Model Output Discussion 18th Nov.2013-12z onwards.

[Cheshire Freeze]

The change all stems from differences in the modelling of the Pacific HP in the earlier stages of the run. The more amplitude that is gained and thus WAA sent towards the middle Arctic, the less PV energy will be left where we don't want it come crunch time i.e Canada/Greenland locale.

 

Hard frosts and temps struggling around freezing by day at days 10 and 11 on the ECM however...so still seasonal. The NH profile still looks interesting too with perhaps further amplification beyond due to persistence of the Pacific ridging.

Edited November 27, 2013 by CreweCold

[nick sussex]

The ECM finally gets there but it looks fraught with complications, low pressure in the eastern USA is waiting Scroogelike to dart across and spoil the party. The pattern isn't sufficiently amplified. However in terms of where the PV should start heading in the outlook this looks more inline with the background signals.

 

If things go right you can have a northerly and east/ne flow because as the PV heads back west to Canada the ridge will topple but you need this further north initially.What could get interesting is if the ridge topples the PV heads west but you retain some amplification upstream because this could help carve more sharpness ahead of it and you might get some energy heading se.

 

Having said all this it could all end in tears even without a northerly if we don't see enough amplification over the eastern USA. The juries still out on a colder snap because as we've seen the ECM is wildly different from its 00hrs run especially in terms of what it does with the PV, the GFS disagrees on phasing of a lobe of vorticity heading west out of the Arctic which phases with shortwave energy crossing the USA, it does this, the ECM doesn't and the UKMO at 144hrs also looks uninterested.

 

It's all a bit of a messy picture, its not a typical northerly toppler scenario, lots of  bumps in the road and the odd cliff to get over, or sadly as the case might be fall over!

 

Still a lot of uncertainty going forward, whats new, its always the same when theres a chance of cold for the UK!

[terrier]

Well their we have it a short sharp northerly blast on the ECM tonight. Now I know gibby has come in for abit of stick today. But I must admit I'm leaning more towards his couple of days cold blast before a return to what we are seeing at the moment. I may be wrong but I can't see any substantial long lasting cold in any of the model output bar a odd few days at the moment.

[Cheshire Freeze]

The ECM finally gets there but it looks fraught with complications, low pressure in the eastern USA is waiting Scroogelike to dart across and spoil the party. The pattern isn't sufficiently amplified. However in terms of where the PV should start heading in the outlook this looks more inline with the background signals.

 

If things go right you can have a northerly and east/ne flow because as the PV heads back west to Canada the ridge will topple but you need this further north initially.What could get interesting is if the ridge topples the PV heads west but you retain some amplification upstream because this could help carve more sharpness ahead of it and you might get some energy heading se.

 

Having said all this it could all end in tears even without a northerly if we don't see enough amplification over the eastern USA. The juries still out on a colder snap because as we've seen the ECM is wildly different from its 00hrs run especially in terms of what it does with the PV, the GFS disagrees on phasing of a lobe of vorticity heading west out of the Arctic which phases with shortwave energy crossing the USA, it does this, the ECM doesn't and the UKMO at 144hrs also looks uninterested.

 

It's all a bit of a messy picture, its not a typical northerly toppler scenario, lots of  bumps in the road and the odd cliff to get over, or sadly as the case might be fall over!

 

Still a lot of uncertainty going forward, whats new, its always the same when theres a chance of cold for the UK!

 

A fair assessment there Nick. I suspect we'll begin to see these N'ly scenarios become more and more pronounced as we head through December. Perhaps a N'ly,W'ly, N'ly pattern setting up if amplification allows.

[Captain Shortwave]

A fair assessment there Nick. I suspect we'll begin to see these N'ly scenarios become more and more pronounced as we head through December. Perhaps a N'ly,W'ly, N'ly pattern setting up if amplification allows.

Pretty much sums the ECM up, the low south of Greenland is only going one way for instance, rolling over the high near the UK, that high retrogresses west with another north/north westerly developing.

Nerve shredding days ahead. I never want a run going near what the GEM showed because that looks likely to leave us with virtually nothing cold wise. Luckily it's the GEM and has probably gone off on one 

Edited November 27, 2013 by Captain shortwave

[Cheshire Freeze]

Well their we have it a short sharp northerly blast on the ECM tonight. Now I know gibby has come in for abit of stick today. But I must admit I'm leaning more towards his couple of days cold blast before a return to what we are seeing at the moment. I may be wrong but I can't see any substantial long lasting cold in any of the model output bar a odd few days at the moment.

 

The thing is that what we have at present isn't sustainable. It's nothing more than a holding pattern. The polar vortex can't settle to due to ridging and repeat bouts of WAA across the other side of the hemisphere. One way or another a pattern change will be completed within the next 2-3 weeks for better or for worse.....(I've nailed my colours to the mast on that one already).

Edited November 27, 2013 by CreweCold

[nick sussex]

A fair assessment there Nick. I suspect we'll begin to see these N'ly scenarios become more and more pronounced as we head through December. Perhaps a N'ly,W'ly, N'ly pattern setting up if amplification allows.

Thanks, well I'm greedy and as its nearing Xmas I want to see a northerly then east/ne flow on the southern flank of the high as it topples! This is possible especially if you look at the ECM 240hrs.

 

What happens if as the PV heads west to Canada and meets up with some amplification, that should develop a deep low and if you look at the low to the west of the UK, that would sharpen in response to an upstream negatively tilted low, sending energy se but the crucial part is the high is further north beforehand.

 

I'll be interested to see the Dutch ensembles tonight to see how many develop an easterly, anyway I shouldn't overplay this scenario because it could go pear shaped easily before we even get a possible northerly.

[Ian Brown]

The thing is that what we have at present isn't sustainable. It's nothing more than a holding pattern. The polar vortex can't settle to due to ridging and repeat bouts of WAA across the other side of the hemisphere. One way or another a pattern change will be completed within the next 2-3 weeks for better or for worse.....(I've nailed my colours to the mast on that one already).

 

I would disagree, I would think any northerly next week will be the last such cold shot for some time, we have a poor set-up but have avoided full on zonality for a couple of weeks through low heights over Europe and some amplification in the Pacific. You would bet against that sustaining and as someone said earlier 'the big purple blob' should soon be settled over Southern Greenland with the attendant height rise over Europe.

[Frosty.]

Looks like snow towards the end of next week, could be a prolonged cold spell or at least below average temps for the next 4 weeks if the met office are right...:-)

[Paul]

Netweather winter forecast now online:

 

http://forum.netweather.tv/topic/78606-netweather-winter-forecast-2013/

[ANYWEATHER]

As for the Northerly toppler on Friday ,forget any wintry stuff unless youre on high ground especially for North eastern Britain. The weekend will see pressure rising so with the usual caveats of frost and fog.T+186 hrs from both models show a pivitol point which has been showing a fair few days now with a big surge of very cold air flowing to the the Uk from Greenland [rpm air]  This synoptic situation wont provide widespread snow, but Looking at the models we could well see some stormy weather developing from this, so some interesting weather from a week now,, I know, a long way off, but certainly something to keep and eye on!.....The ecm and gfs do often differ from the progression from the North Atlantic, Gfs is to progressive, Ecm is to slow to invovle the Atlantic...

[nick sussex]

I would disagree, I would think any northerly next week will be the last such cold shot for some time, we have a poor set-up but have avoided full on zonality for a couple of weeks through low heights over Europe and some amplification in the Pacific. You would bet against that sustaining and as someone said earlier 'the big purple blob' should soon be settled over Southern Greenland with the attendant height rise over Europe.

if the set up was so poor those low heights over southern Europe would have left the scene already, whats been unusual in a sense is that the PV still hasn't settled over Greenland and seems to want to keep on the move. In terms of what comes after any colder shot we've seen that 'big purple blob' before over Greenland but still seen cold in the UK, if the blob doesn't settle over southern Greenland but further north we can still see some colder conditions with an easterly.

 

I think the juries still out Ian regarding what happens to the PV, it depends on whether the models take the whole blob to Canada, or whether they leave some further east.

[winter snow]

ian brown and some others you are really getting people cross for our coldies. you keep saying theres going be no northley when there is and I think we will have 6 days or more off cold snowley weather from late next week. your just doing it to wind people up which isit fair mate. it needs to stop this winding up thing. if you like mild go to Africa or somewhere as we not going to be that mild till may now. yes we have some mild days but u seem to want it every day. its nearly winter cold cold all the way. sorry mods if I have come across abit funny but its upset me ian brown and shedhead and happy days keep say no about colder weather coming when its likely too.

[UV-RAY]

I would disagree, I would think any northerly next week will be the last such cold shot for some time, we have a poor set-up but have avoided full on zonality for a couple of weeks through low heights over Europe and some amplification in the Pacific. You would bet against that sustaining and as someone said earlier 'the big purple blob' should soon be settled over Southern Greenland with the attendant height rise over Europe.

Ian you've been singing from the same hymn sheet for the last few weeks but we have still yet to see full on zonality. I think your analysis is made with preconceived ideas pre 2009, of course you could be right and we may end up under  a long fetch from the Atlantic with the PV anchored over it's favourite location. As ever with these situations time will tell.

[nick sussex]

ian brown and some others you are really getting people cross for our coldies. you keep saying theres going be no northley when there is and I think we will have 6 days or more off cold snowley weather from late next week. your just doing it to wind people up which isit fair mate. it needs to stop this winding up thing. if you like mild go to Africa or somewhere as we not going to be that mild till may now. yes we have some mild days but u seem to want it every day. its nearly winter cold cold all the way. sorry mods if I have come across abit funny but its upset me ian brown and shedhead and happy days keep say no about colder weather coming when its likely too.

In defense of Ian who as people know I've had my share of run ins with he's not a mildie and neither are Shed or HD, they all like the cold and snow. I love the cold and snow but equally I'd say don't bank on a northerly yet, its a complex set up to get there. If the northerly was shown within T144hrs that would be a different story. It's good that this thread doesn't paint an overly rosy picture of the way forward in terms of snow and cold as this can snowball out of control and before you know it theres a stampede at the local sledge shop!

[Paul_1978]

I must admit I'm struggling to get excited over a 2 day northerly or whatever it is. For me decent cold weather will have some sort of longevity.

[winter snow]

fair enough but its true what iam saying

[MR EXTREMES]

ian brown and some others you are really getting people cross for our coldies. you keep saying theres going be no northley when there is and I think we will have 6 days or more off cold snowley weather from late next week. your just doing it to wind people up which isit fair mate. it needs to stop this winding up thing. if you like mild go to Africa or somewhere as we not going to be that mild till may now. yes we have some mild days but u seem to want it every day. its nearly winter cold cold all the way. sorry mods if I have come across abit funny but its upset me ian brown and shedhead and happy days keep say no about colder weather coming when its likely too.

I think Ian has given a very fair assessment although I don't think it will be above average but certainly average and only favored locations will feel the true extent of any cold shot.And my love affair with the vortex still is ongoing this vortex is unlikely to shift for anything to memorable.And still all way out into fi and no cross model agreement.

[Summer Sun]

Latest from Gibby on the 12z models

 

All models show a large High pressure area close to SW Britain and a mild and moist but light cloud laden NW flow over the UK. This pattern remains for another 36hrs or so with just very weak fronts injecting a little more moisture into the atmosphere at times with a little drizzle. On Friday fresher and chillier NW winds blow down over the UK as the High moves a little further away West briefly allowing some showers to occur, perhaps wintry on Northern hills for a time. By Saturday the bright and fresh weather will slowly become eroded from the West by milder Atlantic air, toppling back down over the UK with High pressure close to Southern Britain. As we start next week the High pressure slowly recedes away South or SE but maintaining a ridge across the UK well into the middle of next week maintaining dry and rather cloudy weather with temperatures close to average for many with only limited amounts of fog and frost by night should skies clear.

 

GFS then shows Westerly winds steadily increasing later next week with some rain gradually winding it's way South across the UK reaching the South later on Thursday or early Friday with very much colder and brighter weather following down with wintry showers and strong winds giving some very wintry conditions over northern high ground for a time and even some wintriness in the showers over the South too for a while. Over the weekend conditions moderate for many but it would stay cold with a disturbance as shown bringing rain across the South a week on Sunday and some snowfall in the North before this shifts away SE as pressure builds strongly from the West later. Initially this could mean some very sharp frosts for a few nights early in the second week before an inversion develops with an infill of cloud setting up a cloudy and benign pattern to end the run with the mildness returning to the North in Westerly winds while High pressure remains straddled across the South.

 

UKMO tonight shows High pressure in mid Atlantic with a ridge extending East over the UK with quiet and benign weather continuing at this stage with a lot of cloud, largely dry weather and temperatures close to average.

 

GEM tonight shows a trough bringing a spell of rain SE across the UK next Wednesday followed by another surge of High pressure transferring slowly SE across Southern Britain and away to the SE towards the end of the run. A deep and slow moving Low pressure well North of Scotland sends some rain and strong winds across Northern Britain. A weakening band of rain on a cold front then swings SE across Britain followed by colder weather with wintry showers across the North but mostly dry weather further South.

 

NAVGEM shows a weakening front too moving SE over Britain next week with some rain for a time before clearer and fresher weather moves in behind followed by more unsettled and windy weather reaching the NW later.

 

ECM tonight shows a cold front running South again late next week with a short spell of rain followed by some wintry showers, more especially in the North and East, heavy briefly. Quickly following is another major rise of pressure with the UK returning to dry and benign conditions with frost and fog prior to milder air toppling back into the NW soon after Day 10.

 

The GFS Ensembles show a change to colder conditions soon after midweek next week with a 3-4 day colder interlude before things recover to average levels. It is unlikely that any major snow events will occur over the South with most of any wintry action reserved for more Northern areas before things revert to milder weather towards the end of the run from most members.

 

The Jet Stream flow shows it's axis carrying it well to the North of the UK around the Northern flank of High pressure to the SW of the UK. This persists for the reliable part of the output tonight before in the less reliable period it shows signs of migrating South across Britain, then resetting across Britain from the West. In the far reaches of the run it then is shown to extend back North across the Atlantic towards Greenland and Iceland.

 

In Summary tonight the weather remain very static over the coming 7 days. Beyond that things do turn more interesting for a while as a cold plunge of Arctic air moves down across the UK from the North. There is a strong risk of snowfall over the North for several days mostly in the form of showers while the South is generally unlikely to see anything exciting before fine weather returns in association with more Atlantic High pressure. After some frosty nights towards the end of the second week it looks like milder Atlantic air with High pressure close to the South looks the most likely end result.

 

http://www.norton-radstockweather.co.uk/Model-Analysis%282859336%29.htm

[cooling climate]

I would not trust the NCEP map room charts at the present time. The last 2 or 3 days they

have been showing a strong American mountain torque with a similar rise in global torque

where as tonight there is no sign of either. Can anyone shed any more light on this.

 

The models still dithering about how much amplification there is likely to be over Canada

and into the Arctic from Pacific heights over Alaska and northwest Canada.

I think we are in with a good chance in seeing  a fairly substantial northerly outbreak but

the longevity is still to be decided.

[bobbydog]

In defense of Ian who as people know I've had my share of run ins with he's not a mildie and neither are Shed or HD, they all like the cold and snow. I love the cold and snow but equally I'd say don't bank on a northerly yet, its a complex set up to get there. If the northerly was shown within T144hrs that would be a different story. It's good that this thread doesn't paint an overly rosy picture of the way forward in terms of snow and cold as this can snowball out of control and before you know it theres a stampede at the local sledge shop!

 

ok, lets hold off on the sledges.... for now.... i've just (out of curiosity) gone through the daily archives for december 1962.

now, i don't want to get anyones hopes up but i couldnt help noticing how uncannily similar the n. hemispheric charts are to what we are experiencing now and what is forecast in the models.

 

i could be looking at them through rose-tinted snow-goggles but i would urge anyone to have a look and compare- http://www.meteociel.fr/modeles/archives/archives.php?day=20&month=12&year=1962&hour=12&map=5&mode=0

even if its just to tell me i'm being silly.

 

or.... am i.....?

[terrier]

Another good summary by gibby. As a newby i find his updates very helpful. And by what im reading some snow for the north.Then it does sound like we will be back to milder atlantic air for the foreseable future after this cold blast. Thanks for the updates gibby.

[SnowBallz]

Re: missing data on the Gfs 06 op run I'm afraid I'd have to refer you to one of the more experienced and knowledgeable members on this forum in order to give you a comprehensive answer. However, you must admit this is not the first time this has been stated about this particular run. I can honestly say hardly a day goes by that this whole "lack of data issue" isn't brought up by someone or other.

 

Hi,

 

The idea that runs should only be compared relative to the previous output (0z to 0z, 12z to 12z) due to infinitesimally small (magnitudes of 10th/%) idiosyncrasies in data, doesn't stack up. Even if there were data blind spots (often happens) you either run algorithms to blend and normalise it, or you back-fill with prior cleansed 'control' data. The overriding error correction is the updated observational data, which is the precursor to every initialisation.Therein, to discount any run even though it contains perhaps 98% of all operational data, is not advisable. I could sympathise with such a view if such data blind spots brought the scope down to <85-90%, but that simply isn't the case. I often find intra-run variance to be, in the main, anecdotal; for example, verification against the GFS suite (0z, 6z, 12z, 18z) doesn't actually tend to favour any one particular initialisation - they all have, more or less, periods of better performance over each other - which, to be fair, is exactly what you'd expect from a stochastic model.

 

The matter of data density is only a considerable factor when a critical mass is breached insofar as there is a lack of initialisation variables.  For that to happen, there would need to be a serious lack of data (balloons, buoys, aircraft, nautical) and it's very unlikely that would ever happen.  I'm not sure what the operational parameters are to initialise GFS, but ECM is >= 98.25%.  To give context around that, I think I've read in papers that the average over the last three years is about 99.6%.  So, it's a very stable base state model.  I think it dropped to just below 99% when there was disruption to air traffic post eruption of Eyjafjallajokull.

 

So to surmise, yes some runs lack data relative to others, but it's proportionate weight against that of the depth is what matters.  Equally, any such data gaps can be and often are rendered over with algorithms, to help with calculation smoothing.  You tend to get a value spat out at the end of an initialisation which will evaluate confidence in the starting parameter values, and if that's within a tolerance then you can generally have confidence in the run.  I know that's how the developers parse layer code into the stack, and judge its consequential effect.

 

Hope that helps,

 

SB

[UV-RAY]

Hi,

 

The idea that runs should only be compared relative to the previous output (0z to 0z, 12z to 12z) due to infinitesimally small (magnitudes of 10th/%) idiosyncrasies in data, doesn't stack up. Even if there were data blind spots (often happens) you either run algorithms to blend and normalise it, or you back-fill with prior cleansed 'control' data. The overriding error correction is the updated observational data, which is the precursor to every initialisation.Therein, to discount any run even though it contains perhaps 98% of all operational data, is not advisable. I could sympathise with such a view if such data blind spots brought the scope down to <85-90%, but that simply isn't the case. I often find intra-run variance to be, in the main, anecdotal; for example, verification against the GFS suite (0z, 6z, 12z, 18z) doesn't actually tend to favour any one particular initialisation - they all have, more or less, periods of better performance over each other - which, to be fair, is exactly what you'd expect from a stochastic model.

 

The matter of data density is only a considerable factor when a critical mass is breached insofar as there is a lack of initialisation variables.  For that to happen, there would need to be a serious lack of data (balloons, buoys, aircraft, nautical) and it's very unlikely that would ever happen.  I'm not sure what the operational parameters are to initialise GFS, but ECM is >= 98.25%.  To give context around that, I think I've read in papers that the average over the last three years is about 99.6%.  So, it's a very stable base state model.  I think it dropped to just below 99% when there was disruption to air traffic post eruption of Eyjafjallajokull.

 

So to surmise, yes some runs lack data relative to others, but it's proportionate weight against that of the depth is what matters.  Equally, any such data gaps can be and often are rendered over with algorithms, to help with calculation smoothing.  You tend to get a value spat out at the end of an initialisation which will evaluate confidence in the starting parameter values, and if that's within a tolerance then you can generally have confidence in the run.  I know that's how the developers parse layer code into the stack, and judge its consequential effect.

 

Hope that helps,

 

SB

I had to read this three times before it sunk in, well I think it sunk in.

[ANYWEATHER]

Hi Frosty, just wondering where the "prolonged" cold spell is coming for 4 weeks. Please show me the charts, because there not on my Laptop!!