Monday 10th August
After a cool start to Sunday with variable cloud at first, the heat built steadily to exceed the heatwave threshold with a maximum of 30.6C at 16.02, being a significant 9C above my long-term August average. The past night was mild, compared to the previous chilly nights, with a minimum of 14.2C at 05.59, just after sunrise in Marlborough at 05.44. This low was 2.4C above average.
Monday began with thin high cloud that initially limited the rise in temperature, reaching 18.6C by 08.00. The high pressure centre is currently over the north of the UK but will begin to make a subtle move in position over the next day or two that will result in a significant increase in the temperature from Tuesday onwards.
Today a cold weather front is passing over the country containing a little, variable cloud. The air behind it is cooler, combined with less strong sunshine this morning, will result in the peak temperature today lower than recent days, not sure if it will reach the heatwave threshold. The air stream will veer from north-northwest to north as the day progresses, and north-northeast later this the evening as the high pressure eases towards the North Sea.
The forecast pressure charts indicate that the anticyclone will continue to very slowly migrate eastwards that will result in the wind veering into the southeast or east-southeast for the next few days. The air coming from this direction will carry heat from the Continent with the result temperatures are going to push well above the heatwave threshold, likely into the low 30s by Wednesday.
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.