Model Output Discussion - September Onwards

[Thundery wintry showers]

I see pretty strong agreement among the three main models this morning out to T+144. Today and on Monday we will see the rain belt straddling Scotland and northern England, with the rain on it gradually fizzling out and the associated cloud creeping slowly south, but the southern half of England should remain sunny and hot. On Tuesday and Wednesday the regional split changes, with a weak front bringing cloud and drizzle to the southern two-thirds of England while Scotland and the northern third of England has sunshine and scattered showers. Then on Thursday/Friday the models are agreed on a north-westerly blast with winds approaching gale force towards the NE for a time, and temperatures falling below average.

It's after the north-westerly incursion that we get the major disagreement, but I don't entirely agree with the suggestion of the GFS "reload". It's true that the weather does turn warm and anticyclonic towards FI but it's a very different setup- instead of a hot dry southerly we get a warm moist west to south-westerly flow on the high's northern flank which would promote much cloudier conditions and some drizzle for western areas. Eastern parts of England would most likely see some sunshine come through, in the shelter of high ground, with some favoured spots reaching 20-22C, but not like we've seen recently. ECMWF, in contrast, appears to suggest a continuation of a changeable north-westerly type.

[Candice]

I guess the change Weds into Thurs is a direct result of hurricane Ophelia, will be interesting to see what happens after that.

[bluearmy]

Good morning folks. Here's todays look at the 00zs.

GFS this morning shows a slow cool down over the next few days as winds become westerly drawing in cooler and more cloudy Atlantic air with time. Later in the week a cold front crosses east with a little rain for all followed by cool and showery NW winds. Night times would become chilly with the chance of frost in low lying areas overnight and snow showers on the top of the mountains of Scotlands.. Over next week and beyond the charts are characterized by High pressure close to the South with Westerly winds further North. In weather terms this would mean precious little rain at all for the South and temperatures could rise above normal again at times while the North is more unsettled and breezy with some rain but never a wash out even here.

The GFS Ensembles put the operational above right on top of the pack from the 9th to the 13th while most members prefer to keep the temperatures close to the seasonal average while maintaining lower than average rain in the South.

UKMO brings the slow drop in temperature too for the South in the next few days while the very wet weather in the North becomes less extensive over the next 48hrs. By midweek a cold front sweeps east bringing any remaining above average temperatures in the SE back down to the seasonal norm at the same time as bringing a band of rain eastwards. Behind the front winds would turn NW and be quite strong for a while bringing rather cool conditions and showers to most areas, heaviest in the North. A ridge of High pressure approaches Western Britain by Saturday.

The Fax Charts show weak and decaying cold fronts crossing Southern areas over the next 48hrs gently lowering temperatures and displacing the continental air mass with fresher Atlantic air. A front is shown crossing midweek with cool and fresh and somewhat showery NW flow behind.

ECM continues to show a more sustained breakdown later in the week following the cold front Wednesday/Thursday. Instead it shows the cool and showery NW flow late in the week giving way to further frontal activity and eventual Low pressure moving down off the Northern North Atlantic. So rain at times would develop for all from the weekend with temperatures near to or maybe somewhat below normal especially in the North and NE. Very late in the run High pressure drifts in off the Atlantic behind the Low and could offer a cool, frosty and foggy spell should it verify.

All the models continue to offer a variety of options for the period later this week and beyond. GFS, not for the first time wants to keep things settled and dry and still on the warm side at times in the South while ECM wants to make things much more Autumnal late next week and through the weekend with some rain for all before a cool High pressure developing behind would bring us our first widespread hoar frost and fog by midweek following. We have to wait for future outputs to see which model backs down to the others way of thinking or whether a different resolution develops.

ian, the two suites (ecm and naefs, courtesy of gefs) disagree with the depth and placement of the euro trough beyond next weekend. ecm has the pattern further west and more amplified just to our east. hence the better outlook from the north american models. infact, naefs as an impressive north iberian ridge at T240 on the spreads.

even allowing for this possible better offering from naefs, it doesnt hang around for too long and the pattern becomes very mobile thereafter.

[johnholmes]

The link below shows the situation, it has to be said that the 3 500mb anomaly models have not been that consistent over the past week with their output, so I would be wary of making any definite forecast for around 10 days time.

An interesting item on the ECMWF issue is the marked trough, almost cut off low off the Florida coast. Presumably an attempt to show the possible hurricane/tropical storm for that area? Its not that often that the 500mb anomaly charts from any model show this. Whether it will be correct as ever we have to wait and see.

Edited October 2, 2011 by johnholmes

[tinybill]

ian, the two suites (ecm and naefs, courtesy of gefs) disagree with the depth and placement of the euro trough beyond next weekend. ecm has the pattern further west and more amplified just to our east. hence the better outlook from the north american models. infact, naefs as an impressive north iberian ridge at T240 on the spreads.

even allowing for this possible better offering from naefs, it doesnt hang around for too long and the pattern becomes very mobile thereafter.

The link below shows the situation, it has to be said that the 3 500mb anomaly models have not been that consistent over the past week with their output, so I would be wary of making any definite forecast for around 10 days time.

An interesting item on the ECMWF issue is the marked trough, almost cut off low off the Florida coast. Presumably an attempt to show the possible hurricane/tropical storm for that area? Its not that often that the 500mb anomaly charts from any model show this. Whether it will be correct as ever we have to wait and see.

hi there hurricane ophelia in the area

[johnholmes]

hi there hurricane ophelia in the area

the remains of that storm are the winds and rain for Wednesday of this week.

[Frosty.]

I think the Gfs 12z looks more like the Ecm 00z with no return of the very warm anticyclonic conditions which were on the gfs 00z. The latest gfs run shows an increasingly windy and cooler week with spells of rain mixed with sunshine and showers and the showers becoming wintry across the scottish mountains as arctic air digs south with a deep scandi trough later in the week, some improvement next weekend as a ridge crosses from west to east cutting off the cold air supply to the north, the weather then being changeable with most of the rain in the north and high pressure to the south of the uk bringing the best weather to southern england but temps will be close to average, a little above at times in the south and slightly lower than average at times in scotland.

[Gibby]

Good evening folks. Here's my take on the 12zs tonight.

GFS tonight shows a Westerly flow developing over the UK behind a weak front crossing through late tomorrow. however, for a few more days it will still be quite warm in the South before the major change on Wednesday sees a more active cold front move East over the UK with some rain for all. Behind it a cool or rather cold NW flow develops with showers dying out late in the week as a ridge moves in from the SW. This ridge lies close to the South then East into the following week with fine weather for many and temperatures above normal again for a while. Into FI and the UK is still controlled for the most part by High pressure this time centred NE of the UK with some intrusion from weak Low pressure but still a lot of dry weather for all with temperatures fairly close to average with the chance of some fog and slight frost at night.

As far as the run sits in the GFS Ensembles it is on the warm side from the 9th before dropping below the mean at the end.

UKMO tonight shows the same Westerly flow developing over the next 24 hours, strong in the North. Cooler air would be ushered in from off the Atlantic with a cold front moving East midweek bringing a more dramatic drop in temperature to end the week. With NW winds it will feel cool and showery at the start of the weekend before the weakest of ridges moves in ahead of a warm front.

ECM tonight also shows a cooler week coming up with the sequence of events as described above. At the weekend High pressure is shown to develop strongly to the SW but with small disturbances still allowed to access the UK at times with attendant cloud and a little rain possible, chiefly in the North. The run ends with High pressure very much in control with dry weather though probably with a lot of cloud floating about and temperatures not that far from normal.

In Summary tonight High pressure remains the long term favourite option in the operationals tonight. It looks likely that its position will be somewhere to the SW of Britain with the driest weather towards the South and West with the North favoured for what rainfall there is. Temperatures certainly look more likely to be nearer normal while GFS does give the option of a few warm days early next week.

[Frosty.]

As the current heatwave begins to crumble..now it's the Ecm which brings a return of warmer anticyclonic conditions in around a week from now (low 20's celsius) with pressure then remaining high with an upper ridge building north through scotland out to T+240 hours and beyond. Up to and including next weekend, the gfs and ecm are similar with an increasingly unsettled and cooler week ahead and cold enough for snow on the scottish mountains from midweek but then high pressure pushing east for the weekend, the ecm then becomes very anticyclonic with low pressure well away to the west and north of the british isles towards mid month and no sign of any cold snaps yet...the models are really struggling with the upstream patterm but more often than not, they do suggest that high pressure will feature strongly in FI.

[summer blizzard]

As the current heatwave begins to crumble..now it's the Ecm which brings a return of warmer anticyclonic conditions in around a week from now (low 20's celsius) with pressure then remaining high with an upper ridge building north through scotland out to T+240 hours and beyond. Up to and including next weekend, the gfs and ecm are similar with an increasingly unsettled and cooler week ahead and cold enough for snow on the scottish mountains from midweek but then high pressure pushing east for the weekend, the ecm then becomes very anticyclonic with low pressure well away to the west and north of the british isles towards mid month and no sign of any cold snaps yet...the models are really struggling with the upstream patterm but more often than not, they do suggest that high pressure will feature strongly in FI.

The impression i get from them is that while high pressure attempts to ridge in, they do not really take it east of the UK and as such i would expect the UK to be fairly dry and cloudy.

The link below shows the situation, it has to be said that the 3 500mb anomaly models have not been that consistent over the past week with their output, so I would be wary of making any definite forecast for around 10 days time.

An interesting item on the ECMWF issue is the marked trough, almost cut off low off the Florida coast. Presumably an attempt to show the possible hurricane/tropical storm for that area? Its not that often that the 500mb anomaly charts from any model show this. Whether it will be correct as ever we have to wait and see.

Yes, ECWMF seems to have the slower pattern.

ECWMF has actually suggested the cut-off senario a few times now which is making some of us giddy, the light blue between the two highs is also what will be left of Phillipe so ECWMF on a tropical bender today.

For the moment we can essentially say that until the 5th we keep an above average pattern before a distinctly cool and wet 6th and 7th before the models disagree.

Edited October 2, 2011 by summer blizzard

[Gibby]

Good morning. Here's this morning's 00z output.

GFS continues to show a progressively cooler week with winds steadily increasing from the SW or West over the next 24hrs and allowing an increase of cloud and a little rain for the South. As we move through midweek a cold front runs east over the UK bringing a band of rain across followed by rather cold and showery NW winds to end the week. As we move into the weekend a rise of pressure from the SW brings a ridge east across all areas followed by a warm front with cloud and drizzle near Western coasts and hills. From late weekend on and throughout FI the charts are dominated by High pressure centred near or to the East and NE of the UK. Things would become rather warm for a while before cooling later as fog becomes more and more of a problem with time.

The GFS Ensembles show that the operational above was on the warm side of the pack from the 10th on with the majority of members keeping closer to the long term average though with some colder options too.

UKMO this morning also follows GFS in proceedings through the week also setting up High pressure close to the SW peninsula by the weekend. The cool NW flow with showers would be replaced at the weekend with drier conditions as a ridge crosses west to east ahead of a warm front bringing cloud and drizzle to hills and coasts in the west late in the weekend.

The Fax Charts show weak troughs crossing Southern Britain in the next 48hrs before an active cold front sweeps SE over the UK in the midweek period followed by a strong, cool, showery NW flow.

ECM is also very similar with High pressure building next weekend after a cooler showery phase late in the week. In the extended part of the run the weather remains set fair as High pressure lies close to the SW. However, unlike the recent High pressure this one looks like containing a lot of cloud in its circulation with lower temperatures and mist and fog problems night and morning, especially in the South.

This morning we have a fair amount of untity between the models on events this week. Further out and High pressure is dominant from both GFS and ECM with its innitial position to the SW. Later it looks poised to cover the UK and maybe drift ENE towards Northern Europe. Fog is likely to become a problem under the High pressures but with reasonable daytime weather and sunshine. Most areas continue to be considerably rain starved for the next week or two.

[nodrog]

Thanks Gibby, yes models do look like they are all reading from the same page. Wet and windy mid week then a real good aspect for Autum latter this week with a cooler theme. What a contrast to last weeks bonus!

Keep up the good write-up's.

[Slowpoke]

Indian Summer progged by GFS this morning!

[snowlover2009]

Indian Summer progged by GFS this morning!

I don't what charts you looking at, but 4 days or so of unsettled weather. Replaced by above average temperatures for a couple of days and a cool seasonal high looks very likely to me, with overnight frost and fog. Temperatures near average, if not below. I wouldn't define this as an indian summer.

[Methuselah]

Thanks for the summary, Gibby.

[chionomaniac]

I don't what charts you looking at, but 4 days or so of unsettled weather. Replaced by above average temperatures for a couple of days and a cool seasonal high looks very likely to me, with overnight frost and fog. Temperatures near average, if not below. I wouldn't define this as an indian summer.

I can't see the GFS programming this at all on this mornings run for the bulk of the populated country. Looks to me like the GFS is continuing an Indian summer as Slowpoke suggests.

[snowlover2009]

I can't see the GFS programming this at all on this mornings run for the bulk of the populated country. Looks to me like the GFS is continuing an Indian summer as Slowpoke suggests.

Well on that note this is all i can say, it look like temperatures will drop like a stone this week, with a possible mild up to above average temperatures for sunday/monday, nothing significant and clouds amounts being a problem, looking at the wind flow, thereafter, high pressure rises after with temperatures dropping slightly to around average, or just below, with night time fog and frosts. An Indian summer is characterized as an above average period of temperatures and sunshine. I don't get why people are getting hints of another Indian summer, when the weather looks fairly average to below after the weekend. I know things are likely to change, but at the moment that is what it is showing and the the white average line, is around 5c uppers most of the run. FI would bring consistent overnight fog and frost, with average temperatures or near average.

Can I remind you that an Indian summer is 'a period of considerably above normal temperatures, accompanied by dry and hazy conditions', from wiki, but it is true and I know this. I don't see anything considerably above normal in the forecast after today/tomorrow.

[Radiating Dendrite]

I can't see the GFS programming this at all on this mornings run for the bulk of the populated country. Looks to me like the GFS is continuing an Indian summer as Slowpoke suggests.

Agree.

In the reliable we could be looking at temps into the low 20s once again, with a southerly positioned high.

[Thundery wintry showers]

The weather certainly looks like turning cooler, showery and windy, with winds approaching gale force towards the NE on Thursday, and a fair number of showers firing in from the north-west. Friday looks set to be mostly dry and sunny for the majority though, with the "wishbone effect" in operation restricting showers mainly to coastal areas. Following the northerly plunge there will be a widespread ground frost on Friday night.

The subsequent anticyclonic spell that the models show, at least to begin with, has a rather moist tropical maritime airstream on the northern flank of the anticyclone. Thus I would expect somewhat more cloud and humidity than most of us have been having recently, with drizzle in the west and some more organised rain in western and northern Scotland. However, eastern and central areas do sometimes see the cloud break up somewhat resulting in sunny and notably warm conditions in that setup, and the GFS 06Z run indicates this for the 10th October with plenty of sunshine in eastern and central England and highs around 21-23C.

The long-term evolution towards a dry anticyclonic spell with hazy sunshine and fog patches overnight is a logical evolution from where we end up at T+168, but as it remains out in FI it is open to some question.

[Frosty.]

The impression i get from them is that while high pressure attempts to ridge in, they do not really take it east of the UK and as such i would expect the UK to be fairly dry and cloudy.

The impression I get today from the latest models is that the weather looks like becoming very anticyclonic towards mid month and maybe it will last a few weeks, a huge scandi high forming and other areas of high pressure making for a very blocked weather pattern, not particularly warm but pleasant enough and much more seasonal with overnight fog and ground frosts. The current heatwave is now on it's last legs but even tomorrow and wednesday will see temps of 21-22c across the south & southeast but by thursday it will feel like autumn everywhere with a strong w'ly to nw'ly flow with showers or longer spells of rain, even some snow for the scottish mountains with temps around 12c in scotland and 14-16c across england and wales but then the models show pressure rising from the west by saturday and a gradual trend to more settled weather through next week although there couls be strong sw'ly winds for a time due to a squeeze in the isobars caused by low pressure to the north and high pressure building from the south, even a mini heatwave is possible for the south for a few days after next weekend but then cooling off again and then all parts of the uk look fine and pleasantly warm or at least average with traditional mid october weather..no signs of any potent late october cold snaps yet which some experts are suggesting we will get!

[SP1986]

It does look like an unstable period is coming up, followed by a drier, warmer outlook with high pressure ridging in away from Scotland, Northern Ireland. I think it'll be once again one of those outlooks that encompass great coastal-inland temperatures gradients at night, as we have seen recently.

[Gibby]

Hi folks. Here's a look at the 12zs of the big three.

Up to 144hrs

All three models paint a similar picture this week with the last fragments of the warmth moving away from Southern England as I type with a cooler, breezier couple of days to come with a few spits and spots of rain at times for the South while the North sees bright intervals and a few showers. Wednesday may well feel quite muggy in the SW flow ahead of a cold front which sweeps SE Wednesday night bringing a band of rain and a further drop in temperature as it clears. Thursday and Friday show NW winds and showers, heaviest in the North and West on Thursday becoming more restricted to the North and NE by late Friday. A ridge crosses at the beginning of the weekend with cloud and drizzly rain following to Western coasts and hills as a warm front crosses East.

144hrs +

GFS then shows an Anticyclonic spell with its centre drifting from near to Southern Britain to lie over us for a couple of days before migrating NE to Northern Europe by the runs end. The far North will continue to be exposed to the Atlantic for some of the time with occasional rain on fresh SW winds. Further South though the weather remains set fair with a couple of warmish but probably cloudy days early next week before cooler air advances West on the underside of the High as it moves across to Europe. Some fog patches could occur night and morning if skies clear and winds stay light but frost will probably be very limited, The Autumn drought of Rainfall will continue for the South through this period.

The 12Z GFS Ensemble data shows the Operational above undulating either side of the 30yr mean for the whole period with the majority of members showing temperatures just below the long term mean for the majority of the time before falling close to the average at the end of the run. Rainfall looks generally below average.

ECM tonight shows high pressure to the South of the UK early next week with a moist Westerly flow over the UK with low cloud and hill fog near exposed Western coasts and hills. Thereafter High pressure builds North over the UK with lighter winds. The moist air would promote reasonable daytime temperatures and despite a lot of cloud at times in any Autumn sunshine it could feel quite warm but by night the incidence of fog would be on the increase, slow to clear in the mornings.

In Summary tonight things still look High pressure based as we move into next week. The position of the High pressure as always will be crucial in determining what weather is experienced but on tonights reckoning there is scope for some reasonably warm bright days but conversely fog by night could become a problem with time as it could become persistant in the mornings. Rainfall looks unlikely for many after this week with even the North seeing less rain than is normal for October as the Atlantic tends to look rather dosile after this weeks ex tropical storm passes.

[damianslaw]

The overall theme of a very sluggish atlantic maintains its hold. The change to unsettled conditions mid week is only due to ex tropical storm system - heaviest rain and strong winds reserved for the northern half of the country, the south will barely get a light dose of rain I suspect - so the dry conditions will continue here.

Models especially GFS is showing anticyclonic conditions building in from the SW during the weekend - with a very weak westerly jet ushering further low cloud and rain to the north.

Longer term - anticyclonic looks order of the day - something we have become quite accustomed too in recent Octobers. Where heights settle remains to be seen, but there is a good chance they could migrate NE in time (as shown by GFS). However, unlike recent days, the anticyclonic conditions will bring much more autumnal fare with light frosts and fog but quite probably still quite warm days for the south (high teen maxes not high 20 maxes!).

Even longer term - a northerly/scandi trough development could very easily occur thanks to the continued sluggish atlantic - so those projections of cold weather could still very much come true if the anticylonic conditions develop as being suggested by GFS.

[snowmackem]

I can't see the GFS programming this at all on this mornings run for the bulk of the populated country. Looks to me like the GFS is continuing an Indian summer as Slowpoke suggests.

Without meaning to sound picky, then term "Indian Summer" is a loose phrase bandied about by the media and therefore over time has come to mean any spell of late summer/early autumn warmth/sun. Although there is no official definition of "Indian Summer" in meteorological terms, it is more scientifically understood to mean a period of well-above average temperatures, dry and sunny weather normally occurring towards the end of October onwards, and following at least one spell of widespread frosty late season weather.The term relates to the North American natives rather than Delhi-like temperatures !

Sorry,

Mr. Pedantic lol x

[Gibby]

Good morning folks.

Up to 144hrs.

As with previous runs all three outputs support a fresh Westerly flow for the next few days with plenty of cloud and a little light rain and drizzle at times in the South and bright intervals with a few showers further North. Overnight Wednesday/Thursday a cold front sweeps SE over the UK with a narrow band of rain followed by a further drop in temperatures and bright, windy weather with showers at times, some heavy in the North with snow on the Scottish mountains. A ridge of high pressure moves steadily east over Britain through the weekend with bright dry weather before, breezy westerly winds follow with more humid air with misty low cloud near Western coasts and hills thereafter.

144hrs +

GFS then looks somewhat different to last night with small but subtle differences in pressure locations. This morning the model keeps High pressure close to the South over Northern France with a moist Westerly flow over most areas giving cloudy conditions with some rain at times in the North as disturbances run by to the North. It's only in deep FI that High pressure ridges North over the UK settling things right down with the incidence of fog and frost likely to increase then by night with some hazy afternoon sunshine

.

The GFS Ensembles today suggest the most likely scenario being to maintain temperatures near to normal for the next two weeks with a milder period early next week. Rainfall amounts continue to look generally suppressed.

ECM remains similar to last night in their longer term output by having High pressure to the South of the UK extending North late in the run to introduce a calm and foggy period then with pleasant afternoons once the fog clears. Before then the Westerly flow occasionally brings weak troughs across with moist, cloudy Westerly winds alternating with cool and bright NW winds most effective in the North.

In Summary today both GFS and ECM programmes High pressure South of the UK after this week with Westerly winds bringing cloudy, moist air with mist and drizzle near Western coasts while further North sees proper rain at times. Later on High pressure is suggested to move North over Britain probably bringing our first Autumn period of overnight fog and temperatures close to average. Once more this morning no appreciable rainfall looks likely in the near future.