Royston (Iceni) Weather Station

Daily Weather Observations - August 2005

August temperatures and sunshine were fairly close to the long term averages, but it was a wetter than normal month.

Unusually for a month in recent years the August mean temperature was actually below average, but only by 0.2°C! It was the coolest August since 1998.

The highest temperature in August (by a margin of 3.4°C over the next highest daily maximum temperature) was reserved for the last day of the month. On 31^st the temperature soared to 31.4°C, this being the highest temperature recorded on this day since at least 1972. The previous maximum temperature for 31^st August was 26.7°C in 1991. At the other end of the scale the lowest night minimum temperature recorded in August was 8.5°C on both 7^th and 8^th. The lowest grass minimum temperature recorded in the month was 5.9°C on 8^th.

The lowest day maximum temperature in the month was 15.8°C on 19^th, whilst the highest night minimum temperature was 15.4°C on 31^st.

The mean daily maximum temperature in August was 22.5°C, which is 0.2°C above the 30 Year (1973/2002) average. High temperatures on the last 3 days of the month just managed to raise this value above the long term mean. Night minimum temperatures were a little below average, however, the mean for the month of 12.1°C being 0.5°C below normal.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 18.0°C. The highest and lowest earth temperature values in the month were 19.0°C and 16.7°C on 19^th and 26^th respectively.

The long sequence of drier than average months came to an end in August with rainfall of 62.6 millimetres exceeding the 30 Year (1971/2000) average by 26%. This was the first month with above average rainfall since November 2004. It was the wettest August since 1999.

The number of "rain days" (0.2 millimetres or more) was 13, with rainfall exceeding 1.0 millimetre on 10 of these days. The wettest day in the month was 22^nd with 16.5 millimetres rainfall. Rainfall duration over the whole month was 57.3 hours.

Thunder was heard on 3 days (19^th, 25^th, and 31^st) in August.

Sunshine for the month just failed to reach the 200 hour mark, but the total of 199.3 hours was nonetheless 7% above the 1971/2000 average. The sunniest day of the month was 17^th with 13.4 hours sunshine, whilst 7 other days reached double figures, including each of the last 4 days of the month. Only 1 day (19^th) in August was completely sunless.

August was a fairly calm month, reflected in the overall mean wind speed of 1.7 mph. The highest wind gust speed in the month was 37 mph on 24^th. The highest daily (00/00 GMT) mean wind speed was 6.8 mph on 24^th, whilst the lowest such value was 0.1 mph on both 1^st and 16^th.

Winds with a westerly component feature prominently in the daily (at 0900 GMT) wind direction analysis, with 20 out of 31 days, as follows: NORTH 4 days, NE 1, E 0, SE 3, S 3, SW 4, W 9, NW 7, and CALM 0.

The mean MSL air pressure in August was 1016.3 mB, which is approximately 1 mB below the 1973/2002 mean. The highest and lowest air pressure values recorded in the month were 1025 mB and 1001 mB on 15^th and 25^th respectively.

The mean relative humidity in August was 75.4%. The highest daily (00/00 GMT) mean relative humidity in the month was 96.0% on 22^nd, whilst the lowest daily mean relative humidity was 63.3% on 9^th. The absolute lowest relative humidity reading in August was 32% at 1355 GMT on 3^rd, at 1405 GMT on 9^th and 1455 GMT on 11^th.

No fog (visibility < 1000 metres @ 0900 GMT) was observed in August.

Finally, a few brief details of the Summer (June/August) are given. The mean daily maximum temperature in Summer was 22.2°C (+0.8), the mean night minimum temperature was 12.3°C (+0.5), rainfall was 137.6 millimetres (96%), and sunshine was 590.8 hours (106%). It was the coolest Summer since 2002, and the driest Summer since 2003.

Richard Barker, Met. Observer, Royston (Iceni) Weather Station

5^th September 2005

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