Royston (Iceni) Weather Station

Daily Weather Observations - January 2006

Temperatures and sunshine in January were not far from average, but it was a very dry month.

For the 3^rd successive month temperatures were below average, but only marginally in each case. However, this is the first time such a sequence has occurred since 1996. It was also the coldest January since 2001.

The mean daily maximum temperature in January was 6.2°C, which is 0.4°C below the 30 Year (1976/2005) average for Royston. The mean night minimum temperature was precisely on the average at 2.1°C.

The mildest day was 18^th with a maximum temperature of 11.0°C. In only 6 years since 1973 has the absolute maximum temperature in January been lower than this. In contrast the lowest day maximum temperature in the month was 0.7°C on 24^th.

The lowest night minimum temperature in January was –4.3°C on both 24^th and 25^th. The absolute minimum temperature in January has been lower than this in 14 years since 1973. The lowest grass minimum temperature in the month was –7.8°C on 25^th. The mildest night of the month was 18^th/19^th with a minimum temperature of 8.2°C. In total 9 air frosts and 10 ground frosts were recorded in January. Air frost duration was 91.8 hours.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 4.7°C. The earth temperature ranged from a maximum of 7.0°C on 20^th to a minimum of 2.5°C on 29^th and 30^th.

After 2005 which experienced a 14% deficit of rainfall over the whole year, a very dry January continued the trend and added to the deficit. The month’s rainfall was only 16.8 millimetres, which is 33% of the 1971/2000 average.

The wettest day in January was 3^rd with rainfall of 3.8 millimetres. This is the lowest rainfall for a ‘wettest day’ in January since 1973 (in which year January had a ‘wettest day’ of 2.8 millimetres rainfall, on 22^nd).

The number of "rain days" (0.2 millimetres or more) in January was 13, with rainfall exceeding 1.0 millimetre on 6 of these days. It was the driest January in Royston since 1997.

January was a largely snow free month, with only minimal amounts of snow falling on 3 days (5^th, 7^th and 27^th), and not settling, resulting in no day having snow lying (ground more than 50% snow covered) at 0900 GMT.

The New Year started off on an extremely dull note with the first 10 days of January recording a total of only 3.1 hours sunshine. There was little improvement over the next week or so and this sunshine total had reached only 12.8 hours by 19^th. The situation then changed dramatically and a further 49.1 hours sunshine was recorded by the end of the month. Incredibly this raised the monthly total of 61.9 hours to 11% above the 1971/2000 average!

The sunniest day of the month was 28^th with 7.6 hours sunshine. The number of completely sunless days in the month was 10. It was the dullest January since 2004 only.

A feature of the wind regime was the remarkable stillness of the air on some days. In fact, no fewer than 7 days (2^nd, 5^th, 6^th, 7^th, 22^nd, 24^th, and 31^st) in the month recorded a 24 hour (00/00 GMT) mean wind speed of 0.0 mph (to nearest 1 decimal place). On 24^th the maximum gust speed was only 2 mph (and only 5 mph on 7^th)!

The mean wind speed over the whole month was a relatively low 1.8 mph. The highest daily (00/00 GMT) mean wind speed was 9.3 mph on 20^th, whilst the maximum wind gust speed recorded in the month was 46 mph on 11^th.

Wind directions in January as observed at 0900 GMT daily were fairly evenly distributed as the following analysis shows: NORTH 2 days, NE 5, E 2, SE 4, S 6, SW 2, W 3, NW 2 and CALM 5.

The mean MSL air pressure in January was 1023.2 mB (7 mB above average), pressure reaching a maximum value of 1039 mB on 22^nd and falling to a minimum of 991 mB on 1^st.

The mean relative humidity in the month was 92.3%, with a highest daily (00/00 GMT) mean relative humidity of 98.7% on 7^th and a lowest daily mean of 79.8% on 20^th. The absolute lowest relative humidity reading in January was 48% at 1325GMT on 20^th.

Fog (visibilty < 1000 metres) was not recorded at the 0900 GMT observation hour on any day in January.

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

4^th February 2006

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