Daily Report for 23rd January 2019
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| Measure | Value (anomaly) | Time | Month cumul. | Record High | Record Low |
| Minimum Temperature | -2.2 °C (-4.5) | 23:11 | 2.6 °C (+0.2) | 8.2 °C (+5.9), 2018 | -4.1 °C (-6.4), 2015 |
| Maximum Temperature | 1.8 °C (-5.2) | 15:15 | 7.0 °C (-0.0) | 12.7 °C (+5.7), 2018 | 1.8 °C (-5.2), 2019 |
| Mean Temperature | 0.1 °C (-4.8) | 5.0 °C (+0.1) | 10.6 °C, 2018 | 0.1 °C, 2019 | |
| Minimum Humidity | 86% | 15:07 | 74% | 88%, 2010 | 49%, 2009 |
| Maximum Humidity | 94% | 21:56 | 89% | 98%, 2010 | 83%, 2012 |
| Mean Humidity | 90% | 83% | 95%, 2010 | 71%, 2009 | |
| Minimum Pressure | 997 hPa | 03:03 | 1021 hPa | 1033 hPa, 2011 | 967 hPa, 2009 |
| Maximum Pressure | 1010 hPa | 23:58 | 1028 hPa | 1037 hPa, 2020 | 985 hPa, 2009 |
| Mean Pressure | 1003 hPa | 1024 hPa | 1034 hPa, 2011 | 976 hPa, 2009 | |
| Mean Wind Speed | 2.7 mph (-2.5) | 4.2 mph (-1.0) | 8.1 mph, 2018 | 0.2 mph, 2017 | |
| Maximum Wind Speed | 9.3 mph | 10:38 | 11.9 mph | 16.8 mph, 2018 | 3.7 mph, 2017 |
| Maximum Gust | 15.0 mph | 02:46 | 18.4 mph | 30.0 mph, 2018 | 4.2 mph, 2017 |
| Mean Wind Direction | N | ||||
| Rainfall | 0.0 mm | 12.6 mm (31%) | 11.0 mm, 2009 | ||
| Maximum Hourly Rain | n/a | 5, 2009 | |||
| Maximum 10-min Rain | n/a | 0.9, 2014 | |||
| Maximum Rain Rate | n/a | 6, 2014 | |||
| Minimum Dew Point | -3.2 °C | 23:08 | 0.1 °C | 5.0 °C, 2018 | -5.6 °C, 2015 |
| Maximum Dew Point | -0.1 °C | 15:13 | 4.2 °C | 11.1 °C, 2018 | -0.5 °C, 2013 |
| Mean Dew Point | -1.2 °C | 2.3 °C | 8.5 °C, 2018 | -1.3 °C, 2013 | |
| Measure | Value | Time | Month cumul. | Record High | Record Low |
| Night Minimum (21-09) | * 0.2 °C * | 03:56 | 3.4 °C | 7.7 °C, 2018 | -4.1 °C, 2015 |
| Day Maximum (09-21) | 1.8 °C | 15:18 | 6.8 °C | 12.7 °C, 2018 | 1.8 °C, 2019 |
| Max 10m Temp Rise | 0.2 °C | 20:38 | 0.3 °C | 0.5 °C, 2015 | 0.1 °C, 2010 |
| Max 1hr Temp Rise | 0.4 °C | 15:10 | 1.1 °C | 2.0 °C, 2015 | 0.1 °C, 2010 |
| Max 1hr Hum Rise | 3% | 17:34 | 4% | 7%, 2018 | 2%, 2010 |
| Max 10m Temp Fall | 0.4 °C | 16:54 | 0.4 °C | 0.4 °C, 2016 | 0.1 °C, 2011 |
| Max 1hr Temp Fall | 1.7 °C | 17:34 | 1.2 °C | 1.7 °C, 2019 | 0.3 °C, 2020 |
| Max 1hr Hum Fall | 2% | 01:17 | 6% | 21%, 2014 | 2%, 2017 |
| Max 10m Wind Speed | 7.4 mph | 11:41 | 8.7 mph | 12.7 mph, 2018 | 2.2 mph, 2017 |
| Minimum Feels-like | -5.3 °C | 02:46 | -0.7 °C | 4.9 °C, 2018 | -6.2 °C, 2015 |
| Maximum Feels-like | 1.7 °C | 14:49 | 6.7 °C | 14.3 °C, 2018 | 1.7 °C, 2019 |
| Mean Feels-like | -2.0 °C | 3.1 °C | 10.2 °C, 2018 | -2.3 °C, 2013 | |
| Air-frost Hrs | 7 hrs | 1 hrs | 11 hrs, 2015 | 0 hrs, 2010 | |
| Measure | Value (anomaly) | Month cumul. | Record High | Record Low | |
| Temperature Range | 4.0 °C (-0.7) | 4.4 °C (-0.2) | 11.4 °C (+6.7), 2015 | 1.4 °C (-3.3), 2013 | |
| Humidity Range | 8% | 15% | 44%, 2009 | 5%, 2017 | |
| Pressure Range | 13 hPa | 8 hPa | 18 hPa, 2009 | 2 hPa, 2011 | |
| Measure | Value [% of max] | Month cumul. | Record High | Record Low | |
| Sun Hours | 1.2 [15%] | 45 hrs (102%) [26%] | 6 [77%], 2015 | 0 [0%], 2011 | |
| Wet Hours | 0 | 13 hrs (27%) [2.4%] | 2, 2015 | , 2009 | |
| Cloud Cover | Partly Cloudy with periods of Mostly Cloudy | ||||
| Events | Lying Snow (at 09z): ~1 cm | ||||
| Comments | snow patches persisted | ||||
| Extra Comments | |||||
| Issues | snow melt reassigned | ||||
| Observer Absent? | Yes - observations may be unreliable | ||||
| Pond Temperature (Heath) | n/a | ||||
- 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.
Daily Graph of Conditions
Webcam Summary of Cloud Conditions
Full resolution individual images at up-to 5 minute intervals