Model Output Discussion 26/08/2012

[snow drift]

One thing that is noticeable looking at the model runs, is how little the low moves in any direction. It sits over most of the UK for a period up to 120hrs on most runs. By then I think most will have seen plenty of rain and strong winds and will be please to see it exit East.

[Gibby]

Good morning. Here's my take on the 00zs from this morning Sunday September 23rd 2012.

All models show deep Low pressure centred over the UK over the coming 3-4 days with copious rain events and showers for all in often cool and windy conditions.

GFS then shows continue to be lurking close to the South of Britain to end the week with rain or showers in a cool North breeze. Further North a slack ridge keeps things drier and brighter here and this weather gradually extends South and East to all areas by the start of the new week as high pressure develops over Britain. Towards the end of FI shows high pressure moving away slowly East and allowing a cool SE flow to set up as Low pressure slides SE under a cool high centred to the NW of Britain.

The GFS Ensembles show an unsettled week to come with rain for all. With time uppers rise slowly to a degree or so above normal on average with less in the way of rain particularly for southern locations.

The Jet Stream is currently in a deep trough to the SW of Britain driving NE to the south of the Uk over the next 72 hours or so. In time the flow weakens and tries to rejuvenate on more Northerly latitudes in a week or so.

UKMO for midnight next Saturday shows a Low pressure area over Eastern France and a weak ridge over Britain. A lot of dry and rather cool weather would be expected though a few showers could still occur towards the SE.

ECM prefers to bring another cool trough down from the NW over the weekend more influential to the North. Thereafter, things dry up and warm up considerably in the South early next week as High pressure migrates slowly East into Europe from a position South of the British isles. By midweek a warm SE flow blows over England giving some very pleasant daytime conditions for England and Wales.

In Summary it looks like we are heading for a wet and windy spell of weather this week, gradually easing as we approach the weekend. It looks like from then onwards High pressure to the south of the UK is going to play a part in settling things down somewhat as we go through the following week and in the case of ECM bring some pleasant and warm early Autumn conditions.

[Summer Sun]

A look at the big 3 models and an ensemble viewer this morning

GFS

ECM

UKMO

ensemble

Tuesday

GFS

ECM

UKMO

Ensemble

[johnholmes]

All 3 of the 500 anomaly charts suggests a flow at that height of west (NOAA) and south of west (ECMWF-GFS) with a +ve area moving across the Atlantic towards the SW of the country.

This does indicate the weather settling down from the SW over the time frame they give that is 6-15 days. So a change from the mostly unsettled conditions looking likely in that time frame?

[Summer Sun]

As they say today is the calm before the storm in the north

Monday rain

Wind speeds

[Summer Sun]

GFS keeps it very unsettled for tomorrow there is a goof chance of river flooding for some areas in during today and Monday with some parts seeing rain non stop for a good 20 hours

By midnight it starts to move up from the south

By 6am it continues to move north making it to southern Scotland

By this time the rain totals are starting to build up for wales and the south coast along with the channel islands

By mid-day the rain starts to get heavier for some parts of the west midlands and wales

By this time rainfall totals are getting higher

By 18:00 rainfall totals start to ease out

River Flooding is possible tomorrow for some areas today and tomorrow the one part of the UK which should stay dry for most of tomorrow is the far north of Scotland

[TonyH]

A look ahead to quite an eventful week:

http://forum.netweather.tv/blog/309/entry-4478-weather-guide-monday-24th-to-sunday-30th-september-2012/

[AWD]

FI I know, but some rather notable differences between the GFS & ECM tonight regarding week 2, as we enter October.

The GFS has the UK under high pressure, mild temps and a "bomb" in the Mid Atlantic

The ECm has a small, but potent depression in the north sea, just of the NE coast, bringing windy conditions to the north east, and rain to all of us, with cool temps.

[Gibby]

Good evening. Here is the report of the 12zs from today September the 23rd 2012.

All models show a complex area of Low pressure currently entering the UK from the South and persisting until the midweek period with showers or longer spells of heavy rain and strong winds around too. By Thursday and Friday Low pressure fills and pressure rises to allow less in the way of rain and wind to end the working week.

GFS then shows next weekend with a ridge of High pressure crossing Southern Britain before a trough crosses the North Saturday night with some rain here. FI tonight shows a High pressure dominated period with an innitial cold front clearing away to allow a period of High pressure with dry and quiet Autumnal conditions. The NW will see Atlantic fronts and occasional rain continue at times before the North too enjoy at least some quieter moments.

The GFS Ensembles show fairly average 850's with the very wet conditions early in the period giving way to drier and brighter spells with just occasional lighter rain. In the North a more sine wave pattern evolves indicative of frontal boundaries crossing at times although the average for the group remain close to the long term mean.

The Jet Stream shows a deep troughing of the flow in the Eastern Atlantic before the flow turns NE to the South of Britain. Longer term the flow weakens and buckles as a new arm pushes East across the Atlantic to the British Isles in a week or so time.

UKMO for noon on Saturday shows a weak High pressure ridge collapsing over Southern Britain with a dry and bright day likely here on Saturday. Further North and West a SW flow develops as Low pressure bears down from the NW likely to extend to other areas in the following day or so.

ECM is broadly similar at the same time point continuing to develop a renewed cool and unsettled feed of weather down from the NW as Low pressure lies to the NE with a broad trough SW over Britain to end the run.

In Summary the weather is decidedly unsettled this week with rain, wind and showers all featuring along with local flooding problems. later in the week things calm down as pressure gently rises with the start of next weekend looking OK for most. GFS shows some promise in FI of some quiet, Anticyclonic early Autumn weather to be enjoyed following a cold front SE late next weekend though ECM is not so keen with a more enhanced surge of cool air from Northern latitudes engulfing the UK in a week to 10 days time with it's attendant rain and showers for all.

[bluearmy]

with such a large variation in 500mb pattern between ecm op runs, i'd be cautious about anything once this week trough fills. settled in the south still slightly favoured i reckon.

[johnholmes]

with such a large variation in 500mb pattern between ecm op runs, i'd be cautious about anything once this week trough fills. settled in the south still slightly favoured i reckon.

very definitely according to the 500mb anomaly charts in their timeframe, so probably seeing something starting to show by day 6 and becoming more clear thereafter?

[Gibby]

Good morning. Here's my take on the 00zs from GFS, UKMO and ECM for this morning Monday September 24th.

All models show a Low pressure centred over Britain over the next few days with areas of rain circulating over Britain in often fresh and blustery winds. Later in the week all models show the Low to fill in situ with a weak ridge descending SE over the UK by Friday.

GFS this morning then looks like starting the weekend with a cool NW flow with some occasional showers chiefly in the North and East. Winds then back SW as Low pressure to the NW becomes influential in the start of the new week. The SE will see the best of the drier and brighter spells where it will become rather warmer. To the North and West unsettled weather remains with this extending to other areas later in the run.

The GFS Ensembles show a sustained period of normality with rainfall spread about through the members, though not as much as currently. The warm up for the SE described above is not well supported.

The Jet Stream flow is ddeeply troughed to the West of the UK returning NE over France. This pattern maintains for a while before it disrupts and settles west to East across Britain next weekend and beyond.

UKMO at midnight on sunday shows a SW flow over Britain with a cold front approaching Western Britain later in the day. after a dry and bright start rain will follow from the West through the day.

ECM shows a ridge over Southern Britain on Sundy with the trough further back into the Atlantic. The trough does move through though and although fairly weak in the SE at first by the midweek period a strong and cool Westerly flow cover all of Britain with showers or longer spells of rain for all areas by then.

In Summary the pattern remains a basically unsettled one. Once this weeks Low pressure has filled and moved away the earlier days model indications of a spell of better weather is steadily becoming eroded as further Low pressure is shown to move in from the NW with rain at times next week in a typical mid Autumn westerly flow.

[AWD]

GFS, ECM & GEM all singing from the same hymn sheet for next weekend, and the start of October now.

Unsettled "westerly" conditions for Scotland, Northern Ireland and thee far north of England.

More settled, drier conditions for the southern half of England and Wales, if not a bit breezy at times.

[Summer Sun]

Once this storm clears through on Wednesday GFS shows things to settle down

A weak ridge of high pressure builds

The by Sunday low pressure move across Scotland this time

Into October its a case of settled to the south unsettled across the north

A north westerly is then shown to develop but it don't last long

An area if high pressure then moves back in turning things settled once more

So after this stormy spell is out the way things return back to normal with high pressure shown to settle things down for the south at first then UK wide into early October after a couple of cool days

[A Winter's Tale]

Good evening everyone.

Many areas of the UK have experienced very unpleasant conditions today thanks to an unusually deep area of low pressure for this time of year that's situated over the British Isles bringing very heavy rain and strong winds to many of us. Considering that a month's worth of rain has fallen in areas, it's no surprise that flood warnings have been issued.

At this moment most of Wales and England south of Manchester is now largely dry other than a few showers around the west and south coasts but Northern Ireland, Northern England and Southern Scotland are now experiencing the main area of heavy rain and wild conditions and parts of Yorkshire in particular have experienced some very heavy rain recently. Tonight temperatures should drop to 10-11C widely but I feel that it's best to focus on precipitation and wild conditions during the night.

Tonight the centre of the low of 980mb is centred just off the NE of England in the north sea. There is a steep gradient in air pressure to the north of the low meaning that Scotland should experience strong NEly winds. As the night goes the centre of the low should gradually move towards the Irish Sea. At the moment it looks like the worst of the winds (possible gusts up to 60mph) in Scotland is expected 2100 - 0600hrs and as the winds here turn lighter and gradually change to more of a SEly come Tuesday morning and lunchtime, in Ireland there should be strong northerly winds throughout the day.

The chart below shows where the main area of precipitation is expected at 9pm tonight. As you can see, southern areas of Britain has seen the worst of the rainfall now and should have a largely dry night - particulary in the SE. Ireland, northern England and southern and eastern Scotland should be under the main band of heavy rainfall with the worst of the conditions in NE England. Precipiation also heavy where the relief of land is more mountainous in the Lake District.

As the winds start to pick up in Scotland, the heaviest of the rain in NE England moves further north west into eastern Scottish borders and Lothians and rainfall also spreads northwards and westwards to other parts of Scotland. In Ireland, the precipitation is still heavy as it moves towards the Irish sea in a SWly motion. Again, the hilly regions of northern England and Northern Ireland continue to have heavy rainfall.

Come tomorrow morning, Ireland, northern England and southern and eastern Scotland are under the main band of rainfall with the heaviest of the rainfall in NE Scotland and in the Irish Sea.

By lunchtime, northern Scotland and southern Ireland this time look set to be drenched. The main band seperates and western areas of England and Wales should experience rainfall through the evening. Again tomorrow is another cool day with maximum temperatures of only 10-14C for most of us.

From Tuesday night to Friday, the trend is for drier and calmer weather with some showers but there will be some clear skies at times across the UK although on Friday it looks like some light rain may move into western parts of Scotland. Maximum temperatures on the whole looks like 12-16C and night-time temperatures generally are expected to be 8-11C.

The outlook beyond this looks changeable but fairly typical for this time of year, southern areas from time to time could be settled. Quite cool for places too with winds coming from the NW for periods.

[Gibby]

Hi everyone. Here's the daily take on the 12zs from GFS, UKMO and GFS.

All models show a deep Low pressure area currently centred on Northern England. Over the next few days it drifts SW and fills then it moves SE and becomes a trough into Northern France by Thursday. a cool and rather cloudy NW flow follows to all areas by Friday with a few showers scattered about before a ridge moves across Southern areas on Saturday.

GFS then takes us forward from the second half of the weekend with a return to unsettled conditions as Low pressure to the North of Britain pushes troughs SE over the UK in fresh Westerly winds. After winds turn towards the North early in FI a large anticyclone takes control of the weather nationwide drifting over the UK and on into Scandinavia leaving a ridge SW over the British Isles. The weather will turn very cold by night with frost and fog likely issues though with some bright and pleasant day times with cool temperatures, a pattern that persists through to the end of the run.

The GFS Ensembles show 850's at or a smidgen below the long term mean for both Southern and Northern locations. Once the next few days of heavy rain diminish the weather becomes somewhat drier though rain events are spread about throughout the run even for London. The operational was a cold outlier under the Anticyclone later in the run for locations on the Southern flank of the Scandi High.

The Jet Stream sinks South west of Britain as the British Low pressure draws down to the South of Britain and weakens. It continues then East over France for the next 72hrs. longer term the flow breaks and resets on a more West to East course over Scotland later in the week and next.

UKMO for noon on Sunday shows Low pressure North of Scotland with a broad westerly flow over all of Britain. troughs look like crossing East over Britain through the day with rain followed by showers the most likely scenario.

ECM has a slightly more SW flow than UKMO meaning a somewhat drier and warmer day being possible for the SE on Sunday/ Monday. All other areas would likely see rather cloudy and breezy weather with rain at times as troughs pass over. By midweek an active cold front is shown to cross East over Britain with strong winds and heavy rain followed by cooler and showery weather to see out the run.

In Summary the weather looks like being unsettled for most of this week and changeable thereafter. That means some more wet weather regularly featuring until later in the week when the weather marginally improves to some dry and brighter days mixed with more unsettled interludes as frontal troughs from the Atlantic pass over. Temperatures look like gradually recovering to levels close to the long term average after the cool weather of this week is past.

[Geordiesnow]

It might seem a little predictable whats the weather is going to be like after this low pressure finally fills in and weakens completely but in terms of detail, then keep an eye on the output, its one of those where another strong low could easily come into a picture whilst at the same time an Azores ridge could come in but it does look like a more westerly pattern will kick in and temperatures should return to normal if not slightly above in some areas.

[bluearmy]

very definitely according to the 500mb anomaly charts in their timeframe, so probably seeing something starting to show by day 6 and becoming more clear thereafter?

The trend today is most certainly away from any settled spell and looks more changeable now.

[Gibby]

Good morning. Here's my take on the 00zs for today Tuesday September 25th 2012

All models currently show Low pressure centred over Northern Britain sliping slowly south over the next 24hrs to be near SW England, filling steadily by late tomorrow. It fills further and loses it's identity by late Thursday as a trough of Low pressure swings SE behind it by Friday. Saturday is then showing the UK in a cool run of NW winds with some showers in the North while southern areas enjoy a drier and brighter day.

GFS then shows a mobile pattern throughout the whole of the rest of the run with the basic pattern of Low to the North, troughs passing East followed by a ridge repeated several times over the FI period. All areas would see some rain, heaviest in the North with Westerly winds, strongest in the North, and some decent dry periods longest lasting in the South. temperatures would be close to normal with some cooler intervals behind the cold fronts and in any clear periods overnight.

The GFS Ensembles show changeable weather over the next few weeks. Some rain can be expected for all on occasion. Uppers will be close to the long term mean in the North and somewhat below in the South.

The Jet Stream currently troughed to the South of Britain continues in this way for a few more days before a more direct West to East flow sets up over the UK in three or four days and beyond.

UKMO for midnight on Monday shows Low pressure over the Faroe islands and a strong Westerly flow over Britain. The most likely scenario from the 144hr chart is sunshine and blustery showers in the North while the South would likely be cloudy wit rain at times under a slow moving trailing cold front.

ECM shows a WSW flow at the same time point with troughs embedded in the flow making for unsettled conditions in the north and West though the South and East could hang on to some drier and brighter weather for a fw days before pressure falls with rain and showers in a strong West then cool NW wind. The end of the run sees High pressure build strongly in from the West under a very cool Northerly.

In Summary the best description of the weather pattern from the output is changeable. All areas will see some rain, though thankfully much less than has been experienced by many recently. Winds will blow mostly from a Westerly direction indicating average temperatures though in any NW incursions it would turn rather cool at times. Some decent dry spells are shown too, most likely for Southern and Southeastern areas though perhaps more generally later.

[johnholmes]

The trend today is most certainly away from any settled spell and looks more changeable now.

It never looked like more than a 2-3 day break from unsettled so apologies if my previous post suggested otherwise. I would suggest a more settled short spell of 2-3 days sometime 28 Sept to 03 Oct is still a real probability especially the further SW one lives?

[phil nw.]

It looks like we are going into a typical Westerly type pattern to end this week and going into the new month.

Looking at the NAEF`s and Ens. means for the next 8 days and they all show a mobile Atlantic flow with a series of ridges and troughs crossing the UK during the period.

I think the ECM 00z at T168hrs. is typical of the outputs so far today.

This would bring some rather windy weather at times with frontal rain bands crossing the Uk from time to time with soime brighter drier interludes.

I did notice there`s a tendency to push the Jet stream north in later output with some hints of an Anticylone building across the south of UK but this too far out yet and could well change.

[AWD]

Nothing really settled from the GFS 12z in the reliable timeframe. Drier has we get into the weekend in the south, still showery in the north.

It's basically a westerly flow for the next week or so at least, with rainbands crossing the country from time to time, interspersed by a dry day or two, especially the further south you are. Temps around normal.

In FI it does turn settled and very warm for the time of year as HP drifts over the UK and settles over Europe bringing warm uppers and sunny weather for all. Being FI though it remains to be seen whether this happens or not.

[AWD]

About as zonal as you can get at T144 tonight.

[damianslaw]

Its a changeable outlook, a typical late september/early october pattern under a strong westerly airstream. So once the low pressure clears away to the SW later tomorrow, things will revert back to more average fayre.. with breezy rain or showers thanks to frontal activity off the atlantic interspersed with drier brighter breaks with the threat of frost in any clear lengthy spells at night.

Longer term - both ECM and GFS indicate a shift in the position of the jet - taking a more northerly path allowing the azores high to ridge into southern parts, which would mean milder drier sunnier conditions especially for the south - however, at this time of year it is rare for high pressure to settle over the country for lengthy periods, and if we do see such a pattern change, I wouldn't be surprised with the way the jet has been behaving lately that such a high would quickly ridge NW thanks to the jet riding over the top, setting us up for a possible cool/cold outlook as we move further through the first part of October.

[Gibby]

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

All models show a changeable pattern through the remainder of the week and weekend. Low pressure currently near the Irish Sea will move South and fill up as it moves away into Europe later tomorrow. Following on will be a NW flow of wind with a cold front crossing SE on Friday with a weak ridge of High pressure for Saturday. By Sunday Low pressure will be strengthening it's grip from the North with Atlantic fronts moving steadily East to reach all areas by Monday.

GFS then shows several days of unsettled weather as a broad trough drifts slowly East over Britain. By midweek a ridge builds from the Azores High across Southern areas before developing it's own High cell and crossing it over Southern Britain and on into Europe. By the end of FI several days of warm continental winds would have wafted over the UK with some decent warmth for early October before things cool slightly at the end.

The GFS Ensembles as expected show the operational as a warm outlier in its warm phase. The more likely option is a period of uppers close to the long term mean with some unsettled weather at times too-all this for locations both North and South in the UK.

The Jet Stream moves East over the Atlantic and breaks down the trough currently surrounding the UK The flow then shows a more direct West to East flow across the UK after the weekend.

UKMO for noon on Monday shows a strong Westerly flow over the UK between Low pressure to the North and High pressure near Iberia. fronts in the flow would bring spells of rain or showers to all with the heaviest falls in the North.

ECM too shows a similar pattern at 144hrs though with a little more SW to the flow. thereafter Low pressure digs down into the British Isles with some heavy rain and showers for all areas lasting through to the end of the run in a cool North flow by then as High pressure tries to ridge in from the West.

In Summary the weather looks like maintaining an unsettled theme for the foreseeable. With the general pattern being an Atlantic based one all areas can expect some rain at times with fresh to strong winds from the West at times. There are still hints of better weather in week 2 from GFS though the operational can almost be discounted I would feel as it has little support from its other members. Conversely ECM brings Low pressure into the UK from the NW enhancing the unsettled theme and bringing cooler than average temperatures too.