Model Output Discussion - 30th November onwards

[UV-RAY]

Can anyone give me a link to RJS' winter forecast please? Ta muchly.

Just scroll down.

 

http://forum.netweather.tv/topic/72635-the-seasonal-forecast-thread/page-21

[Severe Siberian icy blast]

although the broad outlook remains with heights rising to our east and remaining high over the nw europe, the 00z extended are more enthusiastic re a stronger flow over the top of the block. that will prevent it getting far enough north to allow any deep cold incursions across the uk (there is a spread remaining on ncep for mid month easterly but this looks doubtful to me).infact, the background noise would seem more attuned to the atlantic making significant inroads over time and forcing the block se somewhat.

the thing about the ensembles and co is they change a lot. Yesterday ian f said all pointers were looking at an easterly . Now its not. What will it show come sat? Nobody knows . If the models change. The forecasts change. Simple as that. 3 days ago the bbc were bigging up this cold snap. Now theres no mention. Why? Because the models have downgraded it. Every forecast out there is fickle . As well as the models .

[TSNWK]

Metoffice 15 and 30 day updates out. Kinda of supporting inversion cold in the southeast for the 1st period, with now only a low prob of something colder from the east for the 2nd period, backing away from the Scandi high option in my view and more towards a MLB in situ towards central europe.

[UV-RAY]

the thing about the ensembles and co is they change a lot. Yesterday ian f said all pointers were looking at an easterly . Now its not. What will it show come sat? Nobody knows . If the models change. The forecasts change. Simple as that. 3 days ago the bbc were bigging up this cold snap. Now theres no mention. Why? Because the models have downgraded it. Every forecast out there is fickle . As well as the models .

I think the whole ens and co have been woeful, I've never seen so much chopping and changing in such a short period of time, that goes for the alleged newly revamped EC32 as well.

Edited December 4, 2013 by Sceptical Inquirer

[Frosty.]

 3 days ago the bbc were bigging up this cold snap. Now theres no mention. Why? Because the models have downgraded it.

They haven't downgraded it for scotland, the northern half looks very wintry & stormy tomorrow and friday looks wintry with further snow showers and continuing cold for most of saturday, only downgraded for the southern half of england and wales and the models never promised anything snowy for the south at any stage, frosty yes, snowy no.

Edited December 4, 2013 by Frosty.

[Yozzer]

Just scroll down.

 

http://forum.netweather.tv/topic/72635-the-seasonal-forecast-thread/page-21

Thanks SI. From a broad brush perspective looks like it could be there or thereabouts, in other words, bland. Whether that's due to science or pot luck, the jury's out on that one. One thing i can't see is the predicted storm around 15th Dec, but plenty of time for that to change.

[bluearmy]

 

Quick update at work - change in the lower strat signals this morning. Support for scandy ridge has fallen away with a much less pronounced ridge shape

 

 

 

but wave 2 warming still forecast and signs possibly of enhancing at day 10

 

 

10 days charts show the predicted easing of the vortex away from the Canadian side underway, but not in a particularly dramatic or disrupted fashion.

 

So unfortunately my hopeful post of yesterday is now less hopeful. Heights will build towards Scandy but probably not get far enough north for any cold and instead we may be on the western edge of the ridge and enjoying some unseasonal warmth. On the output this morning any interest for cold is looking as though it will be after Xmas after all - the call of many on here in mid november.

 

RJS will be smiling this morning.

 

CH, the run is based on yesterday's op run. are you surprised that the scandi ridge signal is lowered? all this proves is that the strat charts are being influenced by the trop ones low down. this makes them unreliable. strat forecast charts are more reliable than trop ones higher up. this is because they are less influenced by the trop patern which we know is poorly modelled post day 6.

[bluearmy]

imo, the ext ens have been pretty good as a forecast tool. you cant just pick one run at random - you do need to be watching each suite so you know whats reasonable and also if a trend is establishing.did ian F promise an easterly? methinks not. we do need to read posts from ian properly before misquoting him or taking him 'out of context'. tbh, the same applies to everyone on here.

[forecaster]

They haven't downgraded it for scotland, the northern half looks very wintry & stormy tomorrow and friday looks wintry with further snow showers and continuing cold for most of saturday, only downgraded for the southern half of england and wales and the models never promised anything snowy for the south at any stage, frosty yes, snowy no.

 

Scotland on Saturday shouldn't be especially cold apart from in the morning:

 

 

Temperatures heading back towards average for most people. 

 

Also, a pretty major "downgrade" occurred for Wales and the southwest. Maximum temperatures on the weekend will be close to average. This is about 5C warmer than what some earlier model runs would have led to. 

Edited December 4, 2013 by forecaster

[Bristawl Si]

References to RJS's winter forecast and more specifically the December part, seem to have been taken out of context by a couple of posters on here.

Firstly it's only Dec 4th; secondly his Dec forecast says "...looks particularly mild" -

i cant see that in models for next couple of weeks, bar a couple of days next week and that's only for down here. Didnt Ian F warn against reading current charts as mild (and teits today).?

Roger's December part of his LRF also says "occasional heavy rainfalls for MUCH of December" - REALLY?! Can anyone see that currently on the charts for next couple of weeks?

I sure can't!

[TonyH]

Whilst I do agree with you Matty, the GFS did also show us all under a stonking northerly flow for a few days a while back… All the main NWP models were sucked into this in one way or another. But as I said, I agree the GFS was much more maligned than others and not with any warrant.

A very cold northerly blast was far from unanimous when I produced my weekly blog at the weekend, and this quote from it illustrates the uncertainty I was feeling, although I did follow ECM and go for a 'cold snap':

 

"Although this cold snap for the end of the week seems likely, the models have not been unanimous over it, and so it must be mentioned here that there is still the chance that the really cold air ends up passing to our east. This guide is going for the cold affecting the UK due to the ECM model having been resolute with this outcome over its recent days output. Alternative scenarios for Friday would be a chilly high pressure over us with frost, or less cold westerly winds and some rain or showers, but here we will predict a cold snap."

Edited December 4, 2013 by TonyH

[shedhead]

References to RJS's winter forecast and more specifically the December part, seem to have been taken out of context by a couple of posters on here.Firstly it's only Dec 4th; secondly his Dec forecast says "...looks particularly mild" -i cant see that in models for next couple of weeks, bar a couple of days next week and that's only for down here. Didnt Ian F warn against reading current charts as mild (and teits today).?Roger's December part of his LRF also says "occasional heavy rainfalls for MUCH of December" - REALLY?! Can anyone see that currently on the charts for next couple of weeks?I sure can't!

Exactly, so best to leave judgement until Dec 31st, whether that be in praise of his forecast or not.

 

Re Ian F...no, simply suggested the SE could be closer to average.

[Interitus]

 

 

Hi sunnijim....it's simply about the model reliability in certain synoptic senarios. All struggle with modelling N'erlies or E'erlies in the mid range...say post T+120hrs.  They don't struggle to model weather from between S and W in quite the same way, so when every model is saying pretty much exactly the same thing right now there's a much better chance of it verifying.  We don't have to like it, but I'm afraid we do have to accept in...at least for now. 

 

Ahh, so you have found proof of this now Shed! Yet again this is your assumption - please can you provide statistical proof that this is the case.

 

There is a lot of research which suggests that this has long been the case and though they are improving, NWP still struggle to forecast blocks in certain positions more than others, and hence the associated air flows.

(However, I hope people will take the time to investigate some the the research to understand the scale of the issue so it doesn't become yet another forum myth which gets churned out ad nauseam.)

 

For example this paper is one of many - Blocking Predictability in Operational Medium-Range Ensemble Forecasts

https://www.jstage.jst.go.jp/article/sola/5/0/5_0_113/_pdf

 

 

This study assesses the forecasting performance of operational medium-range ensemble forecasts: BOM, CMA, CMC, CPTEC, ECMWF, JMA, KMA, NCEP, and UKMO, in terms of atmospheric blocking during DJF (December-January-February) of 2006/07, 2007/08, and 2008/09.

The state-of-the-art medium-range ensemble forecasts performed well in simulating the frequencies of Euro-Atlantic (EA) and Pacific (PA) blockings, even after 216-hr lead time, whereas they did not simulate well the frequencies of Greenland and Ural blockings, even in the middle of the forecast range. The ensemble forecasts are not always able to capture the blockings with high probability in the latter half of the forecast range. During this latter half, blocked flows were frequently predicted with low probability during the active blocking period, whereas they were seldom predicted with similar probability during the non-active blocking period. This result might suggest that the active blocking period is more chaotic than the non-active blocking period. In addition, it was more difficult to predict an onset of EA blocking than to predict an onset of PA blocking, and probabilistic blocking forecasting over the PA sector was more skillful than that over the EA sector. These results suggest that PA blocking has a higher predictability than does AT blocking.

[Jason M]

imo, the ext ens have been pretty good as a forecast tool. you cant just pick one run at random - you do need to be watching each suite so you know whats reasonable and also if a trend is establishing. did ian F promise an easterly? methinks not. we do need to read posts from ian properly before misquoting him or taking him 'out of context'. tbh, the same applies to everyone on here.

I agree with this. I tend to use them a lot. They picked up on the northerly first, they then picked up on the downgrade before the opps and have been strongly pushing a Euro / Bartlett 'type' solution for a few days.As you say, the key is the trends rather than any individual ensemble solution. I tend to disregard any deep FI solutions that show a big Greenland high as GEFS seem to often raise this possibility but it rarely comes to fruition. So looking at the 06Z split ignoring the couple that raise heights over Greenland they are split between warm SE winds (at least warm in terms of 850s)and a more zonal set up. Interestingly, zonal has started to feature more heavily in the 06z set although in my view the 06Z GEFS often over emphasise zonal charts. Either way, the outlook isn't great over the next 10-15 days at least.All my opinion of course, but in the last 24 hours there seems to have been a clear signal against northern blocking.Jason Edited December 4, 2013 by Jason M

[Ian Brown]

I agree with this. I tend to use them a lot. They picked up on the northerly first, they then picked up on the downgrade before the opps and have been strongly pushing a Euro / Bartlett 'type' solution for a few days.As you say, the key is the trends rather than any individual ensemble solution. I tend to disregard any deep FI solutions that show a big Greenland high as GEFS seem to often raise this possibility but it rarely comes to fruition. So looking at the 06Z split ignoring the couple that raise heights over Greenland they are split between warm SE winds (at least warm in terms of 850s)and a more zonal set up. Interestingly, zonal has started to feature more heavily in the 06z set although in my view the 06Z GEFS often over emphasise zonal charts. Either way, the outlook isn't great over the next 10-15 days at least.All my opinion of course, but in the last 24 hours there seems to have been a clear signal against northern blocking.Jason

 

I think with the intensity of the PV we should soon start seeing more conventional zonal charts in the longer range NWP with the High sinking over Europe. Potentially a wet and windy Xmas period.

[Bristawl Si]

Exactly, so best to leave judgement until Dec 31st, whether that be in praise of his forecast or no.

Agree 100%.

[Jack Wales]

I’m surprised to see such a downgrade in the upcoming northerly at such close range. This looks to be the result of the highly amplified polar vortex and short wave toughing to the west of the UK. Consequently the -10C (850hpa) isotherm only reaches mainland Scotland for around 24 hours before being quickly toppled by the Atlantic.

As for looking further ahead, the strength of the polar vertex and the fact it’s anchored around Greenland reduce the opportunities for cold across the UK. Especially when you look at the atmospheric thermal gradient off eastern Canada and the Atlantic (-20C to +15C at 850hpa), which will ensure a highly amplified jet stream. Just look at the sub 960mb lows forming off the Canadian seaboard. If you couple these factors with a blocking Euro high, then the result is a very warm fetch southerly across the UK and western Europe. Don’t be surprised to see temps hitting the 60’s (F) next week in some parts of the UK.

On a different note, good luck to those living in Shetland who should have a wintry next three days ïŠ

[Tamara]

Posted 27 November

 

If the Pacific pattern becomes less favourable i.e an ever deeper -PNA (as some modelling is starting to suggest as we go into December) and the upper vortex intensifies in the absence of any wave breaking (as a result of the Aleution High de-amplifying and becomes less poleward) then this will increase the trough over the US, strengthen further the downstream ridges from Florida, Bermuda to the Azores and correspondingly at the same time revert the bulk of the vortex back to Canada and Greenland. The result will be the pattern will de-amplify and flatten and the PFJ will adjust further northwards as the jet stream aligns SW-NE

 

and then this:

However it is all about equating how much forcing is required from this trop/lower strat activity to disrupt the net energy of the upper vortex and the signals are that it is going to take a lot more than we have seen in previous times to disrupt the vortex.

 

without background support for upper blocking, whether we get a more amplified and colder arctic incursion or not - the vortex is too strong, and wave activitity likely too insufficient, to make next weekends cold shot nothing more than a transitory affair.

 

There are continuing consistent signals in the modelling, post northerly, for the vortex to return towards Canada through Greenland and it is quite conceivable that the upcoming polar incursion presents the 'best' opportunity at wintriness

 

Both the GFS and ECM do agree on this even if they disagree on the northerly strength and duration itself.

 

 

 

Copied these snippets purely for continuity purposes and on the basis that the tenet of the suggestions remains pertinent - especially wrt to the relocation of the vortex across the pole towards Canada

 

Todays ECM mean illustrates this appropriately enough on the 10 day output. We also see an indicated change to the Pacific pattern, as muted possible in earliest copied post above, with the poleward Aleutian ridge here:

 

 

 

.....replaced as below with a trough, and the amplified Pacific ridge flattened and displaced southwards, along with a downstream ridge in response to the lower herights across Canada, across the SE USA. The string of mid latitude ridges persists even further downstream with the Euro High depicted on our side of the atlantic

 

 

 

The shift in pattern results in a loss of the split jet stream energy that has been a feature of the Alaskan upper High and in tandem with a consolidated and well organised upper polar vortex that is running well up to seasonal westerly speed, then any expectations of ridging extending any further north in the 10 to 15 day period and orientating itself favourably over Scandinavia to horse-shoe the jet stream back around the pole and return SW'werds towards the UK with attendant significant cold from eastern and northern europe should be kept low.

 

The more likely evolution suggests an upper high holding closer to Denmark and maybe the Baltic initially, with a rounder shaped orientation and associated anticyclonic feed of cold surface air perhaps into eastern and south eastern parts whilst areas to the NW are closer to the overspill of jet energy from the vorticity over Canada and Greenland.

 

The catch 22 defined here therefore is that the split flow jet stream that has featured the Aleutian High and Siberian vortex pattern, and which hypothetically might enable a better result towards a more favourably orientated and elevated Scandinavian High - is lost under the changes to the upstream pattern and instead the greater energy to the northern arm of the jetstream that will feed from an invigorated Canadian vortex sector is likely too strong this early in the winter, under current stratospheric conditions, to provide the type of interest from the east that most are looking for.

 

Therefore the prognosis looks to continue to be as suggested last week  - essentially dry with mid latitude/Sceuro ridging at least keeping temperatures seasonal to rather below average especially to the east and south east whilst areas to the north west might expect somewhat milder and less settled conditions

Edited December 4, 2013 by Tamara תָּמָר

[shedhead]

 

There is a lot of research which suggests that this has long been the case and though they are improving, NWP still struggle to forecast blocks in certain positions more than others, and hence the associated air flows.

(However, I hope people will take the time to investigate some the the research to understand the scale of the issue so it doesn't become yet another forum myth which gets churned out ad nauseam.)

 

For example this paper is one of many - Blocking Predictability in Operational Medium-Range Ensemble Forecasts

https://www.jstage.jst.go.jp/article/sola/5/0/5_0_113/_pdf

 

 

This study assesses the forecasting performance of operational medium-range ensemble forecasts: BOM, CMA, CMC, CPTEC, ECMWF, JMA, KMA, NCEP, and UKMO, in terms of atmospheric blocking during DJF (December-January-February) of 2006/07, 2007/08, and 2008/09.

The state-of-the-art medium-range ensemble forecasts performed well in simulating the frequencies of Euro-Atlantic (EA) and Pacific (PA) blockings, even after 216-hr lead time, whereas they did not simulate well the frequencies of Greenland and Ural blockings, even in the middle of the forecast range. The ensemble forecasts are not always able to capture the blockings with high probability in the latter half of the forecast range. During this latter half, blocked flows were frequently predicted with low probability during the active blocking period, whereas they were seldom predicted with similar probability during the non-active blocking period. This result might suggest that the active blocking period is more chaotic than the non-active blocking period. In addition, it was more difficult to predict an onset of EA blocking than to predict an onset of PA blocking, and probabilistic blocking forecasting over the PA sector was more skillful than that over the EA sector. These results suggest that PA blocking has a higher predictability than does AT blocking.

 

Thanks for that Interitus.

 

However if we boil this down to simplistics, I think the vast majority of us would have more confidence in a predicted SW'erly pattern verifying more accurately as shown at T+144hrs than N'erly or E'erly pattern...despite the fact we'd hope for the opposite. Now that is not to say we nescessarily have more confidence in the overall pattern, lets face it even later this week the N'erly progged is going to verify to a degree....it's the accuracy of the eventual SW'erly patterns that are far superior imo.

 

Edit: Even within 24hr of tomorrows event the cold has been significantly downgraded, perhaps by as much as 4-7c for many parts of England and Wales...I have never seen anything like that happen with weather progged to come from the SW at that range.

Edited December 4, 2013 by shedhead

[Jack Wales]

I doubt even the most ardent cold ramper could argue that the charts beyond monday look anything but mild. Just look at the enesmbles which gnerally indicate mild right into FI.

Based on the current synoptics, I just can't see any major pattern changes on the horizon. RJS looks to be spot on re December already.

[Cheshire Freeze]

I doubt even the most ardent cold ramper could argue that the charts beyond monday look anything but mild. Just look at the enesmbles which gnerally indicate mild right into FI.Based on the current synoptics, I just can't see any major pattern changes on the horizon. RJS looks to be spot on re December already.

 

 

And how many people have been caught out many, many times by writing weeks off at a time to a particular synoptic to then end up with egg on their faces? No-one knows how the modelling will look in a week's time, let alone longer.

 

 

FWIW, current modelling is very reminiscent of Dec 88. Not a trend we want to see continue!

Edited December 4, 2013 by CreweCold

[Snowyowl9]

References to RJS's winter forecast and more specifically the December part, seem to have been taken out of context by a couple of posters on here.

Firstly it's only Dec 4th; secondly his Dec forecast says "...looks particularly mild" -

i cant see that in models for next couple of weeks, bar a couple of days next week and that's only for down here. Didnt Ian F warn against reading current charts as mild (and teits today).?

Roger's December part of his LRF also says "occasional heavy rainfalls for MUCH of December" - REALLY?! Can anyone see that currently on the charts for next couple of weeks?

I sure can't!

Looks dry just how I want it  the way the euro high looks later.

Maybe some chillier inversions SE-lys later which can get very cold indeed.

[shedhead]

And how many people have been caught out many, many times by writing weeks off at a time to a particular synoptic to then end up with egg on their faces? No-one knows how the modelling will look in a week's time, let alone longer.

 

 

FWIW, current modelling is very reminiscent of Dec 88. Not a trend we want to see continue!

 

True CC, but you seemed pretty happy to back Ian F's call for battleground weather in the 10-15 day range only yesterday.

 

fergieweather, on 03 Dec 2013 - 08:52, said:

The current UKMO view is for a colder set-up to dominate again into the 10-15d trend period, with more progressive solutions in a minority. Possible net result is UK on western bounds of blocking with 'battleground' style issues in west thanks to periodic Atlantic incursions. Latest EC32 from yesterday is an interesting one; it also indicates a signal by Christmas for negative temp anomalies & HP to N; LP to S/SW, but the clusters do show a wide raft of potential outcomes. Anyway, very early days but tentative signs for something more blocked a bit further down the December diary.

 

CreweCold

Over 80 likes on this post. Awesome. Always good when the Metoffice start to pick up on a potential cold pattern change. 'Battleground style issues'........love it!

Edited December 4, 2013 by shedhead

[Troubleatmill]

I doubt even the most ardent cold ramper could argue that the charts beyond monday look anything but mild. Just look at the enesmbles which gnerally indicate mild right into FI.

Based on the current synoptics, I just can't see any major pattern changes on the horizon. RJS looks to be spot on re December already.

 

Not Dissing RJS infact enjoy and respect reading his forecasts right or wrong, as a lot of time and effort go into them, However we cant say that this forecast is spot on for December off current charts becasue : (1) we are only just into december and GFS all the way out to t384 only takes us to the 20th and (2) december forecast :  'I'm expecting some rather lengthy intervals of very mild southwest flow and occasional heavy rainfalls and strong winds during parts of early November, much of December ' I dont see this in any models currently either?.

 

Not to say he wont be right either because of point 1, just as Shedhead said...best wait till the end of Dec. 

Edited December 4, 2013 by Arron B

[Cheshire Freeze]

 

True CC, but you seemed pretty happy to back Ian F's call for battleground weather in the 10-15 day range only yesterday.

 

fergieweather, on 03 Dec 2013 - 08:52, said:

 

CreweCold

Over 80 likes on this post. Awesome. Always good when the Metoffice start to pick up on a potential cold pattern change. 'Battleground style issues'........love it!

 

 

 

I think it was more a quick happy reaction to the Metoffice's picking up on the potential signal more than anything. I've not really been on the forum over the past couple of days due to extended opening hours at work- been getting in at midnight. That was posted on my dinner break- I've had no time to 'back' anything.

 

 

You can see from my winter forecast that I never expected December to be cold- though perhaps didn't envisage a Euro high either!

Edited December 4, 2013 by CreweCold