Category: Commentary

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.

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.