Much has been broadcast recently that last month was the driest September on record – going back as far as 1910. These statistics come from the Met Office and are based on daily weighted totals from a network of stations across England and Wales and calculated by the Hadley Centre, the research arm of the Met Office.
However September in Marlborough defied the national rainfall statistics. Our total rainfall for September was 41.7mm, which is 20mm below the 30-year average.
This total consists almost entirely of the 40.6mm that fell during the night of September 18 when thunderstorms raged from six in the evening to four the following morning.
Since 1984, the driest Septembers in Marlborough were in 2003 and 2009 with just 11.1mm. This year there were 25 totally dry days and four days with insignificant precipitation amounting to daily totals less than 1mm.
The total precipitation of 40.6mm is a record for the wettest September day since my records began in 1984 and beats the previous high of 35.6mm recorded in September 1984.
Often thunderstorms arrive over the south of England from a southerly direction and frequently pass to the west or east of Marlborough. On this occasion the line of storms moved from east to west over central southern England – right over the Marlborough area.
The total amount of evaporation from ground sources, plants and water surfaces, was 51mm, which with the rainfall of 42mm (rounded up) gave a deficit of 9mm. Something gardeners and farmers will have noticed.
This deficit was lower than might be expected considering the reduced rainfall, as there were many days with fog or mist that persisted into the morning and coated the countryside with heavy dew.
The considerable rainfall on September 18 also refreshed the ground. There were several days when spectacular spiders’ webs were covered with droplets of moisture that glistened when the sun broke through the mist.
For much of the month high pressure areas were over or near the UK, which brought us the dry and warm conditions. Unusually for September, winds frequently came from a northeasterly direction and many days were very light in strength.
A maximum gust for the month of 24mph occurred on September 14. Many days the maxima gusts were in single figures or low teens. The mean wind speed for the complete month, day and night, that is usually around 3 – 4mph, was just 1.8mph. Not a good month for wind turbines.
September was a warm month with daytime temperatures consistently above the average. This resulted in a mean maximum 2.2C warmer than the 30-year average.
However, the mean temperature for September, including maxima and minima, was 1.1C above the 30-year average due to several very cool nights. The warmest day was the 9th when the thermometer soared to 22.8C with 19 other days when 20C was exceeded.
There were no occasions when an air frost was recorded. The last time we had an air frost in September was in 2003. The coolest night was September 22 when the thermometer dropped to 2.1C, which caused a slight ground frost for a short while around dawn.
There were 11 days when fog formed overnight, due to the still air and low temperatures, but it usually cleared by mid-morning.
