Royston (Iceni) Weather Station
Daily Weather Observations - April 2001
April 2001 Weather Review
It was a dull and wet April in Royston, but with an average mean temperature.
Although the mean temperature in April was exactly on the 25 Year (1973/1997) average it was nonetheless the coldest April in Royston since 1989. This surprising fact really puts into perspective the mild nature of April in recent years.
The mean daily maximum temperature in April was 12.6°C, which is 0.2°C below average. The highest temperature recorded (19.8°C) came early in the month, on 2nd, after a maximum of 17.4°C on 1st, but this level of warmth was not repeated during the rest of the month. In fact, on 20th the maximum temperature was only 8.3°C, the lowest daily maximum of the month.
The mean daily minimum temperature was 0.2°C above average at 4.3°C. The lowest temperature recorded in April was –0.5°C on 21st, whilst the lowest grass minimum temperature was –3.3°C on 19th. The highest night minimum temperature was 9.0°C on 6th.
Totals of 2 air frosts and 7 ground frosts occurred in April. Air frost duration was 5.7 hours in the month.
The mean earth temperature at 30 cms depth as read daily at 0900 GMT was 9.5°C. The earth temperature reached its highest value of 11.0°C on 30th but declined to its lowest value of 8.0°C as late as 21st.
For the 8th consecutive month rainfall was above average. The total rainfall of 74.0 millimetres was 167% of the 30 Year (1971/2000) average, but April 2000 was wetter (94.4 millimetres), and April 1998 even wetter with 120.7 millimetres rainfall!
Rather than any particularly heavy fall of rain occurring during April the theme of "a little and often" was the main contributory factor in the wet month. The wettest day of the month was 14th with 8.9 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) was 23, whilst on 18 of these days a rainfall amount of 1.0 millimetre or more was recorded.
The showery nature of much of the rainfall resulted in a total of 8 days with hail observed to fall, this being the highest such total in Royston since at least 1972 and 1 day higher than the previous record of 7 days in April in both 1983 and 1986. Snow fell on both 18th and 19th but in insignificant amounts.
Rainfall duration over the whole month was 81.5 hours.
A "little and often" could also be applied to the sunshine regime in April. Despite only 1 day in the month being completely sunless the sunshine total only reached 84% of normal at 119.4 hours, making the month the dullest April since 1998.
The sunniest day in April was 28th with 9.5 hours sunshine, followed by 1st with 9.1 hours.
Wind speeds were unexceptional in April viewed in the light of daily maximum gust speeds, but the mean wind speed of 5.5 mph was the highest for any month so far this year. The windiest day of the month was 4th with a mean 24 hour (00/00 GMT) wind speed of 10.8 mph, whilst the calmest day of the month was 21st with a mean wind speed of 1.3 mph. The highest wind gust speed in April was 41 mph on 5th.
The daily analysis of wind direction as observed at 0900 GMT was NORTH 7 days, NE 1, E 0, SE 1, S5, SW 8, W 3, NW 4, and CALM 1.
The mean MSL air pressure in April was 1012 mB, which is approximately 4 mB below average. The highest air pressure value recorded in the month was 1033 mB on 13th and the lowest 995 mB on both 4th and 6th.
The absolute lowest relative humidity value recorded in April was 42% at 1450 GMT on 13th. The mean relative humidity for the whole month was 80.9% whilst the highest and lowest daily (00/00 GMT) mean relative humidity values were 90.5% on 5th and 67.1% on 13th respectively.
Fog (visibility < 1000 metres) was not observed at the 0900 GMT observation hour on any day in April.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
8th May 2001
Royston Crow (Corvus Cornix)
Return to Daily Weather Observations - April 2001 header page