The averaging period used for the following assessment was 1961-1990.
A dry month across most parts of the UK, with the main exception being the far south-east, which experienced more than average rainfall. Sunshine was close to, or above normal across all areas. Mean temperatures were again above average across the whole of the UK, with the highest anomaly over Scotland E.
Temperature ranged from -3 °C to 20 °C at Altnaharra on 27th. London Weather Centre recorded a temperature of 25.3 °C on 19th.
England and Wales diary of highlights
Rather warm, rather sunny and dry overall. Mainly dry and sunny after a wet thundery start. Some local air frost. Changeable at end of month.
1st to 2nd Occasional thundery showers on the 1st becoming rather warm by the 2nd with scattered showers and sunny periods.
3rd to 5th Low pressure took up residence over the UK bringing heavy thundery showers to many places on the 3rd and 4th and in the north, Midlands and East Anglia during the 5th. It was colder with sunny periods.
6th to 10th The low centre drifted east allowing a northerly air stream to become established. Scattered thundery showers on the 6th became more widespread over the eastern half of England during the 7th. There were outbreaks of occasional rain for the remainder of the period. Temperatures were generally near normal; some thundery outbreaks affected the south-west, Wales and the Midlands on the 10th.
11th to 18th The Azores high extended its influence after thundery outbreaks on the 11th died away, with the exception of light showers in the Hants/Surrey area during the evening of the 13th. There were long sunny periods after early morning patchy mist and fog cleared and it became warmer from the 15th onwards.
19th to 21st The high pressure receded westwards allowing a cold front to move slowly down. It was very warm and sunny in the south at first, 25.3 °C being recorded in central London on the 19th, however some sea fog plagued parts of the south-west. Thereafter becoming cooler with scattered thundery showers affecting some places. Prone areas had a touch of air frost, Shap in Cumbria falling to -2.4 °C early on the 21st.
22nd to 27th With high pressure mostly dominant a dry sunny spell ensued, winds were light and temperatures not far from normal after local overnight air frost. The 26th saw thundery outbreaks affecting a few places in south Wales and south England, these died out early the next day with most areas becoming very warm.
28th to 31st Changeable as low pressure to the west pushed Atlantic fronts erratically across the region bringing further outbreaks of rain and showers, some thundery, to some areas. The north-west received significant rain on the 28th. During the 29th scattered outbreaks of rain affected a number of locations. Central and north-east areas of England had thundery rain later on the 30th, while southern parts of the region reported scattered thundery showers. Eastern areas had a warm sunny bank holiday Monday as further rain spread into western areas from the Atlantic. The south-east and East Anglia stayed mostly dry during this period.
Scotland diary of highlights
Dry and warm.
Several anticyclonic spells dominated May and gave a dry and warm month. Unsettled interludes were brief in comparison.
The month started with a broad ridge of high pressure giving a fine day on the 1st. During the next couple of days the ridge moved south and weakened, allowing a westerly airstream to cover Scotland. Cloud spread south-east on the 2nd followed by sunny periods and showers on the 3rd.
A deep area of low pressure moved in from the Atlantic on the 4th and became slow moving for several days. Its associated fronts gave 24 mm of rain at Eskdalemuir. Thereafter sunny periods and showers predominated, but by the 7th the low pressure had weakened sufficiently for the showers to die out.
On the 8th a warm front moved west across Scotland and introduced a light north-easterly air flow. However, the air was of warm origin and at Baltasound on Shetland the temperature rose close to 20 °C on the 8th and 9th. On the mainland the warmth and humidity gave rise to evening thunderstorms from the 9th to the 11th. At Peebles the temperature reached 24 °C on the 10th. By the 12th high pressure had built from the west and a fine day ensued.
On the 13th and 14th south-westerly winds and weak fronts brought mainly cloudy conditions. However, by the 15th and 16th high pressure developed over England and its influence extended well into Scotland. The far north remained cloudy with a little rain but over the eastern half of the mainland it became warm and sunny with the temperature rising to 23 °C.
From the 17th and 18th westerly winds with weak fronts affected Scotland before winds veered into the north on the 20th and 21st. Mainly mild and cloudy conditions with a little rain were replaced by cooler and showery weather.
From the 22nd to the 27th the high pressure returned to give most of Scotland dry weather with a good deal of sunshine. At first there was some cloud in the far north while further south (on the morning of the 22nd) the temperature fell to -1.5 °C at Tyndrum and Saughall in Ayrshire. Patches of cloud continued to affect some areas but most of this had disappeared by the 27th. On this day the temperature at Altnaharra ranged from -3 °C to 20 °C.
Low pressure in the Atlantic pushed fronts across Scotland on the 28th and 29th giving cloudy weather with some rain. These conditions continued to affect the far north-east on the last two days of the month. However, most places in Scotland experienced a couple of days with more warm sunshine although there were also a few showers.
Northern Ireland diary of highlights
Warm, and very dry overall.
The month started dry with 12 or 13 hours of sunshine in many areas on the 1st. Temperatures were around 16 or 17 °C. During the next few days however, an unusually deep depression for the time of year tracked eastwards to the north of Northern Ireland. This brought showers or longer spells of rain to many areas between the 3rd and the 8th. Indeed the first week brought the bulk of the months rain to many areas with parts of the west and north-west catching 25 to 35 mm during the 3rd and 4th and up to 50 mm in a four day period between the 3rd and the 7th. Some showers on the 6th were thundery in places.
Between the 8th and the 14th slack high pressure brought drier conditions with variable cloud and some sunny spells to all areas. However by the 15th a more substantial area of high pressure was building across the British Isles and this dominated the weather for much of the remainder of the month. Days were often bright and warm and the temperature reached the low 20's on the 16th and 17th. Being May though, nights were still locally quite chilly and widespread grass frosts occurred with a touch of air frost in prone spots on a few nights. The temperature fell to -2.4 °C at Katesbridge overnight on the 20th/21st.
By the 28th a more active frontal system brought a spell of wet and windy weather, but the weather brightened again for the bank holiday weekend with sunny spells and occasional heavy showers. Some thunder was reported on the 30th. Sunny spells on the last day of the month gave way to some patchy rain through the evening.
Rainfall was typically 40 to 50% of the average though parts of Fermanagh had 80% of the average thanks to a very wet spell in the first week. Further east it was very dry and parts of the Ards Peninsula, East Antrim and Co Down had just 25 to 30 mm of rain in the month - this being only 30 to 35% of the average. This led to a series of gorse fires breaking out in the Mournes area during the last week of the month.