May 2009

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

Mean daily maximum: 16.0
Difference from average: +1.7

Mean daily minimum: 6.6
Difference from average: +1.1

Mean air temperature: 11.3
Difference from average: +1.4

Absolute maximum: 23.0 (29th)

Absolute minimum: 2.9 (11th)

Mean grass minimum: 4.4

Absolute grass minimum: 0.1 (12th)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 12.3

Mean soil temperature at 100cm depth: 11.0

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

Total for the month: 38.2
Difference from average: -13.6

Percentage of the average: 74%

Wettest day: 9.4 (15th)

Number of rain days (>0.25mm): 15

Number of wet days (=> 1mm): 11

3-month total rainfall to 31st May: 96.1
Difference from average: -54.3

6-month rainfall total to 31st May: 228.1
Difference from average: -80.4

12-month rainfall total to 31st May: 728.8
Difference from average: +79.8

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 78%

Sunshine
(all averages 1961 – 1990)

Total for the month: 192.5 hours
Difference from average: +24.0

Percentage of the average: 114%

Mean daily sunshine: 6.2 hours
Difference from average: +0.8

Sunniest day: 11.8 hours (24th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 665.7 hours
Difference from average: +139.4

Wind

The mean wind speed: 14.8km/h [8kt]
Difference from average: +2.5km/hr

The highest gust: 76.9km/h [41.5kt] from 198° at 19:07 GMT on 7th

ISSN1350-483

Comments on May 2009
Temperatures in May were well above average, although the mean air temperature was 0.1°C below that last year. The mean maximum temperature was the highest since 2004. The absolute minimum temperature (2.9°C) was the highest since 1986. It was the first May with no ground frosts since 2003.

For the 7th month in a row, rainfall was below average. The 3- and 6- month totals are now both well below average, but with the totals from last July and September still in the sum, the 12-month total is still well above average.

It was the sunniest May since 2001. With only February having been very slightly below average, cumulative sunshine hours are now well ahead of average.

It was a breezy month with above-average wind speed, equal to 2003 and the windiest May since 2000. there was a gust of 77kph on the 7th.

Professor Tim Burt
Department of Geography
Durham University