Royston (Iceni) Weather Station
Daily Weather Observations - August 2001
August 2001 Weather Review
Temperatures, rainfall and sunshine were all a little above normal in August in Royston.
The temperature in August again exceeded 30°C, making it the 6th August in the last 7 years that this value has been achieved (the exception being August 2000). On 15th the temperature reached its highest level for the month when 30.9°C was recorded. However, the temperature the next day, 16th, returned swiftly to average with a maximum of 22.6°C. A similar pattern occurred later in the month when a maximum temperature of 30.2°C on 25th was followed by a maximum temperature of 20.0°C on 26th!
The mean daily maximum temperature in August was 22.9°C, which is 0.7°C above the 25 Year (1973/1997) average. The mean daily minimum temperature showed a greater positive anomaly and was 1.4°C above average at 13.8°C. It was the warmest August in Royston since 1997.
The lowest daily minimum temperature recorded in August was 8.9°C on 10th, whilst the lowest grass minimum temperature was 7.2°C on 28th.
In contrast to the two days mentioned above with maximum temperatures above 30°C, the 9th could manage a maximum of only 16.2°C, the lowest such value of the month. Two nights in the month were particularly warm, namely 15th and 24th, with minimum temperatures of 18.5°C and 18.3°C respectively.
The mean earth temperature at 30 cms depth as measured at 0900 GMT daily was 19.0°C. The highest and lowest earth temperatures recorded in the month were 20.5°C on 1st and 17.1°C on 11th respectively.
Total rainfall in August was 61.5 millimetres, which is 124% of the 30 Year (1971/2000) average for Royston. Despite the wetter than average nature of the month no really wet days occurred, the highest 24 hour measurement being 10.3 millimetres rainfall on 11th. Much of the following 2 weeks was then dry.
The number of "rain days" (0.2 millimetres or more) in August was 15, whilst on 12 of those days the rainfall exceeded 1.0 millimetre. Rainfall duration over the whole month was 50.4 hours.
Thunder was heard on 4 days (4th, 6th, 8th, and 31st) in August. On the morning of 30th slight traces of red/brown dust (mud) were observed as having been deposited in overnight rain. Previous cases of similar depositions have mostly been traced back from wind trajectories to origin in the deserts of North Africa although this has not yet been confirmed in this latest instance.
Sunshine in August got off to a good start on 1st with a total duration of 14.5 hours, the highest daily value of the month. Despite 4 completely sunless days (9th, 12th, 26th and 30th) occurring by the end of the month the August sunshine total was nonetheless 11% above average at 196.9 hours. Other days with over 10 hours sunshine were 14th, 21st, 25th, 27th and 28th. This was the 3rd sunnier than average August in the last 4 years.
Moving on to wind speed and direction, the mean wind speed in August was 3.8 mph. The highest wind gust speed recorded was 35 mph on both 8th and 16th. The highest and lowest daily (00/00 GMT) mean wind speeds were 8.8 mph on 12th and 0.5 mph on 2nd respectively.
The analysis of daily wind directions as observed at 0900 GMT daily was as follows: NORTH 4 days, NE 0, E 0, SE 4, S 7, SW 9, W 5, NW 1, and CALM (no direction) 1.
The mean MSL air pressure in August was some 4 millibars below average at 1013.3 mB. The highest air pressure value recorded in the month was 1027 mB on 1st, whilst the lowest was 998 mB on 7th, 8th and 19th.
The mean relative humidity for the month was 77.2%. The highest and lowest mean daily (00/00 GMT) relative humidity values were 94.3% on 9th and 64.6% on 1st respectively. The absolute lowest relative humidity value recorded in August was 34% at 1435 GMT on 27th.
With August being the final month of the recognised Summer season it is now possible to review the Summer (June/August) as a whole. The mean daily maximum temperature over the whole Summer was 22.1°C, which is 0.7°C above average. The mean daily minimum temperature was 12.5°C, which is 0.8°C above average. The highest temperature recorded in the Summer was 30.9°C on both 29th July and 15th August, whilst the lowest temperature recorded was 4.0°C on 3rd June.
Total Summer rainfall was 141.8 millimetres, which is 99% of average. The wettest day of the Summer was 17th July with 23.5 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) in Summer was 34.
The Summer sunshine totalled 613.7 hours, which is 110% of normal. The sunniest day of the Summer was 25th June with 15.7 hours sunshine.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
6th September 2001
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