Daily Report for 21st July 2017

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Measure Value (anomaly) Time Month cumul. Record High Record Low
Minimum Temperature 13.6 °C (-1.0) 05:13 15.8 °C (+1.7) 17.6 °C (+3.0), 2024 9.7 °C (-4.9), 2020
Maximum Temperature 22.6 °C (-0.7) 17:17 24.6 °C (+1.7) 29.9 °C (+6.6), 2021 19.3 °C (-4.0), 2011
Mean Temperature 18.4 °C (-0.9) 20.1 °C (+1.7) 23.2 °C, 2021 14.9 °C, 2011
Minimum Humidity 45% 15:34 45% 67%, 2011 34%, 2010
Maximum Humidity 76% 23:57 78% 95%, 2009 76%, 2010
Mean Humidity 59% 61% 88%, 2011 53%, 2010
Minimum Pressure 1005 hPa 20:26 1013 hPa 1026 hPa, 2020 1000 hPa, 2025
Maximum Pressure 1011 hPa 03:53 1019 hPa 1028 hPa, 2020 1007 hPa, 2025
Mean Pressure 1008 hPa 1016 hPa 1027 hPa, 2020 1002 hPa, 2025
Mean Wind Speed 6.6 mph (+2.3) 3.7 mph (-0.6) 8.1 mph, 2009 1.1 mph, 2021
Maximum Wind Speed 16.0 mph 08:23 11.4 mph 16.0 mph, 2017 6.6 mph, 2018
Maximum Gust 24.1 mph 08:23 17.5 mph 29.0 mph, 2009 10.2 mph, 2012
Mean Wind Direction S
Rainfall 3.5 mm 49.4 mm (159%) 4.1 mm, 2011
Maximum Hourly Rain 2.0 mm 23:52 3.6 mm, 2011
Maximum 10-min Rain 0.5 mm 23:40 1.6 mm, 2011
Maximum Rain Rate 10 mm/h 23:39 30 mm/h, 2011
Minimum Dew Point 7.9 °C 00:29 9.1 °C 15.5 °C, 2021 6.7 °C, 2020
Maximum Dew Point 12.4 °C 23:35 14.6 °C 20.9 °C, 2021 9.7 °C, 2020
Mean Dew Point 9.9 °C 11.9 °C 17.9 °C, 2021 8.2 °C, 2020
Measure Value Time Month cumul. Record High Record Low
Night Minimum (21-09) 13.6 °C 05:13 15.9 °C 17.9 °C, 2010 9.7 °C, 2020
Day Maximum (09-21) 22.6 °C 17:17 24.6 °C 29.9 °C, 2021 19.3 °C, 2011
Max 10m Temp Rise 0.8 °C 11:41 0.6 °C 0.9 °C, 2012 0.4 °C, 2011
Max 1hr Temp Rise 2.4 °C 12:28 2.2 °C 3.3 °C, 2018 1.5 °C, 2011
Max 1hr Hum Rise 13% 23:11 8% 16%, 2010 5%, 2024
Max 10m Temp Fall 0.5 °C 23:05 0.5 °C 0.6 °C, 2009 0.3 °C, 2016
Max 1hr Temp Fall 1.8 °C 23:01 1.9 °C 2.4 °C, 2020 1.1 °C, 2016
Max 1hr Hum Fall 8% 12:15 10% 17%, 2012 6%, 2022
Max 10m Wind Speed 11.4 mph 08:25 8.4 mph 11.8 mph, 2015 3.4 mph, 2009
Minimum Feels-like 14.3 °C 04:58 17.4 °C 20.9 °C, 2021 8.6 °C, 2020
Maximum Feels-like 24.1 °C 16:52 27.4 °C 37.5 °C, 2021 21.8 °C, 2012
Mean Feels-like 19.6 °C 22.4 °C 29.2 °C, 2021 17.1 °C, 2012
Air-frost Hrs 0 hrs 0 hrs 0 hrs, 2009 0 hrs, 2009
Measure Value (anomaly) Month cumul. Record High Record Low
Temperature Range 9.0 °C (+0.4) 8.9 °C (-0.1) 13.3 °C (+4.6), 2021 5.5 °C (-3.2), 2024
Humidity Range 31% 33% 51%, 2018 26%, 2023
Pressure Range 6 hPa 6 hPa 11 hPa, 2009 2 hPa, 2023
Measure Value [% of max] Month cumul. Record High Record Low
Sun Hours 6 [41%]133 hrs (99%) [43%] 13 [89%], 2021 0.2 [1%], 2011
Wet Hours 2
[Mean rain rate: 1.8 mm/h]		19 hrs (82%) [3.8%] 4, 2009 0, 2010
Cloud Cover Partly Cloudy with periods of Mostly Sunny
Events None
Comments 22- Rain
Extra Comments
Issues Rn data from brixton (switched at 23 from faulty n16)
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 July 2017.
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

day graph

Webcam Summary of Cloud Conditions

daycamsumLarge resolution version

Wind rose