December 2015 was a remarkable month. One area of low pressure after another swept in from the Atlantic bringing gale force winds, high rainfall and exceptionally mild temperatures.
The average temperature in the month was 9.0°C, 5.2°C higher than the December mean and 3.2°C higher than the previous mildest December in 2013. The maximum temperature was 14.8°C at 08:01 on the 19th, with the 7th, 16th and 17th also beating the previous high of 13.0°C set on December 18th 2014. The maximum temperature of 12.9°C, recorded at 19:36, beat the previous warmest Christmas Day record, set in 2011, by 0.7°C, and the maximum temperature of 13.7°C, recorded at 13:04, beat the previous warmest Boxing Day record, set in 2011, by 0.8°C.
On the 12th, a cold front passing over caused the temperature between 18:15 and 19:55, to fall from 11.3°C to 3.3°C – a fall of 8°C in only 100 minutes.
The minimum temperature in the month was 1.4°C at 07:14 on the 13th, meaning there were no frost days in the month for the second time, the previous being in 2013. This was the highest monthly minimum temperature ever recorded here in December. The average daily high temperature was 11.4°C (mean 6.3°C) and the average daily low temperature was 6.3°C (mean 1.3°C).
The maximum dew point was 13.0°C at 07:41 on the 19th, with the minimum dew point being 0.6°C at 07:14 on the 13th. Only 2.75 hours of sunshine was recorded in the month, easily the least sunny month ever. The previous low was November when 16.83 hours was recorded. The UV index remained at 0.0 for the whole month.
Rainfall in December totally 70.6 millimetres, with the wettest days being the 12th and the 30th when 10.2 millimetres fell. Rain fell on 24 days and no snow was recorded. The maximum rain rate touched 100.2 millimetres per hour at 10:01 on the 24th. Although the rainfall total was much higher than the average of 49.7 millimetres, 2011 and 2012 were both wetter, recording 70.8 millimetres and 86.2 millimetres respectively.
The maximum wind speed was 21.00 mph at 00:59 on the 5th, with the average wind speed for the month being 7.82 mph (mean 5 mph). The maximum gust speed was 38 mph at 14:40 on the 24th, with the monthly average gust speed being 11.4 mph. Both averages are December records. The average wind direction was 223° and the total wind run was 5696.9 miles.
The average barometric pressure was 1013.1 millibars. The highest pressure was 1029.4 millibars on the 9th, and the lowest was 998.3 millibars on the 30th. These were the lowest maximum and the highest minimum pressures in December. The average humidity in the month was 88%, equalling the December low set in 2011.
