Sunday, 29 March 2015

Weather guide Monday 30th March to Sunday 12th April 2015

This guide will be looking ahead at the next fortnight's weather, obviously the second week is much less defined and nebulous weather model- wise, therefore entailing more general a prediction and as such is more likely to be incorrect!

Last weeks highlights

A rather cool and showery start to last week, however some areas missed the showers and stayed largely dry and bright and hence temperatures not far off the late March average, much of the Midlands and the sheltered south coast of Wales reached 9 or 10c on Tuesday while showery West Wales (WW) only managed a chilly 7 or 8c with plentiful hail showers and limited sunshine. Quite a sharp frost for the parts of the Midlands Tuesday night, Pershore, Worcerstershire coldest at -3.5c, but a dry Wednesday with sunny spells and a touch below average generally, although still decidedly cool on the Cardigan Bay coast, Aberporth max 7.9c cf 11.1c inland here at Llanwnnen.

Wednesday night then wet, half an inch of rain for parts of WW, with a covering of snow over the Peak District and highest parts of Wales first thing Thursday. Thursday became largely dry and bright once more, but windy, with gale force gusts during the afternoon across the Midlands. Temperatures recovered to average by the end of the week Hereford top spot Friday at 13.1c with all locations away from high ground attaining 10c. This weekend has been milder still although with some spells of rain and quite windy, 15.5c at Pershore on Saturday while the high of 12.6c here at Llanwnnen was the highest reading of what has been a  disappointing month regards early warmth.

Week One: Monday 30th March to Easter Sunday 2015

Headline: Often cool and unsettled, showers or longer spells of rain and some hill snow; dry weekend with frosty nights

Heavy rain and strong to gale force winds across Wales on Sunday morning, parts of Snowdonia getting over an inch of rain in the past 24 hours, while winds have reached 46mph inland here at Llanwnnen and 69mph on the coast at Aberporth. An unsettled week to come with further rain and showers at times, but with dry and bright interludes. It will often be cool too, with even the chance of wintriness for higher ground.

The rain turning to sunny intervals and scattered showers this Sunday afternoon with winds easing, temperatures at their highest early this afternoon at 11 to 13c. Most of the showers dying out tonight and clear spells leading to a ground frost in some places but the breeze keeps up to prevent this for many. A dry and in places bright start to Monday, but the next Atlantic system will quickly bring over cloud and wind by midday with WW turning wet. Spells of rain then afternoon accompanied by a fresh to strong SW to west wind, with gusts perhaps to 60mph on exposed coasts and hills. WW may also see particularly heavy rain at times through the afternoon into the evening. Highs Monday an academic 11 to 13c which is about the average for the very end of March. The rain turns more showery during Monday night, still a strong NW wind driving in some showers though after midnight, and this preventing any frost.

Low pressure away to the NE on Tuesday, a cool, windy and showery day, some of the showers heavy with hail and thunder in places, a chance of sleet or snow above 300m especially during the evening.  As ever with showery days, some sheltered spots escaping with a dry bright day! Highs Tuesday between 8 and 11c (best for sheltered parts of the South Midlands and some South Wales coasts). Showers keep going during Tuesday night for Cardigan Bay, NW Wales and the NW Midlands perhaps with hail quite a feature, and some high ground such as Snowdonia may be waking to a covering of snow on Wednesday morning. The fresh NW wind restricting frost to some extent but there may well be a widespread ground frost, generally temperatures down between plus 1 and 3c. March goes out like a lion somewhat!

Cool and quite showery on Wednesday too, these still wintry on higher hills, however they should be dying down as we go through the afternoon, also sunny intervals and breezy with cool April highs of 7 to 10c. We should see an attempt at a ridge during Wednesday night, so that it should be dry with a touch of frost. This ridge may hold for much of Thursday but some doubt over this as further fronts may be coming through with showery rain at some stage during the day? However a reasonable chance of a mostly dry, bright Thursday, and certainly less in the way of wind, and highs up closer to average at 10 to 13c.

An active trough or even low seems set to sink SE across the UK during Thursday night into Good Friday so showers or longer periods of rain, heavy at times make for a generally wet start to the holiday period, although we may see a ridge drying things out eventually through the afternoon or evening. There may well be some cold air from the north drawn into Friday's sytem so that hill snow is a distinct possibilty, with even an albeit slight risk that the rain turns to sleet or snow for a time on Friday at lower levels too in places? Temperatures on the southern side of this low may be in double figures celsius, say 10 to 12c over South Wales and South Midlands on Friday morning, but with the colder air infiltrating from the north during the day and never much above 6c for Snowdonia and the Peak District where potentially it could be a snowy day, at least over the hills.

Good signs after the inauspicious start to the Easter period that things will actually turn out nice as with high pressure looking set to settle down very close by or over the UK next weekend! Some inherently cool air within this expected high though means the potential for sharp, damaging frosts on both Friday and Saturday night, -5c cannot be ruled out in places, so possibly some very cold nights for April to come. Both Saturday and Sunday look like being pleasant days with plentiful sunshine and maxima near normal in the  10 to 14c range - depending on whether a cool NE breeze occurs or not, at the cooler end if so, milder if not.

Week two: Easter Monday to Sunday 12th April 2015

Headline: Often dry, just the odd shower/ bout of rain; potentially warm and sunny around mid week

The latest GFS model run brings some weak weather fronts across the UK thus spoiling Easter Monday which would in this event be turning cloudy with light rain in places, the ECM model on the other hand keeps it fine and dry. On the whole though, week two is getting a reasonable signals for high pressure to be over or close to the UK for much of the week, bar the occasional weak front from time to time. Thus we can expect a largely dry week with sunny spells. Temperatures and cloud amounts likely to be variable from day to day and region to region, dependent on exact positioning of the highs and attendant wind directions. 

Some of the recent model output has shown high pressure locating over the Continent by the middle of week two, this would be good, as we would be getting warm SE winds and potentially temperatures into the low 20's celsius (above 70f)! Obviously a long way off this hope, and other options are there for cooler, rather cloudy anticyclonic conditions in which temperatures would struggle to reach 15c, and even some decidedly cool days for the Midlands should the high set up to our north (lucky to get max 10c). 

Of course, there is also the possibilty, and this too is suggested by some model output, and given the sheer variety of options they show at 10 to 14 days hence (such a timespan referred to by weather buffs as Fantasy Island), that it turns cool and unsettled by the end of week two! Basically by this stage (almost) anything could happen, but at least there is some prospect of fine, dry weather in the early to middle part of the week at least!

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