Sunday, 3 May 2015

Weather guide May Day Bank Holiday Monday to Saturday 10th May 2015

Headline: Changeable: rain and strong winds at times (particularly Tuesday) with Monday and Thursday looking mostly dry and bright

Last week's highlights

The cool Arctic airmass at the start of last week produced notably low temperatures on Sunday night. It fell to -5.8c at Sennybridge, -5.0c Llanwnnen, -4.2c Trawsgoed and even on the coast -3.5c at Pembrey, with most places out of the cities getting an air frost. This was the lowest temperature this far into Spring that I have recorded. Looking back through the records for comparisons I find that I recorded -3.7c at Cwmann near Lampeter on 5th May 1996, while it is reported in the Climatological Observers Link in the April 1985 bulletin that on the 26th April it fell to -7.0c at St Harmon, Powys and -6.2c at Higham Ferrars, Northamptonshire, so such late frosts are by no means unprecedented. Showery early last week, hail in places, even some snow reported from the Brecon Beacons and no doubt Snowdonia also? Showers few and far between last Tuesday, many places missing them altogether and with decent sunny spells were less cool, several parts of the Midlands managing a near average 13c.

The first appreciable rain many of us have seen for at least a fortnight came through on a front Tuesday night into Wednesday morning with parts of Wales getting half an inch. One this rain cleared though only a few showers dotted about with Wednesday another bright if rather cool day, the Midlands getting up to 13 or 14c and closer still to the average for the very end of April. Thursday too saw very few showers, most places dry but cool again, although Pershore reached 14.6c, it was though the coolest day of the week at Llanwnnen, a max of just 10.7c here. Friday was then another largely dry but cool day, Porthmadog the mildest spot within our regions managing 14.6c and Llanwnnen 13.9c, both about average for the very start of May. Saturday very cool and wet over parts of Wales, even some sleet reported over the Brecon Beacons, although again some parts missed out. Parts of North Wales failed to reach 10c on Saturday with Anglesey getting well over half an inch of rain.

April summary

April 2015 overall was dry, rather warm and sunny. All areas had a dry month with many places getting below half the average rainfall and everywhere had a sunny month, many places getting over 200 hours total bright sunshine.

Some rainfall totals for the month:

RAF Mona, Anglesey 38.4mm
Capel Curig, Snowdonia 82.4mm (54%)
Trawsgoed, Ceredigion circa (c.) 39mm
Llanwnnen 29.5mm (39%)
Aberporth, Ceredigion 26.6mm (50%)
Pembrey Sands, Carms c. 21mm
Llanelli, Carms 21.3mm
Milford Haven, Pembs 27mm
Hereford 15.8mm (31%)
Pershore, Worc c. 15mm
Coleshill, Warks 21.4mm (42%)
Bablake School, Coventry 23.0mm (44%)
Church Lawford, Warks c. 22mm
Long Lawford, Warks 22.3mm (50%)

The week ahead

All areas saw rain on Saturday night lasting into this (Sunday) morning, 24-hour totals amounting to over an inch for parts of North Wales, the front has though introduced milder air from the SW. Sunny intervals and scattered showers for Sunday afternoon some of these heavy but some places missing them, highs between 13 and 17c, warmest over the East Midlands. Breezy with a few remaining showers overnight, no lower than 6c. A little bump of high pressure gives a generally dry and bright May Day Bank Holiday Monday, fairly light southerly winds and highs between 15 and 18c a little above the early May average, so quite a pleasant one. Rain may be arriving during Monday evening, at least into the south of our regions leading into a wet but mild night as a developing low pressure system arrives into SW England.

This active and potentially nasty Spring low then tracks NNE across England on Tuesday bringing wet and windy weather, some very heavy areas of rain about during the morning. The rain turns more showery on Tuesday afternoon, these mostly affecting Wales and driven by a strong, locally gale force SW wind. Some rather warm, humid air in association with this low so the East Midlands could reach 18c, but 13 to 16c more generally the high to come on Tuesday afternoon, and in any case tempered by the wind. The by then deep low is centred close to northern Scotland on Wednesday, another unsettled and windy day to come. A windy and showery day, fresh to strong west winds and some heavy showers with hail and thunder, although as ever some areas miss out and have a dry, bright if windy day.  Rather cool highs Wednesday between 11 and 15c.

Low pressure should be easing away to the NE during Thursday, so any showers should be dying out and with lighter winds and more in the way of sunny spells, Some hope then of a dry, bright calmer interlude on Thursday, maxima better too at 13 to 17c. The next low looks like moving into the SW approaches and seems set to bring further rain and perhaps strong winds to most places during Friday but this not yet certain. Uncertainty about next weekend too which although looking rather unsettled with rain at times may contain some pleasant weather as well? The latest ECM model seems overly optimistic and shows dry, warm sunny weather come next Sunday while the GFS is a cooler, cloudier affair with a little rain!

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