PITSFORD HALL WEATHER STATION NORTHAMPTON, UNITED KINGDOM MONTHLY WEATHER REPORT for SEPTEMBER 2000 BRIEF CLIMATOLOGICAL SUMMARY An unsettled spell of weather marked the first week of September. The 1st saw some thundery activity, but a small ridge of high pressure then made for a short dry period on the 3rd and 4th. The high pressure resulted in a particularly clear night on the 4th and with virtually calm conditions a sharp ground frost was recorded with grass minima at -4C. Rain then returned although the daily totals across Northamptonshire were modest. A succession of lows made for some quite windy weather with gusts reaching 30mph or more on the 2nd and 6th. From the 7th onwards a warming trend was observed reaching the highest daytime maximum of the month (27.9C) on the 11th. From the 11th onwards a progressive deterioration in the weather occurred. Daytime temperatures saw a marked decline and a succession of misty mornings, extensive cloud and periods of heavy rain, especially around the start of the third week, gave a distinctly autumnal feel. 19.5mm of rain fell at Pitsford Hall over a period of 17.1hrs between 0900GMT on the 14th and 0900GMT on the 15th. Further heavy falls occurred up until the 19th when 10.5mm was recorded; the latter resulting in flood warnings being issued for several rivers across the county. The period from the 20th until the 23rd saw a slight recovery with some brighter mornings and more respectable daily sunshine totals. However, from the 24th another very wet spell brought 11.4mm on the 24th and 15.2mm on the 25th. The month then ended with a vigorous Atlantic low dominating the scene bringing further strong winds with gusts of up to 27mph and brief thunder on the 30th. Overall this was Northampton's wettest September since 1995 (121mm) and the 4th wettest since 1981 (94.7mm). STATISTICAL ANALYSIS Air Temperatures The Highest Maximum: 27.9C on 11th The Lowest Maximum: 13.6C on 18th The Highest Minimum: 15.0C on 11th The Lowest Minimum: 5.4C on 4th The Mean Maximum: 18.8C The Mean Minimum: 10.6C The Overall Mean: 14.7C Difference from the Monthly Mean: 0.4C Relative Humidity: Highest Relative Humidity (at 0900): 99.0% on 15th Lowest Relative Humidity (at 0900): 70.7% on 22nd Mean Relative Humidity (at 0900): 86.4 % Dew Point: The Highest Dew Point (at 0900): 16.5C on 11th The Lowest Dew Point (at 0900): 6.9C on 4th The Mean Dew Point (at 0900): 12.8C Rainfall: Total: 83.1mm Difference from the Monthly Mean: 182.2% Duration: 62.7 hrs Highest 24 hour fall (from 0900): 19.5mm on 14th Rain Days (>/=0.2mm): 17 Wet Days (>/=1.0mm): 11 Lowest pH: 5.0 on 24th Sunshine: Total Duration of Bright Sunshine: 125.4 hrs Sunniest day: 9.7hrs on 4th Sunless days: 4 Cloud cover (mean at 0900): 6 oktas or 75% Pressure (reduced to sea level): The Highest Pressure: 1024.2mb on 4th The Lowest Pressure: 994.0mb on 28th Mean Pressure (recorded at 0900): 1011.6mb Winds Run of wind (mean over 24 hrs): 68.8 miles Mean 24 hr wind speed: 3.7 mph Highest 24 hr wind speed: 7.4mph on 6th Run of wind: 2064.43 miles Highest Maximum Gust: 34 mph on 6th Highest wind strength (at 0900): 22 mph on 16th Mean wind strength (at 0900): 8.0 mph Winds from the Following Directions: N 2, NE 0, E 4, SE 4, S 7, SW 3, W 4, NW 5, Calm 1 Ground Temperatures: Lowest Grass Minimum: -4.0C on 4th Mean Grass Minimum: 7.8C Lowest Concrete Minimum: 5.4C on 4th Mean Concrete Minimum: 10.9C Lowest Bare Earth Minimum: 4.5C on 4th Mean Bare Earth Minimum: 10.1C Soil/Earth Temperatures: 5cm mean: 15C 10cm mean: 14.7C 20cm mean: 15.5C 30cm mean: 16.1C 40cm mean: 16.2C 50cm mean: 16.4C 100cm mean: 16.1C Days with: Thunder: 2 Hail less than 0.5cm: 0 Hail greater than/equal to 0.5mm: 0 Snow or snow & rain: 0 Fog: 3 Ground frost: 2 Air frost: 0 Evaporation: Available from the station. Observations made at 0900 UTC. Averages refer to the period 1961-1990.