Royston (Iceni) Weather Station

Daily Weather Observations - August 2004

It was a warmer and wetter than normal August in Royston, with sunshine marginally above average.

August 2004 will go down as an extreme month in many parts of the country, principally due to the very high rainfall amounts recorded in some places and the attendant severe damage caused e.g. Boscastle and Loch Earn. However, Royston missed most of the heavy rainfall even though nearby locations such as Bedford experienced exceptional falls.

Although the number of "rain days" (0.2 millimetres or more) in August was as high as 19, significant rainfall fell on only 1 day (9^th with 15.5 millimetres). The next wettest day was 22^nd with 7.4 millimetres rainfall. The number of ‘wet’ days (rainfall exceeding 1.0 millimetre) was 10.

Total rainfall in August was 57.0 millimetres, which is 130% of the 1971/2000 average. It was the wettest August since 2001 only. Thunder was heard on 5 days (9^th, 12^th, 18^th, 20^th, and 23^rd) in the month. Rainfall duration in August was 49.2 hours.

During the first half of August daily maximum and minimum temperatures were mostly well above their respective 30 Year (1973/2002) daily averages. In the second half of the month temperatures were closer to average with the mean temperature for the month as a whole being 1.5°C above average.

August 2004 thus became yet another month with an above average mean temperature, although it could not quite compete with August last year which contained the record breaking maximum temperatures.

The mean daily maximum temperature in August was 23.5°C, which is 1.2°C above average. The highest daily maximum temperature achieved was 30.5°C on 7^th, this being only one of the two days in the year to date that the temperature has exceeded 30°C (the other being 8^th June with the slightly higher 30.7°C). In contrast, the lowest daily maximum temperature of the month was 18.3°C on 29^th.

The mean night minimum temperature was 14.4°C, which is 1.8°C above average. The warmest night of the month was 8^th/9^th when the minimum temperature was an exceptionally high 21.1°C, this being the warmest night in any month since at least 1^st May 1972 when records began at Royston (Iceni) Weather Station. The lowest temperature recorded in August was 8.9°C on 21^st, whilst the lowest grass minimum temperature recorded was 6.7°C on 31^st.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 19.8°C. The highest and lowest daily earth temperatures in the month were 21.9°C and 17.4°C on 9^th and 31^st respectively.

Sunshine in August just failed to reach the 200 hour mark, but the total of 198.3 hours was still 6% above the 1971/2000 average (but 40 hours below the sunshine total in August last year). Every day had at least some sunshine although this amounted to just one minute on 9^th! The sunniest day of the month was 7^th with 12.5 hours sunshine, whilst on 4 other days (4^th, 6^th, 8^th and 14^th) sunshine exceeded 10 hours.

The mean wind speed in August was 2.5 mph. The highest daily (00/00 GMT) mean wind speed was 6.0 mph on 30^th and the lowest daily mean wind speed was 0.2 mph on 3^rd. The highest wind gust speed recorded in the month was a relatively modest 32 mph at 1010 GMT on 19^th, and also at 1405 GMT on 30^th.

Wind directions containing a westerly component dominated the month as the following analysis of daily wind directions as observed at 0900 GMT shows: NORTH 1 day, NE 2, E 1, SE 3, S 2, SW 11, W 7, NW 3, and CALM 1.

The mean daily (00/00 GMT) MSL air pressure in August was 1009.7 mB, which is 7.5 mB below the 30 Year (1973/2002) average. The highest and lowest air pressure values recorded in August were 1023 mB and 993 mB on 1^st and 19^th respectively.

The mean relative humidity in August was 78.2%, with the daily (00/00 GMT) mean reaching a highest value of 89.7% on 23^rd and falling to a lowest value of 65.9% on 22^nd. The absolute lowest relative humidity reading in August was 32% at 1440 GMT on 7^th.

Fog (visibility < 1000 metres) was not observed at the 0900 GMT observation hour on any day in the month.

To complete this report a few summary details of Summer (June/August) 2004 are given. The mean daily maximum temperature in Summer was 22.3°C, which is 0.9°C above the 1973/2002 average, whilst the mean night minimum temperature was 1.2°C above average at 13.0°C. Total rainfall in Summer was 186.5 millimetres, which is 130% of the 1971/2000 average. Sunshine was 5% above the 1971/2000 average at 585.9 hours. Only 1 day (1^st June) in the whole Summer was completely sunless.

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

13^th September 2004

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