Daily Report for 19th January 2021

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 8.6 °C (+6.3) 00:02 1.0 °C (-1.4) 8.6 °C (+6.3), 2021 -3.5 °C (-5.8), 2016
Maximum Temperature 11.7 °C (+4.7) 10:54 5.9 °C (-1.1) 11.7 °C (+4.7), 2021 0.4 °C (-6.6), 2013
Mean Temperature 10.3 °C (+5.5) 3.5 °C (-1.3) 10.3 °C, 2021 -0.9 °C, 2016
Minimum Humidity 81% 12:39 84% 95%, 2010 55%, 2016
Maximum Humidity 95% 04:25 94% 98%, 2010 80%, 2017
Mean Humidity 89% 90% 98%, 2010 72%, 2017
Minimum Pressure 997 hPa 23:56 1016 hPa 1037 hPa, 2020 977 hPa, 2009
Maximum Pressure 1012 hPa 00:00 1023 hPa 1050 hPa, 2020 998 hPa, 2009
Mean Pressure 1004 hPa 1020 hPa 1045 hPa, 2020 988 hPa, 2009
Mean Wind Speed 12.1 mph (+6.9) 4.2 mph (-1.0) 12.1 mph, 2021 0.3 mph, 2016
Maximum Wind Speed 21.8 mph 23:12 11.7 mph 21.8 mph, 2021 5.4 mph, 2016
Maximum Gust 33.1 mph 08:18 18.6 mph 33.1 mph, 2021 6.2 mph, 2016
Mean Wind Direction WSW
Rainfall 3.6 mm 45.9 mm (136%) 13.0 mm, 2009
Maximum Hourly Rain 2.2 mm 02:42 7.0 mm, 2009
Maximum 10-min Rain 0.7 mm 02:13 0.9 mm, 2012
Maximum Rain Rate 4.8 mm/h 02:13 15 mm/h, 2012
Minimum Dew Point 7.5 °C 00:02 -0.3 °C 7.5 °C, 2021 -7.8 °C, 2016
Maximum Dew Point 9.8 °C 05:48 4.3 °C 11.3 °C, 2012 -0.7 °C, 2016
Mean Dew Point 8.6 °C 2.1 °C 8.6 °C, 2021 -4.9 °C, 2016
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) * 8.0 °C * 21:01 1.8 °C 8.1 °C, 2012 -3.5 °C, 2016
Day Maximum (09-21) 11.7 °C 10:54 5.6 °C 11.7 °C, 2021 0.4 °C, 2013
Max 10m Temp Rise 0.2 °C 05:08 0.3 °C 0.8 °C, 2016 0.1 °C, 2010
Max 1hr Temp Rise 0.7 °C 01:04 1.0 °C 2.9 °C, 2016 0.3 °C, 2010
Max 1hr Hum Rise 5% 13:50 4% 9%, 2012 1%, 2010
Max 10m Temp Fall 0.2 °C 13:54 0.4 °C 1.9 °C, 2012 0.1 °C, 2013
Max 1hr Temp Fall 0.7 °C 14:05 1.1 °C 3.5 °C, 2012 0.3 °C, 2013
Max 1hr Hum Fall 8% 12:38 4% 13%, 2012 1%, 2010
Max 10m Wind Speed 16.1 mph 20:17 9.3 mph 16.1 mph, 2021 3.3 mph, 2016
Minimum Feels-like 4.9 °C 00:20 -3.2 °C 4.9 °C, 2021 -7.6 °C, 2013
Maximum Feels-like 12.9 °C 11:09 5.5 °C 13.5 °C, 2012 0.3 °C, 2013
Mean Feels-like 9.8 °C 1.4 °C 9.8 °C, 2021 -4.3 °C, 2013
Air-frost Hrs 0 hrs 3 hrs 17 hrs, 2016 0 hrs, 2010
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 3.1 °C (-1.6) 4.9 °C (+0.3) 7.1 °C (+2.4), 2016 1.2 °C (-3.5), 2013
Humidity Range 14% 10% 36%, 2012 3%, 2010
Pressure Range 15 hPa 7 hPa 21 hPa, 2009 2 hPa, 2011
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 0 [0%]22 hrs (61%) [16%] 7.6 [100%], 2020 0 [0%], 2010
Wet Hours 4
[Mean rain rate: 0.9 mm/h]
51 hrs (124%) [11%] 6, 2012 , 2009
Cloud Cover Overcast
Events None
Comments o.night rn
Extra Comments
Issues wind from harpenden
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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Webcam Summary of Cloud Conditions

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