Royston (Iceni) Weather Station

Daily Weather Observations - June 2005

The Summer commenced with a warm, dry and sunny June in Royston.

Despite being a warmer than average month, it was nonetheless the coolest June in Royston since 2002. The mean temperature of 16.8°C was 1.7°C above the 30 Year (1973/2002) average.

Two main temperature ‘events’ occurred in June. The first was a slight ground frost in the early morning of 7^th when the grass minimum temperature fell to its lowest value of the month, -0.1°C. This was the first ground frost recorded in June since 2nd June 1991 (-1.0°C). The only other occurrences of ground frost in June since 1972 are 1989 (2), 1986 (1), and 1977 (1).

Then, on 19^th June, the day maximum temperature rose to 31.7°C, this being the highest such value in June since 19^th June 2000, when a temperature of 32.0°C was recorded. This temperature occurred on the 3^rd day of an 8 day hot spell from 17^th to 24^th inclusive, and 30°C was exceeded again on 23^rd (maximum temperature 31.0°C). During this period the mean daily maximum temperature was no less than 27.9°C!

The mean daily maximum temperature in June was 22.0°C, which is 2.3°C above the 30 Year (1973/2002) average. The mean night minimum temperature of 11.5°C was also above average, but by the lesser margin of 1.1°C. The highest daily maximum temperature recorded in June was 31.7°C on 19^th, as noted above, whilst the lowest night minimum temperature recorded was 3.6°C on 7^th.

The mean earth temperature at 30 cms depth as measured at 0900 GMT daily was 17.5°C. The highest and lowest earth temperature values recorded in the month were 20.6°C and 15.4°C on 24^th and 13^th respectively.

For the 7^th successive month in Royston rainfall was below average. June was particularly dry until the last week of the month when 83% of the month’s rainfall was recorded. The rainfall total for June was 41.2 millimetres, which is 82% of the 30 Year (1971/2000) average.

The number of "rain days" (0.2 millimetres or more) in June was 9, with rainfall exceeding 1.0 millimetre on 6 of these days. The wettest day was 28^th with 11.9 millimetres rainfall, with similar falls of 11.3 millimetres on 24^th and 10.4 millimetres on 29^th. Rainfall duration in the month was 17.7 hours.

Thunder was heard in June on 4 days, 20^th, 24^th, 28^th and 29^th. A spectacular lightning display occurred in Royston at about 2130 GMT on 28^th with frequent very bright cloud to cloud flashes and cloud to ground strikes. Fortunately, none of these strikes appears to have occurred immediately overhead, and no damage is believed to have occurred in the town.

In view of the prolonged dry spell the water supply situation is a cause for concern. In the 7 months from December 2004 to June 2005 inclusive rainfall of 238.1 millimetres was recorded, this being only 74% of the average for this period.

Despite a rather dull start to June some very sunny days occurred later in the month, and the total June sunshine of 211.8 hours was 18% above the 1971/2000 average.

The sunniest day of the month was 27^th with 16.2 hours sunshine, but this value was almost equalled on 22^nd which recorded only 2 minutes less sunshine. The sunshine total on 8^th was only a further 1.5 minutes lower than on 22^nd. Only 1 day (25^th) in the month was completely sunless, although 1^st managed only 1 minute sunshine.

June was a relatively calm month with a mean wind speed of 2.4 mph and a maximum gust speed of 35 mph on 4^th. The highest daily (00/00 GMT) mean wind speed in June was 7.9 mph on 4^th, whilst the lowest daily mean wind speed was 0.1 mph on 11^th.

The analysis of wind directions as observed at 0900 GMT daily gives the following result: NORTH 4 days, NE 5, E 0, SE 1, S 7, SW 7, W 4, NW 2, and CALM 0.

The mean MSL air pressure in June was 1017.2 mB, which is equal to the 30 Year (1973/2002) average. Air pressure extremes in the month were 1037 mB and 1003 mB on 8^th and 3^rd respectively.

The mean relative humidity in June was 73.5%, The highest daily (00/00 GMT) mean relative humidity was 92.5% on 25^th, whilst the lowest such mean value was 51.7% on 23^rd. The absolute lowest relative humidity reading in the month was 23% at 1235 GMT on 23^rd.

Fog (visibility < 1000 metres) was not observed at the 0900 GMT observation hour on any day in June.

Richard Barker

Richard Barker,

Met. Observer, Royston (Iceni) Weather Station

4^th July 2005

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