December 2020

Temperatures
(all temperatures in degrees Celsius; all averages 1981 – 2010)

Mean daily maximum: 6.8
Difference from average: 0.0

Mean daily minimum: 2.1
Difference from average: +1.0

Mean air temperature: 4.5
Difference from average: +0.6

Absolute maximum: 12.5 (18th)

Absolute minimum: -2.4 (29th)

Mean grass minimum: 0.8

Absolute grass minimum: -5.4 (31st)

Mean concrete minimum: 0.8

Absolute concrete minimum: -4.2 (31st)

Number of ground frosts: 13

Number of air frosts: 7

Mean soil temperature at 30cm depth:

Mean soil temperature at 100cm depth:

Rainfall
(all totals in millimetres; all averages 1981 – 2010)

Total for the month: 111.0
Difference from average: +51.3

Percentage of the average: 186%

Wettest day: 14.4 (4th)

Number of rain days (>0.2mm): 27

Number of wet days (=>1.0mm): 21

3-month total rainfall to 31st December: 236.6
Difference from average: +64.6

6-month rainfall total to 31st December: 460.0
Difference from average: +113.8

12-month rainfall total to 31st December: 705.2
Difference from average: +56.2

Sunshine
(all averages 1981 – 2010)

Total for the month: 47.2 hours
Difference from average: -4.6

Percentage of the average: 91%

Mean daily sunshine: 1.5 hours
Difference from average: -0.2

Sunniest day: 6.5 hours (31st)

Number of days with no recorded sunshine: 4

Cumulative sunshine since 1st January: 1545.7
Difference from average: +107.4

Note: the monthly sunshine total is now calculated from the UKMO E&NE regional total.
Daily sunshine totals quoted here and in the data summary are uncorrected.

Wind
(all data from West Building roof, Lower Mountjoy)

Average wind speed: 4.1kph

Maximum gust: 61.2kph (18:00, 26th, W)

ISSN1350-483

Comments on December 2020
Mean air temperature was a little above the 1981 – 2010 average, making this the 112th mildest December in 171 years. The mean daily maximum was exactly average and the mean minimum one degree Celsius above average. There were no extreme temperatures in either direction. There were 7 air frosts, 4 fewer than average, and the 26th equal lowest total since 1900 (when a Stevenson screen was first installed). There were 13 ground frosts, three fewer than average and the 17th equal lowest total since 1878. The relative lack of frost no doubt relates to the above-average minimum temperatures; the mean minimum is the equal 51st highest in 171 years.

After a dry day on the 1st, there was not another day without measurable precipitation until Christmas Day. In total there were 27 rain days for the whole month and 21 wet days. The total number of rain days is the second equal highest on record (with 1868 and 1978); only December 2009 has had more rain days (28). It is the third equal highest number of wet days, beaten only by 1868 (23) and 2009 (25). This was the 13th wettest December since 1850. Sunshine was just below average with 15 days having less than one hour’s sunshine.

For the year as a whole and using two decimal places, 2020 is the equal fifth warmest year (with 2006) on record (9.97°C), beaten only by 2014 (10.21°C), 2004 (10.13°C), 2017 (10.10°C) and 2011 (10.03°C). The warmth of the current century is abundantly clear in these figures. The mean maximum is the third equal highest since 1900 (13.8°C), exceeded only in 1949 and 1990 (13.9°C). The mean minimum (6.2°C) is the fifth equal highest on record. The relatively mild nights account for 2020 being one of the least frosty years on record: with easily the lowest number of air frosts (25 – 2014 comes next with 31) and the second-lowest number of ground frosts (65) beaten only by 2014 with 63. It was a wet year (705.2mm), the 57th wettest since 1850 (n=171), but with an especially high number of rain days (206) which is the equal 21st highest annual total since 1850. The number of wet days was not exceptional (124) ranking equal 73rd. The highest daily total was 33.8mm on June 11th, which ranks only equal to 67th on the list of annual maxima. 2020 was a sunny year, well above average, the 14th sunniest year since 1882.

Emeritus Professor Tim Burt
Department of Geography
Durham University