HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY MONDAY SEPTEMBER 29TH 2014.
NEXT UPDATE TUESDAY SEPT 30TH 08:00
THE CURRENT GENERAL SITUATION. A slack pressure gradient remains in place across the Brtish Isles with a front reaching NW Britain tomorrow and a shallow pool of instability in the upper atmosphere crossing NE over Southern Britain today.
MODELS-2 WEEK HEADLINE Continuing largely benign this week with a lot of cloud and a little rain at times especially in the NW. Becoming more unsettled and cooler for all later with more widespread rain at times.
THE JET STREAM ENSEMBLE FORECAST The Jet Stream remains positioned to the NW of Britain for much of this week before it troughs South over the UK next weekend and persists in this trough pattern close to the UK for most of week 2 with varying strengths.
GFS The GFS operational this morning shifts High pressure steadily East and declines it later in the week as pressure falls across the UK from the NW. After a benign start to the period SW winds freshen everywhere late in the week with a much more unsettled feel to the weather everywhere across Britain in Week 2 with occasional rain or showers and fresh winds too lowering temperatures towards the seasonal average as Low pressure engulfs the UK or lies just to the West.
THE GFS ENSEMBLES. The GFS Ensembles are symbolic of the operational through the first half of the run and while some continuation of occasionally wet and windy weather remains through Week 2 pressure is shown to be High to both the East and SW and a linking ridge could cut off the unsettled weather later with just the extremities North and South liable to see further showers in an otherwise return to more benign conditions again.
UKMO UKMO this morning shows High pressure declining later in the week. After a weakening trough crosses East over Wednesday with just a little rain SW winds freshen more markedly by next weekend with more active fromts bringing rain SE across the UK by the end of the run with temperatures falling back towards average values.
THE FAX CHARTS The Fax Charts agree with the pattern of the raw data and remain unedited in any major way. Therefore the weather will be benign through the week but not discounting a little rain midweek as cold fronts are shown to slip SE. A ridge following shows a couple of drier and for some fresher weather days before wind and rain moves down from the NW under a more active SW flow by the weekend lowering temperatures then.
GEM The GEM operational also manintains the trend shown by other output this morning with a shift away from the fine and quiet conditions of much of this week with just a little rain for a time midweek to a much more active weather pattern with a concoction of Lows and troughs circling the UK next week with rain at times along with fresh winds and temperatures generally much cooler than of late.
NAVGEM NAVGEM too shows a decline in conditions by next weekend and the start to the new week with Low pressure becoming resident close to northern Britain with troughs swinging East in the flow. Temperatures will fall back to average after most of this week stays somewhat warm at times and winds will be much more noticeable.
ECM The ECM operational today completes the set with unsettled and windy weather arriving from the NW by the weekend as a deep Low moves down across the UK giving strong cyclonic winds with spells of rain and showers in much cooler weather than of late to start next week.
NOTABLE TREND CHANGES FROM PREVIOUS RUNS There is finally good cross model support for the trend to cooler and more unsettled, windier weather for all areas by the end of the week lasting through week 2.
MY THOUGHTS The models continue to strengthen there trend towards a much cooler and more unsettled period of weather starting at the end of the working week and extending SE to cover all of the UK by the end of next weekend. Changes will feel marked as we have enjoyed some very protracted warmth and calmness to the weather of late so the increase in wind and more pronounced rainfall events will enhance the feel of the lower temperatures we will receive. The change of weather will move down from the NW and with the Jet buckling South to engulf the UK in a trough like form at the weekend and sustaining this pattern well into next week if not beyond. So once the unsettled weather arrives it will probably remain sustained, in particular as some cold air advecting West across Scandinavia next week is shown by several model runs this morning which once engaging with the unstable air over the UK could give rise to even more potent depressions towards the end of the period. However, as always there are always exceptions to this theory and the GFS Ensembles do show a return to High pressure as heights to the East and SW remain High possibly with a linking ridge over the UK late in the period to bring extensive mist and fog problems if that theory evolves rather than wind and rain. Having said all that this morning offers good overall support for Autumn proper to arrive next weekend with some decent amounts of rain and fresh breezes for most areas at times from then on with the much cooler feel of conditions becoming the main talking point as daytime temperatures fall some 5C or more from current daytime values across the South.
Martin G
Kilmersdon Radstock Bath Somerset