Hi folks and good morning. Here is the morning day by day rundown of the midnight outputs from GFS, UKMO, GEM, NAVGEM and ECM and what they mean for us on the surface over the coming 10-14 days forward from today Thursday July 18th 2013.
All models currently show High pressure moving slowly North over the UK with the fine and very warm or hot conditions persisting for some time to come. Subtle changes will occur over the coming days and these are threefold. Firstly the persistent cloud and occasional rain over Scotland will move away North to allow these areas to share in the warmth of areas further South over the coming days. Secondly the highest temperatures will transfer over to the West and SW of the UK as a light Easterly breeze develops across the South and thirdly low cloud and mist will affect many Eastern and some Central counties in the morning's of the coming days clearing by late morning away from the coast itself and consequently holding temperatures down a little on recent values. All areas will stay largely dry but isolated showers or thunderstorms could develop each late afternoon and eve and perhaps a little more widely across Southern England by Monday.
GFS then shows the UK locked in very warm and slack conditions synoptically with no pressure area having overall control. The weather would most likely be humid and still largely dry with a few thunderstorms scattered about, more likely over the South. Late in the week and the weekend more substantial rainfall would develop as Low pressure finally trundles up from the South introducing cooler and fresher air with time from off the Atlantic. Thereafter the latter part of the run suggests cooler and more changeable conditions from an Atlantic regime with occasional rain, average temperatures and rain at times, especially in the North.
The GFS Ensembles still show that around the 26th is the most likely day of change to cooler and more changeable weather as Low pressure looks likely to introduce this change SW to NE across the UK followed by more changeable weather with Low pressure close to the North with fronts crossing East over the UK in a traditional changeable summer pattern.
The Jet Stream is the item that brings about this change. As a response to the declining High pressure area in a week or so the flow relocates South to an Eastward moving flow across the Atlantic and across Southern Britain in the second half of the run.
UKMO today shows pressure having leaked away through the early stages of next week to sub 1015mbs by midweek. This would probably be sufficient enough to spark off rather more thundery showers than previously though at this stage there would continue to be a lot of very warm, bright and humid weather about as there are no major low pressure systems indicated at that time.
GEM today is the pick of the bunch if it is a continuation of the very warm or hot weather your looking for as it maintains a strong influence of High pressure close to or over the UK all next week with only very isolated storms and prolonged sunny spells and temperatures easily reaching 30C at times. The run does degenerate into something more thundery and eventually cooler and fresher in the final days though as a GFS type breakdown looks likely.
NAVGEM today shows a trend toward a somewhat thundery period next week, especially in the South as a cool pool of air undercuts the High pressure over the North as it moves SE over France. It would remain warm or very warm at the surface with more cloud than of late with thundery showers while the North stays largely dry, fine and warm.
ECM today shows changes next week to be slow with a lot of fine and very warm weather still to be found over a large swathe of the UK though next week. High pressure remains largely in control close to northern Britain through the week and though thundery air tries to make progress up from the South through the week it is not until almost the weekend it succeeds with any particular vigour to bring a spell of welcome thundery rain to many Southern and Southeastern parts though it may never reach the North in what will still be temperatures well above average for many if rather humid.
In Summary the pattern remains as shown last night with GFS leading the field in suggesting a change in conditions from around the 26th, well supported by its ensembles. However, the other models remain less than convinced by such a marked change suggesting a rather more gentle approach synoptically though this may be less gentle at the surface as thunderstorms become more likely towards the end of next week. As said before all other models other than GFS show a much less progressive evolution with High pressure remaining close enough to maintain at least some of the very warm air near the UK and with no major Low pressure systems to exert pressure on the High it wouldn't take much for it to rebuild and settle the weather down fully again and don't be surprised if this is hinted at over the coming days outputs. So taking all this into account on balance the weather could be a lot worse and though the very perfect Summer conditions many parts of the South have seen of late may modify somewhat there is still a lot of very decent weather shown in this morning's output.
Martin G
Kilmersdon Radstock Bath Somerset