Good evening folks. From a sweltering West Country here's tonight's report on the midday outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Thursday July 18th 2013.
All models show High pressure centred over Northern Britain with a developing if light Easterly flow setting up across England and Wales. The net effect of this will to temper the intensity of the heat over Central and Eastern areas over the next two or three days as low cloud drifts in from the North Sea night and morning. Any threat of showers over the coming days is so remote it barely warrants a mention with all areas enjoying plenty more very warm sunshine after cloud clears the East each morning.
GFS then shows next week staying hot and humid with a few thundery showers early in the week and rather more later on as a developing Low pressure changes the complexion of the weather entirely next weekend as cool and wet weather develops from a slow moving Low over Southern Britain by then. Through the rest of the run tonight the weather remains cooler and more changeable with rain or showers at times as cooler Atlantic winds maintain Low pressure close to the North.
The GFS Ensembles continue to show the period of change as the 26th to 27th with cooler and more unsettled conditions developing from the SW. The operational one was a cold outlier though from the inception of the cooler conditions however the general pattern shown within the ensemble pack does offer good support for the operational's general evolution.
The Jet Stream shows a worrying shift towards moving South of the British Isles from about a week to 10 days time.
UKMO tonight continues to show a flat pattern covering the British Isles over the middle of next week with hot and humid air near the surface and cooler unstable uppers riding over the top giving rise to the likelihood of some big thunderstorms as we move deeper into next week.
GEM shows pressure falling to the South through next week with a fresh Easerly breeze across England and Wales. Thundery showers would be fed up into Southern Britain at times while the north holds on to something drier and warmer as a ridge holds sway close by.
NAVGEM shows a UKMO type pattern with a shallow and thundery trough straddled across the UK in the middle of next week. With warm air still in place across many areas thundery showers will occur in places at times but may not be widespread with some places staying dry and warm.
ECM though showing an increase in humidity and the risk of thunderstorms next week, high temperatures remain and High pressure albeit weak and somewhat ill defined by the end of next week is still close enough to give some very warm and sunny conditions at times between the showers. There doesn't look much impetus in making any unsettled characteristics to the weather from next week's charts into a full blooded breakdown with Day 10 leaning more towards a more NW/SE split developing with fine and dry conditions looking like returning to the South and East with some rain at times and cooler air in the North and West.
In Summary it's a mixed bag tonight with GFS flying the flag in the breakdown corner with ECM and probably NAVGEM less convincing on this score with further fine and warm weather shown with the occasional summer thunderstorm possible at times. GFS has showed this more progressive change now for some days and backed by it's ensemble data we cannot discount it but it does seem isolated when placed in context to the other models who prefer a more gentle breakdown in synoptics with scattered thunderstorms in continuing warm conditions more likely than general cool Atlantic winds. It's a case of more runs required I'm afraid tonight.
Originally Posted by: GIBBY