Royston (Iceni) Weather Station

Daily Weather Observations - September 2008

September 2008 was a dry, rather dull and cooler than average month in Royston.

Although the mean temperature in September was only 0.6°C below the 30 Year (1976/2005) average it was nonetheless the coolest September since 2001. Perhaps even more significant is the fact that the highest temperature recorded in the month (20.9°C on 19^th) was the lowest absolute maximum temperature in September since records commenced at Royston (Iceni) Weather Station in 1972.

The mean daily maximum temperature in the month was 18.3°C, which is 0.7°C below average. The mean night minimum temperature was 0.5°C below average at 10.3°C. The lowest temperature recorded in September was 6.5°C on 21^st, 26^th and 27^th, whilst the lowest grass minimum temperature recorded was 2.5°C on 26^th.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 15.9°C. The highest earth temperature recorded was 18.4°C on 1^st and the lowest 14.4°C on 29^th and 30^th.

September commenced with a rather wet spell and 83% of the month’s eventual rainfall total had been recorded by 6^th. However, the rest of the month was mostly dry and the rainfall total of 30.4 millimetres was only 53% of the 1971/2000 average. It was the 3^rd consecutive drier than average September and the 6^th drier than average September in the last 7 years.

The number of "rain days" (0.2 millimetres or more) in September was 16 with rainfall exceeding 1.0 millimetre on 7 of these days. The wettest day of the month was 5^th with 6.9 millimetres rainfall.

Rainfall duration in September was 29.9 hours.

Rainfall for January/September 2008 was 495.5 millimetres, which is 118% of average.

Although 1^st, 3^rd and 14^th were fairly sunny days, the first two weeks of September were rather dull overall. Sunshine duration improved thereafter but by the end of the month sunshine was still in deficit and the month’s total of 122.8 hours was only 87% of the 1971/2000 average. This made it the dullest September since 2001, and sunshine was 64 hours less than the September average in the last 5 years (which was appreciably higher than the 30 Year average for the month).

The sunniest day of the month was 20^th with 10.6 hours sunshine. The previous day, 19^th, also recorded over 10 hours sunshine, these being the only 2 such days in the month. The number of completely sunless days in September was 4 (16^th, 17^th, 24^th and 30^th).

The mean wind speed in September was 3.8 mph, whilst the maximum wind gust recorded was 44 mph on 3^rd.

The highest daily (00/00 GMT) mean wind speed was 11.0 mph on 30^th. The lowest daily (00/00 GMT) mean wind speed was 0.2 mph on 17^th during the generally quieter period from 13^th to 21^st.

The analysis of wind directions as observed at 0900 GMT daily shows a fairly even distribution through the month, as follows: NORTH 2 days, NE 4, E 2, SE 0, S 4, SW 6, W 4, NW 5 and CALM 3.

The mean MSL air pressure in September was 1014.1 mB, which is 2.5 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values in September were 1036 mB and 983 mB on 26^th and 5^th respectively.

The mean relative humidity in the month was 86.0%. The highest daily (00/00 GMT) mean relative humidity was 98.0% on 5^th, whilst the lowest daily mean relative humidity was 71.2% on 19^th. The absolute lowest relative humidity reading in September was 31% at 1425 GMT on 19^th.

Fog (visibility < 1000 metres @ 0900 GMT) was observed on 2 days (26^th and 27^th) in September. On the latter date visibility fell below the 200 metre threshold at 0900 GMT.

Met. Observer, Royston (Iceni) Weather Station

8^th October 2008

Royston Crow (Corvus Cornix)

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