Royston (Iceni) Weather Station

Daily Weather Observations - August 2002

It was a rather dull August in Royston, with average rainfall, but temperatures were a little above average.

The "average" rainfall statistic conceals two distinctly different periods in the month. In the first 10 days of August rainfall of 47.5 millimetres was recorded, including 17.4 millimetres in a spectacular thunderstorm during the evening of 7^th. This storm caused the (electronic) automatic rain gauge at Royston (Iceni) Weather Station to fail just when it was needed most during the intense rainfall! However, the standard rain gauge (which is not an electronic instrument) was not affected, so fortunately data relating to the rainfall amount was not lost.

In the remaining 3 weeks of the month a mainly dry spell occurred and only 2.1 millimetres rainfall was recorded. This brought the rainfall total up to 49.6 millimetres, which is exactly 100% of the 1971/2000 average for Royston. The number of "rain days" (0.2 millimetres or more) in the month was 11, whilst on 7 of these days rainfall exceeded 1.0 millimetre.

The wettest day of the month was 7^th, the rainfall total being 17.4 millimetres as indicated above. Thunder was heard on only 2 days in August, on 4^th as well as 7^th already mentioned. Rainfall duration in August was 35.6 hours.

Rainfall for the year to the end of August stood at 397.8 millimetres, which is 110% of average.

Due to the cloudier conditions night minimum temperatures held up well and the mean daily minimum temperature of 13.9°C was 1.5°C above the 25 Year (1973/1997) average. The mean daily maximum temperature for August of 22.6°C was similarly above average, but only by 0.4°C.

The highest temperature recorded in August was 30.0°C on 17^th. The temperature has now reached or exceeded 30°C in August in 7 out of the last 8 years (2000 being the exception). The lowest temperature of the month was 11.0°C on both 21^st and 26^th, whilst the lowest grass minimum temperature of the month was 8.9°C on 21^st. This lowest grass minimum temperature in August was the highest such value for August in at least the last 30 years in Royston.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 19.4°C. The earth temperature ranged from a maximum of 21.0°C on 19^th to a minimum of 17.9°C on 28^th.

It was the dullest August in at least the last 5 years in Royston with the monthly sunshine total only managing to reach 141.1 hours, which is 80% of normal. Despite the rather dull conditions only 1 day was completely sunless, however.

The sunniest day of the month was 14^th with 12.0 hours sunshine. Only 1 other day in the month exceeded 10 hours sunshine, namely 17^th with 11.5 hours. Given the dry nature of much of the month the generally poor sunshine values are even more disappointing.

August was a fairly calm month overall and the mean wind speed throughout the month was only 1.6 mph. The highest wind gust speed in August was a relatively modest 28 mph on both 17^th and 30^th.

The windiest day of the month was 30^th with a daily (00/00 GMT) mean wind speed of 5.7 mph. At the other end of the scale the calmest day of the month was 3^rd with a daily mean wind speed of 0.1 mph.

As regards wind direction, the analysis of wind directions as observed at 0900 GMT daily was NORTH 7 days, NE 1, E 0, SE 2, S 1, SW 3, W 5, NW 6 and CALM 6.

The mean MSL air pressure in August was 1015.6 mB, which is approximately 2 mB below average. The highest and lowest air pressure values recorded in August were 1031 mB and 1001 mB on 31^st and 9^th respectively.

The mean relative humidity in August was 80.5%. The highest daily (00/00 GMT) mean relative humidity value was 94.0% on 9^th, whilst the lowest daily mean relative humidity was 69.6% on 15^th. The absolute lowest relative humidity reading in August was 37% at 1555 GMT on 17^th.

So what sort of a Summer (June to August) has it been in Royston? In statistical terms it has been a duller and wetter than normal Summer, but the mean temperature was a little above average.

The mean daily maximum temperature in Summer was 21.5°C, which is 0.1°C above average. The mean daily minimum temperature was 0.9°C above average at 12.6°C. Total rainfall was 183.7 millimetres, which is 128% of normal, whilst total sunshine was 509.3 hours, which is 91% of average.

The above average rainfall figure tends to disguise the dry nature of much of the Summer, illustrated by the fact that each of the three Summer months contained lengthy mostly dry spells.

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

9^th September 2002

Royston Crow (Corvus Cornix)

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