Another cool damp day on Tuesday

Cool on Tuesday – yes, maximum of 18.9 was 1.2C below the June average. Damp – yes, another 2.3mm of rainfall. A predominantly cloudy day only allowed 2.5 hours of sunshine.

With the depression having moved off into the North Sea the pressure gradient was reduced so the wind was much lighter with a peak gust of 15mph.

There was a little brightness to start Wednesday but cloud soon thickened.

June 2020 Review
After the sunniest May on record there was a dramatic change in our weather on the 3rd following two very warm, sunny days when the thermometer soared to 24.8C on the 2nd during almost 13 hours of sunshine. This peak was 4.7C above the 36-year average and the last of the hot, dry weather that stretched back to May 17th.

The high pressure that had dominated our weather for two weeks departed as a low pressure system, centred over the northern section of the North Sea, rotating anticlockwise as they do, brought strong winds from the northeast ,then north, with a maximum of just 14.4C on the 4th, which was 5.7C below the average.

Meteorological experts say it was unprecedented to have such a dramatic swing from the very wet winter to the very dry and hot start to Spring in such a short space of time.

The Jet Stream throughout that period had principally been looping to the north of the UK allowing the warm air mass to reach our shores but changed again to travel across the UK or to the south from the 3rd. On that day the cold front slowly made its way down across the country, fragmenting as it came, and produced just 0.2mm of rainfall, the first measurable since 23rd May when just 0.8mm was recorded.

On the 8th a nose of high pressure, from an anticyclone near the Azores, brought two fine, dry days that were broken as a depression developed in the eastern Atlantic that moved southwards to the Bay of Biscay bringing unsettled weather. The first modest rainfall in a month fell on the 10th producing 3.9mm making it the wettest day since 1st May.

My May weather report highlighted the reduction in Metrological data collected during Covid 19 due to greatly reduced traffic by air and sea also illness. Weather forecasts require observations around the clock and around the world.

An interesting project names Icarus (International Cooperation for Animal Research Using Space) launched an antenna dedicated solely to tracking the world’s animals. From its perch 240miles above Earth on the International Space Station it receives signals from tiny transmitters, that weigh just 5 grams, which eventually will be attached to more than 800 species of animals from elephants to bats. The system went live in March. In addition to mapping the locations of creatures they will be able to use the system as a meteorological drone to measure temperature and pressure at a multitude of positions.

The World Weather Watch collects data from over 15 satellites, 100 moored buoys, 600 drifting buoys, 3,000 aircraft, 7,300 ships and some 10,000 land based observations. Data from all these has to be comparable and up to agreed standards.

A very slow moving depression began influencing our weather from the 12th and remained in the area for almost a week. It brought flabby air pressure over the area resulting in very light winds during many days due to the low-pressure gradient. On the 12th and 13th for example, the strongest daily movement of air, could not be called a gust, was 12mph and 10mph respectively.

On the 18th there was a convergence of an air mass from the cooler and drier east and from a mild, moist air mass from the south that met over southern England. This resulted in 13 hours of continuous rainfall on the 18th, and after a drier period overnight, resumed in the early hours of the 19th. This resulted in a daily total of 33.8mm making it the wettest day since 18th September 2014. The extremely slow moving and very wide rain band slowly circled the area with the tail of the system returning on the 19th. During a 12-hour period on the 18th the air movement performed an almost complete 380-degree change in direction. Having started from the southwest it veered into the north and late afternoon on the 18th came from the south.

Another change was evident from the 21st as an anticyclone developed to the southeast and migrated to Scandinavia. The result was an importation of hot air from the Continent that gave us five consecutive dry days but more memorable was the extensive strong sunshine. The heat built over several days culminating with a maximum of 31.5C on the 24th making it the hottest day since 25th July 2019 being 11.4C above the 36-year average. Although we had many hours of sunshine, the greatest being over 13 hours on the 22nd and 25th, the sky was not clear and deep blue due to pollutants collected as the air mass passed over Europe. During this period the UV level was for many hours rated as ‘High’ but during the two hours around midday rose to ‘Very High’.

During this period an unrelated but interesting meteorological event occurred over the Atlantic. We occasionally have a light covering of Saharan Dust when the warm, southerly air from North Africa deposits it in rainfall. Every 3 – 5 days from late Spring to early Autumn a dust cloud (Saharan Air Layer) forms above the Sahara Desert before travelling westwards over the Atlantic. This particular event was historic and I discovered that it was the most significant in the past 50 years due to the area it covered and its depth in the atmosphere from 5,000 feet to 20,000 feet, reaching the Caribbean and east coast of America. The dust storm darkened skies, contaminated rainwater, greatly reduced visibility and was very evident from the space station.

The heatwave began to break down on the 26th as the southeasterly breeze veered into the south and then southwest bringing a cooler and moister Atlantic air mass. This change in direction was due to the decline in the anticyclone and a depression forming to the northwest. Rain returned in the early hours of the 27th with much lower temperatures and closer to the average.

The remainder of the month saw sunny intervals and showers predominate, pushed on by strong winds from the west and later southwest. This was the fault of a deep depression that parked itself over Scotland then eased into the North Sea.

The overview of June showed it to be a much wetter month than we associate with this summer month as the total rainfall of 85.6mm was 32mm above the 36-year average. There were 13 days classed as wet when daily rainfall is equal to or above 1mm, the average is 9. June 2020 was the wettest since 2012 with the contrasting years of 2018 that produced as little as 5.3mm and June 1998 with 143.2mm.

Statistics show that we enjoyed 230 hours of strong sunshine and that the equivalent rainfall of 99.3mm was lost to evaporation from ground sources and plant life being 14mm above the rainfall total. The mainly disturbed month was due to the barometric pressure being 4mb below the average that gave us only 10 totally dry days.