Good evening. Here is this evening's look at the 12 noon outputs from GFS, UKMO, GEM, NAVGEM and ECM for Saturday November 16th 2013.
All models show a cold North-westerly flow developing over the UK behind a cold front moving South on Monday. This sets up an interesting and cold spell of weather where the models diverge about outcomes quite early in the coming week.
GFS shows Low pressure sinking South over the East of the UKtowards midweek with a cold and showery flow over the UK intensifying into longer spells of rain, sleet or perhaps snow for a time North to South on Wednesday and Thursday. By Friday pressure rises across the UK with the showers dying away with sunny spells but cold weather with frost and freezing fog developing overnight's, slow to clear. Through the extended part of the run tonight an elongated ridge of High pressure persists across the UK with occasional Easterly winds in the South and Westerly winds across the North. Other than that winds are shown to remain light with rather cold conditions at the surface with varying amounts of night frosts and fogs from place to place and night to night.
UKMO tonight shows a very cold spell coming up, especially in the South as a cold plunge of NNW winds with wintry showers early in the week give way to more prolonged precipitation for a time midweek, falling as snow over the hills. The end of the week sees Southern and Eastern areas cold and cloudy with rain, sleet or snow at times while the North and West see drier weather with frosts at night. A keen and occasionally strong NE flow will blow across the South later in the week.
GEM makes much less of the midweek feature with an innitial surge of chilly NW winds and wintry showers becoming replaced by dry, cold and quieter conditions for a time away from the far East and South with overnight frost and fog. Later in the run winds settle SE and strengthen markedly with some rain or sleet at times across the South and West.
NAVGEM shows a developing Low slipping South down the heart of the UK midweek with rain and sleet in abundance across the UK with snow over the hills. Needless to say it will be cold and windy too at times and as winds settled into the NE or east across Southern Britain at then end of the week and weekend further cold rain will fall at times while the North and West becomes largely dry but cold with some overnight frosts.
ECM tonight shows a cold and unsettled phase through the middle of the week with some wintry showers or rain and sleet at times. This become displaced later in the week, through the weekend and the start of the following week with High pressure ensconced across the UK with cold weather maintained and frost and overnight fog big problems for many.
The GFS Ensembles show a short cold period, shortest in the North as Low pressure migrates to the South of the UK and High to the North. This becomes eroded as pressure becomes fairly High over the UK and uppers dilute out. There will be quite a variation at the surface though as low levels of the atmosphere could become jolly chilly under frost and freezing fog. As usual at the end of the run the weather turns much more undecided with various options being shown.
The Jet Stream shows the flow well to the North of the UK turning South down over the UK early next week with an eventual settling of the flow across the Atlantic and over the UK late in the period.
In Summary tonight the weather is about to turn colder but for how long? The models differ in the evolutions from quite early in the run with differences varying from UKMO's undercutting scenario with the High to the North and NE and Low to the SE to ECM's large UK based and persistent High pressure. All evolutions look like sustaining cold air close to the surface irrespective of uppers as the Uk would develop it's own cold pool under ECM's High pressure based outcome. Chances of snow have increased somewhat tonight as there is rather more made of the midweek feature slipping South near or over the UK. Longer term though no particularly cold weather is likely in the more distant future synoptic patterns as shown would provide potential for further cold weather down the line.
Transcript taken from:-http://www.norton-radstockweather.co.uk/Model-Analysis(2859336).htm
Martin G
Kilmersdon Radstock Bath Somerset