Good morning folks. Here is this mornings look at the midnight outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Sunday September 29th 2013.
The General Situation. The UK is currently covered by a ESE flow between Low pressure to the SW and High to the NE. The effects of the Low to the SW will be limited today with most areas having a fine, breezy and rather warm day with some sunshine at times. Through the next 24 hours a new push of unstable air will move up to affect the South and west with thundery showers tomorrow while other areas continue the breezy and bright weather with some warm sunshine. By Tuesday and Wednesday Low pressure will be edging further North and East up the Western flank of the British Isles pulling winds round to a more Southerly point as well as bringing all of the UK at risk of showers or longer spells of rain with only short drier spells. By the latter stages of the week the Low will be to the NW of Britain and all areas will see winds swing into a cooler SW direction with a much more maritime influence but still carrying rain and showers East to all areas at times right up to the weekend before a slow change to drier and brighter conditions begin to affect the South and East as a brief High pressure ridge looks like grazing Southern Britain as it moves NE.
GFS then maintains a very changeable second week but never too cold anywhere. Further low pressure moves across the North of the UK at times sufficiently far enough South to put the whole of the UK at risk of rain at times with some brighter and drier spells in between. Temperatures would be relatively close to the seasonal average and it would probably be rather windy at times especially towards the North and West.
UKMO shows it's final day chart with the UK under a showery Westerly or WSW flow with sunshine mixed with showers passing through in the breeze. Average temperatures would be likely next weekend so it probably wouldn't feel too cold in any sunshine and away from the cloud and showers which would be heaviest by then in the North and West.
GEM shows a more meaningful push of high pressure up across the South of the UK next weekend from the SW while the North stays a little more changeable with some further rain at times. After a dry and fine few days in the South the High is shown to give way to renewed Low pressure from off the Atlantic with rain and showers in average temperatures extending to all areas by the middle of Week 2.
NAVGEM has High pressure having built over France next weekend but probably insufficiently close to put the whole of the UK under fine weather. Instead a rather cloudy SW flow would likely to have developed with mostly dry conditions in the South and SE while all Northern and Western areas would most likely become cloudy and breezy with rain and drizzle at times. It would be relatively mild though.
ECM also shows a short improvement for the South next weekend before all areas join in again with a strong Low pressure influence to the West and NW of Britain with mostly mild South or SW winds carrying bands of potentially quite heavy rain and showers North and East across all areas at times with the North and West seeing the worst conditions.
The GFS Ensembles paint a slowly cooling picture through this coming week to average temperatures which are then largely maintained through Week 2. After the potentially thundery rain at times through the coming week a reduction in rainfall is likely through Week 2 especially in the South at least for a time.
The Jet Stream's main arm is currently blowing to the South of the UK at the moment in association with the Low to the SW. As that moves North through the coming week so does the Jet flow. Although it's position varies between the members it's most favoured option appears to be a Easterly moving flow close to the British Isles through week 2.
In Summary Week 1 looks fairly agreed upon by most members from all models that the gradual transformation of Low to the SW to Low to the NW will take all week to complete. As this occurs all areas will be susceptible to periods of rain and showers, heavy at times perhaps with thunder, mostly in the SW at first but anywhere from Tuesday. It looks reasonably likely that a brief ridge of high pressure could affect the South for a time next weekend but in general it looks like it may be quite short-lived as there is reasonable support for more changeable weather to develop through Week 2 but it would never be desperately cold with any frost and fog risk very low at this stage.
Martin G
Kilmersdon Radstock Bath Somerset