Royston (Iceni) Weather Station

Daily Weather Observations - August 2009

Temperatures, rainfall and sunshine were all above average in August.

In a similar vein to July this year, August was an equable month with fairly constant temperatures and no unseasonal extremes. Overall, it was the warmest August in Royston since 2004.

The mean daily maximum temperature in August was 23.0°C, which is 0.6°C above the 30 Year (1976/2005) average. The mean night minimum temperature showed a more positive anomaly, at 13.8°C being 1.1°C above average.

The highest daily maximum temperature recorded in August was 28.5°C on 19^th, but just two days later on 21^st the lowest daily maximum temperature (19.3°C) of the month occurred. The lowest night minimum temperature in August was 10.0°C on 29^th. In contrast the highest night minimum temperature in the month was 17.8°C on 6^th. The lowest grass minimum temperature in August was 7.5°C on 29^th.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 18.5°C. The highest and lowest earth temperatures in August were 19.4°C on 7^th, 12^th and 20^th, and 17.3°C on 30^th respectively.

Although most of August was essentially dry with only 13.8 millimetres rainfall occurring between 7^th and 31^st, in the statistics it will go down as wet month due to a very heavy rainfall on 6^th of 52.4 millimetres. This made 6^th the wettest August day in Royston since at least 1972. Unusually for such a heavy rainfall in the Summer months on this occasion the event was not accompanied by any thunder

Total rainfall in August was 77.1 millimetres, which is 155% of the 1971/2000 average. The number of "rain days" (0.2 millimetres or more) in August was 10, with rainfall exceeding 1.0 millimetre on 7 of these days. The wettest day of the month was 6^th as indicated above.

Rainfall duration in August was a relatively low 17.7 hours given the monthly total but this is explained by the intense rainfall event on 6^th. Thunder was heard on only 1 day (25^th) in the month. Significantly this was the 6^th consecutive August with above average rainfall.

The second half of August was much sunnier after a rather dull first two weeks. This is illustrated by sunshine for 1^st/15^th being 70.8 hours, compared with 135.8 hours for the period 16^th/31^st. Total sunshine for the month was 206.6 hours, which is 111% of the 1971/2000 average.

The sunniest day in August was 23^rd with 12.9 hours sunshine. No day in August was completely sunless, although 4^th came close with only 5 minutes sunshine. It was the sunniest August in Royston since 2003.

The mean wind speed in August was 6.4 mph, and the maximum wind gust speed recorded was 40 mph on 26^th. The highest daily (00/00 GMT) mean wind speed recorded was 11.7 mph on 28^th, whilst the lowest daily mean wind speed was 1.9 mph on 8^th.

The analysis of wind directions as observed at 0900 GMT daily shows a strong bias to winds between S and W as per the following table: NORTH 3 days, NE 0, E 0, SE 0, S 9, SW 13, W 4, NW 2 and CALM 0.

The mean MSL air pressure in August was 1013.9 mB, which is 3 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values recorded in the month were 1022.2 mB and 1001.8 mB on 22^nd and 31^st respectively.

The mean relative humidity in the month was 73.1%. The highest daily (00/00 GMT) mean relative humidity was 89.3% on 7^th, whereas the lowest such daily mean value was 56.2% on 23^rd. The absolute lowest relative humidity reading in August was 34% at 1630 GMT on 19^th and 1515 GMT on 23^rd.

Fog (visibility < 1000 metres @ 0900 GMT) was not observed on any day in August.

Summer (June/August) 2009:

It was the warmest, wettest and sunniest Summer since 2006. Each of the Summer months experienced over 200 hours sunshine. The mean daily maximum temperature in Summer was 22.2°C, which is 0.7°C above the 30 Year (1976/2005) average. The mean night minimum temperature in Summer was 0.4°C above average at 12.4°C. Total rainfall in Summer was 203.1 millimetres, which is 142% of average, whilst sunshine of 627.4 hours was 112% of normal.

Met. Observer, Royston (Iceni) Weather Station

10^th September 2009

Return to Daily Weather Observations - August 2009  header page