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Weather guide Monday 28th Jan to Sunday 3rd February 2013 (West Wales and the Central MIdlands)

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TonyH

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[size=4][color=#000000][font=arial][b]Headline: Very unsettled and windy, spells of rain and showers, heavy at times, localised flooding, cooler later[/b][/font][/color]

[color=#000000][font=arial]What a wintry week! Not especially cold for West Wales, surprisingly, with all the snow about, here at Lampeter there were no 'Ice days' and no hard frosts or windscreens to scrape. It was a very overcast spell, the cloud blanket preventing temperatures from falling below -4c here. However the 9cm snow which fell here on Friday 18th only gradually thawed, and was still covering more than half the ground surface on Friday 25th. A week of lying snow is quite an achievement in these temperate Isles, although in November/ December [b]2010[/b] the snow stuck for a fortnight. Warwickshire on the other hand, has had lots of snow and low temperatures with 6 ice days (max below zero) out of the 8 days to Wednesday at Coventry. Bablake School Weather Station ([url="http://bws.users.netlink.co.uk/"]http://bws.users.netlink.co.uk/[/url]) reported the greatest snow depth since 1991 last week (15cm), a measure really of how lacking deep snow has been in that part of the world over the past 22 years. [/font][/color]

[color=#000000][font=arial]Surprise snowfalls that were poorly forecast all around affected South and West Wales on Wednesday and caused some disruption, especially in the Llanelli area, parts of Pembrokeshire and West Ceredigion. Unusually, Llanelli had two quite heavy falls within 5 days. People sometimes ask 'will it snow here tomorrow?' and seem perplexed when the answer is a 'maybe', 'perhaps' or 'possibly'! There are many factors involved with snow prediction so that it is impossible to be certain even a few hours before a snow event, as it's almost always a case 'nowcasting' - looking at the radar, traffic cams and out of the window! There is often a fine line between whether it will rain or snow at a given location. Some of the factors involved:[/font][/color][/size][list]
[*][size=4]height above sea level (places above 200m are much more snowy that near sea level),[/size]
[*][size=4]air temperature close to the surface (closer to zero the better for snow, although it may still rain below zero)[/size]
[*][size=4]temperature up in the clouds (rule of thumb, below -5c means snow will fall)[/size]
[*][size=4]dew points MUST be below zero for snow to fall[/size]
[*][size=4]wind direction - slight shifts make big differences, example SE cold, dry Continental air and snow, southerly moist, milder and rain[/size]
[*][size=4]heavy rain cools surrounding air through evaporation and may turn to snow[/size]
[*][size=4]also local topography, 'thickness' of the atmosphere, etc.[/size]
[/list]
[size=4][color=#000000][font=arial]Interestingly, most rain in the UK starts as snow high in the atmosphere[/font][/color]


[color=#000000][font=arial]Derek Brockway, our BBC Wales weatherman, had some stick on Twitter this week after not forecasting a heavy snowfall in SE Wales on Tuesday, and then again the unexpected heavy falls in SW Wales on Wednesday. This guide is intended to be a general outlook to the coming weather over the week and is not a useful tool for picking out localised heavy snow 3 days in the future, especially given the Met Office did not realise even as the event was underway! Part of the fun with the weather is that it never fails to make fools of the forecasters![/font][/color]

[color=#000000][font=arial]Thunderstorms for many of us in West Wales yesterday evening with some really bright flashes of fork lighning - everything but the kitchen sink lately! Very mild overnight, 11c maxima for Sunday in the early hours here under that warm sector air mass!. All this weather the result of a very deep low to the south of Iceland (938mbar). Nice to see the sunshine this morning... however heavy showers with hail, and again a clap of thunder in places, are set to move into West Wales this afternoon, with an isolated shower into the south Midlands also later, a windy afternoon temperatures reaching around 8c. Another deep low develops out in the Atlantic tonight and is set to bring very windy and wet weather for Monday as its fronts cross the UK. First of all clear spells and only a few showers tonight leading to a ground frost for many by morning, excepting Pembrokeshire where cloud and strong winds arrive by dawn heralding a wet day. Rain, heavy at times through the afternoon, some torrential downpours for West Wales, driven by a strong to gale force SW wind, making it feel quite cold, even though temperatures eventually reach around 8c late on Monday afternoon. The rain clears to a few showers in the evening.[/font][/color]
[color=#000000][font=arial][attachment=158124:PPVA89 VDL 938 showery bright today.png][attachment=158125:PPVG89 wet windy Mon.png][/font][/color]

[color=#000000][font=arial]Yet another vigorous low pressure system comes at us from the Atlantic on Tuesday, this one containing very mild sub-Tropical air. With all this mild, moist air hitting the Welsh hills throughout Tuesday some large amounts of rain here with flooding likely in some areas, as there will be 50 - 75mm rain falling in places. For the MIdlands a cloudy, very mild day with spells of mostly light rain and drizzle. Temperatures on Tuesday reaching 11c for West Wales and 13c in parts of the Midlands. The trailing front from the system gives further spells of rain to south Wales and the south Midlands in particular well into Tuesday night, but drier for northern parts of our regions. Wednesday sees cooler, showery westerly winds, but with some sunny spells developing, especially through the afternoon as a feeble ridge edges over. This transient ridge could just about last long enough for a ground frost to develop on Wednesday night. [/font][/color]
[color=#000000][font=arial][attachment=158126:PPVJ89 Tue copious rain WW v mild.png][attachment=158127:ecmt850.072 next DL L to NI Tue heavy rain espWW v mild sector.png][attachment=158128:PPVL89 bright showery Wed.png][attachment=158129:ecmt850.096 bright showers Wed.png][/font][/color]

[color=#000000][font=arial]The next low moves towards NW Britain on Thursday, with further bands of rain and showers crossing all parts. Temperatures a little above the January average on Thursday reaching 7 to 9c. On Friday the low gets into the North Sea so dragging down colder NW winds, more rain or showers at times on Friday, and possibly sleet or snow for Welsh hills and the Cotswolds, maxima 6 to 8c, and feeling quite cold, although perhaps a drier day for south Wales and the south Midlands this.[/font][/color]
[color=#000000][font=arial][attachment=158130:metslp.120 unsettled colder Fri.png][attachment=158131:ecmt850.144 unsettled colder Fri.png][attachment=158132:h850t850eu FRi colder showery.png][/font][/color]

[color=#000000][font=arial]Next weekend, as usual subject to change, as it is a long way off to forecast! Hinting at a drier interlude with high pressure ridging into the UK from the SW, there will still be troughs coming over the top of this high, so some rain at times, but probably nothing like there will have been earlier in the week, with generally lighter rain or showers over next weekend. Where the cloud breaks there will be the risk of overnight frosts as we will be in a chilly NW flow by then.[/font][/color]
[color=#000000][font=arial][attachment=158133:ecmt850.168 bit of cold R weekend.png][attachment=158134:h850t850eu drier weekend cool.png][/font][/color]

[color=#000000][font=arial]--
Follow me on Twitter [url="https://twitter.com/Lampeterweather"]@Lampeterweather[/url][/font][/color][/size]
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Excellent read as always Tony, many thanks! Think you may mean Nov-Dec 2010 for the fortnight of lying snow rather than 2012?

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[quote name='virtualsphere' timestamp='1359290556']
Excellent read as always Tony, many thanks! Think you may mean Nov-Dec 2010 for the fortnight of lying snow rather than 2012?
[/quote]


Many thanks amended now!

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[quote name='sarafandjak' timestamp='1359295645']
Thought it was going to be dry sunny day, sleet, rain now
[/quote]


I don't cover the far north Midlands, however it always looked showery to me today, although some areas are escaping with a dry, sunny afternoon, as is usually the case in such set ups.

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I made quite a few errors (mainly spelling) this week, had to rush as work in the afternoon!

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