Royston (Iceni) Weather Station

Daily Weather Observations - May 2003

The month of May was warm and dry overall, with about average sunshine.

The mean daily maximum temperature for the month as a whole was 17.9°C, which is 1.1°C above the 30 Year (1973/2002) average. Although the temperature reached 22.6°C as early as 4^th it did not exceed 20°C again until 27^th, and then increased daily until reaching the highest temperature of the month, 26.0°C, which occurred on both 30^th and 31^st. On 30^th this temperature was the highest which has occurred on this date since records began in 1972.

Night minimum temperatures were above average, too, by a similar value. The mean night minimum temperature was 8.4°C, which is 1.2°C above average. It was the warmest May in Royston since 2001 only, however.

The lowest night minimum temperature of the month was 3.4°C on 15^th, whilst the lowest grass minimum temperature was 0.3°C, also on 15^th. In contrast, the highest night minimum temperature was 14.9°C on 31^st. No particularly cool days were experienced in May, the lowest day maximum temperature being 13.0°C on 16^th.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 13.8°C, ranging from a highest value of 17.6°C on 31st to a lowest reading of 12.3°C on both 1^st and 3^rd.

The dry weather of the previous 3 months, during which only one-half of the average rainfall was recorded, continued into May and the total rainfall for the month of 36.7 millimetres was only 78% of the 30 Year (1971/2000) average for Royston. Although the number of "rain days" (0.2 millimetres or more) in the month was as high as 16, modest amounts of rainfall only were recorded on these days. The wettest day of the month was 1^st with 6.4 millimetres rainfall, the same amount as on the previous day, 30^th April, which was the wettest day of that month also. It was the driest May in Royston since 2001 only.

Hail was observed to fall on 12^th only, and thunder was heard on 14^th only. Rainfall duration in May was 43.0 hours.

Total rainfall for the first 5 months of 2003 was 194.5 millimetres, which is 88% of normal.

The first half of May was fairly sunny but then a rather dull period around the 3^rd week of the month saw the cumulative sunshine fall behind average. Increasingly sunny days in the last week of the month retrieved the situation, however, and the sunshine total just passed the average for the month on the very last day!

The total sunshine recorded in May was 202.6 hours, which is 105% of the 30 Year (1961/1990) average. Of this total 80.5 hours is attributable to the last 7 days of the month. It was the sunniest May in Royston since 2001 only. The sunniest day of the month was 30^th with 15.1 hours sunshine. Only 2 days (16^th and 22^nd) in the month were completely sunless.

Winds from a south-westerly direction were dominant in May as the following analysis of daily wind directions at 0900 GMT shows: NORTH 1 day, NE 2, E 0, SE 2, S 5, SW 12, W 7, NW 2, and CALM 0.

The mean wind speed in May was 4.7 mph. The highest daily (00/00 GMT) mean wind speed was 10.1 mph on 20^th, whilst the lowest daily mean wind speed was 0.6 mph on 30^th. The maximum gust speed recorded in the month was 44 mph on 12^th.

The mean MSL air pressure in May was 1015.5 mB, which is close to the May average. The highest air pressure reading recorded in May was 1028 mB on 7^th and the lowest 997 mB on 2^nd.

The absolute lowest relative humidity reading in May was 31% at 1305 GMT on 4^th. The mean relative humidity over the whole month was 74.5%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 91.1% on 17^th and 61.4% on 5^th and 6^th respectively.

The month was fog free in as much as there were no days when the visibility fell below 1000 metres at the 0900 GMT observation hour.

A few summary details of the SPRING (March, April and May) season conclude this report. The mean daily maximum temperature in Spring was 15.5°C, which is 2.2°C above the 30 Year (1973/2002) average. The mean night minimum temperature was 5.5°C, which is 0.6°C above average. Rainfall was 60% of the 30 Year (1971/2000) average at 79.9 millimetres, whilst the sunshine total of 593.5 hours was 134% of normal. It was the warmest Spring since 1999 and the driest since 1997.

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

7^th June 2003

Royston Crow (Corvus Cornix)

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