After a warm, damp start to June, with a substantial fall of rain on the 1st totalling 28.0mm, there was a significant change from the 4th as the wind veered from a southerly quadrant to a westerly direction.
This change to a cool flow of westerly air resulted in a week of below average temperatures by day. The first twelve days all had a maximum below average with the 6th being 5C below the June average. At first, the nights held just above average but sadly for gardeners, there was a significant drop from the 9th to the 11th with almost identical minima being about 2C below the June average, restricting the growth of new plants. This period brought variable rainfall from modest passing showers.
We all began to relax from the 12th as the recent track of the jet stream crossing the Atlantic pushing weather fronts across the UK made a significant change in direction. It began to loop to the north of the UK putting us on the warmer south side, this allowed high pressure to the southwest to edge over the UK and transform the weather from cool and damp to fine, warm and sunny. At last sunshine arrived that boosted the temperatures above average with 21.4C on the 13th, the first in June.
Around the 17th there were signs of a significant anticyclone developing across the Continent. The southern half of the UK was on the edge of the hot air and that lifted the temperatures well above average. The recent depression, centred south of Iceland, was still dominant, which produced occasional weather fronts and humid air that resulted in variable cloud and during the breaks strong sunshine.
It was Sunday 21st when a plume of hot air eventually arrived from the Continent and that sent the thermometer soaring to reach the first day when the heatwave threshold temperature for Wiltshire, of 27C, was exceeded.
The relentless, continuous strong sunshine pushed the temperature higher every day with a peak of 34.9C on the 25th, being 14.1C above my long-term average, setting a new record for this station for June, which surpassed my previous record of 32.2C set in 2017.
We all remember how hot it felt outside in the intensive heat, however, I thought it interesting to have an overview of how the soil, at a depth of 5cm and read every day at 08.00, responded to the wall-to-wall, excessive heat. On the 20th, the day before the heatwave arrived, the temperature was 20.4C, then 21.2C, 22.9C, 23.7C, 25.6C, 25.8C and 26.9C respectively, for the following six days. Since 2014, when this instrument was installed, the average temperature over the intervening 13 years, has risen from 15.5C to 16.3C.
As a matter of interest, the glass soil thermometer has a 90-degree angle, with the horizontal scale just above the surface, on which is the inscribed scale.
The Met Office heatwave threshold was updated ahead of summer 2022. The initial heatwave thresholds were calculated based on the 1981-2010 climatology of daily maximum temperature at the mid-point of the meteorological summer (15 July). The revised thresholds use the 1991-2020 averaging period introduced in January 2022. The geographical differences reflect the differences in climate across the UK.
This second heatwave of 2026, lasting seven days, ended on the 28th as two cold weather fronts crossed the country with a much cooler air stream following as the wind backed into a westerly quadrant. This heralded the arrival of an Atlantic weather pattern to close the month.
To get an overview of how the climate might have changed regarding these very hot days, I delved into my records and took an arbitrary, round figure of 30C. Choosing periods of five years I found that 30C or above was recorded on 5 days between 2011-2015, 19 days from 2016-2020 and 30 days for 2021-2025.
Another angle was to research on how many occasions we had endured a heatwave, a daily maximum of 27C or above for Wiltshire, for at least consecutive three days. Taking the same five-year periods, I discovered that from 2011-2015 there was 1 heatwave on each of three years, from 2016-2020 for three years had 2 heatwaves and during the last period of 2012-2025 for two years we had 3 heatwaves each year. Thus over 15 years a very clear picture of an upward trend in the increasing days of extreme heat for longer periods.
The monthly rainfall total was 66.8mm being 110% of my 42-year record or +5.3mm. The wettest day was on the 1st when nearly half the month’s rain fell with a daily total of 28.0mm. There were 17 totally dry days.
The average temperature for June of 17.85C, was 2.9C above my long-term average, which broke the previous record set in 2023 by 0.31C. Both maxima and minima contributed to this high average with the maximum 2.3C and the minimum 3.4C above average.
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