June 2011 was a cool month and also broke the trend of three consecutive months with below average rainfall. The mean temperature was 14.3°C which is 0.6°C below the long-term average. There were two brief periods (2nd – 4th and 25th – 27th) when we enjoyed warm weather with a maximum of 27.2°C on the 27th. The record for June stands at 31.6° which was recorded on June 30th 1995.
The rainfall of 63.1mm was 115% of the long-term average. Looking at the rainfall data for the first six months of the year I find that 2011 was the sixth driest I have recorded since my station started in 1984.
The solar radiation was 17% below the figure for 2010.
In a previous email I referred to my anemometer (it is sited at the top of a four metre pole that is fixed permanently above the ridge of the bungalow), which had been attacked by a rook. During June there were three nights when the wind dropped out and the instrument was disabled. This time the culprit/s were spiders which overnight had tied up the anemometer and wind vain. It takes a surprisingly strong gust of wind to break the gossamer threads so I have to free the instruments by standing tip-toe on a wall whilst holding at arms length an eight metre fibre-glass pole.
May did bring us some very welcome rainfall, the maximum on the 7th of 22.3mm relieved the parched ground. During the month there were several days with minimal rainfall, these, combined with 6.6mm on the 30th when there were almost eight hours of continous light rain, gave a total of 45.5mm which is 79% of the long-term average. It was a predominantly warm month with no extremes, the highest being 22.6°C on the 6th with the mean 0.8°C above the long-term average.
Looking at the figures for the Spring of 2011, I find that it was the warmest I have recorded and 1.6°C above the long-term average. The change in mean temperatures since I started recording in 1984 is quite remarkeable. It is no surprise to find that the total precipitation for Spring 2011 was very low and in fact a record for my station. With a total of only 64.6mm, which is just 36% of the long-term average, it beat the previous low of 66mm in 1990.
April 2011 was a remarkable month for many reasons and broke several records. With high pressure dominating for most of the month and keeping weather fronts from the Atlantic at bay, it proved a very dry and very warm month. It was the warmest April on record with the mean maximum +5.1°C and the mean minimum +2.3°C. The three warmest Aprils that I have recorded occurred in the last five years. On the 23rd another record was broken when I recorded the hottest April day when the thermometer peaked at 26.2°C. There were 26 totally dry days, another record equalling the years of 1984 and 1987. Out of the four wet days only one produced a substantial amount of precipitation, 4.2mm on the 3rd, the remaining three days brought minimal amounts of 0.7mm, 0.4mm and 0.1mm. The total rainfall of 5.4mm (the long-term average is 60mm) was the second lowest for an April only beaten by the drier April of 1984 which produced only 2mm. Set against the minimal rainfall is the figure of over 82mm of moisture lost to the atmosphere through evaporation and transpiration. During April there were no air frosts, which is another record; the previous low was of just two air frosts in 2004 and 2007.
March began with very cold days and several nights with air frost, which combined with strong winds produced several days with significant wind chill of -5°C and -7°C on the 5th and 7th respectively. It was only when we reached the 8th did temperatures recover to near normal monthly temperatures. As pressure rose from mid-month so did the occurrence of warm days with light winds, which were very pleasant for March. The maximum temperature was 18.3°C on the 25th.
The mean temperature was 0.3°C above the long-term average which was principally due to the mean maximum being +1.3°C whereas the mean minimum was -0.6°C. This was the driest March I have recorded. The total of just 12.7mm was almost 3mm less than the previous record of 15.6mm that fell in March 1997.
My recent analysis of wind speeds over the last ten years show that there have been significant changes, especially since 2008. The average annual wind speed for the years 2001 – 2006 fluctuate between 4.3mph and 4.6 mph. However, the years 2008/09/10 produced falling values of 3.9mph, 3.3mph and 3.1mph respectively. I discovered that during the winter season the incidence of 20mph+ gusts had fallen by four and 30mph+ gust by three. A recent meteorological report suggested that these falling values over the last three years or so were due to “a spell of subdued westerlies with a weak and contorted middle-latitude jet stream”.
February 2011 brought us unusual weather for the last month of winter. The mean temperature was 2°C above the long-term average with the mean maximum +1.6° and the mean minimum +2.3°C. The first two weeks brought day temperatures well above the average but fell away when the wind changed to the south-east and then north-east. The total of only five air frosts was well below the average of eleven for February and was the lowest number since 1997. The total rainfall of 74.5mm was 116% of the long-term average and helped to increase the low figure for the winter period. There were only three totally dry days and an unusually high frequency of days (nine) with minimal precipitation of less than 1mm. The wettest day was the 13th with 20% of the monthly total at 14.9mm.
The period of winter (1st December to 28th February) produced a mean which was 1.4°C below the long-term average. The frequency of air frosts was high with a total of 46 which is 12 above the long-term average. The total rainfall was 212mm, which is just 87% of the long-term average.