Good evening folks. Here is my review of the midday reports issued by GFS, UKMO, GEM, NAVGEM and ECM for today Saturday July 20th 2013.
All models suggest changes afoot as we move through the coming week though the extent and effects of these changes on the surface differ somewhat between the outputs. The High pressure close to Northern Britain remains in place a while longer with the cooler cloudier phase of today, tonight and for a while tomorrow being replaced by a surge of hot and humid weather exported from Europe as winds turn more towards the SE. In addition pressure will be falling to the South and SW to some degree or another and the risk of thunderstorms relevant to this pressure fall moves slowly North into the UK over the next 72hrs and most likely further North too by midweek or soon after.
GFS then holds Low pressure out to the West and SW of the UK for the remainder of next week and weekend with showers or longer spells of rain likely, especially in the West and with temperatures only slowly falling back through the second half of the week and weekend some thunderstorms are still possible at times. In the second half of the run the there is very little change until we move beyond the Day 10 time point when a new Atlantic Low brings a more definitive drop in temperatures with fresh Westerly winds and rain at times in a typical Atlantic Westerly set up.
The GFS Ensembles show a two phase cool off tonight. The first one commences on the 24th as the first wave of thundery weather moves North. the second, following a temporary warmer spell in the SE affects all areas from the 28th when Atlantic rain bearing troughs take over proper with average temperatures with wind and rain likely from thereon till the end of the run.
The Jet Stream Forecast tonight is as this morning with the kindly flow blowing well North of the UK dissipating as I type with a new arm already entering the West Atlantic on a collision course with the UK from the middle of the coming week. It then holds it's position blowing East over or close to Southern Britain for the duration of the remainder of the run.
UKMO tonight has a Low pressure complex over Ireland midweek which opens out across Southern Britain by next weekend. The net result is a thundery breakdown before midweek before a slow decline in temperatures looks likely with a typical heady mix of sunny intervals and thundery showers to end the week when it may well still feel quite warm out and about in light winds.
GEM tonight is less enthusiastic about much in the way of a thundery breakdown as it shows a weaker thundery band of weather moving slowly North and East over Tuesday and Wednesday. Later in the week a slow cool down develops as Low pressure commands control close to the NW and West of the UK with increasing amounts of cloud and showery rain to take us through next weekend and the end of the run.
NAVGEM shows a slow progression to rather thundery conditions through the week with a showery theme continuing on through to the end of it's run tonight as slack Low pressure meanders around Southern Britain in slowly cooling air.
ECM tonight shows a less thundery scenario too to end the hot spell with just isolated storms early in the week and perhaps something a little more organized crossing the SE Tuesday before a slow cool off is associated with sunshine and showers for the rest of the week with the West seeing the most showers while the SE maintain some reasonable temperatures for a while. By next weekend with Low pressure close to NW Britain a sunshine and shower mix seems likely with some SE areas still seeing a lot of dry if cooler conditions. The end days of the run do show a mobile Westerly Atlantic flow as a conveyor belt of troughs and disturbances run East across the UK in temperatures much closer to average for all.
In Summary tonight it still looks like a change to cooler weather is on the way. It looks like the first half of the week will see some residual heat with some thunderstorms in places before a gentle decline in temperature values looks odds on as winds turn to a fresher South-westerly later in the week with further showery rain at times. Once this more Atlantic borne weather establishes it looks like it could last for a time before we can look either SW or NE for our next spell of fine weather to hopefully develop as we move into August.
Originally Posted by: GIBBY