December 2019 Review
The start of December was in direct contrast to the two previous months, as it did not start with heavy rain and strong winds. Polar Air brought dry and cold air. By the 4th we had enjoyed four consecutive dry days, the first since the middle of September, with maxima of only 5.5C and 5.5C.
However, by the 5th normal unsettled weather returned as another procession of depressions crossed the country with considerable rainfall and strong winds. With frequent depressions approaching and crossing the UK it was sometimes difficult to detect the prominent wind direction for each 24-hour period as the wind was constantly changing direction. There were several days when the wind changed up to 180 degrees in a matter of a few hours.
Notable daily rainfall totals were 20.2mm, 13.9mm and 15.9mm on the 12th, 18th and 19th respectively. The rains continued throughout most of December after the 9th with 18 continuous days when varying amounts of rain were recorded from the 10th to the 27th.
On the 19th a depression in the eastern Atlantic, rotating anticlockwise as they do, brought warm air from Iberia with the thermometer rising to a maximum of 10.7 and 10.8 on the 18th and 19th respectively.
There was one dry day between the 5th and 27th whereas conditions in Australia continued to worsen with temperatures rising to 49.9C and averaging almost 42C across the country. Also at this point in the month torrential rains were inflicting disastrous floods in Africa.
One contributory factor to these conditions is called the Indian Ocean Dipole where warm surface water in the Indian Ocean moves either towards or away from each continent. In 2019 the warmer sea surface moved towards Africa and as warm air holds more moisture than cooler air considerable rainfall was the result. The opposite happened in Australia with the cooler air holding much less moisture thus exacerbating the drought and fires.
A local person reported that the heat was so intense that when he put a 1.5kg pork roast joint into a baking tin on his car seat it was done to perfection in 10 hours as the temperature inside the car was logged at 81C. Recent pictures have shown the horrendous conditions resulting from the numerous fires as a result of the on-going drought conditions, strong winds and the intense heat.
At this time in the month reports were coming in that Moscow was experiencing Spring conditions with a lack of snow that allowed snowdrops and rhododendrons to flourish. Artificial snow was brought in for Red Square.
After so may wet and gloomy days in the month it was such a relief to enjoy 5.2 hours of glorious sunshine on Christmas Day.
The month did finish on a drier note with 4 consecutive dry days; however there were only 8 dry days in the month when the average is 13.
The mean temperature for December was 0.8C above the 35-year average due to the frequent cloudy nights minimising any frost occurring, just 6 occasions, with the lowest recorded on 5th when the thermometer fell to -3.4C.
The total rainfall for December amounted to 130.5mm, which was 39.8mm above the 35-year average and the wettest since the record of 157.0mm in December 2013. It was the 7th wettest December since my records began in 1984.
Whilst we enduring the gloomy days that occurred again at the end of December, with temperatures around average, a plume of air from Iberia combined with a weather phenomenon called the Foehn effect, raised the thermometer to 16.8C in northwest Scotland, a record if confirmed, for the end of December on the UK.
No UV light was detected on 14 days when the average is 11.