Model Output Discussion - September Onwards

[nick sussex]

Some very large differences today in the output with the GEM bringing perhaps the biggest change especially for Europe with a big switch from the current heat to winter.

The UKMO really stands out in not wanting to know with a flat jet at 144hrs.

The GEM looks a bit overdone here and the GFS if you look at the 500hpa level on its ensembles has little support with that polar influenced air, the best bet is what we often see here, with a brief skirmish for the far ne of the UK.

After this as has been mentioned above is what happens to that Scandi trough, if it sticks for a while then there might be a further opportunity for a brief north to nw flow.

[snowlover2009]

If the charts are to come by, we could see nearly around 16c drop in the upper temperatures and over 16c drop in temperatures. Temperatures predicted at 26c until Saturday, massive shock to the system.

[Liam J]

GEM flips from summer straight to winter on the latest run, nice charts for winter for sure! a bit extreme with depressions moving down from the north with polar air wrapped around them. Unlikely scenario being overdone.

[summer blizzard]

Some of you are perhaps being a little sensationalist. While the turnaround next weeks does look large, maxima will still be in the 14-16C range for most. Current models would suggest that it is at night when we see the biggest difference.

http://www.wetterzentrale.de/pics/Rtavn1687.png

Very cold air for wednesday and thursday night.

Edited September 29, 2011 by summer blizzard

[Summer Sun]

Lovely GFS for late next week

http://www.wetterzen...s/Rtavn1921.png

http://www.wetterzen...s/Rtavn2161.png

http://www.wetterzen...s/Rtavn2641.png

http://www.wetterzen...s/Rtavn3121.png

http://www.wetterzen...s/Rtavn3601.png

So if tonights GFS is correct then we could be in for a quick return to high pressure not as hot as this week, but it will be very nice, also rain fall continues very low for many.

Edited September 29, 2011 by Gav

[Aaron]

Lovely GFS for late next week

http://www.wetterzen...s/Rtavn1921.png

http://www.wetterzen...s/Rtavn2161.png

http://www.wetterzen...s/Rtavn2641.png

http://www.wetterzen...s/Rtavn3121.png

http://www.wetterzen...s/Rtavn3601.png

So if tonights GFS is correct then we could be in for a quick return to high pressure not as hot as this week, but it be very nice, also rain fall continues very low for many.

Not good

Edited September 29, 2011 by Aaron

[summer blizzard]

Not good

All about preferences. The model output certainly looks fairly dry away from the coasts, which for me is good.

[Gibby]

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

For England and Wales all models show the next three days as fine sunny and exceptionally warm for the time of year as winds continue to waft over the UK from Europe. Later in the weekend and into next week things start to change as cooler air spreads in from the NW.

GFS shows Low pressure well to the North of the UK with a Westerly flow developing over Britain with more cloud and lower temperatures but relatively dry still. Later in the week things continue to cool as winds turn North to Northwest behind a cold front. Bright cool days would prevail at the end of next week with some overnight frost in shelter of the breeze. Thereafter and through FI High pressure anchors near to the UK with sunny days and misty night with light/variable winds. Temperatures would also recover again to levels still somewhat above the seasonal normal providing overnight fog clears quickly enough and that could be a big 'if'.

UKMO has tonight backtracked a little on events next week preferring tonight to keep High pressure close to Southern Britain and a Westerly flow over many areas. Temperatures would fall markedly from current levels to levels near or slightly above normal in the south in any sunnier spells that develop. Further North the weather would be somewhat windier and unsettled with some rain at times in temperatures near or a little below normal.

ECM too brings cooler conditions in earlier next week but with next to no appreciable rain occurring at the transition to cooler weather. There would be a big increase of cloud and breeze though. Later in the week a cold front brings some rain east across all areas followed by even cooler weather with fresh NW winds and showers for the North and East. By night things would become very chilly with frost possible in places sheltered from the wind. Towards the end of the run High pressure is positioned to the SW of the UK with a NW or West flow over Britain keeping things breezy and rather cloudy but with only small amounts of rain away from the far North. Temperatures would not be far from the seasonal norm by the end of the run.

Tonight has seen the models backtrack a little on the sharpness of the drop in temperature next week. Nevertheless, a signifcant drop can be expected though anyone hoping for a change to wet conditions will be disappointed by tonights output. High pressure looks like never being far away from the South with temperatures near to normal for most as a Westerly airflow becomes dominant. GFS goes on to show a return to rather warm settled weather though this looks relatively unsupported in the ensembles while ECM shows a very cool NW flow late next week before the model looks like gradually deteriorating conditions at the end of its run.

Edited September 29, 2011 by Gibby

[Frosty.]

Next week looks like turning much cooler across the whole of the uk as we swap winds originating in western africa for arctic winds although seriously modified, there could be the first wintry showers of the season across high ground in scotland, maybe lower than munro level across the grampians and cairngorms but a relatively cold and showery spell is strongly signaled by the gfs and ecm today with the hot weather beginning to lose it's grip as early as sunday with more cloud and breeze and then losing it's grip a bit more on monday with stronger winds and even more cloud with some showery rain before losing grip completely from tuesday onwards, even a risk of frost for southern england by the end of next week so enjoy the BBQ weather while it lasts as we are probably going to have a much colder and more unsettled 2nd half to next week..thereafter it's unclear although pressure will probably remain high to the south of the BI and low to the north so we could be in a run of mainly westerly winds in FI with changeable weather and with temps around average.

[damianslaw]

Collapsing heights being forced to retreat away to the south, thanks to increasing low heights hammering down on them from the north - the result a much cooler airflow for the north as early as Monday, but the south will cling onto slightly warmer than average conditions for a while yet.

All eyes on the scandi trough - how far south it moves is key to whether we see a pronounced chilly polar maritime blast, or a shortlived cooler blast with a return to westerlies. It may have two bites of the cherry, second time round winning... but this is a long way off. In the meantime, lets enjoy the next couple of days which away from N Ireland and Scotland promise mid summer conditions.

[Frosty.]

Shame we never had a real summer this year, I agree that it may take 2 bites of the cherry with the scandi low and the southward position and shape of the trough is a long way from being resolved but this current hot spell is a bonus to what was a dreadful summer..horribly over hyped during the hot and dry mid to late spring. The latest models have slowed down the change to much colder weather until after midweek but that could easily change again tomorrow, the ecm has been wobbling a bit in the last few days but this current freak hot spell will probably be the last although not ruling it some warm anticyclonic weather further into october.

[snowlover2009]

Posted this in the depth thread, but this thread is always alive, so will post it here, if its ok:

Interesting post from Nickl over on weather outlook:

'this evenings noaa cpc update 6/10 day chart is possibly the most amplified that i can ever recall from the eastern pacific all the way to scandinavia. these set ups can be quite persistant and our outlook for the first half of october depends on where we end up sitting in the overall pattern. the whole of the month could well be quite blocked over the NH which has been quite well trailed.'

Interesting for those who are looking for some early cold/cool weather for October. 'most amplified that i can ever recall from eastern pacific' not sure what this means, however it does sound like a good response for any cold fans. Do you know what he means by that quote?

regards

[Frosty.]

The Gfs 00z has dramatically downgraded the influence of the scandi trough next week although it will still turn cooler everywhere by tuesday, it then looks as though high pressure will make a swift return to the uk later next week into the following week, even a good chance of another heatwave as winds become S'ly or SE'ly once again, quite a blocked looking pattern with lots of high pressure and even in the depths of FI the pressure remains fairly high although temps do then return to normal towards mid october but the summer like synoptics look set to continue according to the gfs 00z despite a bit of a blip for a few days next week.

[Gibby]

Good morning folks. Here's a trip through the 00zs of the big three today.

GFS continue to show the end of the hot spell on Sunday as High pressure relocates South of the UK by Monday setting up a Westerly flow over the UK. Temperatures will fall steadily from Monday to near normal levels everywhere with much more cloud and a little rain in places, chiefly in the North. A cold front runs SE on Wednesday as a weak affair bringing a further drop in temperature and the risk of frost at night but dry, bright days once any windy showery weather clears away from the NE. In FI today High pressure dominates close to Southern Britain for much of the time with a lot of dry, bright weather and should it verify somewhat warmer again too before a change to lower pressure and occasional rain develops towards the end of the run.

The GFS Ensembles today show the above to be a warm outlier once more this morning from the 7th on.

UKMO today shows High pressure re-positioning just to the South of the UK with a Westerly flow over the UK with a steady cool down in conditions from Monday. The weather would remain mostly dry though with an increase of cloud the main difference in the weather apart from the temperatures. Towards the end of the run a cold front crosses East bringing a band of mostly light rain across the UK.

The Fax Charts shows the very warm air over the UK gradually subsiding late in the weekend with a weak, decaying trough bringing more cloud and lower temperatures down from the NW later on Monday and Tuesday.

ECM keeps High pressure close to the South and SE next week giving way later to Low pressure to the North with wind and a little rain by the end of the run. In weather terms a hot weekend looks likely with a change to cooler conditions through Monday and Tuesday. Nevertheless, with a Southerly drift still prevalent for much of next week temperatures could well remain well above normal in the South and East but with more cloud than recently.

In Summary this morning there are still many options possible next week. This morning we range from GFS bringing cold fronts South lowering temperatures progressively through the week as well as UKMO on Thursday while maintaining fairly dry conditions with just a little rain near the troughs. ECM on the other hand keeps things reasonably warm for the South and East as High pressure reasserts itself to the SE. It will be interesting to see where it sits in the ensemble data later. Whichever way it goes rainfall will once more be very sparse next week.

[Frosty.]

The Ecm 00z has had a major wobble overnight and now has much of next week remaining very warm across southern britain and not so bad in the north either, the strong cold Northerly winds have vanished completely although in FI there is a vigorous depression approaching from the southwest but temps continue well above the seasonal average, I would say the ecm has been performing rather poorly in the last few days.

[Thundery wintry showers]

I think perceptions of summers tend to be biased towards the latter part of the summer. This year's summer is now routinely described as "dreadful", and I might just about agree with that if we were talking about August, but in truth rainfall and sunshine were both close to average for most of us during June and July.

In the meantime tomorrow has changed significantly across parts of northern England with the band of frontal rain pushing further south, so for those of us in Cumbria, Northumberland and perhaps Tyne and Wear today may end up being the last of the really warm/hot sunny days. A NW-SE split looks like setting up over the next few days with slow moving rain belts over Scotland and the northern quarter of England, giving rather cloudy muggy weather, while the southern three-quarters of England look like staying dry and mostly sunny and warm, a little less so than we've seen over the last couple of days but still to an unusual extent for the time of year. Perhaps on the ECMWF outputs, which have high pressure further north, the "divide" might end up further north than is suggested by GFS, leaving the far north of England in the clear too, but I'm not sure about this. After midweek things get more uncertain with the trough starting to set itself up over Scandinavia but no immediate certainty of any northerlies.

[Frosty.]

The latest models show another warm up after a cooler blip with temps rising back towards the mid 20's celsius in the south after midweek but at least between monday and wednesday it will become cooler and fresher nationwide before warming up again but even the cooler blip will be above average.

[mezzacyclone]

Is it me or has the GFS had a helluva U-turn in the last few runs?

Arctic plunge yesterday from a mid Atlantic ridge and the convergence off the Greenland tip from tuesday onwards has vanished???

[Methuselah]

Aye, it's still looking good (I do like autumn warmth). Plenty of scope for more wild fluctuations, though...

[Radiating Dendrite]

Is it me or has the GFS had a helluva U-turn in the last few runs?

Arctic plunge yesterday from a mid Atlantic ridge and the convergence off the Greenland tip from tuesday onwards has vanished???

Yep, post 5 days it does not have a clue at the moment!

Current run has the 15c 850s back over the country at one point.

I think the signal is mixed!

[nick sussex]

It's nice to see in an ever changing world one thing remains consistent, that being the GFS and its huge mood swings!

The polar influenced flow it had a few days back has imploded with now the models not sure what to do with that troughing in the Atlantic, the ECM has also been poor over the last week but the wooden spoon surely goes to the GEM which continues to suggest that you'd get more sense from reading the tea leaves!

In terms of the upstream pattern it might be that the UK will stay on the warmer side, of course in winter all the snow lovers wouldn't be happy with the amplification leading to a warmer southerly flow but given the dire summer for the UK best enjoy whatever sunshine is on offer, as we've all seen from past history things can and do change very quickly.

[Frosty.]

The Gfs 06z has backtracked slightly and shows quite a blowy week ahead for the north and east as a low tracks east into scandinavia with a showery and cool NW'ly flow for a few days, the influence of this will be strongest across northern britain but dramatically weakened across the south but a drop in temps of several degrees is assure for the hot south as we go into next week. High pressure then looks like building into the uk yet again and after a slow start, temps again look like being boosted as the high pulls in s'ly winds from the hot continent but perhaps nearer the mid 20's celsius rather than pushing 30c 86f which it will be doing today and especially tomorrow in the southeast, the heatwave reaching it's peak tomorrow before slowly subsiding over the following few days. The Gfs 06z shows high pressure dominating the next few weeks with just a sprinkling of more unsettled days and these will tend to be across northern britain.

[Thundery wintry showers]

Looks like it's "game over" for Scotland tomorrow, and my native Tyne and Wear is looking marginal as a fairly active rain belt straddles southern and central Scotland:

http://hw.nwstatic.c...6/33/ukprec.png

...but further south another warm (hot for some) and sunny day is likely and the 1st October 1985 record of 29.4 is likely to be approached:

http://hw.nwstatic.c...3/ukmaxtemp.png

In support of my earlier post, it doesn't look like Scotland or northern England will see much sunshine on Sunday/Monday as a slow moving frontal system gives cloud and a bit of rain:

http://hw.nwstatic.c...6/57/ukprec.png

By Monday much of the rain will have fizzled out but it stays cloudy in the north:

http://hw.nwstatic.co.uk/gfsimages/gfs.20110930/06/81/ukprec.png

...but the heat still clings on in the SE:

http://hw.nwstatic.co.uk/gfsimages/gfs.20110930/06/81/ukmaxtemp.png

[Rollo]

It's nice to see in an ever changing world one thing remains consistent, that being the GFS and its huge mood swings!

The polar influenced flow it had a few days back has imploded with now the models not sure what to do with that troughing in the Atlantic, the ECM has also been poor over the last week but the wooden spoon surely goes to the GEM which continues to suggest that you'd get more sense from reading the tea leaves!

In terms of the upstream pattern it might be that the UK will stay on the warmer side, of course in winter all the snow lovers wouldn't be happy with the amplification leading to a warmer southerly flow but given the dire summer for the UK best enjoy whatever sunshine is on offer, as we've all seen from past history things can and do change very quickly.

Nice to see you back Nick,I look forward to your views come winter proper.

[nick sussex]

Nice to see you back Nick,I look forward to your views come winter proper.

Thanks. Yes well we've still a way to go, normally I surface a bit later into the Autumn but because of the current heatwave I thought I'd pop in.

Going back to the models this evening, still alot of uncertainty in the outlook with the GFS delivering some colder conditions into eastern Europe, more high pressure but cooler temps for the UK.

The UKMO looks a bit of a halfway house, it seems upstream in terms of degree of amplification is causing this downstream uncertainty, the main point being what happens to troughing in the Atlantic.

It will be interesting to see what the ECM makes of those upstream signals, it's been up and down all week.