PITSFORD HALL WEATHER STATION NORTHAMPTON, UNITED KINGDOM MONTHLY WEATHER REPORT - APRIL 2001 Monthly Assessment April began on a particularly wet and unsettled theme. A succession of lows passed to the north of the county bringing some particularly wet days on the 3rd (16.0mm) and the 5th (10.3mm). Despite the rain, the county enjoyed some warmth with a daytime maximum of 18.2C recorded at Pitsford Hall on the 2nd. However, overnight temperatures fell sharply on occasion giving a slight ground frost on the 5th and a fairly harsh frost on the 8th (-3.8C). The unsettled spell was broken on the 10th as high pressure built across the British Isles. Some clear spells overnight resulted in several more ground frosts. A second unsettled spell occurred through the third week. Rainfall totals were modest, but the rainfall itself was wintry in nature with hail and brief snow and sleet recorded on the 18th and 19th associated with frontal systems tracking south over the North Sea. Winds were persistently northerly in direction. Overnight temperatures fell substantially giving rise to air frosts on the 17th and 19th. The latter half of the month saw a gradual recovery in temperatures as winds swung round from a generally southerly direction associated with a large and complex low pressure system moving in from the west. There were some periods of heavy rain and/or prolonged rain. 9.6mm fell over 11.5 hours on the 22nd and a further 8.9mm fell over 7.8 hours on the 24th. Despite the rain, there were some days which recorded healthy sunshine totals. As the month came to a close, the rain showers gradually petered out. Daily sunshine values increased up to the maximum daily count for April of 11.3 hours on the 30th, although ground frosts persisted. Climatological Statistics Air Temperatures The Highest Maximum: 18.2C on 2nd The Lowest Maximum: 8.6C on 13th & 18th The Highest Minimum: 7.4C on 28th The Lowest Minimum: -0.9C on 19th The Mean Maximum: 12.4C The Mean Minimum: 3.5C The Overall Mean: 8.0C Difference from the Monthly Mean: -0.7C Relative Humidity: Highest Relative Humidity (at 0900): 98.4% on 4th Lowest Relative Humidity (at 0900): 65.1% on 30th Mean Relative Humidity (at 0900): 82.7% Dew Point: The Highest Dew Point (at 0900): 10.7C on 2nd The Lowest Dew Point (at 0900): 0.8C on 13th The Mean Dew Point (at 0900): 5.3C Rainfall: Total: 81.0mm Difference from the Monthly Mean: 154.3% Duration: 58.4hrs Highest 24-hour fall (from 0900): 16.0mm on 3rd Rain Days (>/=0.2mm): 18 Wet Days (>/=1.0mm): 16 Lowest pH: 6.0 on 28th Sunshine: Total Duration of Bright Sunshine: 143.2hrs Sunniest day: 11.3hrs on 30th Sunless days: 3 Cloud cover (mean at 0900): 6.3 oktas (78.8%) Pressure (reduced to sea level): The Highest Pressure: 1032.8mb on 13th The Lowest Pressure: 994.1mb on 4th & 6th Mean Pressure (recorded at 0900): 1011.8mb Winds: Run of wind (mean over 24 hrs): 128.4 miles Mean daily wind speed: 7.0mph Highest 24-hour Wind Speed: 10.7mph on 3rd Run of wind (to date): 3851.4 miles Highest Maximum Gust: 50mph on 30th Highest wind strength (at 0900): 21.9mph on 15th Mean wind strength (at 0900): 9.9mph Winds from the Following Directions: N 7, NE 2, E 0, SE 1, S 10, SW 1, W 1, NW 8, Calm 0 Ground Temperatures: Lowest Grass Minimum: -5.9C on 17th Mean Grass Minimum: -0.1C Lowest Concrete Minimum: -1.0C on 17th Mean Concrete Minimum: 3.1C Lowest Bare Earth Minimum: -0.3C on 21st Mean Bare Earth Minimum: 3.7C Soil/Earth Temperatures (under grass): Surface mean: 9.5C 5cm mean: 7.5C 10cm mean: 8.4C 20cm mean: 8.9C 30cm mean: 8.9C 40cm mean: 8.8C 50cm mean: 8.9C 100cm mean: not available owing to breakage. Soil Temperatures (under bare soil): 5cm mean: 8.3C 10cm mean: 7.4C 20cm mean: 7.8C* *calculated over the period 1st-18th April. The 20cm angle thermometer suffered damage during mowing on the 19th April and was replaced on 1st May. Days with: Thunder: 0 Hail less than 0.5mm: 2: 18th & 19th Hail greater than/equal to 0.5mm: 0 Snow or snow & rain: 2: 18th & 19th Snow lying: 0 Fog: 0 Air Frost: 2 Duration of Air Frost: 1 hour Ground Frost: 16 Evaporation: Reinstated on 1st May 2001. Observations made at 0900 UTC. Averages refer to the period 1971-2000.