Model Output Discussion - September Onwards

[Gibby]

Good morning folks. Here's a look at the 00zs from GFS, UKMO and ECM from my perspective.

GFS shows a cold front moving slowly SE over the UK in the next 48hrs. Its progress will be slow with ripples running NE along it delaying its progress. A band of rain in association with it will move SE over Britain reaching Southern Britain tomorrow. It clears on Wednesday with a legacy of cloud left behind for the south and returns North on Thursday as a weak feature pushed on by winds that will have backed southerly or south-south westerly bringing drier and warmer conditions North as pressure becomes High to the SE. Through next weekend the southerly flow turns back west briefly as a cold front moves east with some rain. By Sunday and on into the following week pressure remains high to the SE and eventually the east allowing warm southerly winds to continue to be drawn up over Britain with deep Low pressure well out in the Atlantic. Through FI this pattern remains for a while with winds backing further towards the SE as pressure builds over NE Europe. With time Low pressure creeps back in from the SW with the potential for some thundery rain towards the end of the run in continuing warm, humid conditions.

UKMO also shows a cold front staggering SE over the next 48hrs with some rain for all for a while. By midweek or soon afterwards this front returns North Thursday as a weakening feature with drier warmer air following NE behind it. The South late in the week becomes drier, brighter and warmer with variable cloud cover. For the North during this time the weather would likely remain unsettled and breezy with further rain at times. By the weekend pressure has leaked away over the South too and I would suspect that rain from a cold front would be approaching from the west by Sunday.

Th Fax Charts today illustrate the nature of the cold front over the next few days staggering SE slowly with waves running along it. By the end of the week pressure is shown to be High just to the SE with Low pressure to the NW and an attendant cold front approaching the NW later.

ECM today also looks very similar with pressure rising to the South by Friday with a fine day following the changeable conditions of the time between now and then. Over the weekend the changeable theme continues with the potential for some rain or sharp showers on Saturday as the air covering the UK would be warm in the inherent Southerly flow. As we move into the following week and the end of the run ECM follows GFS in keeping pressure high to the east and Low to the west with a warm and humid Southerly flow with troughs close to Western Britain. The best weather would likely be in the east while the West and North and later the SW would likely see some potentially thundery rain at times.

In Summary today the first half of the week sees the mix as before with rain from a cold front moving SE followed by showers in the North stalling for a while in the South. Later in the week things dry up and warm up in the South and Southeast, a trend that continues as we move on into the second week as a High pressure block sets up over Europe with warm Southerly winds and the potential for some thundery rain chiefly towards the west in association with a deep mid Atlantic Low.

[mushymanrob]

theres been some wonderful skyscapes this weekend as huge shower clouds tower about the earth...

not a bad week coming up away from the unfavoured north and west, might feel pleasantly warm later in the week in the southeast. so, the general 'normal' early autumn weather looks set to continue.

[nodrog]

Gibby.

"Its a huge commitment to report on the models every time Gibby.

Thank for your explanation as it helps those who may not be as advanced as some.

Keep up the good work as im sure 100's of us all read your reports and appreciate them."

Gordon.

[Bluebreezer54]

Gibby.

"Its a huge commitment to report on the models every time Gibby.

Thank for your explanation as it helps those who may not be as advanced as some.

Keep up the good work as im sure 100's of us all read your reports and appreciate them."

Gordon.

I echo that. For an enthusiastic, but complete novice like myself, I find Gibby's detailed but easily understandable summaries an absolute delight. Long may they continue. Oh.......and they're pretty damn accurate too !!

[johnholmes]

Looking out to the 10 day mark, so end of the month into early October and there are rather more +ve signs of a settled spell than for some time.

All 3 500mb anomaly charts have swung into about the same idea over the past 2-3 days, and yes for the purist the NOAA output has no forecaster input over the weekend I know. All 3 show a +ve area of heights developing east or even NE of the UK, NOAA shows it almost over the eastern side of the country. They also have the trough well west of the Uk. The two things combined give a 500mb flow south of west into the UK. The AO and NAO MAY be more supportive than against although not by much, both suggesting either or not blocking along with a very difficult to work out what its suggesting MJO, still in zone 3 and close to the origin.

Overall I would say the idea of a more settled outlook for the end of the month into early October. How long this may last I have no idea.

Edited September 19, 2011 by johnholmes

[Hairy Celt]

Looking out to the 10 day mark, so end of the month into early October and there are rather more +ve signs of a settled spell than for some time.

All 3 500mb anomaly charts have swung into about the same idea over the past 2-3 days, and yes for the purist the NOAA output has no forecaster input over the weekend I know. All 3 show a +ve area of heights developing east or even NE of the UK, NOAA shows it almost over the eastern side of the country. They also have the trough well west of the Uk. The two things combined give a 500mb flow south of west into the UK. The AO and NAO MAY be more supportive than against although not by much, both suggesting either or blocking along with a very difficult to work out what its suggesting MJO, still in zone 3 and close to the origin.

Overall I would say the idea of a more settled outlook for the end of the month into early October. How log this may last I have no idea.

You get a huge virtual hug for that John. For those of us who work outdoors, the current weather pattern in the northern UK is getting rather tiresome.

[Frosty.]

Interesting model output today with the Ecm 00z showing a potentially very warm and humid end to september with perhaps a thundery breakdown but the Gfs 06z does not show this and instead builds high pressure over the uk through the end of this month into early october. In the meantime, a nw / se split is likely to develop with pressure rising to the south & east across the near continent but with atlantic lows continuing to head towards nw scotland with spells of wet & windy weather, wednesday this week is a good example of this and then again later in the week and through the weekend. The southeast meanwhile looks like becoming warmer and more settled later this week onwards but it really depends which model you believe, the ecm is by far the warmest solution with some early autumn heat offset by some probable thunderstorms whereas the gfs is somewhat cooler but fairly settled eventually.

[johnholmes]

You get a huge virtual hug for that John. For those of us who work outdoors, the current weather pattern in the northern UK is getting rather tiresome.

sadly HC your part of the UK may be one area that sees not much benefit from the proposed weather late this month into next. Maybe a decrease in the unsettled/storminess at least for a few days?

[Frosty.]

sadly HC your part of the UK may be one area that sees not much benefit from the proposed weather late this month into next. Maybe a decrease in the unsettled/storminess at least for a few days?

Hmmm I think that has been the story of the last 5 months! at least the Gfs 06z op run showed high pressure building strongly across the whole of the uk but sadly it's late in FI and has low confidence attached to it but the ecm 00z shows hot & humid air pumping north across all areas and temps can still reach 26c in early october but once again it's all in lala land. The relistic future is for a nw /se split with nw britain catching the worst weather as usual.

[I remember Atlantic 252]

hmmm the FI period on both models looks hot, maybe warmest day of year for some areas? long way off mind you, unusual for warmest day of year in late sep

[Gibby]

Good evening folks.

GFS tonight shows a cold front crossing SE tomorrow over Southern Britain before it moves away SE beginning an increasingly warm spell of weather later in the week and beyond. So after some rain tomorrow in the South away from the far SE and showers in the North a breezy day with some further showers seem likely in the North on Wednesday with rain continuing off and on there through the rest of the week and weekend whereas the south will see three days of fine weather as winds back SW. Over the weekend a cold front crosses east bringing a brief spell of rain across before a return to drier weather later. Into next week and High pressure anchors over Germany and Scandinavia with a warm southerly flow bringing a continuation of warm conditions with some sunny spells in the east and Southeast though rather larger amounts of cloud further west. Then as we move through the rest of FI high pressure remains strong to the east and NE with warm continental winds blowing North,fending off all attacks from the Atlantic leading to spells of fine and dry weather with temperatures comfortably approaching the 70F mark in the south by day.

UKMO follows a similar trend with High pressure close to the South for a while late in the week. However, it then shows a broad SW feed which will bring large cloud amounts on the moist and warm SW breeze with just the far east and SE seeing meaningful sunshine and potential warmth. As is normal the Low pressure in the Atlantic would remain close enough to the North and West to allow troughs in bringing rain off and on still to those areas.

ECM also shows a warm up in a few days time as the current west or southwest winds back south to southwest bringing tropical maritime air up over the UK late in the week and beyond. There will be some rain in the south tomorrow and possibly again on Saturday as a front passes east otherwise a lot of dry weather is shown for the south and east with some warm sunshine possible for the southeast inparticular. Further North and West though things remain disturbed with rain and strong winds affecting upland areas in the warm, moist flow. Late in the run things warm up even more as High pressure settles over Central Europe and with low pressure in the Atlantic winds become southerly and eventually SE everywhere with some dry, bright and warm conditions for all with the far SE importing some very warm air with time.

In Summary tonight a pattern change looks on the way at last. Over repeated runs from most models high pressure has been shown to transfer fron areas to the south of the UK to mainland Europe itself by next week. This will have the result in drawing a warm southerly flow up over the UK. Innitially, it will just be the SE that sees much benefit with rain at times still possible for many. However if both mid term predictions from GFS and ECM are to be believed some pleasant September conditions look possible next week for all with temperatures approaching 21C for Southern Britain and possibly locally 25C in the southeast by next Wednesday and Thursday via ECM.

[ANYWEATHER]

Ummgghhh!! Im not convinced at all of a "major" pattern change in our weather for the Uk in the days ,weeks ahead! Im no "killjoy" but if we look at the past patterns and the actual outcome we could once again be barking up the wrong tree if we just rely on Computer output! Realistically, there looks to be some sort of pattern change in our weather in the short to medium term resulting in something warmer and dryer for a time. My point, and as John Holmes said earlier some parts of the country would certainly not benefit from a 500mb low sitting out to the west of the Uk. The two examples ive shown below are of the gfs @T240 and the Ecm, thats 10days ahead, of course all in fantasy land!!

We have been here loads of times before, and even"IF" these outputs are to be verified there is big questions on how much that "predicted" Anticyclone to the East and NorthEast of the Uk would influence the Uk ,anything from torrential rain, Flooding,An Indian Summer,Thunderstorms, and even stormy conditions for especially the Southern half of the Uk.!...... Ok ,all a long way off but short term things look like being rather mild to warm.!! Interesting Model Watching in the Near Term!!!

[Frosty.]

signs of a spanish plume in FI..hardly saw anything like that throughout the summer but now the models show it in october..typical

[Isolated Frost]

Quick question - any answers much appreciated. Just looking across the Fax charts re: cloudcover under the HP that may reach us later this week, via the SE, and saw a front with crosses (plus signs) and triangles pass through at +60 on the UKMO fax - anyone clarify what it is?

Thanks a bunch

[Gibby]

Ummgghhh!! Im not convinced at all of a "major" pattern change in our weather for the Uk in the days ,weeks ahead! Im no "killjoy" but if we look at the past patterns and the actual outcome we could once again be barking up the wrong tree if we just rely on Computer output! Realistically, there looks to be some sort of pattern change in our weather in the short to medium term resulting in something warmer and dryer for a time. My point, and as John Holmes said earlier some parts of the country would certainly not benefit from a 500mb low sitting out to the west of the Uk. The two examples ive shown below are of the gfs @T240 and the Ecm, thats 10days ahead, of course all in fantasy land!!

We have been here loads of times before, and even"IF" these outputs are to be verified there is big questions on how much that "predicted" Anticyclone to the East and NorthEast of the Uk would influence the Uk ,anything from torrential rain, Flooding,An Indian Summer,Thunderstorms, and even stormy conditions for especially the Southern half of the Uk.!...... Ok ,all a long way off but short term things look like being rather mild to warm.!! Interesting Model Watching in the Near Term!!!

I think the reason for the optimism this time around is the unity between the models. Yes we have seen high pressure shown on all models at some point almost in every run only to be removed by the following but as I indicated in my summary this evening all models indicate that pressure will rise over Europe later this week and next. Things will change over the coming days and it maybe that it is once more a false dawn but as shown tonight it has an even chance of happening this time round as the wider Northern hemisphere synoptics are better placed for it to develop as shown.

[ANYWEATHER]

signs of a spanish plume in FI..hardly saw anything like that throughout the summer but now the models show it in october..typical

Yes, the models show it, but will it happen..???Ha Ha HA.!!!

[Gibby]

Quick question - any answers much appreciated. Just looking across the Fax charts re: cloudcover under the HP that may reach us later this week, via the SE, and saw a front with crosses (plus signs) and triangles pass through at +60 on the UKMO fax - anyone clarify what it is?

Thanks a bunch

Basically when this is shown on a fax chart it identifies an old weak trough where its identity is almost at the point of being non existant and usually contains nothing more than a band of cloud. The triangles mean it originates from a past cold front moving in the direction the triangles face. As far as I know the + signs mean it is stationary at that point and usually returns North as a warm front (semicircles) which is shown on the fax chart in question in its more active point further west. Hope this helps.

[damianslaw]

signs of a spanish plume in FI..hardly saw anything like that throughout the summer but now the models show it in october..typical

Yes it would be a bit annoying to see a settled spell spring up at the end of september and into october in context of no lengthy nationwide very warm spell occuring during the whole summer (5 days +). A lengthy warm settled spell occuring in late sept/early oct would in its timing bear an uncanny similiarity to the spell we saw from mid april to early May.

I guess it is only a matter of time we endure a fairly sustained high pressure spell - the sustained unsettled weather has to break at some stage.

Back to the models - all show signs of stronger ridging of heights moving into southern districts, a pattern that often occurs in September but rather at the beginning of the month as opposed to the end.Perhaps Sept will turn out to be role reverse of how it normally pans out - i.e. an improving month as opposed to a worsening month. A few dry days wouldn't come amiss to us in the rain soaked cloud leaden north, weeks and weeks of relentness gloomy wet days is getting tiresome now.

[Isolated Frost]

Basically when this is shown on a fax chart it identifies an old weak trough where its identity is almost at the point of being non existant and usually contains nothing more than a band of cloud. The triangles mean it originates from a past cold front moving in the direction the triangles face. As far as I know the + signs mean it is stationary at that point and usually returns North as a warm front (semicircles) which is shown on the fax chart in question in its more active point further west. Hope this helps.

As with all of your posts - informative and helpful - priceless member to the MOD Gibby - thanks

[johnholmes]

http://www.metoffice.gov.uk/weather/uk/guide/key.html#pressure

this link to the Met o site gives the exact definitions of the symbols

[Isolated Frost]

Thanks aswell JH Bookmarked.

[Gibby]

Good morning.

GFS this morning shows a slow moving cold front over Southern Britain today moving slowly away SE late tonight and tomorrow. So a band of rain for all in Southern Britain in the next 24hrs or so clearing tomorrow. The North lies under a strong westerly flow with showers while tomorrow, further rain rain and gales affect the NW for a while late tomorrow and early Thursday. The trend from Thursday on is for winds to slacken and back towards the SW or South as pressure transfers east from France to Germany allowing warm winds to be pulled up across the UK by the end of the weekend. This trend continues next week with warm southerly winds wafting North over the UK with low pressure anchored out west. The NW will see a little rain for a while at first before all areas enjoy some drier weather though the odd thundery outbreak of rain could affect the far SW for a while at the latter end of the week. Towards the end of the run and far out in FI the weather breaks down from the west as the high to the east loses grip in response to Low pressure from the west moving closer towards the UK.

UKMO today also shows the trough over the South clearing late tomorrow with drier and warmer conditions likely in the south and east at least for a while. Changeable and windy conditions continue in the NW though throughout as High pressure to the South then east lies too far away for any meaningful influence here. Further South and East a lot of dry and warm weather looks likely until the end of the run though pressure is not particularly high and troughs affecting the NW could come perilously close at times threatening rain with time.

The Fax Charts today continue to show the NW under attack from the Atlantic with fronts crossing east or NE bringing periods of wind and rain throughout the run. High pressure moves up close to Southern Britain behind todays trough to give better conditions in the South though a second cold front is shown cross the South on Saturday as a weakening feature but active enough to give at least a little rain for most.

ECM finally follows a similar pattern up to the weekend with a band of decaying rain crossing the South somewhen early in the weekend and another one possibly early Monday. Beyond that pressure builds strongly to the east and NE bringing a warm and dry continental SE airflow up across all areas by the middle of next week. Even the NW would see benefits from this as by then Atlantic troughs would be pulled out into the Atlantic and skies would break to possibly bring the warmest conditions to sheltered parts of Western Britain and away from North Sea coasts.

'Subtle variations on a theme' is the name of the game this morning with the theme of yesterdays rise of pressure over Europe still there this morning with warmer conditions looking likely to affect all areas by this time next week. It is touch and go whether the NW will see too much benefit from this with the further SE you come the more chance of staying dry and bright under the warmth.

[Methuselah]

Thanks for that, Gibby.

[Backtrack]

GFS seems to be much different from the ECM?

It hardly has any high pressure building from the South, where the ECM has it building strongly by the 27th September and staying there for a time.

If the GFS is right, it's going to be our, this summer exclusively, 3 day settled event before pressure drops allowing the unsettled theme to continue, although there are hints at the very end of the run for some blocking to develop, keeping the Atlantic at bay for a time at least.

GFS:

ECM:

Here's to a settled October!

[summer blizzard]

GFS seems to be much different from the ECM?

It hardly has any high pressure building from the South, where the ECM has it building strongly by the 27th September and staying there for a time.

If the GFS is right, it's going to be our, this summer exclusively, 3 day settled event before pressure drops allowing the unsettled theme to continue, although there are hints at the very end of the run for some blocking to develop, keeping the Atlantic at bay for a time at least.

GFS:

ECM:

Here's to a settled October!

GEM also refuses the high pressure entry to the UK and at 240 hours out, it is as good as the ECWMF.

It may get warmer this weekend however there is no guarantee it will be dry or sunny.