Daily Report for 21st December 2019

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 6.1 °C (+3.1) 00:00 3.9 °C (+0.6) 9.8 °C (+6.8), 2017 -2.9 °C (-5.9), 2009
Maximum Temperature 9.7 °C (+2.2) 13:02 9.3 °C (+1.1) 13.3 °C (+5.8), 2020 1.4 °C (-6.1), 2010
Mean Temperature 8.1 °C (+2.7) 6.8 °C (+0.9) 11.1 °C, 2018 -0.5 °C, 2009
Minimum Humidity 85% 17:51 78% 93%, 2010 72%, 2018
Maximum Humidity 95% 23:08 93% 98%, 2009 83%, 2016
Mean Humidity 91% 87% 96%, 2010 79%, 2016
Minimum Pressure 972 hPa 21:34 998 hPa 1035 hPa, 2017 972 hPa, 2019
Maximum Pressure 986 hPa 00:05 1011 hPa 1036 hPa, 2017 986 hPa, 2019
Mean Pressure 980 hPa 1005 hPa 1035 hPa, 2017 980 hPa, 2019
Mean Wind Speed 6.1 mph (+1.0) 6.1 mph (+1.0) 11.9 mph, 2013 2.0 mph, 2009
Maximum Wind Speed 15.2 mph 19:27 15.6 mph 23.3 mph, 2018 8.1 mph, 2009
Maximum Gust 25.0 mph 06:11 25.3 mph 39.2 mph, 2018 10.2 mph, 2009
Mean Wind Direction S
Rainfall 7.5 mm 84.2 mm (226%) 9.5 mm, 2018
Maximum Hourly Rain 2.2 mm 06:45 4.4 mm, 2018
Maximum 10-min Rain 1.1 mm 06:13 1.2 mm, 2013
Maximum Rain Rate 7 mm/h 06:06 54 mm/h, 2013
Minimum Dew Point 5.0 °C 00:06 2.0 °C 8.3 °C, 2017 -4.4 °C, 2009
Maximum Dew Point 8.0 °C 14:22 7.1 °C 12.2 °C, 2020 0.8 °C, 2010
Mean Dew Point 6.7 °C 4.7 °C 9.8 °C, 2020 -1.5 °C, 2009
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) * 5.8 °C * 22:03 4.6 °C 10.1 °C, 2017 -2.9 °C, 2009
Day Maximum (09-21) 9.7 °C 13:03 9.1 °C 13.3 °C, 2020 1.4 °C, 2010
Max 10m Temp Rise 0.3 °C 00:26 0.3 °C 1.3 °C, 2009 0.1 °C, 2010
Max 1hr Temp Rise 1.0 °C 10:35 1.2 °C 1.9 °C, 2009 0.4 °C, 2017
Max 1hr Hum Rise 5% 20:56 5% 10%, 2013 2%, 2010
Max 10m Temp Fall 0.4 °C 19:24 0.4 °C 1.3 °C, 2009 0.1 °C, 2010
Max 1hr Temp Fall 1.3 °C 20:05 1.3 °C 1.7 °C, 2013 0.3 °C, 2010
Max 1hr Hum Fall 3% 01:24 6% 12%, 2013 2%, 2010
Max 10m Wind Speed 12.2 mph 19:34 11.8 mph 18.8 mph, 2018 5.4 mph, 2009
Minimum Feels-like 1.7 °C 01:07 -0.3 °C 7.3 °C, 2017 -5.7 °C, 2009
Maximum Feels-like 8.4 °C 12:58 9.0 °C 15.7 °C, 2020 1.4 °C, 2010
Mean Feels-like 5.6 °C 4.8 °C 11.7 °C, 2017 -1.2 °C, 2010
Air-frost Hrs 0 hrs 0 hrs 13 hrs, 2009 0 hrs, 2010
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 3.6 °C (-0.9) 5.3 °C (+0.5) 7.0 °C (+2.5), 2014 1.1 °C (-3.4), 2010
Humidity Range 10% 16% 23%, 2018 4%, 2010
Pressure Range 13 hPa 13 hPa 13 hPa, 2019 1 hPa, 2017
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 1.5 [21%]53 hrs (136%) [36%] 2.5 [36%], 2012 0 [0%], 2009
Wet Hours 8
[Mean rain rate: 0.9 mm/h]
90 hrs (214%) [18%] 12, 2013 0, 2012
Cloud Cover Partly Cloudy with periods of Mostly Cloudy
Events None
Comments rn
Extra Comments
Issues None known
Observer Absent? Yes - observations may be unreliable
Pond Temperature (Heath) 5.0 °C
Notes
Times of extremes are computed using the midpoint of the longest continuous period at that extreme value.
Cumulative anomalies are reported according to the expected value for the month-to-date rather than month-end.
Sun hrs are initially pulled from the official weather station at Heathrow, and later adjusted by hand to reflect local conditions based on webcam observations. Wet hrs are dervied algorithmically from rainfall data, though may be adjusted manually. Cloud cover and Events are manually reported, often with multi-week delays.
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Daily Graph of Conditions

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Webcam Summary of Cloud Conditions

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