Winter Model Discussion 18Z 3/2/13 onwards.

[BLAST FROM THE PAST]

I would call cool = Average.

Very mild - +9c

Mild - +6-+9c

Cool + 4-+6c

Cold +2- +4c

Very Cold sub 2c.

ice day sub zero!

Indeed

BFTP

[Frosty.]

Indeed

BFTP

Can't argue with that, this week is cool

[Jason M]

Massive no to any easterly on the 06z, although does maintain a cool cyclonic theme.

I know some don't have faith in the 06z, but it's so far away from the ECM it's unreal.

Still a lot to resolve imho

I wouldnt pay too much attention to the Opp run in FI. I think from say day 7 onwards it is more looking at the ensemble suite to see what level of support is being given to ECM. I suspect SM has called correctly re the pattern and that was a top post earlier from him re surface conditions.

[Panayiotis]

06z ensembles are tasty at 240hrs, I can only see 3 bad ones with the others showing GH(northerly) and easterly..

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

[Troubleatmill]

06z ensembles are tasty at 240hrs, I can only see 3 bad ones with the others showing GH(northerly) and easterly..

http://www.meteociel...&mode=1&ech=240

errr i dont see that? i see a bit of everything but nothing amazing?

[Paul_1978]

We only pay attention to the GFS because it comes out 4 times in 24 hours, ie more frequently than the other models, and we are all eager for our next model fix.

But we have seen that the output is often very iffy indeed, and every 6 hours we have the same conversations.

After the way it's performed this winter, I don't pay any attention to it whatsoever any more. It's ECM all the way for me guys and gals, then UKMO and JMA.

GFS is now firmly in the cannon fodder section for me.

[Tamara]

ECM Ensembles out

As expected quite a bit of divergence after next weekend although the majority stay cold. This is evidence by the ensemble means

<-8 for many eastern and central areas at 168

Still below -6 at 192

That is a significant indication in itself of just how far the ECM journey has come over the last few days. Seven outputs of remarkable consistency and it is beyond dispute that the model has been leading the forward pattern with the other models, up to now, adjusting accordingly. My question would remain the same as the weekend - is it a case of the other models underestimating the amplification of the pattern (and therefore the 'consensus' forecasting outlook) whilst the ECM is gauging this much better upstream? At least to this time. And this is still rolling at the time of typing...

The UKMO remains very fractionally further east of the ECM at t120 to t144, but then it was very fractionally east last night at the same time period last night and has adjusted itself accordingly further west since then. Maybe the model down the middle between the ECM and the eastward bias influenced GFS is itself making very very slight incremental westward adjustments to the ECM?

Will the process continue this evening, or at ECM output number eight will the adjustment hit the point where consensus arrives? I'm no expert forecaster obviously, but I wouldn't bet against this edging into tomorrow before that final adjustment stops. And the GFS may well ensure it takes longer than that as it doesn't do wholesale changes when and if it caves in.

ECM Postage stamps show up to at least 30 at t168 that have an easterly or north easterly with the sliding trough to the south of the UK. Several further have high pressure to the north and the trough over the south of the UK and then a very small minority have the cold air pushed to the east

http://www.ecmwf.int...0400!!chart.gif

Edited February 4, 2013 by Tamara Road

[cornish snow]

While it's a bit quieter here,i'll ask a question i asked a few days ago.

Being a newbie when it comes to the models, how is it that the really cold air in the northern hemisphere always seems to be the other side of the atlantic.

If you look at the hudson bay/newfoundland area,it's nearly allways far colder than say the north scandi siberia area.

Why is this? they both share similar latitudes and are large land masses.

I've got a hunch it might have something to do with the pv which seems to reside there most of the time.(this could be totally wrong though)

[MR EXTREMES]

well ukmo are going with there idears so must be taking note of other models large uncertainties though.

UK Outlook for Tuesday 19 Feb 2013 to Tuesday 5 Mar 2013:

There are large uncertainties at this forecast range. Conditions will most likely start with temperatures close to or a little below average, with fairly typical winter weather across much of the UK. There are signs that a slightly colder spell may then prevail throughout much of the rest of the period, with more widespread overnight frosts.

Issued at: 0400 on Mon 4 Feb 2013

[Yarmy]

While it's a bit quieter here,i'll ask a question i asked a few days ago.

Being a newbie when it comes to the models, how is it that the really cold air in the northern hemisphere always seems to be the other side of the atlantic.

If you look at the hudson bay/newfoundland area,it's nearly allways far colder than say the north scandi siberia area.

Why is this? they both share similar latitudes and are large land masses.

I've got a hunch it might have something to do with the pv which seems to reside there most of the time.(this could be totally wrong though)

http://en.wikipedia.org/wiki/Thermohaline_circulation

[Weathizard]

While it's a bit quieter here,i'll ask a question i asked a few days ago.

Being a newbie when it comes to the models, how is it that the really cold air in the northern hemisphere always seems to be the other side of the atlantic.

If you look at the hudson bay/newfoundland area,it's nearly allways far colder than say the north scandi siberia area.

Why is this? they both share similar latitudes and are large land masses.

I've got a hunch it might have something to do with the pv which seems to reside there most of the time.(this could be totally wrong though)

My answer would be as it has a nice area of warmer water to thrive over, the vortex is most commonly located around there because if I'm not mistaken the Jet deflects most things that attempt to disrupt it here and it tends to build in strength with cold air embedded and warmer sea with warmer/cooler currents prevalent and mixing Apologies if I'm wrong but that has always been my understanding of why the Vortex often takes up shop here.

Edited February 4, 2013 by Weathizard

[Jason M]

While it's a bit quieter here,i'll ask a question i asked a few days ago.

Being a newbie when it comes to the models, how is it that the really cold air in the northern hemisphere always seems to be the other side of the atlantic.

If you look at the hudson bay/newfoundland area,it's nearly allways far colder than say the north scandi siberia area.

Why is this? they both share similar latitudes and are large land masses.

I've got a hunch it might have something to do with the pv which seems to reside there most of the time.(this could be totally wrong though)

There are three factors at play here.

1. Prevailing wind in N hemisphere is west to east as we all know, the areas you quote are on the eastern side of a large land mass therefore will tend to be colder in winter than Scandi with its prevailing onshore winds.

2. Sea currents are a big influence as even allowing for point 1, NW Europe is significantly warmed by the gulf stream

3. Rossby waves (from memory I think this is correct but happy for GP, Chionio to correct), whereby the rockies deflect the jet stream tending to give SW winds across UK and NW Europe.

Jason

[cornish snow]

http://en.wikipedia....ine_circulation

Thanks for that Yarmy.

So in a nutshell,it's all down to the gulf stream.

Didn't realise it's effects whent so far north and east

[SomeLikeItHot]

well ukmo are going with there idears so must be taking note of other models large uncertainties though.

UK Outlook for Tuesday 19 Feb 2013 to Tuesday 5 Mar 2013:

There are large uncertainties at this forecast range. Conditions will most likely start with temperatures close to or a little below average, with fairly typical winter weather across much of the UK. There are signs that a slightly colder spell may then prevail throughout much of the rest of the period, with more widespread overnight frosts.

Issued at: 0400 on Mon 4 Feb 2013

19th of Feb is of course well past the end of the ECM 240 hour run. And yes there is huge uncertainties out past 15days.

The main differences at this point between GFS and ECM are +120 hours. Relevant part of the UKMO guidance with regard this is

UK Outlook for Saturday 9 Feb 2013 to Monday 18 Feb 2013:

Most areas remaining on the cold side this weekend. Some bright spells for many areas, but also some wintry showers in some North Sea coastal areas. Meanwhile parts of western and southwestern UK are likely to be cloudier with some rain, sleet and hill snow, especially later this weekend. Then, next week western parts of the UK are likely to continue to see spells of cloudier weather with rain, hill snow and, perhaps, some snow temporarily to lower levels. Elsewhere conditions will tend to be colder and brighter, though some parts may catch a few wintry showers. Looking ahead to the weekend after next and the start of the following week, conditions most likely to be a little colder than average, with northwestern parts most at risk of unsettled weather.

Edited February 4, 2013 by SomeLikeItHot

[cornish snow]

There are three factors at play here.

1. Prevailing wind in N hemisphere is west to east as we all know, the areas you quote are on the eastern side of a large land mass therefore will tend to be colder in winter than Scandi with its prevailing onshore winds.

2. Sea currents are a big influence as even allowing for point 1, NW Europe is significantly warmed by the gulf stream

3. Rossby waves (from memory I think this is correct but happy for GP, Chionio to correct), whereby the rockies deflect the jet stream tending to give SW winds across UK and NW Europe.

Jason

Yeah,all seems obvious when you put it in simple points.

Feel a bit silly for asking the question now, but thankyou anyway. I've learnt something today.

[Yarmy]

Thanks for that Yarmy.

So in a nutshell,it's all down to the gulf stream.

Didn't realise it's effects whent so far north and east

Mainly, but read Jason's post above for a more detailed (and better!) breakdown.

[Tim Bland]

We only pay attention to the GFS because it comes out 4 times in 24 hours, ie more frequently than the other models, and we are all eager for our next model fix.

But we have seen that the output is often very iffy indeed, and every 6 hours we have the same conversations.

After the way it's performed this winter, I don't pay any attention to it whatsoever any more. It's ECM all the way for me guys and gals, then UKMO and JMA.

GFS is now firmly in the cannon fodder section for me.

Can never understand how model performance is subjective and based on opinions ?!? We have verification stats which mathematicaly and scinetificaly proove which are the best models. Over the past few days the top model has switched between UKMO / ECM / GFS so they are all very close. JMA is getting better but very rarely in the top 3.

ECM looks like it will gradualy water down its bitter cold easterly (by looking at its ensembles) whilst GFS has moved towards the ECM. IMO we are going to see a middle ground. This means nothing record breaking in terms of cold but ofen cold enough for snow. We meandder either side of the PFJ and troughs from the west disrupt over us and occasionaly undercut. I'm often as guilty as others in thnking one model is right and one is wrong but usualy we see a middle ground and this, IMO is what we will see emerge in the next couple of days. Still very good for the UK with marginal snow on and off for a couple of weeks

Edited February 4, 2013 by Tim Bland

[Tamara]

Can never understand how model performance is subjective and based on opinions ?!? We have verification stats which mathematicaly and scinetificaly proove which are the best models. Over the past few days the top model has switched between UKMO / ECM / GFS so they are all very close. JMA is getting better but very rarely in the top 3.

ECM looks like it will gradualy water down its bitter cold easterly (by looking at its ensembles) whilst GFS has moved towards the ECM. IMO we are going to see a middle ground. This means nothing record breaking in terms of cold but ofen cold enough for snow. We meandder either side of the PFJ and troughs from the west disrupt over us and occasionaly undercut. I'm often as guilty as others in thnking one model is right and one is wrong but usualy we see a middle ground and this, IMO is what we will see emerge in the next couple of days. Still very good for the UK with marginal snow on and off for a couple of weeks

It's interesting how we all view things differently I think that the ECM operational has been leading its ensembles and other models in the direction of the trough disruption indicated possibly for Sunday as well as the easterly that follows. Its ensembles to me, rather than water down any colder trend, have been largely following (up to now) the trend set by the operational. If that hadn't been the case then it would have been impossible for the ECM to produce the same replica idea and evolution for so many consecutive outputs by now. Whether we get the sliding trough and consequent easterly, as exactly per the ECM, still needs to be seen for sure - but barely two days ago if the GFS had been right we would not have even got to the stage where a slider low was being modelled at all. The GFS had the pattern and flat Azores High already modelled out for the end of the week. Where are we now with this?

[Blizzardof82]

Yeah,all seems obvious when you put it in simple points.

Feel a bit silly for asking the question now, but thankyou anyway. I've learnt something today.

The only stupid question is the one that is never asked, by you asking that I have learnt something.

[Timmytour]

For me, the inconsistency of the GFS is what give it plausability (assuming there to be such a word)

There are so many factors that come into play when it comes to delivering to the UK a cold spell, so many of them which will always be on a knife-edge, that one almost expects and understands the variety of solutions put forward in so many runs and therefore goes for the trend rather than the results of any one individual run.

I really want the ECM outcome, I really do. But I'm actually suspicious of how rock-solid it's been at delivering the goods time after time. In the end, it's not consistency that matters but ending up getting it right, whatever solution you eventually decide upon.

I don't dismiss the idea that the ECM could prove to have been right all along. But I do doubt it.

Edited February 4, 2013 by Timmytour

[Tim Bland]

It's interesting how we all view things differently I think that the ECM operational has been leading its ensembles and other models in the direction of the trough disruption indicated possibly for Sunday as well as the easterly that follows. Its ensembles to me, rather than water down any colder trend, have been largely following (up to now) the trend set by the operational. If that hadn't been the case then it would have been impossible for the ECM to produce the same replica idea and evolution for so many consecutive outputs by now. Whether we get the sliding trough and consequent easterly, as exactly per the ECM, still needs to be seen for sure - but barely two days ago if the GFS had been right we would not have even got to the stage where a slider low was being modelled at all. The GFS had the pattern and flat Azores High already modelled out for the end of the week. Where are we now with this?

You have made some good points and as you say we all view things differently.. The ECM OP was on the Cold side of its ensembles http://forum.netweat...ttach_id=159019

which probably suggests to me that we will see the Op get slightly watered down over the coming runs. We have already seen the ECM turn more messy and start to back of its channel low with long drawn Easterlys & Sub zero days.

The GFS Ensembles show The OP to be on the mild side http://www.netweathe...s;type=ens;sess=

Which suggests that future runs are likely to be colder Ie more undercuting / Easterly influence.

Hence why i come to the conclusion that the 2 are likely to meet in the middle somwhere and we may see a slack easterly flow with tough disrution over us and marginal snow.

You notice I use the words "probably" and "likely" allot ... this is becuase nothing i set in stone when it comes to the weather and all the models and ensembles "Could" be wrong lol This is why I enjoy the debate and its interesting to see how other people percieve things.

Edited February 4, 2013 by Tim Bland

[SomeLikeItHot]

Can never understand how model performance is subjective and based on opinions ?!? We have verification stats which mathematicaly and scinetificaly proove which are the best models. Over the past few days the top model has switched between UKMO / ECM / GFS so they are all very close. JMA is getting better but very rarely in the top 3.

We don't mathematically and scientifically prove the best model by looking at what happened in a measure over a few days, but by long term stats, and the ECM consistently has beaten GFS over the years.

What about the 5 & 6 days stats though, which is probably where there are real and significant divergences at the moment (and have vastly better confidence) here the ECM is better.

[Tamara]

You have made some good points and as you say we all view things differently.. The ECM OP was on the Cold side of its ensembles http://forum.netweat...ttach_id=159019

which probably suggests to me that we will see the Op get slightly watered down over the coming runs. We have already seen the ECM turn more messy and back of its long drawn Easterlys with Sub zero days.

The GFS Ensembles show The OP to be on the mild side http://www.netweathe...s;type=ens;sess=

Which suggests that future rund will be colder.

Hence why i come to the conclusion that the 2 are likely to meet in the middle somwhere and we may see a slack easterly flow with tough disrution over us and marginal snow.

You notice I use the words "probably" and "likely" allot ... this is becuase nothing i set in stone when it comes to the weather and all the models and ensembles "Could" be wrong lol This is why I enjoy the debate and its interesting to see how other people percieve things.

I agree it very often happens that the middle path is reached as a consensus between two 'extremes' of ideas . With the current pattern evolution however, the ECM has actually had its operational on the cold(er) side of its ensembles for a large part (not all) of the last two to three days and rather than water down its suggestions, it has done the opposite and upgraded them. And it has imo undoubtably been leading the overall direction colder over that time. The question is, how long is that sustained/sustainable?

Either there is final full agreement to the cold trend (disrupted trough and subsequent easterly) from within its own suite and of course the other models come around to the exactly the same idea, or, the ECM operational backtracks to some degree on its theme.

The margin for error of backtrack though is already reduced from where it might have been, say yesterday. No backtrack has happened at all (yet) since the start of the weekend at least and the point is now arriving where all the models agree to some degree to there being a trough poised to disrupt SE (to varying degrees and at varying points further west or east). Thus far it is the ECM that has lead the other models to that situation (the GFS has had to backtrack to this already). It remains to be seen if this trough disrupts favourably far enough west as per the ECM or further east and lifts out the cold further north and east. But the chances for something favourable have been increasing for sure over the last day or so.

[johnholmes]

Yeah,all seems obvious when you put it in simple points.

Feel a bit silly for asking the question now, but thankyou anyway. I've learnt something today.

never ever be afraid to ask a question, that is how most learn from others-so do ask, if you feel uncertain about that I'm happy to chat via pm

[Tim Bland]

We don't mathematically and scientifically prove the best model by looking at what happened in a measure over a few days, but by long term stats, and the ECM consistently has beaten GFS over the years.

What about the 5 & 6 days stats though, which is probably where there are real and significant divergences at the moment (and have vastly better confidence) here the ECM is better.

My point was more that GFS isnt "Cannon fodder" or "Dogs biscuits" as its often refered to in here. I agree that the no 1 model in our region over a long period is the ECM but its not by a massive difference and GFS is still in the top 3 and shouldnt be dismissed. Its still better than the JMA / NOGAPS / BOM etc. the 12Z and the 00Z are often the more accurate of the 4 and I personlay dont take much notice of the 06z and 18z.