Model Output Discussion 26/08/2012

[Frosty.]

The Gfs 12z shows a changeable/unsettled mix of weather across northern britain as the PFJ ripples across to the north of the uk with bands of rain pushing east but with drier, brighter and warmer intervals, the northern half of scotland does not see any of the anticyclonic influence further south. As for the high, it tends to build northeast next week but never makes it that far north so it could also be a bit disappointing across central britain at times but the south of the uk is shown to be warm or very warm with temps in the range of 22-24c, possibly the warmest day being tuesday but a warm 22c for the rest of next week is plenty good enough in early autumn. The northern hemisphere chart I have posted highlights a possible cool blast from the north as a potent trough moves into scandinavia, something the gfs has been regularly showing on recent runs for around the 2nd week of sept.

Edited August 29, 2012 by Frosty039

[SP1986]

It does look like high pressure forecast will decline further in the next few days, so at the end we might see a day or two of 'settled' weather, before a return to wetter, cooler conditions. In the northern half, perhaps no settled weather likely at all. Quite a difference from just a day a go when high pressure influence was set to last for 4-5 days.

[snowfluff]

It does look like high pressure forecast will decline further in the next few days, so at the end we might see a day or two of 'settled' weather, before a return to wetter, cooler conditions. In the northern half, perhaps no settled weather likely at all. Quite a difference from just a day a go when high pressure influence was set to last for 4-5 days.

And a couple of days ago it was set to last at least 8 days.

[Aaron]

It does look like high pressure forecast will decline further in the next few days, so at the end we might see a day or two of 'settled' weather, before a return to wetter, cooler conditions. In the northern half, perhaps no settled weather likely at all. Quite a difference from just a day a go when high pressure influence was set to last for 4-5 days.

Looks like your standard blink and you'll miss it 2 day warm spell for south eastern England only.

[Summer Sun]

ECM's take tonight

We should get 3 or 4 warm days out of that it won't be wall to wall sun but the air will be mild

By Tuesday a break down may happen but high pressure remains close by

[gottolovethisweather]

And a couple of days ago it was set to last at least 8 days.

I must be careful not to derail the Model discussion here but the GFS 12z ensembles for my location in Central Southern England suggest the 31st August right through to the 6th September (7 days plus)will be high pressure dominated. It is at only by that stage, that is there a doubt about the forecast. Not that this is a gimmee and it is only a local view. As an example, the Nottinghamshire (Central England) ensembles show a similar trend.

Nevertheless, I'll await further output, such as JH's summaries before deciding on whether the weather will be kind to the wildlife and us humans for a change.

It does look like high pressure forecast will decline further in the next few days, so at the end we might see a day or two of 'settled' weather, before a return to wetter, cooler conditions. In the northern half, perhaps no settled weather likely at all. Quite a difference from just a day a go when high pressure influence was set to last for 4-5 days.

IMBY opinion maybe? Not being rude just suggesting. EDIT: also see my corresponding post.

Edited August 29, 2012 by gottolovethisweather

[Summer Sun]

After Tuesday's blip of pressure getting pushed away it soon returns

Low pressure slowly pushes the high south

What is clear tonight is the high pressure will never be far away from the south so the further south you are the better chance of seeing some decent weather

Edited August 29, 2012 by Summer Sun

[AWD]

What's all this about HP lasting only a couple of days etc?

A quick scan through the 12z data suggests a very much HP dominated future for the South, even out into FI, and although not as dominant for the north, there is still enough support for many a dry, respectfully warm day for September too.

Certainly no 2 day blip and it's gone. For the first 10 days or so of Sept, HP is much more dominant than LP, especially the further south you are!

[snow drift]

Good to see that during the summer there is as much disagreement on what the models are showing as there is in the winter. We have, "gone in a Blink" to "a settled period for a decent period of time". High pressure is never far away and as is normal, run to run, things are shifted west then east. I would suggest that the next ten days for many will be pleasant.

The ECM out to 192 shows High pressure close and over much of England. I do appreciate that my location is more favourable than many.

[Summer Sun]

Chilly end to FI but again high pressure remains close by

[Gibby]

Good evening. Here is tonight’s look at the 12zs of the big three.

All models show a Low pressure area currently moving east across the area. A showery SW flow veers NW tomorrow as the Low moves further away and pressure rises strongly from the SW. Tonight will see showers scattered about and almost anywhere could se one. This continues tomorrow morning before dry and bright conditions extend East across most areas by evening. By Friday a strong ridge of High pressure dominates Southern Britain with a warm front moving East over the North with rain and drizzle in places though the day. In the South the ridge will ensure dry conditions but a lot of cloud cover will develop through the day. Saturday and Sunday sees a North-South split continue with cloud and some rain in the North while Southern areas see a lot of cloud too but remain mostly dry apart from the chance of a little rain from a weak cold front moving SE late in the day on Sunday. Monday shows better weather as the High to the SW makes a more meaningful push towards Southern Britain bringing warm and bright conditions for these areas through the day.

GFS then shows a further weak trough move SE across England on Tuesday with another zone of cloud and possible rain in places. Wednesday sees another better day with some sunshine before Thursday becomes cloudy from the West once more with some rain in the North and West. Winds then swing more NW with time as Low pressure sets up over Scandinavia with a cool and showery NW flow for northern areas while the South remains quite dry and bright if cooler. In far FI the UK is influenced by High pressure tracking East to the South of Britain to set up a warm South flow later on though with shallow Low pressure close to the West by the end of the run introducing the risk of some rain.

The GFS Ensembles still show a week of above average uppers across most areas before cooler weather returns 850’s to nearer the long term mean values from the start of week two. The weather is shown to be dry for southern locations with rain for Northern locations on the increase as we move through week 2. The operational was on the cool side of the pack for much of the time before switching to a warm outlier right at the end in the South.

The Jet Stream Forecast shows the flow buckling North through the Eastern Atlantic and diving South over the UK by the weekend before settling into a West to East flow close to Northern Scotland as we move into next week.

UKMO shows High pressure down to the SW of the UK on Tuesday with a West-Northwest airflow over the UK. A lot of dry weather remains for Southern areas but still some rain at times likely for the North. A weak cold front crossing down in the flow could bring a little rain in the South too during the day.

ECM too shows a kink in the isobars at midday on Tuesday no doubt with a band of cloud and light rain likely across England as it moves SE through the day. Behind this front pressure builds from the West again and the UK sees a strong ridge of high pressure bringing fine and sunny conditions with temperatures just on the warm side of average, especially in the South. Later in the week things quickly deteriorate again in the North with the return of wind and rain at times while the South remains under loose grip of High pressure to the Southwest with an increase of cloud but very little rain. The run closes on Day 10 with a cooler North flow with a strong but cool High West of Britain bringing dry and bright conditions next weekend with some very chilly nights should it verify.

In Summary the models still show a High pressure domination next week. It is not a conventional summerlike spell though as its position in the innitial stages of next week is conducive to allow cloud from off the Atlantic and the odd weak front to make its way all the way down to the South Coast on occasion. Further North it’s not until midweek that any meaningful effect of this High is felt and even then it looks quite short-lived as the Atlantic fights back quickly. Nevertheless 90% of the time it will be dry in the South and with fairly warm uppers over us up to next weekend cloud or no cloud it will not feel cold anywhere until the risk of a North or North-westerly flow next weekend brings the risk of a more Autumnal feel for all.

[gottolovethisweather]

In Summary the models still show a High pressure domination next week. It is not a conventional summerlike spell though as its position in the innitial stages of next week is conducive to allow cloud from off the Atlantic and the odd weak front to make its way all the way down to the South Coast on occasion. Further North it’s not until midweek that any meaningful effect of this High is felt and even then it looks quite short-lived as the Atlantic fights back quickly. Nevertheless 90% of the time it will be dry in the South and with fairly warm uppers over us up to next weekend cloud or no cloud it will not feel cold anywhere until the risk of a North or North-westerly flow next weekend brings the risk of a more Autumnal feel for all.

I'm now assuming the highlighted bit is precisely where the conflict of opinions was coming from. Nevertheless, let us see where future outputs take us.

Another fantastic summary from you as ever Gibby, Many Thanks.

*back to lurking*

Edited August 29, 2012 by gottolovethisweather

[Frosty.]

Good to see that during the summer there is as much disagreement on what the models are showing as there is in the winter. We have, "gone in a Blink" to "a settled period for a decent period of time". High pressure is never far away and as is normal, run to run, things are shifted west then east. I would suggest that the next ten days for many will be pleasant.

The ECM out to 192 shows High pressure close and over much of England. I do appreciate that my location is more favourable than many.

Yes it looks increasingly like the high next week will only really benefit the southern half of the uk and more specifically the southern half of england and wales, the rippling polar front jet to the north look like stunting the northward progress of the high sadly and scotland and n.ireland will likely be changeable at best but more likely unsettled throughout the period with just the occasional fine day here and there. It's all very unfortunate for the north but the south should do well next week with temps above or well above average and sunny spells, not unbroken sunshine but enough to satisfy most people. To rub more salt in the wound for northern areas, it looks like an even cooler and more unsettled plunge from the arctic will arrive either at the end of next week or very soon after.

[bluearmy]

not sure that the north of the uk will do sooo badly out of this high next week. i'd say generally decent conditions interspersed with wind and rain. thats the opposite to what might be expected having read a lot of posts this afternoon/evening. of course there will be a frontal band likely somewhere across the uk that separates the cooler air in the north and warmer in the south. that frontal band will probably be generally weak and cloudy but could, from time to time, pep up with some rainfall headed west to east along it.

naefs consistent with bringing back lower heights after the first third of the month but as i posted yesterday, the influx of ex TD's into the north atlantic basin promises to make our week 2 output a bit variable and none too reliable.

[johnholmes]

It does look like high pressure forecast will decline further in the next few days, so at the end we might see a day or two of 'settled' weather, before a return to wetter, cooler conditions. In the northern half, perhaps no settled weather likely at all. Quite a difference from just a day a go when high pressure influence was set to last for 4-5 days.

a rather biased view Stephen, the 4x and 2x daily outputs may show that today, a few days ago they showed high pressure as being dominant to start September.

The overall upper pattern most 500mb outputs, be it NOAA, ECMWF-GFS or the NAEFS outputs suggests something rather different and most have done so for the past 4-6 days. That is an upper air pattern with height anomalies west to east across the UK. So I would expect a westerly type surface high set up giving a surface flow from about west rather than south or southwest as perhaps they suggested several days ago. Nevertheless the balanced view to me is for settled rather unsettled for much of the UK. Yes fronts may affect the most NW'ern areas but the major bulk of the UK is going to have a fairly settled 7-10 days it seems to me. Not wall to wall sunshine for most but not rain each day for most either.

Edited August 29, 2012 by johnholmes

[Gibby]

Good morning. Here’s my interpretation of the 00zs today.

All models show a low pressure and associated showery NW flow currently over Britain moving away East as a High pressure ridge moves in from the West later today. The ridge topples SE over Britain tomorrow and becomes absorbed in a High pressure belt just to the South of the UK over the weekend. A Westerly flow develops over most of Britain over the weekend with a weak trough moving South on Sunday, Monday looks brighter as the high reasserts itself over Britain before relaxing once more on Tuesday as a further trough moves down across Britain. The weather translates into a rather cloudy weekend with some brief sunny intervals in the South tomorrow following a very chilly and clear night tonight. The weekend sees a lot of cloud for all with rain at times in the North and at least a little patchy light rain moving SE through England and Wales on Sunday. The start of next week sees a brighter and warmish day on Monday before a further trough moves SE on Tuesday with further patchy light rain likely as it passes.

GFS then shows the High pressure rebuilding and move East over Britain bringing a fine and warm interlude midweek for all this lasting into Thursday before pressure falls from the West and a more active trough moves East through Britain on Friday bringing rain and fresh winds for all. The model then shows a much more unsettled and cool FI with chilly NW winds and rain at times as Low pressure either sits close to Northern Scotland or moves in from the NW.

The GFS Ensembles have shortened the warm spell this morning with uppers falling to nearer normal values by the 5^th. The weather would stay quite dry though in the South for quite some times as rain amounts are not shown to amount to much until the 2^nd week. The operational was on balance on the cool side of the pack for locations North and South with a lot of spread shown from the 5^th.

The Jet Stream Forecast shows it currently ridging North in the Eastern Atlantic settling to a position West to East over Scotland by the weekend. Next week it ridges and troughs repeatedly close to Scotland around the 55 degree N latitude.

UKMO shows High pressure sitting close to Southern Ireland at the close of its run delivering a spell of dry, bright and pleasantly warm conditions in the middle of next week with sunny spells for many but chilly misty nights too. With High pressure better positioned the North could well join in the better weather at this time.

ECM too shows similar synoptic midweek with High pressure covering the UK with attendant fine and sunny weather likely for all with temperatures comfortably above average by day. Once more some chilly, misty nights look likely. The North too would enjoy this phase of weather next week. Later in the run ECM keeps High pressure firmly in control this morning with its centre drifting very slowly East maintaining a strong ridge Westwards across Britain and out into the Atlantic. The weather would be sunny for all and become comfortably warm by day everywhere and possibly very warm in the South. The end of the run shows things becoming a little more slack though the weather would remain basically dry, warm and sunny for the UK.

In Summary this morning the Euro’s are the favoured option. Both UKMO and ECM set themselves up beautifully for a beautiful middle and end to next week with the crud from this weekend’s cloudy High a thing of the past after Tuesday. GFS however has other ideas with a pull SW of high pressure after the middle of next week allowing a cold and unsettled flavour to the weather in FI. Which one is right? Thats the 64 million dollar question and will mean more runs to substantiate the evidence for and against. What it does illustrate though is that if High pressure is centred further North and East such as ECM shows the end product of the weather for the UK is far better when the Atlantic door is blocked-on this occasion everywhere bar the far NW of Scotland.

[Alex]

Good morning. Here’s my interpretation of the 00zs today.

All models show a low pressure and associated showery NW flow currently over Britain moving away East as a High pressure ridge moves in from the West later today. The ridge topples SE over Britain tomorrow and becomes absorbed in a High pressure belt just to the South of the UK over the weekend. A Westerly flow develops over most of Britain over the weekend with a weak trough moving South on Sunday, Monday looks brighter as the high reasserts itself over Britain before relaxing once more on Tuesday as a further trough moves down across Britain. The weather translates into a rather cloudy weekend with some brief sunny intervals in the South tomorrow following a very chilly and clear night tonight. The weekend sees a lot of cloud for all with rain at times in the North and at least a little patchy light rain moving SE through England and Wales on Sunday. The start of next week sees a brighter and warmish day on Monday before a further trough moves SE on Tuesday with further patchy light rain likely as it passes.

GFS then shows the High pressure rebuilding and move East over Britain bringing a fine and warm interlude midweek for all this lasting into Thursday before pressure falls from the West and a more active trough moves East through Britain on Friday bringing rain and fresh winds for all. The model then shows a much more unsettled and cool FI with chilly NW winds and rain at times as Low pressure either sits close to Northern Scotland or moves in from the NW.

The GFS Ensembles have shortened the warm spell this morning with uppers falling to nearer normal values by the 5^th. The weather would stay quite dry though in the South for quite some times as rain amounts are not shown to amount to much until the 2^nd week. The operational was on balance on the cool side of the pack for locations North and South with a lot of spread shown from the 5^th.

The Jet Stream Forecast shows it currently ridging North in the Eastern Atlantic settling to a position West to East over Scotland by the weekend. Next week it ridges and troughs repeatedly close to Scotland around the 55 degree N latitude.

UKMO shows High pressure sitting close to Southern Ireland at the close of its run delivering a spell of dry, bright and pleasantly warm conditions in the middle of next week with sunny spells for many but chilly misty nights too. With High pressure better positioned the North could well join in the better weather at this time.

ECM too shows similar synoptic midweek with High pressure covering the UK with attendant fine and sunny weather likely for all with temperatures comfortably above average by day. Once more some chilly, misty nights look likely. The North too would enjoy this phase of weather next week. Later in the run ECM keeps High pressure firmly in control this morning with its centre drifting very slowly East maintaining a strong ridge Westwards across Britain and out into the Atlantic. The weather would be sunny for all and become comfortably warm by day everywhere and possibly very warm in the South. The end of the run shows things becoming a little more slack though the weather would remain basically dry, warm and sunny for the UK.

In Summary this morning the Euro’s are the favoured option. Both UKMO and ECM set themselves up beautifully for a beautiful middle and end to next week with the crud from this weekend’s cloudy High a thing of the past after Tuesday. GFS however has other ideas with a pull SW of high pressure after the middle of next week allowing a cold and unsettled flavour to the weather in FI. Which one is right? Thats the 64 million dollar question and will mean more runs to substantiate the evidence for and against. What it does illustrate though is that if High pressure is centred further North and East such as ECM shows the end product of the weather for the UK is far better when the Atlantic door is blocked-on this occasion everywhere bar the far NW of Scotland.

As ever a good summary Gibby, the GFS 00z was a cool outlier though so not sure how much attention we can pay it.

[Frosty.]

The Gfs 00z turns into a horror show for all of the uk from next friday onwards but before then, southern britain has a fairly anticyclonic spell, saturday looks a nice sunny day for the southern half of the uk but then a weakening front pushing south on saturday night with a little rain but then sunday looking good once again in the south of the uk with plenty of sunshine and turning warmer, the gfs shows the warmest weather next monday in the south with temps dropping a little through next week but remaining on the warm side, 24c on monday in eastern england but generally 20-22c thereafter, the midweek period looks the most anticyclonic nationwide but it's very brief. For northern britain it's looking unsettled tomorrow and saturday, sunday looks brighter but then more rain on monday, tuesday improving and then the best day next wednesday but then it's downhill all the way with trouble brewing by thursday to the northwest and with a very cool and unsettled further outlook. The Ecm 00z is rather different as Gibby has mentioned above.

[Thundery Shower]

Im dissapointed with todays run, yesterday look promising with mon > wednesday looking high twenties even 25 - 26c possible. It's looking more between 22 - 24c. what happened to the models or is this just a blip?

[johnholmes]

I recommend the site below for all those who watch each and every GFS output and to some extent the same with ECMWF and UK Met.

http://www.weatheron...08290000&HH=144

click on the expert chart link at the top and then the model you want to see, change the time of issue and see how the models do vary sometimes from run to run.

Mind you even the 500mb anomaly charts are not immune to this. GFS and ECMWF have two quite different views this morning. ECMWF brings back the large upper ridge with an actual centre over southern England for 10 days time. GFS has the ridge way west giving a flow north of west at 500mb.

Neither shows any signs of any tropical activity but this is not unusual and I suspect it is this that is causing most models whatever their output lengths to change. Tropical storms do inject huge amounts of energy and moisture into the atmosphere and at this time of year seem most likely to cause weather models real problems.

Edited August 30, 2012 by johnholmes

[gottolovethisweather]

Im dissapointed with todays run, yesterday look promising with mon > wednesday looking high twenties even 25 - 26c possible. It's looking more between 22 - 24c. what happened to the models or is this just a blip?

You are basing your disappointment on one set of runs, which to me is fraught with danger. Furthermore, you appear to be looking at the specifics of each day in too much detail, a common mistake within these model threads. Especially given your location, if you were to assess the situation, in a broader manner, you would spot a trend. The current trend is undeniably for High Pressure to become established for anything up to a week or thereabouts. The HP cell favouring locations, the further South and West you are situated. The one caveat as per usual being the likelihood of some cloudier intervals under the aforementioned weather pattern.

If you stick with it in here, you will continue to get much more detailed model summaries than mine.

[johnholmes]

further to my post at No 95

To illustrate the point about Tropical storms the low shown to cross the country around T+260-T+288 has an interesting history.

Hurricane Isaac ends up merging into the central states as a flabby sort of area of low pressure, see GFS N America about T+72 to T+96 and moves east starting to deepen as cold air to the north interacts with its warm core. By T+168 it’s a centre of below 995mb over the far east of Canada/USA. This can then be picked up on the GFS charts we normally look at. At T+192 it’s a deep low south of Newfoundland. Track its progress then—

So although it’s not actually the hurricane it’s the remnants of it that GFS wants to move across North America and out into the Atlantic.

Have a look then at the Net Wx Extra 1000-500mb charts from T+192 as the low comes across the Atlantic to see just how much ‘heat’ it still carries with it to start with?

Interesting-of course the next run may decide not to have the ex hurricane as a major player but this variation does illustrate the massive amounts of heat and moisture that can so easily upset longer range patterns.

And to complicate matters even more, see NOOA link below about TS Kirk!

http://www.nhc.noaa....?large#contents

and easily seen on the GFS outputs including the Net Wx Extra version.

Interesting times-certainly plenty to ekep most folk interested I would think.

Possible ground frosts in sheltered valleys tonight, a risk of some wet snow on the highest Scottish peaks as the cold air edges into that area. Plenty of snow if you watch the web cams in the Alps from later today and into the start of the weekend.

who said the weather was boring?

Met UK are also showing Kirk on their Fax charts

http://www.weatherch...momslp.htm#t120

Edited August 30, 2012 by johnholmes

[Frosty.]

A better 6z for northern areas next week as the anticyclone eventually pushes further north than the gfs 00z showed, so a sunny few days next week for scotland and n.ireland and for central and southern uk, a very settled spell developing next week but the gfs continues to show the warmest weather early in the week with 23-24c in the south and east of england but then not as warm thereafter. The change to unsettled and windier weather is held back to the end of next week but further into FI still looks more generally unsettled and cooler with some vigorous depressions shown.

[Big Innes Madori]

A better 6z for northern areas next week as the anticyclone eventually pushes further north than the gfs 00z showed, so a sunny few days next week for scotland and n.ireland and for central and southern uk, a very settled spell developing next week but the gfs continues to show the warmest weather early in the week with 23-24c in the south and east of england but then not as warm thereafter. The change to unsettled and windier weather is held back to the end of next week but further into FI still looks more generally unsettled and cooler with some vigorous depressions shown.

Top man Frosty

Appreciate how you manage to find a Model output which invites Big Innes and Co to the good weather party.

Worst summer (word summer used very loosely) ever in these parts

[Frosty.]

Top man Frosty

Appreciate how you manage to find a Model output which invites Big Innes and Co to the good weather party.

Worst summer (word summer used very loosely) ever in these parts

Top man Frosty

Appreciate how you manage to find a Model output which invites Big Innes and Co to the good weather party.

Worst summer (word summer used very loosely) ever in these parts

Thanks

I just hope the 6z is a sign that the gfs is heading more towards the ecm with a more settled outlook for all of the uk and not just the southern half.