Category: Commentary

What a difference between two successive days as the temperature difference between the maxima of Friday and Saturday was almost 20C and very welcome rain. After the residual heat from Friday was lost the thermometer hovered around 13C all day on Saturday rather than 31.3C. The wind had veered into the north and north-northeast, a cooler direction than previous days.

Light rain began to fall for a brief period at 19.05 and more continuous steady rainfall started again at 20.35 amounting to 6.8mm. This was the second wettest day this month, after 8.7mm on the 5th, and brought the monthly total 18.8mm when the average is 54.2mm.

The temperature slipped away to 7.9C overnight.

Sunday was initially cloudy but soon after 07.30 brief sunny intervals occurred that lifted the temperature to 10.6C at 08.00. The wind continues from the north-northeast and brisk. The soil temperature at a depth of 5cm has dropped 8C in twenty-four hours to register 13.3C at 08.00.

The thermometer rose steadily all day on Friday to register a peak of 31.3C at 15.40. This was 11.1C above the 38-year average and the hottest day since 25th June 2020. It was not a record for June as a peak of 32.2C was recorded on June 21st 2017.

The humidity began to rise from a low of 41% after 16.15 and the wind to veer from south to west. It was another day with the UV level reaching Very High again.

The past night was very warm with the thermometer not sinking below 13.5C being 3.4C above the average.

Saturday brought a different start to a day with very misty conditions and the humidity of 91% the highest for a fortnight. By 08.00 the milky sunshine had lifted the temperature to 17.7C. The wind has now veered from west into the north.

Over 5mm of equivalent rainfall was lost on Friday to evaporation bringing the monthly total to 56mm when just 12mm of rainfall has fallen.

In the intense sunshine on Thursday the thermometer soared to 28.5C making it the hottest day since 7th September 2021 (29.2C) and a significant 8.3C above the 38-year average.

It was another dry day with the loss of equivalent rainfall through evaporation from ground sources and plant life reaching 50mm, far in excess of the 12.0mm of rainfall in June.

The heatwave threshold for Wiltshire is three consecutive days with temperatures equal to or above 27.0C. For my station on the outskirts of town and the station well up the garden away from the influence of buildings and paved areas, this won’t quite be reached as Saturday is forecast to be cooler due to a cold front approaching the area. However, in the town where the buildings and paved surfaces hold more overnight warmth, it will likely that the threshold is reached.

The news of extreme heat for London hits the headlines but normal Met Office data is from stations where the instruments are well away from buildings and paved areas.

It has been a very warm night with the temperature overnight not falling below 13.7C, which was 3.6C above the average making it the warmest night since20th October.

The sun on Friday was more muted first thing due to thin high cloud, however the thermometer had already reached 19.8C at 08.00. The light breeze has backed from the southwest to south and light.

Update at 13.30: thermometer reached 30.0C at 13.25.

Update at 18.25: maximum temperature of 31.3C, hottest for two years and only 0.9C below record set in 2017.

As the anticyclone edged closer the temperature on Wednesday rose even higher to reach a maximum of 26.2C, the highest since 8th September 2021 and 6.0C above the 38-year average.

It was another dry day with just 12.0mm of rainfall this month. The heat and many hours of strong sunshine recently have increased the daily loss of equivalent rainfall through evaporation to 4.68mm and 4.76mm during the past two days. The equivalent loss of rainfall this month now totals 46mm, almost twice the actual rainfall.

The thermometer fell way to 6.8C overnight but recovered to 17.8C at 08.00.

Heatwave Threshold.
The thermometer has to reach at least 27.0C for three consecutive days to be classed as a heatwave for Wiltshire. The possibility is that both Thursday and Friday could see that temperature reached but Saturday is forecast to be cooler.

The official Met Office weather stations are situated on large grassed areas well away from any hard surfaces and buildings as these hold the heat. My weather station is on the northern edge of Marlborough and sited well up the garden, therefore a thermometer in the centre of town, midst buildings and solid surfaces, will register an even higher temperature than my station.

Tomorrow I will include up to date data on recent heatwaves and the trends in frequency and temperature.

Update at 19.20: maximum of 28.5C at 16.14. Highest daily maximum since 7th September 2021

Tuesday saw the thermometer soar to 24.7C, which was the warmest day since 26th July 2021 (26.6C) and 4.5C above the 38-year average, under the influence of the anticyclone.

It was another dry day, the tenth this month, with the monthly rainfall still 12.0m when the average is 54.2mm and through evaporation still losing over 3mm of equivalent daily rainfall.

Once again under clear skies the temperature dropped away, last night to a minimum of 5.8C being 4.3C below the average.

Wednesday began with wonderful sunshine that lifted the temperature to 18.8C at 08.00. At that time the soil temperature at a depth of 5cm read 19.1C under the influence of many hours of sunshine and the soil drying out.