Royston (Iceni) Weather Station

Daily Weather Observations - April 2003

It was a dry, sunny, and warm April in Royston.

The most noteworthy feature of the April weather was undoubtedly the 4 day warm spell which occurred from 15^th to 18^th, during which the temperature exceeded 21°C on each day. On 16^th the temperature climbed to a record breaking 25.5°C for April, making it the warmest April day in Royston in at least the last 31 years for which records are available, and probably a lot longer. A sudden cooling occurred on 19^th, however, when the maximum temperature reached no higher than 11.5°C, after a maximum of 21.0°C the previous day.

The aforementioned warm spell helped the mean daily maximum temperature in April up to 15.4°C, which is 2.5°C above the 30 Year (1973/2002) average. Night frosts from 7^th to 10^th inclusive pegged back the mean night minimum temperature, but even so this was 0.5°C above average at 4.8°C. It was the warmest April in Royston since 1999.

The lowest temperature recorded in April was –3.4°C on 8^th, whilst the lowest grass minimum temperature was –6.3°C, also on 8^th. Over the month, totals of 4 air frosts and 8 ground frosts were recorded. This was the highest number of air frosts in April since 1996. Air frost duration in the month was 28.3 hours.

The lowest day maximum and highest night minimum temperatures in April were 7.5°C on 10^th and 10.2°C on 15^th respectively.

The mean earth temperature at 30 cms depth as recorded daily at 0900 GMT was 10.0°C. The highest earth temperature recorded in the month was 12.3°C on 30^th, whilst the lowest earth temperature was 7.3°C on 11^th.

April continued the dry trend of February and March and it was only near the end of the month that the long dry spell was broken, but then not by any significant amounts of rainfall. Rainfall for the 3 month period of February, March and April was only 59.8 millimetres, which is 49% of the 30 Year (1971/2000) average for Royston. The April contribution to this figure was 24.0 millimetres, which is 54 % of average.

It was the driest April since 1997. The wettest day of the month was 30^th with 6.4 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) in the month was 9, and the number of days on which rainfall exceeded 1.0 millimetre was 5. On 2^nd and 9^th snow was observed to fall but in very small amounts only. Hail was observed to fall on 2 days (2^nd and 30^th) in the month, and thunder was heard on 1 day (30^th). Rainfall duration in the month was 28.7 hours.

Until the last week of the month April appeared to be heading for a record sunshine total as in March, but then sunshine of only 20.2 hours over the last 7 days of the month resulted in the sunshine total of 193.0 hours for the month falling short of the March total by 4.9 hours. Despite this it was still a sunny month with the total sunshine exceeding the average by 36%. It was not as sunny as April last year, however, when a total of 15.2 hours more sunshine was recorded.

The sunniest day of April was 16^th with 13.5 hours sunshine and this was followed by 13.4 hours on 17^th and 13.3 hours on 18^th. Although less than 2 hours sunshine was recorded on 14^th, the 7 day spell from 12^th to 18^th inclusive nonetheless returned a very high sunshine total of 76.0 hours.

No completely sunless days occurred in April although 25^th and 28^th came close with only 0.2 hours sunshine each.

The mean wind speed in April was 3.4 mph. He highest daily (00/00 GMT) mean wind speed was 9.0 mph on 27^th, and the lowest daily mean wind speed was 0.5 mph on 24^th. The maximum wind gust speed measured in April was a relatively modest 39 mph on 28^th.

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

The mean MSL air pressure in April was 1017.7 mB, which is about 1 mB above average for April.

The highest and lowest pressure values in the month were 1036mB and 992 mB on 5^th and 28^th respectively.

The mean relative humidity over the whole month was 72.2%. The highest daily (00/00 GMT) mean relative humidity was 91.3% on 28^th, whilst the lowest daily mean relative humidity was 53.8% on 15^th. The absolute lowest relative humidity reading in April was 24% at 1515 GMT on 16^th.

Fog (visibility < 1000 metres) was not observed at the 0900 GMT observation hour on any day in April.

Met. Observer, Royston (Iceni) Weather Station

5^th May 2003

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