PITSFORD HALL WEATHER STATION NORTHAMPTON, UNITED KINGDOM MONTHLY WEATHER REPORT - SEPTEMBER 2001 Headline: Typically autumnal. Generally unsettled with spells of wet and windy weather. Early morning mists and fog becoming more frequent in the latter half. Following a dry start, the first few days of September were generally unsettled as bands of rain swept across the county conveyed on north-westerly winds which brought a general reduction in daily temperatures. Much of the rain fell in several short and heavy bursts with thunder recorded further east but in the county. The north-westerly airstream continued to prevail until the 11th and following the initial unsettled period, the first part of the second week was generally dry. Temperatures remained generally depressed. However, this period was the sunniest time of the month with some good daily totals recorded such as 9.9 hours on the 8th. The days from the 12th to the 19th saw a particularly unsettled spell of weather as an intense low tracked southwards across the United Kingdom from Iceland. Temperatures continued to fall sharply especially around the 17th as winds took on a northerly direction. Peak gusts reached 39 mph on the 17th and 18th, the 17th being a particularly windy day. The low temperatures brought the grass minimum within a couple of degrees of freezing (1.5C on 12th and 1.9C on 16th). A brief window opened on the weather between the 20th and 22nd. As winds dropped fairly sunstantial fog developed in the early hours. The unsettled theme then resumed on the 23rd leading towards a very wet end to the month. The mornings saw some further mist and fog patches forming, especially on the 25th and 26th as winds dropped to calm. However, with the winds having swung round to a more southerly direction, the last few days of September were reasonably warm, the 28th being something of a mini-heatwave with a daytime maximum reaching nearly 23C. Climatological & Agrometeorological Statistics - September 2001 Air Temperatures The Highest Maximum: 22.7C on 28th The Lowest Maximum: 12.9C on 19th The Highest Minimum: 14.9C on 2nd The Lowest Minimum: 5.6C on 22nd The Mean Maximum: 17.0C The Mean Minimum: 9.0C The Overall Mean: 13.0C Difference from the Monthly Mean: -0.7 C Relative Humidity: Highest Relative Humidity (at 0900): 99.0% on 29th Lowest Relative Humidity (at 0900): 71.0% on 4th Mean Relative Humidity (at 0900): 89.9% Dew Point: The Highest Dew Point (at 0900): 15.7C on 2nd The Lowest Dew Point (at 0900): 5.9C on 26th The Mean Dew Point (at 0900): 10.3C Rainfall: Total: 58.4mm Difference from the Monthly Mean: 103.0% Duration: 39.5hrs Highest 24 hour fall (from 0900): 8.0mm on 28th Rain Days (>/=0.2mm): 17 Wet Days (>/=1.0mm): 15 Acid rain (lowest value, pH): 5.10 on 23rd Sunshine: Total Duration of Bright Sunshine: 113.8 hrs Sunniest day: 10.3 hrs on 4th Number of sunless days: 4 Cloud cover (mean at 0900): 6.1 oktas Pressure (reduced to sea level): The Highest Pressure: 1026.5 mb on 1st The Lowest Pressure: 993.2 mb on 30th Mean Pressure (recorded at 0900): 1014.3 mb Winds Run of wind (mean over 24 hrs): 115.2 miles Mean daily wind speed: 6.2 mph Highest 24 hr wind speed: 13.5 mph on 17th Run of wind (to date): 3454.8 miles Highest Maximum Gust: 39 mph on 17th Highest wind strength (at 0900): 26.5 mph on 9th Mean wind strength (at 0900): 9.3 mph Winds from the Following Directions: N 7 NE 0 E 0 SE 4 S 2 SW 0 W 2 NW 12 Calm 3 Ground Temperatures: Lowest Grass Minimum: 1.4C on 10th Mean Grass Minimum: 5.9C Lowest Concrete Minimum: 3.4C on 17th Mean Concrete Minimum: 8.4C Lowest Bare Earth Minimum: 4.9C on 9th Mean Bare Earth Minimum: 8.6C Soil/EarthTemperatures: Surface mean: 11.7C 5cm mean: 11.5C 10cm mean: 12.0C 20cm mean: 13.2C 30cm mean: 14.8C 40cm mean: 14.7C 50cm mean: 15.3C 100cm mean: 14.9C Days with: Thunder: 0 Hail less than 0.5mm: 0 Hail greater than/equal to 0.5mm: 0 Snow or snow & rain: 0 Fog 7 Air frost 0 Ground frost 0 Total Evaporation (tank) 43.25 mm All observations made at 0900hrs at Pitsford Hall weather station. Averages refer to the period 1971-2000. See appendix for details of instrumentation used. All data © Northamptonshire Grammar School.