December 2010 was a month of negative extremes, very cold, very dry and very dull.

The cold and snowy spell at the end of November continued into December and after a brief respite in the second week then intensified with the result that it was the coldest December since at least 1972 (when records began at Royston (Iceni) Weather Station), the mean temperature being 0.2°C lower than in the very cold December of 1981. In fact, longer term climatological records for central England suggest that it was almost certainly the coldest December since 1890. Additionally, December was the 3^rd coldest month of any since 1972, after January 1979 and February 1986.

The highest temperature recorded in December was 8.0°C on 11^th and this was the lowest absolute maximum temperature for December since 1976. At the other end of the scale the lowest temperature recorded in the month was –11.0°C on 20^th. This was the lowest temperature recorded in December since at least 1972, and the lowest temperature in any month since 12^th January 1987.

Seven days in December experienced maximum temperatures below 0°C, the lowest of these being –2.7°C on 19^th. In contrast, the highest night minimum temperature in December was 4.8°C on 11^th. The lowest grass minimum temperature in the month was –14.5°C on 19^th. Totals of 22 air frosts and 24 ground frosts occurred in December. This was the highest number of air frosts in December since at least 1972.

The mean earth temperature at 30 cms depth as recorded daily at 0900 GMT was 3.1°C, peaking at 4.4°C on 31^st and reaching its lowest value of 2.5°C on 27^th.

As well as being extremely cold, December was also a snowy month with snow falling on 10 days and covering the ground on 16 days. The maximum level depth of snow recorded at the 0900 GMT observation hour was 14 cms on 19^th. Total rainfall (including the rainfall equivalent of snow) in December was 24.5 millimetres, which is only 46% of the 1971/2000 average. However, it was the driest December in Royston since 2008 only.

The number of "rain days" (0.2 millimetres or more) was 11, with rainfall exceeding 1.0 millimetre on 7 of these days. The wettest day of the month was 18^th with 8.4 millimetres rainfall (this all fell as snow).

December was a rather dull month and no sunshine at all was recorded on as many as 11 days. Total sunshine in the month was 37.5 hours, making it the dullest December since 2002. The sunniest day of the month was 9^th with 6.1 hours sunshine.

December was a fairly calm month and the highest gust speed recorded of 29 mph on 4^th was the lowest such value for any month in 2010. The mean wind speed over the whole month was 4.5 mph. The highest daily (00/00 GMT) mean wind speed was 9.5 mph on 10^th, whilst the lowest daily mean wind speed was 0.6 mph on 30^th.

Winds from between N and W were the favoured directions in December, as the following analysis of daily wind directions at 0900 GMT indicates: NORTH 7 days, NE 2, E 1, SE 2, S 3, SW 2, W 7, NW 5, and CALM 2.

The mean MSL air pressure in December was 1014.0 mB, which is only 0.3 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values in December were 1037.1 mB on 14^th and 15^th, and 990.0 mB on 18^th, respectively.

The mean relative humidity in the month was 89.1%. The highest daily (00/00 GMT) mean relative humidity was 96.0% on both 30^th and 31^st, whilst the lowest daily mean was 75.0% on 1^st. The absolute lowest relative humidity reading in December was 61% at 1520 GMT on 1^st, and at 1305 GMT on 26^th.

Fog (visibility < 1000 metres @ 0900 GMT) was observed on 7 days in December. On 2 of these days (15^th and 20^th) visibility fell below the 200 metres threshold.

Despite the year being billed in the media as being the second warmest on record globally the Royston temperatures have not followed this trend! The mean temperature of 9.9°C in 2010 has returned to a value more commonly experienced in the 1970s and 1980s, and it was the coldest year since 1996 (when the mean temperature was only 0.1°C lower than in 2010). Earlier than 1996 the next year coldest year was 1987 (9.7°C). The mean daily maximum temperature in 2010 was 13.7°C, which is 0.4°C below the 30 Year (1976/2005) average. The mean night minimum temperature was 0.8°C below average at 6.0°C. Total rainfall in 2010 was 574.1 millimetres, which is 99% of the 1971/2000 average, making it the driest year since 2005. Sunshine in 2010 was 94% of the 1971/2000 average at 1414.0 hours and this was the lowest annual sunshine total since at least 1997.

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

5^th January 2011