Royston (Iceni) Weather Station

Daily Weather Observations - July 2003

Temperatures, rainfall and sunshine were all a little above normal in July.

Although the mean temperature in July was 1.3°C above average, this positive temperature anomaly could not match the previous month (which was the warmest June since 1976). The lowest day maximum temperatures mostly occurred in the first and last weeks of the month, with the intervening period containing a number of hot days.

The hottest day of the month was 15^th when a maximum temperature of 31.0°C was recorded. This was the hottest day in July since 22^nd July 1996. The next day, 16^th, was almost as hot with a maximum temperature of 30.2°C, but the temperature plummeted on 17^th and could only manage a maximum of 18.9°C making it one of the coolest days of the month. Temperatures quickly recovered, however, and 2 days later on 19^th the temperature was back up to 28.8°C. The coolest day of the month was, in fact, 3^rd when a maximum temperature of only 17.3°C was achieved.

The mean daily maximum temperature in July was 23.6°C, which is 1.4°C above the 30 Year (1973/2002) average for the month. The mean daily minimum temperature was 1.2°C above average at 13.7°C. It was the warmest July in Royston since 1999 only.

The lowest temperature recorded in July was 10.4°C on 5^th, and the lowest grass minimum temperature recorded was 8.5°C on 12^th. On the night of 16^th/17^th the minimum temperature was as high as 17.1°C, making it the warmest night of the month.

The mean earth temperature at 30 cms depth as read at 0900 GMT daily was 19.2°C. The highest and lowest earth temperatures in the month were 20.8°C on 16^th and 17.5°C on 4^th respectively.

Sunshine amounts in the early part of the month were disappointing and only 8.2 hours had been accumulated in the first 5 days (compared with the daily average for July of 6.0 hours). Thereafter matters improved considerably and the early sunshine deficit soon became a surplus, but this later became eroded in the last week of the month which returned only 24.4 hours sunshine. In the event, the total sunshine for July was 203.0 hours, which is 9% above the 30 Year (1961/1990) average. It was the sunniest July since 1999.

In contrast to the 24.4 hours sunshine recorded in last week of the month as noted above, the 7 day period from 9^th to 16^th inclusive accumulated a high total of 92.7 hours sunshine, giving a very respectable daily average of 13.2 hours during this spell. The sunniest day of the month was 13^th with 16.0 hours sunshine, whilst 12^th, 14^th and 15^th all exceeded 15 hours sunshine. Three days (3^rd, 5^th and 17^th) in the month were completely sunless.

After 5 successive months with below average rainfall, the July total was 10% above average, but all of this excess actually occurred on 1^st August in the hours prior to 0900 GMT when the "rain day" of 31^st July officially ended!

Much of July was dry, however, characterised by a 12 day dry spell from 4^th to 15^th inclusive in which no measurable rainfall was recorded. The rainfall total for the month was 47.7 millimetres which, as indicated above, was 110% of the 30 Year (1971/2000) average.

The wettest day in July was 26^th with 10.8 millimetres rainfall. The number of "rain days" (0.2 millimetres or more) in the month was 13, with 11 of these days exceeding 1.0 millimetre rainfall. It was the driest July in Royston since 1998.

Thunder was heard on 3 days (16^th, 19^th and 30^th) in July. Rainfall duration in July was 40.1 hours.

The mean wind speed in July was 3.6 mph. The windiest day (00/00 GMT) of the month was 17^th with a mean wind speed of 6.4 mph. The calmest day of the month was 6^th with a mean wind speed of 0.6 mph. The maximum wind gust speed in the month was 32 mph on 25^th.

The analysis of wind directions as observed at 0900 GMT daily was NORTH 2 days, NE 2, E 1, SE 1, S 3, SW 9, W 10, NW 3, and CALM 0.

The mean July MSL air pressure was 1014.6 mB, which is approximately 3 mB below the July average of the last 30 years. The highest and lowest air pressure values recorded in July were 1025 mB and 997 mB on 12^th and 1^st respectively.

The absolute lowest relative humidity in July was 24% at 1425 GMT on 13^th. The mean relative humidity in July was 73.1%. The highest daily (00/00 GMT) mean relative humidity value in the month was 94.7% on 3^rd, whilst the lowest daily mean relative humidity was 54.3% on 13^th.

(Note re post July event: On 6^th August 2003 a maximum temperature of 35.1°C was recorded, this being the highest temperature recorded in any month at Royston (Iceni) Weather Station since records began on 1^st May 1972. This temperature just exceeded the previous record of 35.0°C set on 3^rd August 1990).

Richard Barker

Richard Barker

Met. Observer, Royston (Iceni) Weather Station

7^th August 2003

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