Royston (Iceni) Weather Station

Daily Weather Observations - April 2002

It was a very sunny April in Royston, and also warmer and drier than average.

Despite the high sunshine it was the rainfall, or rather the lack of it, which dominated the April weather. No measurable rainfall was recorded in the 25 day period from 21^st March to 14^th April inclusive. Even after the drought was broken on 15^th April only a small amount (4.6 millimetres) of rainfall was recorded from 15^th/18^th inclusive, and then followed a further 6 completely dry days.

However, the last 6 days of the month were all wet, culminating in the wettest day of the month on 30^th when 10.3 millimetres rainfall was recorded. Thus the final figure for the month was 35.9 millimetres (81% of the 30 Year (1971/2000) average) and this total somewhat masks the drought period referred to above.

The number of "rainfall days" (0.2 millimetres or more) in April was 9, and on 8 of these days 1.0 millimetre was exceeded. Rainfall duration during the month was 34.7 hours. Hail was observed to fall on 2 days, 18^th and 29^th. Overall it was the driest April in Royston since 1999 (29.0 millimetres) only. The cumulative total of rainfall for the year (to the end of April) now stands at 153.5 millimetres, which is 11% below normal.

The April sunshine broke the 200 hour barrier and was, in fact, higher than the average for any month of the year. Total sunshine in the month was 208.2 hours, which is 147% of the 30 Year (1961/1990) average. Every day in April had at least some sunshine, although 15^th only managed 1 minute!

The sunniest day in April was 23^rd with a total of 13.4 hours sunshine. Ten hours sunshine was exceeded on 8 other days in the month (see bar chart below for dates).

For the 4^th successive month the mean temperature in April was above average thus continuing the trend to warmer conditions in recent years. In the 64 months since January 1997 no less than 49 of these months have experienced temperatures above normal. Nonetheless, it was still only the warmest April in Royston since 1999.

The mean daily maximum temperature in April was 15.2°C, which is 2.4°C above the 25 Year (1973/1997) average. This was the highest such value in April since 1987. The highest temperature recorded in April was 22.7°C on 23^rd. This has been equalled in April in 1 year (1987) and exceeded in only 3 other years (1984, 1994 and 1996) during the last 30 years in Royston. At the other end of the scale the lowest day maximum temperature in the month was 10.3°C on 9^th.

The mean daily minimum temperature in April was 4.7°C, which is 0.6°C above average. The lowest temperature of the month of –0.1°C occurred on 7^th, with the lowest grass minimum temperature of –3.4°C being recorded on this date also. The highest daily minimum temperature was 9.5°C on 3^rd. One air frost and 10 ground frosts were recorded in April. Air frost duration was 1.0 hours.

The mean earth temperature at 30 centimetres depth was 10.7°C. Highest and lowest earth temperatures in April ranged from 13.5°C on 25^th to 9.0°C on 16^th.

The mean wind speed in April was 4.3 mph. The highest daily (00/00 GMT) mean wind speed was 12.1 mph on 29^th and the lowest daily mean wind speed was 0.7 mph on 15^th. The maximum wind gust speed recorded in the month was 53 mph at 1625 GMT on 28^th. On 29^th a maximum wind gust speed of 51 mph was recorded at 1440 GMT. Both these wind gusts were from a westerly direction.

As regards the analysis of wind directions as observed at 0900 GMT daily this was as follows: North 3 days, NE 7, E 0, SE2, S 4, SW 4, W 6, NW 4 and CALM 0.

The mean MSL air pressure in April was near normal at 1016.7 mB. The highest pressure value recorded in the month was 1036 mB on 21^st, and the lowest 990 mB on 29^th.

The mean relative humidity value for the whole month was 74.7%. The highest and lowest daily (00/00 GMT) mean relative humidity values were 94.6% on 30^th and 61.5% on 16^th respectively. The absolute lowest relative humidity reading in April was 28% at 1345 GMT on 6^th.

Fog (visibility < 1000 metres at 0900 GMT) was recorded on just 1 day (24^th) in April.

Met. Observer, Royston (Iceni) Weather Station

6^th May 2002

Royston Crow (Corvus Cornix)

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