Daily Report for 21st December 2018

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 9.1 °C (+5.7) 00:07 5.4 °C (+1.7) 10.1 °C (+6.7), 2023 -2.9 °C (-6.3), 2009
Maximum Temperature 12.5 °C (+4.8) 08:28 10.0 °C (+1.7) 13.6 °C (+5.9), 2023 1.4 °C (-6.3), 2010
Mean Temperature 11.1 °C (+5.2) 7.9 °C (+1.7) 11.6 °C, 2023 -0.5 °C, 2009
Minimum Humidity 72% 14:47 77% 93%, 2010 68%, 2023
Maximum Humidity 95% 02:06 93% 98%, 2009 83%, 2016
Mean Humidity 85% 86% 96%, 2010 79%, 2016
Minimum Pressure 995 hPa 05:46 1007 hPa 1035 hPa, 2017 972 hPa, 2019
Maximum Pressure 1007 hPa 19:31 1016 hPa 1036 hPa, 2017 986 hPa, 2019
Mean Pressure 1002 hPa 1012 hPa 1035 hPa, 2017 980 hPa, 2019
Mean Wind Speed 9.2 mph (+4.1) 6.0 mph (+0.9) 11.9 mph, 2013 0.3 mph, 2021
Maximum Wind Speed 23.3 mph 12:43 15.0 mph 23.3 mph, 2018 5.5 mph, 2021
Maximum Gust 39.2 mph 12:43 24.2 mph 39.2 mph, 2018 10.2 mph, 2009
Mean Wind Direction SW
Rainfall 9.5 mm 56.2 mm (146%) 9.5 mm, 2018
Maximum Hourly Rain 4.4 mm 01:33 4.4 mm, 2018
Maximum 10-min Rain 1.1 mm 01:31 1.2 mm, 2013
Maximum Rain Rate 13 mm/h 00:22 54 mm/h, 2013
Minimum Dew Point 6.6 °C 16:30 3.2 °C 8.3 °C, 2017 -4.4 °C, 2009
Maximum Dew Point 11.4 °C 07:06 8.0 °C 12.2 °C, 2020 0.8 °C, 2010
Mean Dew Point 8.6 °C 5.7 °C 9.8 °C, 2020 -1.5 °C, 2009
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) * 8.5 °C * 21:26 6.2 °C 10.1 °C, 2017 -2.9 °C, 2009
Day Maximum (09-21) * 12.3 °C * 09:03 9.8 °C 13.6 °C, 2023 1.4 °C, 2010
Max 10m Temp Rise 0.3 °C 00:57 0.3 °C 1.3 °C, 2009 0.1 °C, 2010
Max 1hr Temp Rise 1.0 °C 01:35 1.1 °C 1.9 °C, 2009 0.4 °C, 2017
Max 1hr Hum Rise 6% 22:35 6% 10%, 2013 2%, 2010
Max 10m Temp Fall 0.3 °C 09:29 0.3 °C 1.3 °C, 2009 0.1 °C, 2010
Max 1hr Temp Fall 1.2 °C 09:53 1.0 °C 2.0 °C, 2021 0.3 °C, 2010
Max 1hr Hum Fall 11% 10:03 6% 16%, 2024 2%, 2010
Max 10m Wind Speed 18.8 mph 11:55 11.3 mph 18.8 mph, 2018 3.5 mph, 2021
Minimum Feels-like 7.0 °C 01:00 2.2 °C 10.1 °C, 2023 -5.7 °C, 2009
Maximum Feels-like 14.4 °C 08:28 10.4 °C 15.7 °C, 2020 1.4 °C, 2010
Mean Feels-like 11.7 °C 6.7 °C 12.2 °C, 2023 -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 3.4 °C (-0.9) 4.6 °C (-0.0) 7.0 °C (+2.7), 2014 1.1 °C (-3.2), 2010
Humidity Range 23% 16% 23%, 2018 4%, 2010
Pressure Range 12 hPa 10 hPa 13 hPa, 2019 1 hPa, 2017
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 0.3 [4%]42 hrs (95%) [28%] 2.5 [36%], 2012 0 [0%], 2009
Wet Hours 7
[Mean rain rate: 1.4 mm/h]		54 hrs (129%) [11%] 12, 2013 0, 2012
Cloud Cover Mostly Cloudy with periods of Partly Cloudy
Events None
Comments o.night Rain; 09 Shower
Extra Comments
Issues None known
Observer Absent? Yes - observations may be unreliable
Pond Temperature @ Hampstead Heath 0.0 °C
Notes
Detailed daily weather report for Hampstead nw3 in London on 21st December 2018.
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 derived based on analysis of webcam observations, but may use data from our closest site, Heathrow, when needed.
Wet hrs are dervied algorithmically from rainfall data, though may be adjusted manually.
Rainfall totals may be manually adjusted after the fact to correct delayed or erroneous data.
Cloud cover and Events are manually reported, often with multi-week delays.
Data is generally reliable and accurate but should always be viewed with some quantity of salt to hand.
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Daily Graph of Conditions

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Webcam Summary of Cloud Conditions

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Wind rose