The very warm conditions that we experienced in late June continued for the first few days of July with maximum temperatures just above the early July average. A cool, brisk north-westerly breeze on the 2nd limited the rise in temperature to 2C above the early July average whist a clear sky and the residue of the cooler north-westerly airstream produced a very cool following night, in fact the coolest since 17th May, that saw the temperature drop to 6.9C being 5.1C below average.
The third heatwave of the year arrived on the 5th when the maximum of 27.2C reached and exceeded the Wiltshire threshold of 27C. That was the start of a prolonged heatwave that last for eight days with a peak temperature of 34.2C on the 9th.
There was a brief respite on the 13th and 14th due to the arrival of cloud from the east that had drifted in from the North Sea overnight, that limited early morning sunshine until the cloud burnt away. The nights over those two days were also cooler.
By the 15th the considerable heat had returned with the maximum again exceeding the heatwave threshold with a peak of 29.2C on the 16th.
The centre of the high pressure began to relocate a little to the west from around the 18th that resulted in the air stream arriving from the northeast but the air having originated from near Iceland. This cooler air stream resulted in maximum temperatures falling away with the coolest day all month on the 19th with a peak of 23.1C, which was just 0.2C above my long-term average. Under clear skies initially the cool air resulted in a minimum of just 6.3C, which made it the coolest day since 16th May, being 5.7C below average.
Around the 24th there were signs that the anticyclone to the southwest was giving up the battle against the depression near Iceland. The barometric pressure had dropped 25mb from its peak on the 21st to its lowest pressure on the 26th with a reading of 1005.0mb. This allowed cloud to drift across the country containing a weak, cold weather front.
This resulted in an unusual weather feature for this month that occurred at around 05.45 Sunday morning of the 26th when light rain fell very briefly, which was repeated at 07.20. Sadly, on both occasions the precipitation was minimal and brief, which made it not measurable thus being recorded as a trace. The rain radar showed small areas of thicker cloud drifting in from the west at those times, however within a few minutes the evidence had evaporated due to the very warm and dry ground. The minimal precipitation broke the run of 24 consecutive totally dry days.
The track of the second cloud area showed the longer and slightly heavier falls over Pewsey and even more so around Amesbury, both to the south of Marlborough, as often happens.
The Azores high fought back from the 28th pushing a ridge back over the country that, after two cool days, saw temperatures rose significantly once again.
The average temperature for July was 3.1C above my long-term July average making it, not surprisingly, the hottest July since this station started in 1984, principally due to the excessive heat by day. Analysing the day/night averages I found that the average maximum was +4.9C whilst the average minimum was +1.3C.
There were fifteen days when the peak temperature was equal to or above the heatwave threshold for Wiltshire of 27C. The hottest day occurred on the 9th with a peak of 34.2C whilst even the coolest day was above the average with 23.1C on the 19th, being +0.2C. This peak did not break my record for the hottest July day as 36.7C was logged in 2022.
The trend for increasing heat is becoming even more obvious as the years roll by. I analysed the number of days over the past fifteen years when the heatwave threshold was equalled or exceeded, broken into three five-year spans. From 2011-2015 there were 24 heatwave days, the period of 2016-2020 brought 57, whilst the latest period of 2021-25 inflicted 75 heatwave days upon us.
The other significant feature of the month was the lack of rain with measurable rain only recorded on one day, the 1st, when a miserly 0.2mm was recorded, being just 0.3% of my 43-year record. The 43-year average July rainfall was 59.4mm. Very brief light rain or drizzle was observed on the 26th and 30th but not measurable, in fact the evidence evaporated within a few minutes from the very warm, dry surfaces.
It is also important to set against the lack of precipitation the loss of equivalent rainfall into the atmosphere due to evaporation from the ground and plant sources, which totalled 155.6mm. The greatest daily loss was on the 5th with 6.6mm of equivalent rainfall compared to just 2.9mm at the end of the month when the wind backed into the west with a slightly more humid air steam and of course after the dry month.
The soil temperature measured at a depth of 5cm daily at 08.00 reflected the intense heat. A peak of 25.1C was logged on the 11th during the eight-day heatwave with the lowest on the 20th with 17.2C.
The Marlborough Playhouse – opening soon
