September 2017

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

Mean daily maximum: 16.1
Difference from average: -0.6

Mean daily minimum: 9.0
Difference from average: +0.3

Mean air temperature: 12.6
Difference from average: -0.1

Absolute maximum: 18.9 (4th)

Absolute minimum: 4.1 (19th)

Mean grass minimum: 7.3

Absolute grass minimum: 1.4 (19th)

Mean concrete minimum: 8.7

Absolute concrete minimum: 4.1 (19th)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 14.6

Mean soil temperature at 100cm depth: 14.5

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

Total for the month: 87.4
Difference from average: +31.8

Percentage of the average: 157%

Wettest day: 15.4 (12th)

Number of rain days (>0.25mm): 20

Number of wet days (=> 1mm): 16

3-month total rainfall to 30th September: 208.6
Difference from average: +36.6

6-month rainfall total to 30th September: 360.8
Difference from average: +14.6

12-month rainfall total to 30th September: 701.7
Difference from average: +52.7

Humidity
(averages for 09:00 hours GMT)

Relative Humidity: 85%

Sunshine
(all averages 1961 – 1990)

Total for the month: 81.8 hours
Difference from average: -42.2

Percentage of the average: 66%

Mean daily sunshine: 2.7 hours
Difference from average: -1.4

Sunniest day: 6.9 hours (28th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 998.9 hours
Difference from average: -125.1

ISSN1350-483

Comments on September 2017
For the second month in a row, mean air temperature was just below average; like August, daytime temperatures were disappointing but night-time minima were above average. Rainfall was well above average, the wettest September since 2012 and 31st wettest since 1850. Whilst the wettest “day” was technically the 12th (15.4mm), the combined total for the evening of the 12th and morning of the 13th was 28mm. It was the 11th dullest September on record, and the worst since 2001.

Emeritus Professor Tim Burt
Department of Geography
Durham University