Sunday 4th January
There were very treacherous conditions on Saturday morning. The cold began to seep further into the ground surface resulting in the residual rain from the early hours began to form black ice in places,I know, as I almost fell a couple of times. The air temperature did not get above zero until just before 10.00 and then only reached a maximum of 2.9C at 13.41, which was 4.2C below average. Under the clear sky and a very bright super moon the temperature dropped steadily in the early evening reaching freezing point (-0.1C) at 17.54 and a minimum -4.2C at 05.18, being a significant 5.4C below my long-term January average.
First light on Sunday revealed a totally clear sky with the thermometer reading -4.1C. The nearby anticyclone is still exercising control of our weather, and for the next three days, that will result in cold days and frost at night, however, it will allow many hours of sunshine. As I complete this report the thermometer has climbed back to 3.6C at 08.30, still a very hard frost.
It will not be until late Wednesday and into Thursday before there will be a slight let up in the very cold weather. This will be the result of the anticyclone easing away southwards and a depression developing to the north of the UK, also easing southwards, bringing cloud and a distinct change to the airflow, a little milder with possible light precipitation, as the wind backs into to the west, cutting off the flow of Arctic air.
The evenings have lengthened by 13 minutes since the shortest day whilst the sunrise has been static at 08.12 since the 26th and won’t change until the 6th. The reason mornings do not lengthen at the same rate as evenings at this time of year is due to a combination of the earth’s axial tilt and its elliptical orbit around the Sun, a phenomenon astronomers call the ‘equation of time’.
Because of the varying speed and the Earth’s tilt, the actual length of a solar day (the time from the sun being at its highest point one day to the next) is not exactly 24 hours. Our clocks, however, assume every day is precisely 24 hours. This difference causes “solar noon” (when the sun is highest in the sky) to shift slightly each day compared to the fixed “clock noon”.
The hours of sunrise and sunset today in Marlborough are 08.12 and 16.12. It will be January 6th before there is a change in the sunrise time.