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Weather guide Monday 23rd December 2013 to New Years Eve

TonyH

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[font=arial][size=3][b]Very unsettled with damaging gales and flooding problems likely at times; variable but often quite chilly temperatures, some frost[/b][/size][/font]

[font=arial][size=3]Wet and windy last week, Llanwnnen had 90mm rain in the past 7 days - 35mm of this fell on Wednesday with localised flooding; rather wet for the Midlands too, Coventry having had 25mm. Temperatures very up and down some days like Monday were very mild, in fact in the early hours of Monday much of the Midlands was above 13c! Thursday was one of the colder days and some parts saw snow showers, we did here at Llanwnnen although it did not lie, the temperature dropped down to just 1c in the mid afternoon sleet and snow. Thunder also featured in the showers for parts of Wales on Thursday, and again on Saturday when a solitary flash of lightning followed by a low rumble was heard during a squall that gave a 53mph gust of wind here. Gales in places last week too, one of the strongest gusts was of over 80mph at Pembrey, Carmarthenshire on Wednesday evening. More very windy and wet weather at times in the coming week as two significant low pressure systems affect the UK. A White Christmas is unlikely although it would only take one flake to fall![/size][/font]

[font=arial][size=3]Sunday, and at least we are seeing sunny intervals, although some areas, as with this morning, are being affected by heavy showers with hail and thunder, while other areas, particularly parts of the Midlands escaping these altogether though, highs on Sunday 7 to 9c, a little above average. Showers tending to die down tonight but a few continuing for West Wales, temperatures down to 1 to 3c with a ground frost in places, coasts escaping though. Cloud and wind increases late in the night as a rapidly deepening depression heads towards Ireland. This low is the main feature of the week as it will be one of the deepest, most intense storms to pass close to the UK in many years, and will be bringing severe damaging gales on Monday - the central pressure will fall below 930mbar! The depression will track to the west of Ireland through Monday, and it will already be blowing a gale with heavy rain to greet the dawn on Monday for Wales and with these conditions quickly spreading to the Midlands through the morning. The Midlands is not likely to escape these damaging winds on this occasion as the isobars (pressure lines) are very tight across all UK. Strong to gale force south to SW winds then, inland gusts exceeding 60mph, while for coasts and hills of Wales 80 to 90mph gusts are likely, these speeds will bring down plenty of trees, cause power outages and structural damage. Not just severe gales but heavy rain too associated with this low, and once the rain starts it is set to last through to at least late evening, and will be very heavy at times, especially for Wales, so flooding too will be a problem as we go though the day for some areas. Parts of South Wales undoubtedly set to receive 2 or 3 inches of rain on Monday with an inch falling on most places. Irrelevant considering the other conditions but it will be a mild day, peak temperatures 9 to 11c during Monday evening. The rain should then turn more showery by the early hours of Tuesday, these showers heavy and quite frequent across Wales with hail and possibly thunder, a windy night but the gales should have abated inland. The low continues to deepen on Tuesday as it tracks past Scotland and may reach as low as 925mbar. Historically, the Braer storm of January 1993 saw an estimated 914mbar, but was further north of Scotland, and is thought to be the deepest extra tropical cyclone on record for the North Atlantic [url="http://en.wikipedia.org/wiki/Braer_Storm_of_January_1993"]http://en.wikipedia.org/wiki/Braer_Storm_of_January_1993[/url][/size][/font]

[font=arial][size=3]Windy and showery on Tuesday, SW winds gusting to gale force. Although winds will be SW, the air has originated over a freezing cold Canada several days previously and is categorised as 'returning Polar maritime' (rPm), and is inherently cold at height if not surface. So a chilly, windy Tuesday with showers, especially across West Wales, parts of the Midlands may escape with a mostly dry, bright day. Cold enough for sleet or snow over the hills on Christmas Eve, above 300m most favoured for wintriness, although it should not settle, many places seeing hail showers on Tuesday. Maxima on Tuesday 5 to 7c. Showers lessening overnight and with clear spells a widespread slight frost develops as the wind decreases substantially, minima by Christmas Day morning around 0c except for milder coasts. A respite from the winds on Christmas Day, we have a slack area of low pressure crossing the SW so moderate breezes at worst! Still rather an unsettled picture with some areas experiencing showers, but more of us managing a generally dry day with sunny intervals. Interestingly we are still in the rather cold rPm air and so if you do see a blob of sleet on the car windscreen on Wednesday then you have technically experienced a 'White Christmas' - I should not rush out and place a late bet though! The Midlands looks best bet for a pleasant bright and chilly afternoon walk, while West Wales will see further rain and hail showers, sleety stuff perhaps for hills. Highs of 5 to 7c for the Big Day. With clearing skies and light winds a widespread slight air frost is likely overnight, although still some showers keep going in places, especially for Wales, again with sleet or wet snow for the hills. Temperatures down to -2c locally.[/size][/font]

[font=arial][size=3]A bit of a respite again for Thursday too, a slight bump of relatively high pressure kills most of the shower activity, still some places catching them though, and much of the day fairly dry and bright with sunny intervals. Highs on Thursday 5 to 7c again and slightly cold for late December. A frost may develop for the Midlands on Thursday evening but more trouble is looming out west! Another deep low is moving quickly towards Ireland on Thursday evening bringing rain and strong winds to Wales. As this system is still 4 or 5 days off it still has to treated with a degree of hypothesis, but again there is a strong suggestion of damaging gale to severe gales affecting Wales and England on Thursday night into Friday. The GFS is this morning showing a 940mbar system tracking close to Ireland then Scotand through Friday with very tight isobars which would produce damaging gales similar to Monday, while ECM shows the low not as deep or damaging perhaps. Suffice to say Friday morning at least looks a washout with strong to gale force winds, the rain heavy in places with flooding potential although it may clear to showers pm. At least it will be mild highs around 10c.[/size][/font]


[font=arial][size=3]Longer term and the very changeable, disturbed theme continues through next weekend and towards the New Year. Atlantic lows still dominating although brief ridges will dry it up at times, albeit briefly for a day at most. Further showers or longer spells of rain, and possibly wintry showers over higher ground as we are mid Winter. Variable temperatures as lows cross, fluctuating between mild and rather cold, the risk of a few slight frosts on occasion. The chance of more gales exists for the 30th or New Years Eve but that is a long way off to speculate!
[attachment=199110:PPVG89 Monday storm.png][attachment=199111:ecmt850.048 sub 920 storm Mon night.png][attachment=199112:h850t850eu ex deep L Mon night.png][attachment=199114:ecmt850.048 sub 930 storm Mon night.png][attachment=199115:PPVJ89 windy showery Tue.png][attachment=199116:PPVL89 r cold some showers Christmas Day.png][attachment=199118:ecmt850.096 light winds chilly Christmas Day frost.png][attachment=199119:h850t850eu sh L ligh winds Christmas Day.png][attachment=199120:PPVO89 respite Th.png][attachment=199121:ecmt850.120 rain pot gales Th night.png][attachment=199122:ecmt850.144 potential gales heavy rain Fr.png][attachment=199123:ecmt850.168 unsettled weekend.png][attachment=199124:h850t850eu pot gale 30th.png][attachment=199125:ecmt850.240 more rain New Year.png][attachment=199127:mgram_Birmingham.png][attachment=199128:prcpSir~Ceredigion~-~Ceredigion very wet Ceredigion.png][attachment=199129:prmslWarwickshire two intense lows.png][attachment=199130:t850Warwickshire fluctuating but r cold temps.png][/size][/font]

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