It was a dry and sunny September in Royston, although the mean temperature was a little below average.

After the very wet April/July period dry conditions have prevailed since 21^st July, and the September rainfall was only half the average. Total rainfall in the month was 27.6 millimetres, which is 51% of average, making it the ‘wettest’ September since 2010 only. In the last 10 years only in 2005 has September rainfall been above average.

The number of "rain days" (0.2 millimetres or more) in the month was 8 with rainfall exceeding 1.0 millimetre on 3 of these days. The wettest day of the month was 23^rd when 14.3 millimetres rainfall was recorded. For the 4^th successive year no thunder was heard in September.

Rainfall from January to September 2012 was 581.9 millimetres, which is 134% of average.

The first half of September was mainly warmer than average, the mean temperature for the period 1^st/15^th being 16.7°C, but this dropped to 12.7°C for the period 16^th/31^st. For the month as a whole the mean daily maximum temperature was 0.5°C above average at 19.7°C, mainly due to some very warm days in the first half of the month.

One of these very warm days was on 9^th when the highest temperature (28.5°C) of the month occurred. In contrast the lowest day maximum temperature of the month occurred on 23^rd with a high of only 13.2°C.

The nights in September were comparatively cooler and the mean night minimum temperature of 9.7°C was 1.2°C below average. The lowest temperature recorded in September was 3.2°C on 22^nd. This was the lowest temperature experienced in any September since 1986 when a minimum temperature of 2.7°C was recorded.

The lowest grass minimum temperature (0.8°C) of the month also occurred on 22^nd and this was the lowest such value in September since 1990, having been equalled in September 1993. The highest night minimum temperature in September was 15.0°C on 10^th. It was the coolest September since 2008.

The mean earth temperature at 30 cms depth in September as observed at 0900 GMT daily was 15.6°C, peaking at 18.0°C on 10^th, and falling to a lowest value of 12.9°C on 30^th.

Sunshine in the month was marginally below September last year but otherwise it was the sunniest September since 2006. Total sunshine in the month was 189.7 hours, which is 131% of average. The sunniest day of the month was 6^th with 12.5 hours sunshine, closely followed by 7^th with 12.4 hours and 8^th with 12.1 hours.

Sunshine for the first half of the month, 1^st/15^th, of 119.4 hours far exceeded the amount (70.3 hours) for the second half. Every day in the month experienced at least some sunshine although sunshine on 23^rd consisted of only 1 minute!

The mean wind speed in September was 6.6 mph and the maximum wind gust speed recorded in the month was 38 mph on 24^th. The windiest day (00/00 GMT) of the month was 14^th with a mean wind speed of 11.5 mph, whilst the calmest day was 22^nd with a mean wind speed of 2.4 mph.

Analysis of wind directions as observed at 0900 GMT daily reveals a remarkable consecutive sequence of 9 days of westerly winds between 11^th and 19^th inclusive with the full analysis giving the following result: NORTH 1 day, NE 1, E 1, SE 1, S 3, SW 6, W 14, NW 3 and CALM 0.

The mean MSL air pressure in September was 1013.7 mB, which is 2.4 mB below average. The highest and lowest air pressure values in the month were 1029.1 mB and 983.7 mB on 6^th and 24^th respectively.

The mean relative humidity in the month was 77.1%. The highest daily (00/00 GMT) mean relative humidity was 93.3% on 24^th, whilst the lowest daily mean relative humidity value was 59.9% on 8^th. The absolute lowest relative humidity reading in September was 27% at 1525 GMT on 8^th.

Fog (visibility < 1000 metres @ 0900 GMT) was not observed on any day in September.

Met. Observer, Royston (Iceni) Weather Station

7^th October 2012