Windrush Weather

March 19, 2009October 23, 2011

Monthly summary February 2009

The weather in February fell very distinctively into two halves. From the 1^st to the 15^th we endured continuous frosts, many quite severe with the lowest being on the 14^th at -6.5°C. Snow fell for seven of these days, with considerable accumulations from the 2^nd to the 5^th. The early dry snow arrived on easterly winds but as the moist air from the south met the cold easterly plume of air, it became wetter and produced the equivalent of considerable rainfall, the heaviest of this on the 9^th amounting to 22.1mm. As high pressure became established to the southwest of the country from the 14^th it deflected Atlantic weather fronts to the north of the country and brought mild air from the southwest. Although much cloud was trapped beneath the anticyclone, there were several days in this second period with maxima well above the average, the maximum occurring on the 22^nd at 11.9°C. Saturday 21^st brought a beautifully warm and sunny day to dispel the gloom. There was only one day of minimal rainfall in this latter fortnight. Analyzing temperatures for the two parts of February I find that the mean period for the 1^st – 14^th was 4.4°C below the long-term average and in contrast the second half was 2.6°C above, resulting in the mean for the whole month being almost 1°C below the long-term average. We have experienced five colder Februarys since 1984, in severity order they were 2006, 1996, 1985, 1991 and 1986, the latter being a bitter 6.1°C below the long-term average. With a total equivalent rainfall of 74.2mm this was 10mm or 16% above the long-term average.

The winter of 2008/09 was the coldest since 1990 being 1.7°C below the long-term average. The total rainfall for the winter was 201mm being only 82% of the long-term average.

March 1, 2009October 13, 2011

First and last frosts

In my report for May 2009 I included data on air frost and how the occurrence of below zero temperatures had changed over the years since my records began in 1984. I have now analysed the pattern for the first frost at this time of year. To see the trend more clearly I have analyzed the data over five-year periods and the average for each period is in the table below, both for Spring and Autumn. Although the warming in Spring is evident from 1985, this trend for Autumn didn’t start until the late 1990’s. For both periods there is now a shift of around one month, for these average figures.

	1985 – 89	1990 – 94	1995 – 99	2000 – 04	2005 – 09
Last Frost of Spring	14^th May	11^th May	5^th May	26 April	22^nd April
First Frost of Autumn	29^th Sept.	22^nd Sept.	9^th Oct.	18^th Oct.	26^th Oct.

The trend in the total degrees of air frost for each month since 1984, November & December 2009 excluded, also produces interesting data, as in the table below. November and particularly December during this period, show an increasing severity of air frost in contrast to the less severe monthly frost totals at the beginning of the year.

January	February	March	October	November	December
-8°	-10°	-3°	-1°	+3°	+20°

February 1, 2009November 28, 2011

Monthly summary January 2009

January 2009 will be remembered as a truly winter month being the coldest January since 1997 and the 4^th coldest I have recorded. The mean temperature was just 1.8°C, this being 2.2°C below the long-term average. There were 18 air frosts, which are 7 above the average and close to the record of 22 in January 1985 and also 21 in January 1987. Not only were these frosts frequent but also quite severe with a record low for January of -13.3°C during the night of the 7^th. There were also some very cold days when the thermometer did not reach a positive figure, namely 6^th and 9^th with -1.0C° and -2.5°C respectively. The rainfall of 71.4mm was 81% of the long-term average. With a wet period from the 7^th to 22^nd, due to mild, moist southerly winds, resulting in the majority of the rainfall and the two wettest days on the 21^st and 22^nd with 14.8mm and 12.3mm respectively. There were five mornings that dawned with fog and four days with light snowfall. My analysis of the diurnal temperatures, the daily difference between the maximum and minimum, shows a gently increasing maximum, a rise of almost 2°C from the 1980’s to this century.