September 2018

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

Mean daily maximum: 17.1
Difference from average: +0.4

Mean daily minimum: 8.7
Difference from average: 0.0

Mean air temperature: 12.9
Difference from average: +0.2

Absolute maximum: 24.0 (2nd)

Absolute minimum: 3.8 (29th)

Mean grass minimum: 6.6

Absolute grass minimum: 0.8 (24th)

Mean concrete minimum: 8.0

Absolute concrete minimum: 2.1 (24th)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 14.7

Mean soil temperature at 100cm depth: 14.7

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

Total for the month: 46.8
Difference from average: -8.8

Percentage of the average: 84%

Wettest day: 20.4 (20th)

Number of rain days (>0.25mm): 13

Number of wet days (=> 1mm): 8

3-month total rainfall to 30th September: 152.6
Difference from average: -19.4

6-month rainfall total to 30th September: 284.8
Difference from average: -61.4

12-month rainfall total to 30th September: 614.2
Difference from average: -34.8

Humidity
(averages for 09:00 hours GMT)

Relative Humidity:

Sunshine
(all averages 1961 – 1990)

Total for the month: 114.4 hours
Difference from average: -9.6

Percentage of the average: 92%

Mean daily sunshine: 3.8 hours
Difference from average: -0.3

Sunniest day: 7.9 hours (12th)

Number of days with no recorded sunshine: 2

Cumulative total sunshine since 1st January: 1099.1 hours
Difference from average: -25.3

ISSN1350-483

Comments on September 2018
September was warmer than average, the sixth such month in a row. There were no frosts, air or grass. There were five days with maximum temperature above 20°C and 12 days with minima above 10°C, the highest being 15.8 on 2nd. There was slightly less rainfall than usual, nearly half of which was contributed by a total of 20.4mm on 20th. Sunshine was also a little below average; nevertheless, it was still sunnier than August, although this is not that unusual with a quarter of Septembers having been sunnier than August in 136 years of record.

Emeritus Professor Tim Burt
Department of Geography
Durham University