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.
Monthly summary March 2011
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”.
Monthly summary February 2011
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.
Wind speeds
I recently decided to analyse my records of wind speeds, the most accurate go back to the year 2000 when my anemometer was moved to a very high position, well above roof height. The initial results gave me concern as recent years have shown a decline in wind speed-readings. I had wondered if the repeated attack on the instrument by a rogue rook, two years ago, had damaged the unit.
My equipment captures data every five seconds and from these records I find that there has been a downward trend in average annual wind speeds since 2007 – the fall being most notable for the last two / three years.
|
2001 |
2002 |
2003 |
2004 |
2005 |
2006 |
2007 |
2008 |
2009 |
2010 |
|
4.3 |
4.6 |
4.3 |
4.3 |
4.4 |
4.3 |
4.1 |
3.9 |
3.3 |
3.1 |
Looking specifically at readings in the winter (meteorological) period, December 1st to February 28th, I discovered a reduction in gusts of 20mph +, by an average of four per year. The statistics for gusts of 30mph + produced a reduction of three per year.
Monthly Summary January 2011
In January 2011 we enjoyed mild if overcast days when the maximum was four to five degrees above the average (12th and 16th) or in contrast as on the 29th when the maximum was only 0°C. Some nights were warm with a minimum of 10.4° and 9.5°C (14th and 13th respectively) when the average is 1.3°. A total of 16 nights of air frost was above the average of 11 over the last 27 years with the early morning of the 31st being extremely cold when I recorded a minimum of -8.5°C. The record stands at -13.3°C in January 2009. The mean temperature was 0.4°C below the long-term average. The frost that occurred in early January gave a coating of ice to everything but the air frost on the 27th went almost unnoticed due to the dry air prevailing and some air movement (82% humidity as opposed to 98% earlier in the month). There were 12 days without rainfall but on four occasions the daily total was in double figures (18.1mm, 17.4mm, 17.1mm and 14.9mm) with a monthly total of 107.8mm, which is 123% of the long-term average.
