Model Output Discussion 26/08/2012

[AWD]

The remains of ex tropical storm Nadine gets wrapped up in the Jet to form a storm of our own by Noon Monday according to UKMO tonight.

http://www.wetterzen...s/Rukm1441.html

Yes, both the GFS & UKMO go for quite a widespread Autumnal depression crossing the whole of the UK Sunday & Monday.

[AWD]

The GFS 12z then keeps the unsettled theme for most of next week, with the trough sat west of the UK, it wont be all that cool aloft, although under the cloud/rain, it will still feel pretty chilly as it does this time of year. In FI, HP starts to play more of a role over our shores, bringing rather quieter weather, although some rain in the north is still possible.

[Zenarcher]

Indeed Sean, and with the low coming from a very warm and moist source then there could be some very high rainfall rates.

The GFS and UKMO disagree on the timing of this low but both models seem to indicate it could head our way by Sunday so as you say, something to keep an eye on.

The outlook for the UK has been a little complex with that flabby low for Thursday causing the models a few problems but the general trend does seem to be a cool outlook with the bright convective showery activity being replaced by more dull and cloudy weather and perhaps something more drier for Saturday as a weak high pressure takes control.

Yes the models have been struggling recently with hurricanes and ex hurricanes etc.

A little update on the latest runs the NOGAPS 12z supports a low pressure system pass over the UK but the GEM 12z does not.

Looking at the ensemble members of the GFS about 10% show a deep low, 33% show nothing at all and 57% of them went for something similar to what the current GFS run says.

[Zenarcher]

ECM this evening starts to disagree with the UKMO and GFS at 96 hours,

Here's a comparison at 120 hours between them,

[ANYWEATHER]

ECM this evening starts to disagree with the UKMO and GFS at 96 hours,

Here's a comparison at 120 hours between them,

Yep. but the ecm 00z run did agree with the latest output!! I think the 12z ecm is on a bevvy!!

[UV-RAY]

ECM this evening starts to disagree with the UKMO and GFS at 96 hours,

Here's a comparison at 120 hours between them,

An halfway house between the UKMO and GFS seems the most likely IMO.

[Gibby]

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

All models show a cool and showery NW airflow weakening and backing Westerly in the next 24 hours. On Thursday a Low pressure slides into Central areas of the UK from the West before a weakening cold front moves SE over the South early Friday. High pressure then builds across Britain to start the weekend with a dry and bright day for most areas on Saturday. At that point is where the similarities between the output ends.

GFS shows a Low pressure area moving up from the SW later on Saturday with some warm tropical air in it's circulation pumping up a deep Low pressure over the SW Sunday to become a complex and deep Low pressure area over Scotland by early next week. Rain and gales would likely affect all areas through this phase. As we move through next week further active Low pressure spins North into the general Low pressure pond over Britain maintaining the wet and windy spell. Later in FI low pressure very slowly loses it's grip as it fills and a weak ridge of High pressure attempts to settle things down somewhat for a while.

The GFS Ensembles show the current cool uppers rise to normal levels in a few days time to levels close to the long term mean for the rest of the run. It looks like a very wet week next week under Low pressure North and South before amounts of rain fall off towards the end of the run as pressure recovers somewhat.

The Jet Stream currently blowing across the UK shows much troughing over the Eastern Atlantic and near the UK as we move into next week. As a result the pattern becomes diffuse with several pockets separating on moving out from the States. As a result of this several active low pressure areas are spawned in the troughing area close to the UK.

UKMO for noon on Monday has a deep Low pressure area near Scotland with a strong West or Southwest airflow over all areas. Periods of heavy rain or showers will affect all areas in strong and cool winds.

ECM shows Sunday as a much more tranquil day than it's rivals with a dry day in the East while the West and Southwest gradually becomes more cloudy with some rain. By Monday rain has moved East over all areas followed by further wet and windy spells through next week as Low pressure gains control centred over or near the UK.

In Summary ECM stands in isolation tonight at a very early timescale too with differences at 120hrs immense. The American and UK model show that the input of tropical air spawned from ex tropical storm Nadine near the Azores will inject energy into a developing frontal feature to the SW at the weekend. This then moves North to become entrained in the general circulation of further Low pressure coming SE from Iceland making a UK complex of Low pressure next week with plenty of rain, showers and wind for all. ECM does eventually catch up but without the aforementioned injection of tropical air fuelling the SW approaches Low it would mean the dry weather in the East hangs on for another day at least before a wet and windy spell evolves thereafter.

[IDO]

I think one thing is almost certain come Monday 24th, that there will be a low somewhere near the UK. That is nearly cross model agreement. However where, timing, strength of, and whether it is part of several lows, not even the runs within the models are consistent. For example ECMW from the last four days 00z runs show four wildly varied scenarios and of course there is another 120 hours+ till t00. So respect to any guesses in the interim. Today's ECM 12z also has a different origin from the GFS, the latter has a low spawned from Nadine (from the south west) whilst the low from the ECM comes from the NW (slower evolution as well)! Prefer the GFS solution for my area (south), warmer temps than the following HP!

So maybe the only certainty is that the models are struggling.

What is consistent is the HP build from late September. GFS Op run has this forecast for three days in a row (GEFS HP more southern centric)) and there is an inkling for ECM at T240. Temps not so high in GFS 12z in that HP (London) but the Op run is on the cool side of the majority of the members (from late September), so maybe one last chance of mild/relatively warm weather before the season takes over.

Edited September 18, 2012 by i'm dreaming of...

[TonyH]

What I am finding most fascinating about the models is just how long ex Nadine sticks close to the Azores for- still there at the end of next week!

Tomorrow

Next Friday

Edited September 18, 2012 by TonyH

[Glacier Point]

and that will have some impact on sea surface temperatures in that region Tony due to mixing of the layers.

[Gibby]

Tonight's faxes go with their own model output.

http://www.meteociel.fr/modeles/ukmo2.php?ech=96&carte=2000

http://www.meteociel.fr/modeles/ukmo2.php?ech=120&carte=2000

[Gibby]

Good morning. Here's my attempt to unravel the 00z output of GFS, UKMO and ECM this morning.

All models show a weakening Westerly flow over the UK with a sunshine and shower mix to the weather these mostly in the North today. A small disturbance moves in off the Atlantic tomorrow actoss Central Britain sinking slowly South on Friday as Higher pressure takes control over the North. All areas share this drier weather over Saturday and much of Sunday before the high pressure cell responsible gets nudged to the East of Britain with an increase of cloud and potential rainfall to Western regions later in the day on Sunday.

GFS then takes us through next week with Low pressure generally dominating though the operational shows a cool ridge extending into the UK from a mid Atlantic High though this is not supported by a lot of members of the ensembles. In FI some drier weather is to be found before a return to Atlantic wind and rain returns late on.

The GFS Ensembles show an unsettled spell to come mostly from the 22nd with rain at times for all with uppers near to or a fraction below the long term mean. The operational was a warm outlier for southern regions in the second half of the run.

The Jet Stream shows the flow diving South to the West of Britain and returning NE towards the English Channel in a few days time. Later in the run the flow remains in a troughing mode close to the UK as the UK low takes hold.

UKMO for midnight on Tuesday shows Low pressure engulfing the UK with a centre just east of Scotland. All areas would see rain or showers at times in cool conditions with winds cyclonic and light or from the West or NW.

ECM shows Low pressure North of Scotland with a trough moving East through the day on Tuesday with rain for all. Thereafter, the weather remains unsettled and wet at times as Low pressure moves slowly South over the UK while filling slowly but maintaining wind and rain at times through to the end of next week in rather cool conditions.

In Summary this morning it looks like the idea of a deep Low moving up from the SW has been dropped to a large degree, at least from the operationals. So the pattern as before has been reintroduced of low pressure moving down from the NW to centre over the UK next week and probably beyond. This means a spell of disturbed weather with rain and showers in brisk rain at times with rather cool conditions especially under the rain. It does mean that one more day of dry weather is possible on Sunday away from the far NW as per GFS and ECM and far South via UKMO before the change arrives more generally arrives.

[Thundery wintry showers]

There is a significant difference between the UKMO and the GFS/ECMWF for this Sunday at 00Z with low pressure close by to the south:

http://cdn.nwstatic..../96/h500slp.png

http://cdn.nwstatic..../ecm500.096.png

http://cdn.nwstatic....9/00/met.96.png

This is worth watching as the UKMO then blows this up into a vicious depression over SE England on Monday which would bring wet and windy weather into the SE much earlier than the GFS and ECMWF show.

The surface weather that we get from next week's low is uncertain. The GFS shows a straightforward sunshine-and-showers setup, and with it being late in the season, inland areas may not see many showers, but the UKMO and ECMWF both strongly hint at secondary low development which would promote active rain belts especially for the west and south of the country. My gut feeling is that the UKMO/ECMWF will probably be nearer the mark with this.

Although the general outlook for the next few days 'looks' quiet we have a slow-moving frontal system which will affect Scotland and northern England tomorow and will then spread into southern areas on Friday.

[legritter]

I've just deleted a whole post, so bottom line looking at todays output fun ahead after Sunday. Will the last week of September be a total opposite of last year? Nothing would surprise me this Autumn and Winter Thanks to regular more technical posters who keep us all informed.

cheers

[nick sussex]

Quite unusual to see such a big disagreement between the ECM and GFS/UKMO at 96hrs.

Both the operational and control run of the ECM are having none of the low pressure moving ne, looking at the ECM ensemble maps very little support also.

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!96!pop!od!enfo!enplot!2012091900!!/

Of course given the higher resolution of the operational runs ensembles can sometimes lose the plot with this type of low pressure development. The UKMO fax charts at 84hrs develop that low to the sw and it will really be something if those charts are completely wrong at that timeframe.

I'm sure all will be revealed this evening when we should get agreement at least on events within 120hrs.

[Bogman]

The Meto's take on it.

Chief Forecaster’s View

A chief forecaster's view has been issued for all regions for Sunday. The forecast for Sunday is very uncertain, but the balance of evidence favours relatively fine and dry weather across England and Wales, and also relatively small amounts of rain across much of Scotland and Northern Ireland.

Edited September 19, 2012 by Bogman

[NorthNorfolkWeather]

The differences between GFS/ECM and the Met office are pretty stark at T120. It seems the ECM keeps a deep low well south, leaving a higher pressure gradient over the UK, The MO evolution looks unusual to me (but there again, I'm no expert), if it verifies, we'll be wet next week, and there's the potential for some quite strong NE gales

[AWD]

Interestingly the GFS 12z now has the depression coming up from the SW. Not as vigorous as the UKMO, but it is a step towards the model on this run.

Instead the GFS brings a rather deep low pressure system down from the north west by early nex week, bringing widespread unsettled conditions to all as it sits to the west of the UK for most of the working week next week.

With cool temps remaining.

JMA however, makes nothing of it.

Whilst it also show a shallower trough compared to the GFS next week, but more directly over the UK, with rainfall and cool temps for everyone.

[phil nw.]

The Meto's take on it.

Chief Forecaster’s View

A chief forecaster's view has been issued for all regions for Sunday. The forecast for Sunday is very uncertain, but the balance of evidence favours relatively fine and dry weather across England and Wales, and also relatively small amounts of rain across much of Scotland and Northern Ireland.

The 12z GFS shows rain moving in for much of the UK through Sunday under the influence of a developing low to the the South West.

Another low will be drifting down from the Iceland area at the same time and both centres merge creating one area of low pressure across the UK early next week.

At this stage still uncertainty whether this will pan out exactly as shown on this run but looking at the steep thermal gradient around our latitude in the next few days then some cyclonic development around the south of the UK looks quite likely.

That warm plume coming north over France meeting the cool Polar maritime air acxross the north of the UK.

12z UKMO shows a shallower feature approaching later on Sunday so the later timing of it`s arrival would mean many places would remain dry for much of the weekend period.However the following few days show the same low pressure area situated across the UK promising similar unsettled conditions.

Edited September 19, 2012 by phil n.warks.

[Zenarcher]

Comparison between GFS and UKMO at 96 hours,

Another comparison at 120 hours,

GFS 12z shows the low passing by on Sunday and into Monday,

Sunday Afternoon strong winds pass over England around 30 to 40mph,

Plenty of rain moves in as well,

By Sunday evening the strong winds move North to Northern England and Eastern Scotland again being around 30 to 40mph,

The heavy rain moves North and seems very heavy for Eastern Scotland,

During Monday morning the winds increase across the far North of Scotland being around 50mph,

Heavy rain is still travelling North by then as well,

Overall we still have disagreement between the models but one thing is for sure there is some unsettled weather on the way for Sunday and Monday.

[AWD]

The GFS keeps the trough to our west/south west throughout the whole of next week, its not until we get to the depths of FI does the trough finally lift out on this run.

However, with the flow from south of west, the air temps shouldn't be too cool, although obviously under cloud/rain it won't feel too special either. With the trough close to the UK however, I can't see there being too many frosts away from sheltered areas for next week.

This also reflected in the Ensembles, with air temps around average for the time of year, and unsettled/wet conditions on the horizon and sticking around thereafter.

The GEM doesn't make too much of the LP coming up from the SW, instead decaying over Biscay. It also keeps the LP coming down from the NW on a more northerly track, staying to the north of Scotland.

Whilst it would still be unsettled across all of the country, this run keeps the heaviest ran to the north. This does however, allow some cool air to drift down over the UK.

The NoGaps run also makes nothing of the LP coming up from the SW, but it does bring the LP coming down from the NW on a more southerly track compared to the GEM, so widespread rain would be evident on this run.

This run shows the LP drift east and the UK under a slack showery flow in FI

The UKMO is the other model that shows the LP coming up from the SW, along with the GFS. However, it does bring it in roughly 24 hours later than the GFS, with a very unsettled start to the working week next week for all.

The UKMO forecasting a rather cold night Friday night with a frost for those up north possible. A cool day on Saturday also follows.

The GFS similiar to the UKMO with the LP to the SW coming up, albeit roughly 24 hours earlier.

The GME model looks to be following the GFS with the LP coming up from the SW on its T72 hour chart.

All in all I think there is a slight move towards a depression coming up from the SW Sunday into Monday. Timing at this stage is still uncertain, but with the GFS & UKMO both showing this scenario, it now looks a good possibility for it to happen. However, other models do not show this , the ECM Op and ECM Ensembles at 0z did not show this at all, so it will be interesting to see the ECM 12z run tonight and see which way it goes tonight.

All models agree on an unsettled week next week though, with a trough close to the west of the UK influencing the weather across the whole of the UK. Temps look to be about average, although I expect feeling a little cooler in the wind & the rain.

[Zenarcher]

The ECM's 12z run this evening moves over to agree with the GFS and UKMO on the unsettled spell of weather ahead.

The ECM seems to be more similar to the UKMO though,

120 hours,

ECM

UKMO

GFS

[AWD]

ECM also goes with the LP coming up from the SW. That is the GFS, UKMO & ECM all forecasting what would be the first notable depression of the Autumn season for England & Wales. Timing differences do vary, but the end result is the same, with wind and rain for all.

Wow, Ireland looks to be heading for some severe weather.

[Cloud 10]

This low is looking a bit nasty now and would likely give some large

rainfall totals with it sucking in some warm air from the continent.

[Summer Sun]

ECM also goes with the LP coming up from the SW. That is the GFS, UKMO & ECM all forecasting what would be the first notable depression of the Autumn season for England & Wales. Timing differences do vary, but the end result is the same, with wind and rain for all.

Wow, Ireland looks to be heading for some severe weather.

All models go for an unsettled Tuesday the question is which will be right

GFS

UKMO

Edited September 19, 2012 by Summer Sun