Royston (Iceni) Weather Station
April 2000 Weather Review
Sunshine and temperature values were near to average in Royston in April, but it was a very wet month.
The rainfall was undoubtedly the main feature of the April weather as the total of 94.4 millimetres was not only as much as 208% of the 35 Year (1961/1995) average, but was also the 4th highest April rainfall total in the Royston rainfall record which commenced in 1853. The wettest April since 1853 was only two years ago in 1998 when severe floods occurred not too far from Royston in the Ouse and Nene valleys, whilst the Aprils in 1919 and 1983 were also wetter.
The number of "rain days" (0.2 millimetres or more) was high at 23, and the wettest day of the month was 2nd with 17.9 millimetres rainfall. This rainfall event continued into 3rd when a further 13.8 millimetres rainfall was recorded. The rainfall over these two days was not particularly intense but was noteworthy for its duration. In the 48 hours from 1800 GMT on 2nd to 1800 GMT on 4th it was raining for a total of 41.4 hours! This caused some more flooding in the Ouse valley around Huntingdon but on a much lesser scale than in 1998. Total rainfall duration in April was 121.3 hours.
Apart from a snow shower on 4th, the month was snow free, but hail was observed to fall on both 4th and 5th.
Temperatures were about average by day but a little higher than normal at night. The mean day maximum temperature was 12.8°C which is exactly on the average for the 25 Year (1973/1997) reference period. The highest temperature in the month was 19.2°C, recorded on 29th. In contrast the temperature only managed to attain a maximum of 3.1°C during daylight hours on 4th.
The mean night minimum temperature was 4.9°C which is 0.8°C above average. The lowest night minimum temperature recorded was –1.5°C on 6th and this reading was accompanied by the lowest grass minimum temperature of the month of –4.9°C. Totals of 2 air frosts and 8 ground frosts were recorded in April. Air frost duration was 11.0 hours in the month.
Although the mean temperature for April was only just above normal it does mean that the month adds to the growing number in recent times with above average mean temperatures. In the 40 months since January 1997 no less than 32 have been warmer than average.
The mean earth temperature at 30 centimetres depth as measured daily at 0900 GMT was 9.7°C. The earth temperature in April ranged from a highest value of 13.0°C on 30th down to the lowest reading of 7.4°C on 6th. Even in mid-month the earth temperature registered only slightly higher than this minimum with a value of 7.8°C.
The sequence of 7 consecutive months (since August 1999) with above average sunshine came to an end in April. However, the month’s sunshine total of 141.3 hours was almost average at 99% (of normal) so it was not a dull month by any means.
After a dull first few days of the month sunshine duration exceeded 10 hours each day in the 5 day period from 6th to 10th inclusive, totalling a very respectable 57.3 hours in the process. The sunniest day of the month occurred on 6th with a total of 12.5 hours sunshine. Four days in April were completely sunless, these being 3rd, 4th, 15th and 28th.
With the prospect of a fairly sunny day on 30th, after 10.8 hours sunshine had been recorded on 29th, it appeared that the sunshine total for the month might just exceed the average, but after a bright start it unexpectedly (per the forecasts) clouded over and rained!
The mean wind speed in April was 3.9 mph, whilst the maximum wind gust recorded was 48 mph on 17th. This day transpired to be the windiest day (00/00 GMT) overall in the month with a mean wind speed of 9.0 mph. At the other end of the scale the calmest day in April was 30th with a mean wind speed of only 0.5 mph.
As regards wind directions as observed daily at 0900 GMT these were N 3 days, NE 6, E 0, SE 0, S 10, SW 6, W 2, NW 2, and CALM 1.
As might be expected in a very wet month air pressure was below normal. The mean MSL air pressure for the month as a whole was 1006 mb which is about 10 mb below average. The highest air pressure reading of the month was 1035 mb on 7th and the lowest 981 mb on 12th.
The mean relative humidity in April was 83.6%, ranging from a highest daily (00/00 GMT) mean relative humidity of 99.0% on 3rd to a lowest daily mean relative humidity of 67.0% on 8th.
So far this year the weather has fluctuated between dry and wet months so it will be interesting to see whether May will be a dry month, bearing in mind that May has been drier than average in each of the last 5 years.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
6th May 2000
Royston Crow (Corvus Cornix)
Return to Daily Weather Observations - April 2000 header page