Model Output - General Discussion

[PB22]

Okay, sorry, I thought the light blues were -10C. I mean -8C.

I restate my previous argument but with -8C (light blues) where I said -10C.

Still -8C 850hPa air evident for Tuesday on the 06Z GFS:

http://www.wzkarten.de/pics/Rmgfs572.html

Granted, not quite as widespread, but I'd hardly call it a downgrade and we can't judge it anyway until the day has passed though.

[SnOwFeSt]

I did not see the 00Z run but i assume by the comments it was showing something similar to the 06Z. So until this model backs down towards the euro's then i'm not going to get too carried away. Also considering we had a 2v1 situation yesterday with the UKMO/GFS vs ECM so it can easily change back(hopefully not!).

The 00z was showing a much slacker pattern with milder air pumped into the low pressure system coming down the norweigan sea, so the 06z is a little better, and the easterly looks more organised (although too far south).

Here's hoping it keeps moving north over the next couple of days, and the ECM doesn't backtrack! As you say, this is a possibility we need to bear in mind!

[Paul]

Sorry folks, but so many posts are already off topic in here, for general discussion of the winter weather, forecasts and the like - this is the thread:

For talk of upgrades/downgrades and the emotive side of the model output, this is the thread:

This thread is for general discussion, solely related to the model output itself, please read this thread for more information:

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

[Ross B]

Sorry folks, but so many posts are already off topic in here, for general discussion of the winter weather, forecasts and the like - this is the thread:

For talk of upgrades/downgrades and the emotive side of the model output, this is the thread:

This thread is for general discussion, solely related to the model output itself, please read this thread for more information:

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

To add to this there is a countryfile forecast topic here: as I have had to delete so many posts regarding countryfile this afternoon!

[Duane S.]

Unfortunately that forecast finds no support with the 06z GFS which shows a washout. This is going to be a Battle of the Models that will decide which of the GFS or ECM is going to influence us more over winter...

I wouldn't look ahead at the charts past three or four days - Friday the charts were still predicting -10C for Tuesday. Now we have -3C

Come of AF, try to give yourself some credibility. Your recent posts have ben, frankly, ridiculous. It's obvious you like Atlantic weather and are not looking forward to the next 10 days or so but try and be objective at least

There is model disagreement but things are still looking good from Wednesday onwards, and that has been the case now for a long time

[weather eater]

I must admit the wobbles and shake that the ECM was going though a few a couple of days back has rather shaken my confidence in its ability to be on the ball now. As for the GFS, while details keep changing, in regards overall handling of the general trend, its operational runs seem to my eyes to be more consistent than the ECMs have been, however I do feel it’s wrong in regards a breakdown and obviously I hope it will evolve towards the ECM. One thing for sure I'm glad I don’t have to produce a forecast for the week ahead.

[snowking]

The beeb always shows the UKMO charts no matter what, if we had the countryfile forecast for last nights UKMO, they probably won't show much in the way of snow graphics and probably would not even menturn the S word. Must also be noted that the forecaster did say snow amounts and where it will be is still up in the air.

I would like to see some substantiation on that claim because as far as im aware the Met Office brief the BBC on a daily basis, and the Met Office make an informed decision on which model(s) they will follow

Anyway back to the discussion, im pretty happy in the ECMWF/UKMO consensus, but even if we are to worry about the GFS, given the recent model correlation it should be the parallel run we worry about, not the operational, which is outperformed by the fore-mentioned 3 models. Would be good to see the parallel heading somewhere more towards the ECMWF

SK

[Interitus]

So someone makes a slight discrepancy which is unfavourable and is attacked for being misleading, and yet the laughable "most of the north will have 3-4ft of lying snow with 20-30ft drifts by this time next weekend when the ECM comes off" goes unmentioned. Hardly an unbiased and credible discussion of model output.

[shuggee]

And with that we can get back to discussing the Models :unsure:

[Paul]

Should really be doing some work at the moment, but couldn't resist a quick look at the ensembles from this morning.

Looking at the 850hpa temp graph for derbyshire (picked as it's central) and there's reasonable agreement up to shortly before xmas for cold of varying degrees with the majority of runs below or around -5 from midweek this week onward:

From the 23rd the diverence appears with a number of the members going for something milder and only the GFS operational (by this time in the lower res part of it's run) and one or two members sticking with the cold theme.

Looking at the postage stamps for xmas eve and it's not hard to see what's happening - basically it wants to bring low pressure in from the atlantic pulling milder air from the south with it:

Digging in a bit deeper though and we can see the low as it runs off of the eastern side of the USA much earlier in the run (96 hours) and it's already got a fair bit of spread between the members. (the spread is the difference between the ensemble members from high to low - the colour scale indicates the level of spread, with higher spread = higher uncertainty).

Following the developments to 144, the low doesn't get far that far, but notice the spread increasing around it.

By 192 it's a map filled with high uncertainty, as you may expect at this range of course but I think it's fair to say that based on all of this, even if you just concentrate on the broad theme and ignore the detail, the outcome beyond the coming 3-5 days is still very uncertain - particularly if you add the differences between the various models into the mix too.

[Buzzit]

Hello

I believe the model output is indicating a more likely snow event for Yorkshire north, South of Yorkshire seems to be continuing to slowly downgrade.

However this is all in FI so this can obviously change and I think there is far too much uncertainty in the models +72 that nothing is certain.

Even with the blips in the ECM lately it is still the most accurate model, and based on the fact that the synoptics are so unusual for this time

of the year in relation to recent winters, I think we all need to take a chill pill and wait and see what happens.

I still favour the accuracy of the ECM, though I also think ECM (and every other model) is likely to change significantly over the next three days. I am sure that the month of December 2009 will go down in model analysis folklore and there is no certain outcome as yet

Mods : Perhaps you can introduce a technical model thread that you have to 'sign up' to join, which will make it easier for you to ban people from

it if they are off topic. I want a easy to find model discussion thread, not 16 different model discussion threads (excuse the hyperbole)

Thanks

Edited December 13, 2009 by Buzzit

[Altohumorous]

Well, I've been following the phenomenal intensity and volume of discussion about the models over the past week or so, and I have to say I'm very impressed that the predictions of a week ago are still more or less on target. Considering how unreliable the models have proved overall at that range it's really quite an achievement to have seen such general (if not smaller detailed) consistency. Especially when you consider that we are dealing with a set-up that is so rare (once in the last 20 years? once in December only in the last 28 years)

And yet strangely enough, it seems that so extraordinary/unusual is this currently developing situation that perhaps that's why models have picked up on it so well.

I'm also delighted that signs and signals, however tentative, during the later autumn that this kind of block was a real possibility of developing in winter have proven (albeit quite possibly by chance?) so far accurate. And that what seemed a defunct weather pattern possibility of the past appears to be quite possible in the present (IF it comes off).

The intensity of debate and analysis of the models on here over the last week or more must mean that many who have participated are exhausted and somewhat memerised by the whole thing. I know for sure that I've kept out of it to avoid that fate. I'm just delighted and very satisfied that the current patterns are interesting, different to recently, and bringing badly needed dry bright weather here with light winds and some night frost - that alone is something to be thankful for in "the even larger teapot". And that the predicted patterns/set-ups are so damn interesting to watch and speculate about.

It currently looks like a nice chilly few days will be followed by something of a colder blast, which may or may not include some significant precipitation. Unlike many on here, I cant be as certain that it will be snow. First of all, those that live on the coast know that it requires a very special set of factors to allow an on-shore wind to bring snow to the coast. It almost always has happened in the months of January to March in my part of the world, and we are currently in mid-december and following a prolonged mild wet spell. Therefore I assume that seawater temperatures are significantly higher than they would be in late Jan/February/March.

I would also wonder if seawater temps are higher now than they were 20 years ago for example?

Then you take into consideration the seeming fact that our sources of serious cold (Arctic, North and east continent) are not as cold as they used to be when cold and snow were a more common occurrence. I wonder does the block need to be stronger/more intense/more wide-ranging in the current climate in order to hold, and is the block itself in at least some way dependent on how cold it is to our north/NE/NW?

With all those factors, when I look out the model output possibilities for this week, I see that there could well be snowy precipitation for some, or even many, but that it's unlikely on the windward coasts, it would require a super-cold burst of air to move quite quickly across from the continent, and that currently looks very unlikely.

Having said all that I'm very much looking forward to the models/patterns for this week, and to enjoy at the very least the seemingly almost certain upcoming spell of very cold weather, with hard frosts (away from windward coasts!), freezing winds, mostly bright days and maybe, just maybe, even a little of the falling white stuff.

Am I just confused when I seem to recall that during the 78/79 winter the pattern that developed in january/feb was one with an Arctic/Greenland block, vortex over Scandinavia and unsettled with repeated (fairly slack for winter) low pressures bringing a mix of northerlies and easterlies? That it was in this way very different to the other prolonged very cold spells of 47 and 63 and 81, where there was a fairly constant widespread block to our north, NW and NE?

It looks to me like this is the type of pattern that the ECM wants to develop in FI. If only it proves to be correct I think I could say that it would be an incredible spell of weather upcoming. And finally, it also shows something we previously discussed and all cold/snow lovers dream of - polar lows moving towards/over these islands!

Here's to a fascinating week, and whatever you do, take time to just enjoy whatever comes.

[kold weather]

Yep Paul there are big uncertainties in that area of the world, whats even more interesting is the ECM 0z run had very little in the way of low pressure in the Atlantic on its op run, I'd be surprised if it was quite so quiet out there by 240hrs, but equally the GFS is probably picking up a new signal and doing what it does quite often and take pattern to its utter extreme and too rapidly bringing it in.

Watch for a complication in the breakdown come in once it reaches 168hrs...probably in the form of a shortwave splitting off from the main developing low...these are never well observed, a great example of that happening was with Feb 2007 which wasn't really picked up at all till 144hrs and even then it was'nt really modelled at all well right upto 24-48hrs out. Thats what I'd watch out for right now, if nothing else a splitting low coming from the main vortex would give a possible big snow event, unlike the big LP solution of the ensembles which would give only a few hours of heavy snow before it changes to rain.

[Cecil Hogmanay Melchett]

Yep Paul there are big uncertainties in that area of the world, whats even more interesting is the ECM 0z run had very little in the way of low pressure in the Atlantic on its op run, I'd be surprised if it was quite so quiet out there by 240hrs, but equally the GFS is probably picking up a new signal and doing what it does quite often and take pattern to its utter extreme and too rapidly bringing it in.

Watch for a complication in the breakdown come in once it reaches 168hrs...probably in the form of a shortwave splitting off from the main developing low...these are never well observed, a great example of that happening was with Feb 2007 which wasn't really picked up at all till 144hrs and even then it was'nt really modelled at all well right upto 24-48hrs out. Thats what I'd watch out for right now, if nothing else a splitting low coming from the main vortex would give a possible big snow event, unlike the big LP solution of the ensembles which would give only a few hours of heavy snow before it changes to rain.

Yes, i know you have been mentioning this for a good few days Kold and its a plausable call,too far out at the moment

but its soemthing im watching for.

However,on a positive note there is no sign of mild weather for the reliable timframe.

What a switch from the deluges in November.

[Snowmad79]

Didnt know which thread to post this and I couldnt find the Teleconnections thread with search function so ill post here.

Was just wondering if and when GP logs on whether he could give us a tele update and decypher the GWO phase space chart updated yesterday :

I asked a similar question in a previous model output thread but got no responce and generaly said that if global friction torques went negative then usually negative mountain torques follow suit and eventually this leads to a strong negative AAM tendancy. Thus meaning the Extended Jet over the pacific colapses and a trough forms on the western flank of the states ( a bit like what happened at the begining of the evolution of the current up coming cold period and i think the trough is still visable just about at 00 on the GFS charts).

Well global friction torques actually went postive as you expect from the mojo's position at the time but the Mountain torques have nose dived into deep negativity recently and now the global tendancy of relative Atmospheric Angular momentum is going negative too which will remove westerly momentum from the atmosphere and would support a renewed trough over the western side of the states along with another break down of the pacific jet( less energy coming our way across the atlantic ?) . My unknowledgable feeling is still of the point I made last time and of what I said with regards to the models FI output of a reload of the current up coming pattern rather than a proper transition into an atlantic regime. I dont see the GH retrogressing into canada personally unless of course we just go off GFS 11 -15 day anomily charts.

I'd appreciate it if GP could decypher all this and the Global Wind Oscillation and Global Atmospheric Angular Momentum etc and clear this up for me in an update please.

(Just for the record, I do not pretend I fully understand what im talking about at this point so dont quote me on anything lol)

Ps . Links to apsects mentioned above :

Tendancy of Relative AAM

Friction torque graph

Mountain Torque graph

Edited December 13, 2009 by Snowmad79

[SMU]

And were off.....

Eyes down for the 12z-

highlights to look out for-

* Better troughing & CAA coming in from the east at around 72-96,

* The area of Cold uppers to be further North effecting the whole of the UK in the 84-120 timeframe-

* The angle of the Shortwave forming over Eastern Greenland- we needs its path & development EAST of the meridian 130-150

* Trough disruption of the system in the atlantic - Ie an elongated trough to the SW at around 180- this will hopefully then not allow a large push of WAA up towards the British Aisles at Day 10-

Steve

OUT TO T66 & We have better isolines to the East & SE-- so far so good- slightly lower 850's as well....+

WEDS MAXIMA- -1c across the central belt...

http://www.wetterzentrale.de/pics/Rmgfs724.gif

S

Edited December 13, 2009 by Steve Murr

[Iceberg]

Yep just at 72 it's better, the HP to the NW is better as well. Definately trending ECM/METO

[Duncan McAlister]

Yep looks like the lower 850s are reaching Great Britain, a better angle for Scotland as well. Good run but it will still change slightly from run-to-run.

[Tom D]

Looks very good so far. GFS following the the European models?

GFS at around +72 hours looks very similar to the ECM, but not sure if it will follow the same result at ECM by +120.

[Altostratus]

Interesting. GFS is showing a potential snow event on weds. Thickness and dew points are good but will the temperature be low enough? Looks like it might well be on this run. Something to keep an eye on anyway.

[Optimus Prime]

Looks to me like there's more high pressure coming out of the arctic?

[Iceberg]

Different angle to the southly Jet, more WAA further west, LP coming over the top of the HP and upto 5mb lower pressure between the UK and Denmark.

All very positive.

Snow in the Midlands and SW Tuesday night, then Wed Turning to snow again futhern North and flowing back again across the midlands and SW, later snow into the NE and East not bad for just the next 3 or 4 days.

[Geordiesnow]

Winds are more ENE on this run so you could argue it trended towards the ECM in that respect but the strength of the easterly is still quite weak.

It topples quickly aswell because of the low gaining further strength towards the North which may bring something colder from the North but regarding the easterly, you can't really say it's a snowfest unlike the ECM.

[SMU]

Looking at the 12z - It seems to be gearing up for more energy in the southern stream- hence the lower heights to the East & a better flow- however its being VERY VERY progressive on the Greenland jet V the 06z

this will be a better run- but the cold cuts off to soon- due to the abive reason-

Steve

Edited December 13, 2009 by Steve Murr

[Neilsouth]

The winds are still much slacker compared to the ecm/ukmo which is abit depressing.. As of yet no model agreement , would like to see stronger winds to filter that deep cold air across quickler and earlier!