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September 2021


September 2021

Temperatures (all temperatures in degrees Celsuis; all averages 1991-2020)

Mean daily maximum: 15.5 Difference from average: +2.3
Mean daily minimum: 11.5 Difference from average: +2.2
Mean air temperature: 15.5 Difference from average: +2.2
Absolute maximum: 28.0 (8th)
Absolute minimum: 5.5 (30th)
Mean grass minimum: 9.5
Absolute grass minimum: 2.6 (30th)
Mean concrete minimum: 11.5
Absolute concrete minimum: 5.2 (30th)
Number of ground frosts: 0
Number of air frosts: 0
Mean soil temperature at 300 mm depth: 16.8
Mean soil temperature at 1000 mm depth: 15.9

Rainfall (all totals in millimetres; all averages 1981-2010)

Total for the month: 44.4 Difference from average: -12.4
Percentage of the average: 78%
Wettest day: 12.8 (14th)
Number of rain days (>0.1 mm): 12 Difference from average: -3
Number of wet days (=>1.0 mm): 9 Difference from average: -1
3-month total rainfall to 30th September 2021: 158.2 Difference from average: -13.8
6-month total rainfall to 30th September 2021: 288.2 Difference from average: -58.0
12-month total rainfall to 30th September 2021: 765.8 Difference from average: -116.8

Sunshine (all totals in hours; all averages 1981-2010)

Total for the month: 134 Difference from average: +1.9
Percentage of the average: 101%
Mean daily sunshine: 4.5 Difference from average: +0.1
Sunniest day: 9.0 (8th)
Number of days with no recorded sunshine: 3
Cumulative sunshine since 1st January: 1264.9 Difference from average: +17.8

Note that the monthly sunshine total is now calculated from the UKMO E&NE regional total. Daily sunshine totals quoted here and in the data summary are uncorrected.

Wind (kph; all data from the West Building roof, Lower Mountjoy campus)

Average wind speed: 3.8
Maximum gust: 53.1 (24th, 13:45, WNW)

Comments on September 2021

This is the second warmest September in the Durham record since 1843 (15.5 °C), surpassed only in 2006 (15.9 C). By 0.05 °C, September was warmer than August, only the sixth time this has happened, and again the first time since 2006. The mean maximum is the third highest on record (behind 1865 and 2006) and the mean minimum is the second highest on record, again behind 2006. The 8th saw the third hottest September day on record (28.0 °C), exceeded only by the first two September days in 1906 (30 °C and 29.3 °C respectively), while the 7th (27.2° C) is the eighth warmest September on record (n=5360). The minima of 15.2 °C on the 10th and 11th are the 28th equal highest September minima on record.

Rainfall was a little below average, almost the same total as for August. There were fewer rain days and wet days than normal. Just three days recorded substantial totals: 10th (9.6 mm), 14th (12.8 mm) and 26th (9.2 mm). Sunshine was almost exactly average for September.

Other than the brief heatwave on the 7th/8th, perhaps the most notable weather event was the passage of a very active cold front on the morning of the 27th. Air temperature fell from 16.5 °C at 0700 GMT to 9.7 °C by 0900; altogether 12.6 mm rain fell in 4 hours (between 0700 and 1100 GMT), with 5.6 mm in the first hour (0700-0800).

Emeritus Professor Tim Burt
Department of Geography
Durham University

[email protected]