Model Output Discussion 22/07/12 Onwards.

[Milhouse]

UKMO also has the brief ridge for Monday.

[AWD]

UKMO also has the brief ridge for Monday.

That chart would probably go on and show things turning progressively cloudier and wetter in Ireland, Wales & South West England as the afternoon progressed.

UKMO still has that LP advancing slightly quicker than the GFS does. But for Eastern England, both the models do show a generally dry day on Monday!

[SP1986]

The talk of high pressure in a weeks time is way way to soon to even start thinking about! The future the next four to five days shows a very unsettled regime, with showers or longer spells of rain, coupled with some quite cool days.. this looks set to remain the case for the forseeable future.

[shedhead]

The talk of high pressure in a weeks time is way way to soon to even start thinking about! The future the next four to five days shows a very unsettled regime, with showers or longer spells of rain, coupled with some quite cool days.. this looks set to remain the case for the forseeable future.

We all need/deserve something to look forward too and Sept will deliver, in shedloads...

[Bobby]

We all need/deserve something to look forward too and Sept will deliver, in shedloads...

Can you explain why, otherwise that's not adding much to the 'model output discussion'??

[Milhouse]

If there looks reasonable confidence in HP building i think people are well within their rights to be seriously considering at as a possibility. The GEFS mean shows the Azores high becoming quite dominant for the second half of the run. You can not guarantee anything at that range but those doubting a settled start to September need to back their assumption up with some evidence rather than just saying its over a week away so probably wont happen.

[johnholmes]

If there looks reasonable confidence in HP building i think people are well within their rights to be seriously considering at as a possibility. The GEFS mean shows the Azores high becoming quite dominant for the second half of the run. You can not guarantee anything at that range but those doubting a settled start to September need to back their assumption up with some evidence rather than just saying its over a week away so probably wont happen.

very true for both sides of any discussion not just to be expected from one side.

[Milhouse]

The 12z GEFS mean has a much flatter look to it compared to the earlier 6z with the Azores high not ridging as far north. It more reflects this mornings ECM mean. The mean upper temperatures remain unchanged so it would still warm up, despite the chances of widespread settled weather appearing less.

I am aware that if you compare one run with the next you are inevitably going to get a lot of ups and downs before they start to firm up nearer the time.

Next Friday sees heights starting to rise from the south west

[Milhouse]

The ECM 12z brings the onset of high pressure forward a bit so next Thursday is shown to be a dry and fairly warm day. That is after 2 fairly unsettled days on Tuesday and Wednesday with a band of rain pushing east and showers following on behind.

[Milhouse]

The run ends with low pressure locked in around Greendland and high pressure stretching right across the north Atlantic, across the UK and into much of Europe as well.

[phil nw.]

Yes some recent op.runs have tended to show a more influencial Azores high for week 2 when compared with the ens mean runs.

The mean thicknesses for T240hrs from the GFS12z do show a rise of pressure from the south but in a flatter flow.

With the fragmented jet still aimed across the UK there may well be weak frontal systems in the westerly flow especially across the north.

This is illustrated in the mean percipitation chart for the same time.

A fair bit of moisture off the Atlantic.

Of course detail may well change and heights may well improve as we get nearer.Some reason though to be wary of some of those teasers from the operationals that far out for now.

[Thundery wintry showers]

The UKMO and ECMWF have backtracked a little towards the GFS regarding Monday's advancing low so there is now strong agreement on eastern England keeping a dry day, with a sunny morning although cloud might thicken from the west in the afternoon, while western areas still look iffy.

Usually when we get strong agreement on winter northerlies at around T+180 to T+240, we do end up with a push of cold air from the Arctic, but it can end up watered down into 36-hour events or shunted out into the Atlantic or North Sea. I feel that a similar thing is true regarding the projected ridge from the Azores High- i.e. it probably will come off in some form, but its likely impacts on our weather remain open to question.

If associated with a long-term pattern change with the jet diverted northwards, it might be that we get a couple of failed "attempts" before we get a strong build of pressure on top of the British Isles. The ECMWF 12Z shows this scenario quite well in my opinion- I feel that the charts from T+192 to T+240 would bring a lot of cloud in off the Atlantic for most of us (maybe some warm sunshine towards the SE) but the T+240 chart would almost certainly be followed by a strong build of pressure and largely clear skies following the Atlantic weather system.

[tinybill]

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=2&ech=204

been reading the comments looking deep into fantasy world cant see much dry weather at the moment

[UV-RAY]

The run ends with low pressure locked in around Greendland and high pressure stretching right across the north Atlantic, across the UK and into much of Europe as well.

Good job it will look nothing like that nearer the time then.

[mushymanrob]

not much sign of any pressure build this morning, though it appears there was some on recent runs. this mornings runs offer a continuation of the unsettled theme into september.

[Snowmadsam]

A lot of value judgements here but what about the actual weather?!

After the current "sunshine and showers" spell, cloudier, wetter and windier conditions certainly look set to spread in on Friday. Most places will be cloudy, wet and breezy on Friday with suppressed daytime temperatures, and Saturday looks similar over Scotland although England and Wales may be brighter with some slow-moving thundery downpours and highs of 20-22C.

Scotland's rain is likely to buckle back southwards on Sunday as the low pressure retreats eastwards. For this reason it will probably start off grey and damp over most of England but with brighter showery weather extending from the north, while most of Scotland, Wales and Ireland will be back to sun and showers. For many western areas Sunday might well turn out to be the best day for most outdoor activities, with relatively few showers around. As the ridge of high pressure moves over on Sunday night, it may well end up an unusually chilly night for late-August.

Monday might be a dry sunny day, but it all depends on how quickly the next low pressure system approaches from the Atlantic. The GFS suggests a dry sunny day in eastern areas but with increasing high cloud in the west, with the rain belt not penetrating beyond Ireland until after dark. However, the ECMWF and UKMO version is more progressive and would have the rain belt spreading across the country during the afternoon and evening. The UKMO/ECM version is quite well supported by the ECMWF ensemble mean which suggests that Monday is looking pretty "iffy" at present especially for western areas.

For the longer-term, there is remarkably strong agreement that after the next low pressure system, high pressure will extend into central and northern Europe in about 10 days' time setting us up for quieter weather into September. It is unwise to get too carried away about this as it's still a long way off, and if the high settles to the south of us rather than over us, we could end up in a grey drizzly west to south-westerly flow, although the odds will favour dry sunny weather if we have the high ridging over us. The FI portion of the latest GFS run shows a drizzly westerly initially but then the high extends NE bringing us drier continental air with sunshine and highs of 22-25C for much of the country.

Just when we go back to school....typical

[DTHFCJ]

nice looking ECM...............192 onwards sign of things to come maybe?

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

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

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

Edited August 23, 2012 by BALE1

[Frosty.]

The latest models show an unsettled spell for the next few days but it's not a washout by any means. The weekend will see significant contrasts, saturday being very unsettled and breezy with heavy showers and longer spells of rain whereas sunday will see a marked improvement from the west, bank holiday monday also looks good in the south and east of england due to brief higher pressure hanging on but a deteriorating situation from the west as a deepening low winds itself up just to the west of the uk. The Gfs 00z shows the southeast having some good weather at times next week due to high pressure over the near continent extending a strong ridge into the southeast quarter of england around the middle of next week with temps up to 22-23c but the ecm 00z is not having it, and shows low pressure dominating the same period through next wed/thurs but then a ridge pushing in from the west towards the end of next week. All in all, not a dire outlook, the gfs 00z has high pressure at times in FI with the south and east most likely to benefit but the north and west probably having longer periods of low pressure in the next few weeks.

[Thundery Shower]

Agreed, next week looks a case of NE/SE split, with warmer dryer weather in the south with mid twenties possibly 24 - 25'c on Wed/Thurs. before another atalantic low dominates. This weekend looks non changable with Friday Evening looks like heavy rain pushing through before Saturday morning, which has 50% of storm risk, so possibly a rumble of thunder thrown in for good measure, Saturday looks like sunshine and showers but struggling to get above high teens. Sunday looking at the latest fax chart has a tough sitting through midlands and to the east, could be something watch for storm lovers, then by Monday looks alot better with high pressure moving up from the south temps between 20 - 22'c so not all doom and gloom.

[Milhouse]

The Azores high in FI is not as strong in this mornings runs so a fast transition to widespread settled weather is by no means looking clear cut. However the GFS is leading in the way in possibly haing a greater influence of high pressure for the SE next week than was previously thought.

The ECM mean has next Thursdays low sitting in a more favourable position to allow an Azores ridge, whereas the GFS is keen to ridge heights towards Greenland and keep the UK under the influence of high pressure over Europe with low pressure situated just to the west of Scotland.

Edited August 23, 2012 by Milhouse

[shedhead]

As is often the case a smooth, linear transition to a different weather type across the model suite is difficult to achieve, but I've seen nothing this morning to suggest a significant and lasting rise of pressure from the southwest is unlikely as we move into Sept, indeed I think ECM are now starting to nail the change. GFS will continue to wobble, but will ultimately settle for something similar towards next weekend imo.

Edited August 23, 2012 by shedhead

[Bobby]

It looks like pressure will be rising as we head into September, with things becoming calmer and more settled, but the NAEFS and enembles do not show support for a strong pressure build. The anomaly maps show pressure to be more or less average. The charts look a bit messy really with no signal for any particular weather to dominate.

NAEFS day 10 pressure anomalies

+384

With a fairly messy slack synoptic pattern there's always a chance of troughs sneaking in (and possibly getting cut off with high pressure to the North) and spoiling the party, the GFS control run shows exactly this, what could happen.

So the weather after next Tuesday's low clears is uncertain with a fairly messy slack pattern deveoping.

Before that, most unsettled to the N and W, not too bad in the SE perhaps.

[The Northern Ramper]

not much sign of any pressure build this morning, though it appears there was some on recent runs. this mornings runs offer a continuation of the unsettled theme into september.

This is classic model performance.

The GFS picks up on a trend in FI and then the ECM comes into line followed by the other models. Then just as you start to look at agreement the GFS has a wobble and goes against what the others show. Confusion reigns for a day or two in this forum until the GFS AND ECM start to move towards each other and find a middle ground, with the GFS doing the most backtracking.

[bluearmy]

This is classic model performance.

The GFS picks up on a trend in FI and then the ECM comes into line followed by the other models. Then just as you start to look at agreement the GFS has a wobble and goes against what the others show. Confusion reigns for a day or two in this forum until the GFS AND ECM start to move towards each other and find a middle ground, with the GFS doing the most backtracking.

ECM cant 'come into line' beyond day 10 SG !! ecm has been, in my opinion, too progressive to build heights next week in its recent fi output. the fact that the mean trough pulls out should be good enough at the end of aug/early sept to give decent conditions.

[johnholmes]

It looks like pressure will be rising as we head into September, with things becoming calmer and more settled, but the NAEFS and enembles do not show support for a strong pressure build. The anomaly maps show pressure to be more or less average. The charts look a bit messy really with no signal for any particular weather to dominate.

Yes if you compare the 12z NAEFS yesterday to the 00z today the +ve area shown over the SW approaches and much of France is quite changed this morning.

The 500mb anomaly charts I use are showing some changes but not of the same degree and rather more emphasising the position of any +ve height rises.

Fairly, not totally consistently, they suggest height rises will occur but not south of the UK but more likely west of possibly even a touch north of west.

Hence my caution in agreeing with posters suggesting surface pressure rises from the SW and a settled spell for early September.

I suspect any settled spell from the SW will be transitory and the main pressure rise is likely to be to the west or WNW in early September.

At this time of year predicting any prolonged periods of settled weather is fraught with difficulty-the major culprit being the development of tropical storms which inject huge amounts of energy into the northern hemisphere regardless of whether any decaying storm actually reaches these shores.

Edited August 23, 2012 by johnholmes