Daily Report for 19th December 2020

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 8.0 °C (+5.0) 22:16 4.6 °C (+1.3) 13.2 °C (+10.2), 2015 -5.3 °C (-8.3), 2010
Maximum Temperature 12.0 °C (+4.5) 12:27 8.3 °C (+0.2) 16.0 °C (+8.5), 2015 0.1 °C (-7.4), 2010
Mean Temperature 10.2 °C (+4.7) 6.6 °C (+0.8) 14.8 °C, 2015 -2.6 °C, 2010
Minimum Humidity 79% 16:02 84% 86%, 2017 57%, 2014
Maximum Humidity 92% 07:06 94% 98%, 2012 82%, 2016
Mean Humidity 86% 89% 94%, 2012 76%, 2014
Minimum Pressure 1003 hPa 05:45 998 hPa 1034 hPa, 2017 988 hPa, 2019
Maximum Pressure 1010 hPa 23:51 1008 hPa 1036 hPa, 2017 1000 hPa, 2010
Mean Pressure 1006 hPa 1003 hPa 1035 hPa, 2017 996 hPa, 2010
Mean Wind Speed 8.0 mph (+2.9) 4.4 mph (-0.7) 8.8 mph, 2015 0.5 mph, 2016
Maximum Wind Speed 18.9 mph 13:22 11.7 mph 18.9 mph, 2020 4.7 mph, 2016
Maximum Gust 29.7 mph 14:08 18.5 mph 29.7 mph, 2020 6.3 mph, 2016
Mean Wind Direction SSW
Rainfall 2.8 mm 52.0 mm (154%) 7.5 mm, 2019
Maximum Hourly Rain 0.7 mm 06:16 3.7 mm, 2013
Maximum 10-min Rain 0.5 mm 13:41 2.0 mm, 2014
Maximum Rain Rate 18 mm/h 13:41 30 mm/h, 2014
Minimum Dew Point 6.0 °C 21:37 3.1 °C 9.4 °C, 2015 -8.0 °C, 2010
Maximum Dew Point 9.4 °C 10:28 6.5 °C 13.5 °C, 2015 -1.6 °C, 2010
Mean Dew Point 8.0 °C 4.9 °C 11.2 °C, 2015 -4.4 °C, 2010
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) * 10.0 °C * 05:25 5.2 °C 12.6 °C, 2015 -4.3 °C, 2010
Day Maximum (09-21) 12.0 °C 12:28 8.3 °C 16.0 °C, 2015 0.1 °C, 2010
Max 10m Temp Rise 0.3 °C 11:43 0.3 °C 0.3 °C, 2010 0.2 °C, 2011
Max 1hr Temp Rise 0.6 °C 11:51 1.0 °C 1.4 °C, 2017 0.3 °C, 2014
Max 1hr Hum Rise 9% 17:02 4% 9%, 2013 2%, 2015
Max 10m Temp Fall 0.5 °C 13:49 0.3 °C 0.9 °C, 2013 0.2 °C, 2015
Max 1hr Temp Fall 1.1 °C 13:51 0.9 °C 2.1 °C, 2013 0.4 °C, 2016
Max 1hr Hum Fall 6% 02:08 4% 17%, 2014 2%, 2016
Max 10m Wind Speed 13.9 mph 13:30 9.1 mph 13.9 mph, 2019 2.5 mph, 2016
Minimum Feels-like 8.0 °C 22:07 1.8 °C 14.9 °C, 2015 -9.8 °C, 2010
Maximum Feels-like 12.8 °C 12:27 8.5 °C 18.6 °C, 2015 0.0 °C, 2010
Mean Feels-like 10.6 °C 5.4 °C 16.7 °C, 2015 -5.9 °C, 2010
Air-frost Hrs 0 hrs 0.3 hrs 23 hrs, 2010 0 hrs, 2012
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 4.0 °C (-0.5) 3.7 °C (-1.1) 7.6 °C (+3.1), 2014 1.9 °C (-2.6), 2016
Humidity Range 13% 10% 34%, 2014 3%, 2016
Pressure Range 7 hPa 10 hPa 18 hPa, 2013 2 hPa, 2017
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 2 [29%]32 hrs (92%) [24%] 6.5 [93%], 2009 0 [0%], 2010
Wet Hours 5
[Mean rain rate: 0.6 mm/h]
55 hrs (143%) [12%] 7, 2012 0, 2009
Cloud Cover Partly Cloudy
Events None
Comments rn spells
Extra Comments
Issues wind from harpenden
Observer Absent? Yes - observations may be unreliable
Pond Temperature (Heath) 6.0 °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

daycamsumFull resolution individual images at up-to 5 minute intervals

Wind rose