Overall it was a colder and drier than average January in Royston with a snowy second week, whilst sunshine was a little in excess of normal.

After the cold and snowy spell in mid-December similar conditions soon returned in the New Year although snow depths were not as great as earlier. The ground was more than half covered with snow (at 0900 GMT) over the period 6^th to 14^th inclusive, and on 30^th with a light covering only.

The deepest snow cover was 4 cm on 11^th whereas in December 2009 a snow depth of 16 cm was recorded. With snow actually falling on 13 days and lying on 10 days it was the snowiest January in Royston since 1985. Total rainfall (and rainfall equivalent of snow) in January was 38.7 millimetres, which is 76% of the 1971/2000 average. The number of "rain days" (0.2 millimetres or more) was 17, with rainfall exceeding 1.0 millimetre on 9 of these days. The wettest day of the month was 14^th with 9.2 millimetres rainfall. Rainfall duration in the month was 45.7 hours. It was the driest January since 2006.

Temperatures in January were well below average and it was the coldest January since 1987. The absolute maximum temperature in January of 8.4°C (on 18^th) was the lowest such value in January since 1979. The lowest night minimum temperature of the month of –7.2°C (on 9^th) was the lowest temperature recorded in January since 1997.

The mean daily maximum temperature in January was 3.5°C, which is 3.1°C below the 30 Year (1976/2005) average. The mean night minimum temperature was 2.4°C below average at –0.3°C. Totals of 17 air frosts and 22 ground frosts were recorded in January, these being the highest such totals in January since 1987. The lowest grass minimum temperature in the month was –13.3°C on 9^th. Air frost duration in January was 252.4 hours.

The mean earth (30 cms depth) temperature in the month as observed daily at 0900 GMT was 3.3°C. The highest earth temperature recorded was 4.9°C on 24^th, whilst the lowest earth temperature in the month was 2.0°C on 9^th to 14^th inclusive. A snow cover is a very effective insulator and prevented any further fall in the earth temperature in this period.

January commenced on a very sunny note, accumulating 28.5 hours sunshine in the first 5 days. Duller conditions soon set in, however, and in the 7 day period from 10^th to 16^th inclusive only 6 minutes sunshine was logged! Despite 13 days in January being completely sunless total sunshine for the month of 64.8 hours still managed to exceed the 30 Year (1971/2000) average by 17%. However, when taking into account the trend to sunnier conditions in January in recent years this sunshine total was 14% short of the average of the previous 12 years. It was the dullest January since 2006.

The sunniest day in January was 30^th with 7.2 hours sunshine.

January was a relatively calm Winter month with a mean wind speed of 4.9 mph and a maximum wind gust speed of 31 mph on 16^th. The highest and lowest daily (00/00 GMT) mean wind speeds in the month were 9.8 mph on 16^th and 0.8 mph on 14^th respectively.

The analysis of wind directions as observed at 0900 GMT daily shows NORTH 1 day, NE 7, E 4, SE 4, S 1, SW 4 W 6, NW 4 and CALM 0.

The mean MSL air pressure in January was 1014.7 mB, which is 1 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values recorded in January were 1042.2 mB on 26^th and 989.6 mB on 29^th respectively. These figures clearly illustrate the steep decline in air pressure in the intervening 3 day period.

The mean relative humidity in January was 88.2%. The highest daily (00/00 GMT) mean relative humidity was 94.9% on 15^th, whereas the lowest mean relative humidity was 79.4% on 30^th. The absolute lowest relative humidity reading in January was 64% at 1630 GMT on 29^th.

Fog (visibility < 1000 metres @ 0900 GMT) was not observed on any day in January.

Met. Observer, Royston (Iceni) Weather Station

5th February 2010