Author: Eric Gilbert

The maximum of 23.9C on Sunday was all above average at +3.3C thanks to the sunshine that began to shine strongly around midday as the cloud began to thin. The warmth built up as the afternoon progressed, the peak was logged at 17.56. More cloud overnight meant a mild night that saw the thermometer not drop below 10.5C, logged at 05.01, which was 0.3C above my 40-year average and made it the warmest night since the 14th.

Monday revealed a misty, foggy start to the new day with the visibility slowly dropping to a minimum of 300mm around 07.30, after which time the sun got to work and by 08.00 patches of blue sky came into view through variable cloud.

The anticyclone will be with us for the next two days but on Wednesday the projection is for another depression to take over control of our weather.

There has been much mention in the press recently of a possible heatwave this week, perhaps the following might be of interest. The forecast for Wiltshire this week, if it is accurate, dose not indicate a heatwave.

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.

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.

The maximum of 21.0C on Saturday was above average, only just at +0.6C, but welcome after the cool days earlier in the month. The breeze from the west was brisk with a maximum gust of 16mph. The day was dry and the UV peaked at 7.9, which was in the Very High category, but to be expected at around mid-summer when the sun shines strongly. The low of 9.1C logged at 04.42 early Sunday was 1.1C below the average.

Sunday brought a cloudy start to the day with no brightness
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The recent high pressure, centred in mid-Atlantic, is drawing away and for a short period we are coming under the inflict of a depression in the North Atlantic that will push a weather front across our area today so a cloudy day is in prospect. The breeze is likely to be light and from the west or west-southwest.

With a maximum of 23.7C on Friday, which was 3.1C above the average, it was another summery day although the brisk wind from the southwest fell a little cool when the sun dropped behind the clouds late afternoon.

The cloud began to drift across from the west late afternoon and thickened overnight that meant a mild night with a low of 13.6C making it the warmest night this month being 3.4C above the average.

A cold weather front passed over our area in the early hours depositing 0.9mm of rainfall.

Saturday arrived overcast with a little drizzle juts before 08.00, but soon after the cloud thinned and lifted to give us the occasional burst of sunshine.

Under the ridge of high pressure on Thursday the sun shone strongly all day and boosted the temperature to a maximum of 23.9C late in the afternoon at 18.17, which was 3.3C above my 40-year average and was the hottest day since 15th September 2023.

Under a clear sky the warmth dissipated into the atmosphere, as a result the thermometer steadily dropped to a minimum of 6.8C early Friday at 05.16, which was 3.3C below average.

Friday brought us another glorious start to a new day with the sun shining strongly after sunrise that lifted the temperature to 17.6C at 08.00.

Under the strong sunshine and light breeze on Thursday the equivalent loss of rainfall due to evaporation from ground sources and plant life rose to 5.01mm for that one day. The total loss of equivalent rainfall for June to date now stands at 64.1mm, far exceeding the rainfall total of 16.1mm for the first 20 days of June.

The barometric pressure has been slowly falling away as depression to the north of the UK begins to make its presence felt. Later today and tonight cloud from an associated weather front with feed cloud across our region and possibly some light rain overnight. The pressure reading at 08.00 was 1014.7mb, down 7mb since that time on Thursday.

Tuesday was disappointing as regards heat, following the warm Monday, as the persistent breeze from the northeast pegged back the temperatures, there was also less sunshine due to variable cloud. The maximum of 20.1C occurred at 14.45 and was 0.5C below my 40-year average. The low of 10.0C was also below average, just, at -0.2C, which occurred very early Wednesday morning at 01.57 thanks to the cloud that rolled in from the east overnight carried along on the persistent northeasterly breeze that was quite gusty after dawn.

Wednesday gave us a disappointing start to a new day as the cloud cover was thick and the northeasterly breeze gusty. There were a few bright intervals just before 08.00 but very brief. The thermometer had risen to 12.2C by 08.00.

The high pressure in mid-Atlantic is building over the UK, the pressure reading at 08.00 was 1020.9mb, up 6mb since Tuesday and 11mb since Monday. This ridge of high pressure should maintain the dry and sunny conditions after the sun breaks through and burns away the cloud.