Although the month began with high pressure and a dry day with 4.4 hours of sunshine, the following week saw a low-pressure system settle over the country and persist. The slack pressure gradient meant days with light winds, gloomy conditions and little sunshine. The early morning of the 4th brought heavy rain that amounted to 10.0mm. The sixth saw very low cloud that at dawn meant visibility was restricted to 500m but as the morning wore on the fog intensified and visibility dropped to 200m.
Throughout this period temperatures, not surprisingly, were depressed, especially when the wind backed into the northeast and then north. The thermometer only reached 2.1C on the 7th being 6.2C below average and the coldest day since 1st February 2019.
Yet again our weather turned upside down during the middle of the month as an intense and large area of low pressure developed in the North Atlantic that brought warm, moist air on south and southwesterly winds with the thermometer rising to its highest in December with a maximum of 12.9C on the 21st being 4.8C above average.
According to the World Meteorological Organization climate change continued its relentless march in 2020, which is on track to be one of the three warmest years on record. The ten-year period 2011-2020 will be the warmest decade on record, with the warmest six years all being since 2015. The WMO state that “Record warm years have usually coincided with a strong El Niño event, as was the case in 2016. We are now experiencing a La Niña, which has a cooling effect on global temperatures, but has not been sufficient to put a brake on this year’s heat”. The average global temperature in 2020 is set to be about 1.2 °C above the pre-industrial (1850-1900) level
Ocean heat is at record levels and more than 80% of the global ocean experienced a marine heatwave at some time in 2020. It has been recently estimated that round 93% of the extra energy accumulating from climate change is stored in the oceans..
The year 2020 has been the warmest year I have recorded since the station began in 1984 with the mean temperature 1.06C above the 36-year average.
Storm Bella was named on the 24th as a deep depression in the North Atlantic that brought wind and rain. The anemometer recorded a gust of 38mph on the 26th, which was the windiest day since 1st November. The depression also brought considerable rainfall with 17.7mm recorded on the 26th being the wettest day since 14th November (26.1mm). As the depression approached the UK winds came from the north, south then west on three successive days.
Up until the last week of December the month had been mild and damp with the mean temperature 1C above the 36-year average. However, on the 28th a cold air mass began to arrive from the north with a maximum of 2.1C and very light, wet snow just before dawn. Another light fall that just about covered the ground fell after dawn on the 29th. The coldest night of the month was logged during the early hours of the 31st when the thermometer dropped to -3.6C being 5.9C below the December average minimum.
The monthly rainfall amounted to 109.1mm being 17.3mm above the 36-year average. There were two particularly wet days on the 13th and 26th with 16.6mm and 17.7mm respectively. Although the mean temperature was well above average for much of the month the very cold spell at the end resulted in a mean temperature 0.09C above average.
There were three days with morning fog and snow was observed on two days, 28th and 29th.