This new thread will hopefully go hand in hand with the faster moving general model discussion to offer a slower paced, more in depth look at the model output.
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#1
Paul
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Posted 12 December 2009 - 22:19
'Views and opinions expressed in this or any other of my posts are my own'
#2
winterfreak
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Posted 12 December 2009 - 22:28
As a newbie i can't understand the models in that they are, effectively, crystal balls (in the meteorlogical sense). I struggle to understand the worship in them. They are just computer models right? They aren't exactly what the weather is doing 'right now'. I mean, it's the same as saying 'if i had a million quid........'
On that basis the ECM or GFS could just put whatever squiggly lines, pretty colours and 850hpa temps on that they like, it doesn't actually mean zip, does it? I can't get my head round the 'well if the ECM verifies, London will be under 18' of snow' etc, surely any scenario is possible if the chart verifies? Please explain to a numpty why computer models are just so thrilling and why so much faith is placed in them......
On that basis the ECM or GFS could just put whatever squiggly lines, pretty colours and 850hpa temps on that they like, it doesn't actually mean zip, does it? I can't get my head round the 'well if the ECM verifies, London will be under 18' of snow' etc, surely any scenario is possible if the chart verifies? Please explain to a numpty why computer models are just so thrilling and why so much faith is placed in them......
Edited by winterfreak, 12 December 2009 - 22:29 .
Location: Tonbridge, Kent. 
#3
chrisbell-nottheforecaster
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Posted 12 December 2009 - 22:32
winterfreak, on 12 December 2009 - 22:28 , said:
As a newbie i can't understand the models in that they are, effectively, crystal balls (in the meteorlogical sense). I struggle to understand the worship in them. They are just computer models right? They aren't exactly what the weather is doing 'right now'. I mean, it's the same as saying 'if i had a million quid........'
On that basis the ECM or GFS could just put whatever squiggly lines, pretty colours and 850hpa temps on that they like, it doesn't actually mean zip, does it? I can't get my head round the 'well if the ECM verifies, London will be under 18' of snow' etc, surely any scenario is possible if the chart verifies? Please explain to a numpty why computer models are just so thrilling and why so much faith is placed in them......
On that basis the ECM or GFS could just put whatever squiggly lines, pretty colours and 850hpa temps on that they like, it doesn't actually mean zip, does it? I can't get my head round the 'well if the ECM verifies, London will be under 18' of snow' etc, surely any scenario is possible if the chart verifies? Please explain to a numpty why computer models are just so thrilling and why so much faith is placed in them......
This is also bugging me, plus the fact tht two different people can see the same model runs and one is getting out his waterproofs and another is looking for the sledge. In the past couple of days I've seen seemingly ebvery possible permutation bar a heatwave.
"In general it's much more difficult for us to do extremes, so whilst many of us love them and crave them, we should perhaps leant to lower our expectation levels and try to enjoy the weather we do get. It maybe difficult for some to accept this fact and to be honest I understand why, but having lived in one of the hottest parts of the world for many years I can assure you there are many millions of people that would give their right arm for our gentle, forgiving climate - we are actually very lucky in the grand scheme of things." -
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#4
johnholmes
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Posted 12 December 2009 - 22:48
Getting different ideas based on a weather model with such a wide range of experience as we have on Net Weather is bound to give widely differing views on what interpretation to put on their output.
Interpretation of the models is something than can be self taught with some basic understanding of the physics involved.
It can also be the result of professional training.
Even with these two levels of knowledge they may well come to a different conclusion.
If we than widen this to those who have no real wish to get into the knowledge angle, no disrespect meant here, but have learnt over a period of time to make decent judgements of the models we see on this site, then we have 3 levels of understanding already.
Add to this mix the enthusiastic newcomer who has not yet learnt how to read them but is excited by the 'buzz' all weather fanatics get, and may mis understand what one poster has said then you can see we have a huge range of understanding on the site.
To take the point of the first poster-I can't agree with your rather down beat view of weather models. Meteorology is based on pure science but with a huge range of variables from T+00 let alone once the models has its 'go' button pressed. All models follow the basic rules of the laws of thermodynamics solved by extremely complex mathematical rules. All of the 3 main models, Met UK, ECMWF and GFS have their own soft ware or algorithms produced by their respective design and forecast teams. One may be better than the other in terms of producing an accurate assessment of the state of the atmosphere at T+6 or T+166 hours. Over a period of time a trained meteorologist gets to know their strong and weak points and will adjust his/her forecast in line with that knowledge. On here of course no one has that deep knowledge or list of + and - points for each model.
The further out from t+00 one goes then obviously the less accurate any model becomes. Unfortunately with two models going out 10 days (T+240) and one to 16 days many on here lose sight of that fallibility.
this is the link to the NOAA model accuracy
http://www.emc.ncep....TATS/STATS.html
One place to see how the models perform in a scientific check is to go to the NOAA website and follow how all the worlds major models perform over 5 and 6 days, for both northern and southern hemisphere, at the level of 500mb. In the old days prior to computers this was known as the level of 'non divergence', which shows how far we have come since then. Its true to a point but not entirely. Again the accuracy of weather forecasts has improved over the decades. In the 50's and 60's it was about 70-75% for 24-48 hours ahead, nothing was done beyond that as the complex equations needed to solve the forecast were way beyond the ability of any human brain. Since then we have got to the stage where the 70-75% accuracy range is now out to about 5 possibly 7 days at times.
I hope this helps to set the ball rolling in a constructive manner and has perhaps addressed a couple of the points raised by the first two posters.
Interpretation of the models is something than can be self taught with some basic understanding of the physics involved.
It can also be the result of professional training.
Even with these two levels of knowledge they may well come to a different conclusion.
If we than widen this to those who have no real wish to get into the knowledge angle, no disrespect meant here, but have learnt over a period of time to make decent judgements of the models we see on this site, then we have 3 levels of understanding already.
Add to this mix the enthusiastic newcomer who has not yet learnt how to read them but is excited by the 'buzz' all weather fanatics get, and may mis understand what one poster has said then you can see we have a huge range of understanding on the site.
To take the point of the first poster-I can't agree with your rather down beat view of weather models. Meteorology is based on pure science but with a huge range of variables from T+00 let alone once the models has its 'go' button pressed. All models follow the basic rules of the laws of thermodynamics solved by extremely complex mathematical rules. All of the 3 main models, Met UK, ECMWF and GFS have their own soft ware or algorithms produced by their respective design and forecast teams. One may be better than the other in terms of producing an accurate assessment of the state of the atmosphere at T+6 or T+166 hours. Over a period of time a trained meteorologist gets to know their strong and weak points and will adjust his/her forecast in line with that knowledge. On here of course no one has that deep knowledge or list of + and - points for each model.
The further out from t+00 one goes then obviously the less accurate any model becomes. Unfortunately with two models going out 10 days (T+240) and one to 16 days many on here lose sight of that fallibility.
this is the link to the NOAA model accuracy
http://www.emc.ncep....TATS/STATS.html
One place to see how the models perform in a scientific check is to go to the NOAA website and follow how all the worlds major models perform over 5 and 6 days, for both northern and southern hemisphere, at the level of 500mb. In the old days prior to computers this was known as the level of 'non divergence', which shows how far we have come since then. Its true to a point but not entirely. Again the accuracy of weather forecasts has improved over the decades. In the 50's and 60's it was about 70-75% for 24-48 hours ahead, nothing was done beyond that as the complex equations needed to solve the forecast were way beyond the ability of any human brain. Since then we have got to the stage where the 70-75% accuracy range is now out to about 5 possibly 7 days at times.
I hope this helps to set the ball rolling in a constructive manner and has perhaps addressed a couple of the points raised by the first two posters.
Edited by johnholmes, 12 December 2009 - 22:51 .
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http://www.johnholmes-weather.co.uk/
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#5
winterfreak
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Posted 12 December 2009 - 22:54
johnholmes, on 12 December 2009 - 22:48 , said:
Getting different ideas based on a weather model with such a wide range of experience as we have on Net Weather is bound to give widely differing views on what interpretation to put on their output.
Interpretation of the models is something than can be self taught with some basic understanding of the physics involved.
It can also be the result of professional training.
Even with these two levels of knowledge they may well come to a different conclusion.
If we than widen this to those who have no real wish to get into the knowledge angle, no disrespect meant here, but have learnt over a period of time to make decent judgements of the models we see on this site, then we have 3 levels of understanding already.
Add to this mix the enthusiastic newcomer who has not yet learnt how to read them but is excited by the 'buzz' all weather fanatics get, and may mis understand what one poster has said then you can see we have a huge range of understanding on the site.
To take the point of the first poster-I can't agree with your rather down beat view of weather models. Meteorology is based on pure science but with a huge range of variables from T+00 let alone once the models has its 'go' button pressed. All models follow the basic rules of the laws of thermodynamics solved by extremely complex mathematical rules. All of the 3 main models, Met UK, ECMWF and GFS have their own soft ware or algorithms produced by their respective design and forecast teams. One may be better than the other in terms of producing an accurate assessment of the state of the atmosphere at T+6 or T+166 hours. Over a period of time a trained meteorologist gets to know their strong and weak points and will adjust his/her forecast in line with that knowledge. On here of course no one has that deep knowledge or list of + and - points for each model.
The further out from t+00 one goes then obviously the less accurate any model becomes. Unfortunately with two models going out 10 days (T+240) and one to 16 days many on here lose sight of that fallibility.
One place to see how the models perform in a scientific check is to go to the NOAA website and follow how all the worlds major models perform over 5 and 6 days, for both northern and southern hemisphere, at the level of 500mb. In the old days prior to computers this was known as the level of 'non divergence', which shows how far we have come since then. Its true to a point but not entirely. Again the accuracy of weather forecasts has improved over the decades. In the 50's and 60's it was about 70-75% for 24-48 hours ahead, nothing was done beyond that as the complex equations needed to solve the forecast were way beyond the ability of any human brain. Since then we have got to the stage where the 70-75% accuracy range is now out to about 5 possibly 7 days at times.
I hope this helps to set the ball rolling in a constructive manner and has perhaps addressed a couple of the points raised by the first two posters.
Interpretation of the models is something than can be self taught with some basic understanding of the physics involved.
It can also be the result of professional training.
Even with these two levels of knowledge they may well come to a different conclusion.
If we than widen this to those who have no real wish to get into the knowledge angle, no disrespect meant here, but have learnt over a period of time to make decent judgements of the models we see on this site, then we have 3 levels of understanding already.
Add to this mix the enthusiastic newcomer who has not yet learnt how to read them but is excited by the 'buzz' all weather fanatics get, and may mis understand what one poster has said then you can see we have a huge range of understanding on the site.
To take the point of the first poster-I can't agree with your rather down beat view of weather models. Meteorology is based on pure science but with a huge range of variables from T+00 let alone once the models has its 'go' button pressed. All models follow the basic rules of the laws of thermodynamics solved by extremely complex mathematical rules. All of the 3 main models, Met UK, ECMWF and GFS have their own soft ware or algorithms produced by their respective design and forecast teams. One may be better than the other in terms of producing an accurate assessment of the state of the atmosphere at T+6 or T+166 hours. Over a period of time a trained meteorologist gets to know their strong and weak points and will adjust his/her forecast in line with that knowledge. On here of course no one has that deep knowledge or list of + and - points for each model.
The further out from t+00 one goes then obviously the less accurate any model becomes. Unfortunately with two models going out 10 days (T+240) and one to 16 days many on here lose sight of that fallibility.
One place to see how the models perform in a scientific check is to go to the NOAA website and follow how all the worlds major models perform over 5 and 6 days, for both northern and southern hemisphere, at the level of 500mb. In the old days prior to computers this was known as the level of 'non divergence', which shows how far we have come since then. Its true to a point but not entirely. Again the accuracy of weather forecasts has improved over the decades. In the 50's and 60's it was about 70-75% for 24-48 hours ahead, nothing was done beyond that as the complex equations needed to solve the forecast were way beyond the ability of any human brain. Since then we have got to the stage where the 70-75% accuracy range is now out to about 5 possibly 7 days at times.
I hope this helps to set the ball rolling in a constructive manner and has perhaps addressed a couple of the points raised by the first two posters.
Edited by winterfreak, 12 December 2009 - 22:57 .
Location: Tonbridge, Kent.
#6
mike Meehan
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Posted 13 December 2009 - 01:18
I have been following the GFS 500/SL charts, together with the Meteociel and each run especially out towards the longer term are fluctuating quite wildly as far as our little maritime spot is concerned.
There are patches of quite cold and probably snowy weather due but it is debatable as to how much will reach us - most of the really cold bits seem to run out of puff on the other side of the channel.
On the other hand the Greenland* high seems to be waxing and waning, and for the moment the westerlies have lost their oomph.
At the moment I get the impression that we are just being teased - we are going into a colder spell for the moment but after all it is December but whether we reach a sub zero state in SE England this side of the New Year, I think is debatable - I expect we will get a little snow, most likely the slushey stuff, most probably just before Christmas. I suspect it will warm for a little while but if the Westerlies are still lacking their oomph, then we could get a proper cold spell in the New Year after the continent has cooled further.
*It was a the setup of a Greenland high on 26.12.1962 which heralded the start to the '62/63 winter.
No matter how many computers we put on the job and how good our maths are the weather still makes its own mind up as to what it is going to do. The best we can hope to do is to get a very broad outline of future events and still not be able to forecast whether hurricane force winds are going into northern France or southern England; sorry for that Michael.
There are patches of quite cold and probably snowy weather due but it is debatable as to how much will reach us - most of the really cold bits seem to run out of puff on the other side of the channel.
On the other hand the Greenland* high seems to be waxing and waning, and for the moment the westerlies have lost their oomph.
At the moment I get the impression that we are just being teased - we are going into a colder spell for the moment but after all it is December but whether we reach a sub zero state in SE England this side of the New Year, I think is debatable - I expect we will get a little snow, most likely the slushey stuff, most probably just before Christmas. I suspect it will warm for a little while but if the Westerlies are still lacking their oomph, then we could get a proper cold spell in the New Year after the continent has cooled further.
*It was a the setup of a Greenland high on 26.12.1962 which heralded the start to the '62/63 winter.
No matter how many computers we put on the job and how good our maths are the weather still makes its own mind up as to what it is going to do. The best we can hope to do is to get a very broad outline of future events and still not be able to forecast whether hurricane force winds are going into northern France or southern England; sorry for that Michael.
I was standing by a lamp post at the corner of the street,
in case a little snow flake passes by,
oh me, oh my,
in case a little snow flake passes by
in case a little snow flake passes by,
oh me, oh my,
in case a little snow flake passes by
#7
Paul
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Posted 13 December 2009 - 11:34
Bumping this as we will now have three model threads on the go, please see this post for more info:
http://forum.netweat...cs-please-read/
http://forum.netweat...cs-please-read/
'Views and opinions expressed in this or any other of my posts are my own'
#8
Thundery wintry showers
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Posted 15 December 2009 - 20:32
Tonight's models are all very interesting.
Firstly, tomorrow: the GFS indicates a front moving south and bumping into some fairly cold continental air that has accumulated over East Anglia and the southeast. For most parts this front will only produce rain- indeed near the east coast it will be several degrees above freezing. But in East Anlgia and the southeast there may be some sleet or snow on the front as it pushes in:
http://charts.netwea.../h850t850eu.png
http://charts.netwea.../uksnowrisk.png
Don't expect any of it to settle though.
Into Thursday/Friday, and the easterly for those two days has upgraded in intensity, both in terms of cold and precipitation, over the last two days. Here's the GFS chart for midnight Thursday/Friday:
http://charts.netwea.../60/h500slp.png
http://charts.netwea.../h850t850eu.png
The ECMWF and the Met Office FAX charts are strongly agreed on this scenario. A very strong east-north-easterly flow is in prospect with sub -10C 850hPa values coming in quite widely. Thursday will have increasingly wintry showers in the east, the possibility of some longer outbreaks of sleet and snow associated with weak fronts embedded in the easterly flow, and localised occurrences of thundersnow cannot be ruled out due to the sharp contrast between the exceptionally cold upper air and the anomalously warm North Sea.
Overnight Thursday/Friday we should see widespread accumulations of snow inland but near the coast a barrage of hail and sleet is likely initially but as the wind slackens accumulations can be expected even along the coast. Showers will become confined to the east coast on Friday.
The upcoming northerly has some disagreement as to its orientation. All models are agreed on a front moving south on Saturday with a pool of warmer air out to the west- I expect this to mean rain or sleet in western Britain but more snow for many eastern districts.
http://charts.netwea.../h850t850eu.png
Further ahead there's some disagreement about the orientation of the northerly flow with GFS going for a straight N'ly with snow showers in the east, while ECMWF goes for a NW'ly with snow showers in the west:
http://212.100.247.1.../ecm500.120.png
http://charts.netwea...120/h500slp.png
Disagreement increases when the question of "when will the setup break down?" arises. The UKMO has a low travelling across the UK already by T+144 (21st December) and potentially bringing in milder air. However, the ECMWF has it slipping by to the south:
http://212.100.247.1.../ecm500.168.png
...and GFS has it quite some way away to the south.
If I had to make a stab as to the likely timing of the breakdown I think 22nd December at the earliest, and most likely around Christmas Day, which leaves the possibility of a white Christmas on a knife edge.
Firstly, tomorrow: the GFS indicates a front moving south and bumping into some fairly cold continental air that has accumulated over East Anglia and the southeast. For most parts this front will only produce rain- indeed near the east coast it will be several degrees above freezing. But in East Anlgia and the southeast there may be some sleet or snow on the front as it pushes in:
http://charts.netwea.../h850t850eu.png
http://charts.netwea.../uksnowrisk.png
Don't expect any of it to settle though.
Into Thursday/Friday, and the easterly for those two days has upgraded in intensity, both in terms of cold and precipitation, over the last two days. Here's the GFS chart for midnight Thursday/Friday:
http://charts.netwea.../60/h500slp.png
http://charts.netwea.../h850t850eu.png
The ECMWF and the Met Office FAX charts are strongly agreed on this scenario. A very strong east-north-easterly flow is in prospect with sub -10C 850hPa values coming in quite widely. Thursday will have increasingly wintry showers in the east, the possibility of some longer outbreaks of sleet and snow associated with weak fronts embedded in the easterly flow, and localised occurrences of thundersnow cannot be ruled out due to the sharp contrast between the exceptionally cold upper air and the anomalously warm North Sea.
Overnight Thursday/Friday we should see widespread accumulations of snow inland but near the coast a barrage of hail and sleet is likely initially but as the wind slackens accumulations can be expected even along the coast. Showers will become confined to the east coast on Friday.
The upcoming northerly has some disagreement as to its orientation. All models are agreed on a front moving south on Saturday with a pool of warmer air out to the west- I expect this to mean rain or sleet in western Britain but more snow for many eastern districts.
http://charts.netwea.../h850t850eu.png
Further ahead there's some disagreement about the orientation of the northerly flow with GFS going for a straight N'ly with snow showers in the east, while ECMWF goes for a NW'ly with snow showers in the west:
http://212.100.247.1.../ecm500.120.png
http://charts.netwea...120/h500slp.png
Disagreement increases when the question of "when will the setup break down?" arises. The UKMO has a low travelling across the UK already by T+144 (21st December) and potentially bringing in milder air. However, the ECMWF has it slipping by to the south:
http://212.100.247.1.../ecm500.168.png
...and GFS has it quite some way away to the south.
If I had to make a stab as to the likely timing of the breakdown I think 22nd December at the earliest, and most likely around Christmas Day, which leaves the possibility of a white Christmas on a knife edge.
"There is always an easy solution to every human problem - neat, plausible, and wrong." - H L Mencken
Weather records for Cleadon, 1993-2011:
http://tws27.50webs....ther/index.html
My personal manifesto can be found here:
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http://tws27.50webs....nemy/index.html
'Views and opinions expressed in this or any other of my posts are my own'
Weather records for Cleadon, 1993-2011:
http://tws27.50webs....ther/index.html
My personal manifesto can be found here:
http://tws27.50webs.com/index.html
My upcoming modification for Doom 3:
http://tws27.50webs....nemy/index.html
'Views and opinions expressed in this or any other of my posts are my own'
#9
Glacier Point
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Posted 15 December 2009 - 20:35
Some highly rarified synoptics being prgrammed right now with a retrogressing high latitude block and polar trough dropping into Scandinavia with the jet stream highly depressed and large puddle of cold air ensconsed over much of NW Europe. The models may well struggle with the detail here, both long and short term. A good time then to step back with some considered analysis.
Overall global angular momentum is slightly above average. Most importantly, positive (west) wind anomalies which developed over the Equator mid November onwards have been fluxed poleward over the last three weeks c/o zonal mean transports. Note the upward spike in angular momentum. This is setting the scene for a cold pattern to return into January. More on that later.
Relative angular momentum is now shaping upward thanks to fluxing of westerlies from the tropics into the sub-tropics across 30N. This can be seen as a positive (west) angular momentum anomaly on the plots. These west winds continue across the Pacific and will prop up realtive and total angular momentum, ensuring that we will continue to orbit around phase 4 of the Global Wind Oscillation.
Latest updates identify a developing positive mountain torque which is driving tendency in relative angular momentum and the GWO well into phase 4:
What this means is that we will more than likely close out the month with the GWO in phase 4. Composites suggest that the upper flow will tend to be flat and extend into Europe. With the cold pool established, any erosion from the south is likely to be attritional and not likely to displace the cold pool totally, more so from the north of the UK.
Some northward extension of the Atlantic airmass is however likely, purely as a downstream result of the Atlantic trough. Where this comes into contact with the cold Arctic airmass, there will be a battleground scenario develop. Christmas or just before looks really interesting from this point of view, perhaps temperatures recovering to average in the south of the UK between Christmas and New Year, the more average conditions pushing slightly further north around New Year.
Moving forward, we are starting to see a convective signal come into the Indian Ocean where SSTAs are supportive of deep convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies which will propagate across the tropics into the sub-tropics. With the west wind additions generated in November still in the system, total and relative angular momentum will increase sending the GWO into a phase 5 orbit. Torques will vary this orbit backwards and forwards around phases 5-6-7 in January.
Composites for these phases suggest a strong -NAO signal with positive height anomalies across the North Atlantic from Newfoundland to Iceland.
Overall global angular momentum is slightly above average. Most importantly, positive (west) wind anomalies which developed over the Equator mid November onwards have been fluxed poleward over the last three weeks c/o zonal mean transports. Note the upward spike in angular momentum. This is setting the scene for a cold pattern to return into January. More on that later.
Relative angular momentum is now shaping upward thanks to fluxing of westerlies from the tropics into the sub-tropics across 30N. This can be seen as a positive (west) angular momentum anomaly on the plots. These west winds continue across the Pacific and will prop up realtive and total angular momentum, ensuring that we will continue to orbit around phase 4 of the Global Wind Oscillation.
Latest updates identify a developing positive mountain torque which is driving tendency in relative angular momentum and the GWO well into phase 4:
What this means is that we will more than likely close out the month with the GWO in phase 4. Composites suggest that the upper flow will tend to be flat and extend into Europe. With the cold pool established, any erosion from the south is likely to be attritional and not likely to displace the cold pool totally, more so from the north of the UK.
Some northward extension of the Atlantic airmass is however likely, purely as a downstream result of the Atlantic trough. Where this comes into contact with the cold Arctic airmass, there will be a battleground scenario develop. Christmas or just before looks really interesting from this point of view, perhaps temperatures recovering to average in the south of the UK between Christmas and New Year, the more average conditions pushing slightly further north around New Year.
Moving forward, we are starting to see a convective signal come into the Indian Ocean where SSTAs are supportive of deep convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies which will propagate across the tropics into the sub-tropics. With the west wind additions generated in November still in the system, total and relative angular momentum will increase sending the GWO into a phase 5 orbit. Torques will vary this orbit backwards and forwards around phases 5-6-7 in January.
Composites for these phases suggest a strong -NAO signal with positive height anomalies across the North Atlantic from Newfoundland to Iceland.
"I submit those who take the time to understand these kinds of issues scientifically will have a better understanding of subseasonal matters/global atmospheric dynamics including making predictions (on average), than those who just use numerical model forecasts as a stand alone."
Ed Berry (2009).
Ed Berry (2009).
#10
bluearmy
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Posted 15 December 2009 - 21:03
http://www.meteociel...0&ech=192&map=1
GP's composite looks a pretty good fit in our part of the NH wrt the GEM/GEFS ens mean.
GP's composite looks a pretty good fit in our part of the NH wrt the GEM/GEFS ens mean.
#11
Jackone
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Posted 15 December 2009 - 23:02
Thundery wintry showers, on 15 December 2009 - 20:32 , said:
Tonight's models are all very interesting.
Firstly, tomorrow: the GFS indicates a front moving south and bumping into some fairly cold continental air that has accumulated over East Anglia and the southeast. For most parts this front will only produce rain- indeed near the east coast it will be several degrees above freezing. But in East Anlgia and the southeast there may be some sleet or snow on the front as it pushes in:
http://charts.netwea.../h850t850eu.png
http://charts.netwea.../uksnowrisk.png
Don't expect any of it to settle though.
Into Thursday/Friday, and the easterly for those two days has upgraded in intensity, both in terms of cold and precipitation, over the last two days. Here's the GFS chart for midnight Thursday/Friday:
http://charts.netwea.../60/h500slp.png
http://charts.netwea.../h850t850eu.png
The ECMWF and the Met Office FAX charts are strongly agreed on this scenario. A very strong east-north-easterly flow is in prospect with sub -10C 850hPa values coming in quite widely. Thursday will have increasingly wintry showers in the east, the possibility of some longer outbreaks of sleet and snow associated with weak fronts embedded in the easterly flow, and localised occurrences of thundersnow cannot be ruled out due to the sharp contrast between the exceptionally cold upper air and the anomalously warm North Sea.
Overnight Thursday/Friday we should see widespread accumulations of snow inland but near the coast a barrage of hail and sleet is likely initially but as the wind slackens accumulations can be expected even along the coast. Showers will become confined to the east coast on Friday.
The upcoming northerly has some disagreement as to its orientation. All models are agreed on a front moving south on Saturday with a pool of warmer air out to the west- I expect this to mean rain or sleet in western Britain but more snow for many eastern districts.
http://charts.netwea.../h850t850eu.png
Further ahead there's some disagreement about the orientation of the northerly flow with GFS going for a straight N'ly with snow showers in the east, while ECMWF goes for a NW'ly with snow showers in the west:
http://212.100.247.1.../ecm500.120.png
http://charts.netwea...120/h500slp.png
Disagreement increases when the question of "when will the setup break down?" arises. The UKMO has a low travelling across the UK already by T+144 (21st December) and potentially bringing in milder air. However, the ECMWF has it slipping by to the south:
http://212.100.247.1.../ecm500.168.png
...and GFS has it quite some way away to the south.
If I had to make a stab as to the likely timing of the breakdown I think 22nd December at the earliest, and most likely around Christmas Day, which leaves the possibility of a white Christmas on a knife edge.
Firstly, tomorrow: the GFS indicates a front moving south and bumping into some fairly cold continental air that has accumulated over East Anglia and the southeast. For most parts this front will only produce rain- indeed near the east coast it will be several degrees above freezing. But in East Anlgia and the southeast there may be some sleet or snow on the front as it pushes in:
http://charts.netwea.../h850t850eu.png
http://charts.netwea.../uksnowrisk.png
Don't expect any of it to settle though.
Into Thursday/Friday, and the easterly for those two days has upgraded in intensity, both in terms of cold and precipitation, over the last two days. Here's the GFS chart for midnight Thursday/Friday:
http://charts.netwea.../60/h500slp.png
http://charts.netwea.../h850t850eu.png
The ECMWF and the Met Office FAX charts are strongly agreed on this scenario. A very strong east-north-easterly flow is in prospect with sub -10C 850hPa values coming in quite widely. Thursday will have increasingly wintry showers in the east, the possibility of some longer outbreaks of sleet and snow associated with weak fronts embedded in the easterly flow, and localised occurrences of thundersnow cannot be ruled out due to the sharp contrast between the exceptionally cold upper air and the anomalously warm North Sea.
Overnight Thursday/Friday we should see widespread accumulations of snow inland but near the coast a barrage of hail and sleet is likely initially but as the wind slackens accumulations can be expected even along the coast. Showers will become confined to the east coast on Friday.
The upcoming northerly has some disagreement as to its orientation. All models are agreed on a front moving south on Saturday with a pool of warmer air out to the west- I expect this to mean rain or sleet in western Britain but more snow for many eastern districts.
http://charts.netwea.../h850t850eu.png
Further ahead there's some disagreement about the orientation of the northerly flow with GFS going for a straight N'ly with snow showers in the east, while ECMWF goes for a NW'ly with snow showers in the west:
http://212.100.247.1.../ecm500.120.png
http://charts.netwea...120/h500slp.png
Disagreement increases when the question of "when will the setup break down?" arises. The UKMO has a low travelling across the UK already by T+144 (21st December) and potentially bringing in milder air. However, the ECMWF has it slipping by to the south:
http://212.100.247.1.../ecm500.168.png
...and GFS has it quite some way away to the south.
If I had to make a stab as to the likely timing of the breakdown I think 22nd December at the earliest, and most likely around Christmas Day, which leaves the possibility of a white Christmas on a knife edge.
Very good summary there Ian, indeed a slight chance of a bit of snow overnight in a few places, but considering what is likely to follow this should not really be that significant.From a westerly perspective I am looking at the front set to push SW into Thursday.
Looking at this the precipitation is likely to start off as rain, but as the colder air digs in, it may well start to turn to snow overnight, as it pushes SW especially over hills. However, dew points are largely just above freezing, so this a very marginal event.
As the colder air digs in from the east later on Thursday, as mentioned elsewhere, heavy and frequent snow showers are likely in eastern areas, with the chance of some getting further west, as shown by the 00Hz chart, this would be much more likely to be entirely snow, but with much less certainty of getting west.
Looking ahead to the weekend. chances of frontal snow edging down from the north, but also with the risk of showers in the west this time from likely NW winds, although showers cannot be ruled either in eastern coastal districts, however if fronts develop with small mild sectors, this is likely to pep up showery activity for many, but making this more marginal for those in the west. However with dew points below zero, this could quite a snowy front.
The breakdown scenario is still far from settled, but at this stage, a cold and snowy one could be very possible, with a very real chance of the cold lasting until Christmas itself.
Find the latest and last for the season Ski and snow Blog for the Alps 2011-2012 here.
http://forum.netweat...season-wrap-up/
Much milder this week for the end of the season.
http://forum.netweat...ions-2011-2012/
Views and opinions expressed in this or any other of my posts are my own
http://forum.netweat...season-wrap-up/
Much milder this week for the end of the season.
http://forum.netweat...ions-2011-2012/
Views and opinions expressed in this or any other of my posts are my own
#12
Glacier Point
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Posted 16 December 2009 - 20:15
Quite a significant update to angular momentum budgets.
Relative angular momentum has increased sharply over the last 24 hours c/o large momentum transport across 20-30N:
http://www.esrl.noaa...m.sig.90day.gif
That's a +1.5 SD anomaly there over the tropics.
Mountain torques are also adding westerlies to the system driving the GWO towards phase 5 (yesterday's assessment was towards phase 4).
http://www.esrl.noaa...gcm/gwo_40d.gif
The evolution being advertised is not unreasonable given the composites for phase 5 in December:
That's a perfect match for the projected pattern across the NH from Christmas onwards on tonight's runs.
However, I am unsure about the extent of mountain torque which would tend to keep the GWO in phase 4 which is would tend to flatten the jet out a little. Also, we have the added complication of tropical convection around the Dateline:
http://cawcr.gov.au/...m/OLR/m.3d.html
which would tend for force height rises to the north over Iceland c/o a suppressed jetstream. As we approach January, seasonal wavelength changes will also take effect, making phase 5 composites more inclined towards height rises over Iceland.
Hugely complicated set up. If pushed I'd still incline towards a more gradual breakdown with pressure lower over the continent which sould take the first shortwave underneath the UK next week, but thereafter, gradually becoming less cold I'd say for a time. However, as per the posting yesterday, the further we get towards phase 5 in January, the better the prospects for a solid -NAO to develop.
Relative angular momentum has increased sharply over the last 24 hours c/o large momentum transport across 20-30N:
http://www.esrl.noaa...m.sig.90day.gif
That's a +1.5 SD anomaly there over the tropics.
Mountain torques are also adding westerlies to the system driving the GWO towards phase 5 (yesterday's assessment was towards phase 4).
http://www.esrl.noaa...gcm/gwo_40d.gif
The evolution being advertised is not unreasonable given the composites for phase 5 in December:
That's a perfect match for the projected pattern across the NH from Christmas onwards on tonight's runs.
However, I am unsure about the extent of mountain torque which would tend to keep the GWO in phase 4 which is would tend to flatten the jet out a little. Also, we have the added complication of tropical convection around the Dateline:
http://cawcr.gov.au/...m/OLR/m.3d.html
which would tend for force height rises to the north over Iceland c/o a suppressed jetstream. As we approach January, seasonal wavelength changes will also take effect, making phase 5 composites more inclined towards height rises over Iceland.
Hugely complicated set up. If pushed I'd still incline towards a more gradual breakdown with pressure lower over the continent which sould take the first shortwave underneath the UK next week, but thereafter, gradually becoming less cold I'd say for a time. However, as per the posting yesterday, the further we get towards phase 5 in January, the better the prospects for a solid -NAO to develop.
"I submit those who take the time to understand these kinds of issues scientifically will have a better understanding of subseasonal matters/global atmospheric dynamics including making predictions (on average), than those who just use numerical model forecasts as a stand alone."
Ed Berry (2009).
Ed Berry (2009).
#13
Glacier Point
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Posted 17 December 2009 - 20:34
So, so much going right now.
It's becoming very evident that the atmosphere is attempting to break out of the shackles of the Nina-like pattern we have been in for the last 3 years. Total and relative anugular momentum is showing a clear and persistent upward trend:
http://www.esrl.noaa...s/aam/glaam.gif
http://www.esrl.noaa...m.sig.90day.gif
The sharp eyed will note that this is almost exclusively coming from a band of anomalously strong zonal westerly winds across 30N. A significant part of this is accounted by a strengthening sub-tropical jet, a real pinneapple express running at 50 - 60 m/s.
Mountain torques are continung to spike upwards and the combination of the torques and upward shift in angular momentum has driven the GWO into high amplitude phase 4.
http://www.esrl.noaa...gcm/gwo_40d.gif
With continued additions of westerly winds very likely, angular momentum will continue to rise towards the Nino attractor side. Thus a transition is underway from phase 4 to phase 5 of the GWO.
The timing looks to be the between Christmas and New Year. Composites as per yesterdays posting - phase 4 flatter flow, phase 5 more amplified and the trough deeper but centred to our west. The transition from cold to less cold looks to be Christmas to New Year.
The real significance of the increase in angular momentum is its implication for January's pattern. There is now a strong -NAO long term signal emerging as phases 5-6-7 of the GWO are now very likley. This teleconnects to a negative NAO.
Looking at it from a different angle, current GFS Ensemble Mean height anomaly days 11-15 depicts the strong 3-wave pattern that has characterised the nothern hemispheric flow over the secod half of the month.
http://raleighwx.eas...htAnomalyNH.gif
Composites for years with this 3-wave pattern also go for....
..... a negative NAO. The trigger, it would seem, are the changing seasonal wavelengths.
Also, take a look at the current SSTA plot:
http://weather.unisy...e/sst_anom.html
There is already a tripole signal there. Note the cold water mid Atlantic. GFS ensembles suggest -4 to -8C 850 hPa anomalies across the 15 days in the central Atlantic. Here's t216 projection:
http://raleighwx.eas...nomalyNH216.gif
Cold air aloft, cold air on the surface = feedback loop for further low pressure. That is another signal for a -NAO to really take charge into January.
It's also worth bearing mind that of all the winter months, December shows the weakest correlation between the AO and NAO. Into January, the NAO and AO become more connected. With the AO absolutely flat lined, and continued blocking signals, we should expect a stronger hook-up between the two aspects of the Northern Annular Mode.
It's becoming very evident that the atmosphere is attempting to break out of the shackles of the Nina-like pattern we have been in for the last 3 years. Total and relative anugular momentum is showing a clear and persistent upward trend:
http://www.esrl.noaa...s/aam/glaam.gif
http://www.esrl.noaa...m.sig.90day.gif
The sharp eyed will note that this is almost exclusively coming from a band of anomalously strong zonal westerly winds across 30N. A significant part of this is accounted by a strengthening sub-tropical jet, a real pinneapple express running at 50 - 60 m/s.
Mountain torques are continung to spike upwards and the combination of the torques and upward shift in angular momentum has driven the GWO into high amplitude phase 4.
http://www.esrl.noaa...gcm/gwo_40d.gif
With continued additions of westerly winds very likely, angular momentum will continue to rise towards the Nino attractor side. Thus a transition is underway from phase 4 to phase 5 of the GWO.
The timing looks to be the between Christmas and New Year. Composites as per yesterdays posting - phase 4 flatter flow, phase 5 more amplified and the trough deeper but centred to our west. The transition from cold to less cold looks to be Christmas to New Year.
The real significance of the increase in angular momentum is its implication for January's pattern. There is now a strong -NAO long term signal emerging as phases 5-6-7 of the GWO are now very likley. This teleconnects to a negative NAO.
Looking at it from a different angle, current GFS Ensemble Mean height anomaly days 11-15 depicts the strong 3-wave pattern that has characterised the nothern hemispheric flow over the secod half of the month.
http://raleighwx.eas...htAnomalyNH.gif
Composites for years with this 3-wave pattern also go for....
..... a negative NAO. The trigger, it would seem, are the changing seasonal wavelengths.
Also, take a look at the current SSTA plot:
http://weather.unisy...e/sst_anom.html
There is already a tripole signal there. Note the cold water mid Atlantic. GFS ensembles suggest -4 to -8C 850 hPa anomalies across the 15 days in the central Atlantic. Here's t216 projection:
http://raleighwx.eas...nomalyNH216.gif
Cold air aloft, cold air on the surface = feedback loop for further low pressure. That is another signal for a -NAO to really take charge into January.
It's also worth bearing mind that of all the winter months, December shows the weakest correlation between the AO and NAO. Into January, the NAO and AO become more connected. With the AO absolutely flat lined, and continued blocking signals, we should expect a stronger hook-up between the two aspects of the Northern Annular Mode.
"I submit those who take the time to understand these kinds of issues scientifically will have a better understanding of subseasonal matters/global atmospheric dynamics including making predictions (on average), than those who just use numerical model forecasts as a stand alone."
Ed Berry (2009).
Ed Berry (2009).
#14
Dingwantssnow
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Posted 17 December 2009 - 21:16
GP, would you say then that the breakdown wont be too mild and will generally be on the cool side up to new year?? Then january has the potential to become alot colder than it is now?
Edited by Dingwantssnow, 17 December 2009 - 21:17 .
#15
Glacier Point
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Posted 17 December 2009 - 21:38
Yes, I would agree with that summary.
Both GFS and GEM day 11-15 mean temperature anomalies both suggest around average values with the colder than average air not too far away over Scandinavia. Thereafter, I think the broad solution offered by the 06z GFS operational looks the most plausible with colder air edging back south-west from the north and north-east as blocking towards Svalbad starts to take effect.
Both GFS and GEM ensembles are starting to suggest this at t360:
http://raleighwx.eas...nomalyNH360.gif
http://raleighwx.eas...nomalyNH360.gif
although I think we need to be looking right across from Newfoundland to Iceland for blocking signals into January.
Both GFS and GEM day 11-15 mean temperature anomalies both suggest around average values with the colder than average air not too far away over Scandinavia. Thereafter, I think the broad solution offered by the 06z GFS operational looks the most plausible with colder air edging back south-west from the north and north-east as blocking towards Svalbad starts to take effect.
Both GFS and GEM ensembles are starting to suggest this at t360:
http://raleighwx.eas...nomalyNH360.gif
http://raleighwx.eas...nomalyNH360.gif
although I think we need to be looking right across from Newfoundland to Iceland for blocking signals into January.
"I submit those who take the time to understand these kinds of issues scientifically will have a better understanding of subseasonal matters/global atmospheric dynamics including making predictions (on average), than those who just use numerical model forecasts as a stand alone."
Ed Berry (2009).
Ed Berry (2009).
#16
Pomeroysnow
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Posted 17 December 2009 - 21:51
Hello GP in your experience have you ever seen a trend like this before especially in a El nino year?
Thanks in advance
Thanks in advance
#17
Glacier Point
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Posted 17 December 2009 - 22:00
Yes - 1958/59, 1963/4, 1965/6, 1968/69, 1979/80 and perhaps 1976/77
"I submit those who take the time to understand these kinds of issues scientifically will have a better understanding of subseasonal matters/global atmospheric dynamics including making predictions (on average), than those who just use numerical model forecasts as a stand alone."
Ed Berry (2009).
Ed Berry (2009).
#18
Pomeroysnow
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Posted 17 December 2009 - 22:07
Quite a gap since the last one then, interesting
#19
BLAST FROM THE PAST
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Posted 17 December 2009 - 23:33
Glacier Point, on 17 December 2009 - 22:00 , said:
Yes - 1958/59, 1963/4, 1965/6, 1968/69, 1979/80 and perhaps 1976/77
Thanks for the update Stewart. Of all the analogue years the 65/6 pattern looks like the one we may well follow.
regards
BFTP
Perturbation cycle, -ve PDO phase playing havoc with the background signals which are supposed to bring a flat and mild pattern. It is IMO clear we are in a new cycle and that the jet is more south, more amplified and that the chances of cold winters or very cold periods in winter are enhanced....
BFTP
BFTP
#20
kippure
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Posted 19 December 2009 - 13:06
Where would i get an up to date veiw of the 850,s from the 1st of febuary to 7th of march 1947. I can view the charts here on NW in the archive section, but has anyone brought them into the way we see the charts nowadays.
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