September 2015

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

Mean daily maximum: 16.1
Difference from average: -0.6

Mean daily minimum: 7.5
Difference from average: -1.2

Mean air temperature: 11.8
Difference from average: -0.9

Absolute maximum: 20.1 (19th)

Absolute minimum: 3.8 (16th)

Mean grass minimum: 5.7

Absolute grass minimum: 1.6 (16th)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 14.5

Mean soil temperature at 100cm depth: 14.4

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

Total for the month: 39.4
Difference from average: -16.2

Percentage of the average: 71%

Wettest day: 10.8 (15th)

Number of rain days (>0.25mm): 8

Number of wet days (=> 1mm): 7

3-month total rainfall to 30th September: 208.2
Difference from average: +36.2

6-month rainfall total to 30th September: 337.6
Difference from average: -8.6

12-month rainfall total to 30th September: 579.0
Difference from average: -70.0

Humidity
(averages for 09:00 hours GMT)

Relative Humidity: 85%

Sunshine
(all averages 1961 – 1990)

Total for the month: 107.9 hours
Difference from average: -16.1

Percentage of the average: 87%

Mean daily sunshine: 3.6 hours
Difference from average: -0.5

Sunniest day: 8.0 hours (6th)

Number of days with no recorded sunshine: 1

Cumulative total sunshine since 1st January: 1128.5 hours
Difference from average: +4.1

ISSN1350-483

Comments on September 2015
In terms of temperature, September was disappointing. It was the coolest September since 1994 and ranks equal 117th in 166 years of record. The 12-month running mean is now the lowest (9.16°C) since December 2013. It was a dry month, although not unusually so, but the amount of sunshine was below average too.

Professor Tim Burt
Department of Geography
Durham University