Daily Report for 21st December 2009
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| Measure | Value (anomaly) | Time | Month cumul. | Record High | Record Low |
| Minimum Temperature | -2.9 °C (-6.3) | 09:04 | 2.0 °C (-1.7) | 10.1 °C (+6.7), 2023 | -2.9 °C (-6.3), 2009 |
| Maximum Temperature | 1.6 °C (-6.1) | 14:23 | 6.4 °C (-1.9) | 13.6 °C (+5.9), 2023 | 1.4 °C (-6.3), 2010 |
| Mean Temperature | -0.5 °C (-6.2) | 4.3 °C (-1.8) | 11.6 °C, 2023 | -0.5 °C, 2009 | |
| Minimum Humidity | 85% | 02:59 | 81% | 93%, 2010 | 68%, 2023 |
| Maximum Humidity | 98% | 21:00 | 97% | 98%, 2009 | 83%, 2016 |
| Mean Humidity | 93% | 90% | 96%, 2010 | 79%, 2016 | |
| Minimum Pressure | 984 hPa | 20:59 | 1006 hPa | 1035 hPa, 2017 | 972 hPa, 2019 |
| Maximum Pressure | 997 hPa | 01:49 | 1014 hPa | 1036 hPa, 2017 | 986 hPa, 2019 |
| Mean Pressure | 990 hPa | 1010 hPa | 1035 hPa, 2017 | 980 hPa, 2019 | |
| Mean Wind Speed | 2.0 mph (-3.1) | 4.6 mph (-0.5) | 11.9 mph, 2013 | 0.3 mph, 2021 | |
| Maximum Wind Speed | 8.1 mph | 11.0 mph | 23.3 mph, 2018 | 5.5 mph, 2021 | |
| Maximum Gust | 10.2 mph | 00:47 | 16.4 mph | 39.2 mph, 2018 | 10.2 mph, 2009 |
| Mean Wind Direction | SE | ||||
| Rainfall / Snow-melt approx. | 6.0 mm | 50.0 mm (129%) | 9.5 mm, 2018 | ||
| Maximum Hourly Rain | n/a | 14:57 | 4.4, 2018 | ||
| Maximum 10-min Rain | n/a | 20:41 | 1.2, 2013 | ||
| Maximum Rain Rate | n/a | 14:57 | 54, 2013 | ||
| Minimum Dew Point | -4.4 °C | 06:34 | 0.3 °C | 8.3 °C, 2017 | -4.4 °C, 2009 |
| Maximum Dew Point | 1.2 °C | 14:18 | 5.6 °C | 12.2 °C, 2020 | 0.8 °C, 2010 |
| Mean Dew Point | -1.5 °C | 2.9 °C | 9.8 °C, 2020 | -1.5 °C, 2009 | |
| Measure | Value | Time | Month cumul. | Record High | Record Low |
| Night Minimum (21-09) | -2.9 °C | 2.8 °C | 10.1 °C, 2017 | -2.9 °C, 2009 | |
| Day Maximum (09-21) | 1.6 °C | 6.2 °C | 13.6 °C, 2023 | 1.4 °C, 2010 | |
| Max 10m Temp Rise | 1.3 °C | 12:08 | 0.4 °C | 1.3 °C, 2009 | 0.1 °C, 2010 |
| Max 1hr Temp Rise | 1.9 °C | 12:54 | 1.0 °C | 1.9 °C, 2009 | 0.4 °C, 2017 |
| Max 1hr Hum Rise | 5% | 15:42 | 4% | 10%, 2013 | 2%, 2010 |
| Max 10m Temp Fall | 1.3 °C | 14:42 | 0.4 °C | 1.3 °C, 2009 | 0.1 °C, 2010 |
| Max 1hr Temp Fall | 1.2 °C | 14:42 | 0.9 °C | 2.0 °C, 2021 | 0.3 °C, 2010 |
| Max 1hr Hum Fall | 6% | 14:42 | 6% | 12%, 2013 | 2%, 2010 |
| Max 10m Wind Speed | 5.4 mph | 00:52 | 7.8 mph | 18.8 mph, 2018 | 3.5 mph, 2021 |
| Minimum Feels-like | -5.7 °C | 06:12 | -1.3 °C | 10.1 °C, 2023 | -5.7 °C, 2009 |
| Maximum Feels-like | 1.6 °C | 13:56 | 6.9 °C | 15.7 °C, 2020 | 1.4 °C, 2010 |
| Mean Feels-like | -0.9 °C | 3.1 °C | 12.2 °C, 2023 | -1.2 °C, 2010 | |
| Air-frost Hrs | 13 hrs | 3 hrs | 13 hrs, 2009 | 0 hrs, 2010 | |
| Measure | Value (anomaly) | Month cumul. | Record High | Record Low | |
| Temperature Range | 4.5 °C (+0.2) | 4.4 °C (-0.2) | 7.0 °C (+2.7), 2014 | 1.1 °C (-3.2), 2010 | |
| Humidity Range | 13% | 16% | 23%, 2018 | 4%, 2010 | |
| Pressure Range | 13 hPa | 8 hPa | 13 hPa, 2019 | 1 hPa, 2017 | |
| Measure | Value [% of max] | Month cumul. | Record High | Record Low | |
| Sun Hours | 0 [0%] | 59 hrs (134%) [40%] | 2.5 [36%], 2012 | 0 [0%], 2009 | |
| Wet Hours | 6 [Mean rain rate: 1.0 mm/h] | 59 hrs (139%) [12%] | 12, 2013 | 0, 2012 | |
| Cloud Cover | not available | ||||
| Events | Snowfall: ~6 cm Lying Snow (at 09z): ~2 cm Air Frost | ||||
| Comments | LS: 2cm; 11-15 SLight-Moderate Rain; 15-17 Heavy Lying Snow | ||||
| Extra Comments | 2cm Lying Snow remains 11-1130 SLight Snow, 1230-15 SLight/Light Rain , Moderate Sleet, 15-17 Heavy Lying Snow to 6cm | ||||
| Issues | None known | ||||
| Observer Absent? | No | ||||
| Pond Temperature (Heath) | 0.0 °C | ||||
- Notes
- Detailed daily weather report for Hampstead nw3 in London on 21st December 2009.
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.
Daily Graph of Conditions
Webcam Summary of Cloud Conditions
Webcam summary not available for this day