Author: Eric Gilbert

The modest change in wind direction on Saturday, coming from the east and east-southeast, meant the air stream had travelled from the Continent rather than over the cool, damp North Sea. As a result the thermometer rose to a maximum of 22.1C at 16.5 being 4.8C above average making it the warmest day since the 2nd. Not only was the air warmer but dryer as the humidity dropped to a low of 29.7% at 16.10, with of course the UK land also being very dry. The overnight minimum of 7.4C, logged at 05.21, at the sunrise time of 05.22 for Marlborough, was the first above average low since the 3rd being plus 0.4C.

The start to Sunday revealed welcome sunshine that was at times a little muted as advance cloud from the depression over the Bay of Biscay is beginning to influence our weather. The centre of the low pressure system is over the Brest peninsula and at 07.30 was already producing numerous thunderstorms over The Isles of Scilly and the Cherbourg peninsula. The big question is how far will the thicker cloud and any possible thunderstorms migrate northwards. Rain has been falling over Cornwall for the past few hours and was edging into west Devon at 08.00. The barometric pressure has fallen another 8mb since yesterday as the depression moved a little closer.

The track of this depression is likely to be centred over the Bay of Biscay today and tomorrow before it is forecast to decay and slip back into the Atlantic as high pressure is likely to build back over the UK from the north, possibly on Tuesday. Monday is likely to come under the influence of the depression with more cloud and possible precipitation, but amounts uncertain at this time.

There was a great improvement in the warmth on Friday as the thermometer reached a maximum of 18.9C late in the afternoon at 16.40 being 1.6C above my long-term average it was also the warmest day since the 2nd (23.7C). The significant change was in the direction of the wind that during the afternoon veered a few degrees from the cool northeast, after crossing the cold North Sea, to come from the southeast, which cut off the flow of cool air with that from the Continent having travelled over land being comparatively warmer. Although the past night saw another below average minimum of 5.4C (-1.6C) at 05.30, it was the equal coolest since the 3rd May.

Saturday saw welcome sunshine from the beginning of the new day in clear blue skies. The anticyclone continues to edge away, a drop of another 2mb since yesterday, but still playing a major influence in our weather with another dry and very sunny day ahead. The drier air from the Continent gave a humidity reading of 73% at 08.00, the lowest humidity reading since the 4th, whilst the thermometer had risen to 12.6C by that time making it the warmest start to a new day since the 2nd.

The low pressure system that I mentioned yesterday, positioned over Iberia and the Bay of Biscay, is likely to slowly edge our way over the next day or two with the likely position over the English Channel tomorrow. As a result, being so close to the UK, it could begin to throw cloud and possible rain over southern England on Monday.

I mentioned the lack of recent rain yesterday. Since the 1st April there have only been five days with any precipitation, four of those being of minimal quantity. This year is the driest March to April period I have recorded since the station was started in 1984 with just 17.4mm. Looking back over the records I found that the year 2011 was the previous driest March and April spell with only 18.1mm, however, by comparison in 2023 I recorded 239mm of precipitation.

Looking at the data on the Thames Water website I see that the ground water state from several boreholes is normal for our area although five out of the seven report the level is falling.

I noted yesterday that several water companies are begin to make plans in case the very dry spell continues into the summer.

Thursday turned out to be the coolest day for three days under variable cloud, limited sunshine and a brisk northeasterly wind. The maximum of 14.4C at 16.24 was 2.9C below average. The minimum overnight was also below average with a low of 2.7C logged at 05.41 just after sunrise having coincided with the cloud arriving. This low was a significant 4.3C below average.

Cloud began to drift across from the North Sea on the northeasterly breeze just before 06.00 on Friday that initially blocked out any sunshine but shortly after 07.30 the cloud thinned and began to break allowing the sun to break through and lift the temperature to 7.7C by 08.00. There is the prospect of a warmer day today with the wind backing into the east cutting off the flow of very cool air from the North Sea.

The disturbance over Iberia, that is developing into a low pressure system, is likely to slowly move northwards tomorrow into the Bay of Biscay and get very close to the UK on Sunday with likely more cloud. However, by Monday, as the recent high pressure eventually relinquishes control the low-pressure system is likely to elbow itself across the Channel to southern England with the prospect of showers, its movement north and east is not certain at this time.

The Government’s national drought group convened with a minister this week as England recorded its driest March to April period since 1956. Drought in the UK is characterised by a prolonged period of unusually low rainfall, leading to water shortages. Specifically, a drought is defined as a period of at least 15 consecutive day with less than 0.2nn of rainfall. We have just had sixteen consecutive dry days with no precipitation.

The rainfall during the March and April period for England was 43% and 56% respectively. Marlborough had far, far less with 9% and 20% respectively. I read that the ground water levels are good at this time.

The thermometer climbed higher again on Wednesday peaking at 17.8C logged at 16.03 in strong sunshine. This maximum made it the warmest day since the 3rd, however, it was only just above average being +0.5C, but going in the right direction. It was the fifteenth consecutive dry day with the UV level climbing into the ‘High’ category, as on the two previous days. The past night was again chilly, although the highest for five days, with a minimum of 5.4C logged at 03.10, however this low was 1.6C below the long-term average.

Thursday after first light revealed a cloudy sky that had been dragged in from the cool North Sea collecting moisture on its travels. The wind persists from the northeast and will again tomorrow.

The recent dominant anticyclone is slowly showing signs of filling and easing towards the Continent, a drop of 4mb over the past two days with a reading of 1021.4mb at 08.00 today. By Saturday, as the high relocates, the wind is likely to veer from the northeast to east pulling in slightly warmer air from the Continent rather than from the cooler north. The temperatures are forecast to slowly rise over the next few days and likely to be a few degrees above the long-term average. A watch needs to be kept on a low pressure system that is forming over Iberia. There is the possibility of this depression moving a little further north over the next few days and could impact our weather, possibly on Sunday or Monday.

Drones or Meteodrones
Drones have been around for a number of years and used for a variety of purposes, both for business and private use. A new era of drones is being developed by a firm in Switzerland called Meteodrones. These are being used to monitor the air mass above ground level for meteorological purposes. They rise up to a height of 6km and measure, like radiosondes, the temperature, humidity, and barometric pressure but in addition to the Radiosondes, wind speed and direction. They have a capability to fly repeatedly both by day and night that allows the collection of significantly more data than traditional methods.

These Meteodrones can be operated directly by a person or remotely located many miles away from the base. Currently there are 15 bases in Switzerland, 30 in Norway with 1 each in France, Italy and Romania. When back at base they are recharged automatically. The propellers are heated to stop icing when at high altitude also being waterproof and snowproof.

The thick bank of cloud on Tuesday morning took until after midday to thin and clear. A maximum of 14.9C, late in the afternoon as the result of strong sunshine, was the turning point after the past cool days being 1C up on the Monday peak, however, it was still 2.4C below average, but going in the right direction. The overnight low of 1.9C was also higher than the previous night but still a significant 5.2C below my long-term average. Although the breeze continued to come from the northeast it was less strong so felt less cold outside.

The change in warmth can be seen in the soil temperature at a depth of 5cm measured at 08.00 each day with 16.7C, 15.6C, 12.8C, 9.0C, and 8.1C respectively, as the warmth slowly left the ground over the past five days, with today a reading of 10.6C, reversing the trend.

We were greeted by welcome sunshine after dawn on Wednesday although a little muted due to thin high cloud. The air temperature recovered quickly having reached 10.4C by 08.00 making it the warmest start to a day at that time since the 3rd.

The forecast track of the Jet Steam, if a little fragmented at the moment, is still lopping around the north of the UK that sees the high-pressure over and around the UK for probably another week with little or no rain likely.

Radiosonde Part 2 – following on from the introduction yesterday.
The first simple radiosonde was invented in France and first flew on January 7th 1929 with much more advanced electronics these days, now being battery powered. The flight of each balloon can last from 90 to 120 minutes and eventually bursts at great height as the barometric pressure has reduced considerably. The maximum altitude attained is determined by the thickness of the balloon and its diameter whilst the temperature at around 25 miles high can have dropped to -90C. Depending on the wind strength the balloon can drift several 100’s kilometres during its flight.

There are six radiosonde stations around the UK, from near Camborne in the southwest to Lerwick and Northern Ireland with around 1,300 worldwide launch sites.

Tomorrow I will include a paragraph on the use of drones to capture meteorological data.