Royston (Iceni) Weather Station

Daily Weather Observations - June 2002

It was a dry and little warmer than average June in Royston, and with sunshine about normal.

For the 3^rd successive year the mean temperature in June was above average, but only by a modest margin as in each of the previous two years. There was an absence of any prolonged hot spells, however, and the temperature exceeded 25°C on only one occasion, 17^th.

At the other end of the scale the lowest temperature of the month, 8.1°C on 28^th and 29th, did create a record in that it was the highest absolute minimum temperature in June since records commenced at this station in 1972. Similarly the lowest grass minimum temperature, 5.5°C on 29^th, in the month was also the highest absolute grass minimum temperature recorded in June since at least 1972. Not unexpectedly the mean daily minimum temperature of 11.2°C for the month was above average (+1.0°C). The highest daily minimum temperature in June was 15.5°C on both 17^th and 18^th.

The mean daily maximum temperature in June was 20.0°C, which is 0.3°C above average. The highest daily maximum temperature was 27.7°C on 17th, whilst the lowest daily maximum temperature was 14.5°C on 5^th.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 17.2°C. The highest and lowest earth temperature values in June were 19.1°C and 15.2°C on 18^th and 10^th respectively.

The most distinctive feature of a somewhat unexceptional June was the rainfall which totalled only 29.4 millimetres, which is 59% of the 1971/2000 average for Royston. Even so measurable rainfall (0.2 millimetres or more) was recorded on as many as 13 days in the month, and on 7 of these days the rainfall was 1.0 millimetre or higher.

The wettest day of the month was 5^th with 10.5 millimetres rainfall. Thunder was heard on just 1 day in June, in the early hours of 18^th when a thunderstorm lasted from approximately 0300 to 0400 GMT giving a number of claps of thunder. For the second successive month a fall of very fine orange/brown dust was washed out in light rainfall, on this occasion in the afternoon of 14^th. Synoptic charts for the period suggest these deposits were most probably wind blown from the deserts of North Africa.

It was the 3^rd consecutive drier than average June in Royston and the 7^th drier than normal June in the last 10 years. However, these dry Junes are to some extent compensated for by the years 1997, 1998 and 1999 when June was notably wet.

Sunshine was at a premium in the first half of June and by 15^th had reached only 62 hours despite over 26 hours being recorded on the first two days of the month. After mid-month matters improved considerably and in the second half of the month almost a further 126 hours sunshine was recorded. This brought the June sunshine virtually up to average.

Total sunshine in June was 188.0 hours, which is 97% of the 1961/1990 average. The sunniest day of the month was 17^th with 16.1 hours sunshine. Other high daily totals were 15.9 hours on 1^st and 15.3 hours on 26^th. A 3 day sunless spell occurred from 5^th to 7^th, otherwise every other day of the month had at least some sunshine. Mean cloud cover as noted at 0900 GMT daily was 64%.

Winds with a westerly component dominated the month, occurring on no less than 22 days. The analysis of daily wind directions as observed at 0900 GMT is as follows:

NORTH 2 days, NE 0 , E 0, SE 3, S 3, SW 9, W 12, NW 1 and CALM 0.

The mean wind speed for the whole of June based on 5 minute observations throughout the month was 4.3 mph. The highest daily (00/00 GMT) mean wind speed in June was 8.3 mph on 10^th , whilst the lowest daily mean wind speed was 1.4 mph on 6^th.

The highest wind gust speed in June was 37 mph, recorded at 1135 GMT on 10^th.

The mean MSL air pressure, again based on 5 minute observations, in June was 1014.7 mB, which is about 3 mB below average. The highest and lowest air pressure values recorded in June were 1029 mB on 24^th/25^th and 996 mB on 5^th respectively.

The mean relative humidity over the month was 74.0%. The highest daily (00/00 GMT) mean relative humidity was 98.9% on 5^th (the wettest day of the month, as mentioned above), and the lowest daily mean relative humidity was 59.7% on 24^th. The absolute lowest relative humidity reading in June was 32% at 1600 hours on 26^th.

Finally, to review in brief the first 6 months of the year 2002, rainfall to the end of June stands at 243.5 millimetres (90% of average), sunshine 854.4 hours (112% of average), and the mean temperature 10.2°C (1.9°C above average). Each of the first 6 months of the year has experienced an above average mean temperature.

Met. Observer, Royston (Iceni) Weather Station

4^th July 2002

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