Good evening. Here is the report on the 12 midday output of GFS, UKMO, GEM, NAVGEM and ECM for today Thursday September 19th 2013.
All models show the pattern that's been shown for days now in that the last rain for a time has recently cleared SE England leading to steadily rising pressure from now on from the South and SW. A ridge crosses East tomorrow with dry and fine weather for most in a light to moderate Westerly breeze with sunshine and passing clouds and temperatures around average. By Saturday a warm front will be moving NE across Northern and Western Britain carryng a lot of cloud and some drizzly rain in places for a time before drier air reaches the SE later and works it's way further North across the UK on Sunday and Monday. It's from that point on that the pattern between the models diverge.
GFS shows High pressure declining away slowly SE through the week with pleasant weather remaining intact for most of Britain for quite a while. Late in the week pressure will of fallen sufficiently to allow fronts to push in from the West and SW with rain a risk for many next weekend as temperatures fall. Then through the rest of the run Low pressure areas from the SW then North come into play for the UK with an ever cooling air mass covering the UK to bring very cool and unsettled conditions to end the run.
UKMO shows High pressure over the top of the UK next Wednesday with sunny and warm daytime weather with clear, cool and potentially foggy nights.
GEM shows pressure falling after midweek with the UK declining away as fronts push up from the SW with some rain and cooler conditions reaching many areas over the weekend.
NAVGEM is looking very isolated tonight in that it shows a rapidly deepening Low near Southern Ireland as early as Tuesday with strong winds and rain developing for many by midweek as the Low ambles around Ireland before sliding slowly back South late in the week. The rain would be most prolific in the South and West with the North and East less likely to see much rain from this scenario closer to High pressure.
ECM tonight shows a large High having developed South of Iceland next Tuesday absorbing our weekend High into a ridge early next week. After a few warm days temperatures would likely steadily fall back to average levels with night's cool and misty with some radiation fog formation under light winds. Later in the week things show signs of turning more unsettled as pressure falls and Low pressure develops to the SW and with a cold feed not far to the NE with rain likely for many next weekend in much cooler air.
The GFS Ensembles show good support for a warm period over the weekend and start of next week before cooler conditions look like developing as well as more unsettled conditions with rain at times from the 27th in the South. The North show a rapid cool off earlier than further South with a huge spread between members from as early as midweek next week.
The Jet Stream shows the flow migrating North of the UK over the next few days with a cut off circulation down to the SW. As this small feature expands it draws down the SW to NE flow more and more SE on its trajectory through the UK so that indications are shown tonight of the flow perhaps moving South of the UK in the outer limits of the run.
In Summary the weather shows two phases tonight. the first phase will occur between now and Tuesday when gradually warmer conditions are likely to develop with some warm daytime sunshine with cool and misty nights. The second phase is from Tuesday onwards when indications are that High pressure will re-position or decline sufficiently enough to allow lowering temperatures, cloudier and eventually more unsettled conditions to develop across the UK as a whole. It is too early to say whether this trend will be maintained or dropped over the coming days but there are growing indications that the fine and warm conditions that looked like lasting some considerable time a few days ago may be a rather shorter spell than we might of hoped.
Originally Posted by: GIBBY