Sunday, 19 April 2015

Weather guide Monday 20th to Sunday 26th April 2015

Headline: Dry and quite warm with sunny spells; turning cooler and unsettled from Friday (belated April showers!)

Last week's highlights

Last week was completely dry (Monday onward) almost everywhere, and it was often rather warm for April, particularly for inland Wales and the West Midlands with several sunny days. There were a few slight frosts or at least ground frosts in many inland places: 

Some rain for most places for a times last Sunday, this cleared to give a widespread air frost inland, lowest at Shawbury, Shropshire -2.7c, but temperatures soon recovered with the strong April sunshine and 18.2c was attained at Pershore.  Unseanable heat flirted with southern England midweek, France getting temperatures above 30c and SE England 25c recorded in places. Nearer home Hereford and Coleshill reached a warm 20.3c on Tuesday with sunny skies, but much cooler along the south coast of Wales where Pembrey managed just 11.7c and was presumably plagued by sea mist. NW Wales was also quite cool Tuesday, a maximum of just 10.7c at Capel Curig, while at Llanwnnen it was a gloriously sunny afternoon with a respectable high of 16.3c.  A similarly very pleasant day for many areas Wednesday, quite high temperatures for the Midlands, widely above 19c, best being 20.8c Pershore and 20.6c Little Rissington, NW Wales dull and quite cool however with highs of just 10c or so. 

An east to NE breeze meant West Wales (WW) was favoured for warmth and sunshine Thursday onwards, with Thursday itself 19.4c at Llanwnnen - this after a dawn ground frost. Still much cooler for many western and northern coasts though, just 12c the best at Aberporth due to the breeze off a still cold sea, and also a cool though bright day on Anglesey. Again with the NE breeze WW continued to fare better on Friday being reasonably bright and warm while much of the Midlands kept a lot of cloud and subsequently supressed temperatures. Maxima on Friday illustrate the favourabilty of WW in a NE flow during Spring with Llanwnnen reaching 17.6c cf. just 11.8c at Coventry. The Cardigan Bay coast even managed 17c Friday with the breeze off land and WW was the warmest part of the country. Sunny for all Saturday (an unbroken 13 hours for some places) and rather warm for WW and the Marches, but nearer average (14c) over the Central and East Midlands with that cool ENE wind.

The week ahead

More fine and quite warm weather to come this week, temperatures pushing 21c (70f) for some areas midweek but the weather is set to breakdown from Friday with an unsettled weekend as the more traditional April showers arrive belatedly for the end of the month! Risk of ground frost for many nights this week given clear periods as winds fall generally light. 

After a touch of frost in places (-0.7c here at Llanwnnen) and a bright start, Sunday afternoon sees plenty of cloud but with some sunny intervals (especially for Pembrokeshire). Just the chance of a light shower affecting parts of the Midlands this afternoon but essentially another dry if rather cloudy day. A rather cool day, maxima 11 to 13c although 15c for brighter parts of WW, with a light or moderate NE breeze. High pressure centred over northern UK through to midweek so a dry picture and with winds perhaps turning more ESE we should be seeing decent sunny spells raising temperatures into the warm category:

Skies may clear on Sunday night leading to a widespread ground frost and touch of air frost locally. Still some troublesome areas of cloud knocking about during Monday but most areas should see some sunny spells, with the best of the sunshine over WW, highs between 15 and 18c and dependent on sun amounts with fairly light east breezes. Clear breaks on Monday night with local frost, minima generally 1 to 4c. Hopeful that Tuesday sees more widespread decent sunshine amounts and be reasonably warm (max 17 to 19c), although with an east breeze temperatures still somewhat restricted for the East Midlands (max 14 or 15c). Once more with clear periods expected, a widespread ground frost cannot be ruled out for Tuesday night, down close to 0c in places.

Winds should have more of a SE tendency about them by Wednesday and such subtle shifts as this may profoundly affect the weather. A SE flow would waft in warmer air from off the near Continent, so we should all get a warm fairly sunny day and highs of 18 to 21c, however some models still keep a North Sea influence (ENE breeze) and subsequently inhibited temperatures over the Midlands (max say 15 or 16c), with some areas of cloud too, although once more West is Best!  Perhaps less of a frost risk for Wednesday night with the anticipated slightly warmer airmass over us. High pressure declines by Thursday but still a legacy ridge across most of the UK means another largely dry and fine day. Decent sunny spells are expected with temperatures reaching 18 to 20c, just the slight chance of a few showers later in the day especially for more southern parts.

Changes afoot from Friday to cooler and unsettled weather as pressure drops across the UK. Hard to detail this breakdown but we may well see quite a deep trough of low pressure form over the UK during next Friday into the weekend bringing showers or longer spells of rain and lower temperatures. The low could deepen sufficiently, and as shown by some of the models, to give a spell of particularly wet and windy weather at some stage during Friday or Saturday. After this spell of rain the weekend looks like being cool and showery but with dry, sunny intervals and with the wind shifting into the NW expect some heavy hail showers and chilly winds. Any clear spells by night means a continued risk of ground frost, perhaps more especially on Saturday night when locally temperatures could potentially drop below zero should the wind fall light. The cool and unsettled theme could then last into the start of May!

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