Model Output Discussion

[TEITS]

I keep saying its my last post for the night.

Anyway the ensembles are a clear example of an E,ly on the way. I have selected 3 locations, Aberdeenshire, W Yorks, Kent. Now take note how the mean is warmer in Aberdeenshire compared to W Yorks but take note how Kent is the coldest. This is normal for an E,ly due to the shorter sea track.

http://charts.netweather.tv/ensimages/ens.20091212/18/t850Aberdeenshire.png

http://charts.netweather.tv/ensimages/ens.20091212/18/t850West~Yorkshire.png

http://charts.netweather.tv/ensimages/ens.20091212/18/t850Kent.png

Now in my opinion the problem for the E,ly isn't so much the temps but the duration if your after snowfall. Intially the surface temps will be warmed due to the effects of the N Sea but the longer the E,ly continues the colder it would become, especially for Kent, E Anglia. Now with -10C upper temps spreading across the N Sea convection would occur very quickly i.e Feb 2nd 2009 only took a few hrs.

So what im basically saying is we need this E,ly to persist for at least 36hrs if your after a decent snowfall. At the moment the further S you are the longer the E,ly will continue which is why I continue to suggest locations such as SE/E Anglia look favourable. If you live further N than these locations then hope the models upgrade the duration rather than the temps. Reason being the longer the duration the colder it will obviously become.

Edited December 12, 2009 by THE EYE IN THE SKY

[LomondSnowstorm]

As for the Models you know as well as I do that what we are seeing

in the next 10 days is fantastic synoptics....1060mb GH, -10 air, reloads ENE then N winds

Once we get the cold we wll experience some fantastic colder temps towards Xmas.

Could someone post nexts THURSDAY chart up againt that of lasts years exact chart?

Think that will stop some of the negativity?

Would anyone on the forum rather have this?

[Geordiesnow]

Those ensembles would suggest to me tetis that the ECM is unlikely as the mean is higher in Aberdeen so it would seem to me that the GFS could well be right on this but you never know i suppose.

ECM might be the best model but it does not mean it's going to be right on this occasion but we shall see.

[Snowaddict]

IMO the ECM is the model that should be taken most seriously by every poster here. This nonsense of disregarding it and all that is just that - nonsense. It is Europes main model. Simple as that. Perhaps every National Meteorlogical Center in Europe pays into it and it is an excellent model. Instead what we have is people getting all upset at one run of a US model which like I said before is free to us because no reputable National agency in Europe would pay to use it. So that is what they think of the GFS. That is why we have the ECM. Im actually supprised that people like John Holmes - who worked for the MO - sit back and allow such commentary about the ECM daily without responding. Some of the comments about it are completely daft. I just don't get it.

Agreed The Eagle,

ECMWF is not freely available apart from a few screenshots so to speak, for exactly the reasons you have outlined above..

Now, whilst it may tone down a bit overnight - I would hope & be quite confident that it is nearest the mark..

For example, the Met Eireann forecasts tonight speak of a wintry spell come mid next week - exactly in line with ECMWF guidance..

In addition, they must have good ensemble support for the operational evolution as they certainly don't call wintry weather unless there is at least a fairly good consensus towards it.

The evolution will change yet but ECMWF is still verifying the best out of all models & has been relatively consistent over the past two days, on all 4 runs..

Fingers crossed.

[Thundery wintry showers]

I do try mate-but have another life besides Net Weather-please read my blogs and lrf to see that ECMW is used as and when I think it should be used as is GFS and UK Met.

I have, somewhere in the bowels of Net Weather posted on several occasions about ECMWF in some detail, if you read my lrf you will almost always see some comment that it is, as it almost always does, outperforms GFS on the northern hemisphere scale.

hope that helps.

I'm off to bed.

Yes- while it has "wobbled" a fair bit in handling this cold spell, on average it certainly has the edge, at least at the T+96-T+144 timeframe for which I did my model accuracy checks back in 2006/07. The main difference, from my checks, appeared to be that while the ECM was every bit as prone to getting the outlook wrong as UKMO and GFS, it tended to be less wide of the mark on those occasions, whereas GFS in particular threw up the occasional run that was wildly inaccurate, and UKMO wasn't very good at T+144.

However the above also lends support to the possibility that the ECMWF could be slightly overdoing the easterly and that GFS might be nearer the mark. We shall see.

[TEITS]

Those ensembles would suggest to me tetis that the ECM is unlikely as the mean is higher in Aberdeen so it would seem to me that the GFS could well be right on this but you never know i suppose.

ECM might be the best model but it does not mean it's going to be right on this occasion but we shall see.

If you want my personal opinion on who is right out of ECM/GFS then to be honest I reckon they will meet each other halfway tomorrow. I would love to be wrong and see the ECM upgrade.

[on the coast]

Control run close to the mean for about a week, but then one of the coldest members in the run up to Xmas before becoming one of the mildest in the longer term. On the +ive side it's good to see all runs being colder than average pre 20th, but countering this the majority of members go for a less intense cold spell at the end of next week. On balance another rather disappointing signal IMO.

The scatter for 48 hours onwards puts everything past this as FI i would think.?

[Snowaddict]

Whatever the outcome, it will be a major test for the ECMWF model...

As I've said earlier, 12Z runs in the past few days have tended to be more potent in terms of cold than the 00Z runs.

However, I would hope that ECMWF is nearer the mark.

I still don't think that this will be sorted until possibly even the 12Zs tomorrow.

Tonight it's ECMWF & GME on one extreme V GFS Middle Ground V Meto at the ''uninteresting'' end of the scale..

Sense would suggest that a middle ground will prevail, but for once it would be nice to see ECMWF verify as shown tonight as the precip charts that I posted earlier are very tasty indeed.

[Just Before Dawn]

Ok, but the equations used must be adjusted at intervals to improve accuracy. This can only be based on learning. If there is no learning then how can forcasts improve?

They do - the GFS Parallel run is evidence that these things get tweaked from time-to-time, but the modelling isn't the final part of the process, it doesn't churn out the final forecast, it churns out theoretical output based on the data input and the laws of thermodynamics and these are then taken and interpreted by a forecaster. We are dealing with systems of mind-boggling complexity, after all and the human factor is roundly ignored (at least on the evidence of the last 10 pages). There's more value in John's blog than there is studying every output from every run of every model, because it has the experienced interpretation of a meteorologist.

On general matters, I've walked into doorframes less painful than this thread is to read - even with heroic moderation. Want a silver lining? Even if this verifies as the UKMO output suggests (which is the least apocalyptic of the runs this evening) then at least it will help to cool the North Sea, one of the primary moderating influences of winter Easterlies. As a large, relatively shallow water body, it should cool fairly quickly, so if this does re-load at some future point, we wont have to worry so much about air mass temps being moderated by a warm North Sea as much.

[JohnG]

Its was not model output discussion i think! but i did reply by saying ggreat post

I know I saw your reply. Cheers! Ive tried looking at different threads but cant find the posts. Oh well. Better get myself another vodka and keep up with this rollercoaster of emotions as Nick Sussex would say. Get the Prozac out!!!!

[Paul]

I think your post may have been removed in error John, apologies for that

Hi all

I think I have posted once in several years of watching this forum. I love reading the comments and analysing the charts esp in winter when there is the possibilty of snow. I like many of the users on this forum love snow and get very excited about snow and like many users my family think I am mad! But tonight I feel compelled to comment. The charts seem at odds with each other even at very short range. So in my eyes They are utterly confused with the current pattern. The charts are showing quite extraordinary patterns for the christmas pudding but will they deliver?? I blimming hope so! I do feel tonight people are squabbling about nothing to be honest - we have to look back at the charts over the last week or so and be happy for what they are showing at present. We havent seen these for along time. I feel very optimistic to be honest and I hope we see a white xmas - in fact I have put a bet on a white xmas at 6-1. I think this cold will stick around for a couple of weeks.

By the way I love reading comments and very balanced views from Nick Sussex, GP, John Holmes, Steve Murr, Ian Brown and I love TEITS optimism. I just wish that BEAST from the EAST will deliver!!! I remember climbing massive 10ft drifts over the tennis courts in Westerham in Kent in 1987 and building igloos in the snow drift in the early 80s and how I wish they would repeat. Perhaps this current pattern will deliver! Keep up the good work guys. I find it utterly fascinating!

John

H again its John G.

"Christmas pudding". I dont know what planet I am on. Too many Vodkas me thinks!!!! Just noticed my typo. I think I meant "Christmas period". Must be thinking about christmas food already!!!!

[kold weather]

Something that is very worth noting on the GFS is how we could quite easily still keep in the cold air, if the upper block over Greenland holds for a little longer (like the ECM) then there is a chance that the low will be at a better angle to promote a cold surface high to stay near the UK. The FI of the models will no really pick up such a feature, indeed often they are missed upto 120hrs and then the models finally clock the pattern.

So whilst the pattern looks bad in FI now, remember the GFS is somewhat progressive with lowering heights and changing patterns too quickly, and also it can overdo the jet sometimes as well which in this set-up make a massive difference to the outcome.

A return to zonality for xmas would probably be the best call right now based on various patterns, but I really wouldn't rule out the chances of a surface high being over the UK either...

[Paul]

This won't be the last time this link is posted into here in the next few days!

Please have a read of it:

http://forum.netweather.tv/topic/58023-winter-topics-please-read/

[mackerel sky]

So whilst the pattern looks bad in FI now, remember the GFS is somewhat progressive with lowering heights and changing patterns too quickly, and also it can overdo the jet sometimes as well which in this set-up make a massive difference to the outcome.

A return to zonality for xmas would probably be the best call right now based on various patterns, but I really wouldn't rule out the chances of a surface high being over the UK either...

Hi Kold... for a couple of days for once it did look like the lower res output of the GFS was for once amazing consistent across all perturbations, but now normal service is resumed with it wanting to bring back zonality in time for Christmas. I must admit, in the 7 years or so I've been watching the GFS output i'd never seen the ensembles so tight out to +384 hrs... but now the scatter is back and so is the fickleness! But to see the ensemble mean in the reliable timeframe for such a period of time consistently below -5C continues to be an exciting prospect. I guess the ECM is hinting now in its back end of a return to Atlantic weather, but it is ridiculous that some would get depressed about that when we haven't even entering what is pretty much going to be the coldest pre-Christmas spell we have had in a decade.

Its all good fun.

[andy_leics22]

Control run close to the mean for about a week, but then one of the coldest members in the run up to Xmas before becoming one of the mildest in the longer term. On the +ive side it's good to see all runs being colder than average pre 20th, but countering this the majority of members go for a less intense cold spell at the end of next week. On balance another rather disappointing signal IMO.

This is a question to anyone and everyone...

How in the world can the ensembles be as scattered as that at 48 hours in this day and age? Absolutely bizzare.

[Paul]

This is a question to anyone and everyone...

How in the world can the ensembles be as scattered as that at 48 hours in this day and age? Absolutely bizzare.

Don't forget that at the closer range (to 180 hours) the gfs is at a higher resolution than the ensembles which can make quite a difference. Plus the way the ensembles work is that each member has a bias added to it to simulate the discrepancies that will always exist in starting conditions, and on occasion those biases will make a difference even at the shortest range.

[snowray]

This is a question to anyone and everyone...

How in the world can the ensembles be as scattered as that at 48 hours in this day and age? Absolutely bizzare.

Very messy charts, HP, SWs, scattered all over the place, if you just look at the Fax chart at T120, which has been posted already, its all over the place.

As a few have already said, if this was a 70s or 80s set up the freeze would have just swept in, these days we have all the classic charts but it can still not happen.

Keep an open mind, things may well sort themselves out quite nicely in the end, tomorrows charts will of course show us something completely diferent.

Don't forget that at the closer range (to 180 hours) the gfs is at a higher resolution than the ensembles which can make quite a difference. Plus the way the ensembles work is that each member has a bias added to it to simulate the discrepancies that will always exist in starting conditions, and on occasion those biases will make a difference even at the shortest range.

Yes I was reading about this the other day Paul, so up to midway the controle run has the highest definition, then the lowest, its all quite strange realy how its worked out. So some members will simply have a mild bias and some a cold one.

[andy_leics22]

Don't forget that at the closer range (to 180 hours) the gfs is at a higher resolution than the ensembles which can make quite a difference. Plus the way the ensembles work is that each member has a bias added to it to simulate the discrepancies that will always exist in starting conditions, and on occasion those biases will make a difference even at the shortest range.

Thanks Paul, much appreciated By the way I hope you don't mind me sneaking this in... But you and every moderator on here are very busy at the moment and I don't envy you at all! lol keep up the hard work all of you.

[cj114]

I can't help thinking that it was best in the 70's, 80's not really knowing what was likely to happen.

The classic Francis Wilson forecast, "Rain then snow" on Thames local news, which came true the following morning etc. When the BBC did not forecast it.

81, when I fell into a snow drift at the top of my parents road. Again just a "Chance" of snow showers.

My daughters 1st Birthday 28th Nov 1980, thick snow.

I love following the models, but the ups and downs are far more stressful than the days when we just did not know what was going to happen.

Off topic, sorry

Whatever happens, I just hope that everyone gets what they hope for!

Cold and dry is fine by me, the days of chilblains etc are hopefully behind me. lol

[weather eater]

Had a lovely evening out with some of my wife's friends on the landrover forum she belongs to, got home and thought I'd have a look at the ECM and the 18z, and then have a read of the model thread. Well the models were ok, ECM very good, the trend and overall picture remains good, and I'm looking forward to how they evolve over the next week. However the read of the model thread was to say the least, a rather painful experience, it was rather like trying to listen to what the adults in the room are saying when 500 screaming children are running round looking for somebody to blame because the toys they were hoping for haven’t yet arrived. Given the amount of posts the mods have removed, I suppose I should be thankful that they must have been worse than some of the petulant drivel that has remained. Please please get it into your heads, models runs evolve, the models do not produce charts that are fixed in time and space, they do not verify, whatever the today’s GFS or ECM projects for 96 or 120hrs will have changed come the time, this is true for every day of every year. When I see a fantastic chart for say 120hrs I don’t get excited, there is no point in doing so because it will change, conversely when I see a rubbish chart at 120hrs I don’t get disappointed for the same reason. All I can see happening if things don’t change, is that the calmer members will just end up blocking a great many members who post in the model discussion thread and chat amongst themselves.

[snowray]

Your probably right mate, many of us on here waste hours looking at charts that never happen most of the time, if we were at a casino we would all be pennyless!

I remember Fracis Bacon on ITV talking about Sleet and very wet Snow on the evening before the start of the Dec 1981 event, it had in fact been pretty mild up til then I remember. By the next morning it was thick snow and -3c in South London, and the cold and snow was unbearable on some evenings, as we were out and about, being young teens just before Christmas. Memorable though.

I think there is still lots of potential, am loking forward to the morning runs.

Edited December 13, 2009 by snowray

[mackerel sky]

Thanks Paul, much appreciated By the way I hope you don't mind me sneaking this in... But you and every moderator on here are very busy at the moment and I don't envy you at all! lol keep up the hard work all of you.

Thanks also Paul for all the clearing out, with a sleepless baby and little time I really appreciate succinct posts. All eyes now should be on the conditions to our east and north east over Europe as this will dictate somewhat. Some snow is already falling in the low countries, but this isn't really the main focus, other than that we could see some wintery precipitation in the east of England ahead of the main push midweek.

[kumquat]

They do - the GFS Parallel run is evidence that these things get tweaked from time-to-time, but the modelling isn't the final part of the process, it doesn't churn out the final forecast, it churns out theoretical output based on the data input and the laws of thermodynamics and these are then taken and interpreted by a forecaster. We are dealing with systems of mind-boggling complexity, after all and the human factor is roundly ignored (at least on the evidence of the last 10 pages). There's more value in John's blog than there is studying every output from every run of every model, because it has the experienced interpretation of a meteorologist.

On general matters, I've walked into doorframes less painful than this thread is to read - even with heroic moderation. Want a silver lining? Even if this verifies as the UKMO output suggests (which is the least apocalyptic of the runs this evening) then at least it will help to cool the North Sea, one of the primary moderating influences of winter Easterlies. As a large, relatively shallow water body, it should cool fairly quickly, so if this does re-load at some future point, we wont have to worry so much about air mass temps being moderated by a warm North Sea as much.

Actually its the humans that came up with the laws of thermodynamics that totally own the model output.

To the OP, the equations do not change unless Euler or Newton or Einstein have recently been undone by some other genius. What does change and can only get better is the initial start data and the boundary conditions that are used for each run. And, of course, these could well use historical data and blend that into the programming, but at this point its getting very complex.

I would suggest looking up Navier-Stokes for some basic fundamentals on fluid flow analysis. Also check out multiphase flow. Honestly, we cant get this stuff right in a straight pipe never mind in the whole atmosphere, but its getting better all the time and the GFS Parallel has been kind of consistant.

edit - of course you're right and the computer programme can get more accurate and take on more data ad infinitum (on what its working with) and the grid can be smaller - like John says vertical and horizontal - but this does all come down to two words that hasn't been cracked yet. Chaos Theory.

Edited December 13, 2009 by kumquat

[sundog]

It seemed that tonight too many people reached for the panic button when they saw the gfs 18z run. I think when it comes to cold weather in the BI the models are only good for spotting a trend,and atm the trend is very good for cold. Picking out little bits of info from each run is pointless (especially regards snow)as it will surely change in the next run. Ive always though when it comes to cold weather in the BI you just have to wait for the cold to arrive and take each day as it comes when it does arrive,if not your just wasting your time. When it comes to snow that will always be pretty much a nowcast situation in the BI. Anyway i cant remember the last time things looked so promising for a good bout of cold in Dec,maybe the second half of Dec 2000 was the last time (some might say 2nd half Dec was nothing too special but id take it any day)and that was without being able to look at the models.

Edited December 13, 2009 by sundog

[mackerel sky]

I would suggest looking up Navier-Stokes for some basic fundamentals on fluid flow analysis.

One of the first essays I remember having to write at undergraduate level involved the Navier-Stokes equation in regard to the Sargasso Sea, salinity and the Gulf Stream. Would go on, but the baby is screaming, so exit right Anthony.