Royston (Iceni) Weather station

Daily Weather Observations - April 2007

April was yet another month of extremes in Royston: very mild, very dry and very sunny!

It was an exceptionally warm month, especially by day with a mean daily maximum temperature no less than 5.0°C above the 30 Year (1976/2005) average. Relatively lower night minimum temperatures reduced the overall mean temperature to 3.5°C above average, but this was enough to make the month the warmest April since at least 1972 in Royston.

The previous warmest April in this period was in 1987 but the mean temperature in that month was 1.1°C lower than in April 2007. The highest temperature recorded in the month was 23.0°C (on 15^th) and this value has been exceeded in April in only 3 other years since 1972. The lowest temperature recorded in April was 0.2°C on 4^th, meaning any air frost in the month was narrowly avoided. A total of 4 ground frosts did occur in the month, however..

The mean daily maximum temperature in April was 18.1°C, which is 5.0°C above normal, as noted above. The mean night minimum temperature was 1.9°C above normal at 6.4°C.

The lowest day maximum temperature was 8.8°C on 3^rd, whilst the highest night minimum temperature was 13.3°C on 25^th.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 11.9°C, the earth temperature peaking at 14.3°C on 25^th, and falling to its lowest value of 8.7°C on 4^th.

Probably the most significant feature of April was its extreme dryness, making it the driest April in the Royston rainfall record which goes back to 1853. The previous driest April was in 1893 with 3.3 millimetres rainfall which was double this April’s total of 1.6 millimetres (4% of the 1971/2000 average).

This dry month followed a March which had been rather dry from 6th onwards, resulting in the 56 days from then until the end of April registering only 15.8 millimetres rainfall. The Royston area is consequently exhibiting an unusually dry appearance for so early in the season.

The number of "rain days" (0.2 millimetres or more) was not surprisingly as low as 3, and the highest daily value was only 0.6 millimetres, on both 23^rd and 25^th. Rainfall duration in the month was 3.8 hours. No hail or thunder was recorded in April.

It was an exceptionally sunny April with the sunshine total of 232.1 hours being 159% of the 1971/2000 average. It was the sunniest April in Royston since at least 1997. The sunniest day of the month was 30^th with 13.9 hours sunshine and this was the sunniest April day in this 10 year period (but only had 5 minutes more sunshine than on 30^th April 1999). There were no days in the month with no sunshine at all, although 3^rd and 23^rd had only 1 minute and 14 minutes sunshine respectively.

It was a fairly calm month and the maximum wind gust speed in April was only 30 mph (on 3^rd). The mean wind speed over the whole month was 1.6 mph. The highest daily (00/00 GMT) mean wind speed was 3.4 mph on 1^st, whilst the lowest daily mean wind speed was 0.1 mph on 5^th, 7^th, 11^th, 12^th, 14^th and 15^th.

The prevailing wind in April was from a northerly direction, perhaps surprisingly in view of the exceptional warmth of the month. This is illustrated in the following analysis of wind directions at 0900 GMT daily: NORTH 12 days, NE 5, E 0, SE 1, S 1, SW 4, W 5, NW 2 and CALM 0.

The mean MSL air pressure in April was 1020.9 mB, which is approximately 6 mB above the 1976/2005 average, thus confirming the anticyclonic nature of the month. The highest and lowest air pressure values recorded in April were 1030 mB and 1008 mB on 2^nd and 25^th respectively.

The mean relative humidity in April was 77.2%, with highest and lowest daily (00/00 GMT) mean values of 95.0% and 63.0% on 13^th and 22^nd respectively. The absolute lowest relative humidity reading in April was 26% at 1435 GMT on 1^st and 1455 GMT on 30^th.

Fog (visibility < 1000 metres @ 0900 GMT) was noted on just 1 day (13^th) in April.

Met. Observer, Royston (Iceni) Weather Station

4^th April 2007

Royston Crow (Corvus Cornix)

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