized vortex in FI, great news all around

Edited November 21, 2017 by Jonan92
Missing chart

[Derecho]

Very strong trend for a high pressure to our NW at T144 with all 3 major models, GFS swings further to the other two.

Fingers crossed the PV strays away from the immediate west from Greenland, if so some strong blocking could develop
 

[Man With Beard]

13 minutes ago, feb1991blizzard said:

Here are the aforementioned clusters.

 

Such a long way out, surely they are stonkers (the last 2)

or am I missing something?  I hate those charts - I wished they were on meteociel, I'm used to the angle now, I view everything hemispherically on meteociel.

I haven't a clue what the colours mean, but I do understand the lines. I would say not enough ridging to the north to get excited. I think you need a decent area of heights above 546 and preferably 564 to be confident you are seeing a prominent ridge. Yes I know what you mean about the comparison to Meteociel!!

Bluearmy described the T240 chart earlier, here it is in colour:

so on the second chart, you see the lines run flat from west to east, representing a fairly flat pattern - the first one is tilted a bit more from the WNW and you can imagine the small trough in the Atlantic introducing colder conditions behind it.

 

[bluearmy]

Off to sleep having checked that all three ens suites are in agreement that the AO never really returns to positive values, save for a brief flirtation in a few days time and that's only marginally positive. not sure that we will get a deeply neg phase again without  a very amplified n Pacific ridge of some kind. 

And as far as those Icelandic charts are concerned, i expect the blues and reds represent height anomalies. dont get hung up on the detail of the upper flow on ensemble output. Use it as a general guide.

model wobble Wednesday tomorrow !

Edited November 21, 2017 by bluearmy

[feb1991blizzard]

Just now, Man With Beard said:

I haven't a clue what the colours mean, but I do understand the lines. I would say not enough ridging to the north to get excited. I think you need a decent area of heights above 546 and preferably 564 to be confident you are seeing a prominent ridge. Yes I know what you mean about the comparison to Meteociel!!

Bluearmy described the T240 chart earlier, here it is in colour:

so on the second chart, you see the lines run flat from west to east, representing a fairly flat pattern - the first one is tilted a bit more from the WNW and you can imagine the small trough in the Atlantic introducing colder conditions behind it.

 

I know what they mean, its just the angle and that its a tiny zoom in, there's a lot more than just the area shown that can affect us - the colours are the anomalies btw.

[Derecho]

Just a flick through the ens however shows that after the shortwave passes through the block on Sunday, some show a pressure rise over Central Europe which we must avoid too much of so there is still potential for it to go wrong.

Hopefully it won't but still some uncertainties.

However saying that  the vast majority of ensemble members build strong heights to the NW at T168 and the release of arctic air encourages heights on many members over Europe to shift east. So that is very encouraging.

Edited November 21, 2017 by Quicksilver1989

[Devonshire]

1 hour ago, bluearmy said:

on plenty of occasions where uncertainty has reigned, we have seen the mean end up closest to verifying as opposed to the clusters or ops. 

ahhh - now that I can appreciate: verification stats of mean versus op, but isn't it in the nature of clusters that there are more than one - you therefore have to choose which cluster to assess for verification -  I am in danger of disappearing up a black hole at this point ... but having worked with multivariate modelling in a totally different field I really do like cluster analysis, and you can get an idea of (or indeed actually calculate) a mean from clusters, but in no way can infer clusters (or any information about distribution) from a sole mean. There, the bee firmly out of the bonnet!

[Mucka]

Some interesting developments in GFS ensembles, I will use p20 as an example but a few others show something similar.

The initial ridge is being modelled to be stronger generally and on some runs the diving low  does not phase with the main trough and manages to get way South.

The upshot is that the UK remains in a cold N/NE flow and doesn't suffer a blown up low crossing the country, cutting off that flow and bringing wet weather as it phases with the main trough over the UK (a la Op)

Only later phasing as it crosses the South.

This could give a good opportunity for snow so long as the uppers in place are cold enough which with a maintained N/NE flow could well be.

Still plenty of options and a wide range of possibilities anyway.

18z ensembles on the chilly side and though there is no classic cold spell looming there is enough cold air for most people to have a shot at snow at some stage over the next two weeks or so.

[Thunder Snow]

Away from cold hunting, the 18z charts are awful for Cumbria and southern Scotland 

[mpkio2]

Hello all one again!!!

You know its been a good day of model watching when you go away and return to see four new pages of posts!

With over 100 members on here tonight, the place is absolutely buzzing!

And for good reason, especially when the models are showing encouraging signals for cold....

12z GFS 21/11 t90:

12z ECM 21/11 t192:

12z UKMO 21/11 t96:

12z GEM 21/11 t192:

12z JMA 21/11 t100:

(Just some of my favorites from the pack! )

You know somethings up, especially when all models are showing an overall agreed theme of cold weather for the UK!

But the real question (And this is important for a cold evolution pattern to take hold further on!), do we have any kind of "Cross-model-agreement"? (Even in the short-term? )

Well....

12z GFS 21/11 t96:

12z ECM 21/11 t96:

12z UKMO 21/11 t96:

12z GEM 21/11 t96:

12z JMA 21/11 t96:

Err...woah....

So....when was the last time all the models looked so....similar...?

All joking aside, cross-model-agreement is a GO until t96, with even the less GEM/JMA in agreement with the Big Three!!!

FL for me anyway, is anything after, seeing how all models develop on to something different in look and what the UK "might" receive, but the theme and trend for a "COLD" snap/spelli very strong within them, as well! 9Look above at my faves of the day! ). All models see the Main lobe of the PV taking a holiday towards East Russia, Centered Arctic high with Atlantic heights ridging up, a trough over Scandi digging down cold N/NW winds with a mixture of Snow/sleet/rain affecting the country. Very, very good!

The models also agree on the secondary low that crosses the Atlantic at a NW/SE axis and joins the first trough around the t96-t144, but all not agreed on how fast the low will speed across the Atlantic or how shallow or "bulb" like it is, thus the different outcomes that develop after (As @nick sussex and @Steve Murr have alluded to.)

Overall, another great day, with the signal for a cold snap/spell to affect the UK increasing.

But caution, as always, as developments in the short-term can hinder us too and wipe everything away - which has happened many a time for us cold/snow starved coldies!

Please...don't be taking us down the Graden Path models.....

Hopefully, the Siberian Express gains speed. Fingers crossed.

~mpkio2~

[Geordiesnow]

8 minutes ago, Thunder Snow said:

Away from cold hunting, the 18z charts are awful for Cumbria and southern Scotland 

Yep, localised flooding is a possibility as the rainfall continues into wednesday night and into the early hours of Thursday although it gets more messy by then but its certainly one to watch as localised disruption could well occur e.g disruption on the west coast main line. Gusty winds are also forecast as the low deepends during the day as it heads northwards and Eastwards then convective weather for Thursday and then Friday's uncertainty with the shallow coming into play although i'm still surprised the ECM is still going for a slightly different option and still one I would rather too happen personally.

[georgiedre]

1 minute ago, Geordiesnow said:

Yep, localised flooding is a possibility as the rainfall continues into wednesday night and into the early hours of Thursday although it gets more messy by then but its certainly one to watch as localised disruption could well occur e.g disruption on the west coast main line. Gusty winds are also forecast as the low deepends during the day as it heads northwards and Eastwards then convective weather for Thursday and then Friday's uncertainty with the shallow coming into play although i'm still surprised the ECM is still going for a slightly different option and still one I would rather too happen personally.

I would have thought that nw Wales would receive more than southern Scotland tbh we shall see. I'm thinking capel curig will have most rainfall

[feb1991blizzard]

1 hour ago, nick sussex said:

Lol! It’s an Amber Green combo ! The committee meets tomorrow morning to discuss going to green! 

Nick - not to poo poo your warning system (I love it), however, I don't really think you can give it a green yet, to me a green is when you are practically guaranteed a right ol dumping across decent swathes of the country to low levels, my warning system is the exact reverse to the Met Office's!  -  a Red is pretty much as yours, reliant on the trigger shortwave at range or when that dreaded close up of the heights in between two areas of troughing to our North starts to happen with each run (dec 2012), Amber is when its greater than 50/50 and you get at least half the GEFS flatlining around -10c 850's from about 192- end of run (this is around the point when everything starts to implode usually), Yellow is when you have the -10c isotherm whistling into Ireland with a robust High (not a surpressed PPN sinker type), or -12c - 15c in Feb (need lower because of SST;s later in season), Green is all clear - a feb 91 orJan 87 event going to happen - a foot of snow in my back yard guaranteed!

[Thunder Snow]

13 minutes ago, georgiedre said:

I would have thought that nw Wales would receive more than southern Scotland tbh we shall see. I'm thinking capel curig will have most rainfall

Im going for Cumbria

[JBMWeatherForever]

Those 18z rainfall charts look very similar to about two years ago when we had some very bad flooding locally, with a bridge coming down in a village 5 miles to our north. I do hope that the front doesn't stall for any longer than is currently suggested.

And then we open the doors to a cold spell - with cross model agreement (Makes a change), and the prospect of it getting even colder during next week. It's funny also how in many media forecasts when we move into such a spell that they seem to underestimate the cold at first and then gradually adjust accordingly. Its looking like a decent period of cold weather with plenty of scope for it to become very cold, some lovely looking runs now from the big three.

Will not be surprised to see some classic E/NE'lys showing up soon with such a disorganised PV, and to think that just a few days ago some were talking of Euroslugs and Iberian Heights that don't go away (these days) ???   Some were even writing off winter when its still only Autumn !   We have so much to look forward to in the coming months !!!   

Edited November 22, 2017 by JBMWeatherForever

[Sparkiee storm]

A look at potential snow chances from Friday to Sunday from GFS 18z . 

And obviously the details will change, hopefully for the better so more of us see some of the white stuff .

 

Edited November 22, 2017 by Sparkiee storm

[A Frayed Knot]

BEEB Going for a Milder outlook next week with cold incursions in some parts of the UK.... I like the way they are saying the Snow word , But a Big Butty ' will we get it ?

Nice charts looking through them all ' But i never trust Computer Models ' I stick to FAX CHARTS ONLY ' Thanks to you all though as what you Contribute to this Group ' i love it ' Drinks all around if we get some white stuff . .

[Nick L]

2 hours ago, Thunder Snow said:

Away from cold hunting, the 18z charts are awful for Cumbria and southern Scotland 

 

Yes some horrendous rainfall totals looking likely over Cumbria over the next 36 hours. The usually reserved UKV has 24 hour totals approaching 100mm in places.

[Nick L]

21 minutes ago, A Frayed Knot said:

BEEB Going for a Milder outlook next week with cold incursions in some parts of the UK.... I like the way they are saying the Snow word , But a Big Butty ' will we get it ?

Nice charts looking through them all ' But i never trust Computer Models ' I stick to FAX CHARTS ONLY ' Thanks to you all though as what you Contribute to this Group ' i love it ' Drinks all around if we get some white stuff . .

Yes, because computer models have zero input or influence on FAX charts... 

[Ali1977]

00z a bit of a climb down with regards heights into Greenland around day 5/6, I guess this was to be expected. Still, it's looking festive, will be cold, frosty and all together 100% better than the last few years. The PV is weaker in North America this run though, that's never a bad thing ?