Daily Report for 11th March 2021

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 5.2 °C (+2.0) 23:55 2.7 °C (-0.2) 11.0 °C (+7.8), 2017 -2.1 °C (-5.3), 2013
Maximum Temperature 11.8 °C (+2.0) 13:05 8.1 °C (-1.3) 16.9 °C (+7.1), 2017 0.6 °C (-9.2), 2013
Mean Temperature 9.4 °C (+2.0) 5.4 °C (-0.7) 13.4 °C, 2017 -0.8 °C, 2013
Minimum Humidity 58% 14:40 68% 83%, 2018 46%, 2015
Maximum Humidity 88% 01:20 91% 97%, 2009 79%, 2013
Mean Humidity 74% 81% 92%, 2018 66%, 2019
Minimum Pressure 990 hPa 04:45 1020 hPa 1034 hPa, 2012 988 hPa, 2018
Maximum Pressure 1007 hPa 23:56 1028 hPa 1038 hPa, 2012 997 hPa, 2018
Mean Pressure 997 hPa 1024 hPa 1036 hPa, 2012 992 hPa, 2018
Mean Wind Speed 15.1 mph (+9.9) 4.5 mph (-0.7) 15.1 mph, 2021 1.4 mph, 2016
Maximum Wind Speed 27.9 mph 04:33 12.6 mph 29.5 mph, 2020 6.7 mph, 2016
Maximum Gust 45.6 mph 07:49 19.2 mph 45.6 mph, 2021 8.7 mph, 2012
Mean Wind Direction WSW
Rainfall 1.4 mm 11.2 mm (75%) 2.4 mm, 2018
Maximum Hourly Rain 1.2 mm 04:24 2.4 mm, 2018
Maximum 10-min Rain 1.0 mm 04:19 2.0 mm, 2018
Maximum Rain Rate 7 mm/h 04:17 40 mm/h, 2018
Minimum Dew Point 2.0 °C 21:58 0.1 °C 6.5 °C, 2017 -9.0 °C, 2013
Maximum Dew Point 9.0 °C 01:05 4.2 °C 11.0 °C, 2017 -2.6 °C, 2013
Mean Dew Point 5.0 °C 2.2 °C 9.0 °C, 2017 -6.0 °C, 2013
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) * 8.9 °C * 04:40 3.0 °C 11.0 °C, 2017 -1.0 °C, 2013
Day Maximum (09-21) 11.8 °C 13:05 8.0 °C 16.9 °C, 2017 0.2 °C, 2013
Max 10m Temp Rise 0.6 °C 04:58 0.4 °C 1.1 °C, 2011 0.2 °C, 2014
Max 1hr Temp Rise 0.8 °C 10:11 1.2 °C 2.8 °C, 2012 0.8 °C, 2021
Max 1hr Hum Rise 16% 15:26 7% 16%, 2021 3%, 2017
Max 10m Temp Fall 0.8 °C 15:10 0.4 °C 1.0 °C, 2020 0.2 °C, 2015
Max 1hr Temp Fall 1.8 °C 15:20 1.2 °C 2.3 °C, 2012 0.6 °C, 2019
Max 1hr Hum Fall 9% 14:39 8% 13%, 2012 4%, 2014
Max 10m Wind Speed 21.6 mph 07:13 9.2 mph 21.6 mph, 2021 3.8 mph, 2016
Minimum Feels-like 1.0 °C 23:17 -0.5 °C 11.4 °C, 2017 -11.0 °C, 2013
Maximum Feels-like 11.8 °C 00:48 8.1 °C 18.7 °C, 2017 -3.9 °C, 2013
Mean Feels-like 7.6 °C 3.8 °C 14.2 °C, 2017 -7.6 °C, 2013
Air-frost Hrs 0 hrs 0.3 hrs 20 hrs, 2013 0 hrs, 2009
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 6.6 °C (-0.0) 5.4 °C (-1.1) 11.9 °C (+5.2), 2009 2.7 °C (-4.0), 2013
Humidity Range 30% 22% 40%, 2009 13%, 2018
Pressure Range 16 hPa 7 hPa 16 hPa, 2021 1 hPa, 2013
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 3 [29%]28 hrs (79%) [25%] 9 [87%], 2016 0.1 [1%], 2013
Wet Hours 1
[Mean rain rate: 1.4 mm/h]
13 hrs (69%) [4.9%] 1, 2013 , 2009
Cloud Cover am: Mostly Cloudy
pm: Partly Cloudy
Events None
Comments 04 rn, 15 sh
Extra Comments
Issues harpenden wind stopped at 08, replaced at 16. Came back online a few days later
Observer Absent? Yes - observations may be unreliable
Pond Temperature (Heath) 4.5 °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