The year ended with a very wet December, whilst temperatures and sunshine in December were not far from normal.

A near double the average rainfall total in December helped propel the year 2012 in to the top 3 wettest years since at least 1853 when rainfall records began in Royston (see annual summary at the end of this report).

Total rainfall in the month was 97.7 millimetres, which is 195% of normal, making it the wettest December in Royston since 1989. The wettest day was 19^th with 18.5 millimetres rainfall, this being the wettest December day since 19^th December 1995 when 25.0 millimetres rainfall was recorded. The number of "rain days" in December was 20, with rainfall exceeding 1.0 millimetre on 16 of these days.

On the morning of 5^th Royston awoke to an unexpected snow cover which gave a level depth of 6 centimetres. The frosty night which followed ensured the snow remained for another day, the depth still being 6 centimetres at 0900 GMT on 6^th. After 6^th all traces of the snow rapidly disappeared.

A frosty week then followed and the lowest temperature of the month, -7.0°C, occurred on 12^th. This was accompanied by the lowest grass minimum temperature, -9.6°C, of the month. The 7 air frosts in December all occurred in the first half of the month, whilst only 2 out of a total of 14 ground frosts were recorded after mid-month.

Much milder conditions prevailed in the second half of December and a highest night minimum temperature of 10.7°C was recorded on 23^rd. The highest day maximum temperature of the month was 13.1°C on 22^nd, whilst the lowest such day maximum temperature in December was –0.2°C on 11^th, giving the only ‘ice day’ of the month (a rare event in any Winter month).

The mean daily maximum temperature in December was 7.8°C, which is 0.8°C above average. The mean night minimum temperature of 2.8°C was 0.1°C below average. The December overall mean temperature of 5.3°C was 1.1°C lower than in 2011, but 5.1°C higher than in the exceptionally severe December 2010. Air frost duration in December was 102.2 hours.

The mean earth (30 cms depth) temperature as recorded at 0900 GMT daily was 5.0°C, which is 0.5°C below average. The highest and lowest earth temperatures recorded in December were 7.0°C and 3.0°C on 29^th and 14^th respectively.

Twice as much sunshine was recorded in the first half of December than in the second half of the month, the final total of 64.9 hours being 115% of average. The sunniest day of the month was 2^nd with 6.7 hours sunshine. A total of 9 days in December failed to record any sunshine at all. Although the December sunshine total was above the 30 Year (1981/2010) average it was, in fact, 5.8 hours below the average of the last 15 years.

The mean wind speed in December was 8.5 mph and the highest wind gust speed recorded was 43 mph on 14^th. The highest and lowest daily (00/00 GMT) mean wind speeds were 14.7 mph and 1.4 mph on 30^th and 13^th respectively. These figures indicate that unusually the highest gust speed of the month was recorded the day after the calmest day of the month!

The analysis of daily wind directions as observed at 0900 GMT was NORTH 1 day, NE 0, E 0, SE 5, S 7, SW 8, W 7, NW 3, and CALM 0.

The mean MSL air pressure in December was 1006.6 mB, which is 8.2 mB below average. The highest pressure reading was 1030.7 mB on 11^th whilst the lowest pressure value was 973.1 mB just 3 days later on 14^th.

The mean relative humidity in the month was 91.0%. The highest daily (00/00 GMT) mean relative humidity was 98.4% on 20^th; the lowest daily (00/00 GMT) mean was 81.7% on 30^th. The absolute lowest relative humidity reading in December was 71% at 1550 GMT on 9^th.

Fog (visibility < 1000 metres @ 0900 GMT) was observed on just 1 day (8^th) in the month. On this occasion the fog was thick and visibility fell below the 200 metres threshold.

YEAR 2012: It was the wettest year since 1958. Only one other year (1903) in the Royston rainfall record which goes back to 1853 was wetter than both 1958 and 2012. The 2012 mean temperature of 10.7°C was virtually on the 30 Year (1981/2010) average. The mean daily maximum temperature in 2012 was 14.5°C , which is 0.2°C above average, whilst the mean night minimum temperature of 6.9°C was 0.1°C below average. Total rainfall was 836.6 millimetres, which is 139% of average. Sunshine for the year totalled 1652.3 hours, which is 106% of normal.

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

5^th January 2013