Model Output Discussion 22/07/12 Onwards.

[Bristawl Si]

Agree with this Nick.

We had a pattern change in mid July which moderated us away from the early summer deluges, and we are now looking with increasing probability of a further step change.

Four tropical storms active with continued suggestion of more to develop in the coming weeks by NWP. MJO showing signs of eastward propagation and gaining amplitude in the eastern Indian Ocean (that is ofcourse if you ignore GEFS bias uncorrected version). Ensemble mean anomalies picking up on a fading easterly zonal wind anomaly across the Arctic and increasing vorticity over Greenland allowing for some much needed cooling of the uppers there. PNA reversing its trend over teh summer with much more +ve signal developing.

Looks good for a Euro-ridge Atlantic trough in the 2-3 week timeframe and we should begin to see a rise in tendency in relative angular momentum in due course to confirm this - atmosphere starting to engage with surface El Nino ?

Great to see that Summer could be extended into September - i usually regard Sept as Summer in most years.

Hope the longer range model output turns out correct.

[Summer Sun]

A lovely start to September from GFS tonight

I wonder what the odds are of another september close to last year, a repeat is most welcome

Roll on September

Edited August 21, 2012 by Summer Sun

[phil nw.]

Looking ahead towards the end of the week we see those weak heights to our south falling away as the south westwards extension to the large Scandi/Siberian trough spawns an Atllantic low moving towards the UK just in time for the BH weekend.

Unfortunate timing indeed and it marks the start of a more unsettled spell which looks like seeing out the rest of the month.

The T240hrs 00z Ens means anomolies still show the unsettled outlook.

Rain bands crossing the UK from time to time and becoming somewhat cooler with temperatures closer to normal for most.

Beyond next week there are hints from later modelling that some rebuild of the Azores high towards the UK may show it`s hand with some better weather spreading in as we go into September.

For the time being though the overall pattern is now settling into a more traditional Westerly flow with those Arctic heights falling away and the Azores High further away for now.

[MP-R]

A lovely start to September from GFS tonight

I wonder what the odds are of another september close to last year, a repeat is most welcome

Roll on September

I'd happily take another last September - predominantly very wet and windy with a heatwave at the end. GFS however is showing another 'too little too late' scenario for September as it seems to do without fail at this time in August. I wouldn't put it past it to downgrade over time as has been the case with every spell this summer bar the final week in July.

[shedhead]

Been saying it for weeks now, September is going to be a cracker, I see this kind of chart predominating for much of the month and even quite well into October - shades of early Autumn 2011.

Edited August 21, 2012 by shedhead

[Summer Sun]

Been saying it for weeks now, September is going to be a cracker, I see this kind of chart predominating for much of the month and even quite well into October - shades of early Autumn 2011.

Yes I would not surprise me one bit to see September been dominated by high pressure at least we can still get some enjoyable hot weather during September as last year proved

[UV-RAY]

Yes I would not surprise me one bit to see September been dominated by high pressure at least we can still get some enjoyable hot weather during September as last year proved

Just like cold in late March onwards, a wasted opportunity for those who like their weather to be seasonal.

[Bottesford]

Interesting charts for September but far too long away to take with anything but a pile of salt.

Still if it is gonna be a sunny/warm one best hope (for those working Mon-Fri) it falls at weekends as weekdays it'll be dark too early to be of much use!

[legritter]

current models are at present showing a possibility of perhaps more in the way of settled conditions for perhaps the first 10days of september , but must stress possible . it will need that jet to start moving north ,which is starting to show on modells at current predictions .but before that a LOT of very unsettled conditions with copiouse amounts of rain for some areas with very breezy conditions . also some quite warm conditions could move into eastern and southern parts later next week . but as i ponted out the jet although modelled to eventually pull north ,is full of surprises these days and untill we understand the very edge of our atmosphere it will always be a surprise in its continuouse variations .i am of course refering to the amount of pressure in the upper atmosphere ,well above any weather , and temperatures at these great heights ,i will stop now as getting off topic and a bit brain dead . was going to mention AXIS of JET but i think todays surprise thunderbolt as clouded my thoughts .tonights met office fax will be interesting should give us a clue as to sun /mon weather in a bit more detail .it will be interesting to see the gfs modell on its precipitation predictions for this weekend and next week ,cheers

[MP-R]

On August 8th, the GFS was showing a length hot spell with winds from the E-SE lasting from the 9th-18th+ with a very robust Scandi high hovering just to the east of us. Then it showed a much more unsettled spell with low pressure in control. The theme of high pressure returned before the reality was actually that of warmth as a result of low rather than high pressure.

Yesterday, the GFS was showing a very unsettled start to next month with a deep low crossing us notably on the 3rd/4th yet now the jet is nowhere to be seen and highs are forming all over the place in FI. Just goes to show the models can't be relied on when picking run from run.

In the reliable, a changeable pattern (I won't say washout because bar a few days, it isn't). Certainly more unsettled though with a predominantly westerly theme going on. My guess is that this will continue into September and that any warm spells will be as a result of a ridge being thrown up ahead of an Atlantic low, followed by a brief plume with a return of the westerlies shortly after. It's been a common theme this summer when it has occurred over the UK.

[rob48]

A lovely start to September from GFS tonight

I wonder what the odds are of another september close to last year, a repeat is most welcome

Roll on September

Good of you to decide that on everyone's behalf - as usual!

[Robbie Garrett]

Agree with this Nick.

We had a pattern change in mid July which moderated us away from the early summer deluges, and we are now looking with increasing probability of a further step change.

Four tropical storms active with continued suggestion of more to develop in the coming weeks by NWP. MJO showing signs of eastward propagation and gaining amplitude in the eastern Indian Ocean (that is ofcourse if you ignore GEFS bias uncorrected version). Ensemble mean anomalies picking up on a fading easterly zonal wind anomaly across the Arctic and increasing vorticity over Greenland allowing for some much needed cooling of the uppers there. PNA reversing its trend over teh summer with much more +ve signal developing.

Looks good for a Euro-ridge Atlantic trough in the 2-3 week timeframe and we should begin to see a rise in tendency in relative angular momentum in due course to confirm this - atmosphere starting to engage with surface El Nino ?

Very interesting read there GP, practically sums up probably what will happen.

I note you mentioned that the easterlies are starting to fade in the uppers, does this mean going into Autumn and possible winter we could be locked in quite a neutral NAO, with lack of support for any shift to something more favorable for a cold winter?

Are we likely to see a return of the displaced Azores High with lows thrashing northern Scotland and the pressure gradient providing quite a windy winter for most? Or is it a case of Athmospheric Profiles wont be coming more online till we get a colder upper stratosphere with a polar vortex.

Edited August 21, 2012 by Robbie Garrett

[damianslaw]

Reliable timeframe - becoming much more unsettled for all as yet another low pressure arrives on our shores in time for the weekend, how many time have we seen charts like this on a Friday this summer.. far too many and therefore very apt. The weekend itself looks very dissapointing, by no means a washout, but often cloudy cool and windy with showery downpours for many.

Into next week and the models are showing a westerly airflow, much as we have now, however, GFS and ECM are showing the azores high ridging NE as we head into September with the promise of a fine settled warm start to the new month. All eyes on the jet stream and where it decides to position itself, it does appear to be moving northwards, which would allow azores high ridging, but whenever it has tried to do this in earnest in recent months it has failed. We shall see, a settled start to September is very normal, but by no means a guarantee of a settled month in the main, people saying a repeat of late sept 11 on the cards are getting far too carried away!

[mushymanrob]

the prospect of a settled spell into september was always on the cards, it seems that decent september spells are quite common after pretty poor summers.

[shedhead]

the prospect of a settled spell into september was always on the cards, it seems that decent september spells are quite common after pretty poor summers.

Agreed Mushy - we've seen this kind of thing across the last few years and the way the charts are stacking up we are going to see it again this September.

The pattern is starting to look increasingly set as we move into the early part of next month and once established can last a decent amount of time, so those suggesting a repeat of Sept 11 is not possible are getting far too carried away...

Edited August 22, 2012 by shedhead

[Summer Sun]

ECM is also moving towards a settled start to September

[Bobby]

Looking unsettled for the next week or so with plenty of rain about (could be very windy too at times) especially in the N and W, then signs that things will settle down as we head into September with pressure building, although the not particularly strongly so far, the NAEFS showing a return more to average.

NAEFS unsettled at day 7

By day 12 high pressure ridging in from the south

One thing that caught my eye flicking through the ensembles is that quite a few develop a tropical cyclone, even a hurricane America way with signs it may head our way.

A long way off but I wonder what effect that might have on our weather?

Edited August 22, 2012 by Barb-

[UV-RAY]

ECM is also moving towards a settled start to September

I expect a settled first half of the month but then a detiorating second half. Temp wise I feel they will come in around average for the month on a whole.

[MP-R]

Agreed Mushy - we've seen this kind of thing across the last few years and the way the charts are stacking up we are going to see it again this September.

The pattern is starting to look increasingly set as we move into the early part of next month and once established can last a decent amount of time, so those suggesting a repeat of Sept 11 is not possible are getting far too carried away...

We are of course forgetting that September 2011 was very unsettled with a few hot days at the end. This September is looking quite different with plenty of settled weather for the first week.

Already the GFS is showing the Azores High being squeezed on either side by an Atlantic low and a Scandi low. Time will tell just how sunny this spell will be or weather we get a run of cloud over the top of the high.

[shedhead]

September will be a cracking month imo, the Summer we never had.,,

[Spurry]

GFS starting to show signs of a ridge of HP stretching over the country thru's sunday/Mon, perhaps the BH might not be so bad after all

[bluearmy]

GFS starting to show signs of a ridge of HP stretching over the country thru's sunday/Mon, perhaps the BH might not be so bad after all

monday looks dry but sunday ......................... doesnt look that great at the moment though no countrywide washout

[Thundery wintry showers]

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.

[Guest pjl20101]

GFS starting to show signs of a ridge of HP stretching over the country thru's sunday/Mon, perhaps the BH might not be so bad after all

Think that's what GP has suggested of the mean trough moving westwards to allow some better weather coming in.

[Milhouse]

It looks a warm chart for Monday but i can see why the southerly is only forecast to bring average temperatures. The high begins as quite a cool airmass in the north Atlantic and the approaching low doesnt have time to inject any proper warmth northwards. But the 12z shows the rain holding off till late in the day so a decent bank holiday Monday looks likely at this stage.