Overall, April was a cold and dry but sunny month in Royston.

The unseasonably cold weather in March continued almost to mid-April and it was only on 13^th that the daily maximum temperature reached its 30 Year mean for the first time since 6^th March.

On 4^th the day maximum temperature reached only 3.8°C, this being the lowest such value in April since 5^th April 1989 and the second lowest such value in April since records began (1972). The cold start to the month contributed to it being the coldest April since 1989, and it also continued the trend of each month so far in 2013 being colder than average.

The second half of the month was much warmer resulting in the mean daily maximum temperature of 13.3°C for the month as a whole being only 0.4°C below average, The mean night minimum temperature did not recover as much and was 1.3°C below average at 3.5°C. The highest night minimum temperature in the month was 11.4°C on 25^th.

The highest temperature recorded in April was 21.9°C on 25^th and the lowest temperature was –4.4°C on 2^nd. This was the lowest absolute minimum temperature recorded in April since at least 1972. The lowest grass minimum temperature of the month also occurred on 2^nd and the reading of –9.5°C was also the lowest in April since at least 1972. Totals of 10 air frosts and 13 ground frosts occurred in April, the former being the highest total in April since at least 1972. Air frost duration in April was 43.1 hours.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 7.8°C, which is 2.3°C below average, a figure undoubtedly influenced by the very cold March causing low values at the start of the month. The highest and lowest earth temperatures recorded in March were 12.5°C on 26^th and 3.5°C on 2^nd (and 5^th) respectively.

April was a dry month (the 3^rd so far this year) with the rainfall total of 26.2 millimetres being only 60% of normal. The number of "rain days" (0.2 millimetres or more) in April was 10 with rainfall exceeding 1.0 millimetre on 5 of these days. It was the 7^th drier than average April in the last 10 years, with less than one quarter of last April’s rainfall of 113.1 millimetres.

Minimal amounts of snow were observed to fall on 1^st and 4^th, whilst hail was recorded on 12^th and 27^th. Total rainfall for 2013 to the end of April was 143.9 millimetres, which is 83% of average.

April was a sunny month accumulating 192.9 hours of sunshine, which is 124% of normal. This total was 49.8 hours more than in April 2012, but 35.8 hours less than in April 2011, indicating high variability of the April sunshine! The sunniest day in April was 20^th with 13.7 hours sunshine, with 2^nd (12.5 hours), 23^rd (12.4 hours) and 30^th (10.4 hours) also exceeding 10 hours sunshine. No day in April was completely sunless.

The mean wind speed in April was 7.3 mph and the maximum wind gust speed recorded was 44 mph on 18^th. The windiest day of the month was 18^th with a 24 hour (00/00 GMT) mean wind speed of 16.1 mph. At the other end of the scale the calmest day of the month was 6^th with a mean wind speed of 3.5 mph.

The analysis of wind directions as observed daily at 0900 GMT shows NORTH 2 days, NE 8, E 2, SE 0, S 6, SW 7, W 2, NW 3 and CALM 0.

The mean MSL air pressure in April was 1014.1 mB, which is 1 mB below average. The highest and lowest pressure values recorded in April were 1034.4 mB on 20^th and 991.8 mB on 12^th respectively.

The mean relative humidity based on 5 minute observations in April was 74.5%. The highest daily (00/00 GMT) mean relative humidity was 95.6% on 11^th. The lowest daily mean relative humidity was 62.8% on 7^th. The absolute lowest relative humidity reading in April was 31% at 1550 GMT on 7^th.

Fog (visibility < 1000 metres @ 0900 GMT) was not observed on any day in April.

Met. Observer, Royston (Iceni) Weather Station

4^th May 2013

   Royston Crow (Corvus Cornix)