Author: Eric Gilbert

The air stream, originating from far south, continued to bring the subtropical air on Thursday that gave us a very warm and sunny day with the thermometer rising to a peak of 24.1C at 15.38, which made it the second warmest day this month after the very high of 28.1C on the 1st, being a significant 6.8C above average. This trend continued overnight giving us a very mild night with the thermometer not sinking below 13.8C logged at 04.57, almost exactly at sunrise in Marlborough at 04.58, also being a significant 6.8C above my long-term average. The day was dry with the UV level of 7.0 again, reaching at its peak, rising to the ‘Very High” category.

At first on Friday there was variable cloud, however, by 07.30 this was beginning to disperse and breaks of sunshine appeared. As the anticyclone to the south edges closer the wind today will become much less breezy than of late varying in direction between west-southwest and west. The day will be even warmer than on Thursday, however, the air is more humid than of late due to the long-travel of the air over the Atlantic.

The high pressure to the South is winning the battle of the two main weather systems, edging a little further north, with the pressure continuing to slowly rise, up 5mb since Tuesday. Thus there is little evidence at the moment of any precipitation over the next few days.

The rainfall total for May stands at just 23.9mm against the 41-year average of 60.4mm, whilst the last two days has seen the equivalent of 3mm of rainfall lost to the atmosphere due to evaporation from plant life and the ground.

The very strong sunshine on Wednesday pushed the thermometer to a peak of 19.8C early in the afternoon at 14.47, which was 2.5C above my long-term average and the warmest day for almost a week. There was an extremely strong burst of sunshine from 12.58 to 13.00 when the UV level briefly rose to a value of 7.2 being in the ‘Very High’ category for the second time this month after a similar occasion on Monday. For much of the hours just before and after that the UV level was in the High category between cloud breaks.

It has been a very mild night, that is three in succession, with a low of 12.4C logged in the early hours of Thursday at 01.59 being a significant 5.4C above my long-term average. This was due to the persistent thick cloud cover and the passing of a warm front that also produced a little rainfall amounting to 0.3mm that triggered the automatic rain gauge at 04.39.

Thursday revealed a sky with 8/8 cloud cover being the hang back of cloud from the warm front that passed our way in the early hours. As the low-pressure fills and the high pressure fills, today will be the last day of strong winds for the next few days.

The depression centred over the north of the Scotland is the predominant driving force of our weather for the next couple of days bringing unsettled conditions. This low-pressure system is combining with the anticyclone currently centred over the Bay of Biscay that is bringing us a westerly air flow of sub-tropical air, hence the above average temperatures. However, the anticyclone will continue to moderate our weather as low pressure systems arrive from the Atlantic towards the north of the UK, with little indication of any substantial rainfall, any precipitation will arrive in the form of shower activity.

There have been yet again been headline reports in the press of heatwaves arriving with the UK basking in very high temperatures. However, the Met Office last month put out a statement that “different simulations produce different pictures of the weather forecast and one-off, single charts, do not provide the broader forecasting picture. The actual forecast is developed using a mix of of hundreds of computer model simulations”.

The gardeners on Tuesday would have welcomed the twelve hours of almost continuous rain although those on half term break would not have appreciated the very wet and cool day. The precipitation was never very heavy thus no damage to crops. The rain and drizzle started just after 07.30 and ceased just before 22.00, amounting to 9.0mm, making it the wettest day since 26th February. The additional precipitation took the monthly rainfall to 23.6mm when the 41-year average is 60.4mm.

Not surprisingly, under the thick blanket of cloud and no sunshine, the day was cool with the maximum of 16.0C, logged at 14.01, being 1.3C below average, the first below average since the 15th, in fact there have only been five below maxima this month. Conversely, the cloud provided a duvet to keep in the warmth overnight thus the minimum of 12.2C, logged at 05.20 just after sunrise at 05.00 in Marlborough, was a significant 5.2C above my long-term average.

Wednesday revealed some bright internals at first but cloud built up after around 08.00 from narrow rain bands crossing the area, shown on the rain radar mainly to the south of Marlborough. However, a weak, brief ridge of high pressure will later in the morning bring us a mainly dry day with the possibility of occasional showers.

Tomorrow will see the high pressure sink southwards over France when we will again be in more unstable conditions as the low pressure near Iceland today, sinks south across the UK.

The UK continues to be trapped between the two weather systems. There was a pressure differential at midnight, between the centre of the depression at 990mb and the centre of the anticyclone at 1030mb, thus the wind will continue to be brisk as the air rushes from high pressure to low pressure.

The rise in temperature on Monday was limited by the cloudy conditions that built up around midday with a maximum of 17.6C at 12.37 being just 0.3C above average. The peak UV value of 7.3, the highest since 11th August 2024, took it well into the ‘Very High’ category, but only for a brief period before the clouds thickened and rain showers arrived again, the first at 10.30 then 14.30 and a more consisted fall at 17.00, which in total amounted to 5.8mm making it the wettest day since 28th February. That fall then took the monthly total to 14.6mm compared to my 41-year average of 60.4mm. The past night was very mild that saw the thermometer not drop below 11.7C at 05.2, thanks again to the overnight cloud cover under the hang back of cloud from the weather front.

Tuesday arrived with continuing cloud cover from the unsettled weather as we are still under the influence of the depression to the north of the UK. The rain radar at 08.00 showed heavy rain moving in from the west, already having reached Devon, and making its way to southern England mid-morning, with hopefully for gardeners, a substantial fall. Currently the rain radar indicates that the weather front is fragmented so not sure how consistent the rainfall will be as it crosses from the West Country.

The depression, with its centre just north of Scotland, had a centre pressure of 976mb at midnight, compared to the anticyclone in the eastern Atlantic, reaching across into France, with a centre pressure of 1031mb. This considerable pressure gradient is producing the string winds, that will strengthen in the gusts ahead of the rain arriving mid-morning. The airstream is circulating anticlockwise around the depression and clockwise around the high pressure, as they do, hence the wind from a southwesterly or west-southwest direction today. The barometric pressure at 08.00 read 1012.9mb. There are indications from the rain radar that this approaching rain band will bring a more consistent and heavier fall of precipitation lasting for several hours.

It will all change on Wednesday as the low pressure gives way to a temporary ridge of high pressure that will bring us a much warmer and drier day.

Bowood Gardens, near Calne in Wiltshire, has a large area of varied rhododendrons that are spectacular at this time of the year.

The significant feature on Sunday, weather wise, was the ‘Very High’ UV level with a value of 6.7, the highest since 15th August last year. The very high level occurred in the bursts of strong sunshine, not continuous, until just after 14.00. The maximum of 18.9C was logged at 15.19 being 1.6C above average. The past night was little cooler, although still above average (+2.4C), with a minimum of 9.4C at 05.35 just after sunrise in Marlborough at 05.02. The other significant feature was the strength of the wind with a maximum gust of 24mph, logged at 10.02, the strongest this month.

There was another splash of rain that triggered the automatic rain gauge at 02.39 early this morning amounting to just 0.7mm, another splash that evaporated very quickly after sunrise.

Monday revealed broken cloud and bursts of sunshine that had lifted the thermometer to 12.2C by 08.00. The depression to the north of the UK will continue to feed a predominantly southwesterly unsettled airstream over the UK that as the temperatures rises, will likely trigger some shower activity, but no consistent heavy rain likely.

We are all aware of the very dry months of Spring 2025. Set against my 41-year average, March gave us just 9%, April 20% and May to date is just 15%. This has resulted in a deficit of 154.7mm compared to the average over the three months with just six days left in the season. Although shower activity is forecast in the unsettled weather for the reminder of the month at the moment the only possibility of any substantial rain is likely to be later on Tuesday, but quantities are uncertain. Whilst the rain has been minimal, there has been an equivalent loss of rainfall totalling 223.5mm through evaporation from plant life and the ground due to the many hours of strong sunshine and brisk winds.

Bowood Homes and Gardens: The images this week were taken at Bowood near Calne in Wiltshire, which is a Grade 1 listed Georgian house set in extensive grounds designed by Lancelet “Capability” Brown.