July 2007

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

Mean daily maximum: 18.8
Difference from average: -0.5

Mean daily minimum: 10.9
Difference from average: +0.5

Mean air temperature: 14.9
Difference from average: +0.1

Absolute maximum: 21.5 (24th)

Absolute minimum: 5.9 (10th)

Mean grass minimum: 8.4

Absolute grass minimum: 1.9 (10th)

Number of ground frosts: 0

Number of air frosts: 0

Mean soil temperature at 30cm depth: 16.7

Mean soil temperature at 100cm depth: 15.4

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

Total for the month: 112
Difference from average: +60.5

Percentage of the average: 218%

Wettest day: 22 (18th)

Number of rain days (>0.25mm): 17

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

3-month total rainfall to 31st July: 271
Difference from average: +115.9

6-month rainfall total to 31st July: 374.4
Difference from average: +79.1

12-month rainfall total to 31st July: 756.8
Difference from average: +107.8

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: %

Sunshine
(all averages 1961 – 1990)

Total for the month: 124.8 hours
Difference from average: -30.1

Percentage of the average: 86%

Mean daily sunshine: 4.0 hours
Difference from average: -1.0

Sunniest day: 7.8 hours (7th)

Number of days with no recorded sunshine: 1

Cumulative total sunshine since 1st January: 836.8 hours
Difference from average: -8.1

Wind

The mean wind speed: 12.2km/h [6.6kt]
Difference from average: +0.7km/hr

The highest gust: 61.1km/h [33kt] from 211° at 11:42 GMT on 13th

ISSN1350-483

Comments on July 2007
This was another disappointing month, although as unusual as reports in the media suggested. Mean air temperature just about exceeded average, on the basis that nights were warmer than usual, balancing the relatively cool days. However, it was the same mean air temperature as 2004 and 2002, and better than 14.1°C in 2000. Memories are clearly short when it comes to a cool July! There was the lowest maximum temperature since 1965, which probably accounts for the disappointment.

Following the 2nd driest on record in July 2006, this was the wettest July since 1940 and the 12th wettest since 1852. Even so, it hardly competed with the wettest July on record, 206.6mm in 1888. There was an exceptionally heavy fall of rain on the afternoon of 18th, lasting an estimated 32 minutes either side of 15:00 hours BST; 19.2mm fell at a maximum hourly rainfall  intensity of 36mm per hour (This is calculated on the basis of the highest 10-minute running total during any hour).

Dave O’Hara, a local enthusiast from Ferryhill, kindly pointed out to me that this is the 10th time at Durham since 1880 that two months in a row have received over 100mm rainfall. For the record, the others are:

9/10 1880, 7/8 1891, 7/8 1930, 12/1 1938/9, 7/8/9 1950, 9/10 1976, 4/5 1983, 10/11 2000.

Looking at the long-period totals, this was the highest 12-month total since December 2004, and the highest 3-month since October 2004.

This was the 3rd month in a row with below average sunshine. Even so, it was only the dullest July since 2001. Curiously, despite all the rain, there was only one day with no bright sunshine.

Professor Tim Burt
Department of Geography
Durham University