Model Output Discussion - September Onwards

[Iceni]

http://forum.netweat...h/page__st__500

Although monitoring only really starts in November

thanks

[Thundery wintry showers]

I can't remember many September gales in recent years, and there has certainly been an anomalous frequency of calm, anticyclonic weather in recent Septembers, with not much cloud trapped within the anticyclones. Thus, this rather boisterous start to September certainly makes a change if nothing else!

The outlook through to Wednesday is of the "sunshine-and-showers" variety until next Wednesday. There will be a persistent rain belt clearing out of the way of eastern areas by tomorrow lunchtime, and another belt moving through overnight Sunday/Monday, otherwise we will be in polar maritime air- though the models do have a habit of not picking up on secondary low/shortwave development until near the time. Monday certainly looks like featuring widespread gales as the ex-hurricane moves eastwards just off north-west Scotland, having been revised further south on recent model outputs. As often happens, northern and western Scotland look like being heaviest hit.

I don't think much of the anticipated high pressure towards the end of the week- if we get it for a sustained length of time, it will most likely be far south enough to drag a lot of cloudy moist tropical maritime air in on its northern flank, even to southern parts of England. The GFS evolution has an alternative scenario with a temporary 36-48 hour ridge giving sunshine and not many showers, but then evolves to that rather cloudy-looking westerly on the northern flank of the high towards T+180.

Edited September 9, 2011 by Thundery wintry showers

[Gibby]

Just an overall summary from me tonight and no report tomorrow I'm afraid as work takes me away from my PC. Back on Sunday.

In Summary tonight all three models programme the storm to pass by or over NW Scotland with severe gales over Northern and Western Britain with western and southwest Scotland, Northern Ireland and the Central Belt currently progged to experience the worst of the winds Elsewhere will be very windy too with heavy rain and showers rushing through on the wind. Thereafter, things quieten down with High pressure to the SW becoming more controlling of the weather with dry if rather cloudy condition and both GFS and ECM offer risk of unsettled weather at times later in their run with winds remaining between NW and SW.

[Rocheydub]

Could be interesting model watching tomorrow... This tail end of Katia could bring worse weather than the models are predicting from my experience...

[TonyH]

Very unsettled until mid week at least, temperatures close to average after today's warmth in central and eastern parts. The north-westerlies behind ex-Katia turns thing briefly on the cool side though.

Uncertainty beyond mid week, with high pressure attempting to influence things although with troughing uncomfortably close by.

ECM would have a warm dry SE flow to end the week:

Whilst GFS has a shallow low in control at the same stage:

Edited September 10, 2011 by Tonyh

[graupel]

Anyone got a good link for free wx radar, my meteo has just ceased so it seems.

Thanks in advance apologies for being in the wrong place !

[Grimsby Snow Lover]

Have you tried raintoday.co.uk? I find this is one of the best freely available precipitation radars available, hope this helps

Edited September 10, 2011 by Grimsby Snow Lover

[Ben_Cambs]

It's looking fairly changeable for the forseeable future. It appears now that the strongest winds from ex-hurricane Katia that will affect NW Britain most will occur on Monday night into Tuesday, as the centre of Katia has been shifted NW on recent runs. Looking very wet too for Scotland, NI and some parts of N'ern England, though it will be difficult to pinpoint rainfall accumilation till much nearer the time.

Further into next week, the weather looks to turn more settled though there is a risk of showers at first in the north. Thursday and Friday could be fairly warm across the SE in particular though it should be very pleasant too elsewhere:

http://www.wetterzentrale.de/pics/Rukm1441.gif

Beyond then, increasing signs of unsettled weather taking over again, though model divergence as usual at this timeframe really means that nothing is finalised beyond next Friday.

[Geordiesnow]

It's looking fairly changeable for the forseeable future. It appears now that the strongest winds from ex-hurricane Katia that will affect NW Britain most will occur on Monday night into Tuesday, as the centre of Katia has been shifted NW on recent runs.

Indeed although the ECM model might have it right regarding the positioning but as the forecasters keep on stating, its positioning will alter slightly so all is still not concrete just yet.

I menturned a few days ago how the models want to ridge the Azores high slightly which leaves a NW'ly flow via the Azores high and ex hurricane Katia, this appears to of been upgraded slightly again but all models agree any NW'ly flow will be brief and will be cut off quite quickly but still a sign of Autumn in terms of actual temperatures and heavy blustery showers in the NW! The next few days in NW Scotland will be very interesting weatherwise I feel.

Models are hinting at another possible warm up at the end of the week with a slack low pressure to the West and high pressure to the East, this evening runs suggest the low will break through but its one to keep an eye on, especially for those who may still crave for some summer warmth and sunshine.

[Summer Sun]

The Ensembles are fairly settled in the North once Katia passes through,

pressure stay's either just below or above 1000mb to the 25th

http://nwstatic.co.uk/ensimages/ens.20110910/12/prmslAberdeenshire.png

Precipitation isn't too high either

http://nwstatic.co.uk/ensimages/ens.20110910/12/prcpAberdeenshire.png

Pressure is even higher once you move further south

http://nwstatic.co.uk/ensimages/ens.20110910/12/prmslDurham.png

Precipitation is a bit higher

http://nwstatic.co.uk/ensimages/ens.20110910/12/prcpDurham.png

Pressure stays above 1000mb throughout for London

http://nwstatic.co.uk/ensimages/ens.20110910/12/prmslLondon.png

This would indicate heavy downpours

http://nwstatic.co.uk/ensimages/ens.20110910/12/prcpLondon.png

Looks like it should settle down once the pressure gets stable again, a mix of sunshine and showers with cloudy day's

[Backtrack]

The Ensembles are fairly settled in the North once Katia passes through,

pressure stay's either just below or above 1000mb to the 25th

http://nwstatic.co.u...erdeenshire.png

Precipitation isn't too high either

http://nwstatic.co.u...erdeenshire.png

Pressure is even higher once you move further south

http://nwstatic.co.u...prmslDurham.png

Precipitation is a bit higher

http://nwstatic.co.u.../prcpDurham.png

Pressure stays above 1000mb throughout for London

http://nwstatic.co.u...prmslLondon.png

This would indicate heavy downpours

http://nwstatic.co.u.../prcpLondon.png

Looks like it should settle down once the pressure gets stable again, a mix of sunshine and showers with cloudy day's

Erm, isn't that what the weather does everyday of the year? It's either sunny, raining, showery (varied precip) or cloudy?

[Liam J]

Since the 12z runs EX Katia has been recorded with a pressure of around 954mb over the Atlantic which is well under the model guidance of around 970mb, I expect to see an upgrade of this system on the 18z runs given the new data?

[damianslaw]

Staying unsettled in the reliable timeframe - the atlantic is very much ruling the roost in what is a very disturbed pattern. Any ridging will be brief, suspect low pressure will crash through the country towards the end of the week again.

Very typical unsettled autumnal conditions - but they have arrived much earlier than in recent years despite the current warmth still.

[Hairy Celt]

18z already has ex-Katia as 4mb deeper than the 12z did at t18.

Hmm, may have jumped the gun there.

Edited September 10, 2011 by Hairy Celt

[Backtrack]

18z already has ex-Katia as 4mb deeper than the 12z did at t18.

Hmm, may have jumped the gun there.

Not to mention that to me the isobars look tighter on the Southern flank. Looks like giving the South winds slightly stronger than the previous run.

[Liam J]

Storm slightly further south on the 18z and with a lower central pressure, oh what an exciting day of model watching coming up through Sunday!!

[Gibby]

Good morning.

GFS today shows tomorrow and Tuesday's storm less worrying for the majority of the UK away from the NW as it's now pretty definite to move NE just to the NW with the severest gales close to the core on the southern flank of the Low. A band of wind and rain would move east tomorrow, once more sporadic in the south but heavy further North before the whole system moves away by midweek. A dry day or two then looks likely for the North and East before Low pressure moves slowly into southern and western regions by the end of the week with its influence moving further NE with time exasipated by further Low pressure migrating SE from Greenland. In FI this morning high pressure, apart from the occasional ridge is generally held away from the UK by Low pressure either over or close by maintaining rain at times and normal temperatures.

UKMO today also shows the storm in the next 48hrs passing close to NW Scotland with a 48hr window of severe gales for the NW and very windy conditions elsewhere too. A band of rain moves east tomorrow clearing later with just a few showers in the south but further squally rain at times further North. By Thursday high pressure develops near eastern Scotland and slides out into the North sea by the weekend with a weak low pressure area down to the SW a SE flow develops with some rain possible in the extreme SW though dry weather prevailing elsewhere.

The Fax Charts show the storm system moving NE past NW Scotland to Scandinavia in the next 48hrs with a weak ridge of high pressure developing later in the week.

ECM also follows UKMO up until Thursday then is quite close to the GFS solution thereafter with the storm of tomorrow and Tuesday moving off towards Scandinavia with a ridge developing midweek from the SW. From 144hrs it pushes the ridge away east from the UK allowing the disturbance to the SW to make inroads across the UK by Friday as it becomes absorbed by Atlantic Low pressure developments in time for an unsettled weekend with rain and wind renewed for most. Things then continue unsettled and breezy then to the end of the run.

In general this morning tomorrows storm away from Scotland and the NW of England and Ireland should not present too many problems though travel disruption is likely for those areas mentioned above. Aside of the wind a band of rain moves through tomorrow though amounts look fairly trivial in the south as the trough bringing it speeds on through quickly. Thereafter something of a ridge midweek will bring a dry and quiet few days before a weak low pressure ahead of an Atlantic return brings rain back into the UK by the weekend and thereafter.

[03jtrickey]

Latest GFS 6Z has an extratropical Hurricane Maria gracing our shores into FI...

[Rob]

That bodes well with the latest NHC advisory which sees the storm beginning to take a NE path as it moves up to the east of the USA, something to watch out for!

[Ladyofthestorm]

It is I think Maria, its coming into F1 around the same time as Katia did, one to watch as the GFS has so far impressed me. Heavy rain next weekend for the south and west???

[Thundery wintry showers]

A lot depends on specifically how the feature interacts with the jet stream, so I doubt that its precise track will be accurately modelled until within 5 days of the event, but I think the odds do favour that ex-hurricane getting close to the British Isles, given the likelihood of the mobile westerly type persisting for at least the next 5-10 days.

Looks like conditions may get pretty wild in Scotland and parts of northern England (the west coast of northern England and also anywhere north of Teesside) with a very tight squeeze indicated on the isobars. I don't think we can expect anything as severe as the wind-storms of the 16th October 1987 or 25th January 1990, but I think it could well end up on a par with the event of the 11th November 2010, with some limited structural damage and probably some significant rush-hour disruption in the evening, as that's when the strongest winds are likely to hit. Winds are likely to approach gale force even in the southern half of the country but probably not damaging away from exposed west-facing coasts and hills IMO.

The ridge of high pressure towards the end of the week is looking rather more significant on the latest runs. I think it will get pushed out of the way by Sunday, but it does look like the majority of the country will be dry and sunny on Thursday and Friday, with close to average temperatures. The GFS is suggesting some pretty active rain belts associated with the low that initiates the breakdown, which might see us import some thundery activity from the continent, though with temperatures not rising far above average, I think thunder activity probably won't be widespread.

[Summer Sun]

GFS FI gives continued hope of a settled spell during the last full week of September,

Something a bit fishy here

http://www.wetterzentrale.de/pics/Rtavn3601.png

[Geordiesnow]

GFS FI gives continued hope of a settled spell during the last full week of September,

Something a bit fishy here

http://www.wetterzen...s/Rtavn3601.png

The only fishy thing from that chart is that you don't want too see that pattern dominating in the winter months with the jet stream to the North of Scotland and the weather coming from the Atlantic. Infact the chart you posted don't look all that settled and probably won't remain settled for long.

Still keep an eye on that ridge though, it may provide one last significant warm spell especially if the low to the West stalls and brings up warm air from France but again at this stage, the models predict the low to break through.

[damianslaw]

Temporary ridge thursday looks like being quickly swept aside by further low pressure from the sw. Unsettled, nothing else to say.

[Gibby]

Good morning. A new working week and how will the weather behave in relation to the charts shown.

GFS today shows the storm affecting the North currently pulling away NE by Thursday leaving a ridge of high pressure moving into the UK through Wednesday and settled over us on Thursday. So a stormy day for the North today with the NW worst affected by sometimes damaging gusts later. Some heavy rain for the North while the south becomes dry after a damp start. With a day of sunshine and squally showers tomorrow things dry up for a while thereafter as the ridge moves in. Then towards the end of the week a small Low slips SE over the UK with further rain at times developing, especially in western and southern areas. Through the weekend its all eyes to the Atlantic once more as we enter next week with a deep Low near Iceland setting up a North/South split as High pressure moves in close to the south. The rest of the run maintains the changeable theme with bands of rain (worst in the North) alternating with drier and brighter spells under ridges of high pressure.

UKMO also shows the storm moving away by Wednesday with a ridge of high pressure moving east on Thursday with a dry and bright day before a trough of Low pressure affects the south and west particularly for a while late in the week and at the start of the weekend. The final chart shows a tenuous ridge lying across the UK with deep Low pressure to the NW and the remains of the previous days rain close to SE England.

The Fax Charts show the storm system moving away with weakening occluded troughs dissipating slowly near the UK as the ridge moves in through the week. Later on a weak array of troughs lie close to Southern and Western regions.

ECM today looks quite unsettled for the duration with todays storm system moving away by Wednesday taking its rain and showers with it. Thursday looks the best day of the week before Low pressure brings rain as we move towards another unsettled weekend. From then on a strong westerly flow brings a mix of rain bearing troughs east in association with Low pressure to the North interspersed with brighter and more showery days.

In Summary September is proving very different this year. The Atlantic is active and any ridges of high pressure shortlived as they are powered out of the way by Atlantic storms. Therefore, a continuation of the mix of recent days with some rain at times for all with only brief drier interludes and strong winds too. The South would see the longest drier spells though even here rain will never be that far awy. Temperatures look like staying near to the seasonal normal everywhere.

Edited September 12, 2011 by Gibby