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 | n/a | SSE | NW, 2023 | NE, 2010 | |
| Rainfall | 6.0 mm | 50.0 mm (129%) | 9.5 mm, 2018 | 0.0 mm, 2012 | |
| Maximum Hourly Rain | n/a | 14:57 | 1.0 mm | 4.4 mm, 2018 | 0.2 mm, 2016 |
| Maximum 10-min Rain | n/a | 20:41 | 0.2 mm | 1.2 mm, 2013 | 0.2 mm, 2016 |
| Maximum Rain Rate | n/a | 14:57 | 0.3 mm/h | 54 mm/h, 2013 | 0.6 mm/h, 2011 |
| 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% | 16%, 2024 | 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 | |
| Minimum PM2.5 | n/a | 0.0 µg/m3 | 0.0 µg/m3, 2009 | 0.0 µg/m3, 2009 | |
| Maximum PM2.5 | n/a | 0.0 µg/m3 | n/a | n/a | |
| Mean PM2.5 | n/a | 0.0 µg/m3 | n/a | n/a | |
| Measure | Value (anomaly) | Month cumul. | Record High | Record Low | |
| Temperature Range | 4.5 °C (+0.2) | 4.4 °C | 7.0 °C, 2014 | 1.1 °C, 2010 | |
| Humidity Range | 13% | 16% | 23%, 2018 | 4%, 2010 | |
| Pressure Range | 13 hPa | 8 hPa | 13 hPa, 2019 | 1 hPa, 2017 | |
| Observation | Detail | ||||
| Sun Hours | 0 hrs [0%] | ||||
| Wet Hours | 6 hrs | ||||
| Cloud Cover | not available | ||||
| Events | Snowfall, Lying Snow, Air Frost | ||||
| Comments | LS: 2cm; 11-15 SL-M Rn; 15-17 H Lyn Snwxx | ||||
| Observer Absent? | No | ||||
| Pond Temperature | 0.0 °C | ||||
- Notes
- Detailed daily weather report for Hampstead, NW3, London on 21st December 2009. Times of extremes use the midpoint of the longest continuous period at that value. Cumulative anomalies are relative to the expected value for the month-to-date. Sun and wet hours are derived from webcam/rainfall analysis and may be adjusted. Data should be viewed with appropriate caution.
Daily Graph of Conditions
Wind direction
Air pollution
Wind rose
Webcam Summary of Cloud Conditions
Webcam summary not available for this day.