February 2021 began with very mild weather that produced a maximum of 12.1C on the 2 Feb being 4.4C above the 37-year average. However, over the next three days the warmth slowly evaporated with cooler days and nights.
A wintry blast arrived from 6 Feb as the wind backed into the north then northeast. There followed eight successive nights with sub-zero temperatures, the coldest of which saw a minimum of -4.6C in the early hours of 11 Feb. The 9 Feb was notable in that the thermometer did not rise above freezing all day with a maximum of -0.2C, which was 7.7C below the 37-year average. It was the coldest day since 20 January 2013 (-0.6C).
Wind chill was a factor during many days with it often feeling like -7C rather than +1 or +2C. The soil thermometer at a depth of 5cm indicated how the cold had penetrated the ground with five mornings when it showed a negative value at 08.00 the lowest of which was -2.7C on the 13 Feb.
Earlier in the month there were reports in the press that a meteorological phenomenon called Sudden Stratospheric Warming might affect our weather. This refers to a rapid warming of up to about 50C in just a couple of days, between 10 and 50 kilometers above the earth’s surface. A Polar Vortex is present all year round rotating anti-clockwise, this girdle of winds keeps the frigid air corralled at the North Pole. It sits about 48km above the earth’s surface, around 32km above the jet stream, a meandering river of strong westerly winds around the Northern Hemisphere. When uneven warm air disrupts it from below, referred to as Sudden Stratospheric Warming, it causes the jet stream to weaken and buckle, eddies of cold air are pushed down, sending warmer air close to the poles.
While these events happen about six times per decade, according to the National Oceanic and Atmospheric Administration, many scientists claim that climate change has increased the frequency with which the polar vortex weakens and allows the cold air to run amok.
Although we had a brief, very cold spell accompanied by snow at the beginning of the month, this event did not happen over the UK this year as did occur in 2018 and referred to then as the Beast from the East. The sudden atmospheric warming brought exceptionally cold weather to Texas in mid-February when temperatures by day are normally around 15C, however they dipped as low as -18C accompanied by deep snow and freezing rain that saw many millions without power. Over 4,000 turtles were cold-stunned and rescued. At the same time Athens experienced unusually cold weather with so much snow they were able to build snowmen on the nearby beach.
During the evening of the 13 Feb the thermometer stopped falling and began to climb again after 19.00. This was the first sign of a major change in our weather as the high pressure that had been centered over Scandinavia for several days, which brought the biting cold, began to fill and an Atlantic depression to ease in from the west.
There followed several days with exceptionally mild, moist weather brought on a brisk southerly air stream. Several days saw maxima above 11C, which were 3.8C above average followed by mild nights. The warmest occurred on the 17 – 18 Feb when the thermometer did not fall below 7.8C being 6.3C above average.
The third week in the month brought wind coming from the south on eight successive days with very warm weather on the 23 and 24 Feb. This was due to sub-tropical air coming all the way from North Africa crossing Iberia in its travels. As a result the thermometer rose to 14.8C on the 24 Feb, which was 7.1C above the 37-year average. The nights were also mild with minima several degrees above the average, 9.4C on the 21 Feb was 7.9C above the average.
The end of the month saw an anticyclone settle close to and then over the UK with very high barometric pressure. As a result we enjoyed several quiet days with little wind and many hours of welcome sunshine. The penalty with clear skies at overnight was the return of air frosts with a minimum of -2.5C during the early hours of the 26 and 27 Feb. A pressure reading of 1042.3mb on the 27 Feb was the highest barometric pressure since 4 January 2019.
The month overall was 0.37C above the 37-year average. It is interesting to see the variation over the years as in 1986, a cold month, the mean temperature was 2.02C below the average and in 1990 we enjoyed a very warm month with the mean temperature 7.04C above the long-term average.
February was a relatively dry month that produced 10 totally dry days and the monthly rainfall of 55.2mm, which was 12mm below the 37-year average. The river levels have been falling, not only because of below February rainfall, but that 21.1mm of equivalent rainfall was lost to evaporation from the ground, water sources and plant life. The contrasting years were an exceptionally dry February in 1986 with only 9.9mm and 2014 with 151.6mm. The long-term average is 67.2mm.
There were nine mornings when an air frost occurred, three mornings when we woke to see fog in evidence with visibility down to 200mm on two days and light snow on three days.
Overall Winter 2020/2021
Brief statistics show that the past winter, which consists of the complete months of December to February for the ease of handling the data, was cool with the mean temperature 0.13C below the 37-year average. Rainfall for the three months totalled 266mm, which was 15mm above the 37-year average of 251mm. The contrasting years were the very dry winter of 1991/1992 when only 94mm fell and the exceptionally wet winter of 2013/2014 when 528mm was recorded.