Windrush Weather

Category: Commentary

  • All change today – gone is the extreme heat after the record breaking June

    All change today – gone is the extreme heat after the record breaking June

    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.

  • What a scorcher yesterday at a peak of 31.3C, but change is afoot

    What a scorcher yesterday at a peak of 31.3C, but change is afoot

    The very strong, relentless sunshine on Monday, combined with the UV level ‘Very High’ again, pushed the thermometer to 31.1C at 16.36. This peak was a significant 10.7C above my long-term average making it the hottest day since 14th August 2022 when 33.2C was logged.. The hot air persisted overnight that saw the thermometer not drop below 18.5C, logged at 05.17 early Tuesday, just after dawn in Marlborough at 04.54.

    Tuesday began with variable cloud and some early sunshine, but cloud began encroaching from the northwest so by 07.00 it became muted. The considerable heat by day and night has resulted in a ground temperature at a depth of 5cm reading 25.2C at 08.00.

    A cold weather front is edging down from the north, which is bringing the increased thin and variable cloud that heralds the change in our weather pattern.

    We have recently been under the edge of a heat dome that was centred over Spain, Portugal and France that had been trapping hot, stagnant air beneath it. As the weak weather front eases southwards today, combined with a low pressure system in the North Sea, the wind will come from the west, bringing a fresher air stream as the day progresses, thus the peak temperature today will not quite reach the high of Monday as the recent heat is slowly being edged eastwards.

    There is news today of the first ever geostationary satellite to provide 3D profiles for temperature and humidity for Europe being launched today. This will provide data to enhance the next generation of weather forecasts. It is the second satellite as part of a series of six which will revolutionise and safeguard weather forecasting across Europe for the next 20 years. The Met Office say ” This international collaboration is vital in ensuring that recent improvements to forecast accuracy can be safeguarded and enhanced in the coming years.”

    Due to family commitments the June review will be one day late and appear tomorrow.

  • Solar energy and UV yesterday the highest since last August. Beware ‘Very High’ UV around 13.00 again today

    Solar energy and UV yesterday the highest since last August. Beware ‘Very High’ UV around 13.00 again today

    With little breeze from the west and relentless strong sunshine the thermometer slowly edged up all morning on Sunday hovering for a while at 27C at 15.24 before a sustained burst of sunshine and accumulated heat lifted the maximum to 27.4C at 16.24. The highest solar energy was logged at 12.55 with 1257W/m2 recorded, simultaneously, the UV peaked with a value of 8.5, the highest since 13th August 2024, which was at the top end of ‘Very High’. Initially the thermometer slowly edged downwards overnight, under clear skies, with a minimum of 13.6C logged in the very early hours at 03.09 on Monday, however the back track of the cloud radar showed thin, high cloud drifting in from the south just before 04.00. Early risers would have seen on Monday morning that the cloud limited the sunshine after dawn with misty conditions but by 07.30 the sun was beginning to find breaks and lifted the temperature to 19.9C by 08.00.

    Monday will see the temperatures rise very high again, especially as the air stream backed from west yesterday to southeast overnight with this morning wafting hot air from the Azores region courtesy of the Azores High. The centre of the high has eased a little eastwards over the Netherlands hence the change in direction.

    A small disturbance, minimal low pressure area, will form off the southeast coast of the UK tomorrow, so there is an outside chance of some light rain in the afternoon, with the wind briefly backing into a northerly quadrant.

    With no rain possible today the total rainfall for June will stand at 37.1mm against my 41-year average of 52.9mm. Due to the heat and warm winds there has been an equivalent loss of rainfall, due to evaporation from ground sources and plant life, of 110.1mm.

    The opposite to wind chill in the winter was again apparent on Sunday. Using data from the wind strength, temperature, humidity and also solar activity, outside at 14.00 it felt more like 30.9C when the thermometer registered 25.3C.

    I am starting a new series of images for a week or two of bees that are so important to crops, taken from my library over the post 50 years. They were taken at various times in the year.

  • Officially a heatwave.

    Officially a heatwave.

    The sunshine was intense on Saturday pushing the thermometer mid-afternoon to a maximum of 28.7C being a significant 8.1C above average. Light variable cloud limited any further rise but this was the hottest day since the 21st when 29.7C was logged. The past night was slightly cooler than the previous but a minimum of 17.1C was still 6.9C above average.

    The start to Sunday revealed a mainly cloudy sky although there were brief brighter intervals in the minimal cloud breaks before 08.30. The thermometer had risen to 20.0C by 08.00.

    The anticyclone is now firmly in control of our weather until at least Wednesday although Monday will probably bring the peak temperature. The centre of the high pressure, current barometric pressure is 1026.5mb, lies over the English Channel that will see the continuation of a westerly breeze today, backing into a more southerly direction on Monday that will increase the heat, and then likely to change significantly into a northerly quadrant on Tuesday before temperatures fall away considerably on Wednesday. By Tuesday we will have had four consecutive days with the maximum above 27C.

    The heatwave threshold for the Marlborough area is 27C. The maximum yesterday was above that figure, which will happen again today and also tomorrow. Thus we are technically experiencing a heatwave, which 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.

  • Warmest night since August 2020

    Warmest night since August 2020

    The nearby anticyclone really began to dominate our weather on Friday that brought heat and humidity and saw the temperature rise to a maximum of 26.8C being 6.2C above my long-term average. The UV level of 7.9 for the second consecutive day was well into the ‘Very High’ category. Cloud cover overnight persisted and looking at the track on radar it indicated that it began to thicken around 05.00, which is why the minimum of 18.4C was a significant 8.2C above average and made it the warmest night since 13th August 2020 when a low of 19.4C was logged.

    The heat factor, using the data of temperature, wind speed, humidity and solar activity, calculated that outside it felt more like 31.5C when the thermometer read 26.6C.

    Saturday revealed low, thick cloud and thus no sunshine to greet the new day. The anticyclone has continued to build and dominant our weather with the barometric pressure reading of 1023.7mb at 08.00, up 10mb since Wednesday.

    The forecast is for the heat to continue to build and peak on Monday, with Tuesday down a few degrees and the rest of the week much closer to July temperatures. It is likely that we will technically be experiencing a heatwave over the next three consecutive days as maxima are likely to equal or exceed 27C, which is the heatwave threshold for Wiltshire.

    The image taken in 2015 is from St Peters Church tower in Marlborough, looking south with Savernake Forest in the background.