The April 2011 weather in Royston was exceptional in that it was a very warm, very dry and very sunny month!

Such was the warmth of April that the daily maximum temperature fell below its 30 Year (1981/2010) daily mean on only 1 day (13^th) in the month, all other days being warmer than average. With the April mean temperature being 4.0°C above average it was the warmest April since at least 1972 when records began at this weather station.

Another station record occurred on 23^rd. This day was the warmest April day since at least 1972 with a maximum temperature of 27.1°C. In contrast the lowest day maximum temperature was 11.8°C on 13^th, but this was only 0.6°C below the 30 Year average for this day.

The lowest temperature in April was 2.5°C on 10^th, thus indicating that unsurprisingly the month was air frost free. However, 3 ground frosts were recorded, the most ‘severe’ of these being on 29^th when the grass minimum temperature fell to –2.0°C.

Despite the month being so warm, no really mild nights occurred and the highest night minimum temperature of the month was 11.8°C on 6^th. However, the mean night minimum temperature of 7.3 °C was nonetheless 2.5°C above the 30 Year (1981/2010) average. The mean daily maximum temperature in the month showed a much greater anomaly and was an exceptional 5.5°C above average at 19.2°C.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 12.0°C. The highest and lowest earth temperature values in April were 14.5°C on 24^th and 9.9°C on 1^st respectively.

The Spring drought which commenced at the beginning of March had become a serious problem by the end of April after another exceptionally dry month. The March/April period with only 9.2 millimetres rainfall was the driest such period in Royston since 1893 (when 7.6 millimetres rainfall was recorded).

Total rainfall in April was only 4.8 millimetres, which is 11% of the 30 Year (1981/2010) average. The number of "rain days" (0.2 millimetres or more) in the month was 3 (which equalled the record lowest number set in 2007), but with all of these days exceeding 1.0 millimetre rainfall. The ‘wettest’ day of the month was 3^rd with 2.5 millimetres rainfall. It was the driest April since 2007 only, however, when some places in East Anglia recorded no rainfall at all, whilst in Royston rainfall reached only 1.6 millimetres (exactly one-third of the rainfall this April!).

Total rainfall for 2011 to the end of April stands at 114.2 millimetres, which is 66% of the 1981/2010 average.

In the light of the very warm and dry April as highlighted above it is perhaps no surprise that sunshine occurred in abundance. Total sunshine in April was 228.7 hours, which is 157% of the 30 Year (1971/2000) average. Even this high total (which far exceeds the average for any Summer month) could not quite match the 232.1 hours sunshine in April 2007.

The sunniest day in April was 30^th with 13.5 hours sunshine. No day in April was completely sunless although both 13^th and 14^th could manage only half a minute of sunshine each!

The mean wind speed in April was 5.2 mph, and the maximum wind gust recorded in the month was 40 mph on 5^th. The highest daily (00/00 GMT) mean wind speed was 13.5 mph on 5^th whilst the lowest daily mean wind speed was 1.7 mph on both 18^th and 19^th.

The analysis of daily wind directions as observed at 0900 GMT shows half the days in the month included a northerly component, as follows: NORTH 6 days, NE 6, E 3, SE 0, S 4, SW 5, W 3, NW 3 and CALM 0.

The mean MSL air pressure in the month was 1019.2 mB, which is 4 mB above the 1981/2010 average. The highest and lowest air pressure values in the month were 1029.6 mB on 12^th and 1006.2 mB on 2^nd respectively.

The mean relative humidity in April was 72.4%. The highest daily (00/00 GMT) mean relative humidity was 86.9% on 5^th, and the lowest daily mean 56.8% on 23^rd. The absolute lowest relative humidity reading in April was 28% at 1520 GMT on 10^th.

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

Met. Observer, Royston (Iceni) Weather Station

6^th May 2011