December is one of the cooler months of the year in Harpenden, with average highs near 6.8°C and lows around 2.1°C (mean 4.5°C). It is about average for rainfall, averaging 67 mm of rainfall and 95% relative humidity across the period.
December is one of the cooler months of the year in Harpenden. Across 45 years of records, the warmest December in Harpenden was 2015 — when the month averaged 9.2°C — while the coldest were 1981 and 2010 at -0.6°C. Typical December days reach 6.8°C with nights near 2.1°C. The long-term trend is warming, about 0.5°C per decade.
December is about average for rainfall in Harpenden, averaging 67 mm of rainfall. The wettest December on record was 2012 with 118 mm, while the driest was 1988 at 19 mm.
Relative humidity in Harpenden during December averages 95%. The most humid December was 1981 at 97%, and the least humid was 2015 at 92%.
December receives about 0.6 kWh/m²/day of solar energy in Harpenden. The sunniest Decembers were 2001, 2008 and 2014 at 0.8 kWh/m²/day, and the cloudiest were 1998, 2002 and 2021, among others at 0.5.
Average wind speed in Harpenden during December is 3.7 m/s. The windiest December was 2015 at 5.2 m/s, while the calmest were 1995 and 2016 at 2.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 4.2°C | 3.8°C | 4.2°C | 5.0°C | 5.6°C | +1.4°C |
| Avg High | 6.5°C | 6.2°C | 6.6°C | 7.5°C | 7.9°C | +1.4°C |
| Avg Low | 1.8°C | 1.4°C | 2.0°C | 2.6°C | 3.4°C | +1.6°C |
| Avg Rain | 64 mm | 65 mm | 62 mm | 69 mm | 79 mm | +15 mm |
December temperatures in Harpenden have risen by about 2.3°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -8.6°C (1981) to a record high of 14.1°C (2015).
Rainfall in December is about average for rainfall, averaging 67 mm, with a wettest year of 118 mm.
A quieter season to visit Harpenden
If your dates are flexible, the more temperate months of July and August tend to be the most comfortable for visiting Harpenden. That said, December — with days averaging 6.8°C and nights around 2.1°C (mean 4.5°C) and moderate rainfall (67 mm) — can still be rewarding for travellers who don't mind the cooler conditions, and often means fewer crowds.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 8.7°C | 6.4°C | 4.1°C | 13.2°C | -1.6°C | 87 mm | 95% | 4 m/s | — |
| 2024 | 8.5°C | 6.4°C | 4.2°C | 13.8°C | 0.6°C | 54 mm | 95% | 4.1 m/s | 0.6 |
| 2023 | 8.7°C | 6.5°C | 4.3°C | 13.2°C | -3.4°C | 103 mm | 94% | 4.6 m/s | 0.6 |
| 2022 | 6.2°C | 3.8°C | 1.4°C | 12.0°C | -5.4°C | 61 mm | 96% | 3.4 m/s | 0.7 |
| 2021 | 8.4°C | 6.0°C | 3.7°C | 14.1°C | -3.2°C | 68 mm | 95% | 3.6 m/s | 0.5 |
| 2020 | 6.8°C | 4.6°C | 2.4°C | 12.5°C | -2.8°C | 101 mm | 96% | 3.4 m/s | 0.7 |
| 2019 | 8.0°C | 5.6°C | 3.3°C | 11.9°C | -2.3°C | 91 mm | 95% | 3.9 m/s | 0.7 |
| 2018 | 8.6°C | 6.2°C | 3.8°C | 12.9°C | -3.6°C | 83 mm | 95% | 3.5 m/s | 0.7 |
| 2017 | 6.5°C | 4.1°C | 1.8°C | 11.7°C | -4.1°C | 95 mm | 96% | 3.9 m/s | 0.6 |
| 2016 | 8.3°C | 5.8°C | 3.3°C | 12.8°C | -1.9°C | 26 mm | 97% | 2.7 m/s | 0.7 |
| 2015 🔥 | 11.4°C | 9.2°C | 7.0°C | 14.1°C | 2.9°C | 71 mm | 92% | 5.2 m/s | 0.6 |
| 2014 | 7.3°C | 4.6°C | 1.9°C | 12.4°C | -3.3°C | 51 mm | 94% | 4.1 m/s | 0.8 |
| 2013 | 8.5°C | 5.6°C | 2.8°C | 11.8°C | -0.3°C | 61 mm | 94% | 4.2 m/s | 0.7 |
| 2012 🌧️ | 6.6°C | 4.2°C | 1.8°C | 12.1°C | -4.0°C | 118 mm | 96% | 4 m/s | 0.7 |
| 2011 | 7.8°C | 5.3°C | 2.7°C | 11.6°C | -1.4°C | 69 mm | 93% | 4.5 m/s | 0.7 |
| 2010 | 1.5°C | -0.6°C | -2.7°C | 5.7°C | -6.3°C | 28 mm | 96% | 2.8 m/s | 0.6 |
| 2009 | 4.9°C | 2.8°C | 0.7°C | 11.2°C | -5.6°C | 83 mm | 96% | 3.3 m/s | 0.7 |
| 2008 | 5.5°C | 3.1°C | 0.8°C | 11.5°C | -3.6°C | 40 mm | 96% | 3 m/s | 0.8 |
| 2007 | 7.3°C | 4.5°C | 1.7°C | 13.3°C | -3.1°C | 51 mm | 94% | 3.9 m/s | 0.7 |
| 2006 | 8.5°C | 6.3°C | 4.1°C | 12.5°C | -0.2°C | 61 mm | 94% | 4.1 m/s | 0.6 |
| 2005 | 6.3°C | 4.1°C | 1.9°C | 10.0°C | -3.4°C | 46 mm | 95% | 3.3 m/s | 0.7 |
| 2004 | 6.9°C | 4.5°C | 2.2°C | 11.5°C | -3.0°C | 39 mm | 96% | 3 m/s | 0.6 |
| 2003 | 6.8°C | 4.3°C | 1.8°C | 12.0°C | -3.1°C | 72 mm | 95% | 3.3 m/s | 0.6 |
| 2002 | 7.0°C | 5.0°C | 3.0°C | 12.1°C | -2.7°C | 109 mm | 95% | 3.4 m/s | 0.5 |
| 2001 | 5.6°C | 2.7°C | -0.1°C | 12.3°C | -3.8°C | 29 mm | 95% | 3.2 m/s | 0.8 |
| 2000 | 6.9°C | 5.2°C | 3.4°C | 12.5°C | -3.0°C | 93 mm | 95% | 4.2 m/s | 0.6 |
| 1999 | 6.3°C | 4.0°C | 1.6°C | 12.1°C | -4.6°C | 82 mm | 94% | 4.5 m/s | 0.6 |
| 1998 | 7.4°C | 5.0°C | 2.5°C | 13.1°C | -3.6°C | 79 mm | 96% | 3.7 m/s | 0.5 |
| 1997 | 7.2°C | 5.2°C | 3.1°C | 12.6°C | -1.9°C | 75 mm | 95% | 3.9 m/s | 0.5 |
| 1996 | 4.3°C | 1.9°C | -0.6°C | 11.0°C | -7.1°C | 32 mm | 93% | 3 m/s | 0.6 |
| 1995 | 3.4°C | 1.2°C | -1.0°C | 10.6°C | -6.5°C | 88 mm | 96% | 2.7 m/s | 0.6 |
| 1994 | 8.3°C | 5.8°C | 3.2°C | 13.2°C | -3.3°C | 68 mm | 95% | 4.4 m/s | 0.7 |
| 1993 | 6.9°C | 4.4°C | 2.0°C | 13.1°C | -3.4°C | 95 mm | 94% | 4.8 m/s | 0.6 |
| 1992 | 5.6°C | 3.1°C | 0.6°C | 12.5°C | -3.9°C | 49 mm | 96% | 3.3 m/s | 0.7 |
| 1991 | 6.0°C | 3.6°C | 1.2°C | 12.6°C | -6.7°C | 22 mm | 94% | 3 m/s | 0.7 |
| 1990 | 6.1°C | 3.5°C | 0.9°C | 11.1°C | -2.8°C | 56 mm | 93% | 3.8 m/s | 0.6 |
| 1989 | 6.4°C | 4.2°C | 2.0°C | 12.4°C | -3.0°C | 113 mm | 95% | 3.2 m/s | 0.6 |
| 1988 | 8.3°C | 6.0°C | 3.6°C | 12.2°C | -1.5°C | 19 mm | 95% | 3.6 m/s | 0.6 |
| 1987 | 7.0°C | 4.9°C | 2.7°C | 13.0°C | -3.8°C | 31 mm | 96% | 3.5 m/s | 0.5 |
| 1986 | 7.4°C | 4.7°C | 2.0°C | 13.7°C | -2.4°C | 70 mm | 94% | 4.7 m/s | 0.6 |
| 1985 | 7.9°C | 6.0°C | 4.0°C | 13.0°C | -5.8°C | 92 mm | 94% | 4 m/s | 0.5 |
| 1984 | 6.8°C | 4.5°C | 2.2°C | 11.1°C | -2.6°C | 69 mm | 96% | 2.9 m/s | 0.6 |
| 1983 | 7.0°C | 4.5°C | 2.1°C | 12.3°C | -4.4°C | 60 mm | 94% | 4 m/s | — |
| 1982 | 5.9°C | 3.2°C | 0.5°C | 11.3°C | -4.0°C | 60 mm | 95% | 3.7 m/s | — |
| 1981 ❄️ | 1.9°C | -0.6°C | -3.1°C | 10.0°C | -8.6°C | 64 mm | 97% | 3.1 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 6.8°C with lows near 2.1°C (mean 4.5°C), based on 45 years of NASA POWER data.
December averages 67 mm of rainfall in Harpenden, about average for rainfall. The wettest on record was 118 mm in 2012.
The hottest December reached 14.1°C in 2015. The coldest dipped to -8.6°C in 1981.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 2.3°C. Daytime highs moved from 5.9°C to 8.1°C and overnight lows from 1.1°C to 3.5°C over the same span.
December is one of the cooler months of the year in Harpenden and about average for rainfall, so plan for around 6.8°C daytime highs and 2.1°C at night.
Not quite — December is the 3rd coolest month in Harpenden, averaging 4.5°C.
For December in Harpenden, pack warm layers and a jacket for chilly mornings, with typical highs of 6.8°C and lows of 2.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 95% — quite humid.
Average wind speed in December is 3.7 m/s. The windiest December on record averaged 5.2 m/s (2015).
The wettest December on record was 2012 with 118 mm. On average, December sees 67 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Harpenden behaves each December, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for December specifically, along with year-by-year records and how the month has changed over the decades.
