Model output discussion - 5th December 2016 - Into Winter we go

[Summer Sun]

 

[Summer Sun]

29 minutes ago, Gael_Force said:

Wind charts on there too.

surface wind in knots.

 

So max wind gusts around 60mph for exposed areas?

[Gael_Force]

2 minutes ago, Summer Sun said:

So max wind gusts around 60mph for exposed areas?

@knocker will be your man for working that out.

[Summer Sun]

A windy start to Christmas day but improving as the day goes on with the low pulling away quite quickly

[stewfox]

I had assumed there was no PM left and it was 15c now until end of year

GFS 06z shows a different story with PM -5c over whole of uk 24/12

Of course its brief but not a total mix out. The PM distribution changes every 6hrs but hasn't gone.

[Tamara]

One final repeat (I promise) of the misnomer about longer range signals that continues to persist despite the attempts to correct these and give true perspective

The risk of low angular momentum phase (adding up to a stronger and flatter northern branch of the jet, steepened gradient due to cold air coming out of Canadian arctic and consequent cyclogenesis threat ) was flagged over 3 weeks previously at a time when the consensus modelling gave good support to a cold blocked evolution through most of December.

We have seen a lot of blocking, but it has not been the variety perhaps anticipated and hoped for as autumn was coming to a close.

That unpopular phase possibility, that seemed a long way and, understandably, rather unlikely maybe to many back then, is now arriving this week - just when it is least wanted. The (usually) low AAM bias driven GEFS modelling unfortunately looks like striking accuracy with unerringly bad timing this week  (much as it did in early June to provide that highly underwhelming first half of summer)  

The upside possibilities were based on both an ocean/+AAM atmospheric circulation and tropospheric/upper +WQO driven stratosphere disconnect being sustained much longer than has proved the case.

Conclusion: It is not the "background signals" that have failed. It is simply that downside potential based on the different paths those signals might take, that has come to being, and it is the expectations of (some) of the audience, who have focussed on the upside possibilities at the expense of the less appealing option that showed what could go wrong, who are left disappointed and believing that those signals are wrong/pointless instead.

Nick S butterfly effect also is highly relevant here - especially when looking at signals almost a month ahead. In the case of the GSDM (essentially a model system that combines tropical and extra tropical forcing signals to provide "ahead of time" forecasting assistance to gauge jet stream and global weather patterns) it requires a non-bias approach to the findings in order to fully utilise the full worth of this "weather tool"

Otherwise, skewed interpretation leads (most obviously) to inaccurate results and a lack of growth in progressive knowledge and undestanding 

So the reason for my continued repetition is simply for genuinely well meant reasons to want to give the truth, and certainly not to try to appear holier in any way It shouldn't really need stating, but I can say that my own preferences are highly in tune with the majority. I'm disappointed as well, and would readily agree it not always easy to stay wholly objective when there are compelling NWP signals that appear to support upside long range underlying signals.

Having worn the t-shirt for quite a few years though, (and hopefully learning a few things on the way as well), it seems more and more wise to emphasise what can go wrong as early as that becomes apparent. This should, at least logically in theory, reduce the sense of expectations being overly short-changed. It also is another lesson that both long range NWP ensembles and also long range model stratospheric forecasts should be treated with caution - as tempting as it is to want to embrace the good things they might suggest at a given time.

Yet another year, but essentially, its the same lesson. Human preference and emotion are not equal to the science that drives the weather patterns - irrespective of what one may hope for

With that said, TEITS has a very good point about instinct. Human intervention, interpretation, and drawing on past experiences is important in deciphering and making much more user friendly, the robotics of model calculations and conclusions. It also adds much needed personality into what can otherwise appear a soulless, over geeky straight-jacket. I doubt many would post on here if it was an exclusive robot club 

A bit of further extra reality is needed though. There are far worse things happening in the outside world of the net weather bubble, and - more positively as mcweather rightly suggested this morning, there are families and friends to focus on with Christmas approaching. However appalling the weather looks set to be.

We all know that the UK lies at a massive traffic light junction with a massive ocean one side and very large continental landmass the other. Unfortunately the colder (in winter) landmass lies downstream from us, and our prevailing weather, usually, comes from upstream. All the more reason why ocean/atmospheric signals that engage the Pacific and determine the patterns there, are fundamental to our "fate" in terms of weather patterns.

That, in conjunction of course with the function of the winter-time stratospheric vortex. After all, the coriollis effect of the earth spinning from west to east can only be exacerbated by a westerly spinning top (as augmented by a westerly phase of the QBO)

It remains true that the faster they spin, the faster they can fall. But this isn't a time to try to attempt to turn to any future "jam tomorrow". A good time to take a break and prepare for the festive season

So, a happy Christmas to all and here is to much better things in the New Year

 

Edited December 18, 2016 by Tamara

[Faronstream]

Horrible charts from both GFS and EWCMF, strenghtening PV and mild upper air temperatures will give us another green christmas, at least the rain could wait until the 26-27th december

[johnholmes]

The post by T illustrates very well the difficulty, even for experienced professional forecasters, in being totally objective in deciding what and how to present a forecast. They are on national BBC at any rate, until the change next year, all professionally trained and present the forecast as they along with guidance from the senior 'man' at Exeter decide is the correct course. That still leaves the few seconds for a knowing wink or off hand sentence to cheer up those wanting to hear something different.

Meantime there is nothing in the anomaly charts I use to suggest anything other than an upper trough governing the UK weather into and out of the Christmas period.

ECMWF-GFS

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

NOAA

http://www.cpc.noaa.gov/products/predictions/610day/fxus06.html

 

Edited December 18, 2016 by johnholmes

[Daniel*]

The exact whereabouts of the cold pool at T48 doesn't seem to be nailed yet. It's trended more north, would be hilarious, if anyone in southern districts managed a flurry. 

Staggering -4C 850hpa temps S of IOW.

Edited December 18, 2016 by Changing Skies

[Captain Shortwave]

Not much on offer in terms of a breakthrough in terms of cold weather. The GEFs do suggest that the core low heights might back further west after Christmas.

      

This would potentially allow heights to build closer to the UK again so after a potentially rather wet and windy Christmas we could see conditions improve from the south with the Azores high ridging closer to the UK, how this transpires is unknown, it could be a strong Euro/Scandi ridge, a UK high or cut-off heights with low heights over the Mediterranean, all possible evolutions. 

 

[Iceaxecrampon]

06Z

Well the big day is  wintery on this run.

....if you want to go looking for it.

Scafell Pike anyone?

 

[Frosty.]

There is plenty of cold zonality on the Gfs 6z so northern hills and mountains would see lots of wintry ppn with snow at elevation and the scottish mountain resorts would do very nicely thanks very much.

Ps..fab post as usual Tamara, merry Christmas to you

Edited December 18, 2016 by Frosty.

[ArHu3]

43 minutes ago, Tamara said:

One final repeat (I promise) of the misnomer about longer range signals that continues to persist despite the attempts to correct these and give true perspective

The risk of low angular momentum phase (adding up to a stronger and flatter northern branch of the jet, steepened gradient due to cold air coming out of Canadian arctic and consequent cyclogenesis threat ) was flagged over 3 weeks previously at a time when the consensus modelling gave good support to a cold blocked evolution through most of December.

We have seen a lot of blocking, but it has not been the variety perhaps anticipated and hoped for as autumn was coming to a close.

That unpopular phase possibility, that seemed a long way and, understandably, rather unlikely maybe to many back then, is now arriving this week - just when it is least wanted. The (usually) low AAM bias driven GEFS modelling unfortunately looks like striking accuracy with unerringly bad timing this week  (much as it did in early June to provide that highly underwhelming first half of summer)  

The upside possibilities were based on both an ocean/+AAM atmospheric circulation and tropospheric/upper +WQO driven stratosphere disconnect being sustained much longer than has proved the case.

 

 

 

What is AAM, or how does it impact the weather? I managed to Google the meaning but not really how it impacts us. Low AAM, more chance of blocking or deep troughs and ridges?

[carinthian]

Just looking at the latest synoptic chart for our region ( Central Europe ) we have reports of moderate snowfall under Euro High centre of 1034mb mainly in Slovenia but also Northern Salburgerland. Looks like a upper cold spreading, not sure why and  how the instability has developed but we here are seeing convectional cloud developing. Indeed, our fine mesh snow model going for 7cm at 1650m asl over the next 12 hours. Just going to show how sometimes the weather produces the unexpected especially in the middle of the high pressure centre. Anyway it will be a bonus.

 C

[carinthian]

28 minutes ago, Changing Skies said:

The exact whereabouts of the cold pool at T48 doesn't seem to be nailed yet. It's trended more north, would be hilarious, if anyone in southern districts managed a flurry. 

Staggering -4C 850hpa temps S of IOW.

Yep, the French have -5c 850hpa over the home counties of England on Tuesday ! Its just developing now over the Northern Alpine region.

C

 

[Man With Beard]

Great post @Tamara - totally unscientific but I like your comparison with last summer - you didn't say it but of course fortunes turned unexpectedly in mid-July just as a lot of people were writing off the whole season, and then many of us ended up with a succession of short heatwave. I think coldies would settle for that in reverse in mid-January! 

But no model output to back up the idea. Except perhaps, the hope that the long range model output won't be wrong for an entire season!! 

Look forward to hearing if AAM looks like approaching a more favourable window any time soon.

[blizzard81]

23 minutes ago, Man With Beard said:

Great post @Tamara - totally unscientific but I like your comparison with last summer - you didn't say it but of course fortunes turned unexpectedly in mid-July just as a lot of people were writing off the whole season, and then many of us ended up with a succession of short heatwave. I think coldies would settle for that in reverse in mid-January! 

But no model output to back up the idea. Except perhaps, the hope that the long range model output won't be wrong for an entire season!! 

Look forward to hearing if AAM looks like approaching a more favourable window any time soon.

I notice the met office never seem to mention AAM. The trouble is most of the less knowledgable on this forum (myself included) have to take the word of the more knowledgable ones. How do we know for sure that low AAM and a storm or two in the pacfic lead us to this big fail? If it did, how come the predictions of high AAM were so way off target?

[blizzard81]

A very interesting point made by Tamara earlier on was that gut instinct and comparisons to years gone by. I had two (admittedly wet) snow falls in November. This is quite significant in relation to what Tamara was saying. November snow falls for this area have been incredibly rare for the last 30 years or so. However, I remember quite a few back in the 80's. Most of the 80's Decembers were mild and very similar to 2016. However, there were quite a few cold and snowy Jan and/or Febs in the 80's. This season feels very similar to the 80's

 

 

Edited December 18, 2016 by blizzard81

[NeilN]

3 minutes ago, blizzard81 said:

A very interesting point made by Tamara earlier on was that gut instinct and comparisons to years gone by. I had two (admittedly wet) snow falls in November. This quite significant in relation to what Tamara was saying. November snow falls for this area has been incredibly rare for the last 30 years or so. However, I remember quite a few back in the 80's. Most of the 80's Decembers were mild and very similar to 2016. However, there was quite a few cold and snowy Jan and/or Febs in the 80's. This season feels very similar to the 80's

 

 

My Mum said the same - she said this feels like December 1986 - cold start, mild throughout then cold towards the end and freezing January's and February's. Nothing is a write off, however I am cautious of a stormy Christmas. 

[mcweather]

3 hours ago, Tamara said:

One final repeat (I promise) of the misnomer about longer range signals that continues to persist despite the attempts to correct these and give true perspective

The risk of low angular momentum phase (adding up to a stronger and flatter northern branch of the jet, steepened gradient due to cold air coming out of Canadian arctic and consequent cyclogenesis threat ) was flagged over 3 weeks previously at a time when the consensus modelling gave good support to a cold blocked evolution through most of December.

We have seen a lot of blocking, but it has not been the variety perhaps anticipated and hoped for as autumn was coming to a close.

That unpopular phase possibility, that seemed a long way and, understandably, rather unlikely maybe to many back then, is now arriving this week - just when it is least wanted. The (usually) low AAM bias driven GEFS modelling unfortunately looks like striking accuracy with unerringly bad timing this week  (much as it did in early June to provide that highly underwhelming first half of summer)  

The upside possibilities were based on both an ocean/+AAM atmospheric circulation and tropospheric/upper +WQO driven stratosphere disconnect being sustained much longer than has proved the case.

Conclusion: It is not the "background signals" that have failed. It is simply that downside potential based on the different paths those signals might take, that has come to being, and it is the expectations of (some) of the audience, who have focussed on the upside possibilities at the expense of the less appealing option that showed what could go wrong, who are left disappointed and believing that those signals are wrong/pointless instead.

Nick S butterfly effect also is highly relevant here - especially when looking at signals almost a month ahead. In the case of the GSDM (essentially a model system that combines tropical and extra tropical forcing signals to provide "ahead of time" forecasting assistance to gauge jet stream and global weather patterns) it requires a non-bias approach to the findings in order to fully utilise the full worth of this "weather tool"

Otherwise, skewed interpretation leads (most obviously) to inaccurate results and a lack of growth in progressive knowledge and undestanding 

So the reason for my continued repetition is simply for genuinely well meant reasons to want to give the truth, and certainly not to try to appear holier in any way It shouldn't really need stating, but I can say that my own preferences are highly in tune with the majority. I'm disappointed as well, and would readily agree it not always easy to stay wholly objective when there are compelling NWP signals that appear to support upside long range underlying signals.

Having worn the t-shirt for quite a few years though, (and hopefully learning a few things on the way as well), it seems more and more wise to emphasise what can go wrong as early as that becomes apparent. This should, at least logically in theory, reduce the sense of expectations being overly short-changed. It also is another lesson that both long range NWP ensembles and also long range model stratospheric forecasts should be treated with caution - as tempting as it is to want to embrace the good things they might suggest at a given time.

Yet another year, but essentially, its the same lesson. Human preference and emotion are not equal to the science that drives the weather patterns - irrespective of what one may hope for

With that said, TEITS has a very good point about instinct. Human intervention, interpretation, and drawing on past experiences is important in deciphering and making much more user friendly, the robotics of model calculations and conclusions. It also adds much needed personality into what can otherwise appear a soulless, over geeky straight-jacket. I doubt many would post on here if it was an exclusive robot club 

A bit of further extra reality is needed though. There are far worse things happening in the outside world of the net weather bubble, and - more positively as mcweather rightly suggested this morning, there are families and friends to focus on with Christmas approaching. However appalling the weather looks set to be.

We all know that the UK lies at a massive traffic light junction with a massive ocean one side and very large continental landmass the other. Unfortunately the colder (in winter) landmass lies downstream from us, and our prevailing weather, usually, comes from upstream. All the more reason why ocean/atmospheric signals that engage the Pacific and determine the patterns there, are fundamental to our "fate" in terms of weather patterns.

That, in conjunction of course with the function of the winter-time stratospheric vortex. After all, the coriollis effect of the earth spinning from west to east can only be exacerbated by a westerly spinning top (as augmented by a westerly phase of the QBO)

It remains true that the faster they spin, the faster they can fall. But this isn't a time to try to attempt to turn to any future "jam tomorrow". A good time to take a break and prepare for the festive season

So, a happy Christmas to all and here is to much better things in the New Year

 

 A great post Tamara. Your posts have always pointed out that despite the various LRF,s (including the Meto) that there were always things that could go wrong and as a veteran of 56 winters I know that if it can go wrong it probably will. As Nick Sussex often points out in his posts we need so many things to fall into place for us to get a sustained cold shot and then even more to fall in place for widespread snow away from the usual suspects on high ground in the north. 

Living in central south Dorset within a couple of miles of the English channel I always start each winter from the stance that I probably won't see any long lasting cold or snow at all and then work forward from there. That way anything I do get is a bonus and I would advise any members living in lowland southern England to do the same.  Every so often a great cold spell comes along and occasionally some heavy snowfall but they are much  the rarities. The recent spell between 2008 to Dec 2010 provided some great winter weather for many but also I think raised the expectations of many in lowland England to a new higher level of expectancy than is justified by our natural climate.  In my own locale Dec2010 was the coldest and snowiest ever ( colder and snowier than 1890 or 1981) but I didn't kid myself that was the new norm because the vast majority of my other 56 winters weren't like that at all .

I am lucky enough to have memories  from 1963(just) and the snowy winters of the 1980's along with the greatest weather event of my life, The amazing southwest Blizzard of Feb 1978 the latter being an element that all lowland ( and especially) southern lowland snowlovers should hang onto and that is that you don't need a 63 or a 47 to have a phenomenal snow event of historic proportions . The models in the short to medium term look pretty dire but they can and most probably will change and with just a little bit of luck they will change enough to give lowland southern snowlovers a nice surprise at some point during the first few months of the new year.

 

Edited December 18, 2016 by mcweather

[Scandinavian High.]

I no this is a long way out it looks very cold eastern Europe starting push west uk looks to be cooling to but its 384 hours away.

[karyo]

1 hour ago, carinthian said:

Just looking at the latest synoptic chart for our region ( Central Europe ) we have reports of moderate snowfall under Euro High centre of 1034mb mainly in Slovenia but also Northern Salburgerland. Looks like a upper cold spreading, not sure why and  how the instability has developed but we here are seeing convectional cloud developing. Indeed, our fine mesh snow model going for 7cm at 1650m asl over the next 12 hours. Just going to show how sometimes the weather produces the unexpected especially in the middle of the high pressure centre. Anyway it will be a bonus.

 C

Yes, once you have the cold in place, nice surprises can crop up. Enjoy it while it lasts.

[Seasonality]

1 hour ago, carinthian said:

Just looking at the latest synoptic chart for our region ( Central Europe ) we have reports of moderate snowfall under Euro High centre of 1034mb mainly in Slovenia but also Northern Salburgerland. Looks like a upper cold spreading, not sure why and  how the instability has developed but we here are seeing convectional cloud developing. Indeed, our fine mesh snow model going for 7cm at 1650m asl over the next 12 hours. Just going to show how sometimes the weather produces the unexpected especially in the middle of the high pressure centre. Anyway it will be a bonus.

 C

Had a bit of a sprinkling in Warsaw today too.

[Frosty.]

13 minutes ago, Northwest NI said:

Seen it all before mate. Don't want to clutter the thread with non model related posts but I've had it this year.

You have snow showers to look forward to later in the week, one of the coldest parts of the uk from a cold zonal westerly flow!

Edited December 18, 2016 by Frosty.

[radiohead]

On the latest GFS(P) the big day is looking pretty wild for northern parts.