Good morning. Here is today's and this week's extended look at the midnight outputs of GFS, UKMO, GEM, NAVGEM and ECM for today Sunday September 22nd 2013.
The General Situation. A broad and warm SW flow covers the UK on the NW flank of High pressure close to South Eastern Britain. With the air very moist in it's lowest levels a lot of low cloud, mist and hill fog affects many upland areas of the UK and will continue to do so for a while to come. Well inland and in the East the cloud should break with some warm sunshine over the coming few days with temperatures well above average. Towards the middle of the week pressure is shown by all models to begin to fall with details in weather conditions at the surface very hard to pin down currently as slack pressure develops over the UK. This should mean temperatures slowly falling away to average with areas of cloud drifting South over the North as well as up from the SW. This will bring some outbreaks of rain almost anywhere by the latter days of the week as pressure continues to fall. By the weekend most output shows Low pressure forming somewhere near the North or West of the UK with rain moving NE in strengthening South or SW winds in average temperatures.
The GFS operational this morning shows slack conditions persisting well into next weekend with no one pressure system High r Low having overall control over the UK weather. As such there will still be a lot of dry weather around with just patchy outbreaks of rain in what would most likely cloudy and misty conditions. It's not until well into the following week when conditions deteriorate more markedly as Atlantic low pressure more meaningfully crosses the UK with windier and wet conditions for all towards the end of the run in average temperatures.
UKMO today shows a cocktail of weak troughs over the UK next weekend having either fed down from the North or up from the SW. As a result there will be patchy rain spread about over the UK with almost anywhere at risk of some showery outbreaks from cloudy skies. By the end of the run it does look like a more organised area of rain will form over the North as Low pressure develops there.
GEM is also slow to deliver Low pressure in any meaningful sense to the British Isles this morning with the benign pattern of rather cloudy weather late in the week with patchy rain lasting into the weekend. Banks of Low pressure are queing up in the Atlantic and they make there move early next week with marked and substantial areas of rain moving bodily East and NE through the British Isles then with some heavy rain for all along with strengthening winds from the SW innitially but turning NE from the North by Day 10 as substantially colder air arrives from the North.
NAVGEM today shows Low pressure gradually becoming more dominant over the British isles next weekend as systems move NE across the UK. At the same time a deep Low forms West of the UK and looks set to swing NE over the UK early next week with rain and strong winds likely for all then in temperatures close to average in mostly overcast conditions.
ECM also shows Low pressure strengthening close to the West and SW late this coming week and more especially over the weekend. After a cloudy end to the week with patchy outbreaks of rain the weather looks like turning decidedly wet and windy before the start of next week as troughs cross the UK from the SW with a strong and chilly SE flow shown affecting the North by midweek next week. the heaviest rain looks like affecting the South and West though all areas are at risk from some in temperatures close to average overall.
The GFS Ensembles point towards a more changeable pattern developing over the UK from the 27th in the South and before in the North. In the interim period the warm uppers currently felt will dissolve away back towards the seasonal average by the end of the week, a level at which they are generally maintained thereafter. Some members indicate some quite wet periods through Week 2 when 10mm plus could fall on some days both North and South of the UK.
The Jet Stream driving this pattern shift is complex this morning with the general consensus being that the flow weakens to the North of the UK later this week to relocate at a more Southerly point across the Atlantic where it is then steered NE across the UK, probably close to Southern England from next weekend.
In Summary this morning the models are again struggling to deal with complex synoptics as Autumn 2013 digs it's heals in. With pressure fairly high over the Arctic with time the Jet Stream is forced South opening the door to the engagement of cool Autumnal air well formed to the north of the UK with the tropical maritime air out to the SW of the UK. The potential for some quite potent depressions and areas of attendant heavy rainfall is very real by next weekend but in the short term things look like remaining quite benign if rather cloudy with patchy rain late in the week. After a period of warm temperatures early in the week temperatures will fall back to levels we would normally expect at this time of year by the end of the week. As we look deeper into the following week it looks like a classic October setup could develop with deep low pressure areas tracking across the Atlantic and ending up near or over the UK with heavy rain and potential gales at times. There is some hesitancy in taking these depressions right across to exit East of the UK though and if things happen as shown it could feel quite warm and humid in the SE at times. However, if a GEM type route is taken cold northerlies could blow down over the UK in the wake of the depressions and bring some very cool air down from the North with wintry showers over Northern hills. So taking everything into account there is something for everyone in todays extended report with a lot of scope for changes as the day to day detail looks impossible to account for at the moment beyond the general trend.
Edited by user
22 September 2013 07:51:55
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Reason: Not specified
Martin G
Kilmersdon Radstock Bath Somerset