Royston (Iceni) Weather Station

Daily Weather Observations - July 2007

It was a cooler and wetter than average July in Royston, with about average sunshine.

This month brought to an end the remarkable sequence of 10 consecutive warmer than average months (since August 2006), although the mean temperature was only 0.6°C below average. It was the coolest July since 2000.

Temperatures this July were in sharp contrast to those of the very hot July in 2006. The mean temperature was 4.6°C higher in July 2006, whilst the mean daily maximum temperature was no less than 6.5°C higher last year. Last year the highest temperature recorded in July was 35.2°C but this July a rather modest 24.5°C (on 19^th) was the highest temperature achieved. This was the lowest absolute maximum temperature in July since 1988 (when the highest temperature was only 22.6°C). There were no really cool days in July, however, with the lowest day maximum temperature being 17.5°C on 11^th.

The lowest temperature recorded in July was 8.8°C on 30^th/31^st, although in the 30 Year (1976/2005) averages this is one of the warmest nights of the year! The warmest July night this year was 15^th/16^th when a minimum temperature of 17.1°C was recorded. The lowest grass minimum temperature in the month was 5.6°C on both 8^th and 31^st.

The mean daily maximum temperature in July was 21.3°C, which is 1.0°C below the 30 Year (1976/2005) average. The mean night minimum temperature was 0.1°C below average at 12.5°C.

The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 18.3°C. The highest and lowest earth temperature values in July were 19.5°C and 17.8°C on 17^th and 1^st respectively.

The most significant July day for rainfall was 20^th when a relatively short burst of heavy rainfall produced the highest daily total, 16.3 millimetres, of the month. This was the day when very high rainfall totals (140 millimetres reported in some places) were experienced in Gloucestershire and around which caused the devastating floods in Tewkesbury and Gloucester. Compared with these downpours Royston thus escaped almost unscathed.

Total rainfall in July was 59.8 millimetres, which is 138% of the 1971/2000 average. The number of "rain days" (0.2 millimetres or more) was 15 whilst on 11 of these days rainfall exceeded 1.0 millimetre. Although a ‘wet’ month compared to the average, the July rainfall was significantly exceeded in two of the previous 3 years (103.9 millimetres in July 2004 and 93.4 millimetres in July 2006). Rainfall duration in July was 35.9 hours.

A brief thundery spell occurred at the beginning of July with thunder being heard on 2^nd, 3^rd and 4^th. Otherwise the only other day in the month with thunder was 9^th.

Sunshine remained below average for most of the month but a sunnier last few days of July brought the sunshine total to within 3% of the 1971/2000 average. The total sunshine for the month was 186.4 hours, and whist this figure was almost up to the average it was still 45.7 hours below April 2007!

The sunniest day of the month was 31^st with 13.3 hours sunshine. Every day in the month recorded at least some sunshine, although this was restricted to 8 minutes on 23^rd.

With low pressure anchored to the west of the British Isles for much of the month and with no significant anticyclonic spells it was a rather breezy July at times. The mean wind speed over the whole month was 3.2 mph, whilst the highest wind gust recorded was 41 mph on 26^th. The highest daily (00/00 GMT) mean wind speed in July was 9.8 mph on 6^th and the lowest daily mean wind speed was 0.1 mph on 15^th, 19^th and 31^st.

No less than 24 days in July had a westerly component in the wind direction as shown in the following analysis of wind directions as observed daily at 0900 GMT: NORTH 0 days, NE 1, E 2, SE 0, S 3, SW 10, W 9, NW 5, and CALM 1.

The mean MSL air pressure in July was 1007.8 mB, which is almost 10 mB below the 1976/2005 average. Highest and lowest pressure values in the month were 1020 and 993 mB on 31^st and 23^rd respectively.

The mean relative humidity in July was 77.1%. The highest daily (00/00 GMT) mean relative humidity was 91.9% on 20^th, whilst the lowest daily mean relative humidity was 62.8% on 8^th. The absolute lowest relative humidity reading in July was 26% at 1659 GMT on 31^st.

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

Met. Observer, Royston (Iceni) Weather Station

7^th August 2007

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