Model Output Discussion 26/08/2012

[Frosty.]

There is agreement within the latest ensemble mean extended range for high pressure to become established to the southeast over the near continent and will influence the weather at least across the southern half of the uk but more especially the southeast quarter, this is all beyond the T+168 hours range but the gfs 6z and ecm 00z ens mean look fairly similar with their idea of an improving trend from the south later but a lot of unsettled weather to come before that happens, especially towards the middle of next week with low pressure close to northern scotland next midweek. So it looks like a mobile zonal (fairly mild) pattern will persist with only shortlived ridges, a flat ridge pushes east across the uk on saturday but then it turns more unsettled by sunday, then next week we keep a generally unsettled pattern, especially further north with lows either to the northwest or north of the BI throughout the outlook but there are signs of something more settled in the south later but probably with overnight mist and fog and temps close to average for most of the time with no sign of any significant amplified patterns bringing colder showery weather to the uk..for a while yet.

Edited September 27, 2012 by Frosty039

[shedhead]

Think we are looking at a period of something resembling mobility, at least for a time, but more amplification looks likely come the 2nd week of October. Thereafter the signals look very mixed, but hopefully we will see an increase in heights to our north as the rest of the month unfolds.

[legritter]

just a very quick one from me ,looks like high pressure over central and s/east Europe at around 192 Hrs will perhaps save many places from another seriouse soaking .BUT I think there are many synoptic possibilities at the moment looking at current charts .looking forward to tonights charts to see if LOW pressure gets pushed further south to our far west , catch up later .

[Gibby]

Hi Folks. here's another chapter from the 12z output of GFS, UKMO and ECM tonight.

All models show a Westerly flow over the UK with an occlusion moving SE down over the UK in the next 18hrs. It is a fairly weak affair with just showery bursts of rain for many before clearer weather with showers spread down from the NW. A ridge of High pressure crosses on saturday which holds on in the South through most of Sunday. In the NW winds and cloud increase from the West as Low pressure to the NW takes hold with rain moving steadily SE through the day. Following a cold front clearing SE early Monday is a broad Westerly flow with a heady mix of sunshine and showers, heavy and prolonged in the NW but relatively few in the SE, a pattern that lasts into Tuesday too.

GFS continues to push Low pressure slowly East just to the North of Britain with showers or longer spells of rain blown on in a cool and fresh West wind. By Thursday a ridge moves across from the West damping the showers down and giving a dry day for Southern areas. through the latter end of the day a warm front moves NE over the North carrying rain with Friday seeing a strong and mild SW wind blow over the South with hill fog and drizzle in the West and more appreciable rain further North. FI tonight shows a very mild SW flow over the South with only small amounts of rain as cold fronts pass by on a couple of occasions. Further North the weather remains unsettled and windy with rain at times in temperatures close to normal.

The GFS Ensembles tonight show a changeable couple of weeks to come. The operational is a little bit of a warm outlier in the phase when high pressure lies close to the SE with the preferred trend for temperatures to be close to or even a fraction below at times with rain off and on.

The Jet Stream is currently setting itself up for a sustained period of a West to East flow across the Atlantic and over the British Isles undulating slightly North to South at times.

UKMO for midday on Wednesday shows a Low pressure area West of Norway with a second centre over the Irish Sea. An unstable cyclonic airflow covers the British isles with outbreaks of sometimes heavy rain or showers circulating around in the flow.

ECM keeps Low pressure deeper with a squeeze of isobars over Southern Britain bringing a spell of rain and gales on Wednesday followed by squally showers. Thursday sees a weak ridge move through with renewed Low pressure entering the NW with an associated trough bringing rain back NE with strong winds over most parts through the day. Late in the run a broad, mild and strong SW flow with rain in the North could give way to dry and rather warm weather in the South as High pressure builds from Europe. However, unsettled and breezy conditions will be more reluctant to leave the Northwest.

In Summary the weather looks like being in 'mobile' mood in the coming week or so. There will be rain and wind at times for all though amounts of rain in the South will be small at times. There are tentative signs still of the weather becoming less unsettled especially in the South as we move towards the week after next as High pressure to the South builds North and brings dry and potentially rather warm conditions later on.

[damianslaw]

Reliable timeframe - a very typical set up for the time of year with a mobile westerly airstream bringing frontal activity off the atlantic and temporary ridge development. Heaviest rain always reserved for the NW quarter of the country, driest and sunniest conditions reserved for the SE. Very average temperatures everywhere with cool minima under any ridge developments should they occur during the night.

As we move further through the first part of October, there are indications that we might see stronger ridge development from the SW - building over southern parts as heights rise to our SE which would if it evolved set up quite a 'warm' dry pattern for the SE at least, however, if we also see heights building over Greenland at the same time - which does look very plausible any warm set up would likely be shortlived as the trough will be forced forced to sink SE with heights quickly building to the north, setting us up to a possible chilly northeasterly - but this is a long way off and all conjecture at the present.

[Guest pjl20101]

Agree with Gibby and Frosty039 that a NW/SE split looks the most likely evolution ATM. Other different things I have picked up on are the SOI index being positive currently so despite the MEI in a weak el niño state the atmosphere is more akin to a niña or a neutral evolution and the niño development has eased off a tad so I reckon these things may have translated into the atmosphere of why we have been so unsettled recently. Will be doing some detective work on the BOM site as that seems to be very helpful too.

[Gibby]

Good morning. Heres my take on the 00zs from GFS, UKMO and ECM.

All models currrently show a NW airflow with an occluded front clearing SE through the day today. A ridge of High pressure then builds across tomorrow settling things down briefly before a slow slide to less settled conditions commences from Sunday as Low pressure takes hold from the NW on Sunday. Asscociated fronts or front will cross the UK by Monday with a progressively cool, breezy and unsettled spell digging in the early and middle part of next week.

GFS then shows winds backing slowly towards the South as pressure builds strongly over Europe. The weather would warm up over many Southern and Eastern areas with some very respectable early October daytime temperatures should it verify. In the remainder of FI high pressure over europe declines and High pressure from greenland transfers East towards Scandinavia with Low pressure pulling into the UK from the West bringing an unsettled end to the run for the UK.

The GFS Ensembles seem not to like the run of warm operationals shown of late and prefer to keep a more changeable them going for all of Britain with rain at times and temperatures closer to the long term mean although there is some unity in a High pressure moving in somewhat close to Southern areas for a while later next week.

The Jet Stream is shown to blow west to East across the UK in the reliable timeframe this morning.

UKMO for midnight on Thursday shows Low pressure centred between the Faroe Islands and Shetland with a trough in the North Sea. The UK lies in a cool and unstable showery west or NW airflow.

ECM brings High pressure from Europe into play late next week, backing winds off to the south and sending warm air North over the UK. The west may see some rain briefly as a weakening frontal band buffers into the High with the run closing with High pressure settled over the UK and Scandinavia with fine and settled conditions predominating for all with mist and fog problems night and morning.

In Summary the weather looks like being changeable for the next week with rain or showers at times in a mostly Westerly airflow. Rain or showers would be experienced by all in this phase. The trend is then shown by both GFS and ECM for High pressure to build from Europe with a spell of warm Southerlies. Its longevity and the location that High pressure locates itself will determine what conditions are felt at the surface and the GFS operational in particular shows what may happen if the European part of the High breaks down with Low pressure trundling in. If the ECM outcome evolves though quite a few days of pleasnat mid Autumn conditions could develop though mist and fog clearance each morning could be an issue.

[Troubleatmill]

Some good northern blocking showing up on the GFS FI this morning, way to early to know if this is a good sign for later in the Autumn, but has to be better than a ominous polar vortex showing signs of limpet like setting up to our North?

Always good to see the first snows of Lapland as well !

http://alk.tiehallinto.fi/alk/english/kelikamerat/kamera-C1453202.html

[johnholmes]

There is some support on the anomaly charts for the idea of some kind of northern blocking. This is most evident on the ECMWF-GFS models so it will be interesting to see the NOAA output this evening to see if it also moves that way. Its too early to see just how the upper pattern will be in about 10 days time but certainly the first two are changing from the overall broad westerly flow they have shown over the last few days. This settled interlude could start as early as next weekend (the 1st one in October). As to it being a warmish or a coldish one its not possible to call that today. The odds to me slightly favour a warmish rather than cold?

[Frosty.]

The latest ensemble mean guidance is firming up on a more settled and warmer spell further into FI, the ecm in particular is indicating a warm anticyclonic spell fairly early into october. The first signs of this is the mass of high pressure across the azores and further east into spain and pressure looks increasingly likely to be rising further north into the uk towards the end of next week but before then it looks mainly unsettled and windy at times but at least tomorrow is looking like a fine day as a ridge pushes east across the uk, then it's turning unsettled from the northwest through sunday and continuing unsettled for most of next week but then the jet looks like being forced further north as pressure rises to the south and southeast but northwest britain will probably remain generally unsettled with low pressure to the nw. The ens mean is showing a southerly feed of air from southern europe so there would be potential for a very warm spell but with mist/fog overnight but then the gfs ens indicate low pressure resuming control and a trend towards colder westerly winds by mid october.

Edited September 28, 2012 by Frosty039

[chionomaniac]

Classic modeling of a Greenland high that does not deliver due to a Euro high in the FI outputs so far today.

Let's keep that one in autumn!!

[phil nw.]

The next week or so looks reasonably straightforward wrt the modelling of the Atlantic pattern wiith the trough/ridge type conditions giving changeable conditions.The 00z ECM at T120hrs is typical of the outputs.

Looking at the mean hts anomols at 500hPa by day 10 we see signs that Euro heights may come into play.I have pasted the ECM 00z and NAEFs` 00z outputs to illustrate the forecasted pattern at that time.

It seems with a mean trough situated in the Atlantic we could indeed be on the warm side of the setup if this was to verify.At least for a while would bring some quite pleasant weather ,especially further south, with the caveat of possible overnight fog considering the time of year.The far north west of the UK still looks likely to remain changeable with low pressure never far away.

[chionomaniac]

Phil, it looks like a battle between Euro high and Scandi high by day 10. Big differences between runs and between models. FI is most certainly at 5 days.

I am going with Scandi high due to MJO phasing and low early season stratospheric mean zonal wind anomalies.

Which way will August go?

(Probably combined euro Scandi high dragging warm uppers from Africa to Svalbard!)

[phil nw.]

Phil, it looks like a battle between Euro high and Scandi high by day 10. Big differences between runs and between models. FI is most certainly at 5 days.

I am going with Scandi high due to MJO phasing and low early season stratospheric mean zonal wind anomalies.

Which way will August go?

(Probably combined euro Scandi high dragging warm uppers from Africa to Svalbard!)

Do you mean October Ed?lol

Yeah i noticed that the mean zonal`s havent really picked up yet but i am not convinced on MJO Phasing -still rather low amplitude last time i looked.

There`s certainly some capacity for blocking but i think with modelling showing the main PV core currently towards Canada then i think that heights more East of the meridian is likely for now..

Looking at the mean thicknesses from the 00z outputs

you would tend to favour the Euro cell at present although there`s every chance that the main core of heights could move north later if the flow remains less mobile and therefore. becomes more meridonal.Certainly with the continuing more southerly jet a Scandi High is more likely at some point.

[chionomaniac]

I am going with the MJO forecasts, Phil, they do gain amplitude in MJO phase 6 moving to 7, not the current amplitude. If that is correct then there is more chance that any blocking will be further north.

http://www.cpc.ncep....clivar_wh.shtml

Oh yes I do mean October, (my brain still hasn't adjusted to the fact that we haven't had a summer)

Edited September 28, 2012 by chionomaniac

[Frosty.]

The way I read the latest meto update today suggests they are going more with the gfs ens mean rather than the ecm 00z, the gfs also shows a more settled spell for the south and east but it's more transcient looking compared to the more full on ecm mean which is suggesting a more prolonged and widespread anticyclonic spell, the further outlook also appears to be following the gfs ens trend beyond T+300 hours for a dip in temps brought about by a colder westerly flow of polar origins by around mid october onwards so there could be a more amplified pattern from around mid month onwards with wintry showers for upland parts of scotland by then.

Edited September 28, 2012 by Frosty039

[chionomaniac]

I guess we are not privy to a lot of UKmet info, Frosty. I wouldn't want to rely on the GFS ensembles though.

The mean H500 anomalies for days 11-15 are all over the shop!

http://raleighwx.ame...son500mbNH.html

Edit- and the mean is more suggestive of a Scandi high! That is the last chart.

Edited September 28, 2012 by chionomaniac

[Frosty.]

I guess we are not privy to a lot of UKmet info, Frosty. I wouldn't want to rely on the GFS ensembles though.

The mean H500 anomalies for days 11-15 are all over the shop!

http://raleighwx.ame...son500mbNH.html

Edit- and the mean is more suggestive of a Scandi high! That is the last chart.

Yes there is a lot of data we can't access but I just thought it looked more like the gfs from scanning through the charts, the latest update seems to be indicating a more transcient fine spell restricted to the south and east before low pressure crashes in again from the northwest, the ecm ens mean looks a lot more settled in the medium term for a wider area but all we really know is the next 6-7 days are going to be generally unsettled with just a few ridges breaking up the unsettled pattern and then pressure rising from the southwest by the end of next week.

Edited September 28, 2012 by Frosty039

[gottolovethisweather]

The next week or so looks reasonably straightforward wrt the modelling of the Atlantic pattern wiith the trough/ridge type conditions giving changeable conditions.The 00z ECM at T120hrs is typical of the outputs.

Looking at the mean hts anomols at 500hPa by day 10 we see signs that Euro heights may come into play.I have pasted the ECM 00z and NAEFs` 00z outputs to illustrate the forecasted pattern at that time.

It seems with a mean trough situated in the Atlantic we could indeed be on the warm side of the setup if this was to verify.At least for a while would bring some quite pleasant weather ,especially further south, with the caveat of possible overnight fog considering the time of year.The far north west of the UK still looks likely to remain changeable with low pressure never far away.

Hi,

Just a quick question, can somebody please indicate to me wher the UK might be situated on the 2nd image, i.e. the ECM chart.

[chionomaniac]

Hi,

Just a quick question, can somebody please indicate to me wher the UK might be situated on the 2nd image, i.e. the ECM chart.

It's just north of France, gltw!

[gottolovethisweather]

I am going with the MJO forecasts, Phil, they do gain amplitude in MJO phase 6 moving to 7, not the current amplitude. If that is correct then there is more chance that any blocking will be further north.

http://www.cpc.ncep....clivar_wh.shtml

Oh yes I do mean October, (my brain still hasn't adjusted to the fact that we haven't had a summer)

That is a very useful link there Chio, I would love to see that used in conjunction with the Stratosphere thread, as soon as it gets off the ground. As to my understanding of these things at this stage, I would use a British Rail analogy. There are a lot of leaves on my line, which I will need to clear before I can make progress.

[phil nw.]

Hi,

Just a quick question, can somebody please indicate to me wher the UK might be situated on the 2nd image, i.e. the ECM chart.

Middle right just to the left of the lower of the blue H`s GLTW-hope that helps-as you can see the Americans like their neck of the woods easier to read.

[gottolovethisweather]

Middle right just to the left of the lower of the blue H`s GLTW-hope that helps-as you can see the Americans like their neck of the woods easier to read.

Cheers Phil,

My interpretation, when using only that particular chart puts me in Southern England, near HP cells to my south and southeast, a LP out in mid-Atlantic and a LP due northwest of the UK.

Can you confirm if my interpretation is correct, as maybe when I can read the charts, I might be able to then make further progress?

[phil nw.]

Cheers Phil,

My interpretation, when using only that particular chart puts me in Southern England, near HP cells to my south and southeast, a LP out in mid-Atlantic and a LP due northwest of the UK.

Can you confirm if my interpretation is correct, as maybe when I can read the charts, I might be able to then make further progress?

Yup you `ve got it mate.Blues(lows) and Yellows(high`s).

[johnholmes]

That is a very useful link there Chio, I would love to see that used in conjunction with the Stratosphere thread, as soon as it gets off the ground. As to my understanding of these things at this stage, I would use a British Rail analogy. There are a lot of leaves on my line, which I will need to clear before I can make progress.

i think you will find that those who attempt to do predictions of the time scale involved do use MJO (when its any use, ie not very close to the origin) along with Stratospheric chart predictions to come up with an idea of what the upper flow may be, along with attempting some kind of verification closer in using the 500mb anomaly charts.

Well that is my way anyway!