April 2007

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

Mean daily maximum: 15.4
Difference from average:

Mean daily minimum: 5.9
Difference from average:

Mean air temperature:
Difference from average:

Absolute maximum: 23.3 (16th)

Absolute minimum: 0.2 (4th)

Mean grass minimum: 4.4

Absolute grass minimum: -2.0 (4th)

Number of ground frosts: 2

Number of air frosts: 0

Mean soil temperature at 30cm depth: 11.0

Mean soil temperature at 100cm depth: 9.8

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

Total for the month: 12.6
Difference from average: -34.9

Percentage of the average: 27%

Wettest day: 5.8 (24th)

Number of rain days (>0.25mm): 6

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

3-month total rainfall to 30th April: 103.4
Difference from average: -36.8

6-month rainfall total to 30th April: 337
Difference from average: +18.3

12-month rainfall total to 30th April: 603.7
Difference from average: -45.3

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 73%

Sunshine
(all averages 1961 – 1990)

Total for the month: 171.5 hours
Difference from average: +38.3

Percentage of the average: 129%

Mean daily sunshine: 5.7 hours
Difference from average: +1.3

Sunniest day: 11.2 hours (4th)

Number of days with no recorded sunshine: 1

Cumulative total sunshine since 1st January: 467.1 hours
Difference from average: +110.1

Wind

The mean wind speed: 11.7km/h [6.3kt]
Difference from average: -1.7km/hr

The highest gust: 61km/h [33kt] from 186° at 13:47 GMT on 24th

ISSN1350-483

Comments on April 2007
This was the warmest April on record at Durham since 1850, beating the previous record holder, April 1949, by a massive 0.9°C. Not surprisingly, both the mean maximum and mean minimum were records, the latter equalling the 2004 value. Only 17th April 2003 (24.1°C) has been a hotter April day in Durham than 16th April 2007. It is only the third time since 1962 that there has been no air frost in April in Durham. Although there were only two ground frosts, this is more than in both 2004 (1) and 2003 (0). From the 5th to the 15th, only one day had a maximum below 15°C with both the 5th and the 15th above 20°C, no doubt one of the warmest Easter breaks in Durham.

Regular readers of this report will know that each month in 2007 has seen the record broken for the warmest ever 12-month period in Durham; April is no exception. Mean air temperature for the ‘year’ to 30th April 2007 has been 10.75°C, an increase of 0.22°C on last month’s figure.

Comparison with the Radcliffe Observatory at Oxford University (the weather station I ran before coming to Durham) is instructive. The 12-month period to March 2007 was also the warmest ever at Oxford, mean air temperature exceeding 12°C for the first time ever. Oxford is usually just over 1°C warmer than Durham on average. We only have to go back to June 2006 to find a 12-month average for Oxford of 10.72°C, very close to the current value for Durham (the equivalent value for Durham was 9.67°C). So, we are only a year behind Oxford, and Durham can hardly be thought on the polar fringes any longer!

April was also a dry month, the driest in Durham since 1997 and the 11th driest since 1852.

Sunshine was well above average again this month, and the cumulative total is well ahead of the average. Nevertheless, 17 Aprils have been sunnier in Durham since 1882.

Professor Tim Burt
Department of Geography
Durham University