Author: Eric Gilbert

The maximum of 19.3C on Friday made it the coolest day since the 15th being 1.3C below my 40-year average thanks to the very brisk wind from the west. The past night was very cool as the thermometer dropped to 5.9C, the coolest night since the 13th, being 4.3C below the average. Even the UV level at 6.2, rated High, was the lowest since the 13th.

Saturday started with welcome strong sunshine that had lifted the temperature to 14.8C by 08.00.

The soil temperature at a depth of 5cm has also reflected the reduction in heat with 22.1C, 20.9C,18.0C and 17.3C respectively over the past four days logged at 08.00

Thursday marked the change between the very hot and dry weather over the past three days to the cooler, windier weather that saw a drop of 8C between the extreme maxima. The peak on Thursday was 21.5C, just 0.9C above my 40-year average. The past night was also cooler logging a minimum of 11.0C at 05.27 early Friday being 0.8C above average. These changes were due to the low pressure system to the northwest.

Friday produced variable brief sunshine first thing but breezy. The wind continues from the west.

The unusually deep depression, for summer time, combined with a developing depression to the west of Ireland, will continue the flow of brisk, westerly winds that will again today moderate the temperatures by day.

To date we have lost over 90mm of equivalent rainfall through evaporation from ground sources and plant life. The daily rate recently has increased to over 4mm thanks to the heat and brisk wind. The rainfall total for June is currently just 20.5mm, therefore with little rain in the forecast it is likely to be the driest month since February 2023.

The peak of 29.3C that was logged at 15.43 on Wednesday made it the hottest day since 9th September and a significant 8.9C above my 40-year average. The ground is holding a lot of warmth so it was not surprising, with cloud drifting in overnight, to find the minimum of 14.9C, logged 03.34 early Thursday, was 4.7C above the average and the warmest night since 12th September 2023

There was variable sunshine on Thursday after 07.15 as the cloud associated with a weather front passing our way, eased away eastwards.

The depression just off the west coast of Scotland produced the cold front that crossed our area in the early hours of Thursday, and as its name suggests, brought cooler weather with significantly lower temperatures than endured over the past three days, could be a drop of at least 10C. Not only will it be cooler but the breeze is forecast to strengthen significantly as the day progresses.

A disturbance in the Atlantic near the Cape Verde Islands has a greater than 60% chance of later forming the first tropical storm of the season as it moves in a westward/northwestward direction towards the Caribbean.

The strong, continuous sunshine on Tuesday boosted the temperature to a maximum of 27.6C at 13.37 before variable cloud limited any further rise until later in the afternoon when the cloud thinned and a peak of 28.5C was logged at 17.17. This was 7.9C above my 40-year average and the hottest day since 9th September 2023 (31.0C).

The ground has absorbed the heat over the past three days so a mild night followed with a minimum of 12.5C at 05.18 before the sun rose. This was 2.3C above the average and made it the warmest night since 7th October.

Wednesday began with strong sunshine after sunrise that by 08.00 had pushed the thermometer to 20.7C.

Update at 16.35: maximum of 29.3C logged at 15.43.

The hot sunshine has been absorbed by the ground over the past four days with a temperature at a depth of 5cm reading 16.7C, 17.2C, 21.4C and 22.1C respectively.

The recent anticyclone has been slowly losing its pressure as a depression edges closer from the northwest. As a result today will be the last of the hot, sunny days as advance cloud from the low pressure system will begin to cover the sky on Thursday. The barometric pressure at 08.00 read 1013.6C, down 7mb since Monday.

A maximum of 25.6C at 15.22 on Monday was 5.0C above my 40-year average and the hottest day since 9th September 2023 (31.0C). This high was 1.4C short of the heatwave threshold. The low of 10.8C at 05.17 on Tuesday was just above average for June at +0.6C.

Tuesday revealed a splendid start to a new day with strong sunshine after sunrise that quickly dissipated the radiation fog by 06.15, which had formed in the early hours along the River Og valley.

Update at 16.15: day maximum of 27.6C logged at 13.37. Tomorrow should be similar but not Thursday so hot spell will not be classed as a heatwave.

Further update: Late afternoon surge with strong sunshine saw the thermometer climb back up to a high of 28.5C at 17.17

Why do heatwaves happen?
Heatwaves are most common in summer when high pressure develops across an area. High pressure systems are slow moving and can persist over an area for a prolonged period of time, such as days or weeks. They can occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer. This can allow high pressure to develop over the UK resulting in persistent dry and settled weather.ilat

In England & Wales on Sunday, the Met Office issued a 4-day Heat Health Alert from 08.00 Monday 24th, a system which places each Local Authority region into one of four levels.

In March 2022 the Met Office announced that the official heatwave thresholds were being updated ahead of the summer, resulting in eight counties having their threshold increased by 1C. The heatwave threshold for Wiltshire was raised from 26C to 27C and must be equalled or exceeded for three consecutive days to be classed as a heatwave.

The original thresholds were derived from the distribution of July maximum temperatures in a 1981-2010 reference climate period and the change in threshold results from the Met Office update to a 1991-2020 reference climate.