April 2011

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

Mean daily maximum: 16.5
Difference from average: +5.5

Mean daily minimum: 5.9
Difference from average: +2.8

Mean air temperature: 11.2
Difference from average: +4.2

Absolute maximum: 21.8 (23rd)

Absolute minimum: -0.2 (28th)

Mean grass minimum: 3.6

Absolute grass minimum: -3.3 (28th)

Number of ground frosts: 5

Number of air frosts: 1

Mean soil temperature at 30cm depth: 11.1

Mean soil temperature at 100cm depth: 10.0

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

Total for the month: 7.2
Difference from average: -40.3

Percentage of the average: 15%

Wettest day: 4.4 (1st)

Number of rain days (>0.25mm): 3

Number of wet days (=> 1mm): 3

3-month total rainfall to 30th April: 90.0
Difference from average: -50.2

6-month rainfall total to 30th April: 331.2
Difference from average: +12.5

12-month rainfall total to 30th April: 674.6
Difference from average: +25.6

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 72%

Sunshine
(all averages 1961 – 1990)

Total for the month: 225.6 hours
Difference from average: +92.4

Percentage of the average: 169%

Mean daily sunshine: 7.3 hours
Difference from average: +2.9

Sunniest day: 13.0 hours (30th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 514.1 hours
Difference from average: +156.3

Wind

The mast is still broken, we hope to replace it soon.

ISSN1350-483

Comments on April 2011
April was an exceptionally warm month, the warmest April on record at Durham since 1850, easily breaking the previous record (2007) by the very large margin of 0.5°C. Both the mean maximum and the mean minimum were the highest on record since 1900. The mean daily maximum in particular, a massive 5.5°C above average, is the largest difference between a record maximum and the average for any month of the year; July 2006 was 5°C above average. The absolute maximum (21.8°C), not a record, was the highest since 2007; the highest minimum, 11.1°C on the 6th is also worth noting, a remarkably warm night for April!

These very high temperatures reflect a notable warming in April in recent years; of the top ten warmest Aprils, five have occurred since 2003. The period January-April 2011 has been 3rd warmest (6.7°C) since 1850 (equal to 2004), beaten only by 1990 (6.8°C) and 2007 (7.3°C). The 12-month running mean has gone back above 9°C for the first time since the period ending in February 2010.

April was also a very dry month, the fifth driest April since 1850, just 15% of the expected amount. 1938 holds the record with only 2.2mm! The last three months have been very dry; the 3-month total (90mm) is the 178th lowest since 1850 (n = 1934). The 12-month total remains just above average and the 6-month total has now just about returned to average; it remains to be seen if we move rapidly from a time of excess to a drought.

April was the 2nd sunniest on record since 1882, beaten only by 1914 (238 hours). It is also the 2nd sunniest start to a year, beaten only by 2003.

Professor Tim Burt
Department of Geography
Durham University