The sunshine was intense and relentless again on Tuesday resulting in a maximum of 30.1C being logged very early in the afternoon at 13.28. This high was 7.4C above my long-term average but down 1.2C on the extreme heat on Monday. Recently the peak has been later in the afternoon as the heat continued to build throughout the day but the advance thin, high cloud and the arrival of sightly cooler air meant the thermometer began to fall a couple of degrees during the afternoon. Data is read at 08.00 daily with an overnight minimum of 16.1C recorded at 07.02 early Wednesday, which was 4.2C above average.
The start to Wednesday revealed total cloud cover resulting from the back edge of the cold front having passed our way during the early hours that has seen the air temperature very slowly edge downwards again to reach 15.6C at 08.30. The rain band associated with the cold front is edging eastwards towards London and giving us a miss. The cold front also brought a change in wind direction, now coming from a northwesterly direction, that has brought the cooler air.
The very high temperatures of recent days are now a memory as the next few days will see maxima close to the average for July of 22.7C. Thursday will see an anticyclone begin to exert itself from the Atlantic for a couple of days before a low pressure, currently around Iceland, begin to take charge with more cloud and the possibility of some light precipitation, but too early to be certain also a slight drop in temperatures.
June 2025 Review
Following the warm end to May it was quite a contrast to find that the beginning of meteorological summer began with numerous below average maxima. The days and nights were cool with very small amounts of daily precipitation after the previous three relatively dry and warm months. The heaviest fall was recorded on the 7th with 7.9m, which was deposited over many hours during the daytime and a light shower overnight.
The brisk westerly breeze on the 7th and 8th originated from just south of Greenland, hence the moderated temperatures with a maximum of only 15.9C being 4.7C below my long-term average.
A short drier period followed that saw temperatures increasing daily, especially by the13th as a flow of very warm air from Iberia had arrived that lifted the temperature to a maximum of 26.2C, being 5.6C above average.
Often in winter I mention that wind chill is a factor as if outside it would feel colder than that indicated on a thermometer, referred to as the THW Index, that uses temperature, humidity and wind strength data. On the 13th the opposite was true when the THSW Index indicated if felt more like 30.2C outside on the skin, rather than the thermometer temperature of 26.2C, when the additional factor of strong sunshine was considered.
High pressure saw the heat build from the 16th to the 21st with maxima well above my long-term average. The peak of 30.7C was logged on the 19th being a significant 10.1C above average. These conditions were brought about by hot, dry air drafted across on a southeasterly breeze from the Continent. The humidity level dropped very low in the afternoons to just over 40% on several days with the land drying out. There were several days when the equivalent loss of rainfall, through evaporation from ground sources and plant life, was in excess of 5mm daily.
The heatwave threshold for the Marlborough area is 27C. A 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.
There was a significant contrast in peak solar activity mid-month during several days when the wind veered into the west following days after a southeasterly was in control. The peak solar activity was at least 30% higher when the cooler, clearer air came from the Atlantic rather than the polluted hot air that had travelled across from the Continent brought on a southeasterly breeze.
It was all change from the 22nd when low pressure to the northwest began to bring an Atlantic influence to our weather with maxima dropping closer to normal. The air having travelled over the sea was much less polluted than that from the Continent during the previous week. The peak solar radiation reached 1172W/m2 on the 24th compared to around 800W/m2 when we endured the hot, dry Continental air.
The month finished with a heatwave, thanks to the Azores high pressure system, that once again saw three consecutive days when the maxima were equal to or above 27C to qualify as a heatwave. The peak solar activity occurred on the 29th when 1257W/m2 was logged at 12.52 just as the highest UV of 8.5 was recorded, which was at the top end of ‘Very High’. The last day of the month brought intense heat as the thermometer soared to a maximum of 31.3C making it the hottest day since 14th August 2022 when 33.2C was recorded.
June 2025 was the hottest June I have recorded since the station was set up in 1984 with the average temperature a significant 2.5C above my 41-year average. It was not surprising to find that both the average maximum and average minimum were well above average at +2.72C and + 2.34C respectively.
The total rainfall for June was 37.1mm being 70% of my 41-year average or minus 15.8mm. Due to the intense heat and warm winds the loss of equivalent rainfall due to evaporation from the ground and plant sources amounted to 116.1mm for the month.
Although both January and February were wet months, because the following four months were much drier than average, the rainfall for the January to June period was only 296.2mm set against my 41-year record for that period of 390.9mm.