Royston (Iceni) Weather Station

Daily Weather Observations - January 2005

The year 2005 commenced with a mild, dry and sunny January in Royston, a continuation of similar conditions in December 2004.

For the 4^th consecutive year January was milder than average, although it was the mildest January since 2002 only. The mean daily maximum temperature was 8.6°C, which is 2.0°C above the 30 Year (1973/2002) average. Night minimum temperatures were also above average, the mean night minimum temperature being 1.7°C in excess of the 30 Year mean at 3.8°C.

The highest temperature recorded in January, 13.9°C on 7^th, was in fact the second highest for January since at least 1972. It was exceeded only by the maximum temperature of 14.2°C in January 1999, but was equalled in both January 1975 and 1983. The lowest day maximum temperature recorded in the month was 2.9°C on 24^th.

The coldest night of the month was 25^th/26^th when minimum and grass minimum temperatures of –2.6°C and –7.0°C respectively were recorded. In contrast, the highest night minimum temperature of the month was as high as 10.4°C (on 7^th ). This is actually 4.1°C higher than the 30 Year mean maximum temperature for this day!

January was relatively frost free as might be expected given the mean temperatures noted above, and only 3 air frosts were recorded. This is the lowest number of air frosts in January since 1990 (in which year January was completely air frost free). A total of 9 ground frosts occurred in the month.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 5.5°C, the highest such value in January since 1990. The highest and lowest earth temperature values were 7.0°C and 3.9°C on 8^th (and 11^th) and 27^th respectively.

For the second successive Winter month January suffered a deficit of rainfall, which does not bode well for water supplies next Summer as the aquifers rely on Autumn and Winter rainfall for recharging. The situation is not helped by Autumn 2004 having been 14% deficient in rainfall, and next month, February, being the driest month of the year on average.

Total rainfall in January was 31.5 millimetres, which is 62% of the 1971/2000 average for Royston. The number of "rain days" (0.2 millimetres or more) was 16, whilst on 11 of these days rainfall exceeded 1.0 millimetre. The wettest day of the month was 20^th with a somewhat modest 5.5 millimetres. It was the driest January since 2000. Rainfall duration in January was 51.1 hours.

Snowfall in January was limited to a few snow showers in the morning of 24^th giving a temporary light cover in places, followed by a hail shower at 1310 GMT (this being the only hail observed to fall in the month).

Despite the last few days of January being rather dull (only 5.7 hours sunshine from 27^th to 31^st) the month still managed to return a sunshine total of 87.0 hours, which is 57% above the 1971/2000 average! The sunniest day of the month was 23^rd with 6.9 hours bright sunshine. The number of completely sunless days was 4 (4^th, 10^th, 27^th and 28^th). It was the sunniest January since 2001, and the 8^th consecutive sunnier than average January.

The first half of January was rather windy at times with the highest wind gust of the month, 62 mph, occurring on 8^th. Other notable wind gusts were 51 mph on 1^st and 60 mph on 7^th. The highest daily (00/00 GMT) mean wind speed was 16.3 mph on 7^th, whilst the lowest daily mean wind speed was 0.0 mph (to nearest 1 decimal point) on 22^nd. The mean wind speed for the whole month was 6.4 mph.

Winds from directions between S and W dominated the month, and even during a northerly spell from 23^rd to 29^th inclusive the air arrived from a SW source, having travelled around an anticyclone before reaching the eastern side of the British Isles. The analysis of daily wind directions as observed at 0900 GMT was NORTH 5 days, NE 0, E 0, SE 0, S 5, SW 13, W 5, NW 1 and CALM 2.

The mean MSL air pressure was 1021.3 mb, which is 5 mB above the 1973/2002 average. The highest and lowest pressure values in the month were 1035 mB and 993 mB on 26^th and 18^th respectively.

The mean relative humidity in January was 87.1%. The highest daily (00/00 GMT) mean relative humidity in the month was 97.9% on 29^th, whilst the lowest such mean value was 73.7% on 2^nd. The absolute lowest relative humidity reading in January was 48% at 1345 GMT on 8^th.

No fog (visibility < 1000 metres) was observed at the 0900 GMT observation hour on any day of the month.

Richard Barker

Richard Barker,

Met. Observer, Royston (Iceni) Weather Station

7^th February 2005

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