Royston (Iceni) Weather Station

Daily Weather Observations - June 2004

The Summer got off to a good start in Royston with a dry, warm and sunny June.

It was, in fact, the 3^rd warmest June since at least 1972, only June 1976 and June 2003 being warmer. This was principally due to the hot weather in the first half of the month; this was followed by a rather cool spell covering most of the 3^rd week, temperatures recovering to average or above during the last week.

The highest temperature achieved in the month was 30.7°C on 8^th. This is the earliest date in the year that 30°C has been exceeded in records going back to 1972 (although 30°C was reached on 7^th June 1996). The previous day, 7^th, was also hot with a maximum temperature of 27.5°C. In contrast, the lowest day maximum temperature in the month was 15.5°C on 1^st.

The mean day maximum temperature in June was 21.5°C, which is 1.8°C above the 30 Year (1973/2002) average. The mean night minimum temperature was 1.7°C above average at 12.1°C. The coldest night of the month was 19^th with a minimum temperature of 5.5°C, and a grass minimum temperature of 3.2°C. The warmest night in June was 7^th/8^th when the minimum temperature dropped to a value no lower than 16.6°C.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 18.1°C. The lowest earth temperature of the month of 16.5°C occurred on both 2^nd and 25^th, the lower air temperatures prior to the latter date as mentioned above being largely responsible for this surprise downturn near the end of the month. The highest earth temperature recorded in June was 20.0°C on 17^th.

The only significant rainfall recorded in June was on 22^nd when an unusually active (for the time of year) depression crossed the country bringing strong winds also to the Royston area. This combination of wind and rain resulted in some crop damage in the district (see http://www.roystonweather.net/index/0406.htm for photograph).

Total rainfall in June was 25.6 millimetres, which is 51% of the 30 Year (1971/2000) Royston average. It was the 5^th successive June with below average rainfall. The number of "rain days" (0.2 millimetres or more) was 9, whilst rainfall reached or exceeded 1.0 millimetre on 7 of these days. In addition, very small amounts of rainfall recorded as 0.1 millimetre or "trace" occurred on a further 12 days in the month. Thunder was heard on only one day (21^st) in June, and hail was observed to fall on one day (20^th) also. Rainfall duration over the whole month was 30.4 hours.

Rainfall at the mid-point of 2004 stands at 299.4 millimetres, which is 111% of the January/June normal, so despite the dry June annual rainfall is still a little in excess of the average.

Sunshine remained below average for the first 6 days of June but daily values of sunshine of 15.2 hours on 7^th (the sunniest day of the month) and 11.4 hours on 8^th recovered this deficit, and by the end of the month a total sunshine value of 200.8 hours had been achieved, which is 112% of the 30 Year (1971/2000) average. Only one day (1^st) in June was completely sunless.

June was a typical ‘westerly’ month with the wind direction as observed daily at 0900 GMT containing a westerly component on no less than 25 days. The full daily wind direction analysis at 0900 GMT was NORTH 0 days, NE 0, E 0, SE 1, S 4, SW 5, W 13, NW 7, and CALM 0.

The second half of June was rather windy, particularly 23^rd and 24^th when mean wind speeds over the 00/00 GMT 24 hour period were 11.3 mph and 11.4 mph respectively. This latter value was the highest daily mean wind speed in the whole month. The lowest daily mean wind speed was 0.1 mph on 1^st. The mean wind speed over the month was 3.7 mph. The highest wind gust speed recorded in June was 46 mph on 23^rd.

The mean MSL air pressure in June was 1017.0 mB, which is precisely on the average for the 30 Year (1973/2002) period. The highest air pressure value recorded in June was 1034 mB on 13^th, whilst the lowest such value was 989 mB on 23^rd.

The mean relative humidity in the month was 72.5%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 93.7% and 60.2% on 1^st and 25^th respectively. The absolute lowest relative humidity reading in June was 30% at 1500 GMT on 14^th.

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

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

5^th July 2004

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