Model Output Discussion

[SP1986]

I must admit I'm starting to come around to the idea of an easterly now in that I am more confident that it will occur. Last time I went around to the idea though it collapsed completely and there was major disappointment, let's hope not this time!

The ensembles (GFS) do have the start of a trend to them it seems, and all of the big models are setting up for either an easterly or a northeasterly.

Obviously I am aware that it is still largely in FI, and even the building blocks could change, but it looks a little more promising in my eye, as I was expecting it to completely collapse today.

Today the models broadly agree with each other in their operationals, and the ensembles are showing perhaps the start of some agreement so a little more positive for me.

Still I wont be 100% happy until the there is very coherent agreement at a plausible timescle.

[grab my graupel]

Let's keep on topic, please, folks

There's a seperate thread for Media forecast discussion etc.

Thank you

[J10]

Overall some very good charts today, a very likely end to the Atlantic dominated wet weather. OF course there remain major differences as to whether we get the snow fests forecasted by the GFS or a slightly drier conditions favoured by the ECM but still with snow for a time.

If either were to occur, there would be very cold temps with ice days quite possible due to the low sun at this time of year. Of course as well if there were repeated snow showers to eastern areas, there would be a greater chance of snow accumulations than if a similar event happened at the end of February (as in 2005). There is also the double edged sword of warmer sea temps off the east coast at this time of years, on the one hand this would pep up showers, but also make the make any snowfall in coastal areas far more marginal.

If GFS came off, this could be a very significant event for recent times, but we have also seen events less this implode at shorter time frames than this. So despite the justified excitement with the charts, Caution is also needed, in case things do go wrong.

[tinybill]

http://www.meteociel.com/modeles/gfs/precipitations/180h.htm

well its looking very cold in france and the low countries and it looks like it could be coiming our way fingers crossed!!!!

[snowlover2009]

In these kind of setups what gfs is showing for example, would that result in france being very cold and colder than the UK and also have more snow, like would Paris get more snow than london.

Btw when do the ecm ens come out? thanks

[Ian Fergusson]

If GFS came off, this could be a very significant event for recent times, but we have also seen events less this implode at shorter time frames than this. So despite the justified excitement with the charts, Caution is also needed, in case things do go wrong.

Spot on: a properly-tempered analysis: i.e., it's got potential, but equally the potential to manifest nothing extraordinary whatsover.

And noteworthy how the latest (3 versions of) UKMO detailed 6-15 day briefings wholly downplay any hint of significant (or for much of southern UK, effectively any) snow risk whatsoever, albeit maintaining the rather prolonged colder theme. Yes, they highlight various caveats to this idea but 'Cold & Largely Dry' effectively sums-up the essence of their 1-2 week prognosis. Sure, this could prove utterly erroneous but - as so many have already rightly cautioned here on this thread - the models (and especially post-T+144!!)can shift so significantly as to render any longer-range validity of discussion into the mere 'ramping' category, as beloved by certain daily newspapers... irrespective of the season.

[nick sussex]

Regardless of how good the outputs been this evening I think we need to step back a little. On the face of it a big switch in the ensembles but we've been here before, last February being a recent ensemble trauma when from very good agreement it imploded in one run.

The gefs ensembles because of their lower resolution are not to be trusted with shortwaves, even operationals always have tremendous difficulties with these features. Easterlies come in many forms, coming up we get this brief easterly as the euro high heads north, easy isn't it! because its a straightforward evolution with no shortwave!

To get to the cold nirvana we need to see the right WAA into the Arctic whilst at the same time hoping the SW behave themselves and then relying on the right jet curve to advect the cold westwards, alot of factors have to work together and for this reason and putting aside my obvious excitement at the output, to get from where we are now to where the gfs or ecm are past 168hrs is still not the most likeliest outcome.

If the models do somehow keep this trend then perhaps towards the end of the week we can be more certain of the outlook. My advice is simply this absolutely do not trust any output that relies on a shortwave. For older members who have been through many previous shortwave induced dramas they certainly know why i'm so reluctant to want to look much further than 120hrs.

[Nick F]

The only problem with this set-up is that it requires quite a lot of small parts to move correctly to get the best of the cold shot. The models today succed however its quite possible that if one part fails we will miss out on he deep cold and instead get stuck in the cold high pressure set-up, which still would be decent enough for the early days of winter, how many legendary cold spells and winters got going this early, even 1962-63 was only showing teases.

Yes, still some synoptic features that models will have yet to resolve, you can see clearly on the 12z ECM the shortwave low crossing the GIN corridor then down across Scandinavia - which happens to eventually trigger an easterly. GFS doesn't have such a prominent feature and has ridging much further N, though it does have a subtle shortwave moving S down the east coast in the Nerly upper flow around t+168, which allows low pressure to develop over the Low Countries which in turn pulls in an easterly as the low drifts SW.

In the end, both models end up with an easterly of sorts, and the general broad picture from the models is in good agreement for colder air from the east, but just how cold and snowy we will not find out for sure for a while yet until the more mesoscale features, such as these shortwaves dropping down on the eastern flank of the ridge building N are resolved by the models.

Interesting times ahead!

[snowlover2009]

hmm try again

In these kind of setups what gfs is showing for example, would that result in france being very cold and colder than the UK and also have more snow, like would Paris get more snow than london.

Btw when do the ecm ens come out? thanks

[guitarnutter]

Spot on: a properly-tempered analysis: i.e., it's got potential, but equally the potential to manifest nothing extraordinary whatsover.

And noteworthy how the latest (3 versions of) UKMO detailed 6-15 day briefings wholly downplay any hint of significant (or for much of southern UK, effectively any) snow risk whatsoever, albeit maintaining the rather prolonged colder theme. Yes, they highlight various caveats to this idea but 'Cold & Largely Dry' effectively sums-up the essence of their 1-2 week prognosis. Sure, this could prove utterly erroneous but - as so many have already rightly cautioned here on this thread - the models (and especially post-T+144!!)can shift so significantly as to render any longer-range validity of discussion into the mere 'ramping' category, as beloved by certain daily newspapers... irrespective of the season.

A wise post. You should be a weather forcaster or sumink!

[weather eater]

Very happy that the ECM12z has gone with the earlier runs, broad consensus with the development of the high pressure in the crucial period between 96 and 120hrs, that will do for me at the moment. Interesting conversation about short waves, it could be that this time it's not about how they will scupper things, but where and how big an impact we get snow wise, that would make a nice change.

Edited December 7, 2009 by weather eater

[stewfox]

If the models do somehow keep this trend then perhaps towards the end of the week we can be more certain of the outlook. My advice is simply this absolutely do not trust any output that relies on a shortwave. For older members who have been through many previous shortwave induced dramas they certainly know why i'm so reluctant to want to look much further than 120hrs.

What do we need to happen/ see in the T96 time span

I keep seeing all these T240 charts being posted which are nice but still F1 ,not much discussion in the shorter time frame ? . Its not good for my nerves seeing all these F1 charts

[nick sussex]

hmm try again

In these kind of setups what gfs is showing for example, would that result in france being very cold and colder than the UK and also have more snow, like would Paris get more snow than london.

Btw when do the ecm ens come out? thanks

It all depends on the setup, if you get a very cold strong unstable flow over the north sea then eastern and se areas would get plenty of snow showers, if for example you had the same upper cold as Paris this would be colder as an easterly there would not be modified by the sea but drier. If you go on to southerly tracking lows under the block it would depend on how far north these got, its really impossible to say accurately at this timeframe but as a rule any easterly/ne would normally favour the east and se. But continental europe would always be colder given the same depth of cold.

[mcweather]

Regardless of how good the outputs been this evening I think we need to step back a little. On the face of it a big switch in the ensembles but we've been here before, last February being a recent ensemble trauma when from very good agreement it imploded in one run.

The gefs ensembles because of their lower resolution are not to be trusted with shortwaves, even operationals always have tremendous difficulties with these features. Easterlies come in many forms, coming up we get this brief easterly as the euro high heads north, easy isn't it! because its a straightforward evolution with no shortwave!

To get to the cold nirvana we need to see the right WAA into the Arctic whilst at the same time hoping the SW behave themselves and then relying on the right jet curve to advect the cold westwards, alot of factors have to work together and for this reason and putting aside my obvious excitement at the output, to get from where we are now to where the gfs or ecm are past 168hrs is still not the most likeliest outcome.

If the models do somehow keep this trend then perhaps towards the end of the week we can be more certain of the outlook. My advice is simply this absolutely do not trust any output that relies on a shortwave. For older members who have been through many previous shortwave induced dramas they certainly know why i'm so reluctant to want to look much further than 120hrs.

Good advice Nick. I always enjoy reading your input.

Of course just because so many other cold scenarios have imploded doesn't mean this one necessarily will

you never know it might be underplaying things. I,m sure just as many cold scenarios probably imploded back in the 60's 70's and 80's.

but indeed as you say if something similar is showing come thursday/friday time then we could be looking at something quite significant.

[snowlover2009]

It all depends on the setup, if you get a very cold strong unstable flow over the north sea then eastern and se areas would get plenty of snow showers, if for example you had the same upper cold as Paris this would be colder as an easterly there would not be modified by the sea but drier. If you go on to southerly tracking lows under the block it would depend on how far north these got, its really impossible to say accurately at this timeframe but as a rule any easterly/ne would normally favour the east and se. But continental europe would always be colder given the same depth of cold.

thanks for that.

[Ian Fergusson]

The METO seem to have a standard update for whenever colder conditions are on the way which always mentions 'increasingly wintry showers in the North and East'. They have issued so many ludicrous warnings over recent winters at some of the most innocuous of set-ups that they will be praying the GFS doesn't come to fruition.

I'm not here to corporately defend the MO (that's for their own staff to do) but instead I'm merely citing their standpoint. Whether others accept it or not is neither here nor there. I'd imagine their medium range forecast team in Exeter have no specific axe to grind on the veracity of GFS, JMA, ARPEGE or any other national model versus their Global, NAE or other products, at least based on the essential point that they're scientists foremost, and thus (I would hope) interested in accurate science - whatever its origins.

Indeed, I think it's noteworthy how all the detailed briefings I read each day from their medium range team strive to highlight, analyse and importally - critically contrast the likes of GFS output versus anything 'owned' by UKMO.

And quite often, I note how they discard their own product output / solutions and accept those of others, be it GFS or whatever. To me, that suggests proper, robust and impartial scientific method and ethos. After all, the folks working at Exeter are essentially no different to those here on this thread: above all else, they're weather nuts!

(Incidentally - I will certainly defend the MO's guys on their February snow warnings this year; I sat through many briefings from them ahead of those events and with very few exceptions their areal and temporal accuracy down to sub-regional level was extremely good).

Edited December 7, 2009 by Ian Fergusson

[nick sussex]

Good advice Nick. I always enjoy reading your input.

Of course just because so many other cold scenarios have imploded doesn't mean this one necessarily will

you never know it might be underplaying things. I,m sure just as many cold scenarios probably imploded back in the 60's 70's and 80's.

but indeed as you say if something similar is showing come thursday/friday time then we could be looking at something quite significant.

Thanks MC

Some good news from the ecm ensembles good support for the operational run, funnily its acually a mild outlier for a few days!

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

Some scatter towards the end but expected at this timeframe.

In answer to stewfox, in the earlier timeframe you need to see a strong southerly flow heading north towards Greenland, the eastern Canada trough you want to see as far west as possible, the shape of this trough will help, a more elongated north/south trough with again a southerly heading into the Arctic, preferably we dont want those highs near us to split, the further north the initial euro high can get the better, and finally the shortwaves, one of these we need to run quickly se with pressure building north behind it, there is more but lets just start with that!

Edited December 7, 2009 by nick sussex

[Eugene]

excellent runs tonight for cold weather fans and like i said this morning a better ECM 12Z and the ensembles are excellent too.

http://www.wetterzentrale.de/pics/MT8_London_ens.png

Edited December 7, 2009 by grab my graupel
Quite obvious

[Cecil Hogmanay Melchett]

Thanks MC

Some good news from the ecm ensembles good support for the operational run, funnily its acually a mild outlier for a few days!

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

Some scatter towards the end but expected at this timeframe.

Hmmm,im not so sure i like them Nick,they delay the cold stuff again.At this rate it will be after christmas by the

time any cold reaches us!

[kold weather]

Going to be very interesting to see what the 18z GFS shows, I think the first stages and probably even the 2nd stage (which drives a cold easterly into Central Europe) looks nailed on, now the key phase that is still showing model disagreements is stage 3, where the shortwave dives down and we see the upper high rotate round, at the same time we get another shortwave which comes across the Iceland region, this being stage 4 and is the one which would be the one to give the holy grail.

So like the others have suggested, we are probably nailed on for some sort of cold high set-up, but probably still very 50:50 as to whether we get the full works...but always remember, very often in cold winters even if the first shot fails it'll lay the ground work for another one up the road...

[weather eater]

Hmmm,im not so sure i like them Nick,they delay the cold stuff again.At this rate it will be after christmas by the

time any cold reaches us!

Don't look at them in that case HD, just go with the operationals, besides I'm not sure looking at them leaves the viewer any wiser.

Edited December 7, 2009 by weather eater

[Snowaddict]

What an interesting period in model watching!

Around this time last year, perhaps a little later, we once again had great hype and excitement with regard to wonderful model output. Some might say that it's no different this time round & that's true in the context that any specifics beyond T+120 should be taken very lightly. Broad trends are alright up to T+144 & on some occasions up to T+168. This year is certainly different in terms of the intensity (or lack of intensity) of the polar vortex over Greenland, it's usual home in so many of the recent winters, helped by a to date, warmer than average temperature at the 30mb level:

http://ds.data.jma.g...e/pole30_n.html

Broadly tonight, all major model guidance is pointing towards cold, perhaps significant cold over the course of the next 7 - 10 days. Specifics will change, it may be that we end up with a stationery high over the British Isles, perhaps centred over Eire, or we may get that long awaited significant, real cold blast that is so well deserved by many faithful model watchers on here! From looking at all of the latest guidance I think it's certain now, greater than 90% that after initially being mild, conditions will cool down significantly in the next 7 days. Thereafter, we still don't know but the idea of cold to very cold upper air encroaching upon at least the eastern part of the UK over the next ~ 10 days is certainly gaining momentum, I would rate it at a solid 50% chance at the moment.

Watch out for changes towards the T+96 - T+144 timeframe, those are the most important.

We are by no means fully there yet but things are looking quite good.

Also, just to add a ramp here's the ECM 850mb Temps from this evening - Steve M called it fairly right: -15's into the E at T+216, -15's widely across the UK at T+228:

T+216 & T+228

Here's to an impending, increasingly bitter cold spell, with the potential for eventual snowfall occuring at a time when the power of the sun will be at it's minimum

Edited December 7, 2009 by Snowaddict

[snowmadchrisuk]

Just going to post a couple of charts here and would like to know what people think. The first chart is from the 1st December

predicting todays weather 7 days out. and the 2nd chart is todays +0 . How do you think GFS has done from these charts ?

1st Dec predicting the 7th

Today's +0

[kold weather]

Ensembles are great HD...the ensembles are faster then the 12z ECM op by a good 12-24hrs in general, also the GFS is probably going to slow down over the next few outputs if it continues with this cold set-up, there is little chance things progress quite as fast as it suggests IMO.

The key thing is the ECM ensembles are trending colder and colder and that there are now around 80% going for a colder option...all good news guys at the moment but we could very easily still end up with a Jan 09 style event....not that I would moan, that was one of the colder spells of the 00s.

[nick sussex]

Hmmm,im not so sure i like them Nick,they delay the cold stuff again.At this rate it will be after christmas by the

time any cold reaches us!

They look okay, the rise in the middle is of course for the Netherlands as the shortwave develops and heads se changing the flow to onshore, once this clears theres quite a drop, but as weather eater says we should take most guidance from the operationals as they will have a better handle on the dreaded SW!