The new month began with above average temperatures and two days with light showers. However, that was about to change.
From the 4th the jet stream had begun to loop northwards towards Greenland and then down across the UK carrying with it a very cool airstream with the wind from the northeast or easterly direction. This resulted in both maxima and minima below average for early May. In the early hours of the 7th a low of 1.8C was recorded.
It became very cold from the 9th, for a week, as a flow of Arctic air arrived on a strong north-westerly wind that saw maximum and minimum temperatures well below average for early May. The coldest day of the month occurred on the 11th when the thermometer struggled to reach 12.9C, being 4.4C below average. During nights when the sky cleared, the air from north Scandinavia produced sub-zero temperatures with an air frost in the early hours of the 11th and 12th that saw the thermometer drop to -1.6C on the latter day.
This period saw a battle between several low-pressure systems to the east, with the air circulating anticlockwise and the high to the west circulating clockwise, as they do, feeding from the northwest, strong winds with a gust of 32mph on the 13th. This period also saw the feature of wind chill that outside it felt much colder than that indicated on a radiation shielded thermometer.
The first sign of a significant change in our weather arrived on the 16th when the wind had backed from the northwest into the west, a cool direction but a less cold direction. The temperature overnight 16th into 17th was the highest in a week but still just below average.
An anticyclone began to build across the near Continent, from the 20th, just in time for the holiday weekend that initially resulted in both maximum and minimum temperatures creep back above average, after a cold week. A maximum of 18.3C on the 20th was the first above average for ten days.
Heatwave conditions arrived on the 24th when the maximum of 30.6C was above the heatwave threshold for Wiltshire of 27C. An official heatwave is described as three consecutive days with temperatures rising above the heatwave threshold. The original heatwave thresholds were based on the reference climate period of 1981-2010 and were intended to be flexible and revised in the light of climate change, therefore the heatwave thresholds were revised in 2022, using the most recent 1991-2020 climate averaging period, with the local threshold temperature rising from 26C to 27C. The review saw six counties move from 27C to 28C, one from 26C to 27C and one from 25C to 26C, the areas changed were in the south of the UK and the Midlands.
The official May heatwave lasted for five days. My record for the maximum May temperature was set in 2018 with a high of 28.3C. That record was smashed with a peak of 32.8C on the 26th. Usually, records are broken due to a small increment, but it is significant that this year the increase was a sizeable increase of 4C. The official heatwave last for five days.
With the topic of high heat at the end of the month, reaching 30C or more, I did some digging in my records. I was looking to see if there was a pattern of climate change in the years that 30C was reached or exceeded. I discovered that taking the ten-year spans from 1990-1999, 2000-2009 and 2010-2019, the first had 3 years when 30C was reached, the second span 5 years and the third span 6 years. The current span from 2020 to 2026 has seen each of the six years reach 30C or more.
Meteorological spring ended with the dominant high pressure having departed and a depression approaching from the west, heralding a significant change after the very hot and dry month, to an Atlantic weather pattern of cooler and more moist air with the first possible rain after 12 consecutive dry days without measurable precipitation.
The rainfall for May totalled just 20.0mm being 29% of my 42-year record, which made it the third driest May since my records began in 1984. The rainfall in the year 2020 amounted to 8.2mm and back in 1990 just 6.7mm was recorded. The wettest day occurred on the 18th when 6.8mm was recorded. There were 22 totally dry days.
However, that was only part of the story as the very hot and dry month meant much moisture was lost to the atmosphere. A total of 98.3mm of equivalent rainfall was lost due to evaporation from ground sources and plant life, thus a deficit of 78.3mm compared to an average May month.
The mean temperature for May was 12.4C, being a significant 1.9C above my long-term average, in addition, it was the warmest May I have recorded since the station was set up in 1984 with professional recording equipment.
In the winter when it is cold and combined with a strong breeze, a wind chill makes it feel colder outside than indicated on a radiation shielded thermometer. In summer there is an index that indicates that it feels hotter outside than on a shielded thermometer, the THSW index. This uses data on temperature, humidity, solar and wind strength. The formula was originally developed by Robert Steadman in 1979 and is primarily used in professional weather stations. On the 25th at 16.00 I noted that although the radiation protected thermometer read 32.0C, the THSW index meant it felt more like 35.2C outside.
Spring 2026
The mean temperature for the three meteorological spring months of March, April and May was 10.86C, being 1.5C above my long-term average and exceeded the previous record by 0.3C, set in 2024.
The rainfall for spring 2026 was just 63mm making it the second driest spring since 2025 when only 41mm was recorded. The wettest spring was in 2024 with an exceptional 285mm.
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