April 2012

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

Mean daily maximum: 10.7
Difference from average: -0.3

Mean daily minimum: 2.7
Difference from average: -0.4

Mean air temperature: 6.7
Difference from average: -0.3

Absolute maximum: 15.3 (1st)

Absolute minimum: -2.7 (5th)

Mean grass minimum: 0.6

Absolute grass minimum: -6.4 (5th)

Number of ground frosts: 15

Number of air frosts: 4

Mean soil temperature at 30cm depth: 9.2

Mean soil temperature at 100cm depth: 9.0

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

Total for the month: 134.4
Difference from average: +86.9

Percentage of the average: 283%

Wettest day: 25.6 (26th)

Number of rain days (>0.25mm): 22

Number of wet days (=> 1mm): 17

3-month total rainfall to 30th April: 162.4
Difference from average: -9.6

6-month rainfall total to 30th April: 274.4
Difference from average: -71.8

12-month rainfall total to 30th April: 652.0
Difference from average: +3.0

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 84%

Sunshine
(all averages 1961 – 1990)

Total for the month: 87.9 hours
Difference from average: -45.3

Percentage of the average: 66%

Mean daily sunshine: 2.9 hours
Difference from average: -1.5

Sunniest day: 11.3 hours (5th)

Number of days with no recorded sunshine: 3

Cumulative total sunshine since 1st January: 438.7 hours
Difference from average: +80.9

ISSN1350-483

Comments on April 2012
Mean air temperature in April was below average but not greatly so, the 62nd equal coolest April at Durham since 1850. It was the contrast with March that made it seem so disappointing. There have been 21 years since 1850 when March has been warmer than April (roughly one in eight years therefore). This year has seen the 2nd largest difference (1.7°C); only 1938 had a bigger difference between a warmer March and colder April (1.9°C). The largest difference in the other direction was 1867 when April was 5.9°C warmer than March!

This was a very wet April but not the record total, unlike locations further south: Oxford, for example, saw the wettest April on record since 1767. This was only the 3rd highest total at Durham since 1850, beaten relatively recently in 1998 (151.0mm) and 2000 (150.0mm). Whilst the 3-month total is now back to normal, the 6-month total remains well below average. The 26th was the wettest day at Durham since 6th August 2011.

It was also a very disappointing month for sunshine, the 7th lowest April total since 1882 but only the dullest April since 2004. Like mean air temperature, March was much sunnier, over 90 extra hours of bright sunshine in March despite the shorter day length. Nevertheless, the cumulative total of bright sunshine to the end of April remains well above average.

Professor Tim Burt
Department of Geography
Durham University