Royston (Iceni) Weather Station

Daily Weather Observations - December 2002

The year ended with a wet and very dull December, but with the mean temperature above average.

The lack of sunshine was a notable feature of the December weather. With shorter daylight hours around the winter solstice, not surprisingly December receives on average less sunshine than any other month of the year, but this year the total December sunshine of 30.4 hours was no less than 22.9 hours below the previous lowest total in any month of the year over the last 5 years.

Total sunshine was only 65% of the 30 Year (1961/1990) average, whilst on 15 days of the month no sunshine at all was recorded. In contrast 6.7 hours sunshine was recorded on 9^th, making it the sunniest day of the month.

The very wet conditions experienced in Royston in November were repeated throughout much of December with the result that the number of "rain days" (0.2 millimetres or more) was as high as 21. On 15 of these days rainfall of 1.0 millimetre or more was recorded.

The rainfall total for the month was 83.5 millimetres, which is 158% of the 30 Year (1971/2000) average. The wettest day of the month was 21^st with 18.0 millimetres rainfall. It was the wettest December in Royston since 1989. December was a completely snow-free month.

Rainfall duration in the month was 120.3 hours and this was the highest such value for any month this year, even exceeding the very high November figure by 4.5 hours.

December commenced on a mild note and finished in a similar fashion, but in the middle two weeks of the month temperatures were only average or below. In the monthly temperature means the milder weather gained the upper hand resulting in the mean temperature being 1.0°C above average. It was the mildest December since 1998 only and had the same mean temperature as in December 2000. In the 72 months since January 1997 the mean temperature has been above average in no less than 55 of these months.

The mean daily maximum temperature in December was 7.6°C, which is 0.5°C above average. The mean daily minimum temperature of 4.4°C showed a greater positive anomaly of 1.4°C, however.

The highest daily maximum temperature recorded in December was 12.9°C on 24^th, whilst the lowest night minimum temperature of the month was –1.2°C on 20^th. The contrasting extremes were a lowest daily maximum temperature of 1.7°C on 10^th, and a highest night minimum temperature of 9.7°C on 24^th.

The lowest grass minimum temperature recorded in December was –5.6°C on 20^th. Totals of 5 air frosts and 8 ground frosts occurred in the month. This was the lowest number of ground frosts in December since 1988 (but equal with December 1993). Air frost duration was 27.4 hours in December.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 6.7°C. The highest and lowest earth temperatures recorded in the month were 8.4°C on 1^st and 2^nd, and 4.5°C on 20^th, respectively.

The analysis of wind directions in December as observed at 0900 GMT daily was NORTH 2 days, NE 8, E 4, SE 2, S 4, SW 4, W 3, NW 2 and CALM 2.

The mean wind speed in December was 3.6 mph. The highest daily (00/00 GMT) mean wind speed was 9.5 mph on 2^nd, whilst the lowest daily mean wind speed was 0.2 mph on 18^th. The highest wind gust recorded in the month was 46 mph on 30^th.

The mean air pressure in December reduced to mean sea-level was 1013.5 mB, which is approximately 1 mB below average. The highest and lowest air pressure readings in December were 1035 mB and 987 mB on 18^th and 27^th respectively.

The mean relative humidity in December was 93.7%. The highest daily (00/00 GMT) mean relative humidity was 99.8% on 15^th, whilst the lowest daily mean value was 81.7% on 2^nd. The absolute lowest relative humidity reading in the month was 67% at 1445 GMT on 1^st and 1320 GMT on 9^th.

Fog was observed at the 0900 GMT observation hour on only 2 days in the month, 16^th and 21^st. On the latter date the fog was thick with visibility falling below 200 metres.

A few summary details of the year 2002 as a whole conclude this report. The outstanding feature in the 2002 annual means is that the mean temperature was the highest in at least the last 30 years in Royston, although it exceeded the mean temperature in 1990 by less than 0.1°C. The mean daily maximum temperature for the year as a whole was 15.1°C, which is 1.1°C above average. The mean night minimum temperature was similarly 1.1°C above average at 7.8°C. Total rainfall in the year was 682.8 millimetres, which is 117% of normal, whilst total sunshine was 1533.5 hours (103% of average). Totals of 15 air frosts and 47 ground frosts were recorded in the year. Snow was observed to fall on only 1 day in the whole year, the lowest annual total in at least the last 30 years.

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

7^th January 2003

Royston Crow (Corvus Cornix)

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