Royston (Iceni) Weather Station

Daily Weather Observations - July 2009

July 2009 was a wet month in Royston, whilst temperatures and sunshine were near average. The month was very similar to July last year.

The month started on a dry note with 5 completely dry days; thereafter the rainfall regime was " a little and often" and by the end of the month a total of 68.9 millimetres rainfall had been achieved. This amount is 159% of the 1971/2000 average making July the 10^th wetter than average July in the last 11 years.

The number of "rain days" (0.2 millimetres or more) in July was 19, with rainfall of 1.0 millimetre or more on 16 of these days. The wettest day of the month was 16^th with 11.5 millimetres rainfall. Rainfall duration in July was 51.2 hours.

Thunder was heard on 4 days ( 16^th, 17^th, 24^th and 30^th) in July.

With the wetter than average June, and now the wet July, the Summer rainfall has begun to redress the rainfall deficit in the Spring months. Rainfall for the year to the end of July stands at 326.1 millimetres, which is actually 4% above the 1971/2000 January/July average.

The only real warmth in July came at the beginning of the month and after 5^th temperatures were unexceptional giving a mean temperature for the month as a whole virtually coinciding with the 30 Year (1976/2005) average.

The mean daily maximum temperature in July was 22.2°C, which is 0.1°C below the 1976/2005 average. The mean night minimum temperature was 0.2°C above average at 12.8°C. The highest daily maximum temperature recorded in July was 29.1°C on 1^st. After the very hot July in 2006 (when a maximum temperature of 35.2°C was recorded) this is now the 3^rd successive July when the temperature has failed to reach 30°C.

The lowest night minimum temperature in the month was 9.1°C on 10^th and on the same date the lowest grass minimum temperature (7.4°C) of the month was recorded.

The opposites of these extremes were on 17^th when the lowest daily maximum temperature (18.7°C) in July was recorded, and on 3^rd when the highest night minimum temperature (16.5°C) of the month occurred.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 18.8°C. The highest and lowest earth temperatures in July were 21.0°C and 17.4°C on 3^rd and 31^st respectively.

Despite July having higher than average rainfall, and a high rainfall duration, and only average temperatures, sunshine nonetheless managed to keep up with the daily averages and by the end of the month had actually exceeded the 1971/2000 average by 10%. Total sunshine in July was 210.2 hours which is only 2.1 hours below the total recorded in July last year, but as much as 87.1 hours below July 2006!

The sunniest day in July was 2^nd with 14.7 hours sunshine. Only 1 other day (25^th) exceeded 12 hours sunshine. No day in July was completely sunless, with only June and March so far this year additionally achieving this status.

July was a rather breezy month but without any really strong winds. The mean wind speed in July was 7.1 mph and the maximum wind gust recorded was 33 mph on 6^th, 18^th and 29^th. The highest daily (00/00 GMT) mean wind speed was 11.4 mph on 18^th, whilst the lowest daily mean wind speed was 1.9 mph on 2^nd.

The following analysis of wind directions as observed at 0900 GMT daily shows that winds with southerly and westerly components accounted for all but one day in the month: NORTH 0 days, NE 0, E 1, SE 2, S 6, SW 13, W 9, NW 0, and CALM 0.

The mean MSL air pressure in July was 1010.3 mB, which is 7 mB below the 1976/2005 average. The highest and lowest pressure values in the month were 1022.5 mB and 999.0 mB on 1^st and 23^rd respectively.

The mean relative humidity in July was 73.1%, with a highest daily (00/00 GMT) mean relative humidity of 90.3% on 17^th and a lowest daily mean relative humidity of 61.2% on 31^st. The absolute lowest relative humidity reading in July was 35% at 1630 GMT on 5^th.

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

Met. Observer, Royston (Iceni) Weather Station

7^th August 2009

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