Royston (Iceni) Weather Station

Daily Weather Observations - October 2004

It was a slightly wetter than normal October in Royston, but temperatures and sunshine were about average.

For much of the month the day maximum and night minimum temperatures struggled to keep up with the respective 30 Year (1973/2002) daily averages, but milder conditions towards the end of the month nudged both elements into positive territory by the end of the month.

The highest day maximum temperature of the month, 17.3°C, did not occur until 24^th. This is a rather low absolute maximum temperature for October , having been exceeded in 30 of the previous 32 years. In contrast the lowest day maximum temperature was 10.0°C on 15^th.

The lowest night minimum temperature of the month was 4.1°C on 9^th, whilst the lowest grass minimum temperature was 0.2°C on 27^th. Thus the month was completely ground frost free, for only the 5^th time in October in the last 33 years. In comparison, 13 ground frosts were recorded in October last year.

The mean daily maximum temperature in October was 14.7°C, which is 0.4°C above the 30 Year average. The mean night minimum temperature was similarly 0.4°C above average at 8.2°C. It was the warmest October since 2001.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 12.4°C. The highest and lowest earth temperature values in October were 15.2°C and 10.9°C on 1^st and 27^th respectively.

Apart from the period 4^th to 11^th when only 1.1 millimetres rainfall was recorded, October was a generally rather wet month but without any noteworthy large daily amounts of rainfall. In fact, the wettest day yielded only 11.0 millimetres which is not a particularly high amount when compared with the highest daily amounts recorded in October over the years.

Total rainfall in October was 69.4 millimetres, which is 122% of the 1971/2000 average for Royston. The number of "rain days" (0.2 millimetres or more) in the month was 15, whilst on 14 of these days the rainfall reached or exceeded 1.0 millimetre. It was the wettest October since 2001 only. Rainfall duration in October was 73.9 hours.

The first third and last third of October were rather sunny but the intervening mid-month period was dull with only 14.8 hours sunshine being recorded between 11^th and 20^th. This duller period reduced the total sunshine for the month to 108.7 hours, which is 5% below the 1971/2000 average. Sunshine in October last year was somewhat higher at 167.2 hours!

The sunniest day of the month was 21^st with 8.8 hours sunshine. Surprisingly this day was also the windiest day of the month (see below). No sunshine at all was recorded on 3 days (3^rd, 12^th and 15^th) in the month. It was the dullest October since 2002 only.

The analysis of daily wind directions as observed at 0900 GMT shows a bias towards SW, as follows: NORTH 0 days, NE 5, E 0, SE 4, S 3, SW 10, W 5, NW 1, and CALM 3.

The mean wind speed in October was 3.7 mph. The highest and lowest daily (00/00 GMT) mean wind speeds were 12.6 mph and 0.1 mph on 21^st and 30^th respectively. The maximum wind gust speed of the month, 53 mph, was recorded on 21^st at 0155 GMT (from S).

The mean air pressure (reduced to mean sea-level) in October was 1006.2 mB, which is 8 mB below the 30 Year (1973/2002) average, illustrating the unsettled nature of the month’s weather. The highest daily mean MSL air pressure was 1022.1 mB on 31^st and the lowest 990.8 mB on both 20^th and 28^th.

The absolute lowest relative humidity reading in October was 51% at 1220 GMT on 10^th. The highest and lowest daily (00/00 GMT) mean relative humidity values in October were 97.7% and 77.2% on 20^th and 21^st respectively.

Fog (visibility < 1000 metres) was observed at the 0900 GMT observation hour on 2 days (15^th and 31^st) in the month.

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

4^th November 2004

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