Tag: February

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 13^th with 20% of the monthly total at 14.9mm.

The period of winter (1^st December to 28^th 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.

February 2010 was another cold month, which completed the statistics for the winter season. It was the coldest February since 2006 and the sixth coldest recorded here, the mean temperature being 1.1°C below the long-term average. There were seven days when snow fell as flakes or pellets and there was considerable wind chill from 8^th – 11^th with the lowest being -7° C. There were nine days with air frost, none severe; the lowest was recorded on the 21^st when the thermometer fell to -3.2°C. The total rainfall of 66.2mm was 103% of the long-term average and most fell in modest daily amounts, the wettest being the 27^th with 10mm. There were just four totally dry days in the month, the lowest since February 1955. During the night of 23^rd/24^th warm air managed to edge in from the south as the cold air mass, which had dominated our weather for most of the month, eased away.

The temperature at the Earth’s surface, as we know, is a balance between heat energy arriving from the Sun and heat energy escaping from the Earth. This loss is progressive throughout winter until strengthening energy from the sun reverses the trend. Bare soil is a poor conductor of heat, but snow is worse, thus night-time drop in temperature is accentuated when there is snow cover, especially fresh, deep snow.  For many years I have kept data on the coldest night of the year and it is proving remarkably consistent. From 1984 to 1996, averaged over the winter months, the coldest night was 13^th February. In 1997 the 14^th moved into second position and in 1997 it became the coldest on average and has remained in this position ever since.  It is more remarkable that although there is approximately 0.1°C or less separating the next six nights, in temperature order, the divergence between first and second is seven times greater, a significant difference.

The past winter was the coldest I have recorded, even beating the severe weather experienced in 1984 and 1985, mainly due to the frequency of sub zero nights rather than depressed day time maxima. The rainfall of 235mm was 97% of the long-term average. However, not all of this precipitation seeped into the aquifers. Due to evapotranspiration, 31mm found its way back into the atmosphere through evaporation from ground and water surfaces, with minimal transpiration from plant material at this time of year.

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.