Sunday, 2 August 2015

Weather guide Monday 3rd to Sunday 9th August 2015

Last weeks review: Very cool and unsettled becoming drier and warmer

24th -29th July was an almost unprecedented cool spell for what is on average the warmest time of the year. Here at Llanwnnen the temperature during these 6 days did not exceed 18c (the late July average being 21c) and with several notably cool days. Higher and more exposed parts of Wales were shockingly cool for High Summer with constant Autumnal temperatures and weather conditions, Capel Curig in Snowdonia failing to reach just 60f (15.6c) during this same period. Late July was also very dull, especially across Wales, at Llanwnnen there was only an estimated 17 hours sun during the 8 day period of 20th - 27th inclusive, bearing in mind that a single day of unbroken sunshine at this time of year would provide almost 15 hours worth.

Last Sunday was cool with rain at times (Pershore 18.1c, Milford Haven 18.0c) although much of the North Midlands and North Wales did not exceed 16c. 28mm rain fell at Foel Friog, near Machynlleth (Powys) on Sunday, 20.0mm at Market Bosworth (Leic) in the 24 hours to 0600 Monday and 19.8mm at Coventry for the meteorological day ending 0900 GMT.  Cool, rather cloudy and breezy with some mostly light showers Monday. Very cool across most of Wales in particular, some places not bettering just 15c (Capel Curig 13.9c) while somewhat better over the central Midlands (Coleshill 18.5c). The 14.8c max here at Llanwnnen is the lowest I have recorded so late in July in the 10 year record. Sunny intervals and a few showers scattered about during Tuesday, some localised heavy downpours, temperatures well below average once more and another breezy day (Church Lawford 19.3c, Milford Haven 17.1c). Some places did stay completely dry on Tuesday, as is the nature of showery conditions, and Herefordshire saw plentiful sunshine with 11 hours recorded at Shobdon.

Cool with a scattering of showers once more for Wednesday, parts of NW Wales and the West Midlands saw more frequent and at times heavy showers, while much Pembrokeshire and the SE Midlands tended to miss the showers (Nottingham 18.5c, Pembrey 18.5c). Very cool indeed at Capel Curig max 13.1c and Cardigan Bay (Aberporth 15.1c). Thursday was mainly dry and bright but still very much on the cool side for July (Pershore 19.2c, Mumbles 17.5c) and especially around Cardigan Bay (Aberporth 14.8c) as well as Snowdonia. An exceptionally cool July night followed with a ground frost in places by dawn Friday. At Llanwnnen the air temperature fell to +0.7c (a record) with a ground frost - this the first time in my life I have witnessed a July frost! Elsewhere it was the coldest July night on record or for decades in many places, e.g. at Coventry the low of 4.7c was the coldest in July since 1990. Some other minima Tirabad (Powys) 0.9c, Shobdon 2.6c, Pershore 2.7c and Trawsgoed 3.1c. The final day of the month did at least become more clement with sunny spells and near normal temperatures (Hereford & Pershore 21.3c, Llanwnnen 19.8c), however parts of WW were still cooler and cloudier (Capel Curig 16c).

Weak but troublesome fronts gave a lot of cloud and showery rain across Wales on Saturday, this only falling in quite small amounts though away from Snowdonia (Capel Curig 15mm), while the Midlands was mostly dry and bright, at least until late on when a few showers arrived. Temperatures mostly below average yet again (Pershore 21.0c, Aberdaron 15.3c) although southern Cardigan Bay fared better (Aberporth 18.3c) as did the Swansea area (Mumbles 19.1c) both being close to average.
Unusually cold July night

July ground frost Llanwnnen

July review: Rather cool, dull and unsettled; wet in places

In spite of the hot opening to July when parts of the Midlands reached 34c on 1st, the rest of the month was rather uninspiring and with the final week or so (as detailed above) decidedly cool and cloudy. Sunshine levels below average virtually everywhere with NW Wales very dull (Shobdon, Herefordshire 184.5 hrs, Llanwnnen est 144 hrs). Rainfall for July varied from just below average to rather wet. Some July rainfall totals:

Valley, Anglesey 66.6mm
Llanwnnen 96.6mm  95%
Aberporth c. 94mm
Pembrey Sands c. 72mm
Llanelli 91.4mm
Mumbles, Swansea 73.2mm
Lawrenny (Pembs) 86.6mm

Nottngham c. 60mm
Coleshill 66.0mm
Coventry Bablake School 71.6mm 143%
Long Lawford, Rugby 64.4mm 115%
Church Lawford c. 60mm
Hereford 52.2mm
Pershore c. 72mm
Little Rissington c. 74mm (25.4mm 25th)

The week ahead: Changeable, some rain or showers at times but often dry; temperatures around average

Although continuing changeable, early August will be an improvement on the second half of July, offering the prospect of more in the way of warmth and sunshine although with some rain or showers from time to time still. For a change its reasonably warm out there this Sunday afternoon, sunny spells but breezy, maxima 21 to 24c as southerly winds waft up, a few showers may affect NW Wales for a time however. Milder than of late tonight as well, clouding over across Wales with light rain arriving after midnight, staying generally dry for the Midlands, becoming quite windy over Wales in particular, no lower than 13c. The band of light rain moves east turning patchy into the Midlands during Monday while it clears WW early morning. An unseasonably deep low is situated NW of Ireland on Monday with a central pressure below 980mbar, the proximity of this low means fresh to strong SW winds during Tuesday afternoon and evening for WW especially and driving through a few blustery showers. Cooler on Monday, 16 to 19c WW but perhaps the East Midlands still in the relatively warm air at 22c. Clear intervals and just a few scattered showers for Monday night, no lower than 10c, fresh to strong winds continuing for WW.

The deep low is slowly passing just north of Scotland during Tuesday so another windy day, more in the way of showers, some heavy with thunder, these most frequent across Wales with parts of the south Midlands escaping dry and bright. Highs on the cool side, most places in the 17 to 19c range, perhaps only 15c for shower prone Snowdonia with the odd 20c for brighter spots of the south Midlands. Most of the showers dying out on Tuesday night and the wind moderates too. A bit of a ridge on Wednesday but this quickly being eroded as a new low approaches SW Ireland. At least a rather warmer day as the winds turn more towards south. Probably a dry day for most but a few light showers about, sunny intervals and average temperatures of between 19 and 22c. More general showery rain perhaps moving into WW during the evening or night with the Midlands remaining dry.

A slack pressure regime Thursday looks a warm and mostly dry day, however WW on the fringes of this warmth and it may turn out somewhat cooler and cloudier here with a few showers. Highs potentially of 26c over the Midlands, it may be nearer 20c over WW though. A messy picture of competing weak fronts/ ridges for Friday and there is likely to be some areas of showery rain about, probably not a lot though, with many places escaping largely dry but perhaps rather cloudy. Temperatures likely to be somewhere around average at this stage with quite light winds.

High pressure should be close enough to southern Britain during next weekend to weaken any Atlantic fronts that come our way. Plenty of dry weather, WW more likely to be plagued by cloud and some rain and drizzle from time to time as these fronts move through, with the Midlands tending to stay drier and brighter. Temperatures again close to average, but any sunshine would put the Midlands in the warm category at 24c or so.

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