Temperatures, rainfall and sunshine were all below normal in January.

The first and last weeks of the month were rather mild, but the intervening two weeks were very cold (and snowy) resulting in the mean temperature for the month as a whole showing a negative anomaly. For the period from 10^th to 25^th inclusive the mean temperature was as low as –0.6°C. However, it was the coldest January in Royston since 2010 only, and the 4^th colder than average January in the last 5 years.

The mean daily maximum temperature in the month was 5.4°C, which is 1.5°C below average. The mean night minimum temperature was 0.8°C below average at 1.7°C. The highest temperature recorded in the month was 13.8°C on 29^th, whilst the lowest temperature recorded was –7.5°C on 17^th. This was the lowest temperature recorded in January since 1997. The lowest grass minimum temperature of the month was –11.0°C on 17^th.

In total 14 air frosts and 16 ground frosts were recorded in January. Air frost duration was a substantial 226.0 hours.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 4.9°C, which was actually 0.4°C above average. The main reason for this was the prevailing snow cover for almost 2 weeks which partly insulated the ground against penetration of frost. The highest and lowest earth temperature values were 7.6°C and 2.9°C on 9^th and 26^th respectively.

Although less than half of the month’s precipitation fell as snow it was sufficient to give a complete snow cover for 13 days from 14^th to 26^th inclusive. The maximum depth of level snow as measured at 0900 GMT daily was 13 cm on 21^st. The number of days with snow falling was 11, but only in very small amounts on some of these days.

Although the Great Ouse catchment suffered more floods this month, this appears to be mainly as a result of sudden snow melt around 25^th rather than from high rainfall, as in Royston at least rainfall was below average. The month’s rainfall total of 45.4 millimetres (which includes the rainfall equivalent of snow) was 91% of normal. January was a little wetter than January 2012 but significantly drier than January 2011.

The wettest day of the month was 26^th with 8.0 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) was 13, with rainfall exceeding 1.0 millimetre on 12 of these days.

A significant feature of the January sunshine regime was the remarkable 8 day period from 18^th to 25^th inclusive when not a single ray of sunshine was recorded! This reduced the January sunshine total to 52.5 hours, which is only 81% of average.

This made January the second dullest January in the last 16 years, the dullest being in 2011 when only 42.7 hours sunshine was recorded. The sunniest day of the month was 31^st with 6.5 hours sunshine. The number of sunless days in January was 15.

The mean wind speed in January was 6.6 mph and the maximum wind gust speed recorded was 45 mph on 28^th. The windiest day (00/00 GMT) of the month was 31^st with a mean wind speed of 15.4 mph, whilst the calmest day (00/00 GMT) of the month was 13^th (and 16^th) with a mean wind speed of 1.1 mph.

The analysis of wind directions as observed at 0900 GMT daily shows NORTH 1 day, NE 5, E 2, SE 2, S 5, SW 7, W 8, NW 1, and CALM 0.

The mean MSL air pressure in the month was 1012.4 mB, which is 3.4 mB below average. The highest and lowest pressure values registered in January were 1036.7 mB and 989.2 mB on 4^th and 27^th respectively.

The mean relative humidity in January was 91.0%. The highest daily (00/00 GMT) mean relative humidity was 98.1% on 11th and the lowest such mean was 77.8% on 31^st. The absolute lowest relative humidity reading in the month was 58% at 1430 GMT on 31^st.

The number of days with fog (visibility < 1000 metres @ 0900 GMT) was 3 (6^th, 10^th and 16^th). On two of these days (10^th and 16^th) the fog was thick and visibility fell below the 200 metres threshold.

Met. Observer, Royston (Iceni) Weather Station

4^th February 2013