December is one of the cooler months of the year in Castle Rock, with average highs near 4.9°C and lows around -6.6°C (mean -0.8°C). It is one of the drier months, averaging 19 mm of rainfall and 56% relative humidity across the period.
December is one of the cooler months of the year in Castle Rock. Across 45 years of records, the warmest December in Castle Rock was 2025 — when the month averaged 4.6°C — while the coldest was 1983 at -5.7°C. Typical December days reach 4.9°C with nights near -6.6°C. The long-term trend is warming, about 0.6°C per decade.
December is one of the drier months in Castle Rock, averaging 19 mm of rainfall. The wettest December on record was 2006 with 56 mm, while the driest was 2002 at 5 mm.
Relative humidity in Castle Rock during December averages 56%. The most humid December was 1983 at 70%, and the least humid was 2021 at 44%.
December receives about 2.3 kWh/m²/day of solar energy in Castle Rock. The sunniest Decembers were 1995, 2001 and 2021, among others at 2.5 kWh/m²/day, and the cloudiest was 1987 at 2.
Average wind speed in Castle Rock during December is 2.6 m/s. The windiest Decembers were 1996 and 2008 at 3.2 m/s, while the calmest was 1986 at 1.9 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | -2.0°C | -0.9°C | -1.3°C | -0.8°C | 1.6°C | +3.6°C |
| Avg High | 3.6°C | 4.8°C | 4.5°C | 5.0°C | 7.6°C | +4°C |
| Avg Low | -7.7°C | -6.6°C | -7.0°C | -6.6°C | -4.4°C | +3.3°C |
| Avg Rain | 23 mm | 14 mm | 19 mm | 18 mm | 19 mm | -4 mm |
December temperatures in Castle Rock have risen by about 4.2°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -23.8°C (1982) to a record high of 21.2°C (2021).
Rainfall in December is one of the drier months, averaging 19 mm, with a wettest year of 56 mm.
A quieter season to visit Castle Rock
If your dates are flexible, the more temperate months of July and August tend to be the most comfortable for visiting Castle Rock. That said, December — with days averaging 4.9°C and nights around -6.6°C (mean -0.8°C) and low rainfall (19 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 🔥 | 11.1°C | 4.6°C | -2.0°C | 19.2°C | -10.1°C | 16 mm | 50% | 2.9 m/s | — |
| 2024 | 8.8°C | 2.9°C | -2.9°C | 15.0°C | -8.4°C | 11 mm | 47% | 2.2 m/s | 2.3 |
| 2023 | 6.8°C | 1.4°C | -4.0°C | 15.6°C | -9.7°C | 22 mm | 55% | 2.5 m/s | 2.2 |
| 2022 | 5.0°C | -1.2°C | -7.4°C | 13.1°C | -21.1°C | 31 mm | 54% | 2.8 m/s | 2.1 |
| 2021 | 9.4°C | 2.9°C | -3.7°C | 21.2°C | -9.7°C | 14 mm | 44% | 2.9 m/s | 2.5 |
| 2020 | 4.7°C | -0.9°C | -6.5°C | 15.1°C | -12.6°C | 21 mm | 52% | 2.7 m/s | 2.2 |
| 2019 | 5.4°C | -0.2°C | -5.7°C | 12.2°C | -13.9°C | 17 mm | 55% | 2.3 m/s | 2.3 |
| 2018 | 4.7°C | -0.9°C | -6.5°C | 11.8°C | -17.4°C | 7 mm | 52% | 2.3 m/s | 2.4 |
| 2017 | 7.5°C | 1.3°C | -4.9°C | 15.7°C | -11.9°C | 12 mm | 49% | 2.5 m/s | 2.4 |
| 2016 | 4.1°C | -1.9°C | -8.0°C | 11.4°C | -18.0°C | 22 mm | 55% | 2.7 m/s | 2.4 |
| 2015 | 3.9°C | -1.5°C | -7.0°C | 13.8°C | -14.5°C | 20 mm | 58% | 2.6 m/s | 2.3 |
| 2014 | 4.7°C | -0.7°C | -6.1°C | 15.9°C | -20.2°C | 22 mm | 61% | 2 m/s | 2.1 |
| 2013 | 4.0°C | -2.2°C | -8.3°C | 12.0°C | -18.4°C | 15 mm | 59% | 2.7 m/s | 2.4 |
| 2012 | 5.0°C | -0.9°C | -6.8°C | 17.5°C | -13.9°C | 15 mm | 53% | 2.4 m/s | 2.1 |
| 2011 | 3.9°C | -1.9°C | -7.7°C | 12.7°C | -17.2°C | 30 mm | 59% | 2.4 m/s | 2.4 |
| 2010 | 7.1°C | 1.3°C | -4.6°C | 12.7°C | -17.2°C | 15 mm | 58% | 2.2 m/s | 2.3 |
| 2009 | 1.0°C | -4.6°C | -10.1°C | 9.7°C | -20.7°C | 19 mm | 60% | 2.6 m/s | 2.2 |
| 2008 | 4.1°C | -1.9°C | -7.9°C | 14.4°C | -18.0°C | 19 mm | 58% | 3.2 m/s | 2.3 |
| 2007 | 2.6°C | -3.0°C | -8.6°C | 15.4°C | -17.9°C | 30 mm | 61% | 2.9 m/s | 2.2 |
| 2006 🌧️ | 4.0°C | -1.6°C | -7.2°C | 14.1°C | -16.9°C | 56 mm | 67% | 2.7 m/s | 2.1 |
| 2005 | 4.6°C | -1.5°C | -7.6°C | 15.1°C | -20.0°C | 16 mm | 56% | 2.9 m/s | 2.3 |
| 2004 | 6.2°C | 0.5°C | -5.3°C | 11.6°C | -16.4°C | 12 mm | 56% | 2.8 m/s | 2.4 |
| 2003 | 6.8°C | 0.8°C | -5.2°C | 13.6°C | -11.2°C | 12 mm | 50% | 2.8 m/s | 2.3 |
| 2002 | 5.8°C | 0.4°C | -5.0°C | 11.9°C | -12.2°C | 5 mm | 52% | 2.2 m/s | 2.3 |
| 2001 | 5.8°C | -0.2°C | -6.1°C | 11.9°C | -11.2°C | 10 mm | 51% | 2.6 m/s | 2.5 |
| 2000 | 4.2°C | -1.6°C | -7.5°C | 11.9°C | -14.2°C | 15 mm | 58% | 2.5 m/s | 2.4 |
| 1999 | 5.1°C | -0.2°C | -5.5°C | 14.5°C | -10.4°C | 24 mm | 54% | 2.7 m/s | 2.2 |
| 1998 | 5.7°C | -0.5°C | -6.7°C | 19.2°C | -18.2°C | 17 mm | 56% | 2.4 m/s | 2.2 |
| 1997 | 2.9°C | -2.0°C | -7.0°C | 10.6°C | -12.4°C | 21 mm | 64% | 2.7 m/s | 2.2 |
| 1996 | 4.5°C | -1.3°C | -7.1°C | 13.5°C | -20.3°C | 20 mm | 56% | 3.2 m/s | 2.3 |
| 1995 | 5.9°C | 0.3°C | -5.3°C | 16.1°C | -12.4°C | 13 mm | 57% | 2.1 m/s | 2.5 |
| 1994 | 7.0°C | 1.3°C | -4.4°C | 14.6°C | -12.8°C | 8 mm | 51% | 2.2 m/s | 2.3 |
| 1993 | 4.8°C | -0.8°C | -6.3°C | 12.7°C | -14.8°C | 13 mm | 54% | 2.8 m/s | 2.4 |
| 1992 | 3.9°C | -2.2°C | -8.3°C | 11.9°C | -14.5°C | 16 mm | 60% | 2.5 m/s | 2.4 |
| 1991 | 5.2°C | -0.3°C | -5.7°C | 11.8°C | -13.0°C | 5 mm | 59% | 2.5 m/s | 2.5 |
| 1990 | 3.2°C | -3.1°C | -9.4°C | 14.3°C | -22.2°C | 8 mm | 53% | 2.7 m/s | 2.4 |
| 1989 | 2.9°C | -2.7°C | -8.3°C | 14.4°C | -19.7°C | 20 mm | 58% | 2.7 m/s | 2.3 |
| 1988 | 4.4°C | -1.4°C | -7.3°C | 13.2°C | -16.3°C | 24 mm | 53% | 2.6 m/s | 2.2 |
| 1987 | 2.6°C | -2.7°C | -8.0°C | 15.4°C | -17.2°C | 37 mm | 64% | 2.7 m/s | 2 |
| 1986 | 4.4°C | -0.8°C | -6.0°C | 9.8°C | -15.5°C | 10 mm | 59% | 1.9 m/s | 2.5 |
| 1985 | 3.7°C | -2.0°C | -7.7°C | 10.5°C | -20.6°C | 17 mm | 61% | 3 m/s | 2.2 |
| 1984 | 5.6°C | -0.3°C | -6.2°C | 12.6°C | -11.7°C | 13 mm | 60% | 2.8 m/s | 2.3 |
| 1983 ❄️ | -0.4°C | -5.7°C | -10.9°C | 7.5°C | -23.0°C | 25 mm | 70% | 2.6 m/s | — |
| 1982 | 3.8°C | -2.2°C | -8.2°C | 13.1°C | -23.8°C | 39 mm | 62% | 2.7 m/s | — |
| 1981 | 5.6°C | -0.4°C | -6.3°C | 16.4°C | -16.3°C | 27 mm | 55% | 2.9 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 4.9°C with lows near -6.6°C (mean -0.8°C), based on 45 years of NASA POWER data.
December averages 19 mm of rainfall in Castle Rock, one of the drier months. The wettest on record was 56 mm in 2006.
The hottest December reached 21.2°C in 2021. The coldest dipped to -23.8°C in 1982.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 4.2°C. Daytime highs moved from 3.7°C to 8.2°C and overnight lows from -7.9°C to -4°C over the same span.
December is one of the cooler months of the year in Castle Rock and one of the drier months, so plan for around 4.9°C daytime highs and -6.6°C at night.
Not quite — December is the 2nd coolest month in Castle Rock, averaging -0.8°C.
For December in Castle Rock, pack warm layers and a jacket for chilly mornings, with typical highs of 4.9°C and lows of -6.6°C.
Relative humidity in December averages 56% — moderately humid.
Average wind speed in December is 2.6 m/s. The windiest December on record averaged 3.2 m/s (1996).
The wettest December on record was 2006 with 56 mm. On average, December sees 19 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 Castle Rock 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.
