Royston (Iceni) Weather Station

Daily Weather Observations - July 2004

It was a very wet July in Royston, but temperatures and sunshine were close to the average.

For the first month since October 2003 (and February 2003 before that) the mean temperature in July was actually below average, but only by 0.2°C! Temperatures ran below the 30 Year (1973/2002) cumulative daily averages for much of the month, but warmer weather during the second half of July, especially during the last few days, enabled a significant catching up to occur by the month end.

The mean daily maximum temperature in July was 21.9°C, which is 0.3°C below the 30 Year (1973/2002) average, whilst the mean night minimum temperature was precisely on the average at 12.5°C. Overall, it was the coolest July since 2000.

The highest temperature recorded in July was 27.9°C on 29^th. This is not a particularly high maximum for July, having been exceeded in July in 18 years since 1972. At the other end of the scale the temperature could manage a maximum of only 16.7°C on 9^th, the lowest such value of the month.

The coldest night of the month was 6^th/7^th when both the lowest air and grass minimum temperatures occurred, these being 8.4°C and 5.4°C respectively. In contrast, the highest night minimum temperature in July was 16.3°C on 15^th/16^th.

The mean earth (30 cms depth) temperature as recorded at 0900 GMT daily was 18.4°C. The earth temperature peaked at 20.3°C on 24^th after recovering from the monthly minimum of 16.4°C on 10^th.

Although much of the month of July was dry in character, with conditions in the Royston area being dry and dusty once again by the end of the month, it was in fact a very wet month! This was principally due to just two very wet days, 7^th when rainfall of 38.0 millimetres was recorded, and 8^th which experienced a further 33.9 millimetres rainfall. The former figure made 7^th July the wettest day in any month of the year since 30^th July 2002. It was also the wettest month of any since July 2002.

The number of "rain days" (0.2 millimetres or more) in July was 15, with the rainfall reaching or exceeding 1.0 millimetre on 10 of these days. Rainfall duration over the whole month was 39.0 hours.

Thunder was heard on 3 days (1^st, 7^th and 8^th) in July.

As with temperatures, sunshine struggled to keep up with the average but by the end of the month had registered a shortfall of just 2% against the 1971/2000 normal. Total sunshine in July was 186.8 hours, making it the dullest July since 2002 only. The sunniest day of the month was 6^th, with 15.0 hours sunshine. No completely sunless days occurred in July, the last such day being on 1^st June.

July was a fairly calm month with a mean wind speed of 2.5 mph. The highest wind gust speed was a relatively modest 37 mph on both 3^rd and 7^th.

The highest daily (00/00 GMT) mean wind speed was 8.5 mph on 3rd, whilst the lowest daily mean wind speed was 0.1 mph on 26^th.

The analysis of daily wind directions as observed at 0900 GMT shows a strong bias towards directions with a westerly component, as below:

NORTH 0 days, NE 2, E 0, SE 2, S 4, SW 6, W 15, NW 2 and CALM 0.

The mean MSL air pressure in July was 1015.3 mB, which is almost 2 mB below the average of the last 30 years. The highest and lowest air pressure values recorded in July were 1027 mB and 1005 mB on 24^th and 8^th respectively.

The mean relative humidity in July was 75.6%. The highest daily (00/00 GMT) mean relative humidity value was 92.4% on 8^th whilst the lowest daily mean was 60.4% on 24^th. The absolute lowest relative humidity reading in July was 31% at 1525 GMT on 6^th.

Fog (visibility < 1000 metres) was not noted at the 0900 GMT observation hour on any day in July.

Met. Observer, Royston (Iceni) Weather Station

5^th August 2004

Return to Daily Weather Observations - July 2004 header page