April 2009

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

Mean daily maximum: 13.7
Difference from average: +2.7

Mean daily minimum: 4.1
Difference from average: +1.0

Mean air temperature: 8.9
Difference from average: +1.9

Absolute maximum: 18.6 (20th)

Absolute minimum: -0.7 (12th)

Mean grass minimum: -0.7

Absolute grass minimum: -6.1 (12th)

Number of ground frosts: 20

Number of air frosts: 1

Mean soil temperature at 30cm depth: 9.9

Mean soil temperature at 100cm depth: 9.2

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

Total for the month: 36.8
Difference from average: -10.7

Percentage of the average: 77%

Wettest day: 23.2 (28th)

Number of rain days (>0.25mm): 8

Number of wet days (=> 1mm): 6

3-month total rainfall to 30th April: 93.5
Difference from average: -46.7

6-month rainfall total to 30th April: 230.7
Difference from average: -88.0

12-month rainfall total to 30th April: 712.2
Difference from average: +63.2

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 81%

Sunshine
(all averages 1961 – 1990)

Total for the month: 151.8 hours
Difference from average: +18.6

Percentage of the average: 114%

Mean daily sunshine: 4.9 hours
Difference from average: +0.5

Sunniest day: 12.6 hours (20th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 328 hours
Difference from average: -29.8

Wind

The mean wind speed: 12.6km/h [6.8kt]
Difference from average: -0.7km/hr

The highest gust: 72.8km/h [39.3kt] from 221° at 15:05 GMT on 4th

ISSN1350-483

Comments on April 2009
This was the 8th warmest April at Durham since 1850. Even so, mean air temperatures were higher in 2003, 2004 and 2007! It was the 8th highest mean maximum – exceeded in 2003 and 2007 – and the 15th highest mean minimum temperature.

It would have been a very dry month except for the fall of  23.2mm on the 28th of which 18.2mm fell steadily over 8 hours during the evening.

Professor Tim Burt
Department of Geography
Durham University