Royston (Iceni) Weather Station
Daily Weather Observations - July 2001
July 2001 Weather Review
Temperature, rainfall and sunshine were all above average in July in Royston, but by relatively modest margins only. It was the 3rd successive warmer than average July.
The most significant temperature event of the month occurred on July 29th when the temperature exceeded 30°C for the first time in July since 22nd July 1996 (when a maximum temperature of 31.5°C was recorded). On 29th the maximum temperature reached its highest value of the month, 30.9°C. Despite a rather cool period covering most of the middle two weeks of the month, hot spells at the beginning and end of the month resulted in the temperature exceeding 25°C on no less than 13 days in the month.
In contrast to the hot days mentioned, the maximum temperature on 19th reached only 17.6°C, almost 5 °C below average and the lowest such value of the month. The mean daily maximum temperature in July was 23.3°C, which is 1.1°C above the 25 Year (1973/1997) average for Royston.
The lowest temperature recorded in July was 7.7°C on 16th. This was the lowest minimum temperature in July since 17th July 1996 (when a minimum temperature of 7.5°C was recorded). The mean daily minimum temperature for the whole month was 13.6°C, which is also 1.1°C above the 25 Year average.
The lowest grass minimum temperature in July was 5.0°C on 16th. The mean earth temperature at 30 cms depth as measured at 0900 GMT daily was 18.9°C. Highest and lowest earth temperature values were 21.4°C on 31st and 16.9°C on 20th respectively.
July rainfall in the latest 30 Year mean period (1971/2000) shows a reduction on earlier periods, probably mainly due to a lessening of thunderstorm activity in this month in more recent times. The total rainfall in July this year was 59.3 millimetres, which is 137% of the new 1971/2000 average. This above average rainfall total was, however, achieved without thunderstorms as thunder was heard on only 1 day (12th) in the month, and this day produced only 1.5 millimetres rainfall! The solitary day with thunder made it the least thundery July since 1992.
The number of "rain days" (0.2 millimetres or more) was 11, whilst on 8 of these days rainfall greater than 1.0 millimetre was recorded. The wettest day of the month was 17th with 23.5 millimetres rainfall. Rainfall duration in July was 35.7 hours.
July appeared to be heading for a low sunshine total until a sunny last week pushed the month’s sunshine total to 8% above average. The sunshine total for the month was 200.5 hours, an increase of 57 hours on July 2000 (which was a particularly dull month), but 41 hours less than in July 1999. The last 3 years thus show a marked variability in July sunshine values.
The sunniest day in July was 4th with 15.5 hours sunshine. No other day reached 15 hours sunshine, the next highest value being 13.8 hours on 3rd. Only 1 day (7th) in July was completely sunless.
The mean wind speed in July was 3.4 mph. The windiest day was 11th with a 24 hour (00/00 GMT) mean wind speed value of 11.6 mph. This day also registered the highest wind gust (51 mph) of the month. The calmest day in July was 16th which registered a mean wind speed of 0.8 mph.
As regards daily wind directions as observed at 0900 GMT the totals in 45° divisions were NORTH 3 days, NE 3, E 1, SE 3, S 1, SW 8, W 6, NW 4 and CALM 2.
The mean MSL air pressure in July was approximately 5 mB below average at 1012.6 mB. The highest pressure value recorded in the month was 1028 mB on 2nd , whilst the lowest pressure value recorded was 993 mB on 18th.
The mean relative humidity for the month as a whole was 73.0%. Highest and lowest daily (00/00 GMT) relative humidity values ranged from 93.7% on 7th to 55.5% on 29th. The absolute lowest relative humidity reading in July was 30% at 1535 GMT on 29th.
Fog was noted at the 0900 GMT observation hour on only 1 day (7th) in the month.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
7th August 2001
Royston Crow (Corvus Cornix)
Return to Daily Weather Observations - July 2001 header page