HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY THURSDAY DECEMBER 18TH 2014. NEXT UPDATE FRIDAY DECEMBER 19TH 08:00 THE CURRENT GENERAL SITUATION A strong and mild WSW flow will be replaced by a colder NW flow later today, tonight and tomorrow behind a SE moving cold front. MODELS-2 WEEK HEADLINE Remaining changeable with rain at times especially across the North and West with snow on hills there at times. Becoming colder post Christmas with some snow and ice in places, at least for a time. THE JET STREAM ENSEMBLE FORECAST The Jet Stream Ensemble forecast shows the flow slowly moving South to lie South of the UK post Christmas as pressure rises over the Atlantic and to the NW temporarily with Low pressure affecting the UK and NW Europe and High pressure near the Meditteranean. GFS OPERATIONAL The GFS operational this morning shows a mild SW flow in the run up to Christmas with occasional rain and drizzle in a strong WSW flow. Christmas itself is shown to be rather cold with a NW airflow and some wintry showers across the North and East with some frost at night. Post Christmas and in the lead up to the New Year a cold plunge between Low pressure to the East and High to the West would give rise to our best chance yet this season of snow showers more generally in a keen North wind and harsh night frosts. The cold would then most likely be maintained into the New Year as High pressure becomes dominant over or near the UK with hard frosts and freezing fog likely events under such synpoptics. THE GFS PARALLEL RUN As one would expect in the first week of its run and the lead up to Christmas the mild weather the operational shows is duplicated with a similar scenario over Christmas too of a chillier NW flow with wintry showers, especially in the North with frost at night. Post Christmas the UK comes under onslaught fom a bitter North and later NE flow as High pressure builds strongly over the NW Atlantic and in the Greenland area. There would plenty of snow showers and even longer spells of snow especially in the East and perhaps SE for a time with widespread hard frosts at night and temperatures struggling to freezing point by day too in places. THE GFS CONTROL The GFS control run shows similar synoptcs to the other two in the run up to Christmas and indeed Christmas itself before the cold plunge from the North takes place soon after. However, on this run the plunge is less dominant and is quickly shunted East by sinking High pressure to the West of the UK allowing a milder Westerly or NW flow to round the High and down across the UK towards the New year with cloudy and benign conditions in milder temperatures likely then. THE GEFS ENSEMBLES While in some ways I like the Ensembles this morning with some mouthwatering synoptics shown for the snow hungry fraternity my concern lies with the longevity of such an attack and pressure rise to the NW. There is plenty of evidence for this to subside later in the period to return less cold conditions across the UK in an unfavourable Jet flow late in the period. UKMO UKMO today shows the UK under a strong Westerly or SW flow to start next week lying between High pressure to the South and Low to the North. This maintains mild and in places unusually mild weather with rain and drizzle at times until Christmas Eve sees a cold front crossing SE over the UK with colder temperatures, bright weather with some wintry showers in the North as we enter Christmas. THE FAX CHARTS The Fax Charts today show a cold front clearing the SE tomorrow to leave a cooler and showery NW flow across the UK. Then a returning and large warm sector behind a warm front advances across the UK later in the 5 day period with mild WSW winds and occasional rain and drizzle for all to start the Christmas Week. GEM GEM also maintains a mild Westerly flow predominating across the UK through the beginning of next week before a cold fron crosses SE towards Christmas Eve leaving Christmas in a rather cold and showery NW flow, deepening in intensity as we exit Christmas in response to a strong pressure rise across the Atlantic with a deep Low pressure area developing over Scotland by Day 10 with cyclonic and cold winds across the UK with showers or longer periods of rain, sleet and snow for all, the snow mostly but not exclusively concentrated towards higher levels everywhere. NAVGEM NAVGEMs term of just 180hrs makes it harder to decipher where the model takes us thereon but as far as it goes it too shows a chillier NW flow across the UK at Christmas following a mild start to Christmas week in WSW winds and rain and drizzle. To my eyes it looks less confident in developing the cold depth that some of the other output shows post Christmas but this is speculative to my untrained eye. ECM ECM this morning shows a classic example of close but no cigar with many of the ingredients to bring cold to the UK thwarted on this run by pressure too High over Southern Europe and High pressure near Greenland only serving to spawn large and wet depressions close to the UK as the cold arctic winds engage with the warmer air to the South of the UK. While Christmas itself would turn increasingly cold and wintry in places with some snow in showery form especially on Boxing Day it looks like wet and wild weather could be developing post Christmas rather than cold and snowy but Im sure that there will plenty of changes shown in this evoluton over the coming days. ECM 10 DAY MEAN The ECM 10 Day Mean Chart supports the highest chance being that High pressure will lie to the West of the UK with Low pressure over Scandinavia with a cold Northerly flow across the UK with snow showers in the North and East in particular. This overall slant is made up of a variety of members supporting cold and snowier solutions along with some milder Westerly ones under a sinking High. NOTABLE TREND CHANGES FROM PREVIOUS RUNS Trends this morning have maintained their strongest indication of a pattern change afoot as the Azores High becomes less influential as pressure rises to the West and perhaps NW with a stronger dig of cold North winds at least for a time likely post Christmas. MY THOUGHTS The charts this morning do show the most potential for those seeking a pattern change to something more seasonal than they have at anytime so far this Winter with some mouthwatering examples of cold, snowy charts turning up in some of the output this morning. The GFS Parallel run is a real gem for those liking a sustained cold and frosty anticyclonic spell following a snowy period and would give rise to some very low temperatures should it verify. Others including the ECM operational show a much more tentative dip into icy waters as it quickly turns a cold Northerly into a cyclonic Westerly as the opposing air masses generate powerful Low pressure close to the UK later with a more patchy mix of rain, sleet and snow. However, if the positioning of this trough is further to the East then it too could dive us into a direct Northerly plunge soon after with a more widespread risk of snowfall. My concern still lies as last night that an Atlantic High with the Jet flow riding over the top would eventually sink the pressure pattern South and allow milder air to slip down across the UK around its Northern flank towards the start of 2015 especially if pressure is not permitted to ridge high enough into the Greenland area and there are plenty of options shown for this to be the end result unfortunately. The ECM 10 Day Mean Chart shows good support for Northerly winds to be the most likely option in 10 days time with snowfall likely for those areas prone to it under a direct Northerly which may not do much for the majority of the UK under shelter of such a flow. If I had to take a stab at where the ECM mean takes us in the following days after Day 10 I would edge my bets that a UK High of sorts would be likely with very cold and frosty weather likely rather than sustained snowy weather. However, these are very exciting times for model watchers as at last there is a positive sign of change and there is likely to be many ups and downs over the coming days while the computers number crunch the solutions but I would urge that the words cautious optimism should be adhered too in the run up to Christmas for your own sanity as nothing is a given when it comes to predicting cold and snow in the UK in Winter and if things fail to materialise it wont be the first time I and Im sure others on here and elsewhere end up eating humble pie with my own family when things go belly up. Heres to another day of frenetic model watching. Source and credit .................... norton-radstockweather.co.uk/index.htm
Posted on: Thu, 18 Dec 2014 14:04:10 +0000
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