It was a cold and wet but very sunny December in Royston.

The main feature of the month was undoubtedly the heavy snowfall which occurred on 17^th/18^th resulting in a level depth of snow of 16 cms at 0900 GMT on 18^th. Further smaller amounts of snow fell in the next few days but the snow cover gradually dwindled to 1 cm by 25^th, although snow patches survived in the countryside around Royston until the next main snowfall on 6^th January.

A heavy mid-December snowfall in Royston is very unusual, the last such event being as long ago as 1981. The depth of snow on 18^th as noted above was the greatest depth of snow recorded in December since at least 1972 and the number of days (8) with snow lying (ground more than half covered with snow @ 0900 GMT) was the highest since December 1995. The number of days (7) with snow falling in the month was the highest since December 1981.

Total rainfall (including rainfall equivalent of snow) in December was 77.7 millimetres, which is 145% of the 1971/2000 average. The wettest day of the month was 29^th with 14.5 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) in December was 20 with rainfall exceeding 1.0 millimetre on 18 of these days. Rainfall duration in December was 85.2 hours. It was the wettest December in Royston since 2002.

It was the second successive colder than average December, the mean temperature this year being 1.5°C below the 30 Year (1976/2005) average, and the coldest December since 2001.

The mean daily maximum temperature in December was 5.7°C, which is 1.4°C below average. The mean night minimum temperature was 1.6°C below average at 1.4°C. The highest daily maximum temperature recorded in December was 12.2°C on 5^th, whilst the lowest daily maximum temperature recorded was 0.2°C on 18^th.

At the other end of the scale the lowest night minimum temperature of the month was –5.1°C on 19^th. The highest night minimum temperature in December was 10.4°C on 6^th. The lowest grass minimum temperature of the month was –10.1°C on 19^th. The number of air frosts in the month was 11, and the number of ground frosts 16. The equivalent figures in December 2008 (which was a snow free month) were 12 and 18 respectively. Air frost duration in December was 138.8 hours.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 5.6°C. The highest and lowest earth temperatures in December were 7.8°C on 10^th and 3.6°C on 29^th respectively.

December sunshine appeared to be heading for a December record of over 100 hours until the last 3 days of the month when only 0.9 hours sunshine was recorded. In the event the sunshine total for the month was 92.9 hours, which is 195% of the 1971/2000 average, and it was the sunniest December since 2005 only.

The sunniest day of the month was 10^th with 6.8 hours sunshine. The number of completely sunless days in December was 6.

The mean wind speed in December was 6.4 mph and the maximum wind gust speed recorded was 40 mph on 17^th. The highest and lowest daily (00/00 GMT) mean wind speeds were 12.4 mph on 6^th and 1.2 mph on 14^th respectively. The distribution of wind directions (at 0900 GMT daily) was NORTH 3 days, NE 4, E 0, SE 1, S 6, SW 8, W 6, NW 2 and CALM 1.

The mean MSL air pressure in December was 1005.5 mB, which is 9 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values were 1033.6 mB on 11^th and 982.8 mB on 22^nd respectively.

The mean relative humidity in the month was 89.3%. The highest daily (00/00 GMT) mean relative humidity was 94.9% on 30^th and the lowest daily mean was 81.3% on 27^th. The absolute lowest relative humidity reading in December was 68% at 1415 GMT on 6^th.

Fog (visibility < 1000 metres @ 0900 GMT) was observed on 2 days (11^th and 14^th) in December.

YEAR 2009: Although the year commenced with a cold January and February and ended with a cold December the additional warmth in the intervening months resulted in the mean temperature for the year as a whole being 0.6°C above the 30 Year (1976/2005) average. It was only the equal 7^th (with 2000) warmest year of the decade. For the 4^th consecutive year rainfall was above average but it was nonetheless the driest year since 2005. It was the sunniest year since 2003.

The mean daily maximum temperature in 2009 was 14.9°C, which is 0.8°C above average. The mean night minimum temperature in 2009 was 0.4°C above average at 7.2°C. Rainfall in 2009 was 624.8 millimetres, which is 107% of average. Sunshine for the year was 1813.8 hours, which is 121% of average.

Met. Observer, Royston (Iceni) Weather Station

7^th January 2010