Royston (Iceni) Weather Station
November 1999 Weather Review
The November weather in Royston was very reasonable for late Autumn, the month being mild, dry and sunny.
A cold third week with temperatures well below average failed to prevent the mean temperature for the month as a whole from being above average, a feature of the weather which has been persistent in most months over the last two years or so in Royston. One manifestation of this was the lack of any air frost at Royston (Iceni) Weather Station, but the fact that the lowest temperature recorded of 0.0°C (32.0°F) came so close to the definition of air frost (-0.1°C or below) might mean that lower lying parts of Royston may just have experienced an air frost.
The last time November escaped an air frost was in 1990, and beyond that over the last 25 years in 1986, 1984, 1981, and 1974. However, ground frost did occur on 8 nights in November this year, although the lowest grass minimum temperature was not particularly low at –2.7°C (27.1°F) on 21st.
The highest temperature recorded was 16.5°C (61.7°F) on 1st. This value is not too far behind the highest recorded in November in the last 25 years, which was 17.8°C (64.0°F) on 2nd November 1984. At the other end of the scale the lowest day maximum temperature was 5.3°C (41.5°F) on 18th. The temperature similarly failed to reach 6°C on 3 other days, 17th, 19th and 20th.
The mean daily maximum temperature over the whole month was 10.2°C (50.4°F), which is 0.7°C above the 25 Year (1973/1997) average. The mean night minimum temperature was also above average (+0.8°C) at 5.4°C (41.7°F).
The mean earth temperature at 30 cms (1 foot) depth as measured at 0900 GMT daily was 8.4°C (47.1°F). The highest earth temperature recorded was 11.5°C (52.7°F) on 2nd; a steady decline then set in to its lowest value of 6.0°C (42.8°F) on 20th, 21st, and 22nd before a recovery to 7.5°C (45.5°F) by the end of the month.
Perhaps the most noteworthy feature of the November weather was the sunshine which totalled 82.0 hours in the month, which is almost 25% above normal. Only 2 days (22nd and 29th) experienced no sunshine at all whilst the sunniest day was 2nd with 7.7 hours sunshine.
Although measurable rainfall (0.2 millimetres or more) fell on no less than 16 days in November the amounts involved were mostly small and the total rainfall of 25.4 millimetres (1.00 inches) was only 48% of the 35 Year (1961/1995) Royston average. It was only the driest November since 1995, however. The wettest day of the month was 5th with 6.6 millimetres (0.26 inches) rainfall.
Rainfall duration in November was 41.1 hours. Hail was observed to fall on 20th, the first hail in November since 1991.
The mean wind speed as determined by 5 minute observations over the whole month was 4.9 mph. The highest and lowest daily (00/00 hrs) mean wind speed values were 11.2 mph on 28th and 0.7 mph on 15th and 21st respectively. The highest daily maximum gust speed was 46 mph on 30th. Gusts of 44 mph were recorded on 26th and 28th. Daily wind directions as observed at 0900 GMT were N 6, NE 2, E 0, SE 0, S 3, SW 8, W 5, NW 4, and CALM 2.
The mean MSL air pressure over the month was 1020.1 mb, ranging from a highest value of 1039 mb on 9th to a lowest value of 990 mb on 5th. The mean was some 6 mb above normal. Mean cloud cover as observed at 0900 GMT was 5.1 oktas (64%).
The mean relative humidity in November was 88.6%. The highest and lowest daily (00/00 hrs) mean relative humidity values were 96.7% on 13th and 77.3% on 6th respectively.
To conclude this report the means for Autumn (September/November) make interesting reading. The mean daily maximum temperature of 15.5°C (59.9°F) was the highest since records began at Royston (Iceni) Weather Station in 1972. This value was 1.4°C above normal, whilst the mean night minimum temperature of 8.5°C (47.3°F) was 1.0°C above normal. Taking the mean of these two values it was only the mildest Autumn since 1995, however.
The Autumn rainfall total was 138.6 millimetres (5.46 inches), which is 88% of average. Sunshine was 25% above average at 397.2 hours, making it an exceptionally sunny Autumn in Royston.
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
6th December 1999
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