Model Output Discussion 26/08/2012

[Gibby]

Hi Folks. Here's a look at the 12zs tonight.

All three models indicate a cool off in the next 48hrs. A cold front crosses East over Britain later Monday bringing fresh and cool winds down from the NW. Through the rest of the week winds blow strongly from the West over all areas with rain or showers at times, heaviest in the North and West with longer drier spells to the South and East and in the lee of high ground to the West.

GFS then shows a cool NW wind next weekend before backing off to a slacker westerly towards the start of the following week. The basic pattern of rain at times remains and with High pressure close to the South most of the rain will fall to Northern and Western areas of England and Wales and Northern Ireland. Towards the middle and end of the week after next FI shows pressure building in mid Atlantic with a cool North to Northwest flow over Britain bringing occasional showers, before a toppling ridge gives a chilly drier interlude before unsettled conditions spread back again to the South and West at the end of the run as Low pressure moves in from the West.

The GFS Ensembles shows a return to unsettled conditions within 48hrs. This also means cooler weather as 850's return to levels close to the long term mean. The operational was a cold outlier in the final third of the run. Rain at times occurs in all areas from the 11th.

The Jet Stream currently blowing West to East north of Scotland weakens and buckles over the next two to three days before strengthening markedly next week over the Atlantic and across the British Isles.

UKMO tonight shows a strong westerly flow over Britain with weak high pressure to the South and Low pressure to the North. Pressure will be falling over the UK with troughs straddled across the nation bringing the risk of rain at times in the vicinity of those troughs.

ECM shows a weak ridge replacing the cool NW winds next Saturday with a showery North and East of the UK being replaced by drier weather further South and West. Towards the end of the run a slack High pressure does migrate slowly over the UK but with inherently cool air some low night minima could occur with mist and fog problems first thing in the mornings too. By day 10 low pressure leaks it's way back into the UK from the SW bringing some cloud and rain into Southern and Western areas.

In Summary it looks like an unsettled week with rain at times is on the way. It could become notably windy in the second half of the week while at the same time it becomes much cooler, especially early next weekend. Further on and the weather looks like continuing with a North/South split to the weather as per GFS or more settled for a while if Autumnally cool as per ECM.

[phil nw.]

Thanks again to Gibby for his excellent and objective daily summarys of the model outputs.

The changeover to a more unsettled and cooler outlook is now on our doorstep.

The current high pressure is now starting to leak away to the south as a deepening Atlantic low heads towards Iceland pushing it`s attendant fronts towards the west of UK through tomorrow.

The jet stream currently just to our North heads south again in a few days- compare today and T72hrs.

bringing the UK a cooler westerly flow with rain crossing from west to east followed by showers .The greatest amounts always further north nearer to the low pressure.

We can see the changed pattern here on the T72hrs fax alongside the 850hPa profile indicating the incursion of cooler air from the north west.

A typical +NAO setup being modelled for the next few days then with low pressure moving across to the North of the UK and the Azores High located near it`s natural home to the south west.

So quite a change in the offing compared with the warm and sunny Summer- like conditions that much of England and Wales have recently experienced.

[Weather Boy]

It's really interesting how at this time of year, the various models swing back and forth. I've seen suggestion of copious amount of rainfall (for the south) to warm, dry and sunny, and (part way)back again.

Seems like modelling still has lots to learn, and requires that "Human touch"

Hmmm, I used the words 'copious rainfall' in the same sentence as 'south' but what I actually said was, "amounts of rain might not be too copious in the south where the pressure remains relatively high".

I don't think that anyone said that there is likely to be copious rainfall in the south so fear that you may have misinterpreteted my post, it saying the opposite!

[damianslaw]

A change is on the way for all courtesy of a change in the position of the jet - which is about to unbuckle away from its northern trajectory kicking aside the azores high and forcing it to retreat back to its more 'normal' position for the time of year.

What this will do is allow atlantic weather fronts and associated low pressure to cross the country and pull down much cooler conditions from the NW - we can see this happening on Tuesday. Further into the week and it remains unsettled under a strong westerly flow before another low pressure attack brings more rain and wind and further quite cool conditions.

There are signals longer term of mid atlantic heights developing and a rather chilly northerly flow setting up with the trough positioning itself where it has been for much of the time since April which could mean a very disturbed cool end to the month with low pressure forced on a southerly track - but this is a long way off yet...

So after a very pleasant warm if not very warm start to September for some, things look set to become much more unsettled with temperatures back down where they should be and for the north and west in particular it is a proper autumnal outlook with rain, strong winds and at times quite chilly air. I did expect things to become much more unsettled as we moved in the second full week of the month and for such conditions to persist preety much through to the end of the month.

[Gibby]

Good morning. Here's my take on the 00zs from the models this morning.

Through this week all models show a return to more unsettled and at times windy condition as Low pressure troughs move in from the West on a strengthening Westerly wind sandwiched between Low pressure to the North and High pressure to the South. There could be some rain everywhere at times but most of it will fall in Northern and Western areas of Scotland Wales, England and northern Ireland. By the weekend High pressure moves close to Southern Britain with drier and brighter conditions returning here.

GFS then takes us through next weekend with a North South split in the weather. Though rather cloudy only a little light drizzly rain looks likely on Sunday as a weak trough crosses East while the North may see heavier rain for a while. By early week High pressure having moved just East of Britain brings a dry and warm interlude for many before another brief unsettled spell in association with Low pressure moving East over the UK follows around midweek. In far FI the South looks like fairing rather well as High pressure remains over or close by while further North further Low pressure incursions from the Atlantic could bring some rain intermittently on some days.

The GFS Ensembles look rather better again this morning especially for southern locations as another warm up or two looks possible in a week or so as High pressure moves East. There is some rain shown for all at times but amounts look generally small in the SE. The North continue to see a more unsettled pattern with 850's closer to the long term mean.

The Jet Stream is shown to ridge and trough over the atlantic over the next three days before settling on a path West to East over the Atlantic to Northern Scotland late this week and beyond.

UKMO's closing chart for midnight next Sunday shows a WNW flow over Britain between Low pressure over the Norwegian Sea and High pressure in the SW approaches. A rather breezy day looks likely next Sunday though may Southern areas may be dry some showers or rain is likely the further North one travels.

ECM shows High pressure close to Southern Britain late next weekend extending across other areas early in the week that follows bringing increasingly dry, bright and at times warm conditions with rainfall dying out altogether even in the North by the end of the run as high pressure takes firm control, centred over the UK.

In Summary the models have flipped again overnight. Gone is yesterdays deeply unsettled, windy and potentially stormy chart offerings away from the far NE and in there place comes High pressure rebuilding from the south from next weekend with a fine spell likely for all should ECM verify. GFS is not quite as good but is a marked improvement from some of yesterdays output. Of course we have this week to get through first which continues to show wind and rain at times though even this looks likely to be less significant in the South than what's been shown in recent days.

[Frosty.]

Not a bad Gfs 00z operational run with plenty of anticyclonic weather throughout the run and some unsettled interludes at times but really I was expecting something worse than this. Today is the last day of the current southeast heatwave (maybe another one soon) and temps will reach at least 28c but possibly 29c 84f in london but by tomorrow the temps will be nearer 21c with much more cloud and the hot uppers pushed away to the continent, then it looks generally cooler and fresher with the PFJ across the middle of the uk for the first half of the week but tending to pull northwards towards friday onwards with pressure rising again to the south so this indicates most of the cool unsettled and windy weather will be across the northern half of the BI in the week ahead and the southern half will be less cool and less wet for most of the time but windy at times. The further outlook shows fairly prolonged spells of high pressure at least for the south but probably more changeable/unsettled for scotland and n.ireland but with some interludes of fine weather. The Ecm 00z looks even better, so it looks like we will have to wait a while longer for a full blown change in our weather pattern, maybe into october?

Edited September 9, 2012 by Frosty039

[Summer Sun]

Nice to see the cold weather in FI been removed and replaced by higher pressure with any storms staying away in Iceland and Greenland and the UK stays settled thanks to high pressure

The possible stormy weather for the east on Friday has also been remove and its now just the far north of Scotland which will see the Gales

Of course we've got an unsettled week to get through this week first though the East if likely to see very little rain this week, but all in all the pattern in general looks like keeping any major storms away from the majority UK for the foreseeable future at the moment

Edited September 9, 2012 by Summer Sun

[johnholmes]

Not only the 4x and 2x synoptic charts are varying, the 500mb anomaly charts also show too much variability to be sure of the uper air pattern in the 6-15 day time frame.

Possibly the form horse is for pressure at the surface to be fairly high to the south or SW and for lows to track ENE across the Atlantic affecting mostly the NW'ern third of the country but its far from a done deal.

The ECMWF version has shown a marked NW pattern on one day with +ve anomalies out west and -ve ones to the E/NE giving a distinctly coldish pattern. It has also shown +ve heights over the UK. GFS has been less variable keeping the idea I mooted at first=Wly with higher pressure S/SW. NOAA seems to have mostly favoured this idea although there are signs now and then of the ECMWF idea.

So far from clear which is not unusual thanks to the inputs from Tropical Storms at this time of the year.

Edited September 9, 2012 by johnholmes

[Backtrack]

Loving the ECM run. It has plenty of variety. Just what I like in September.

First of all we have a cool, refreshing day on Tuesday with some heavy showers, with the temperatures barely making double figures in the North. There will be some sunshine in between, which will make it feel like a true Autumn's day.

Thereafter we see high pressure attempting to ridge in from the south west, at first it does get flattened somewhat by the jet as it is running across central Scotland, but then we see the jetstream moving further north allowing the high to ridge across the country, bringing brighter skies, and some more of the lovely above average temperatures we have been seeing this week as the 10C+ 850HPA line crosses the UK once more.

Afterwards into FI, we see a potential record breaking chart, with a low situated to the SW, pumping up hot, tropical air from the tropics.

We see the 15C isotherm across much of England & Wales, with the 20C isotherm starting to drift up from the south, flirting with the SW of England.

I think should the ECM be on the money 10 days out, we could see records broken for England & Wales as that low continues to move NE.

Exciting times transitions of seasons! You can still get the extreme summer heat, whilst the mountains in the north can receive snow. Awesome.

[Dorsetbred]

Hmmm, I used the words 'copious rainfall' in the same sentence as 'south' but what I actually said was, "amounts of rain might not be too copious in the south where the pressure remains relatively high".

I don't think that anyone said that there is likely to be copious rainfall in the south so fear that you may have misinterpreteted my post, it saying the opposite!

Hi, the suggestion wasn't yours I was referring to, it was a rainfall chart from GFS, apologies if there was any form of misunderstanding.

[TonyH]

A look at the coming week comparing expected weather for west Wales with that of the central Midlands:

http://forum.netweather.tv/blog/309/entry-4475-weather-guide-monday-10th-to-sunday-16th-september-west-wales-and-central-midlands-compared/

[A Winter's Tale]

Good afternoon.

For a good part of England and Wales today and indeed much of September so far has seen some lovely late summer weather with temperatures into the high teens in a few places and of course widespread sunshine, but further north and west there has been more in the way of cloud cover and rain at times aswell as lower temperatures. Through the rest of today, cloud cover will increase from the west and push that lovely sunshine across much of England further east out into the north sea. And there'll be some rain in a few places - particulary in western Scotland. Tonight is set to be overcast for just about all of us with lots of patchy light rain across western areas. A mild night too with lows of 16-18C.

Monday morning should be largely overcast for almost everywhere with a few patches of rain and more persistent and heavy rain will move in from the west and reaching Ireland first. The band of rain should bring a wet afternoon for Scotland and Ireland and skies should remain largely cloudy for most and afternoon highs should be 12-21C. The band of rain should move further south east over night across much of England and Wales. Showers should follow the frontal rainfall for western Scotland and Ireland as we develop a cooler NWly. Quite cold in the north and west with lows below 10C but milder in the SE.

Tuesday again looks quite cloudy and it's likely to be showery in the north and west and there could be snow on the tops of the Scottish mountains. Mildest in the south east but a cool day for many of us with highs below 15C. Another area of persistent rainfall is expected to reach Scotland and Northern Ireland during Tuesday night - drier further east but mostly cloudy and minimum temperatures are expected to be around 8-11C.

The heavy rainfall should clear into the north sea for Wednesday and there could be some sunshine at times for Scotland and northern England - cloudier for the rest of England and Wales however. Maximum temperatures of around 14-17C. Wednesday night could be another cool one with lows of 9-10C and largely dry with a few clear spells and some rain near the far north of Scotland.

[Milhouse]

Next weekend is shaping up quite nicely with high pressure building to deliver a mostly dry and settled spell with temperatures in the high teens/low 20s although it could be just Sunday that sees these sort of temperatures. Therafter there are tentative signs that high pressure may shift east drawing up a hot southerly for a time as shown by the GFS, ECM and GEM models.

Before that its a very different week to come compared to September so far with a cool feel for much of the time with a strong westerly winds blowing at times. Tomorrow will likely see temperatures a little above average but from then in its a case of average or below average temperatures possibly with the exception of Thursday.

[Polar Maritime]

Tue 11 Sep

A bright day with a mixture of sunny intervals and blustery showers. A colder day with freezing levels near the summits so some sleet or snow in the showers across the higher Munro tops. Strong to gale northwesterly winds with severe gales on some tops and this will bring a significant to severe wind chill .http://www.metoffice.gov.uk/public/weather/mountain-forecast/

[summer blizzard]

Caution to you all, the warm spell shown in a week depends on a TS, this has not yet formed and its track may change.

[johnholmes]

GFS shows the remains of both Leslie and Michael well into the Atlantic and one maybe a combination of them both is the low east of Iceland at T+120 hours. Beyond that and its far from clear just what effect any TS will have. No model is very good at predicting more than 48-120 hours their effect and track.

[Summer Sun]

Snow is possible for the high ground in Scotland on Tuesday

[AWD]

The 12z GFS suggest some very warm weather from a week today through into the following week. However, whilst it may start of settled and sunny, LP to the west gradually becomes more influential so it looks like warm, humid, cloudy and at times showery weather in the medium term after a cool and more Autumnal working week this week!

[johnholmes]

this is a pdf to show how difficult it can be to decide which model is correct a fair way out.

Its at T+192 and is for 10 September and the model was the JMA version.

Interesting to see so I think worth a read?

JMA chart at T+192 hours for 10 September 12.pdf

[Dorsetbred]

I believe quite a lot of it is the inputs from Tropical storms as I've commented before?

agreed

[snowmadchrisuk]

A Nice looking hotspell showing up in FI with +20 850's approaching the South. The TS that has not yet formed doesn't look on satellite that it has become much better organised , but the water vaper image shows dry air close to the wave so until that clears off , can't see much happening , this is the reason Issac took so long to develop . As for the cold weather I think Snow in September on the mountains is quite normal , although it is quite early in September if it happens.

[Milhouse]

Next Sunday would be a repeat performance of today if the GFS verifies

[Summer Sun]

A lovely warm end to ECM tonight

Could see some thunder and lots of humid air around with the last chart

Edited September 9, 2012 by Summer Sun

[Gibby]

Good evening people. Are we heading towards a cool wet autumnal spell or another late summer burst. Read on to find out.

All models show a cooler run of winds moving down over Britain from the NW late tomorrow and on Tuesday. These West or North-West winds will be fresh to strong at times with some rain or showers on occasion through the week as troughs move through in the flow. By the end of the week signs of a pressure rise from the SW is shown by all models in time for the weekend.

GFS shows slack pressure over the weekend with still a little rain about here and there. By Monday though High pressure builds across the UK sliding gently East and bringing a surge of warm air North from Europe as Low pressure fdevelops out in the Atlantic. Later in the run this by then very deep depression swings slowly NE past the NW of Scotland and continues to influence the UK through to the end of the run with some rain and strong winds at times the heaviest and most widespread of this falling towards the NW of the UK.

The GFS Ensembles show another warm spell from the 13th and if the operational verifies extends on to the 21st though this was a huge outlier at this point. Rainfall amounts continue to show much less than was showing a few days ago for Southern locations though much more is shown further North. the final days of the run do show a return to the long term mean 850's even in the South.

The Jet Stream is shown to be powering across the Atlantic South of Iceland and down over the UK in the next 72hrs. Longer term it is programmed to settle back to a West to East flow close to Scotland by next weekend.

UKMO for midday next Saturday shows High pressure centred over SW England with fine and bright conditions for all of Southern Britain. Things shouldn't be too bad in the North either without major Low pressure close by but a lot of cloud could spill in off the Atlantic and down over other northern and Eastern areas of Britain.

ECM brings High pressure right over the South of the UK next weekend before slackening the wind flow off to a light Southerly drift. Some warm and sunny conditions would likely occur especially towards the East while pressure falls to the SW by the end of the run bringing a risk of some potentially thundery rain in from the SW by day 10.

In Summary the weather looks to be playing 'guess the season' tonight'. Having just enjoyed one fairly widespread warm spell it looks like we could be shaping up for another for a while from next weekend. There are a lot of caveats attached to how the evolution develops to bring this about late this week and it maybe the North sees only limited improvement but tonight's charts are far from a washout with only limited rainfall in the South through the working days of this week and very little in the week thereafter though I'm sure it will feel noticeably chillier in the days to come before we see higher temperatures return from the weekend.

[SMU]

http://www.meteociel...ype=0&archive=0

a VERY amplified ECM tonight especially in the latter stages- some meaningful snow developing in central / Northern Canada- & a few other areas-

However for the UK the PF isnt strong enough yet to break south of us- resulting in us sitting on the warm side of the euro high-

So for now, enjoy the late taste of Summer

& Just for the 'person' that commented on me having an agenda witn the weather with respect to things like the debate around the ice melt effecting the UK-

Heres the Winter 500 MB anomaly chart for the NH since 2007 ( the last lowest minima)

THis Winter will be very interesting with a muted ENSO signal not the overiding player we look to the stratosphere & the Arctic to see whats happening-

As things fire up into Oct it will be interesting to see the NET strength of the zonal wind & if theres more of a negative component this winter...

S

Edited September 9, 2012 by Steve Murr