July 2019

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

Mean daily maximum: 21.0
Difference from average: +0.9

Mean daily minimum: 12.5
Difference from average: +2.1

Mean air temperature: 16.7
Difference from average: +1.1

Absolute maximum: 32.2 (25th)

Absolute minimum: 6.7 (8th)

Mean grass minimum: 11.1

Absolute grass minimum: 5.1 (8th)

Mean concrete minimum: 13.0

Absolute concrete minimum: 8.6 (3rd)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 18.1

Mean soil temperature at 100cm depth: 15.5

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

Total for the month: 69.2
Difference from average: +13.7

Percentage of the average: 125%

Wettest day: 24.2 (27th)

Number of rain days (>0.25mm): 18

Number of wet days (=> 1mm): 12

3-month total rainfall to 31st July: 215.8
Difference from average: +43.8

6-month rainfall total to 31st July: 329.0
Difference from average: -17.2

12-month rainfall total to 31st July: 594.2
Difference from average: -54.8

Sunshine
(all averages 1961 – 1990)

Total for the month: 121.1 hours
Difference from average: -41.6

Percentage of the average: 74%

Mean daily sunshine: 3.9 hours
Difference from average: -1.3

Sunniest day: 9.9 hours (25th)

Number of days with no recorded sunshine: 1

Cumulative total sunshine since 1st January: 820.6 hours
Difference from average: -61.1

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

Average wind speed: 5.3kph

Maximum gust: 56.3kph (17:00, 22nd, W)

ISSN1350-483

Comments on July 2019
The highest temperature recorded at the Durham Observatory since 1900 was in the early afternoon of 25th July when 32.86°C was reached. There was a higher temperature recorded on 16th July 1876 of 33.6°C but this was obtained from within a ‘Glaisher screen’ which were well known for overestimating maximum temperatures. On that same day in 1876 the maximum recorded in the ‘North Shed’ (on the north side of the Observatory) was only 30.1°C, a more likely reflection of the true maximum that day. 32.86°C is the highest temperature recorded at Durham since a Stevenson screen was installed in 1900. Note that Gordon Manley did not analyse maximum and minimum temperatures before 1900, confirmation that maximum and minimum temperatures could not be trusted before that. This was the same day as the national record was broken at Cambridge Botanic Gardens and at the Radcliffe Observatory in Oxford, with a daily record of temperature from November 1813, the highest ever temperature there was also recorded.

Mean air temperature was equal 9th highest since 1850, but July 2019 was not quite as warm as July 2018. It was the 4th highest mean minimum since 1900, the highest since 2013; only 1983 and 2008 have been higher. The mean maximum was above average but only the equal 40th highest since 1900. Rainfall was a little above average, mainly because of a fall of 24.4mm on the 27th. It was the 24th dullest July since 1882.

Emeritus Professor Tim Burt
Department of Geography
Durham University