Model Output Discussion 26/08/2012

[Gibby]

Good morning. Here's the morning view of the 00zs.

All models show a generally changeable pattern over the UK over the next few days with troughs moving East over Britain replacing the filling Low pressure over the South of the UK today. Saturday though shows a temporary ridge moving through giving a short if decent spell for all.

GFS then takes us through an unsettled spell during the first few days of next week with breezy and unsettled weather for all with Low pressure close to the North of Scotland. Later in the week sees pressure build with FI dominated by High pressure over the UK with fine and settled conditions developing for all with sunny spells by day and areas of mist and fog together with patchy ground frost by night.

The GFS Ensembles continue to trend just below the long term mean after a milder blip at the turn of the month. The operational was again a ilder option later in the run and rainfall is present from some members throughout the run even in the Southeast.

The Jet Stream forecast shows the flowstill troughing South of the UK though in time it takes up a more direct west to east flow across Britain next week.

UKMO for midnight on Tuesday shows Low pressure to the North of Scotland with a broad WSW flow over Britain. troughs from this setup would be entrained across the UK with rain or showers at times heaviest in the North.

ECM as last night keeps things very unsettled next week driving a deep Low pressure centre across Scotland by midweek with rain and gales for many before lots of squally showers follow to all areas to end the week before a weak ridge looks likely to give a drier day on Day 10. It would feel very cool in the wind.

In Summary the weather looks like staying very unsettled and changeable over the next week or so. Low pressure to the North of Britain looks like controlling things pulling troughs East from off the Atlantic across Britain. The operational from GFS does show a totally different evolution as a large Autumnal high takes over though as yet this hasn't got much cross model support.

[phil nw.]

Thanks again Gibby for your summary.

There`s seem low confidence in the modelling beyond the next few days according to last nights discussions on the NOAA site.

http://www.cpc.ncep....day/fxus06.html

Looking at the 00z run it` is only the GFS Op. run that shows a building high across the UK by day 10.

ECM and GEM and the mean outputs all favour a flatter looking Westerly type with just occasional weak ridging.

It would be a pleasant change from the deluge of the last 2-3 days if the GFS 00z were to be correct but at the moment it has to be considered the outside bet when viewed against the rest of the outputs.However there is this uncertainty so as ever we need to wait to see how the pattern develops.

Edited September 26, 2012 by phil n.warks.

[BLAST FROM THE PAST]

Posted by BLAST FROM THE PAST on 06 September 2012 - 20:32 in Forecasting Model Discussion

I think the models will pick up on an interesting latter 2/3rds to half of Sept. I think the jetstream will become very meridional and we'll see some very southerly tracking LPs. Cool and active for me. ECM and GFS are hinting as such, let's see if FI firms up and materialises as such. I cannot see this 'northern' jet holiday hanging on too long.

BFTP

I think some models did quite well with this storm. Above was some musing of mine and models were certainly picking up on it around 13th, dropped it but quickly came back in. I was amazed at SE news BBC forecast 2 days before the LP came up from Biscay that they forecast it to go out into North Sea and away from us. I went straight to the models and UKMO showed that but GFS and ECM swirled it round like it has done. very poor forecast it was.

So for me GFS and ECM did well overall on this occasion

BFTP

[AWD]

Unsettled GFS all the way through tonight. The flow always from the west or north of west.

Rain will affect all parts of the country, although heaviest in the north, with the longest drier spells to the south.

Typical autumnal pattern sums that run up!

Edited September 26, 2012 by AWD

[chionomaniac]

Posted by BLAST FROM THE PAST on 06 September 2012 - 20:32 in Forecasting Model Discussion

I think the models will pick up on an interesting latter 2/3rds to half of Sept. I think the jetstream will become very meridional and we'll see some very southerly tracking LPs. Cool and active for me. ECM and GFS are hinting as such, let's see if FI firms up and materialises as such. I cannot see this 'northern' jet holiday hanging on too long.

BFTP

Wasn't the daughter of Nadine about as northerly tracking as one can get, Fred? Up from the Bay of Biscay to the north of the England before stalling?

Edited September 26, 2012 by chionomaniac

[BLAST FROM THE PAST]

Wasn't the daughter of Nadine about as northerly tracking as one can get, Fred? Up from the Bay of Biscay to the north of the England before stalling?

It didn't come from our west or NW or deflect to our NW.......no the jet was very ampilfied and way south of normal in places. So you saying we had a strong northern arm C? Come on, shouldn't you also highlight very meridional?

BFTP

Edited September 26, 2012 by BLAST FROM THE PAST

[SMU]

http://modeles.meteociel.fr/modeles/gfs/runs/2012092612/gfsnh-0-156.png?12

Evening ALL- take NOTE people- The zonal train isnt coming...

Its about this time of year the models especially the GFS starts going into a faster jet mode with im sure the model tendancy to be historical norm of the mean jet at X speed over certain locations-

With this in mind if you look back on VERY zonal years you will find the models over do the height & amplitude of the blocking wavelength, & also low pressures tend to end up further North & east into Europe-

THe same is vice versa in anomaly years where the jet is slow-

Blocking appears in the mid term over greenland or Scandi & everything is shunted west- sometimes LARGE SCALE west if the jet is very slow.

What you see tonight in the above link by the GFS is the first sign that the expected zonal flow of the jet isnt going to be as strong as initially progged, with higher than normal residual pressure over greenland-

Does thing ring any bells-? SHould we surprised. NO

because its been the pattern ALL summer & for large portions of the last couple of years-

I expect the models to hone that time frame even more to display heigher than normal heights over southern greenland ( NOT a full block just yet )) but the net effect will be a split flow with shortwaves & low pressure systems diving South East as opposed to Straight East-

If we engage enough cold air in October there could be some early lowland snow for Scotland & the extreme North....

S

[BLAST FROM THE PAST]

http://modeles.meteo...nh-0-156.png?12

Evening ALL- take NOTE people- The zonal train isnt coming...

Its about this time of year the models especially the GFS starts going into a faster jet mode with im sure the model tendancy to be historical norm of the mean jet at X speed over certain locations-

With this in mind if you look back on VERY zonal years you will find the models over do the height & amplitude of the blocking wavelength, & also low pressures tend to end up further North & east into Europe-

THe same is vice versa in anomaly years where the jet is slow-

Blocking appears in the mid term over greenland or Scandi & everything is shunted west- sometimes LARGE SCALE west if the jet is very slow.

What you see tonight in the above link by the GFS is the first sign that the expected zonal flow of the jet isnt going to be as strong as initially progged, with higher than normal residual pressure over greenland-

Does thing ring any bells-? SHould we surprised. NO

because its been the pattern ALL summer & for large portions of the last couple of years-

I expect the models to hone that time frame even more to display heigher than normal heights over southern greenland ( NOT a full block just yet )) but the net effect will be a split flow with shortwaves & low pressure systems diving South East as opposed to Straight East-

If we engage enough cold air in October there could be some early lowland snow for Scotland & the extreme North....

S

Absolutely, Steve. I see no reason why that theme should 'disappear'

BFTP

[chionomaniac]

It didn't come from our west or NW or deflect to our NW.......no the jet was very ampilfied and way south of normal in places. So you saying we had a strong northern arm C? Come on

BFTP

Agree with that BFTP.

Encouraging signs from the MJO forecasts. I would say a large amplitude phase 7 is not a bad starting point and a lot of forecasts are heading that way.

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

Complete disruption af the jet as Steve highlights above.

MJO October phase 7 forecast:

Unfortunately I think that this has no correlation to the coming winter.

[TonyH]

But does the fact that a particular pattern has been dominant over several years mean it will continue for another 6 months?

Edited September 26, 2012 by TonyH

[chionomaniac]

But does the fact that a particular pattern has been dominant over several years mean it will continue for another 6 months?

No, I don't think it does Tony.

Look at the years at the bottom of the MJO analogue - we have EL Nino, La Nina and neutral ENSO years..........However, when you add the other signals for this winter it is not a bad trend to have...

[BLAST FROM THE PAST]

But does the fact that a particular pattern has been dominant over several years mean it will continue for another 6 months?

No Tony, but it does show the persistency and that reminds me of the opposite we had during previous 25 years when we had the persistency of a roaring jet. There were brief disruptions back then too.....so encouraging conditions remain IMO

BFTP

[TonyH]

Ok thanks Guys, we have been stuck in a rut it seems since 2007 with our weather patterns.

[Methuselah]

And - we seem to have gone somewhat off-topic...

[snowfluff]

And - we seem to have gone somewhat off-topic...

True pete, tis interesting reading though,and keeps the thread ticking over.Of late this thread has had 8 hour gaps between posts......

[Gibby]

Good evening. Here is the evening look at the 12zs from GFS, UKMO and ECM.

The pattern is agreed upon between the models between now and Sunday. The remains of this weeks monsoon depression will move away into Europe over the next 12 hours. A NW flow with a cold front embedded then moves down over the UK on Friday with a showery Westerly flow over the North on Saturday while a ridge of High pressure crosses the South. The following 48 hours see winds back to the WSW and freshen as new Low pressure moves East towards the North of Scotland spreading a trough East across all areas with rain for all, heaviest in the North.

GFS then moves towards the middle of next week with Low pressure situating close to Northern Scotland and a fresh to strong Westerly flow over the British Isles with showers and some longer periods of rain too. Later in the week a slider Low moves ESE across the South of Britain bringing a spell of quite heavy rain before clearing SE by Friday and leaving a cool, blustery and showery NW flow over Britain to start the weekend. FI is then shown to have Low pressure to the North and High to the SE with a West or Southwest flow continuing to bring alternating spells of cloudy breezy weather with some rain and brighter, drier but cooler spells.

The GFS Ensembles tonight continue to programme a return of near or just below average uppers along with changeable weather with occasional rain. However, rainfall amounts in general will be far less than recently experienced.

The Jet Stream currently troughed over the UK gradually weakens over the coming days before a new arm directs the flow on an eastward path across the Atlantic and the British isles as we move into next week.

UKMO for noon on Tuesday shows Low pressure just to the NW of Scotland and a fresh to strong WSW flow over Britain. Subject to any troughs straddling the South of the UK when and if persistent rain would occur the most likely scenario is for a sunshine and shower mix the majority of which would fall in the West and North.

ECM is not good news for those looking for dry weather. It shows a WSW flow over the UK next Tuesday with rain and showers almost anywhere. As we move through midweek and beyond Low pressure slides East over Central regions with heavy rain at frequent intervals here and severe gales over Southern England. Further North winds are much lighter but the air would be cool and unstable with the chance of showers, becoming wintry over Mountains and some frost at night should skies clear. The run ends with improvements from the South as the strong West winds push North along with the rain leaving Southern regions in breezy, rather cloudy but dry and milder conditions.

In Summary the models show that the weather remains changeable over the next few weeks. There is almost something for everybody tonight shown in the charts with a real cocktail of Autumn weather on offer over a period when almost anything could happen. The main common theme though is that the pattern of Low pressure to the North and High to the South offers spells of rain or showers and some drier and brighter spells too chiefly in the South.

[William of Walworth]

Interesting discussions and recent signals/models. Looks like transient, weakish HP influence is all there is to look forward to this Autumn for most ....

At least, short term, this coming Saturday** is looking reasonably pleasant for many.

**Our positively, definitely very last outdoor/tent-based w/e outing of this year! Forest of Dean based ... damp Friday to wet Monday with a (probably) nice Sat inbetween ...

After this,, I'm likely to be retiring from this thread most of the time, I'm not a Winter model watcher overall.

I'll storm back in May and as we lead up to late June 2013! (Work that out! ). And thereafter.

Meanwhule, thanks a lot for all the fascinating guidance and analysis on various models since May this year. I[pve particularly appreciated the perceptiveness and objectivity of John's, GP's, Frosty's, Gibby's. phil n warks's, TWS's and several others' contributions.

Ta folks! Will still look in occasionally over coming months.

Edited September 26, 2012 by William of Walworth

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2012092612/ECH1-168.GIF?26-0

Plenty of developing trough disruption on the ECM tonight ( Not seen yet in the last 3 or 4 runs)

It all looks a tad far west-

However day 6 or 7 is the day to be looking towards if your hoping for an early bout of cold..

S

[phil nw.]

An interesting analysis Steve.

Looking at the GFS/ECM around T144-168 i can`t see anything to suggest any change from the 00z forecasts as we go into week 2 .

At the moment it`s fair to say the vortex is starting to form and the outputs suggest spin off lows breaking off the main core around the Canadian Maritmes.This would allow some ridging in the gaps but really nothing more than temporary heights at this stage?

The jetstream does look strong enough at the moment to give us a typical Atlantic spell of mobile Westerlies.

12Z GFS mean

Chio,the MJO is forecast to increase slightly in amplitude as we go into October with the prospect of some Eastward progress but not that much for me to be confident of it`s effect on medium term modelling.

http://www.cpc.ncep....O/foregfs.shtml

GFS op.has been all over the place for week 2 and has now dropped the idea of an Anticyclone over the UK by day10 which underlines the uncertainty expressed earlier today.

[Glacier Point]

CPC tonight are basically saying we don't have a clue beyond day 6 scoring confidence at 1 out of 5, so not a day to be placing a lot of faith in ensemble mean products, let alone operationals beyond day 5.

As noted, the MJO is getting organised as strengthening westerlies over the Indian Ocean and far west Pacific converge with low level easterlies around the Dateline. Models (especially GFS) will be exposed to this in the longer timeframe.

However, the GWO is lagging behind with total and relative angular momentum much lower - centred around phase 2.

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

Frictional torques have turned positive, so a global response increase in angular momentum is likely within the next 5-10 days. That takes us towards phases 3 and 4.

From my point of view, phases 2-3-4 look the call for early October..

Either way, upper level zonal winds are still very light for the time of year across the polar field, and as we get deeper into the autumn, expect some very amplified patterns to develop.

[Cloud 10]

Thanks for that GP,looks like a wet october and becoming colder after mid-month

if those composites came off.

[Gibby]

Good morning folks. Here's a look at the 00zs from today Thursday September the 28th 2012.

All models show a NW flow blowing over the UK in the wake of the past few days troublesome Low. Apart from scattered showers the weather would be bright and breezy. a trough slides SE in the flow tonight followed by an advancing ridge of High pressure over southern Britain in the first half of the weekend. Later in the weekend Low pressure closes in to the NW with a freshening Westerly wind driving troughs across Britain and clearing SE on Monday. Areas of rain in association with these troughs cross the UK hanging on in the far South for much of Monday.

GFS then follows on for much of next week with West or SW winds and rain at times as the basic synoptic pattern remains unchanged. The SE will see the driest conditions between just light rain or showers and temperatures here could recover from recent values somewhat. In FI a North/South split seems the most likely trend with rain and wind at times in the North, in the proximity of Atlantic Lows to the North while the South sees longer dry spells and just occasional bursts of rain close to High pressure to the south or SE. Temperatures would likely become somewhat above normal at times in the South and Southeast.

The GFS Ensembles do not like the look of the operational in it's second half of the run showing it as a major outlier with the preferred likelihood of uppers near the long term mean in rather changeable conditions at the surface the moxt likely outcome.

The Jet Stream is realigning steadily to a West to East flow across the UK in a few days time now that the deep trough in the flow around the UK is weakening.

UKMO for midnight on Wednesday shows Low pressure to the North of the UK with a fresh to strong Westerly flow over the UK. The most likely weather from this would be showers and longer spells of rain for all, heaviest in the West and North.

ECM shows a very mobile pattern in its latter stages with Atlantic Low pressure passing East close to Northern Scotland driving troughs and attendant rain bands East across all areas with sunshine and showers in between.

In Summary the models seem to be firming up on a typical Atlantic based mobile weather pattern for the next few weeks. As is always the case in these situations at any time of year the heaviest and most widespread falls of rain will be in the North and west but indications are that the Lows are close enough in to the North of the UK to affect the south too with trailing fronts delivering rain or intervals of showery weather too with the best of any dry spells most likely in the SE. It looks like temperatures will hold close to normal generally.

[chionomaniac]

The ECM synoptically this morning looks like a winter lovers dream, with Greenland blocking prevalent from T+168, as we move into October.

The cold pooling further north is not sufficient to allow too much cold air to flood south.

The GFS plays with a similar theme before defaulting to the zonal train.

[Glacier Point]

Continued bouncing around in the ensemble means....but fwiw, today's 00z GFS ensemble mean looks reasonable based on last night's analysis, with particular reference to phase 4 type pattern....

I would place that anomalous ridge a touch further north so perhaps a suggestion of an easterly draw there in the extended range. In the medium term, probability that the models are underdoing the persistence of any ridging in the North Atlantic (or towards Greenland).

Edited September 27, 2012 by Glacier Point

[chionomaniac]

Continued bouncing around in the ensemble means....but fwiw, today's 00z GFS ensemble mean looks reasonable based on last night's analysis, with particular reference to phase 4 type pattern....

I would place that anomalous ridge a touch further north so perhaps a suggestion of an easterly draw there in the extended range. In the medium term, probability that the models are underdoing the persistence of any ridging in the North Atlantic (or towards Greenland).

That is certainly a very atypical October anomaly chart, GP, with an apparent lack of westerlies.