May 2017

Temperatures
(all temperatures in degrees Celsius; all averages 1961 – 1990)

Mean daily maximum: 16.6
Difference from average: +2.3

Mean daily minimum: 8.0
Difference from average: +2.4

Mean air temperature: 12.3
Difference from average: +2.4

Absolute maximum: 25.3 (26th)

Absolute minimum: 1.8 (10th)

Mean grass minimum: 6.1

Absolute grass minimum: -0.2 (10th)

Mean concrete minimum: 8.4

Absolute concrete minimum: 0.0 (23rd)

Number of ground frosts: 1

Number of air frosts: 0

Mean soil temperature at 30cm depth: 13.3

Mean soil temperature at 100cm depth: 11.4

Rainfall
(all totals in millimetres; all averages 1961 – 1990)

Total for the month: 19.8
Difference from average: -32.4

Percentage of the average: 38%

Wettest day: 6.4 (27th)

Number of rain days (>0.25mm): 9

Number of wet days (=> 1mm): 6

3-month total rainfall to 31st May: 91.2
Difference from average: -80.8

6-month rainfall total to 31st May: 251.5
Difference from average: -94.7

12-month rainfall total to 31st May: 588.1
Difference from average: -60.9

Humidity
(averages for 09:00 hours GMT)

Relative Humidity: 78%

Sunshine
(all averages 1961 – 1990)

Total for the month: 158.0 hours
Difference from average: -10.5

Percentage of the average: 94%

Mean daily sunshine: 5.1 hours
Difference from average: -0.3

Sunniest day: 11.3 hours (5th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 576.2 hours
Difference from average: +49.9

ISSN1350-483

Comments on May 2017
May had the highest mean minimum on record since 1850 (8.0°C), well ahead of 2003 and 2014 (7.7°C). The mean maximum was the 14th equal highest on record since 1850. It is no surprise therefore that the May mean air temperature was 2nd warmest on record since 1850, exceeded only in 1952. The absolute minimum on 26th (14.1°C) was the 3rd equal highest for any May night at Durham since 1850, beaten only in 1858 and possibly 2004 (this value is open to doubt*). The minimum of 13.8°C on 24th was the 6th highest ever May value. Altogether there were 7 occasions when the absolute minimum was above 10°C, mainly towards the end of the month; this total has only been exceeded in 1953 (9). There were 6 straight days with maxima above 20°C but this May total is by no means a record, only the 16th equal highest total since 1850; there were 11 days with maxima above 20°C in 1918 and 1952.

This was the equal 16th driest May since 1850, equal to 2005, and the driest since 2001.

It was the 3rd warmest spring on record since 1850 (9.5°C), exceeded only in 2004 and 2011; it was the 27th driest spring, reflecting the dry, warm conditions generally across the country.

*Daily records of maximum and minimum temperature for May 2004 were declared to be too high and require correction.
Mean values were based on Copley.

Professor Tim Burt
Department of Geography
Durham University