Thursday gave us a very cloudy morning and early afternoon that limited the rise in temperature to a maximum at 13.38 of 25.9C, being 3.2C above average. That broke the recent pattern of heat building throughout the afternoon. The reason was a very moist air stream from a warm weather front that crossed during the day. This weather pattern gave us another very mild night with a low of 16.0C at 03.41, which was 4.1C above average. The humidity at 16.00 was high at 64% and by 18.00 had risen to 78% when last week I was registering humidity around 40% in the afternoons.
The start to Friday was in contrast to recent mornings as the very moist air and low cloud meant the Marlborough Downs and Savernake Forest were draped in cloud. Initially, the visibility was limited to 500m, but this improved very quickly that by 07.50 had lifted into low cloud. The humidity at 08.00 was 89.1%, the second highest this month. The cloudier conditions today are thanks to a cold front crossing the UK. There are currently three modest low pressure systems around the UK so unsettled conditions are likely for the next few days, with sunshine and possible showers also less extreme temperatures.
The recent heatwaves made headline news with three in succession have occurred in 2025, so far, when the heat threshold for Wiltshire of 27C was equalled or exceeded. I have analysed the last thirty years of my records to find the incidence when a daily maximum of 27C was equalled or exceeded and discovered a distinct rising trend over that period. In the early 1990’s there was an average of 7 days when those conditions were met whereas in the 2020s that figure had risen significantly to 14 each year, on average. The extremes were in 1998 when no days reached a maximum of 27C, which contrasts with the year of 2018 when 28 days of 27C or above were recorded. This year we have so far had 13 days when the maximum of 27C or above was recorded.
The image is of a scarlet tiger moth, active during day and night. It flashes its red hindwings as a warning to predators.