Model output discussion - 1st December onwards

[Ali1977]

7 minutes ago, Hocus Pocus said:

Yet it's just as likely to verify as any other chart posted in FI.

I meant it's not BBQ weather, it may be about 13-14c....toasty, I might get my speedos on.

[knocker]

5 minutes ago, Newberryone said:

Were this to verify, would this not see temps above average with a far fetch southwesterly bringing something we've all become so very accustomed to by now, showers or longer spells of rain. 

It's all academic New as it has no chance of verifying along with the other charts post day 8.( just plucked that no out). I was merely trying to illustrate that there is no point in jumping up and down after one run, especially the way the outputs are wandering of late, particularly so far down the line. A quick look at the five day GEFS mean over the ten day period.

Chart weatherbell

 

[Summer Sun]

GFS 06z is a cold outlier when compare to the mean

[nick sussex]

Morning all

I see the GFS 06hrs run has come out with yet another different solution, I think the issue with that run is the strength of the southern arm of the jet and these southern stream lows are complicating matters.

In terms of the earlier 00hrs run no surprise to see the ECM 00hrs ditch last nights output in favour of yet another solution, this current run to run changes are expected when you have a complicated pattern.

We are however seeing some convergence in the shorter term, the agreed on signal is to develop a high pressure cell to the west.

So for comparisons:

UKMO  00hrs run T144hrs

ECM 00hrs run T144hrs

 

GFS 06hrs run T138hrs

 

I wouldn't look any further than T144hrs because where this high pressure cell ends up will be dictated by the pattern over the eastern USA.

To be honest the use of mean values far into FI when you have background chaos in the modelling is IMO illogical and will not give a true picture because within that are different clusters of solutions, and its obvious that theres large disagreements within the ensembles. The issue would be different if the mean was supporting the operational run but its clear that this is not the case. And especially when you have constant changes in FI from all the longer range operational outputs.

So I think its a case for the timebeing of waiting to see whats the definitive trend in the operational runs more especially from the GFS and ECM from T168hrs to T240hrs.

 

[Man With Beard]

Knocker - actually, this is nowhere near as mild as one of yesterday's GFS runs, which actually brought the 12C line to Cornwall under reasonably high pressure - now that could be barby weather.

I wouldn't actually be at all surprised if it happened. We've had so many ridiculously mild days in the past few weeks - 16C in sunshine yesterday was quite crazy. But when charts like this are showing just a few days earlier:

then it really is pot luck.

My hunch - as ECM had a comparable idea - it seems increasingly likely that low pressure will get under a ridge in the west Atlantic next week - this could lead to a whole host of options, but I would say a few genuinely cooler days are likely as a northerly element gets into the flow round the ridge. And after that - who knows but a re-set to mild of course is one of the possibilities.

[chrisbell-nottheweatherman]

13 minutes ago, nick sussex said:

To be honest the use of mean values far into FI when you have background chaos in the modelling is IMO illogical and will not give a true picture because within that are different clusters of solutions, and its obvious that theres large disagreements within the ensembles. The issue would be different if the mean was supporting the operational run but its clear that this is not the case. And especially when you have constant changes in FI from all the longer range operational outputs.

 

 

 

Though I cannot speak from any exprience meteorologically, if I might be arrogant for a moment, as a trained scientist, this is something that jumps-out at me.  Mean averages on their own, without standard deviations and statistical calculations of confidence intervals are not always helpful, in particular, as you say, when data is clustered rather than a more standard Gaussian distribution.

Edited December 8, 2015 by chrisbell-nottheweatherman

[Frosty.]

Nobody can rule out a wintry spell before christmas when we have charts like this from the GEFS 6z control run!

[Rocheydub]

4 minutes ago, Frosty. said:

Nobody can rule out a wintry spell before christmas when we have charts like this from the GEFS 6z control run!

OK, let's see how confident you are... Let's make a bet? I say that this chart will not verify, and I'm so confident, I'll give you 5-1 odds? 

Knowing my gambling history, You'll win the bet, and we'll both be happy! :-) 

[nick sussex]

2 minutes ago, chrisbell-nottheweatherman said:

 

Though I cannot speak from any exprience meteorologically, if I might be arrogant for a moment, as a trained scientist, this is something that jumps-out at me.  Mean averages on their own, without standard deviations and statistical calculations of confidence intervals are not always helpful, in particular, as you say, when data is clustered rather than a more standard Gaussian distribution.

You lost me at the Gaussian distribution! lol But have looked at that now and yes I agree. A mean by itself is pretty useless, especially because it can mute out what the different clustering is suggesting.  We often see this divergence between operational run and ensembles when theres a change in pattern, generally what happens is one backs down, so either the ensembles will move towards the operationals or the latter will move the other way. In strongly zonal patterns a slight tweak in starting conditions within the ensembles often makes little difference however in complex patterns things can go wrong.

We often see easterlies poorly modelled by the ensembles and these will be slow to come on board, every synoptic pattern needs to be viewed in a different way.

Generally if cold spells are suggested I view things as what can go wrong to decide on how many hurdles need to be jumped. For this reason any type of Scandi high scenario has a code red warning!

 

[Frosty.]

5 minutes ago, Rocheydub said:

OK, let's see how confident you are... Let's make a bet? I say that this chart will not verify, and I'm so confident, I'll give you 5-1 odds? 

Knowing my gambling history, You'll win the bet, and we'll both be happy! :-) 

I'm not into gambling, just banging the drum for all the coldies in response to those who don't believe or want any cold weather to visit the uk!

[Jeremy Shockey]

Well we have a chance Frosty if the Jet digs this far South ! Lets see if we can get a Greenland high forming in future runs.

[Rocheydub]

4 minutes ago, Frosty. said:

I'm not into gambling, just banging the drum for all the coldies in response to those who don't believe or want any cold weather to visit the uk!

 

4 minutes ago, Frosty. said:

 

Just kidding Frosty... But I would love a stats chart to see how many of those FI cold charts you post came to fruition...

Anyway, the WTF moment a couple of years back is something all us coldies will never forget!!!

Edited December 8, 2015 by Rocheydub

[chrisbell-nottheweatherman]

1 minute ago, nick sussex said:

You lost me at the Gaussian distribution! lol But have looked at that now and yes I agree. A mean by itself is pretty useless, especially because it can mute out what the different clustering is suggesting.  We often see this divergence between operational run and ensembles when theres a change in pattern, generally what happens is one backs down, so either the ensembles will move towards the operationals or the latter will move the other way. In strongly zonal patterns a slight tweak in starting conditions within the ensembles often makes little difference however in complex patterns things can go wrong.

We often see easterlies poorly modelled by the ensembles and these will be slow to come on board, every synoptic pattern needs to be viewed in a different way.

Generally if cold spells are suggested I view things as what can go wrong to decide on how many hurdles need to be jumped. For this reason any type of Scandi high scenario has a code red warning!

 

 

Thanks for providing the meteorological explanation on that, Nick - it helps me see the link between the basic side of it I already knew and the details of the current situation.  Presumably, your comments regarding ensemble means being more reliable in straightforward zonal set-ups is due to low Shannon entropy, whereas the expected pattern change and resulting high entropy/low confidence is likely to result in a greater spread within the ensembles and therefore the ensemble mean has to be treated with more caution?

[Rocheydub]

1 minute ago, chrisbell-nottheweatherman said:

 

Thanks for providing the meteorological explanation on that, Nick - it helps me see the link between the basic side of it I already knew and the details of the current situation.  Presumably, your comments regarding ensemble means being more reliable in straightforward zonal set-ups is due to low Shannon entropy, whereas the expected pattern change and resulting high entropy/low confidence is likely to result in a greater spread within the ensembles and therefore the ensemble mean has to be treated with more caution?

Absolutely spot on. When such a wide range and divergence on the cards, the mean is of no use.

[Ali1977]

I hope Ian F, Tamara, Snowbalz and all the other knowledgable types are still around, been a while since we've heard from them. Their input is vital if we are to know what is really happening weather wise.

[mountain shadow]

5 hours ago, Dr. Astro said:

Yea, nothing remotely cold on the horizon.

 

Of course my post was made before the ridiculous 6z ops run.

If that happens,  I will happily eat my hat whilst rolling naked in my snowdrift. 

[nick sussex]

1 minute ago, chrisbell-nottheweatherman said:

 

Thanks for providing the meteorological explanation on that, Nick - it helps me see the link between the basic side of it I already knew and the details of the current situation.  Presumably, your comments regarding ensemble means being more reliable in straightforward zonal set-ups is due to low Shannon entropy, whereas the expected pattern change and resulting high entropy/low confidence is likely to result in a greater spread within the ensembles and therefore the ensemble mean has to be treated with more caution?

Yes totally agree. Not sure how long you've followed the forum for but Scandi high scenarios have led to many bitter disappointments in here.

[JOPRO]

One mans Outlier is another mans trend setter...! Am sure the 12hrs will be different again, this time showing a beasterly........

[Rocheydub]

2 minutes ago, Ali1977 said:

I hope Ian F, Tamara, Snowbalz and all the other knowledgable types are still around, been a while since we've heard from them. Their input is vital if we are to know what is really happening weather wise.

Yes, they are very knowledgable, but there are plenty more in here that are just as good. The NWP shows what it does, a lot of that time, it keeps some people from posting as there is no real good news for coldies etc. Steve Murr was a classic example of that.

I'm here about 6 years now and have learned who's input to cherish. Nick, John, Steve, Stuart, Chiono to name a few. You won't go wrong with these guys if your preferred guys are not posting.

[Nick F]

Quite large surface difference between 00z ECM and 00z/06z GFS this weekend over the UK. EC has a ridge for us on Saturday before bringing rain in across the N and W on Sunday. However, 00z and 06z GFS bring a shallow low east across central parts, with some heavy rain with it affecting N England - which is obviously not good news:

00z GFS vs 00z EC for 12z Saturday (Weather Bell)

Similar to 00z the 06z GFS for Saturday

As Nick Sussex mentions, models perhaps differing in the way they are handling the split jet over the Atlantic from the weekend and beyond. So IMO best not to take too much literally beyond T+96 surface feature wise atm, though the general broad scale 500mb pattern in the medium range over the N Atlantic and Europe is not too dissimilar between GFS and EC op/det. and their ensemble means, with a mid-Atlantic trough becoming slow-moving and perhaps eventually cut-off, ridging near or over the UK and also over far NE Canada/Labrador - which may spread over southern Greenland as per 06z GFS

Interestingly, the 00z EPS control to day 15 day builds a big Scandinavia high with Atlantic trough digging beneath, so we could see some interesting changes ahead in the second half of December.

 

 

Edited December 8, 2015 by Nick F

[chrisbell-nottheweatherman]

12 minutes ago, nick sussex said:

Yes totally agree. Not sure how long you've followed the forum for but Scandi high scenarios have led to many bitter disappointments in here.

 

Long enough to remember a couple.

[Swave Snow]

35 minutes ago, Ali1977 said:

I hope Ian F, Tamara, Snowbalz and all the other knowledgable types are still around, been a while since we've heard from them. Their input is vital if we are to know what is really happening weather wise.

We have Nick Sussex, John Holmes , Chionomaniac, Steve Murr, Nick F not to mention a lot more on at the moment.

Edited December 8, 2015 by Swave Snow

[Mucka]

Just read through the comments and I have no idea why anyone would want to talk in absolutes with so much uncertainty in the output.

Clearly there is potential for a cold shot though currently any cold looks like being fairly short lived.

Still nothing has changed from a few days ago. We are heading into a more amplified pattern, ridge/trough/ridge in our vicinity, common sense tells us that will always give us a chance of dragging in colder air from time to time.

We are seeing quite a complex pattern set up across the Atlantic which makes forecasting for the UK fraught with difficulty - especially anything beyond 5 days. With the jet digging South there is scope for undercut of these ridges which could give cold and snow as winds temporarily switch to a N/NE flow. I say temporarily because the overall longwave pattern suggests too much forcing to maintain any blocking at the moment.

John gave a fair summary of what the anomaly charts show but others have misinterpreted this. It is frustrating because time and again it has been said what anomaly charts are good for and what they are not so good for. They are good for giving an overall indication of the likelihood of a blocking pattern setting up but poor for picking out details within the longwave pattern - especially in a situation as complex as this where there is wide divergence between ensembles and often the Op and control runs are at odds at anything beyond day 5-7. 

The reality is potential blocks have been repeatedly modeled across the output in the 7-10 day time-frame, only to break them down again. Within those patterns there is scope for something wintry before the pattern is overrun once more. No prolonged blocking, no prolonged cold, but enough for a decent chance of some lucky folk to see snow falling at least.

I'm not forecasting cold, there is no way to know how any temporary block may set up and it is all very fine margins. As an example take this mornings 00z which far from a bad run if you are not taking the charts as gospel and looking at the overall pattern. Shift the pattern a little West and tone down the forcing low 1% and you would have the UK flooded with very cold air from the North from around day 8/9. Previous to that it makes a weak attempt to build high pressure just to the North of the UK.

I mentioned a few days ago the set up looked like it could produce a cut off high somewhere just to the North of the UK and that still looks like it is very much on the table which COULD give us a cold shot (depending on latitude, persistence and orientation) before being overrun but it is by no means they only route to a cold shot in the 8 day+ time-frame.

If we don't get lucky then I hope people don't take that as proof we never had a chance of a cold shot because that is not what the model output is currently showing.

[Gavin Hannah]

Would happilly take the 06Z all the way to Xmas with the minor change to the last 48 hours of the output. Would like to see the HP cell rotate, around it's southern tip towards Scandi if it MUST move, rather than simply fade away...

 

Edited December 8, 2015 by Gavin Hannah

[northwestsnow]

On 12/5/2015 at 6:54 PM, Nouska said:

By the time this month is finished, I wonder just what staggering rainfall totals can be accumulated for Ireland and the north west of the UK.

That's up to another 20 cms forecast for the parts now under the most severe conditions.

How on earth do i stop this from happening!!!! Every time i want to post on the thread it keeps making me quote a post from days ago arrrghghgh