Royston (Iceni) Weather Station
Daily Weather Observations - October 2000
October 2000 Weather Review
It was an exceptionally wet October in Royston, but the mean temperature was near average and sunshine only a little below average.
The rainfall was certainly the main feature of the October weather, and it was the wettest October in Royston since 1865. It was also the wettest month of any since September 1995. The total rainfall in the month was 137.7 millimetres, which is 275% of the 35 Year (1961/1995) average.
The two heaviest falls of the month both occurred in the overnight period, the first on 20th/21st (34.3 millimetres) and the second on 29th/30th (29.2 millimetres). This second rainfall event was accompanied by stormy conditions and at 0505 GMT on 30th the maximum wind gust speed (62 mph) of the month was registered. The rainfall total for 20th as noted above made this the wettest October day since 2nd October 1982 (when a fall of 38.1 millimetres was recorded).
The number of "rain days" in October was 23, the highest such figure in October since at least 1972, and exceeding the number in October 1976 by just 1 day. With regard to the rainfall so far in the year it is worthy of mention that on 21st October the annual average rainfall for Royston (584.2 millimetres) was reached. The year 2000 is thus destined to be a wetter than average year but by how much remains to be seen, of course. No thunder was heard or hail observed to fall in October.
The mean temperature in October was once again above average (in line with most months in the last 4 years), but this time only by a somewhat insignificant 0.2°C. In fact, the mean daily maximum temperature of 13.9°C was 0.4°C below the 25 Year (1973/1997) average, but this was more than offset by the mean night minimum temperature of 8.4°C being 0.8°C above average.
The highest temperature recorded in October was 18.5°C on 1st; by near the month end the 30th could only manage a day maximum temperature of 9.8°C. The lowest temperature of the month was 5.0°C on 9th, whilst the lowest grass minimum temperature was 2.6°C on 20th. The highest night minimum temperature was 12.1°C on 4th.
These figures indicate that no air frost or ground frost was recorded in October this year. Although October has experienced air frost in only 5 of the last 29 years, it is unusual for October not to have any ground frost. In fact, this is only the 3rd October in the last 29 years without any ground frost, the other years being 1977 and 1989.
The mean earth temperature at 30 cms depth as recorded daily at 0900 GMT was 12.0°C. The highest and lowest earth temperature values in the month ranged from 14.9°C on 1st to 10.1°C on 31st indicating as expected a steady cooling down of the soil as the Autumn progresses.
With October being so wet it is perhaps not surprising that sunshine failed to reach the average for the month. Even so the sunshine total of 100.9 hours was only 7% short of the 1961/1990 normal. The sunniest day was 1st with 9.0 hours, whilst 19th recorded 8.8 hours and 17th 8.1 hours. The number of days with a NIL sunshine value was 5 (7th, 14th, 21st, 24th, and 27th).
October in Royston was a fairly windy month, especially in the last week. The stormy conditions which affected much of the country overnight on 29th/30th also gave Royston a very windy night and, as indicated above, the wind reached its peak at 0505 GMT on 30th with a gust of 62 mph. The mean wind speed remained in the region of 20/25 mph for several hours around this time.
The mean wind speed for the whole month was 5.5 mph. The windiest day was 30th with a mean wind speed (00/00 GMT) of 15.2 mph, whilst the calmest day was 20th with a mean wind speed of 0.7 mph.
The daily wind directions as observed at 0900 GMT were North 0 days, NE 0, E 0, SE 1, S 7, SW 12, W 8, NW 2 and CALM 1.
The mean MSL air pressure in October was 1006.7 mB, which is approximately 8 mB below average. This is the lowest mean value for October since 1976. The highest pressure value recorded was 1025 mB on both 6th and 21st, and the lowest pressure value recorded was 962 mB on 11th. This was the lowest air pressure value recorded in any month of the year in Royston since the reading of 957 mB on 25th February 1989.
The mean relative humidity in October was 87.2 %. The highest and lowest daily (00/00 GMT) mean relative humidity values were 99.8% on 21st and 73.8% on 4th respectively. The absolute lowest relative humidity reading in the month was 52% at 1400 GMT on 6th.
Fog was virtually non existent in October but the visibility did fall below the 1000 metres threshold for fog at the 0900 GMT observation hour on 2 mornings in the month, 16th and 21st.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
6th November 2000
Royston Crow (Corvus Cornix)
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