The averaging period used for the following assessment was 1961-1990.
On the whole it was a dry, warm and sunny month throughout the UK. Although, it was generally cool and unsettled midmonth, with frequent heavy thundery rain over the south of the UK. Cooler and more unsettled conditions again over the UK towards the end of the month.
Many places in Scotland were closest to their warmest May on record. Aberdeen Airport had its sunniest May since records began in 1946.
England and Wales diary of highlights
Very warm with some thunder after a chilly start. Cool wet spell with thunderstorms mid-month. Mostly dry very warm and sunny thereafter, more changeable towards end of month.
1st to 3rd Rather unsettled and mostly cold with some thundery rain especially in south-east England and East Anglia. Drier and brighter in the north-west.
4th to 12th With high pressure firmly established off Scotland the weather was mainly dry and sunny especially in the north. There was patchy fog at times especially around coasts. Many places had overnight frost at first, Shap Fell / Cumbria fell to -3.9 °C early on the 7th. Some thundery rain with hail and spectacular lightning broke out overnight the 9th/10th mainly over south-east England, East Anglia and south-west England. Thunderstorms also occurred over the south-east Midlands on the 11th. By the 11th and 12th it had become very warm or hot in many areas with prolonged sunshine, Southampton peaked at 27.3 °C on the 12th.
13th to 17th Low pressure centres traversing the region brought frequent outbreaks of heavy thundery rain to many areas, especially in the the south, south-east and Midlands, with some localities experiencing torrential downpours. It was very warm at first but became colder later, the 17th being especially cold, wet and windy.
18th to 25th After some scattered showers and thundery outbreaks petered out on the 18th high pressure migrated quickly from the south-west to cover the region. Although somewhat cloudy at first in north-western areas long sunny periods soon prevailed everywhere. Dry, warm or very warm conditions were established, especially in Wales and western areas. Counties nearer the relatively cool North Sea had their temperatures moderated to some extent by the onshore breezes.
26th to 27th As the high pressure moved south more changeable (though still warm) weather began to affect the region. As weak fronts crossed England and Wales, patchy rain and drizzle with hill and coastal fog affected many western and north-western areas, with the rain being heavy over north Wales on the 27th.
28th to 31st The warm or very warm theme continued with most places having long sunny periods, although there were areas of patchy rain in the west at first. During the 30th heavy rain affected northern England, and thunder was reported from Norfolk later. The 31st was cooler with showers down the east coast of England..
Scotland diary of highlights
Very dry, warm and sunny.
May 2001 was outstandingly dry, warm and sunny across most of the Scottish mainland. Generally, the month did not break records for individual elements, but the combination of dryness, warmth and sunshine was notable. May 2000 was almost as warm, and sunnier in the south-west, but not as dry.
Two fine and sunny spells dominated the weather in May, and were separated by more unsettled conditions.
The first fine spell was already knocking on the door during the first four days of May as an anticyclone near the Azores pushed a ridge of high pressure towards the British Isles. Weak fronts and a few showers were in evidence, but already there was much dry and sunny weather. There were also some cold nights with frost in places.
The anticyclone had moved close to Scotland by the 5th and lasted until the 13th. It took a couple of days for most of the cloud to disperse, and then most places enjoyed sunny conditions for several days. There was still night frost in a few places at first, but it became steadily warmer and by the end of the spell temperatures were exceeding 25 °C in some locations.
The most unsettled weather of the month occurred between the 14th and 19th as a large-scale fall of pressure took place, resulting in a depression forming over Scotland on the 16th. This gave a period of rain before cool and showery weather spread across the country in the wake of the low.
A steady build of pressure ensued and a new anticyclone took residence close to Scotland from the 20th to 24th. Once again, it took a couple of days for the cloud to break and then there was more warm sunshine with temperatures reaching 25 °C in one or two places.
By the 25th the high was slipping to the south to enable a changeable west to south-westerly airstream to cover Scotland. Weak fronts gave some outbreaks of rain, but it remained warm, with temperatures reaching 21 °C at some place in Scotland until the 28th. After this the winds veered into the north-west and it became cooler, with bright and showery conditions alternating with more organised bands of rain.
Northern Ireland diary of highlights
This was another dry, sunny May month. Although not as sunny as in May 2000 (nor May 1997).
1st to 13th Largely dry and very sunny, but with showers and thunderstorms recorded locally on the 9th and 10th. Very warm on 12th and 13th.
14th to 16th Cold, dull and wet.
17th to 20th Dry and bright, but cool.
20th to 24th Dry, very warm and very sunny.
25th to 31st Turning increasingly unsettled, but staying quite warm and sunny until 29th. Much cooler on 30th and 31st.