Model Output Discussion - September Onwards

[nick sussex]

Thanks all for the warm welcome back. I normally begin to surface as we head into October! Looking at the longer term output this could be quite an extended period of drier weather, the hottest conditions look likely for Saturday but even after this if the models flatten the jet out and keep it north then at least for southern areas it could be a very nice spell of weather.

To be honest I'm glad this set up didn't appear earlier in the summer down here, given the fantastic September here so far with lots of dry and hot weather this in July would have been a very long period of 30+ temps with quite a few extremely hot days, I like it hot but when it starts approaching 40c it really is horrid.

[chionomaniac]

Seems to me that the 0Z ECM is trying to develop a west based -ve NAO by the end of the run. The weakened jet still cuts through the Atlantic though.

[summer blizzard]

ECWMF and GFS 12z model runs are very similar to yesterday. ECWMF has a complete breakdown at day 9 while GFS resets the pattern.

We also have Ophelia and Phileppe in the mix later which is likely to confuse the model outputs.

[Gibby]

Good evening.

As with last night the weather from all three models is the same up until Sunday with High pressure anchored to the East of the UK with a broad Southerly flow over the UK falling calm at the weekend. The weather would be fine and very warm with prolonged sunny spells after any early mist and fog has cleared.

GFS tonight brings progressively cooler conditions in next week from the NW but with dry weather continuing as High pressure remains close to SW Britain. This is then the basic trend through FI with temperatures falling to levels somewhat above normal in the Aouth with progressively cooler conditions further North. Rainfall amounts would remain suppressed for the time of year.

UKMO's final frame shows that High pressure is sliding away to the SE opening the door to the NW with SW winds taking hold slowly from the NW meaning temperatures commencing a slide down from the record high levels of this coming weekend.

ECM finally follows the UKMO theme of moving High pressure slowly away SE as next week commences with Low pressure near Iceland taking dominance by pushing a cold front SE down over the UK bringing a marked drop in temperature with more cloud, wind and even a pulse of rain as the trough passes. Once passed if anything it would turn rather cold for Northern regions with the chance of overnight frost in the North but cool, showery and bright weather by day as compensation. Towards the end of the run High pressure remains to the west or southwest of the UK but with an increasingly unstable North-Westerly flow over Britain with the door ajar to Low pressure and some rain to move in off the Atlantic and followed by cold and showery conditions from the North by the runs end.

In Summary things are beginning to firm up a little on the sequence of events for next week. It looks like temperatures will fall off after the weekend in response to a SW flow moving down from the NW as High pressure slips further away to the SE. It looks like there will still be a lot of dry weather around especially in the South. With cold air not far to the North the North and Northeast could become rather cold and breezy at times withwinds from the NW.

[johnholmes]

Well ec-gfs 27 for 7 oct have rather different outputs-positions of troughs, areas of +ve values-so no idea what to make of it

Neither very similar to noaa from last evening either

Be interesting to see what noaa shows this evening

not much consistency from the 3 ouputs over the past 2-3 days.

The settled weather with its comparitive heat for some areas is certainly gone but replaced by what?

The outputs from the 500mb anomaly charts are not the best for anyone seeking guidance over the past couple of days.

I've not yet seen the NOAA ouput this evening but my comment into my own lrf file this morning had the comment above?

Edited September 27, 2011 by johnholmes

[damianslaw]

Too much divergence between GFS and ECM at present when looking beyond the weekend - consequently the prospects for next week look very much up in the air at this stage. One of two likely scenarios probably develop -

Scenario 1 (as shown by GFS) - heights will gradually transfer further south and east allowing a sw flow off the atlantic to develop but with a flat northern arm of the jet enabling heights to remain relatively strong to our sw, which would mean further dry but cooler and probably much cloudier conditions next week, northern parts influenced by weak troughs/fronts from the west.

Scenario 2 (as shown by ECM and trending by UKMO) - heights moving south and east but at the same time we see amplification in the jetstream causing the development of a deep low pressure to our north which will swing SE over scandi/n sea pulling in a cold NW blast. Somehow, I think ECM is being rather bullish...

Perhaps the safest option would be to opt for something inbetween - i.e. a return to a westerly flow, with fronts/troughs affecting the north and near average/slightly cooler than average temps and the south staying relatively dry with slightly above average temps.

[chionomaniac]

I still see the west based -ve NAO is present in both the GFS and ECM in the extended output. I wouldn't at all be surprised to see this move eastwards with the Scandinavian trough building at the same time. If the MJO forecasts remain consistent then one could expect to see a cold snap starting around 10th October.

[Frosty.]

The Gfs 00z shows the hot & sunny spell lasting until next tuesday across southern england but turning cooler (nearer average) and fresher everywhere else by tuesday but then after a few fresher days it warms up again as another high builds in from the west bringing more very warm and sunny weather later next week..it is only towards the middle of october that there is the potential for a big change in the weather with colder and more unsettled conditions with NW'ly winds and even a risk of wintry showers for scottish hills and a high risk of frosts becoming more widespread, even in the south. A very wintry looking chart to finish the 00z, a reminder that winter is coming and some experts think it could be a cold one with continued low solar activity and la nina. It will be interesting to see the Ecm 00z as the 12z made more of the cooldown next week and less of anticyclonic conditions returning so quickly.

Edited September 28, 2011 by Polar_ Low

[Gibby]

Good morning folks. Well the very warm weather has arrived. Will the models show it lasting?...read on.

GFS this morning is almost entirely High pressure based throughout. With a centre to the east unusually warm Southerly or SE winds are now blowing up over the UK from the Continent. From now until Monday the weather will be dry, sunny and very warm for many with temperatures some 10C above the norm for late Sept/early October. There would be precious little in the way of cloud and mild misty nights with local fog patches. As we move through next week and beyond things remain settled and dry though with time temperatures will fall back somewhat though it will remain on the warm side in the South at least. High pressure close to the UK eventually is shown to give way from the NW with wind, rain and colder conditions far out in FI.

In The GFS Ensembles this morning the operational is a slight warm outlier between the 8th and 11th with many members showing a cool down to values near to or a little below the long term average with time. A fairly dry scenario is indicated throughout.

UKMO this morning also shows a very warm or even hot period coming up lasting through to Sunday with light Southerly winds falling calm by the weekend and temperatures miles above the seasonal norm with sunny daytime skies and misty clear nights. As High pressure over Europe relaxes by the start of next week high temperatures are squeezed away South as a Westerly flow takes hold by Tuesday with lower temperatures and much more cloud and some rain eventually in the North.

The Fax Charts indicate a very warm Southerly or SE flow with High pressure to the East and Low pressure to the West with weakening frontal activity repeatedly over the far NW.

ECM today is similar to last nights model and shows the hot spell as the others out until Monday when it follows UKMO in bringing Westerly winds South over the UK early next week with attendant cloud cover and much lower temperatures. By midweek or soon afterwards a marked drop in temperatures will have occurred everywhere as winds turn NW or North over all areas with some showers in the North and East and some noticeably cold nights with frost possible in places and overall temperatures by then a little below normal.

In Summary the rest of the week will remain more like July with plenty of uninterrupted sunshine lifting temperatures to near or at record breaking values early in the weekend. As we move into next week a steady fall off in temperatures looks likely as two of the three models show Westerly winds taking hold bringing in more cloud off the Atlantic. Further out still whilst GFS continue a High pressure based theme going with dry, sunny and rather warm (by day) conditions ECM once more shows a cold blast from the North bringing us back into the correct season rather abrubtly by the end of the next working week.

[Frosty.]

The Ecm 00z looks very similar to the 12z last night and is nowhere near as optimistic about a return to hot anticyclonic weather once the current hot spell is blown away from the uk on mon/tues next week, the ecm looks much more showery and cooler than the gfs but the gfs could still be right.

[Geordiesnow]

Models are now firming up that this warm and sunny spell will end on Sunday for most areas although Southern areas will still have a sunny and warm Sunday.

Hints are coming in low pressure will try and come in and with some half hearted ridge, we get a cooler NW'ly shot but in sitations like this, higher pressure does not tend to be far away so all in all the further South and East you are, the likelyhood of its being drier whilst the NW will see more rain.

Of course, if we get a successful ridge into Greenland a more sustained cooler shot is likely with those colder uppers edging into Northern Britain.

[Isolated Frost]

GFS 12Z

Today, Thursday and Friday keep a very warm flow with a S/SW'ly flow throughout, uppers are steady or falling slightly, especially in the west, but temperatures should gradually rise, highs in the mid to high twenties in much of England and Wales, and around 18-22C on Western coasts and NI/NW Scotland. Minimum should keep in double figures, around 13-17C on the whole, slightly cooler in the North - expect high humidity and more condensation. Then, into the weekend - we develop a slight split as HP moves in from the SW/W, so the south and east keep on to warmer uppers on Sat, and experience 23-26C highs, while the north and west slightly cooler with a higher chance of cloud - but still very much above average. On Sunday, the HP moves in and covers the nation, with a more mean E'ly flow in the south, and a W'ly in the north; temperature in the high teens in Scotland and NI, low twenties in much of Northern England, the Midlands, Wales and the South West, but still quite warm with temperatures reaching 25C and beyond in the south and southeast.

Next week, as Monday begins, the high moves south and the North especially develops a more breezy, cooler note, with temperatures yet again cooler in the North and West, but less mild in the South at last, in the early to mid twenties in the usual hot areas. By Tuesday, a fully fledged NW'ly moves in, as the HP positions perfectly - and very cool uppers arrive, even possibly -2/-3C uppers in the far North. This moves slowly east as we approach Wednesday and Thursday, and, despite this being fairly far out in the run (+160 onwards), there are -4C/-5C uppers nearing the Highlands with -6C/-7C uppers edging into the Shetlands.

Summary would be - heat lasting until Friday and Saturday in the North, and Monday in the South, with 25C easily passed on each day of this week, but early into next week, a Polar Maritime setup moves in to the North especially, with the possibility of wintry showers around Northern and Eastern Scotland, with snow possible in the Highlands and the Northern Isles.

[J10]

A difference in the short term tomorrow with NAE indicating more cloud hitting western parts of Wales and SW England. NMM showing this staying further west, GFS keeping this further west, interesting to see which is correct.

It should turn brighter later across all parts anyway.

[Summer Sun]

The low pressure ECM had this morning for late next week has been replaced with high pressure

http://www.wetterzentrale.de/pics/Recm1921.gif

http://www.wetterzentrale.de/pics/Recm2161.gif

http://www.wetterzentrale.de/pics/Recm2401.gif

[Liam J]

The low pressure ECM had this morning for late next week has been replaced with high pressure

http://www.wetterzentrale.de/pics/Recm1921.gif

http://www.wetterzentrale.de/pics/Recm2161.gif

http://www.wetterzentrale.de/pics/Recm2401.gif

I noticed that aswell, however FI can and will change quite significantly just like the ECM - from LP to HP on the next run.

[Gibby]

Good evening folks. Here's a look at the 12zs from GFS, UKMO and ECM.

All models maintain the very warm if not hot sunny and settled conditions for England and Wales for the rest of the week and the weekend. For Scotland and Northern Ireland things change markedly as early as tomorrow with more cloud and eventually rain from a slow moving cold front straddling Scotland SW-NE by Friday. Here temperatures will be well down on todays values.

GFS then moves into next week with a marked cold front moving SE over the UK with probably an insignificant band of rain on Tuesday followed by a sharp drop in temperature bringing a significant chill to the way things feel over recent events. There would be some showers in the North and East for a while midweek with some very chilly and potentially frosty nights before things dry up everywhere as high pressure re-asserts itself close to the UK bringing dry and warmer conditions again by the end of the week, though not as warm as currently. At the very end of the run things become more unsettled.

The GFS Ensembles tonight show a sharp dip in temperatures early next week with the operational becoming a warm outlier for a period again thereafter.

UKMO brings cooler weather in early next week although its progress looks fairly inocuous with breezy and more cloudy conditions with Westerly winds pulling temperatures back down to normal levels by midweek and precious little rainfall likely anywhere.

ECM finally follows UKMO with a much less impactive cold front next week. Nevertheless after Sunday the winds turn Westerly or Northwesterly bringing temperatures back down to near normal levels by midweek but as with the other models shows very little chance of significant rain for anyone as High pressure builds slowly back into the UK from the SW by the end of the run.

In Summary it seems as though things are definitely going to cool down as we move into next week. There is a lot of to and fro between the models run to run in the way things pan out after the cold front crosses SE on Tuesday but the general concensus seems that High pressure would remain close by with little if any rain next week with temperatures much nearer normal though hints from GFS and ECM late on in their runs that things might warm up a little again by day later.

[Frosty.]

It looks like once the current astonishing heatwave ends next mon/tues, a few days of cooler more average days with NW'ly winds will arrive by tues/wed and last a day or so before another anticyclone builds northeastwards across the uk but we will be in a cooler airmass so temps will be closer to average and with a risk of a touch of ground frost but the models then indicate a rise in temperature as winds once again begin to turn more S'ly to SW'ly although probably no repeat of the 28-29c expected in the next 3-4 days. It also looks like some rain will occur across more northwestern parts of britain for the remainder of this week and through the weekend and then scotland will catch the strongest winds and coolest temps into next week with showers. The Ecm 12z now looks more anticyclonic in FI, as is the Gfs 12z and there is no sign of any significantly cold weather out to mid october.

[Guest]

It looks like once the current astonishing heatwave ends next mon/tues, a few days of cooler more average days with NW'ly winds will arrive by tues/wed and last a day or so before another anticyclone builds northeastwards across the uk but we will be in a cooler airmass so temps will be closer to average and with a risk of a touch of ground frost but the models then indicate a rise in temperature as winds once again begin to turn more S'ly to SW'ly although probably no repeat of the 28-29c expected in the next 3-4 days. It also looks like some rain will occur across more northwestern parts of britain for the remainder of this week and through the weekend and then scotland will catch the strongest winds and coolest temps into next week with showers. The Ecm 12z now looks more anticyclonic in FI, as is the Gfs 12z and there is no sign of any significantly cold weather out to mid october.

GFS 120hr spread looks good for England...low pressure arriving from the NW so not so good for Scotland:

[Gibby]

Good morning. Here's my take on the 00zs of the big three today.

GFS shows High pressure to the east and a unseasonably warm Southerly flow over the UK with a trailing front close to the far NW. For much of England and Wales this means a continuation of clear blue skies and high temperatures between now and Sunday with just misty nights. The far NW will be cloudy and cooler with some rain. Through the early days of next week High pressure to the East collapses and Westerly winds develop over the UK pushing the warm and sunny skies away SE, to be replaced with cloudier and cooler conditions before a cold front moving SE Tuesday brings much colder air down with showers in the North and East and temperatures no better than normal and below in the North and East. The first Autumn frosts could occur later next week. In FI the air over the UK remains inherently cool despite High pressure moving in so sunny weather will be mixed in with cold nights for a while with likely frosts in places before cloud and wind increase again from the West by the end of the run as High pressure to the South collapses away.

The GFS Ensemble data shows the operational run described was a cold outlier between the 5th and the 11th.

UKMO also brings cooler weather to the UK from Monday as Low pressure to the North bring a spell of strong West winds for Scotland and breezy conditions elsewhere with a little rain at times. Temperatures would be back to near normal by midweek.

The Fax Charts continue to show a very warm Southerly drift over most of the UK though with troughs near to the NW gradually weakening as they extend SE with time late in the weekend.

ECM follows a similar pattern with cooler air extending South to all areas on a freshening Westerly breeze from Monday of next week. There would be a band of rain moving east introducing the cooler air. Thereafter winds remain from the West or NW with progressively cooler weather as Secondary depressions run ESE to the North of Scotland piulling ever cooler and unstable air down over the UK as the week progresses.

In Summary this morning things have firmed up on the pattern for next week. There is general agreement between the models that we will lose the heat from the South by Monday with next week seeing a West or NW flow delivering much cooler and fresher conditions with a stiff breeze too. No doubt things will feel distinctly cool after what the South has become accustomed to of late. There will be some rain at times next week but in the South and SW amounts look like being small. In any clear skies at night next week there looks ample chances that frost could occur locally with time.

[Summer Sun]

GFS has gone back to low pressure again for next week as per ECM

http://www.wetterzen...s/Rtavn1141.png

http://www.wetterzen...s/Rtavn1381.png

http://www.wetterzen...s/Rtavn1621.png

http://www.wetterzen...s/Rtavn1861.png

http://www.wetterzentrale.de/pics/Rtavn2041.png

If the 00z is correct then it will be a massive for some, maybe as much as 15c to 18c, i wouldn't rule out snowfall for the highest ground either in Scotland.

[Radiating Dendrite]

Quite a switch around from the GFS!

By this time next week we may only be scraping double figures if it is to be believed.

Wintry showers in the North, with snow possible up over 400m I would say.

[johnholmes]

Its not often that there are such differences between the 3 500mb anomaly charts as the last day or two are showing.

Both the ECMWF and GFS version go for meridional extension giving colder air at 500mb from a north west direction. NOAA is, as of last evening, refusing to join this idea with it having the 500mb flow a touch south of west.

Both GFS and ECMWF synoptic outputs mirror what the 500mb anomaly charts from the same centres show. Another thing that is not all that often seen.

So 10 days time we will know which model is correct, or should I say nearer the mark as the end result is often a compromise between the models.

I should also add that GEM is with GFS and ECMWF.

Edited September 29, 2011 by johnholmes

[chionomaniac]

Its not often that there are such differences between the 3 500mb anomaly charts as the last day or two are showing.

Both the ECMWF and GFS version go for meridional extension giving colder air at 500mb from a north west direction. NOAA is, as of last evening, refusing to join this idea with it having the 500mb flow a touch south of west.

Both GFS and ECMWF synoptic outputs mirror what the 500mb anomaly charts from the same centres show. Another thing that is not all that often seen.

So 10 days time we will know which model is correct, or should I say nearer the mark as the end result is often a compromise between the models.

I should also add that GEM is with GFS and ECMWF.

I suspect that we are seeing uncertainties relating to the transfer of main trough from the Atlantic region to the Scandinavian area. This has been suggested for some time now and I think is related to the forecast change in MJO with quite a distinct pulse of tropical convection transfering eastwards across the tropics. It very much looks like the modelling in our region is following this. If the MJO forecasts halts around phase 7/8 then we could have a Scandi trough around for some time and those forecasting wintriness for October could be closer to the mark than we can invisage presently.

[johnholmes]

I suspect that we are seeing uncertainties relating to the transfer of main trough from the Atlantic region to the Scandinavian area. This has been suggested for some time now and I think is related to the forecast change in MJO with quite a distinct pulse of tropical convection transfering eastwards across the tropics. It very much looks like the modelling in our region is following this. If the MJO forecasts halts around phase 7/8 then we could have a Scandi trough around for some time and those forecasting wintriness for October could be closer to the mark than we can invisage presently.

yes I agree with the idea of the MJO change ch-a very interesting splt with the 3 models though, rare to see it so marked.

[chionomaniac]

yes I agree with the idea of the MJO change ch-a very interesting splt with the 3 models though, rare to see it so marked.

Yes - look at the MJO forecasts, John. All very similar.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml