Royston (Iceni) Weather Station

Daily Weather Observations - March 2007

It was a milder than average and a very sunny March in Royston, whilst rainfall was a little below normal.

The first half of March was exceptionally mild but lower temperatures from 18^th onwards resulted in the mean temperature being reduced to only 1.1°C above average.

The mean daily maximum temperature in March was 12.2°C, which is 1.8°C above the 30 Year (1976/2005) average. The mean night minimum temperature was also above average, but by only 0.4°C. It was the mildest March in Royston since 2003.

The highest day maximum temperature recorded in the month was 17.5°C on 12^th, whilst the lowest night minimum temperature was –1.5°C on 21^st. This was the highest absolute minimum temperature in March since 1999. The ‘opposites’ of these extremes shows the lowest day maximum temperature as 5.9°C on 22^nd, and the highest night minimum temperature as 8.8°C on 6^th. The lowest grass minimum temperature in March was –5.6°C on 22^nd. Totals of 2 air frosts and 13 ground frosts were recorded in March. Air frost duration in the month was 9.7 hours.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 7.9°C. The highest and lowest earth temperatures recorded were 9.2°C and 7.0°C on 18^th and 22^nd/23^rd/24^th respectively.

Rainfall between 1^st and 5^th March accounted for three-fifths of the total rainfall in the month. The wettest day of the month, 2^nd, occurred within this period with rainfall of 10.7 millimetres. Thereafter the highest daily rainfall was only 2.6 millimetres, on both 19^th and 29^th.

Total rainfall in March was 36.2 millimetres, which is 85% of the 30 Year (1971/2000) average. The number of "rain days" (0.2 millimetres or more) was 15, with rainfall exceeding 1.0 millimetre on 9 of these days. Rainfall duration in March was 42.4 hours. Despite rainfall being 15% below average it was nonetheless the wettest March since 2001.

Small amounts of snow fell on 4 days in the month, 18^th, 19^th 20^th and 22^nd, but did not result in lying snow (ground more than 50% covered at 0900 GMT) on any day. Hail accompanied the snow on 3 days (18^th, 19^th and 20^th). These were the only days with hail in March.

Deposits of dust were washed out in a very small amount of rainfall (0.1 mm) overnight on 25th/26th. The colour was mid-grey with no trace of the reddish brown colour normally associated with previous falls of Sahara sand. A possible source of this dust is agricultural fires in the Ukraine and Russia but no there is no confirmation of this. A thick haze drifted in from the continent over the next 2/3 days.

Perhaps the most notable feature of March was the exceptional amount of sunshine. The average sunshine for the whole month had been exceeded by 16^th, and whilst the remainder of the month was not as sunny the final sunshine total of 177.1 hours was still 66% above the 1971/2000 average. It was the sunniest March since 2003 only, however, and in that year March sunshine was 20 hours higher!

The sunniest day of the month was 13^th with 10.2 hours sunshine. The number of days in the month which were completely sunless was 3.

Wind directions in March were almost exclusively from SW through N to NE, as the following analysis of wind directions at 0900 GMT daily shows: NORTH 4 days, NE 4, E 0, SE1, S 2, SW 7, W 8, NW 5, and CALM 0.

The mean wind speed in March was 3.5 mph and the maximum wind gust speed recorded was 51 mph on 5^th. The highest and lowest daily (00/00 GMT) mean wind speeds were 11.7 mph and 0.0 mph (to nearest 1 decimal place) on 18^th and 27^th/28^th respectively.

The mean MSL air pressure in March was 1013.8 mB (1 mB below the 1976/2005 average). The highest pressure value recorded was 1035 mB on 14^th and the lowest 985 mB on 1^st.

The mean relative humidity in March was 83.2%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 98.9% and 71.4% on 24^th and 13^th respectively. The absolute lowest relatively humidity reading in March was 28% at 1535 GMT on 11^th.

Fog (visibility < 1000 metres @ 0900 GMT) was experienced on 3 days (26^th, 27^th and 28^th) in March, with visibility falling below the 200 metre threshold on 27^th and 28^th.

Met. Observer, Royston (Iceni) Weather Station

5^th April 2007

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