May 2020

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

Mean daily maximum: 17.4
Difference from average: +2.5

Mean daily minimum: 6.9
Difference from average: +0.8

Mean air temperature: 12.2
Difference from average: +1.7

Absolute maximum: 24.9 (20th)

Absolute minimum: -0.6 (6th)

Mean grass minimum: 4.7

Absolute grass minimum: -3.5 (6th)

Mean concrete minimum: 6.8

Absolute concrete minimum: 0.3 (6th)

Number of ground frosts: 4

Number of air frosts: 1

Mean soil temperature at 30cm depth: 15.7

Mean soil temperature at 100cm depth: 12.8

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

Total for the month: 18.0
Difference from average: -26.8

Percentage of the average: 40%

Wettest day: 6.4 (1st)

Number of rain days (>0.2mm): 11

Number of wet days (=>1.0mm): 4

3-month total rainfall to 31st May: 48.4
Difference from average: -123.6

6-month rainfall total to 31st May: 201.4
Difference from average: -144.8

12-month rainfall total to 31st May: 743
Difference from average: -94

(all averages 1981 – 2010)

Total for the month: 236.2 hours
Difference from average: +47.9

Percentage of the average: 125.4%

Mean daily sunshine: 7.6 hours
Difference from average: +1.5

Sunniest day: 10.5 hours (7th, 15th)

Number of days with no recorded sunshine: 0

Cumulative sunshine since 1st January: 773.4
Difference from average: +182.9


Comments on May 2020
This was the third equal warmest May at Durham since 1850 – equal to 2018 and beaten only by 2017 and 1952. The mean maximum temperature is the equal highest on record for May (with 2018 and 1952) and the mean minimum temperature is the 14th equal highest on record. Like April, anticyclonic conditions dominated the weather and wind direction determined whether Durham was warm or cool. There was a notably low maximum of 8.6°C on the 10th and only 10.7°C the next day during a spell of northerly winds. In the second half of the month there were seven days with maxima above 20°C.

It was the 13th driest May on record, with rain recorded on only 11 days and only 4 days having totals of 1mm or more. The wettest day was the 1st with 6.4mm. It was the 9th sunniest May on record.

It was the 4th equal warmest spring on record at Durham (with 2003 and 2004), and beaten only by 2007, 2011 and 2017. Notably, all these warm springs have been this century. It was the second driest spring on record at Durham (48.4mm); only spring 1956 (45.3mm) has been drier. It was the 3rd sunniest spring on record at Durham since 1882, beaten only by 2009 and 2011.

Note that no data are available this month from the West Building AWS.

A note on sunshine records at Durham since 2000
I have been worried about the sunshine data for some time and comparison with other stations locally and in the NE region confirms that totals have been significantly underestimated during the period April – October since the automatic weather station was installed on the lawn in from of the Observatory in autumn 1999. The exposure is deficient to the north because of obstruction by vegetation. Totals are now being estimated and we will look to relocate the sunshine recorder, either back to the Observatory roof or to another suitable location on the University campus. I used a 70-year overlap with Cockle Park near Morpeth to derive a method of correction; comparison with Ken Cook’s station at Copley provides a helpful cross-check too, but there was unfortunately no pre-2000 overlap to allow a calibration curve to be developed.

For the same reason, no figures are quoted for the sunniest day. Whilst Durham\’s maximum in May was 10.5 hours, Copley recorded days with more than 15 hours sunshine.

Emeritus Professor Tim Burt
Department of Geography
Durham University