Royston (Iceni) Weather Station

Daily Weather Observations - December 2004

The Winter in Royston commenced on a reasonable note with a mild, dry and sunny December.

For the 11^th month in 2004 the mean temperature was above average, the only exception in the year being July which experienced a marginal deficit only. However, the highest temperature recorded in the month, 12.7°C on 23^rd, was not exceptional, having been exceeded in December in 21 out of the last 32 years.

At the other end of the scale the lowest temperature recorded in December was –2.1°C on 26^th, whilst the lowest grass minimum temperature was –6.1°C on 20^th. Also on 26^th the temperature reached its lowest daily maximum value (3.1°C) of the month. In contrast, the highest night minimum temperature of the month was 9.6°C on 23^rd.

The mean daily maximum temperature in December was 8.1°C, which is 0.9°C above the 30 Year (1973/2002) average. The mean night minimum temperature was 3.4°C, which is 0.4°C above average. It was the mildest December in Royston since 2002 only. Totals of air and ground frost were 6 and 13 respectively. Air frost duration was 50.4 hours.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 6.3°C. The highest earth temperature value was 7.9°C on both 9^th and 16^th, whilst the lowest such value was 3.8°C on 29^th.

December commenced on a very dry note with only 0.6 millimetres rainfall in the first two weeks of the month. It was a little wetter thereafter but the final total of rainfall for the month was still only 52% of the 1971/2000 average at 27.3 millimetres. The number of "rain days" (0.2 millimetres or more) was 7, and the wettest day of the month was 21^st with 9.7 millimetres rainfall. It was the driest December since 2001 only.

For only the 7^th occasion since 1972 no snow was observed to fall in December. Rainfall duration in the month was 31.4 hours.

Despite experiencing 7 sunless days in the first half of the month a brighter second half projected the monthly sunshine total to 69.5 hours, which is 146% of the 1971/2000 average. The sunniest day of the month was 28^th with 6.3 hours sunshine. The 19^th was the only other day in the month to record over 6 hours sunshine. It was the 6^th sunnier than average December in the last 7 years with sunshine being 39% above average in this period.

As far as wind strength is concerned December was a fairly quiet month, the maximum wind gust of in the month being a relatively modest 41 mph on 22^nd. The mean wind speed over the month as a whole was 3.3 mph.

The highest daily (00/00 GMT) mean wind speed in December was 10.1 mph on 23^rd, and the lowest daily mean wind speed was 0.0 mph (to nearest 1 decimal place) on both 1^st and 2^nd.

Winds from directions between S and W dominated the month as the following analysis of wind directions as observed at 0900 GMT daily shows: NORTH 1 day, NE 1, E 2, SE 1, S 4, SW 15, W 5, NW 1 and CALM 1.

The mean MSL air pressure in December was 1017.2 mB which is approximately 3 mB above the average of the 30 Years 1973/2002. The highest pressure reading recorded in December was 1033 mb on 8^th, whilst the lowest pressure reading in the month was 990 mB on 17^th.

The mean relative humidity in December was 90.5%. The highest and lowest daily (00/00 GMT) mean relative humidity values in the month were 97.8% and 80.1 % on 21^st and 24^th respectively. The absolute lowest relative humidity reading in December was 56% at 0335 GMT on 24^th.

Fog (visibility < 1000 metres) was observed at the 0900 GMT observation hour on 2 days (9^th and 21^st) in December. On 9^th the visibility at this hour fell below the 200 metre mark.

This report concludes with a few summary details for the year 2004 as a whole. The mean daily maximum temperature was 14.9°C, which is 0.9°C above the 30 Year (1973/2002) average. The mean night minimum temperature was 1.0°C above average at 7.7°C. Total rainfall was 630.2 millimetres, which is 108% of the 1971/2000 average. The annual total of sunshine was 1563.3 hours, which is 104% of the 1971/2000 average. It was the 5^th warmest year (with 1997 which had the same mean temperature) since 1972, the wettest year since 2002 only, whilst sunshine was 434.2 hours less than in 2003!

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

5^th January 2005

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