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May 2017

The averaging period used for the following assessment was 1981-2010.

At the start of May, a slackening low pressure system brought rain and showers to the south but it was mostly dry and sunny in the north.  During the first 11 days, the weather was anticyclonic with mainly easterly winds, which brought plenty of warm dry sunny weather especially to Northern Ireland and western Scotland, but it was often cooler and cloudier in the south-east and in counties bordering the North Sea.  It turned unsettled around mid-month with bands of rain interspersed with brighter showery weather.  There was a notable hot sunny interlude for much of the UK between the 24th and 26th, with temperatures widely in the mid to high 20s Celsius, followed by widespread thunderstorms on the 27th-28th.

The UK mean temperature was 12.1 °C, which is 1.8 °C above the 1981-2010 long-term average, making it the second warmest May in a series from 1910 (behind 2008).  Mean maximum temperatures were generally about 2.5°C above normal in Scotland and Northern Ireland, but nearer 1.5°C above in the south, while mean minimum temperatures were between 1 and 2°C above average in all regions.  Rainfall was above normal in Lincolnshire, East Anglia and south-eastern and central southern England, but mostly below normal elsewhere, substantially so in some parts, with 82% of average overall.  Sunshine was 112% of average, and it was a very sunny May in Northern Ireland and western Scotland with excesses of over 50% in some places, but sunshine was close to average in East Anglia and southern England.

The UK monthly extremes were as follows:  A maximum temperature of 29.4 °C was recorded at Lossiemouth (Morayshire) on the 26th.  A minimum temperature of -5.1 °C was recorded at Shap (Cumbria) on the 9th.  In the 24 hours ending at 0900 GMT on the 16th, 167.8 mm of rain fell at Ennerdale, Black Sail (Cumbria).  A wind gust of 54 knots (62 mph) was recorded at Culdrose (Cornwall) on the 5th.

Weather impacts

Although the weather was largely quiet throughout the first two weeks of May, there were some localised weather impacts reported – localised flooding in Maesteg, south Wales on the 11th, and reports of a tornado causing damage in Stapleford, Nottinghamshire.  The first organised rain for some time on the morning of the 15th prompted concerns over potential for surface water flooding in south-west Scotland, but no impacts were reported.

Very localised, temporary flooding and lightning impacts were reported, mainly across south and south-east England, during Wednesday 17th to Friday 19th.

Thunderstorms broke out between the 27th and 29th following a spell of very warm/hot conditions. 

The thunderstorms started in south-west England during the early hours of the 27th, with both Cornwall and Devon and Somerset Fire and Rescue Services reporting a number of callouts due to lightning strikes. Flooding was reported in North Yorkshire and more than 500 properties lost power in the Lake District due to lightning strikes. In Scotland, localised flooding was reported in Lanarkshire and in Cupar in Fife.        

Subsequently, heavy rain and lightning mainly affected southeast England during the morning of the 29th. Kent Fire and Rescue Services reported a house roof fire following a lightning strike near Maidstone, with a number of other reports of lightning strikes on buildings. Localised road and rail flooding was also reported.     

England diary of highlights

May started with some rain or showers in the south, but otherwise the first third of the month was settled with mainly easterly winds, warm and sunny in the north-west but often cool and cloudy in the south-east.  The second half was more changeable but mostly warm.  There was a notable hot and sunny spell from the 23rd to 26th, followed by significant thunderstorms across many areas on the 27th and in the south-east on the 28th/29th.

The mean temperature for May was 1.7 °C above the 1981-2010 long-term average and it was the third warmest May in a series from 1910. Rainfall was mostly above average in Lincolnshire, East Anglia and the south-east but it was much drier in the north-east and parts of the north-west, with 98% of average overall.  Sunshine was 104% of average overall, and was above average in the north but close to average in East Anglia and in southern counties.

1st to 4th

The 1st was dry with sunny spells across the north but showery across the south, the showers heaviest across Cornwall. The 2nd was similar with rain and showers across southern parts while it stayed drier further north, sunny in the north-west but cloudy in the north-east. The 3rd was sunny and dry across the north with 14.0 hours of sunshine recorded at Boulmer (Northumberland) but cloudier further south with patchy rain across south-eastern parts.  It was cloudy and cool with some early patchy rain across the south and east on the 4th, warmer and sunny for the north and west. 

5th to 10th

It was sunny over most of the country on the 5th but cloudy and breezy across southern counties with a gust of 62 mph at Culdrose (Cornwall).  It was cloudier and somewhat cooler on the 6th with rain for the far south-west and a little light rain across the Midlands.  Western parts were bright or sunny on the 7th but the east was cloudier with some drizzle along the coast.  The 8th was sunny for western parts, but again cloudier over the east with drizzle in places. The 9th had a cold start when the temperature at Shap (Cumbria) fell to -5.1 °C, followed by a mainly cloudy day through the Midlands and East Anglia but otherwise sunny, and was dry everywhere. It was largely dry on the 10th after a chilly start with -3.3 °C at South Newington (Oxfordshire), turning showery across parts of the south-west later.

11th to 20th

The 11th was warm with 22.9 °C recorded at Northolt (Middlesex), but increasingly showery later with isolated thundery outbreaks. It was cloudier and unsettled on the 12th with rain spreading north, heaviest in the west and north Midlands. The 13th was quite warm but wet with showery rain reaching all areas by nightfall. Overnight rain cleared early on the 14th followed by sunshine and showers throughout.  Rain for all parts during the 15th, drier for a time across the Midlands before more rain filtered down from the north-west.  It was bright or sunny for the south-east on the 16th, but a band of rain from Northumberland to Cornwall spread steadily south-eastwards during the day. An area of heavy rain on the 17th moved slowly eastwards affecting the south and especially central and eastern parts, where rainfall totals exceeded 30 mm. An area of rain moving slowly northwards from France affected the south-east from early afternoon on the 18th, and reached north-east England by evening. The 19th was wet throughout in central and north-eastern regions, while showers developed along the south coast but ceased by late afternoon. The 20th started dry and bright but cloud increased from the west during the morning, bringing a band of heavy, thundery showers, which cleared the east by dusk, but the south-east stayed dry throughout.

21st to 26th

The 21st was mainly dry and cloudy but some brighter spells developed in places.  Mainly light rain crossed the north-west on the 22nd, clearing away mid-afternoon, and it was sunny and warm elsewhere. It was dull and drizzly across the south-west on the 23rd, sunny and warm elsewhere.  The 24th was cloudy over parts of the north-west, otherwise sunny and warm, particularly in the south-east.  Fog across the north-west on the 25th cleared by mid-morning, leaving a warm, sunny day everywhere.  The 26th was hot sunny day for many areas; temperatures widely reached the mid to high 20s Celsius with 28.6 °C at Blackpool (Lancashire).

27th to 31st

Overnight thunderstorms in the south-west on the 27th decayed for a time as they headed north-east, before another area of thunderstorms and torrential rain/hail developed over the north from mid-afternoon and moved northwards, giving 52.6 mm of rain at Levens Hall (Cumbria).  The 28th started dry and bright or sunny, before rain and isolated thunderstorms moved north across southern counties and into the Midlands and East Anglia.  Rain persisted over the north on the 29th with showers or thunderstorms developing across the south later. It was mostly cloudy on the 30th, with showers again, heaviest across the north-west from mid-afternoon. It was mainly dry on the 31st with only very isolated showers in central and southern areas, and it was sunny in the north.

Wales diary of highlights

May started wet in the south, but otherwise the first ten days were dry and generally sunny with mostly easterly winds.  It turned unsettled around mid-month, but the last third was quieter.  There was a marked warm sunny spell from the 23rd to 26th, followed by a thundery breakdown for some.

The mean temperature for May was 1.8 °C above the long-term average, making it the third warmest May in a series from 1910.  Rainfall was generally near or below average, with 84% of average overall.  Sunshine was 116% of average and it was a sunny month except in some parts of the south.

1st to 10th

The 1st was quite warm, but wet across southern parts, brighter across the north. The 2nd was warm, dry and sunny throughout with 13.9 hours of sunshine recorded at Aberdaron (Gwynedd). The 3rd was breezy but warm, dry and sunny again throughout, with the best of the sunshine across the north.  Extensive morning cloud on the 4th and 5th burned away to leave sunny days for all parts. It was sunny in the south-west on the 6th but cloudier and cooler elsewhere with some morning drizzle.  Early cloud in the south on the 7th burned away to leave a sunny day everywhere.  It was sunny and dry throughout on the 8th and 9th with 14.3 hours of sunshine recorded at Aberdaron on the 9th. Dry, sunny and warm again on the 10th after a cold frosty start with -2.5 °C recorded overnight at Sennybridge (Powys).

11th to 20th

A dry, bright start on the 11th was followed by showers with thundery outbreaks spreading north from late morning, with a high of 22.9 °C recorded at Porthmadog (Gwynedd). The 12th was cloudy and wet with the first widespread substantial rainfall for several days, heaviest in the north-west. It was brighter across the north on the 13th after a warm night but wetter across the south with persistent rain.  After early rain cleared, the 14th was mainly fine and warm with just isolated showers, before rain spread from the west later.  It was wet all day on the 15th, with 66 mm recorded at Capel Curig (Gwynedd), and windy around coasts and hills.  It was wet again for most on the 16th, but became drier and brighter from the north-west in the afternoon. The 17th was wet towards the south-east, but the north and west remained drier. It was dry and sunny for most on the 18th but with some well-scattered showers in the east. The 19th started dry but showers developed in the afternoon, mostly in central and eastern counties, while coastal regions remained fine and sunny. The 20th brought some bright spells but heavy, thundery showers moved east across the country, clearing by late evening.

21st to 26th

The 21st was mainly dry and cloudy with some bright or sunny spells developing in places.  Some patchy morning rain for the north on the 22nd but it became sunny and warm everywhere during the afternoon.  Cloudy with light rain or drizzle over the south on the 23rd, sunny and warm elsewhere.  It was cloudy along the west coast on the 24th but sunny and very warm elsewhere.  Fog in central areas on the 25th cleared by mid-morning, otherwise it was a warm, sunny day.  Warm and sunny for all parts on the 26th with temperatures widely in the mid to high 20s Celsius, Porthmadog (Gwynedd) reaching 28.9 °C; Valley also recorded 15.3 hours of sunshine.

27th to 31st

There was rain and thunderstorms to start the 27th, clearing later before patchy rain returned to the south from early afternoon.  Dry and bright or sunny on the 28th, but clouding over from the south with rain reaching southern coasts by evening.  Patchy rain over the north on the morning of the 29th cleared but then more widespread showers developed in the afternoon. After a warm night, the 30th was a showery day, with the heaviest showers across northern and central parts.  The 31st started dry but showers developed during the day.

Scotland diary of highlights

The first third of May was generally dry and sunny with mostly easterly winds, warm in the west, although cloudier further east, especially near the coast.  It turned more unsettled between the 12th and 22nd.  There was a notable hot sunny spell from the 25th to 27th, followed by a thundery breakdown in the south.

The mean temperature for May was 1.8 °C above the long-term average, making it the second warmest May (after 2008) in a series from 1910.  Rainfall was generally below normal, with 63% of average overall.  It was a sunny month except near the east coast, with 120% of average overall.

1st to 11th

The 1st was dry, warm and sunny throughout. The 2nd was warm and dry, with widespread sunshine again, and Achnagart (Sutherland) reached 21.0 °C. The 3rd was again dry, warm and sunny across all areas.  Morning cloud in the north-east on the 4th burned away to leave everywhere dry and sunny with 15.0 hours of bright sunshine recorded at Stornoway (Isle of Lewis).   It was sunny everywhere on the 5th apart from some low cloud around the east coast and Northern Isles.  Low cloud persisted around the Moray Firth on the 6th but it was otherwise another sunny day, after a cold start with -5.0 °C at Braemar (Aberdeenshire).  Persistent cloud covered the north and east on the 7th and 8th, but it was brighter over the south-west. Cloudy and cool across the Northern Isles on the 9th but warm and sunny elsewhere with 14.6 hours of sunshine at Drummond Castle (Perthshire). It was largely dry and sunny across most counties on the 10th but it turned showery across the north. The 11th was largely dry and warm, sunniest across southern parts.

12th to 16th

The 12th was particularly warm across the north-west Highlands with a high of 21.9 °C at Drumnadrochit (Inverness-shire) but it became showery later. The 13th was quite warm, but increasingly showery across western parts later. The 14th had widespread sunshine across the Western Isles before showers turned increasingly frequent.  Very wet and windy for all parts on the 15th, Forest Lodge (Kirkcudbrightshire) recording 51 mm, although the rain cleared southwards by early evening.  It was cloudy and drizzly in the south on the 16th, with some showers elsewhere, brightening up for most parts later.

17th to 22nd

The 17th was warm, dry and sunny in the east, but some showers affected the west and moved north-eastwards. Showers developed during the day on the 18th, heaviest over the Moray Firth, but the east remained dry and bright.  It was a fine morning on the 19th but an area of rain slowly moving westwards from the North Sea reached the east coast by noon and central Scotland by dark. The 20th was wet, with a band of heavy rain slowly moving north and heavy showers moving across the southern half of the country, but it became drier in the north by late evening while showers persisted in the south. A dry and fairly cloudy start for the 21st but rain moved in from the south-west in the morning, progressing north-east through the day and becoming light and patchy.  It was wet for many on the 22nd with bands of rain crossing the country during the day.  

23rd to 26th

It was bright or sunny initially for all parts on the 23rd before rain developed over the west and spread east to most parts during the afternoon.  It was sunny and warm across the south-east on the 24th but elsewhere there was variable cloud with isolated patches of rain.  Fog over the south-west on the 25th cleared away by mid-morning to leave a warm, sunny day everywhere with 16.1 hours of sunshine at Kinloss (Morayshire).  It was generally warm or hot and sunny on the 26th with Lossiemouth (Morayshire) recording 29.4 °C although cloudier over the west and foggy across the Northern Isles.

27th to 31st

Sunny for all parts to start the 27th before rain spread from the south, heaviest over the west, which turned thundery with torrential rain in the south from late afternoon.  It was mainly dry and bright or sunny on the 28th apart from some patchy rain over the north and east, the rain fizzling out during the afternoon.  It was generally cloudy and wet for most places on the 29th, with only the north-east staying dry. The 30th saw showers developing, heaviest across north-eastern parts, whilst the south stayed brighter. A dry and bright day for most on the 31st but northern areas saw more in the way of cloud.

Northern Ireland diary of highlights

May began with a spell of dry, mostly warm and exceptionally sunny weather which lasted until the 10th.  The middle third of the month was more unsettled, with showers and some longer spells of rain.  There was a marked sunny and warm spell from the 24th to 26th.

The mean temperature for May was 1.9 °C above the long-term average, making it the second warmest May in a series from 1910.  Temperatures were generally between 2 and 3 °C above average by day and about 1 °C above by night.  Rainfall was mostly near or a little below average, with 78% of average overall.  It was the equal-third sunniest May in a series from 1929, with 139% of average.

1st to 11th

The 1st, 2nd and 3rd were dry, warm and sunny, with 20.5 °C recorded at Castlederg (County Tyrone) on the 1st, but a strong easterly breeze developed on the 3rd.  The dry sunny weather continued on the 4th and 5th, and Aldergrove (County Antrim) recorded 14.3 hours of sunshine on the 5th.  The 6th was another warm, sunny day.  There was virtually unbroken sunshine again on the 7th with temperatures exceeding 20 °C in places.  It was cooler on the 8th but still with unbroken sunshine. It remained dry into the 9th with widespread sunshine after a frosty start for many. There was some early frost again on the 10th followed by another warm, dry and sunny day. It was frosty in the southeast to start the 11th, staying warm, dry and sunny elsewhere, but showers developed in the evening.

12th to 21st

Rain spread north through all counties on the 12th, heaviest in the south-west.  After a very mild night, the 13th was wet again throughout, the rain heaviest across the north-west. The 14th turned increasingly showery, especially across the north-west, before further more widespread cloud and rain moved in with 30.1 mm of rain at Trassey Slievenaman (County Down). It was wet and windy on the morning of the 15th, followed by showers.  Sunshine and showers on the 16th, but the showers died away in the afternoon to leave a sunny evening. Showers, locally heavy, affected all counties on the afternoon of the 17th. Sunshine and showers on the 18th, the showers heaviest and most frequent around the coast. A dry morning on the 19th, but a band of rain developed in the afternoon and moved slowly eastwards to reach central parts by evening. The 20th was a day of bright spells and heavy, thundery showers, becoming drier by late evening. A wet start on the 21st, rain soon clearing the north coast but with scattered showers developing in the afternoon, becoming drier by the evening but remaining cloudy.

22nd to 26th

After a wet morning on the 22nd, the afternoon was drier and warmer with sunshine and a few showers.  Generally bright or sunny on the 23rd with some short-lived patchy rain in the afternoon.  It was bright or sunny on the 24th with temperatures widely into the low 20s Celsius.  Fog in central areas on the 25th burned away by mid-morning to leave a warm, sunny day.  The 26th was another dry, warm and sunny day with a maximum temperature of 26.2°C at Castlederg (County Tyrone) and Lough Navar (County Fernanagh), and Aldergrove recorded 14.9 hours of sunshine, although showers reached the west by evening.

27th to 31st

It was cloudy on the 27th, turning wet for all parts from mid-morning. The 28th was fine and bright. It was very wet on the morning of the 29th, the rain lighter and patchier by the afternoon.  After a band of morning showers on the 30th, it turned brighter and drier, and then the 31st was dry with sunny spells.

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