Royston (Iceni) Weather Station

Daily Weather Observations - October 2005

It was a very mild October in Royston, with rainfall and sunshine near average.

The Autumn season had commenced on a warm note with the milder than average September, and this trend continued in October with an even higher positive mean temperature anomaly.

The last week of October was particularly warm compared to the average. On 27^th the temperature rose to 20.0°C and this made it the warmest day in the last week of October since at least 1972. Then, on 30^th, a maximum temperature of 19.3°C was recorded, this being the second warmest day in the last week of October since at least 1972. The previous record for the last week of October stood at 18.5°C on 30^th October 2001.

The daily maximum temperatures in October failed to reach the 30 Year (1973/2002) mean maximum for the month on only 2 days (18^th and 31^st) and this perhaps best illustrates the relative warmth of the month. Overall it was the second warmest October in Royston since at least 1972, with only October 2001 having a higher mean temperature (and then only by 0.3°C).

The mean daily maximum temperature in October was 17.2°C, which is 2.9°C above the 30 Year (1973/2002) average. The mean night minimum temperature was similarly 2.9°C above average at 10.7°C. The highest and lowest temperatures recorded in the month were 22.5°C and 6.2°C on 10^th and 4^th respectively.

The lowest day maximum temperature was 13.5°C on both 18^th and 31^st, as noted above, whilst the highest night minimum temperature was 15.9°C on 12^th. The lowest grass minimum temperature in October was 2.3°C on 18^th. As might be expected in such a mild Autumn month no air or ground frost was recorded.

The mean earth temperature at 30 cms depth was 13.8°C, with a ‘high’ of 15.3°C on 1^st and a ‘low’ of 12.5°C on 24^th.

The first half of October was rather dry with only 2.0 millimetres rainfall up until 11^th, and only 13.4 millimetres by 17^th. In contrast the period 18^th to 31^st yielded 50.0 millimetres rainfall. Total rainfall in the month was thus 63.4 millimetres, which is 111% of the 1971/2000 average for Royston.

The number of "rain days" (0.2 millimetres or more) in October was 14, whilst on 9 of these days rainfall exceeded 1.0 millimetre. The wettest day of the month was 23^rd with 18.3 millimetres rainfall. For the first time in October since 1998 thunder was heard, on 19^th at 1455 GMT. Rainfall duration in the month was 61.2 hours. A rainfall deficiency still exists in 2005 with the January/October rainfall of 430.1 millimetres being 10% below normal.

October was a marginally sunnier than average month, and the sunniest in Royston since 2003 only (but with 42.1 hours less sunshine than in October 2003). Total sunshine was 125.1 hours, which is 109% of the 1971/2000 average.

The sunniest day in October was 4^th with 9.9 hours sunshine. Two other days, 9^th and 10^th, experienced sunshine totals above 9 hours. Four days, 5^th, 6^th, 7^th and 14^th, in the month were completely sunless.

October was a relatively calm month with a mean wind speed of 2.0 mph. Unusually, it was dead calm at the 0900 GMT observation hour on no less than 5 days in the month. On two of these days, 3^rd and 6^th, the mean wind speed over the 24 hour period from 00/00 GMT was 0.0 mph (to the nearest 1 decimal place). Maximum wind gusts of 9 mph on 3^rd and 5 mph on 6^th did occur on these two days, however, so they were not completely calm over the whole 24 hours. The highest daily (00/00 GMT) mean wind speed was 9.6 mph on 25^th, and the highest wind gust speed recorded in the month was 44 mph on 24^th.

As regards daily wind directions at 0900 GMT the monthly analysis was as follows: NORTH 0 days, NE 3, E 1, SE 6, S 7, SW 7, W 0, NW 2 and CALM 5. It is very unusual for a W wind not to be recorded on any day in a month, for example the monthly average for this year up to September being 6 days.

The mean MSL air pressure in October was 1013.9 mB, which is 0.5 mB below the 30 Year (1973/2002) average. The highest and lowest air pressure values recorded in the month were 1032 mB and 990 mB on 3^rd and 21^st respectively.

The mean relative humidity in October was 89.9%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 97.7% and 78.7% on 24^th and 2^nd respectively. The absolute lowest relative humidity reading in October was 35% at 1445 GMT on 10^th.

Fog (visibility < 1000 metres) was noted at the 0900 GMT observation hour on 3 days, 6^th, 15^th and 16^th, in the month.

Met. Observer, Royston (Iceni) Weather Station

4^th November 2005

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