General Model Output Discussion

[grab my graupel]

To help those who are unsure of where they should place their posts, I've re-posted this little message from Paul:

There are topics available for pretty much every possible winter related subject here so there really is no reason to randomly post into an unrelated thread - particularly the model thread. We know it is a popular area, but it cannot be a free for all so please only make posts in there if they are related to the models and are adding something to the discussion - more light hearted non model related posts can be made in the general winter chat threads.

Because of the problems we're facing at times with the shear number of off topic (or off forum guideline) posts being made we will be seeking to stop the most persistent offenders from making any further posts for a period of time, please don't let that be you!

Please continue

[yamkin]

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

[HotCuppa]

:cold:

http://www.wzkarten...._London_ens.png

:cold:

Nick Sussex I absolutely agree, I think there where some crossed wires there my apologies.

I asked a question that was previously answered on another thread my apologies.

Why doesnt Liverpool have ensembles? seems everywhere but the north west has them

Edited December 28, 2009 by HotCuppa

[mountain shadow]

Some crunch 12z coming up with hopefully some agreement between the models on the northerly extent of the precipitation. The GFS brings it as far north as the North of Ireland, with METO no further north than north wales. I expect it will be somewhere in the middle.

Into the medium term turning cold or very cold for everyone with hopefully the start of another cold spell, which of course hasn't stopped in parts of NI, Scotland and Northern England.

[nick sussex]

Nick Sussex I absolutely agree, I think there where some crossed wires there my apologies.

This morning I saw warnings on the meto site for the whole of the north of england..no mention of wales midlands.. I thought this was a bit strange given there was no clear clue where this low would end up. (this warning was in place around 7am ish or close to 8am) then suddenly whan gone replaced with some warnings for wales and west midlands and only advisories replacing the warned area. Do the met office do regional checks on their early warning system or have they decided to back track a bit and have this low further south than they thought? I have a suspicion it was only some sort of warning test this morning.

No worries Lets hope the models can at least agree on this low tonight. In terms of the ensembles if you go to the meteociel site to gfs europe then gefs ensembles, click on diagrammes at this point go to carte europe, you can use your mouse to click on the map and the ensemble will pop up, it doesn't show all the cities but you can get close enough by using the map.

Edited December 28, 2009 by nick sussex

[Cecil Hogmanay Melchett]

No worries Lets hope the models can at least agree on this low tonight.

Yes we should surely see some agreement this evening on the low.Only trouble with ecm is that we can't see it before 72hrs.

Hopefully gfs will track it further south allowing the colder air in quicker!!

fwiw i cant see the snow reaching as far north as the NW of England but parts of wales could get snowed in.

Edited December 28, 2009 by happy days

[snowlover2009]

its amazing highest temperature on saturday was around 4c here and that was the mildest day of this cold spell. it looks like we are in for another week of very cold weather and potential snow for here towards the end of the week. i don't remember last years winter staying this cold so so long. we have had cold since 15december and it is now 28th december and it looks like this cold will last up to at the very least next weekend which is 3rd. 19 day cold spell or maybe longer.

[bennytes]

update from Ian Fergusson on the 'South West' thread....

Afternoon folks.

Well, an interesting morning and doubtless tomorrow (and Wed, and Thurs) will prove equally challenging. There's a lot at stake, forecasting wise, because for some areas - some - this next bout of wintry weather could prove highly newsworthy as well as downright dangerous / disruptive.

You've doubtless seen how this morning, after further consultation through the PWS, the UKMO issued an early warning for severe (snowy) weather, applying, at present, to parts of Wales and adjoining English counties. A broader swathe of advisories (and note, these a different to warnings in the strict sense) apply to other areas - including the westcountry - albeit for differing but well-reasoned potential consequences.

Since I started work at 0355 today, I've seen and been briefed on two separate NAE runs, alongside some detailed high-res prognoses for rainfall / snowfall totals. An earlier snapshot of such UKMO Chief Forecaster briefing output is viewable on my blog today (http://bbc.co.uk/ianfergusson) for those interested - it offers a flavour of how we tweak our TV and local radio forecasts to cater for the sort of sub-regional outcome expected in the next 48hrs.

Here's the latest thinking, in summary:

RAINFALL - some heavy and in itself likely to be disruptive for some areas - is the core story for most of the westcountry overnight and into tomorrow. Localised flooding quite possible for some. The very tight WBFL gradient developing overnight on the northern flank of PPN will mean an equally tight areal discrimination from transition of rain to snow, with the WBFL typically around 200-400m but as you might expect, this will be readily dropping in heavier PPN to offer a wintry flavour. Equally, into tomorrow the surface temp variance will be extremely marked; e.g., Plymouth and much of Cornwall positively basking (despite the inclement skies and wind!) at >10C whilst up in the likes of Bristol and Glos, ambient will be closer to 3C. Either way, a drab and pretty ghastly day wherever you happen to venture.

The prospect of anything other than rain for all of lowland SW Peninsula and lowland Somerset / Dorset / Wilts is effectively tiny. High-res modelling gives around a 30% risk of snow further north over high ground of Somerset (Mendips Plateau) and upland mid-Wilts, but this risk is elastic and low confidence.

SNOWFALL - the only (westcountry) area with fairly high confidence for possibly quite potent snowfall developing tomorrow is Gloucestershire. We've been at pains to signal this on TV and in much more detail in forecasts today on BBC Glos. Specifically, the Forest of Dean looks like an area where the situation could quickly deteriorate during tomorrow (as you might have guessed, with it nestled alongside the area of most concern delineated on the UKMO Warning page). Cotswolds also look likely to take a wallop, and we've equally been at pains to warn residents there how smaller roads could become impassable and remain so for quite a time.

Snow risk elsewhere - e.g., Bristol, Bath, B&NES, S Glos - remains every bit as marginal as before (see yesterday's forum posts) but clearly, the UKMO has to play the pragmatic card and retain the existing advisories, now extended into other districts, e.g., of Wilts. Effectively, for these regions we'll be forced into a nowcast / short-range forecast and warning scenario through tomorrow, given the low confidence bounds that separate mere 'snow' from snow befitting an actual warning, versus mere advisory. Trust me, it's not plucked out of thin air - these upgrades only happen after detailed analysis and debate via PWS expertise. ]

For our (BBC) part, we've elected (rightly, I think most would agree) to highlight the snow potential for these marginal arreas rather than downplay it, because history amply demonstrates to us how the backlash of forecasting rain but not correctly forecasting disruptive snow is massive and potentially deadly; conversely, forecasting rain that never becomes promised snow largely bothers / upsets schoolkids, skiers and varied snow aficianados, but is otherwise speedily forgotten (and often a major relief for travellers).

SNOWFALL TOTALS: This might shock some other forums here (Midlands / Wales), but our new NAE run is eager to talk-up some 50cm of snow by the end of Wednesday for parts of central/SE upland Wales (and that's even without the drifting, which will be a major factor everywhere). Our best estimate for neighbouring areas such as Forest of Dean could total 20-30cm (same caveat re drifting) and more widely >10cm. Whatever the end result, a recipe for some very, very nasty conditions and some areas such as the Brecon Beacons, parts of Herefordshire etc., will be wholly impassable.

REST OF THE WEEK: Sees the frontal zone effectively stall over the same areas into Wednesday and then sink southwards and yield a moore expansive area of (perhaps disruptive) snow across much of southern England, perhaps ultimately all the way down to the south coast. Some of our modelling of the New Year's Eve events are deeply troubling, with a risk of severe weather (blizzards) into southern-central / SE England and London, which would clearly have major ramifications at a time whhen many people are either travelling or otherwise planning New Year's Eve events, etc. But that's miles away and obviously confidence is low.

If time allows, I will post on updates from the next NAE run.

Best

Ian

[andy_leics22]

Ok I am confused as anything. The BBC say the band of rain/sleet/snow will make it as far North as Mid Wales and South Birmingham and the GFS say the band will make it as far North as Yorkshire and will be rain for the whole of Wales and the Midlands.

What I don't understand though... how can it possibly snow in Wales and the Midlands tomorrow with uppers like this...

[loopydreamer]

update from Ian Fergusson on the 'South West' thread....

yea! just been to south west thread and seen that! amazing read

[Iceberg]

Thanks, Ian is a fantastic contributor over on the SW thread (his forecasts are very good on telly as well ! ).

Sorry if this has been said (but there is no way I am trawling through the 500 posts on the other thread).

ECM ensembles support some very good and prolonged weather after new year, this also shows how warm the GFS was in the shorter time frame and that the ECM was a bit too cold forecasting forecasting a maximum of -5C of the 4th of Jan. ! However the average of the runs barely takes the London temperature above freezing right through out.

Good agreement on the precip between the 30th and 1st which would very likely be snow.

BTW the above from Ian is the first time I've ever heard an experienced forecaster warn of 50cm of snow so If you live in the said areas take it very very seriously.

[andy_leics22]

Some crunch 12z coming up with hopefully some agreement between the models on the northerly extent of the precipitation. The GFS brings it as far north as the North of Ireland, with METO no further north than north wales. I expect it will be somewhere in the middle.

Into the medium term turning cold or very cold for everyone with hopefully the start of another cold spell, which of course hasn't stopped in parts of NI, Scotland and Northern England.

I also find that bizzare too, on the UKMO precip charts they have the precip much further North than the BBC forecasted. It's covering the whole of Ireland and Northern England lol.

[loopydreamer]

Ok I am confused as anything. The BBC say the band of rain/sleet/snow will make it as far North as Mid Wales and South Birmingham and the GFS say the band will make it as far North as Yorkshire and will be rain for the whole of Wales and the Midlands.

What I don't understand though... how can it possibly snow in Wales and the Midlands tomorrow with uppers like this...

omg! that isnt going to happen no way! that will be snow! what is it oing on about!

[Iceberg]

Ok I am confused as anything. The BBC say the band of rain/sleet/snow will make it as far North as Mid Wales and South Birmingham and the GFS say the band will make it as far North as Yorkshire and will be rain for the whole of Wales and the Midlands.

What I don't understand though... how can it possibly snow in Wales and the Midlands tomorrow with uppers like this...

Quite simply that's the global model, not the meso model, also we don't have access to the UKMETO and ECM Ensemble suite for 850 temps or thicknesses, I've got a feeling the 00Z was on the warm side of the METO's own models.

[bluearmy]

andy - the ecm and other meto modelling doesnt agree with the raw ukmo output. hence the forecasts are further south.

[Geordiesnow]

I also think the beeb might now be starting to use the 06Z data and that apparently has the low further southwards thus the front further southwards.

We'll soon find out which model is right and which is wrong, in fairness, even the GFS predicted something similar to the ecm but they obviously since then predicted the low to be further northwards.

[nick sussex]

For those looking at the ukmo 00hrs output, the met office as Ian has just pointed out have also used other data including the latest ukmo mesoscale model which ties in with their forecasts, unfortunately in these situations it often becomes a nowcast scenario with such small margins between rain and snow.

Edited December 28, 2009 by nick sussex

[mountain shadow]

I also find that bizzare too, on the UKMO precip charts they have the precip much further North than the BBC forecasted. It's covering the whole of Ireland and Northern England lol.

This is exactly the problem. We have a 200 mile difference between the northerly extent of the precipitation between the GFS and the UKMET for a event startin around T+24.

Given the UKMETs updated weather warnings, the GFS must back down in the 12z for sure.

[andy_leics22]

Thanks for those replys :lol: Well I have to say I am just completely amazed at how different the models are at such a short timescale. There is a difference of 200 miles or so in PPN positions and where the low will be positioned. If the GFS still doesen't back down on the 12z and 18z then what the heck are we supposed to believe?

The GFS may not be the main model for the UK but it is in high res and it has not backed down one bit for the past 24 hours. It's fun though don't you think? It's like being back in the 70's and 80's where we never had any computer models we could check all the time and we had to trust mother nature and see what happened.

[fine wine]

I would urge people to remember last Monday nights event when the Meto quite correctly predicted the northern extent of the precipitation. The GFS said it would just clip the extremem SE whilst the Meto model quite rightly predicted the rainfall would move further north with more significant snow - this was their Meso model suggesting this. This time its the other way round but I would have more confidence in their prediction based on last weeks event. That said, I still struggle to see the ingredients for snow with such high uppers, although the Meso model must be predicting these to stay well south of the UK

[tinybill]

I would urge people to remember last Monday nights event when the Meto quite correctly predicted the northern extent of the precipitation. The GFS said it would just clip the extremem SE whilst the Meto model quite rightly predicted the rainfall would move further north with more significant snow - this was their Meso model suggesting this. This time its the other way round but I would have more confidence in their prediction based on last weeks event. That said, I still struggle to see the ingredients for snow with such high uppers, although the Meso model must be predicting these to stay well south of the UK

all i say its any ones guess

[yamkin]

update from Ian Fergusson on the 'South West' thread....

Ian Fergusson might be onto something in his last paragraph. Take a look at what Joe B from AccuWeather has just updated his European Blog........... (MODS hope this post is ok)

THREAT OF HEAVY SNOW SHIFTING SOUTH

Here is part of his blog...........Enjoy

The UKMET is considerably farther north than the European on this, which shifts to the main threat to southern England, including the threat of heavy, disruptive snow around London. It bothers me in looking at the map this morning, that sneaky chilly air has pushed into southeast England and an adjustment south in the storm track is needed. How much is still a question, but it does appear there is a threat for heavy snow before the core of cold presses south. The opening week of the New Year, and this is what this post and the one before are mere offshoots of, the idea over a week ago, is going to be very cold across much of Europe north of 40 north, probably harsher than a) the December outbreak and last year's cold outbreak.

Edited December 28, 2009 by yamkin

[Snowaddict]

12Z NAE... To T+24:

Looks quite good to me:

Also, 12Z GME to T+42 looks very decent to me:

http://www.meteociel.fr/modeles/gmee_cartes.php?&ech=42&mode=0

SA

[Matty M]

Most eagerly awaited model runs for a long time.

Very interested to see what the GFS does

[grab my graupel]

GFS 12z run rolling out shortly, which can be viewed here on Netweather

http://www.netweather.tv/index.cgi?action=nwdc;sess=