The averaging period used for the following assessment was 1961-1990.
Temperatures were again above average across the whole of the UK. Scotland and Northern Ireland had a very wet and dull month. In comparison England and Wales as a whole had average sunshine, with some southern areas of England experiencing less than average rainfall.
Central London recorded a high of 29.1 °C on the 31st, with Bastreet (Cornwall) recording a low of -3.4 °C on the 15th.
England and Wales diary of highlights
A changeable month, unsettled with thundery rain at times, hot at end.
1st to 4th With low pressure over or close by the UK, unsettled and very wet weather prevailed for the first few days with frequent rain and showers, often heavy and thundery. It became drier and warmer away from the north-west during the 3rd and 4th.
5th to 10th More changeable and settled away from the west and north-west as weak fronts traversed the region. However, there were scattered thundery outbreaks on the 5th. It became sunny and warm for a time especially in the south-east. The 9th saw scattered light rain or showers in western areas, while rain and drizzle affected many places on the 10th.
11th to 14th A depression tracking eastwards over northern parts of the UK brought progressively cooler air as winds veered to north-west. A rather unsettled regime was established with frequent rain and showers, some heavy with thunder and hail, in particular over the south-east and East Anglia. Most parts though had sunny periods. A violent storm struck Abinger Hanger, Surrey on the 13th - a lightning strike in the village caused much local damage.
15th to 21st A complex low-pressure area to the north-west drifted east-north-east to Scandinavia during the period. The 15th started dry after widespread overnight frost, -3.4 °C being recorded at Bastreet in Cornwall. However rain moved into Devon and Cornwall later as fronts from the Atlantic pushed in from the south-west. A rather cool, unsettled period ensued as bands of rain and showers often heavy with hail and thunder moved across the region. North Wales and north-west England were especially affected. A violent thunderstorm was noted at Coulsdon/Surrey on the 19th. Hill and coastal fog shrouded some southern areas on the 21st as fresh Atlantic fronts moved in.
22nd to 25th Mostly unsettled as a low east of Scotland moved south-east. Patchy rain, hill and coastal fog on the 22nd gave way to more showery conditions later with sunny periods. There were some significant thundery outbreaks over the Midlands, the south-east and East Anglia on the 24th, with downpours reported in some places.
26th to 31st An anticyclone over the Azores brought mainly dry, sunny and very warm conditions as it migrated to southern Scandinavia. After the clearance of patchy hill and coastal fog and some light rain or drizzle occurred in southern and western areas on the 26th and 27th. Temperatures steadily rose under the combined effect of prolonged sunshine and warmer air being drawn in from the continent. Sea fog affected places in the south on the 28th, while northern England had some outbreaks of heavy rain at times during the 29th and early on the 30th. Many places became hot during the 30th and 31st - central London recording 29.1 °C on the 31st. Thundery showers broke out over the Midlands and north-east England during the evening of the 31st.
Scotland diary of highlights
Dull, wet in west.
Unsettled south-westerly weather prevailed throughout May, although pressure rose during the month. The first week was cyclonic with frequent bands of rain and this was followed by a long spell of showery weather. The last week was warm and humid, often with cloudy skies and occasional rain. There was a marked gradient of weather across the country, with most of the cloud and rain in the southwest.
During the first week of May, four depressions moved north-east close to the north-west of Scotland. These pushed bands of rain across the country with showery conditions between. The west bore the brunt of the weather and here there were strong winds at times, with a gust of 68 m.p.h. at Barra in the early hours of the 8th.
During the second week low pressure remained slow moving to the south-east of Iceland, and a showery south-westerly airstream covered Scotland.
A ridge of high pressure moved in from the west on the 14th and 15th to give fair weather across most of the country.
Two low pressure systems dominated the weather between the 16th and 25th. The first depression remained to the west of Scotland whereas the second moved slowly across the country. After the associated fronts and attendant bands of rain cleared Scotland, showery conditions prevailed.
During the last week high pressure became established near the North Sea, maintaining the south-westerly winds across Scotland. The air was warm and humid so that there was a lot of cloud, and there continued to be occasional rain. Brighter weather allowed the temperature to rise to 26.6 °C at Lossiemouth on the 31st.
Northern Ireland diary of highlights
Very wet and dull.
Although this was a dull month throughout Northern Ireland, the second week of May was very sunny everywhere. Total weekly sunshine durations recorded over this time equated to over a third of the total monthly sunshine for May.
1st to 4th Atlantic depressions and their associated weather fronts brought unsettled conditions across the country at the start of the month. Rain and showers, which were at times locally heavy, occurred on each day during this period, with hail recorded on the 1st. In most places the first day of the month was a sunny day, while the 2nd was also quite sunny in the west and north of the province. The 3rd and 4th were duller days with shorter spells of sunshine between the rain or showers. Temperatures overall were lower than average, with most areas recording a slight ground frost on the morning of the 3rd.
5th to 14th It was at times rather cool across the province during this period with a mixture of sunny spells interspersed with moderate to heavy showers. Some heavier downpours occurred locally, most notably on the 9th, 11th, 12th and 13th and these were at times accompanied by hail and thunder. Blustery wind conditions also occurred throughout much of this time, which affected the nature of the showers, especially the heavier ones. Many areas recorded little or no rainfall on the 8th and 14th. Widespread slight ground frosts were recorded between the 9th and 11th, as clearer skies developed through the nights.
15th to 25th A succession of Atlantic frontal weather systems tracked eastwards across the country bringing unsettled weather throughout Northern Ireland. Bands of rain and showers, which were again heavy and thundery at times, were recorded on each day in most places. Sunny spells were recorded over this period, however conditions were overcast on the 16th and 21st across the province. On the whole overall temperatures were around normal for this time of the year, with the exception of the 22nd which was rather warm in many areas. Slight ground frosts were recorded on the morning of the 15th, but apart from that day, no air or ground frosts occurred during this period.
26th to 31st An Azores high-pressure system dominated the weather over the remainder of the month. A southerly airflow brought warm, dry and at times sunny conditions across Northern Ireland over this period. Many areas were affected by early morning fog on the 27th, though it dispersed quite quickly. The 30th was a very sunny day, resulting in daytime temperatures recording values of between 9 and 10 degrees above the normal for this time of the year, with one of the highest values recorded during the day being 24.3 °C. Indeed most areas recorded between 10 and 11 hours of sunshine on this date alone. Cloudy conditions developed throughout the 31st and brought light rain and showers to some areas during the late evening and night.