Royston (Iceni) Weather Station

Daily Weather Observations - August 2008

August was a very dull and wet month in Royston, although the mean temperature was near average.

It was the 4^th consecutive August with a below average mean temperature, but by only 0.1°C this year. Nonetheless it was the warmest August since 2004.

The mean daily maximum temperature in August was 21.3°C, which is 1.1°C below the 30 Year (1976/2005) average. However, the mean night minimum temperature was 1.0°C above average at 13.7°C, this positive anomaly being mainly attributable to the persistent cloud cover preventing the radiation of heat to space at night.

As regards the temperature extremes the highest and lowest daily maximum temperatures were 25.0°C and 17.1°C on 30^th and 8^th respectively, whilst the highest and lowest night minimum temperatures were 17.5°C and 9.3°C on 29^th and 23^rd respectively. The lowest grass minimum temperature in August was 6.9°C on 23^rd.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 18.4°C, peaking at 19.9°C on 1^st and falling to its lowest value of 17.5°C on 14^th and 15^th.

One of the main features of the August weather was the excess of rainfall, the total for the month being 92.0 millimetres, which is 185% of the 1971/2000 average. It was the wettest August in Royston since 1977 (but rainfall exceeded August 2006 figure by only 0.6 millimetre).

Two thunderstorms on 7^th were responsible for the high rainfall total of 40.4 millimetres on that day, this being not only the wettest day of the month but the wettest August day since 31^st August 1988. The number of "rain days" (0.2 millimetres or more) in August was 19, with rainfall equalling or exceeding 1.0 millimetre on 9 of these days. Rainfall duration in August was 53.2 hours. Thunder was heard on 2 days (7^th and 31^st) in August.

Sunshine was at a premium in August and the monthly total of sunshine was only 126.4 hours, which is 68% of the 1971/2000 average. It was the dullest August since at least 1998, and only January and March so far this year have experienced less sunshine!

The sunniest day in August was 15^th with 11.8 hours sunshine. Surprisingly for such a dull month there was only 1 completely sunless day (5^th).

August was a rather breezy month and the mean wind speed was 6.0 mph, with a maximum gust speed of 46 mph being recorded on 13^th. The highest and lowest daily (00/00 GMT) mean wind speeds were 11.1 mph and 0.9 mph on 19^th and 29^th respectively.

Wind directions were dominated by those with a westerly component, this being a factor at 0900 GMT on no less than 26 days. The full analysis of daily wind directions at 0900 GMT is as follows: NORTH 1 day, NE 0, E 0, SE 1, S 3, SW 13, W 10, NW 3, and CALM 0.

The mean MSL air pressure in August was 1006.3 mB, which is 7 mB below the 30 year (1976/2005 average). The highest pressure value in August was 1018 mB on 26^th, and the lowest 983 mB on 12^th.

The mean relative humidity in August was 83.6%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 96.3% and 71.7% on 5^th and 15^th respectively. The absolute lowest relative humidity reading in August was 30% at 1350 GMT on 15^th.

Fog (visibility < 1000 metres at the 0900 GMT observation hour) was noted on only 1 day (31^st) in August.

SUMMER (June/August) 2008: It was both the driest and warmest Summer since 2006 only. It was the 2^nd consecutive Summer with an absolute maximum temperature below 30°C (after a run of 13 successive Summers all having one or more days with the temperature exceeding 30°C, including 1995 with 15 such days and 2006 with 10 days). The mean MSL air pressure this Summer of 1010 mB (same as in Summer 2007) was the lowest since at least 1973. Despite the wetter than average nature of the Summer the number of days (5) with thunder was the lowest since 1996.

The mean daily maximum temperature in Summer was 21.3°C, which is 0.1°C above the 30 Year (1976/2005) average. The mean Summer night minimum temperature was 1.0°C above average at 12.6°C. Total rainfall in Summer was 189.5 millimetres, which is 133% of the 30 Year (1971/2000) average. Summer sunshine was 545.6 hours, which is 98% of the 1971/2000 average.

Met. Observer, Royston (Iceni) Weather Station

5^th August 2008

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