Author: Eric Gilbert

It is very unusual for two successive days to have the same maximum temperature but both Sunday and Monday saw the thermometer rise to just 13.9C, being 3.4C below average. This peak was logged at 16.20 thanks to the afternoon sunshine as the day had been dominated by variable cloud. As on previous nights under clearing skies what residual warmth there was dispersed into the atmosphere with a slow rate of decline in the air temperature reaching a minimum of 0.7C at 05.54, producing a ground frost, being a significant 6.4C below my long-term average. This low was held for just 7 minutes before the thermometer began to climb reaching 5.1C at 08.00. This was principally due to some glorious sunshine after dawn but a large bank of cloud, that had been drifting in from the northeast, eventually overcame the sun at 06.52.

The large bank of cloud seen on Tuesday after 07.00 was the result of the air having travelled over the cold North Sea picking up moisture on its travels. This thick cloud will take a time to thin and melt away today so it is not going to be a very warm and sunny day, however, it should improve as the day progresses.

The anticyclone is going to hang around for the rest of the week, which will continue the trend of dry weather but as it relocates a little further south from today, and closer to the UK, the wind will, thankfully, be less strong with variable sunshine but a slow rose in temperature. There is little chance of any significant rain over the next few days.

Data Collection Part 1
We are aware of satellites overhead watching the development of weather systems but the air mass directly above the ground is what immediately affects us, for which regular, accurate data is vital.
Radiosondes are sent up at regular intervals to gain the vital data for the numerous forecasts via different media. There are 6 radiosonde stations around the UK from near Camborne in the southwest to the Orkneys, Northern Ireland and in between. These stations prepare a balloon made of latex, and after inflation with either helium or hydrogen, are released at precise intervals being at midday and midnight, these are internationally agreed timings. There are around 1,800 stations globally. The balloons rise to a height of around 25 miles and are tracked for wind speed and direction whilst the radiosonde records temperature, humidity and barometric pressure every two seconds, which is then signalled back to the relevant ground station.

The strong northeasterly on Sunday, that propelled the cool air from near Iceland and then travelled over Scandinavia, gave us a chilly day with the thermometer struggling to reach a maximum of 13.9C at 15.49. This was 3.4C below my long-term average and the coolest day since 18th April. The wind, gusting to 20mph, produced a wind chill so that outside it felt more than 1C cooler than that indicated on a thermometer. Under mainly clear skies the thermometer slowly edged downwards reaching a low of 1.5C at 05.37. This low was held for just 5 minutes before the temperature began to recover after sunrise, which was at 05.23 for Marlborough, when it began to edge back upwards.

Variable cloud greeted the new day on Monday although there was a clearer break in the cloud drifting in from the northeast just before 08.00 that lifted the temperature to 5.0C. However, more cloud then arrived around 08.30 on the brisk northeasterly breeze.

Wind chill will be a factor again today, often described as the ‘feels like’ temperature. The temperature, wind strength at a height of about 150cm (human height) and humidity are combined to produce a wind chill. These three items of data use a formula, which is not standardised, to calculate the effect of moving heat away from the body making it feel colder.

After two very dry months when the total combined rainfall was a significant 103.5mm below my 41-year average, May is continuing that trend. In fact, the high pressure is going to dominate our weather for this week and likely to have a reduced effect into next week so there is minimal chance of any substantial rainfall in the near future. During these two months we lost the equivalent of 130mm of rainfall through evaporation from ground sources and plant life that continues this month with another 15mm already lost.

The images for the next few days were taken at Malmesbury Abbey Gardens a few years ago.

Although there was variable sunshine on Saturday the cooler air had fully arrived that saw the thermometer rise slowly to reach a maximum of 18.3C in the early afternoon at 13.29 before thicker cloud and an increase in wind strength prevented any further rise. This high was a significant 10C below the peak on Thursday making it the coolest day since 26th April. A slow loss of warmth into the atmosphere overnight, under clear skies, meant the thermometer reached a minimum of 2.8C at 04.17 being 4.2C below my long-term average. Variable cloud then drifting down from the north, saw the thermometer make an about turn to reach 6C just before 06.00 so thankfully no air frost.

Sunday first thing revealed that a bank of cloud continued to drift down from the north obscuring the sun but by 07.15 the cloud had begun to thin and break up that resulted in the temperature rising to 9.2C by 08.00.

The air stream today is originating just to the east of Iceland, travelling around the north side of the anticyclone and then descending down across Scandinavia, hence the considerable reduction in temperature compared to previous days. This will continue again on Monday with the wind coming from a northeasterly quadrant and strengthening after mid-morning on both days, which will make it feel very cool after the heat of last week. By Tuesday the anticyclone is forecast to be closer to the UK hence the reduction in wind strength.

The outlook is for this anticyclone to hang around for a few days, slipping a little further south towards the UK, that will by Tuesday see a slight improvement in temperature but still be subject to the northeasterly breeze.

Following two very dry months there is no indication of substantial rain in the week ahead. I earthed up my potatoes yesterday, in case of a slight frost overnight, and the soil is understandably very dry with little moisture even deep into the ground.

Today and for the next few days I will add a selection of beautiful images of tulips captured at Malmesbury Abbey Gardens a few years ago giving a splash of colour.

The beginning of a cooler air flow on Friday meant the maximum of 23.7C was almost 5C below the heat of Thursday but still 6.4C above the long-term average. The variable cloud limited the rise in UV to just a Moderate level after several days when it peaked at High. Variable cloud overnight meant an above average minimum of 8.8 (+1.7C) early on Saturday.

Saturday began with total cloud cover but just before 07.45 the thick cloud that had been drifting down from the north began to clear and break up allowing the sun to break through and raise the temperature to 11.9C by 08.00. The area of thunderstorms and heavy rain that is currently over the Isles of Scilly and Britanny is edging slowly northwards across the channel approaching the south coast.

For the next three or four days our weather will be dominated by an anticyclone, currently centred just south of Iceland, which is feeding a much cooler air stream down from the north, originating over Scandinavia. This high pressure system is forecast to slowly drift southwards that for the weekend will maintain the cooler but mainly dry weather. By Monday onwards the anticyclone will be much closer to the UK, as a result the wind will have a more easterly component, so a little less cool but maintaining the trend of dry days and becoming a little more breezy.

This will be the last images of bluebells from West Woods near Marlborough. Starting tomorrow will be a walk through the Malmesbury Abbey Gardens enjoying the beautiful tulip displays.

The continuous and strong sunshine on Thursday boosted the temperature to a maximum of 28.1C at 15.41 being 10.8C above my long-term average it was also the warmest day since 12th August. It was the ninth consecutive dry day with the UV peak level of 5.5 reaching the category of ‘High’ again. Much warmth stored in the ground overnight meant the minimum of 10.0C logged at 05.41 early Friday was 3.0C above average.

Friday brought another sunny start to the new day but a cold front will wander across the country today, just to the north of our area, that will herald the arrival of a cooler northerly air stream. Variable cloud could push up from the depression just off the coast of Portugal later today.

The anticyclone just off the coast of Ireland is likely to dominate our weather over the weekend and continue the flow of cooler northerly air but with little rainfall.

April 2025 review

The high-pressure system just to the northeast of the UK became the dominant feature for the first week in April bringing fine dry days with wall-to-wall sunshine on many days.

The temperatures, as a result, rose well above average with a peak of 21.8C on the 4th that made it the warmest day since last September. However, the brisk wind, gusting up to 30mph, produced a wind chill so outside it felt much cooler, especially out of the sun.

The downside to the clear skies were the cool nights as the minimum slowly began to fall away with 4.4C, 2.5C, -0.1C and -1.2C on the 8th respectively making the latter the coldest night since 16th March.

The anticyclone that had been so dominant for many days eventually gave up the fight with the depression to the southwest beginning to elbow in and produce a significant change in our weather form the 12th as barometric pressure began to drop significantly. The first rain after seventeen consecutive dry days occurred during the evening and night of the 14th/15th, but the amount was minimal with just 0.8mm.

The first below average maximum was logged on the 14th being the first below average since the 17th March at -0.6C. This was due to cloud being thrown up from the depression moving up from Britanny, producing the widest and densest cloud bands since early March.

A depression edged in from the Atlantic on the 22nd that brought very welcome rainfall during the night amounting to 8.6mm being the wettest day since 26th February. This was a great help to gardeners as it had time to be absorbed by the soil, which was very dry. The previous 52 days had brought us just 8.8mm, much of which was very light and had quickly evaporated.

A ridge of high pressure built on the 24th and then built further to form an extensive anticyclone from the 25th resulting in the temperatures rising by day but giving chilly nights under clear skies, also more dry days. The maximum of 25.6C on the 30th was a significant 14.1C above my long-term average also the warmest days since 28th August 2024. Looking back through the records I found that it was the warmest April day since 2018 when a peak of 26.5C was logged.

The total rainfall for April amounted to just 11.7mm being only 20% of my 41- year average or minus 45.9mm. Not only was there minimal rainfall there was an equivalent loss of rainfall, through evaporation from ground sources and plant life, of 82.5mm due to the very warm days, of which 24 were totally dry.

It was not surprising to find that the average temperature for April was 1.6C above my long-term average. Only three maxima were below average during the whole month which is why the average maximum temperature was 2.9C above the long-term average whereas the average minimum temperature was just 0.2C above average.

There have been headlines in the press recently about heatwaves or mini heatwaves. An official heatwave occurs if we experience three consecutive days when the maximum exceeds the heatwave threshold, that naturally varies across the country. The threshold for Wiltshire was recently revised upwards to 27C.

Early morning fog was observed on two days also five air frosts were logged.