Daily Report for 18th December 2019

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 1.7 °C (-1.4) 06:30 3.4 °C (+0.0) 12.4 °C (+9.3), 2014 -6.0 °C (-9.1), 2010
Maximum Temperature 10.4 °C (+2.8) 23:24 9.0 °C (+0.8) 13.7 °C (+6.1), 2015 0.3 °C (-7.3), 2010
Mean Temperature 6.8 °C (+0.7) 6.4 °C (+0.4) 13.0 °C, 2014 -2.5 °C, 2010
Minimum Humidity 80% 15:55 77% 87%, 2010 73%, 2018
Maximum Humidity 98% 09:27 93% 98%, 2010 82%, 2016
Mean Humidity 90% 86% 93%, 2010 81%, 2016
Minimum Pressure 1004 hPa 22:54 1001 hPa 1032 hPa, 2016 988 hPa, 2013
Maximum Pressure 1012 hPa 09:57 1014 hPa 1040 hPa, 2016 995 hPa, 2010
Mean Pressure 1009 hPa 1008 hPa 1036 hPa, 2016 992 hPa, 2010
Mean Wind Speed 4.9 mph (-0.2) 6.1 mph (+1.0) 10.3 mph, 2020 0.8 mph, 2016
Maximum Wind Speed 14.5 mph 23:19 15.5 mph 21.5 mph, 2014 4.7 mph, 2016
Maximum Gust 26.5 mph 21:36 25.2 mph 34.4 mph, 2013 6.3 mph, 2016
Mean Wind Direction S
Rainfall 2.4 mm 54.0 mm (169%) 8.0 mm, 2010
Maximum Hourly Rain 0.9 mm 23:56 4.2 mm, 2013
Maximum 10-min Rain 0.4 mm 23:56 1.3 mm, 2013
Maximum Rain Rate 1.7 mm/h 23:56 9 mm/h, 2013
Minimum Dew Point 0.8 °C 06:29 1.4 °C 10.4 °C, 2014 -7.8 °C, 2010
Maximum Dew Point 8.8 °C 23:39 6.8 °C 11.5 °C, 2014 -0.4 °C, 2009
Mean Dew Point 5.2 °C 4.2 °C 10.9 °C, 2014 -3.5 °C, 2010
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) 1.7 °C 06:30 4.1 °C 12.1 °C, 2014 -6.0 °C, 2010
Day Maximum (09-21) * 9.7 °C * 20:50 8.8 °C 13.7 °C, 2015 0.3 °C, 2010
Max 10m Temp Rise 0.7 °C 08:45 0.4 °C 0.7 °C, 2019 0.2 °C, 2009
Max 1hr Temp Rise 2.8 °C 09:34 1.3 °C 2.8 °C, 2019 0.4 °C, 2020
Max 1hr Hum Rise 5% 18:17 5% 10%, 2018 2%, 2016
Max 10m Temp Fall 0.4 °C 01:41 0.4 °C 0.5 °C, 2017 0.1 °C, 2014
Max 1hr Temp Fall 2.0 °C 02:31 1.3 °C 2.0 °C, 2017 0.3 °C, 2014
Max 1hr Hum Fall 5% 10:35 6% 7%, 2013 1%, 2016
Max 10m Wind Speed 10.6 mph 15:55 11.6 mph 16.2 mph, 2013 3.2 mph, 2016
Minimum Feels-like 0.1 °C 07:56 -1.0 °C 14.1 °C, 2014 -8.9 °C, 2010
Maximum Feels-like 11.1 °C 23:37 8.7 °C 15.5 °C, 2014 0.3 °C, 2010
Mean Feels-like 5.1 °C 4.2 °C 14.7 °C, 2014 -4.4 °C, 2009
Air-frost Hrs 0 hrs 0 hrs 21 hrs, 2010 0 hrs, 2012
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 8.7 °C (+4.2) 5.6 °C (+0.8) 8.7 °C (+4.2), 2019 1.2 °C (-3.3), 2014
Humidity Range 18% 16% 20%, 2018 3%, 2016
Pressure Range 8 hPa 13 hPa 27 hPa, 2013 2 hPa, 2014
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 3.5 [50%]51 hrs (153%) [40%] 7 [100%], 2017 0 [0%], 2010
Wet Hours 5
[Mean rain rate: 0.5 mm/h]
63 hrs (175%) [15%] 5, 2018 0, 2011
Cloud Cover am: Mostly Sunny
pm: Partly Cloudy transitioned to Overcast
Events None
Comments 18- rn
Extra Comments
Issues None known
Observer Absent? Yes - observations may be unreliable
Pond Temperature (Heath) 5.5 °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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Wind rose