Model Output Discussion 26/08/2012

[Gibby]

Hi Folks. here's my take on the 12z outputs from GFS, UKMO and ECM taking in the GFS Ensemble and Jet stream data on the way.

All models show a windy and changeable spell of weather between now and Friday with a succession of troughs moving east and SE over the UK at times with rain at times particularly currently, Wednesday and Friday. In between there will be some drier and brighter spells especially in the South on Thursday and towards the weekend. Temperatures will be on the cool side of normal tomorrow before they rise to levels close to the mid september average by the end of the week in the South.

GFS then shows High pressure moving gently east over the south of the UK before exiting East early next week. With a slack pressure gradient over the UK and the source of wind from Europe it will be quite warm and while a lot of areas stay dry for a while a gentle fall in pressure results in Low pressure slipping up from the SW midweek bringing some rain NE with it. The remainder of the run shows alternating pressure patterns between deep low pressure to the NW bringing rain and wind at times mixed with short dry interludes as High pressure croses east over the South.

The GFS Ensembles show a warm up at the end of the week with a very slow fall off towards average 850's by the end of the run for the South with very little rain showing here either until late in the run. The operational was a wildly alternating mild and cold outlier later in the run. For the North things remain more unsettled with rain featuring frequently with 850's stying very slightly above average throughout.

The Jet Stream powers down across the UK in a few days time before weakening somewhat and settling on a West to East axis close to Scotland over the weekend and beyond.

UKMO at noon on Sunday shows High pressure close to the SE with a warm and gentle wind over the South and a light Westerly further North. The likely scenario favours High pressure to move gently East in the following 24hrs with a slack Southerly flow bringing a continuation of warmish conditions in the early days of next week.

ECM mirrors the UKMO output at day 6 evolving on with Low pressure feeding up from the SW becoming a low complex out to the NW by the end of the run. periods of rain and wind look likely for most through the mid stages of next week though with High pressure fairly close to the South again at the end of the run things might not stay unsettled for too long in the South as a ridge is likely to be pumped up from an ex tropical storm approaching the Azores at day 10.

In Summary the mixing of ex tropical storms with the general Atlantic synopses is still playing havoc with the evolutions of the models again tonight. Details are unimportant really as they are likely to change run to run but the general concensus that I can take from the models tonight is that a period of typical early Autumn weather looks likely. That means there will be occasional rain for all when high winds could also occur, all this especially in the North. There will also be periods of dry, bright and at times warm weather, this especially in the South.

[legritter]

aproximately 1900 HRS TO GO AND ITS WINTER . 80 ROTATIONS OF OUR COMPLEX PLANET , 320 gFS UPDATES .160 ecm UPDATES AS MANY UK MET OFFICE UPDATES , LOOK AT THOSE LOVELY RED BERRY UPDATES ,LEAVES A RICH COLOUR UPDATE , OUR FRIEND ACROSS THE WATER UPDATE ,SWANS COMING IN FROM RUSSIA UPDATES , NEWSPAPER UPDATE [ FRIGID WINTER TO GRIP EUROPE AND BRITISH ISLES ,ICE BREAKERS TO BE EMPLOYED IN ENGLISH CHANNEL ,HERE IS MY UPDATE , ENJOY THE MODEL OUTPUT DISCUSSION ITS FREE AND WE WILL LEARN FROM ALL this information , and i must admit meteorological science is starting to pinpoint certain factors that effect the long term weather , i e /density and temp at extreme hights ,and solar influenses .as of the present models , a good old blow for northern parts ,and the possibility of a warm spell next week in the south ,THEN perhaps a northerly ,cheers gang .

[SnowBallz]

https://twitter.com/...124904893161472

What is the success rate of the ECMW winter forecast from three months out?

At the moment it is forecasting a continuation of the zonal mess we have had for a while.

(Flipped from last month, so covering all bases)

As Matt Hugo suggests, mild wet and windy.

Though I suspect the knowleagable will tell that its not worth the paper its printed on.

Intertesting to know though, and as this site is pro ECMW, someone may well have the data.

Thanks in advance.

In short, not even worth consideration.

Think about it: even the most reliable weather model is just about reaching subtle confidence with forecasts out to days 7-10. That in itself represents a massive step forward. There is significant, massive variance in the monthly 30-dayer ECMWF forecast - so much so that I rarely give that much credence either, so why anyone would even begin to take a 3mth forecast, 3mths in advance - it's laughable.

Yes we have patterns, but patterns change - and it's the rate of change/decay which can often be crucial. Put simply, there is absolutely no model on the planet which can accurately forecast out to this range these subtle nuances. I'm sure that - in time (and it will take a VERY long time) confidence will extend to such ambitious ranges, but - until then - I would treat these 'forecasts' with an absolute truck load of salt.

And I have neither a preference for either cold nor mild, by the way - I just know mathematical nonsense when I see it; and believe me, 3mth 'forecasts' are the work of Comedy Central.

[Milhouse]

Still looking odds on for another dry and warm weekend, perhaps becoming very warm in the south on Sunday and more widely on Monday. Whether the warm spell lasts into Tuesday is still unsure but by Monday we should have some very warm air over the south of the UK so if the warm spell were to last till Tuesday it would likely be the hottest day of the upcoming spell. But as has been mentioned its the track of low pressure to the west that will be the all important factor.

Before that its an unsettled, breezy and cool picture during the middle of this week but temperatures tending to rise again and showers becoming more isolated as high pressure nudges in to end the week.

[johnholmes]

https://twitter.com/...124904893161472

What is the success rate of the ECMW winter forecast from three months out?

At the moment it is forecasting a continuation of the zonal mess we have had for a while.

(Flipped from last month, so covering all bases)

As Matt Hugo suggests, mild wet and windy.

Though I suspect the knowleagable will tell that its not worth the paper its printed on.

Intertesting to know though, and as this site is pro ECMW, someone may well have the data.

Thanks in advance.

as others seem to be suggesting any forecast issued 3 months in advance by any model is likely to fail, even with human input from those with a great understanding of the many aspects that need to be taken into account the probability of success is fairly poor in my view. No disrespect to those who are very objective and detailed in their analysis of the data.

A 24 hour forecast has a success rate of about 80% in this country and indeed in any area within the Disturbed Temperate which this country is in. By 10 days that success rate is down to about 60 sometimes 70%. Going further ahead there is no sudden improvement, indeed usually the reverse, so by 3 months the odds on getting the correct synoptic set up is, in my view again, about 1 in 10 if that.

Edited September 10, 2012 by johnholmes

[BLAST FROM THE PAST]

https://twitter.com/...124904893161472

What is the success rate of the ECMW winter forecast from three months out?

At the moment it is forecasting a continuation of the zonal mess we have had for a while.

(Flipped from last month, so covering all bases)

As Matt Hugo suggests, mild wet and windy.

Though I suspect the knowleagable will tell that its not worth the paper its printed on.

Intertesting to know though, and as this site is pro ECMW, someone may well have the data.

Thanks in advance.

Take it with a pinch of salt. Its pretty wet down here tonight and that wasn't forecast even by MetO 24 hrs ago......

BFTP

[Geordiesnow]

We always seem to have posts worrying about what the models are forecasting for the winter months even though its still well over 12 weeks away, happens every year and experience will tell me we will see more post like them in the coming month - regardless what they are showing.

Meanwhile, it seems the models today are going for a slightly windier outlook than last nights outputs were showing which is good too see on a personal POV but the trend has remained the same, generally a deep low pressure in the Norwegian Sea with high pressure just off the coast of Spain and the UK in the middle with gusty westerly veering more to a NW'ly by the end of the week.

The trend for high pressure continues as we head into next weekend, so a drier set up is looking more likely, its just a question how dry and warm its going to be, orientation of the high is going to important. On paper, the ECM output looks better for a warm and sunny weekend than the UKMO does.

[Frosty.]

The Gfs 00z op run is showing another anticyclonic spell developing towards the weekend in the south and then extending further north during the weekend into the start of next week, so a warming trend with increasing amounts of sunshine but offset by some overnight mist/fog and rather cool starts but another fine spell on the way, the gfs then goes on to show a gradual breakdown next week as low pressure to the west edges slowly eastwards, slow progress due to a strong anticyclone to the east so it could be a struggle for the low but eventually a showery trough is directly over the uk. Further into FI the gfs shows a Northerly flow from the arctic and the later stages of FI also looks unsettled and very cool. As for the rest of this week, the large autumn low containing the remains of ex ts leslie and also the remains of michael looks like tracking a bit more to the north than previous model runs indicated, so it's not looking quite as bad in the far north but still very windy and unsettled for a time on thurs into friday but pressure will soon be rising from the southwest, then summery weather returns.

Edited September 11, 2012 by Frosty039

[Gibby]

Good morning. Here's a run down of the 00zs for today Tuesday September 11th.

All models show a cool NW flow for all today. Tomorrow this backs Westerly and strengthens somewhat as a series of troughs cross East over Britain. A ridge crosses over the south on Thursday followed by more fronts Friday (weak in the south) when a very strong Westerly gale develops for the far North. The weekend shows pressure having risen from the South with much less windy, brighter and eventually warmer weather for all away from the far North by Sunday. All this translates into changeable conditions with some rain at times between drier and brighter interludes away from the troughs with a better weekend to follow especially in the South by Sunday.

GFS then shows next week starting with High pressure migrating to the East with a warm Southerly drift over the UK. Pressure will be falling and a cold front crosses by midweek introducing fresher, cooler conditions behind a band of rain. The model then shows FI to be cooler and fresher with rain at times as High pressure sits in mid Atlantic steering Low pressures down from the NW to the British Isles.

The GFS Ensembles show the operational and control run colder options in the later stages of the run. The mean for the pack rise above average at the weekend before cooling to levels near the long term mean later. Rainfall is sparse in the South until after the 19th though in the North more evenly distributed. There is a huge spread in the Scottish ensembles from the 17th.

The Jet Stream is shown toppling South over the UK in the next 72hrs before reverting to a West to East low near Scotland over the weekend.

UKMO for midnight next Monday shows high pressure centred over Germany with a light SE flow over the South and a light SW flow in the North. A lot of dry, bright and very warm weather would be likely in the South for a few days with less bad conditions for the North where it too should stay dry with rather more cloud than further South.

ECM too looks very similar to UKMO at 144hrs moving forward with a few days of unsettled weather midweek before High pressure builds back strongly from the SW to affect much of Britain with drier and brighter weather as we move towards the weekend.

In Summary the weather can best be described as changeable as we go through the next few weeks. There is likely to be rain at times for all though longer dry spells in between for the South as High pressure always remains close by chasing the troughs away. Further North some very windy weather looks likely for a while before some dry days are possible here too at times early next week. It looks like becoming very warm again especially in the South early next week. The models diverge in the longer term with GFS sitting High pressure out in mid Atlantic with cool and unsettled weather for all in a NW to SE flow while ECM in 10 days shows a strong ridge of High pressure centred to the SW ridging strongly North.

[Gavin P]

Hi all,

Here's todays model based video musing looking at the weather for the second half of September;

http://gavsweathervids.com/

A "mixed" picture - Thinking the last week of September may turn cool and unsettled, but confidence is low.

Edited September 11, 2012 by Gavin P

[Milhouse]

We now look almost guaranteed to see a warm and pleasant weekend with temperatures not as high as some recent runs have been suggesting. For example the suggestion by the GFS of mid 20s temperatures on Sunday has now been replaced by temperatures in the low 20s. Monday looks to see winds veering more southerly as we import some heat from the continent, so temperatures in the mid 20s look likely. According to the GFS and ECM Tuesday is looking like another potentially very warm day but with a breakdown moving eastwards throughout the day compacting the settled weather to just the SE by the end of the day.

[Chris K]

For the 12z GFS run, it shows conditions becoming quite changeable after what looks likely to be a pleasant settled few days this weekend/early next week, for a good chunk of the UK.

Even though it shows a more changeable outlook for the second half of September and FI, there still seems to be a trend of transient/reloading high pressure setups with unsettled blips inbetween.

A quite typical September really in this run? Not dire by any means although perhaps some windier spells to come when unsettled, particularly in more NW areas?

Edited September 11, 2012 by Chris K

[Frosty.]

A nice increasingly warm weekend coming up for southern britain according to the GFS 12z with high pressure in control but not so good for northern britain with more breeze and more cloud with cooler temps. High pressure next week not looking so dominant, becoming centred to the southwest of the uk it could allow a cloudier wnw'ly flow around the top of the high during the first half of next week but then as the high transfers east across southern areas, probably more sunshine and warming up again but notice a flood of arctic air coming south from iceland into the atlantic, maybe a northerly toppler or two later in FI.

Edited September 11, 2012 by Frosty039

[Gibby]

Hi Folks. Here's how I see the output of the big three forecasting models tonight.

All models show a Westerly flow over the UK veering NW at times. A succession of troughs will cross the UK in the flow followed by cooler NW winds. By the weekend High pressure develops near Southern Britain though westerly winds remain strong over the far North. The weather translates to changeable conditions overall with some rain at times mixed in with drier interludes. Temperatures will be slightly on the cool side before temperatures rise in the South at the weekend.

GFS then shows a very changeable pattern as we move through next week with the first half seeing High pressure more dominant in the South at least though with occasional wea troughs bringing the risk of rain on occasion. As we move into FI the weather turns colder as a sharp trough moves through turning winds Northerly and dropping temperatures abrubtly with rain followed by showers. Through the rest of the run the weather turns more Autumnally changeable with strong winds, rain, cool and fine weather all featuring at some point.

The GFS Ensembles show the warm up at the weekend before a gradual fall off to levels slightly below average later in the run. In scotland a similar pattern is shown though as usual rainfall is more prominent throughout the run than locations further South.

The Jet Stream is shown to dip SE over the UK in the coming days before settling West to East near scotland over the weekend and next week.

UKMO shows High pressure engulfing Southern Britain at midday on Monday with several days of fine and dry weather from that chart with high temperatures likely.

ECM couldn't be different to it's European cousin tonight bringing Low pressure quickly in at the start of the week with the rest of the run showing Low pressure domination for all with a chill NNW flow later in the week accentuating an Autumnal spell.

In Summary the models are all over the place from as early as the late weekend. ECM and UKMO are unusually at total odds at 144hrs with GFS somewhere in the middle. In essence with that degree of difference between the models all options shown thereafter must be taken with a pinch of salt as it's likely they will all have different evolutions by the morning. So in conclusion FI is at t100hrs tonight with no real idea of a trend from the output.

[Frosty.]

Tonight's Ecm 12z op run is a bit of a mixed bag, the coming weekend is still looking fine and fairly warm in southern areas closest to the anticyclone to the south but the north is looking more changeable, much as the gfs 12z really except the gfs weekend high is a bit further north. The ecm next week is on a downward trend to a very unsettled and cool midweek period although then there is a slight recovery later next week but all in all, a bit of a disappointment compared to recent times with the atlantic/azores high pressure becoming centred well to the southwest of the BI with a rather cloudy wnw'ly flow riding over the top of the high and over the uk later..yuck.

Edited September 11, 2012 by Frosty039

[Frosty.]

The Gfs 00z op run seems to be downgrading the weekend anticyclonic spell even more, saturday still looks fine and warm in the south of england and wales but progressively less good further north and then by sunday, things are going pear shaped with a band of rain heading southeast although the south looks dry but probably clouding over through sunday, high pressure then pushes in from the west early next week to give a fine few days for most of the uk for a change but it then looks like turning cooler and more unsettled later next week and then the mid to late FI period looks cool and unsettled with the Polar Front Jet to the south of the uk so maybe there is a proper pattern change on the way later this month..or maybe not.

[Gibby]

Good morning. Here's the latest output review from GFS, UKMO and ECM.

The next few days are the only firm agreement there is between the models with a West then NW flow pulling troughs SE across Britain today. A lighter West flow is shown tomorrow before overnight Thursday becomes very windy everywhere with gales in the North as an intense depression passes by to the north. Troughs cross too, very weak in the South but more active further North, By Saturday some improvements are shown as winds decrease and high pressure moves in close to the south before a further trough pushes it away as it moves SE over England on Sunday. All this translates to a very changeable picture with Thursday and Saturday the better days for the South with the biggest chance of rain in the North at anytime but more especially tomorrow night and Sunday.

GFS then shows an improving day for Monday with brighter spells developing and decreasing winds. Tuesday is better still as a ridge crosses the UK with a bright dry day after a cool start. Improvements are short-lived as rain bearing fronts and depressions gradually become more prominent as they pull steadily down from the NW through the week.bringing rain to all areas by midweek or soon afterwards. FI is shown to become cool, windy and autumnal as the Atlantic ramps up Low pressure over Britain.

The GFS Ensembles show 850's close to the long term average once the warmer blip occurs at the weekend. Rainfall is not much of a feature until after the 20th in the South with the operational a wet outlier towards the end of the run. Further North rain is shown at anytime. The most notable thing with the ensembles this morning is the shortening of the warm snap at the weekend.

The Jet Stream currently driving SE over Britain settles to a position West to East over Scotland as we move into the latter part of the weekend and next week.

UKMO shows High pressure down near SW England at midnight next Tuesday with a NW flow over the North and East. Some fine and dry weather looks likely though Northern and Eastern areas could stay rather cloudy.

ECM looks much less bullish about unsettled conditions this morning and is much closer to the UKMO than last night. Nevertheless, after a dry and bright few days early in the week it looks like unsettled weather returns soon after midweek with rain at times, heaviest in the North.

In Summary the models are still showing different evolutions run to run at the moment. The only rock solid model in the last 24hrs is UKMO who continue to show High pressure close to the SW early next week with attendant fine weather at least in the South. GFS and ECM have come together somewhat at this point too with ECM bringing unsettled conditions back for a while at least soon after midweek while GFS brings Low pressure into the heart of the UK in its latter stages with wet and windy conditions for all.

[johnholmes]

thanks Gibby for your usual clear summary and also frosty-I hope you both keep this going through the winter as they are just what is needed for a balanced view and must be very helpful to visitors and our newer members.

my input from daily checks on the 500mb data

Wed 12 September

ec-gfs

changes again this morning

ec has built +ve areas and now gives a flow n of west into uk, quite similar to noaa last evening and it also drops 500mb heights over uk

gfs has a similar build of heights not that different in size or position but keeps the trough shape such that the flow into the uk is still s of west but it too drops heights

I suspect noaa/ec will be the pattern with gfs following but not enough confidence yet to go for this, only 1 day with ec/noaa showing this –I prefer to see 2-3 days of basic similarity for real confidence.

what does this probably mean for the surface weather 6-15 days down the line?

Coolish and unsettled but with the usual caution at this time of the year-it may all change if there are any major TS inputs into the northern hemisphere in that time scale.

Edited September 12, 2012 by johnholmes

[legritter]

Good morning gang. Just had a look on different weather sites over Northern hemisphere and a good look on our charts and data. To me it looks like an interesting period weather wise. Could start to materialise from about the 20th of September with low pressure in charge but positioning of main trough the hardest to predict at the moment. As John Holmes points out, we must keep an eye on any TS that get put into the mix down the line.

Catch up with you all later, cheers

[Gibby]

thanks Gibby for your usual clear summary and also frosty-I hope you both keep this going through the winter as they are just what is needed for a balanced view and must be very helpful to visitors and our newer members.

my input from daily checks on the 500mb data

Wed 12 September

ec-gfs

changes again this morning

ec has built +ve areas and now gives a flow n of west into uk, quite similar to noaa last evening and it also drops 500mb heights over uk

gfs has a similar build of heights not that different in size or position but keeps the trough shape such that the flow into the uk is still s of west but it too drops heights

I suspect noaa/ec will be the pattern with gfs following but not enough confidence yet to go for this, only 1 day with ec/noaa showing this –I prefer to see 2-3 days of basic similarity for real confidence.

what does this probably mean for the surface weather 6-15 days down the line?

Coolish and unsettled but with the usual caution at this time of the year-it may all change if there are any major TS inputs into the northern hemisphere in that time scale.

I do aim to keep the reports going over the winter but if things get too chaotic unlike last year I show them on my website which is linked below which should give an alternative place where they can be viewed in isolation from the off topic posts that clutter this thread here and other forums through the winter months.

[Thundery Shower]

Next week from friday looks bleh.. sods law the week i go on holiday. however this is all changeable of course.

[Buzzit]

Hello All

I think the difference between the UKMO and GFS is largely down to the treatment of TS Nadine. The UKMO has Nadine moving in a more northerly direction (Greenland) compared to the GFS with a more easterly direction (Spain). To early to tell yet but I think TS Nadine will continue to play havoc with the model output for the next few days, especially as the speed of intensification of TS Nadine is uncertain at this time.

Edited September 12, 2012 by Buzzit

[Gavin Hannah]

The last two GFS runs show FI developing high pressure ridge out the west in the Atlantic with colder air being pulled down over the uk from the north north-east. Too early to tell but we could see a HP cell taking up residence over the Atlantic which would divert TS and ex hurricanes up the Greenland or into mainland Europe.

[johnholmes]

The last two GFS runs show FI developing high pressure ridge out the west in the Atlantic with colder air being pulled down over the uk from the north north-east. Too early to tell but we could see a HP cell taking up residence over the Atlantic which would divert TS and ex hurricanes up the Greenland or into mainland Europe.

You may have it the wrong way round as the energy put into the atmosphere by TS's is way way beyond anything input by high pressure belts.

However, in meteorology its almost always everything is linked and one is dependent on the other.

Edited September 12, 2012 by johnholmes

[Gavin Hannah]

Is it possible for a HP cell to become stuck over the Atlantic?