Monday 6th brought a maximum gust of 30mph, the strongest gust since May 11th and overnight the barometer dropped to 993mb, the lowest since August as a depression moved across southern England. The disturbance brought considerable daily rainfall of 10.1mm with heavy rainfall starting just before 0300 today.
Yesterday morning the air temperature dropped to 0.7C and there was a very obvious ground frost with much vegetation covered briefly in white. Today, as the weather front moved across us bringing heavy rain, the wind was gusting to over 30mph.
The maximum on the 4th was 6.5C below the highest temperature on the previous day, which at 14.1C was close to the long-term average after a very warm start to October. The temperature dropped as a cold front moved across the area and the wind direction veered from the south into a north-westerly direction. The total precipitation was 7.5mm over four hours and behind it the barometer rose sharply gaining over 10mb in 10 hours.
Much has been broadcast recently stating that September 2014 was the driest on record, going back to 1910. The statistics given by the Meteorological Office are based on daily weighted totals from a network of stations within each of five England and Wales regions calculated by the Hadley Centre, the research arm of the Meteorological Office.
The total rainfall for September was 41.7mm, which is 67% of the 30-year average or 20mm below. The driest Septembers in Marlborough were in 2003 and 2009 with just 11.1mm, which contrasts with the wettest year in 2006 that produced 131.9mm. There were 25 totally dry days and four days with insignificant precipitation amounting to daily totals less than 1mm. However, the total consists almost entirely of the 40.6mm that fell during the night of the 18th when thunderstorms raged from 6pm to 4am the following morning.
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 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.
The total amount of evaporation from ground sources, plants and water surfaces, was 51mm, which with the rainfall of 42mm gave a deficit of 9mm. This 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 the 18th 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 was 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 the 14th. 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.
It was a warm month with daytime temperatures consistently above the average, which 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 occurring in September was in 2003. The coolest night was the 22nd 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 usually cleared by mid-morning.
Due to warm continental air coming in from a south-easterly direction maximum temperatures are still held high, especially now we are at the end of September. The maximum for sunday 28th was 22.2C. With only one wet day when precipitation was 40.6mm and three days with minimal rainfall, all less than 1mm, it is an exceptional autumn month. The last two days have also been notable for the minimal wind strength, a maximum gust of only 9mph on both days.