Royston (Iceni) Weather Station
Daily Weather Observations - August 2000
AUGUST 2000 WEATHER REVIEW
After the cool, wet and dull July in Royston this year, August 2000 completely reversed these trends with above average temperatures and sunshine, and below average rainfall.
The month was consistently warm but without any really hot days, evidenced by the fact that the temperature failed to reach 21°C (70°F) on only two days, and achieved a relatively low (for August) monthly maximum of 27.4°C (on 12th). In fact, this was the lowest monthly maximum temperature for August since 1993.
The mean daily maximum temperature in August was 23.1°C, which is 0.9°C above the 25 Year (1973/1997) average. The mean night minimum temperature was similarly 0.9°C above average at 13.3°C. It was the warmest August in Royston since 1997.
Surprisingly the lowest temperature recorded in August occurred on the same day as the second highest day maximum temperature. An overnight minimum temperature of 9.3°C on 24th (at 0335 GMT) was followed by a rapid rise in temperature to 26.0°C (at 1350 GMT), giving a temperature range for the day of 16.7°C. The lowest grass minimum temperature in August was 6.6°C on 30th.
The mean earth temperature at 30 centimetres depth as observed daily at 0900 GMT was 18.8°C. The highest and lowest earth temperatures recorded in the month were 19.9°C on 10th and 13th, and 17.5°C on 31st respectively.
The August rainfall was principally comprised of two thunderstorms, on 3rd and 20th. The latter storm yielded the heaviest rainfall of 17.8 millimetres. The first thunderstorm on 3rd was arguably the more spectacular, however, as its 8.4 millimetres rainfall included a very intense 5 minute rainfall of 5.7 millimetres between 1430 and 1435 GMT. The temperature dropped sharply during this storm, from 20.3°C at 1400 GMT to 14.3°C at 1455 GMT. Large hail (over 5 mm diameter) was also a feature of this storm. No other instances of hail and thunder were recorded during the month.
Total rainfall in August was 43.3 millimetres, which is 82% of the 35 Year (1961/1995) average. The number of "rain days" (0.2 millimetres or more ) was 10. A lengthy dry spell occurred in July and August, the rainfall from 11th July to 19th August inclusive amounting to only 24.1 millimetres (half of which fell on 3rd August). It was the driest August in Royston since 1995 (but rainfall was equal to August 1998).
One further note to the August rainfall is that during a light shower at approximately 0900 GMT on 26th the rainfall brought with it a deposition of sandy brown mud which showed up particularly well on parked cars! The origin of these deposits was probably North Africa, although it was noted that the orange colour of the previous such deposits this year on 24th March and 7th May was absent on this occasion.
A feature of the August sunshine regime which is rarely achieved in any month of the year was that sunshine occurred on every single day in the month. The total sunshine duration value for the month was 209.9 hours, which is 118% of normal. The sunniest day of the month was 12th with 13.2 hours sunshine. The next highest daily value was 12.1 hours on 25th.
The mean wind speed in August was 3.3 mph, with a highest daily (00/00 GMT) mean wind speed of 7.3 mph on 2nd, and a lowest daily wind speed of 0.5 mph on 20th. The 2nd also experienced the highest wind gust speed (32 mph) of the month.
As regards the wind direction as observed at 0900 GMT daily the monthly totals for each (45°) direction were North 1, NE 3, E 0, SE 1, S 2, SW 9, W 8, NW 6, and CALM 1. Mean cloud cover at 0900 GMT was 4.0 oktas (50%).
The mean MSL air pressure in August was 1016.0 mb, which is approximately 2 mb below normal. The highest and lowest air pressure readings in the month were 1025 mb on 5th and 1002 mb on 31st respectively.
The mean relative humidity for the month was 74.4%. The highest daily (00/00 GMT) mean relative humidity was 88.3% on 18th, whilst the lowest daily mean relative humidity was 63.1% on 11th. The lowest actual relative humidity reading was 32% at 1450 GMT on 12th.
To complete this review, data is now to hand for Summer (June/August) 2000. It has been a very marginally warmer than average Summer, due mainly to night minimum temperatures being slightly above normal, whilst rainfall and sunshine have both been a little below average.
The mean daily maximum temperature for the Summer was 21.3°C, which is 0.1°C below the 25 Year (1973/1997) average for Royston. The mean night minimum temperature of 12.3°C was 0.6°C above normal, however. Total Summer rainfall was 137.3 millimetres, which is 92% of the 35 Year (1961/1995) average. Total sunshine of 537.3 hours was 96% of the 30 Year (1961/1990) average.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
7th September 2000
Royston Crow (Corvus Cornix)
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