Monthly retrospective for May 2016

It was quite but not especially a warm month temperature wise but rainfall was very variable due to the showery nature of the precipitation although wet in places, though sunshine was very close to average again, as in April in the main for most parts.

The (Hadley) CET mean temperature was near 12.5C, about 1.4C above average. Whilst nowhere was below average many parts were only just above average. The pressure was near average right across the UK.

The warmest mean maximum was at Heathrow (outer London) with 18.9C and surprisingly the highest daily maximum was 27.7C as far north as Plockton in Ross and Cromarty.
The coldest mean minimum was at Aboyne (Aberdeenshire) with 4.6C, the coldest absolute minimum by night was -5.7C at Tulloch Bridge in the Scottish Highlands with -9C on the grass. This was the lowest temperature in May for 4 years.

May was both a dry and wet month in places, Inverbervie in the Highlands saw just 22% of it expected average whilst Wattisham (Suffolk) saw 160% partly due to a single high daily storm total of 40mm. Generally places in the north were below average and most parts of the south were above average. The far SW was a dry exception though, Scilly for example only seeing 61% of its average.

Sunshine was near average everywhere. Valley however saw 123% of its average whilst Brize Norton (Oxon) again was one of dullest places and saw only 86%. Stornoway (Outer Hebrides) and Edinburgh both saw individual days with as much as 15.9 hours.

Frost was again rather above average generally for most parts though this didn't translate to especially low overall minimum figures perhaps surprisingly, apart from in the Highlands. As in April it was not a particularly stormy month though, with few windstorms of any note.

By the end of April sea temperature anomalies had fallen to about 1-2C below average around most UK coasts but by the end of May they were again above average though only just; much of the N Atlantic and Biscay remained below average (but again only just) and temperatures around the south east were 1-2C above average. Soil temperatures were almost uniformly near or slightly below average in the south & Midlands but generally near or slightly average in the north and soil moisture fell during the month away from the areas that received above average rainfall where it remained closer to average.

 

Now looking at May in more detail.

May 1st saw a cold start to the day in places, Santon Downham (Norfolk) fell to -3.3C with -7C on the grass at Hurn (Dorset) & -6C at High Wycombe (Bucks), Benson (Oxon) & Brize Norton (Oxon) but then it was a sunny day for many but cloudy & quite wet in the far NW however where Skye saw 25mm in the 24 hours to 21Z. May 2nd was a wet day in parts of the Highlands and far north, Achnagart saw 53mm in the 24 hours to 21Z with some localised flooding in places. On May 3rd after a chilly night in places with -4C on the grass at Hurn (Dorset) it was a dry, sunny day away from Scotland where it was quite wet again in places, Loch Glascarnoch (Highlands) saw 22mm of rain despite the prevalence of high pressure. On the 4th, under high pressure and still a relatively chilly airmass, it was a cold night in parts of the south, it fell to -5C on the grass at Pershore (Worcs), Shawbury (Salops) and Hurn (Dorset). The 6th saw a mild SE'ly flow cover the UK giving quite a warm and sunny day in places, Northolt reached 23.8C whilst in N Ireland, Magilligan saw 13.4 hours of sunshine.

The 7th saw a very warm day in parts of the Uk under a SE'ly flow but a chilly night in Scotland to start where Altnaharra fell to -1.7C and -3C on the grass however Marham (Norfolk) reached 24.9C by day. Thunderstorms broke out in central and western areas in the afternoon, some rather heavy in places. On the 8th under a continuing SE'ly flow it was a very warm and sunny day in parts of the UK, after a locally very mild night. St Helier in the Channel Isles only fell to 15C. By day 27.1C was reached at Northolt and St James Park, London. This temperature was only just below the all time max for May 8th. By the 9th it became sunny, very warm, and even a hot day in places in Scotland, after a chilly start with Braemar down to 0.7C, Plockton (Ross and Cromarty) reached 27.7C. On Skye at Lusa, a new May record was set of 26.7C with 14.8 hours of sunshine at Aberdeen Dyce. Thundery showers affected the Welsh border counties & central Wales though with 20mm in the 24 hours to 21Z at Whitechurch (Salops). The 10th May saw low pressure over N France and an easterly flow in the north allowed air to warm as it sank over the Highlands and gave a maximum of 25.6C at Skye Lusa after a chilly start in places with 0C on the grass at Aboyne. A very sunny day here too, Kinloss saw 15.1 hours of sunshine. There were heavy showers with isolated thunderstorms by the afternoon in the Midlands however.

The 11th saw a slack area of low pressure to the south- south east of the UK in the Channel which saw slow moving bands of showery rain overnight & through the day gave a very wet day in parts of the south with nearly 75-80mm in parts of NE Woking (Surrey) with an estimated 60mm in just a three hour period. There was localised flooding reporting in particular in parts of SE London in the morning and Woking in the afternoon. There was also flooding in South Wales where two adults and two children were rescued from a car stranded in flood water in Vale of Glamorgan. The incident at Ewenny was one of a number in south Wales between 17:00 BST and 19:00 as heavy rain fell. In Cardiff, 40mm fell in the 24 hours to 21Z mainly in a short period and the cellar of the Royal Oak pub on Broadway flooded, while sewage water entered a fabric shop on City Road after drains had blocked. The Anchor Inn in Tintern, Monmouthshire, also flooded. Two funnel clouds were spotted at Middle Wallop (Hants) in the afternoon, another between Weymouth and Dorchester on the Ridgeway and another near Oxford. Further heavy showery rain moved in the coastal parts of E Sussex and SW Kent in the late evening with another 20mm in places here and giving further localised flooding in the Eastbourne area. In the far north though it was very sunny, Lerwick saw 15.4 hours.

The 12th was a sunny day in parts of the far NW, Tiree (Outer Hebrides) saw 14.2 hours and a warm day in parts of west Wales, Porthmadog (Gwynedd) reached 24.7C. Parts of south Dorset & south Devon saw thunderstorms in the afternoon though, with local hail, quite heavy in places. Radar suggested short lived rainfall events giving 25mm in places in the New Forest area with localised flash flooding. The 14th saw a very cold night for May, -5.7C was recorded at Tulloch Bridge in the Scottish Highlands with -9C on the grass. This was the lowest temperature since March 31st and the lowest in May since 2012. A very sunny day followed in places, esp the Western Isles where Tiree saw 14.8 hours.

On the 15th there was another cold night in places and in the Highlands esp so, Tulloch fell to -4.4C and -8C on the grass, very chilly for mid May even in the Highlands. The 16th again saw another cold night in places but esp in N Ireland where Katesbridge (Co Down) fell to -3.2C and it fell to -5C on the grass to at Eskdalemuir in Southern Scotland.

There followed a period of quiet uneventful weather but on the 21st it was very wet in parts of the central north due to intense thundery downpours and Rochdale (Greater Manchester) saw 40mm in the 24 hours to 21Z. The 24th saw a cold night in N Ireland where Katesbridge (Co Down) was the coldest low level spot in Europe overnight with -1.1C. The 25th again saw a cold night in places for late May, Shap (Cumbria) fell to -0.7C and it fell to -3C on the grass there and at Tulloch Bridge (Highlands). On the 27th some heavy slow moving thundery showers developed across Wales in particular & esp in the Brecons. On the 28th there were various thundery showers in the south & east but it was quite wet in parts of west Wales where slow moving thundery showers developed and Swyddffynnon (Ceredigion) saw 31mm in the 24 hours to 21Z. The 31st was sunny and quite warm in Scotland but with low presure to the SE conversely it was very wet in places in the east, Wattisham (Suffolk) saw 53mm of rain in the 24 hours to 21Z with localised flooding.

 

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