Model Output Discussion - September Onwards

[bybo1999]

summer blizzard, on 06 September 2011 - 17:44 , said:

The models have downgraded the warmth quite significantly. Rather than coming from ridges and approaching +15C in the upper atmosphere, the warmth is now associated with warm fronts and low pressure which will in the main provide cloud and high minima.

The models are strugling with Hurricane Katia as it has strengthened more than predicted and is a FISH.

Sorry, but " FISH". What does this mean? apart from the freshwater type. Cheers

It just means that she is staying out at sea , not making landfall!

[Gibby]

Good evening folks.

GFS tonight continues to show a changeable theme out to next Monday with todays Low pressure slowly pulling away North leaving behind a broad westerly flow with showers chiefly in the West and North. On Thursday breakaway troughs run east in the flow making for a cloudy day for many with outbreaks of rain at some point during the day. By Friday winds back SW with warm, moist conditions moving up across all areas and in any sunnier breaks in the lee of high ground to the SW it could become very warm. Over the weekend a new Low pressure moves NE past NW Scotland with troughs crossing all areas bringing rain and strong winds east followed by brighter but windy weather once more. As a ridge crosses east over Sunday night the remains of hurricane Katia is winding up in the Atlantic moving NE between Iceland and Scotland (935mb). Winds would become strong SW in the North and West with a narrowing band of rain crossing east through all areas on Monday. From Tuesday on pressure builds from the SW with FI dominated by High pressure for a while before troughs cross east again as the High slips away into Europe.

UKMO follows a similar pattern through this week and the weekend with rain at times for all. There will be some drier spells too especially in the South and East where it will become very warm on Friday if the sun breaks through. Towards the end of the run the remains of Hurricane Katia pass harmlessly by to the NW with its effect likely to just bring traditional wind and rain to Northern and Western areas while drier if rather breezy conditions look more likely in the south.

ECM also keeps the same pattern as GFS and UKMO up until Sunday when the depression bringing the weekend rain to the UK becomes absorbed by the remains of hurricane Katia to make an intense depression in mid Atlantic with strong West to Southwest winds blowing all over the UK. In the early days of next week the weakening storm systems moves east to the North of Scotland with strong winds continuing with troughs sweeping east in the flow bringing further rain at times. Towards the end of the run a secondary depression near Iceland slides ESE to the NE of Scotland bringing cool and showery conditions through the UK in NW and later very cool NNW winds which could allow ground frosts to form in places by night where winds fall light.

A real mixed bag in the models tonight. They all agree in the pattern up until the weekend but deal with next weeks ex tropical storm rather differently. GFS and as far as its run goes UKMO too take the storm well NW of the UK with an advantageous effect on the weather long term probably for the UK. ECM on the other hand shows what could happen if the Low winds up closer to the UK and gets to our NE. A large High pressure block builds in Mid atlantic and a cool and showery NW flow develops over the UK with some very cool air entrenched, the effects of which would be most felt at night should it verify. However, its only one of a multitude of possible outcomes and until the exact behaviour of next weeks ex tropical storm is nailed then many other switches and variations will follow in subsequent runs.

[Liam J]

Certainly some interest in the track of ex hurricane Katia next week, a few models and runs are bringing her very close to NW britain as a severe depression with around 950hpa centre. Now if she was to track closer to or even over the uk this would be a MAJOR wind event.

The most likely track will be between Scotland and Iceland, this could change and run more towards the UK and cause mayhem if it did.

Edited September 6, 2011 by james12

[tinybill]

Certainly some interest in the track of ex hurricane Katia next week, a few models and runs are bringing her very close to NW britain as a severe depression with around 950hpa centre. Now if she was to track closer to or even over the uk this would be a MAJOR wind event.

The most likely track will be between Scotland and Iceland, this could change and run more towards the UK and cause mayhem if it did.

well, it could be another great storm that hit the south east we all know what the last one did a few years ago!!

Edited September 6, 2011 by tinybill

[Aaron]

Certainly some interest in the track of ex hurricane Katia next week, a few models and runs are bringing her very close to NW britain as a severe depression with around 950hpa centre. Now if she was to track closer to or even over the uk this would be a MAJOR wind event.

The most likely track will be between Scotland and Iceland, this could change and run more towards the UK and cause mayhem if it did.

Ooh, that sounds exciting! Call me crazy but I hope she crosses our path.

[Gibby]

Good morning. Still a mixed bag this morning beyond early next week.

GFS shows a windy spell of weather up to and including Tuesday of next week. In that period the main change will be a rise in temperatures as warm sub tropical air moves NE over the UK from tomorrow. In any sunshine it could feel very warm for a while over Friday and Saturday though with pressure relatively low showers or rain at times could still occur. In the North and West it could be very wet at times. As we then move through next week High pressure moves steadily North over the UK with a fine and settled spell developing with sunny spells by day and some mist and fog patches overnight this lasting throughout FI.

UKMO shows a similar period up to the end of the weekend with warm moist SW winds and outbreaks of heavy rain with nowhere being immune. It also shows the chance of some fairly high temperatures in the SE over Friday and Saturday with the potential for any rain to be thundery in places. As we move towards next week UKMO shows ex hurricane Katia as a much weaker affair than GFS but bringing it in closer to the UK with further rain then showers occurring in strong west winds by Tuesday.

The Fax Charts today show close similarity to the raw output of UKMO with deep low pressure to the North and West throwing troughs NE and East through Britain in warm, moist and frequently strong winds.

ECM also shows a windy and unsettled spell of weather between now and Sunday as deep low pressure crosses NE to the NW of Scotland. It will become mild and humid and warm in the SE but not necessarily dry while the North and West see copious rainfall at times. Then into next week ex Hurricane Katia steams up to the North of Scotland before slowing down and influencing the UK weather with a period of rain and gales followed by cooling temperatures as winds veer west or northwest with showers, heaviest and most frequent in the North and west.

In Summary this morning the models continue to handle the ex tropical storm next week rather differently. GFS keeps it as a very intense feature well away to the NW which benefits the UK as it pumps up warm and higher pressure from the South bringing decent weather eventually after a strong blow for a day or two with rain at times. UKMO and ECM keep it a shallower feature but closer to our shores continuing the unsettled, windy theme going. The most worrying thing of note this morning is the return later of rising pressure near Greenland and the Atlantic from ECM pulling winds round towards the Northwest and keeping the UK in increasingly cool showery conditions in response to Low pressure over Scandinavia. The GFS solution couldn't be more different.

Edited September 7, 2011 by Gibby

[grab my graupel]

Certainly some interest in the track of ex hurricane Katia next week, a few models and runs are bringing her very close to NW britain as a severe depression with around 950hpa centre. Now if she was to track closer to or even over the uk this would be a MAJOR wind event.

The most likely track will be between Scotland and Iceland, this could change and run more towards the UK and cause mayhem if it did.

Indeed, the majority of ensemble panel members are suggesting that the track of the storm will, most likely, be too far North to be of major concern. However, as you say, it could still change.

[Ladyofthestorm]

hmmm I think its going to clip Northern Scotland, hit the shetland isles and give the western isles a good battering. The models keep wanting to bring her southwards mid atlantic before swinging back NE wards again.

[Ja23]

Latest gfs run shows it near the UK but a downgrade from the last run. ECM has picked it up but UKMO not interested and makes the low nothing worrying.

[Mark Bayley]

Some big differences between the ECM and the GFS this morning. The ECM deciding on height rises over Greenland with a cool northwesterly while the GFS has heights remaining low with high pressure building in from the azores. The GFS also keeps Fridays storm further North, while the ECM and UKMO bring it closer to our shores. The MJO is currently in phase 3, with composite suggesting the following. However, with such a low amplitude, im unsure what impact the MJO would have.

[Ja23]

06z shows it hit Western Scotland but another slight downgrade from the run before. Not sure what to believe GFS or the ECM and UKMO.

[Iceaxecrampon]

Certainly some interest in the track of ex hurricane Katia next week, a few models and runs are bringing her very close to NW britain as a severe depression with around 950hpa centre. Now if she was to track closer to or even over the uk this would be a MAJOR wind event.

The most likely track will be between Scotland and Iceland, this could change and run more towards the UK and cause mayhem if it did.

http://hw.nwstatic.c...airpressure.png

Yes looks "interesting" been watching this for a few days now it has been evident on most runs and entering a reliable timescale - Forum unusually quiet on this and surprised most posters are looking for warmth - maybe the Daily Express has got it right for once?

Iain

Edited September 7, 2011 by Iceaxecrampon

[Backtrack]

http://hw.nwstatic.c...airpressure.png

Yes looks "interesting" been watching this for a few days now it has been evident on most runs and entering a reliable timescale - Forum unusually quiet on this and surprised most posters are looking for warmth - maybe the Daily Express has got it right for once?

Iain

That chart isn't the ex-hurricane. That just shows low pressure over us, the hurricane is 2 days later, it's to the far left of the chart you posted.

[Iceaxecrampon]

Correct Kam.....! - but still a drop in millibars in the LP before that to "soften" N Scotland up on the Saturday.

Iain

Apologies - just seen separate thread Hurricane - I need to get out more - hopefully Sunday? - might take the kite - will make interesting flying at 3000ft

[Weather Boy]

06z is keener to bring the storm closer to our shores than the ECM or UKMO and then adamant on a stronger pressure build from the south which eventually covers the whole of the UK to the end of the run. The Meto seem to prefer the GFS solution, apart from possibly the bit about it covering the whole country.

If this run verified, then there would be severe gales in Scotland and it would be pretty brisk down south too, although nowhere near as much. I note, however, that the ensembles for the Highlands have the ops run as not exactly an outlier, but the lowest pressure of all the members, so does that indicate that the ECM/UKMO solution is more likely, with the eye of the storm tracking more or less half way between the coasts of Scotland and Iceland?

Looking further ahead to the GFS pressure rise in about a week, again the ops run is a high member, for the Hertfordshire ensemble which potentially undermines the GFS's credibility in the significant pressure rise on the fringes of FI.

Can a more experienced member help with a query? Am I right to assume that when we look at the GFS run on netweather, that that is the equivalent of the ops run in the ensembles? If not, which one is it?

[Costa Del Fal]

GFS has strong agreement for a pressure rise into next week. The OP and Control are at the top end of the members but not outliers with almost all memmbers giving High pressure of sorts and pleasantly warm summer like weather with it too. However ECM is a different story so much to be resolved and Tropical depressions/Hurricanes is making forecasting beyond just a few days tough!

[ICETAB]

Looks like high pressure wants to move to greenland on the ECM model. If the current ECM 240 chart verified at the end of November we would be looking at a country wide snow event. Lets hope it comes off and then the pattern repeats in a couple of months. I can't wait for winter!

[Iceaxecrampon]

Looks like high pressure wants to move to greenland on the ECM model. If the current ECM 240 chart verified at the end of November we would be looking at a country wide snow event. Lets hope it comes off and then the pattern repeats in a couple of months. I can't wait for winter!

All good - Some serious convection happening now BTW (sorry to be OT) gutters not holding water.....

Edited September 7, 2011 by Iceaxecrampon

[Gibby]

Good evening.

GFS shows the weather remaining distinctly unsettled and changeable for the next 4 or 5 days as Low pressure moves in close to NW Britain over the weekend. It is then joined by the remains of Hurricane Katia which moves swiftly into NW Scotland on Monday with severe gales and heavy rain to those areas with progressively lighter winds and less rain the further SE one goes. By Tuesday the storm moves away NE with a secondary depression meandering east over the UK as it fills on Wednesday and Thursday with a Northwesterly flow in its wake bringing cooler but drier conditions with showers. Then over the days leading into FI the showery NW flow persists for a while gradually giving way to Atlantic High pressure which would bring settled and rather cool conditions with fog at night and maybe a touch of grass frost in places although it could become somewhat warmer by the end of the run.

UKMO tonight shows a deep Low pressure passing by NW Ireland on Saturday with rain or showers for all replacing the warm and humid weather of late tomorrow and Friday when it could become very warm in the SE if the sun breaks through. It would become very windy in the North and West especially with gales on coasts and hills there and fresh to strong breezes elsewhere too. By Monday a deep low pressure which carries the remains of Hurricane Katia crosses by NW Scotland with a band of heavy rain and gales crossing east through all areas followed by an improvement on Tuesday as the storm moves away especially in the south.

ECM also shows the same sequence of events over the next week with the storm system early next week once more progged to pass to the NW of Scotland. The evolution thereafter looks a little better tonight with high pressure inching in from the SW from the middle of next week with progressively drier and settled weather everywhere by the end of the run with dry and bright days with near to normal temperatures with mist and fog patches night and morning.

Not a lot of change in the models tonight with all three models taking the storm system close to NW Scotland over Monday and away on Tuesday. Thereafter both GFS and ECM are broadly similar in bringing high pressure up from the SW settling things down with bright and possibly sunny weather by day but chilly misty nights with fog patches. With regard to temperatures they would probably remain close to normal but the afternoons could become locally warm in the south with time.

[Geordiesnow]

Still looking an Atlantic dominating outlook but with winds coming from the SW, instead of the clearer but showery airstream, we have a cloudy, humid airflow which will rise temperatures but sunshine will be more limited.

Be interesting how the low that is going to hit us will affect the ex hurricane Katia although the ECM 12Z seems the most realistic set up in terms of tightness of the isobars as the GFS tends to overdeep the lows. Be interesting how the models handles this although there is still a chance that the jetstream might kink and bring up a ridge instead of the reminisents of Katia hitting us.

[damianslaw]

Short term - unsettled in the main and very dull indeed with limited sunshine especially for the west. Becoming warm in central and eastern parts by Friday and into the weekend thanks to warmer uppers from a SW fetch, but also very limited brightness hence lack of sunny spells. It looks a rain fest for the foreseeable future for western districts in particular and with some very strong winds by Friday evening and into Saturday.

Medium term - all eyes on the path of ex hurricane katia, all main models agree it will take a path close to the NW shore of Scotland, but too early to call its exact path and therefore how strong winds will become. It will bring much rainfall for NW parts early next week. BBC are giving an early heads up about possible very strong winds, not often they hedge there bets beyond the 4 day range.

Longer term - GFS keen on mid atlantic ridge/heights developing, with UKMO suggesting something similiar. Much will depend on the track of ex hurricane katia. A deeper low pressure system will be better for stronger ridging... not sure what I'd rather have i.e. a storm followed by promise of a decent settled spell, or a half baked storm followed by more of what we are experiencing this week, probably the former it has to be said, these early autumnal conditions are making for a very dismal feel it has to be said, it feels like we have gone straight into mid autumn, bypassing the mellow fruitfulness stage..

Edited September 7, 2011 by damianslaw

[William of Walworth]

Not sure about that, IF this suggested ridge develops as nicely as some evolutions suggest is possible for later next week, that could feel pretty mellow and fruitful for a fair few of us!

To use a non meteorological term, we're overdue another spell of proper High Pressure dominated conditions. Owed it even!

[Gibby]

Good morning. Here's a look at the 00zs.

GFS today shows that the weather will become increasingly windy within the next 24 hours or so and last throughout the weekend and start of next week. This in response to deep Low pressure moving NE to the NW of Britain with the remains of ex Hurricane Katia also moving NE past NW Scotland on Monday. There would be rain at times too especially in the North and West with warm conditions for a while before things cool down as winds turn westerly early next week. Thereafter High pressure in the Atlantic steers winds more from a NW quarter with cool and breezy weather with showers for a while. Then throughout the lower resolution part of the run high pressure remains to the west and at the end of the run south of the UK with incursions from low pressure at times keeping things rather changeable with temperatures near to or perhaps a little below normal particularly where skies clear at night.

UKMO shows an unsettled spell coming up though the identity of Katia has practically evaporated to nothing this morning. However, after a couple of warm if rather cloudy days with a little rain to the NW winds increase markedly over the weekend in response to deep Low pressure to the NW with bands of rain eventually crossing west to east cooling things down and leading us into an unsettled start to next week with rain at times as pressure remains Low to the North and a westerly wind persists.

The Fax Charts today reflect a period of windy weather with a complex windy trough structure rushing east over the UK on Monday although the 96hr and 120hr charts interpret events supplied by yesterdays 12z data.

ECM also shows a complex and intense Low pressure structure to the NW later in the weekend as the remains of Katia get caught up in an existing Low pressure system there. This then moves away NE next week with High pressure gradually gaining control later next week. So rain at times though not much in the South and East until later in the weekend where it would be warm for a while. After a band of rain and gusty, squally winds sweep east around Monday things are shown to calm down next week although a further spell of rain is possible late in the week as a disturbance moves SE. Temperatures would return to near normal next week and perhaps a little on the cool side after midweek.

Things seem to be firming up on next weeks storm path with unified agreement on the storm passing NW Britain on Monday being absorbed within existing deep Low pressure there. Its effect on the UK looks like being little different now from a standard deep Autumn depression although severe gales can be expected in the NW and gale force gusts over a much wider area. It looks like things will slowly settle down thereafter as High pressure gradually moves in from the west or southwest although with a northerly component to the wind high temperatures look unlikely.

[Ladyofthestorm]

I thought the GFS was throwing up some pretty dry settled but autuminal weather. Frosty nights and warm sunny days. Maybe Im wrong.

Has anyone else noted the possible winter setup for snow in the forecoming months...

http://hw.nwstatic.co.uk/gfsimages/gfs.20110908/00/336/airpressure.png

Edited September 8, 2011 by Ladyofthestorm

[chionomaniac]

I thought the GFS was throwing up some pretty dry settled but autuminal weather. Frosty nights and warm sunny days. Maybe Im wrong.

Has anyone else noted the possible winter setup for snow in the forecoming months...

http://hw.nwstatic.c...airpressure.png

LOTS

Were that a winter set up that chart would be screaming toppler to me!

Edited September 8, 2011 by chionomaniac