Royston (Iceni) Weather Station

Daily Weather Observations - October 2002

It was a duller and wetter than normal October in Royston, although the mean temperature was very close to the average. The weather event of the month was undoubtedly the severe gale which occurred on 27^th.

After the record breaking warmth of October last year, relatively high temperatures were experienced in the first week of October this year, but thereafter for much of the remainder of the month temperatures struggled to reach the average

The mean daily maximum temperature in October was 14.1°C, which is 0.2°C below the 25 Year (1973/1997) average for Royston. The mean night minimum temperature was 0.1°C above average at 7.7°C, thus giving a mean temperature just fractionally below average. This is only the second month so far this year in which the mean temperature has failed to exceed the average. Overall it was the coldest October in Royston since 1997.

The highest day maximum temperature recorded in October was 21.5°C on 1^st. In contrast the maximum temperature on 30^th was only 10.0°C, the lowest such day maximum temperature of the month. The lowest night minimum temperature of the month was 1.1°C on 19^th, whereas on 2^nd and 3^rd night minimum temperatures of 13.6°C and 13.5°C respectively were recorded.

The lowest grass minimum temperature in October was –1.9°c on 19^th, this being the second ground frost of the Autumn. The first ground frost occurred on 17^th October, and another on 20^th, giving a total of 3 ground frosts for the month.

The mean earth temperature at 30 centimetres depth as measured at 0900 GMT daily was 11.8°C. The highest earth temperature recorded in the month was 15.1°C on 3^rd, whilst the lowest earth temperature was 9.0°C on 20^th.

Although October was a little wetter than normal, the rainfall total was less than half than that recorded in both October 2000 and 2001, and it was the driest October since 1999. Total rainfall was 65.5 millimetres, which is 115% of the 1971/2000 Royston average.

The first 10 days of October were mostly dry with only 1.5 millimetres rainfall in this period. A 5 day wet spell then followed in which 2/3 of the month’s rainfall was recorded. The wettest day of the month was 15^th with 21.4 millimetres rainfall.

The number of "rain days" (0.2 millimetres or more) in October was 15, whilst on 10 of these days more than 1.0 millimetre rainfall was measured. Rainfall duration in the month was 62.3 hours. The rainfall on 20^th was accompanied by a deposit of orange brown dust, the origin of which is shown by a wind trajectory analysis to have been the Sahara Desert. Rainfall for the year to the end of October was 501.3 millimetres (105% of normal).

The beginning of October was fairly sunny with almost half of the month’s sunshine total being recorded in the first 10 days of the month. By the end of the month, however, a total of 6 days had accrued on which there was no sunshine at all.

Total sunshine in October was 98.0 hours, which is 90% of the 1961/1990 average. The sunniest day of the month was 4^th with 8.9 hours sunshine. It was the dullest October in Royston since 1998.

October had not been a particularly windy month until 27^th when a low pressure system which had been deepening rapidly to the south-west of the British Isles on 26^th swept across the country bringing gale force winds in its wake. The storm peaked in Royston in the morning of 27^th when at both 0915 and 1035 GMT a wind gust speed of 71 mph was recorded, the highest wind gust speed of the month. This was sufficient to cause much tree damage in Royston, consisting mainly of fallen branches. Some structural damage also occurred, including to a house hit by a fallen tree.

Although a higher wind gust speed (78 mph) was recorded on 13^th December 2000, this latest gale appears to have been the most severe in Royston since the notorious afternoon gale which occurred on 25^th January 1990.

The mean wind speed in October was 3.3 mph. The highest daily (00/00 GMT) mean wind speed was 16.9 mph, not surprisingly on 27^th. At the other end of the scale the calmest day of the month was just 3 days later on 30^th with a 24 hour (00/00 GMT) mean wind speed of 0.1 mph.

The analysis of daily wind directions as observed at 0900 GMT was NORTH 1 day, NE 4, E 0, SE 5, S 2, SW 1, W 8, NW 4 and CALM 6.

The mean MSL air pressure in October was 1011.0 mB, which is approximately 4 mB below average. The highest air pressure value recorded in October was 1031 mB on 4^th, whilst the lowest was 977 mB on 22^nd.

The mean relative humidity in October was 84.7%. The highest and lowest daily (00/00 GMT) mean relative humidity values in the month were 98.6% on 30^th and 73.6% on 26^th respectively. The absolute lowest relative humidity reading in October was 48% at 1245 GMT on 7^th and 1320 GMT on 1^st.

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

6^th November 2002

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