Model Output Discussion - 18z - 6th December onward

[Paul]

And we're away again, please keep it on topic and friendly

Some useful threads for non model related chat:

Winter emotions and moaning

General winter chat

Stratosphere watch

And don't forget the regional threads for more local chat:

http://forum.netweather.tv/forum/142-regional-discussions/

[Ian Brown]

I am a bit concerned people are assuming the 500mb anomaly charts are infallible. They are not. Last night I mentioned we'd get this reaction today. It is of course one or two "experienced" posters that are ruining this thread for anyone who wants to know anything other than will it snow or not. For the very vast majority it will not. That is almost a fact and will be a fact end of next week. Last nights charts were isolated and the coming runs will continue to deviate from them. It will be colder than average by a very big margin next week and some eastern areas in UK and Ireland especially in the north will get some snow before I suspect a break down form the south. BTW, where is the massive and permanent High over Greenland certain to be here by now in the 500MB charts? 10 days ago it was a certainty?

I did question this 500mb with JH the other week - that they are surely only a prediction in the same way that the NWP is.

Anyway, the ECM ensembles show a big scatter after the back end of next week, with the OP and Control in the colder section. I'm becoming less convinced about the retrogression of the HP to Greenland. We could see some sort of attempted breakdown or full breakdown before a rebuilding of heights as the ECM might show if it went further than T240.

Edited December 6, 2012 by Ian Brown

[Paul]

Anyway, the ECM ensembles show a big scatter after the back end of next week, with the OP and Control in the colder section. I'm becoming less convinced about the retrogression of the HP to Greenland. We could see some sort of attempted breakdown or full breakdown before a rebuilding of heights as the ECM might show if it went further than T240.

That would actually tie in fairly well with what the ECM32 has been showing regularly over the last couple of weeks.

[IDO]

T240 ECM mean:

http://www.meteociel...H1-240.GIF?06-0

T240 GFS Mean:

http://modeles.meteo...21-1-240.png?12

Same synoptic pattern, Atlantic moving closer. However there are massive divergences by D8 (ECM Ens) & the ECM op not having much support in its later stages. That is both GFS and ECM agreeing that there is a 3/5 day cold N'Easterly, then great uncertainty.

When some posters mention that there is a possible breakdown we are told that its FI, dont worry, etc. Yet there is clear evidence of an Atlantic attack and several options from there. That's what the two main models are saying, and to analyse that and to comment that it is a downgrade, is in my opinion just stating the obvious. Of course the cold may continue and the next run may start a trend in that direction. However at the moment the main three models are hinting at a breakdown by next weekend (proviso: low confidence with any subsequent outcome).

Edited December 6, 2012 by i'm dreaming of...

[chris55]

De Blit 10 days, large scatter for next weekend!! No clear solution there. Op coldest of the lot.

Edited December 6, 2012 by chris55

[Methuselah]

IMHO, the beauty of the 500mb charts lies in their simplicity and not in any notions of infallibility...That they give an indication, but without all the shortwave malarkey, should be a good thing...A better guide, in many ways, than the ever-changing synoptic models, which tend to overburden the viewer with unnecessarily-detailed predictions?

[Alex95]

I'll say it one more time: On Christmas Day 2009 there was strong ensemble support for a full breakdown of the cold starting on Boxing Day, but by the 27th there was a complete turnaround and it became clear that the cold air would remain in Northern England and Scotland until a bitter NE'ly set in on the 31st. I thought it must have been a blip due to missing data over Christmas or something, and the charts would soon revert back to mild. By 9am on New Years Day though there was 10-15cm across the North East, and of course the first 10 days of January 2010 saw loads more snow almost everywhere in the UK. The moral of that story is not to look too far ahead.

[Grimsby Snow Lover]

I think the important thing to remember is the cold looks good for next week in the semi reliable charts. What happens after 5 days usually changes quite widely between runs anyway so best not to get too obsessed with breakdowns, extended cold just yet. Lets get the cold easterly here first and then see what happens.

[Cheshire Freeze]

De Blit 10 days, large scatter for next weekend!! No clear solution there. Op coldest of the lot.

From those it looks like we go one of two ways......cold or mild......those are the two clusters.

[SMU]

ECM updated- good to see the control on the same page as the operational-

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

Got a feeling the 18z will be a stunner follwing the ECMs tracks-

S

[bluearmy]

having looked through the ecm mean and naefs for the next 10 and 16 days respectively, i have to say that i dont envy the metoffice. it seems clear that the uk will straddle the area where wet becomes white for much of the period. forecasting where that line moves, north/south east/west is going to be quite a challenge.

[nick sussex]

Looking at the ECM De BIlt ensembles and following on from Ians post:

You can see the operational run as a cold outlier towards days 9 and 10. Perhaps the ECM is slackening the flow out too much over there, you have a cluster of still very cold solutions and then just cold with a few members bringing in something milder.

So its unlikely looking at those that we're going to see a big push east of Atlantic air into the continent from the sw.

The output past 168hrs is likely to be even more error prone than normal because of these shortwaves floating about.

Generally in easterly set ups its the low pressure moving in from the sw that complicates matters but you have to add in what those shortwaves might do in terms of phasing with any attack from the sw which makes it even more complicated to forecast.

I think its unlikely now that we're going to see a sustained long draw easterly, whats lacking is deeper low heights in the northern Med.

If you look at the shape of the high we can see one large centre to the east and a ridge extension:

Because of the troughing over the continent you can see we're not likely to get that sausage shaped high so I think it might be better to see a separation with one cell edging west and north this would then exhibit more forcing on any Atlantic attack.

Edited December 6, 2012 by nick sussex

[Cheshire Freeze]

ECM updated- good to see the control on the same page as the operational-

http://www.knmi.nl/e...agse/index.html

Got a feeling the 18z will be a stunner follwing the ECMs tracks-

S

A lot of scatter though Steve and worryingly it looks like more members in the mild camp

[fergieweather]

That would actually tie in fairly well with what the ECM32 has been showing regularly over the last couple of weeks.

Absolutely - and as also repeatedly hinted at in UKMO MR trend standpoint. The wide spread in EC12z members by next weekend, after the significantly colder spell well-signalled until at least Thursday, does beg many questions as to how things will evolve by end of next working week - let alone further on by 20/21st, when (much akin to EC Monthly), the EC ensembles offer another meaningful cluster suggestive of Greenland blocking. A highly dynamic state of affairs into the medium range, for sure, and I'd not want to sit in the MR chair at Ops Centre, Exeter, trying to pen some focused sense from things (as they stand now) post next mid-week onwards.

[Cheshire Freeze]

Why the bemused face. There are few members that follow the mean i.e a big spread with 2 main clusters......one cluster cold and one heading into mild category. True for the 10 day ensembles anyway.

[IDO]

From those it looks like we go one of two ways......cold or mild......those are the two clusters.

Support for a snowy breakdown/battle next weekend?

http://www.weerplaza..._snow_06260.png

(PS Earlier for us).

Edited December 6, 2012 by i'm dreaming of...

[Cheshire Freeze]

Absolutely - and as also repeatedly hinted at in UKMO MR trend standpoint. The wide spread in EC12z members by next weekend, after the significantly colder spell well-signalled until at least Thursday, does beg many questions as to how things will evolve by end of next working week - let alone further on by 20/21st, when (much akin to EC Monthly), the EC ensembles offer another meaningful cluster suggestive of Greenland blocking. A highly dynamic state of affairs into the medium range, for sure, and I'd not want to sit in the MR chair at Ops Centre, Exeter, trying to pen some focused sense from things (as they stand now) post next mid-week onwards.

I might be partial to a bit of Greenland blocking just in time for Christmas......

I remember Christmas day 2004 fondly (although that was only a toppler scenario), heavy snow falling thick and fast whilst I was sat eating my Christmas dinner......laaaavly!

Edited December 6, 2012 by CreweCold

[weather eater]

I did question this 500mb with JH the other week - that they are surely only a prediction in the same way that the NWP is.

They are and I’m sure they do change Ian, but my take on them is that they are more likely to give a clearer and steadier picture of pressure distribution, less inclined to wax and wane as the general model output does. You know as well as I that the models run with an idea and then drop it and may or may not pick it up again, if this tool shows itself as a good method to see through that then excellent. Unfortunately (although that’s a matter of opinion) we have quite a number of members who do not want to look long term, they appear to enjoy the fluctuations of each model run, maybe for them the highs and lows are what make model watching fun, I guess each to their own.

Edited December 6, 2012 by weather eater

[Downburst]

I'll say it one more time: On Christmas Day 2009 there was strong ensemble support for a full breakdown of the cold starting on Boxing Day, but by the 27th there was a complete turnaround and it became clear that the cold air would remain in Northern England and Scotland until a bitter NE'ly set in on the 31st. I thought it must have been a blip due to missing data over Christmas or something, and the charts would soon revert back to mild. By 9am on New Years Day though there was 10-15cm across the North East, and of course the first 10 days of January 2010 saw loads more snow almost everywhere in the UK. The moral of that story is not to look too far ahead.

Is that a standing order? I mean I really don't buy that easterlies can't break down after 4 days because on Christmas day in 2009.....I am not downhearted. I am excited about next week and will actually be out enjoying it. What is interesting and pointless is the drive for perfection and then comments on anything but. I am sorry but your post might be correct for that event but that's all.

[Jonan92]

I would put in here what I wrote in the other topic before it closed

So far none has mentioned the biggest difference in the medium range between GFS and ECM .

In the gfs the atlantic low is very well blocked and the energy is moved around the GH

Therefore, there is no low moving towards Iberia at t144

On the other hand, the ECM shows that low moving towars Iberia

[SilverWolf]

I think the important thing to remember is the cold looks good for next week in the semi reliable charts. What happens after 5 days usually changes quite widely between runs anyway so best not to get too obsessed with breakdowns, extended cold just yet. Lets get the cold easterly here first and then see what happens.

Thank you, been on here a lot today as laid up ill, that's the most level headed thing I've read today!

[Downburst]

They are and I’m sure they do change Ian, but my take on them is that they are more likely to give a clearer and steadier picture of pressure distribution, less inclined to wax and wane as the general model output does. You know as well as I that the models run with an idea and then drop it and may or may not pick it up again, if this tool shows itself as a good method to see through that then excellent. Unfortunately (although that’s a matter of opinion) we have quite a number of members who do not want to look long term, they appear to enjoy the fluctuations of each model run, maybe for them the highs and lows are what make model watching fun, I guess each to their own.

Not sure that is the case I am afraid. If that was the case do away with the models all together. The anomaly charts do not wax and wane because they are set over a period and are the "average" of data that is waxing and waning. They do not speak of surface conditions. Excellent resource of course.

[Methuselah]

The bat-shaped HP has turned into egg-on-toast!

[Paul T]

Gfs rolling out now, but looking at tonight ECM and focusing on the 850's and potential cold pool;

Im not too fussed about much after 144hrs at the moment, personally i think an undercutting low up the channel will produce serious snowfall; if this happens we therefore need serious cold to be sitting over the UK prior to this 'attack'.

My focus is on the cool pooling potential.

00z ECM:

12Z ECM:

Massive improvement in the lower temps @ 850 on the continent

[Timmytour]

The GFS 18z has delivered two splendid runs in succession. It's time for it to deliver another one, one that materialises and shakes off once and for all its tag of "pub run", instead earning the respect it deserves!