December is one of the cooler months of the year in Santa Rosa, with average highs near 12.9°C and lows around 3.6°C (mean 8.3°C). It is a relatively wet time of year, averaging 145 mm of rainfall and 81% relative humidity across the period.
December is one of the cooler months of the year in Santa Rosa. Across 45 years of records, the warmest December in Santa Rosa was 2023 — when the month averaged 10.4°C — while the coldest was 1984 at 6.4°C. Typical December days reach 12.9°C with nights near 3.6°C. The long-term trend is warming, about 0.2°C per decade.
December is a relatively wet time of year in Santa Rosa, averaging 145 mm of rainfall. The wettest December on record was 2005 with 392 mm, while the driest was 1989 at 2 mm.
Relative humidity in Santa Rosa during December averages 81%. The most humid December was 1983 at 93%, and the least humid was 2013 at 61%.
December receives about 2.1 kWh/m²/day of solar energy in Santa Rosa. The sunniest December was 2013 at 2.7 kWh/m²/day, and the cloudiest was 2010 at 1.5.
Average wind speed in Santa Rosa during December is 1.6 m/s. The windiest December was 1987 at 2.1 m/s, while the calmest were 1986 and 1994 at 1.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 8.1°C | 7.9°C | 8.0°C | 8.4°C | 9.2°C | +1.1°C |
| Avg High | 12.8°C | 12.8°C | 12.3°C | 13.0°C | 13.8°C | +1°C |
| Avg Low | 3.5°C | 3.0°C | 3.6°C | 3.8°C | 4.5°C | +1°C |
| Avg Rain | 121 mm | 128 mm | 192 mm | 131 mm | 153 mm | +33 mm |
December temperatures in Santa Rosa have risen by about 1.3°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -6.1°C (1990) to a record high of 22.1°C (1989).
Rainfall in December is a relatively wet time of year, averaging 145 mm, with a wettest year of 392 mm.
A quieter season to visit Santa Rosa
If your dates are flexible, the more temperate months of September and July tend to be the most comfortable for visiting Santa Rosa. That said, December — with days averaging 12.9°C and nights around 3.6°C (mean 8.3°C) and higher rainfall (145 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 | 14.7°C | 10.3°C | 5.8°C | 18.8°C | 1.5°C | 150 mm | 88% | 1.5 m/s | — |
| 2024 | 13.9°C | 9.6°C | 5.3°C | 19.1°C | -0.1°C | 161 mm | 89% | 1.6 m/s | 2 |
| 2023 🔥 | 15.2°C | 10.4°C | 5.7°C | 19.7°C | 1.0°C | 134 mm | 85% | 1.4 m/s | 1.9 |
| 2022 | 12.1°C | 7.6°C | 3.1°C | 16.9°C | -1.6°C | 228 mm | 87% | 1.5 m/s | 1.9 |
| 2021 | 11.3°C | 7.4°C | 3.5°C | 19.4°C | -0.7°C | 195 mm | 90% | 1.5 m/s | 1.9 |
| 2020 | 15.3°C | 9.6°C | 3.8°C | 21.1°C | -0.1°C | 51 mm | 72% | 1.5 m/s | 2.4 |
| 2019 | 12.5°C | 9.0°C | 5.4°C | 15.8°C | 1.3°C | 183 mm | 91% | 1.5 m/s | 1.7 |
| 2018 | 13.2°C | 8.6°C | 4.1°C | 15.9°C | 0.1°C | 71 mm | 83% | 1.5 m/s | 2.1 |
| 2017 | 15.2°C | 9.4°C | 3.6°C | 18.2°C | 0.2°C | 2 mm | 69% | 1.5 m/s | 2.5 |
| 2016 | 11.7°C | 7.2°C | 2.6°C | 17.1°C | -2.3°C | 129 mm | 84% | 1.6 m/s | 2.2 |
| 2015 | 11.9°C | 7.7°C | 3.5°C | 17.6°C | -2.1°C | 117 mm | 85% | 1.6 m/s | 2 |
| 2014 | 13.4°C | 9.9°C | 6.5°C | 17.9°C | -0.9°C | 335 mm | 91% | 1.5 m/s | 1.6 |
| 2013 | 14.5°C | 8.0°C | 1.5°C | 21.5°C | -4.2°C | 13 mm | 61% | 1.5 m/s | 2.7 |
| 2012 | 11.4°C | 7.4°C | 3.4°C | 16.4°C | -1.9°C | 238 mm | 86% | 1.6 m/s | 2 |
| 2011 | 14.6°C | 8.3°C | 2.0°C | 20.3°C | -1.1°C | 5 mm | 64% | 1.5 m/s | 2.6 |
| 2010 | 12.0°C | 8.5°C | 5.0°C | 18.3°C | -1.9°C | 215 mm | 90% | 1.4 m/s | 1.5 |
| 2009 | 10.9°C | 6.5°C | 2.0°C | 17.8°C | -4.4°C | 81 mm | 83% | 1.3 m/s | 1.9 |
| 2008 | 11.8°C | 6.9°C | 1.9°C | 19.2°C | -2.7°C | 70 mm | 80% | 1.4 m/s | 2.1 |
| 2007 | 11.5°C | 6.8°C | 2.0°C | 18.6°C | -1.4°C | 114 mm | 80% | 1.5 m/s | 2.1 |
| 2006 | 12.6°C | 7.8°C | 2.9°C | 18.2°C | -2.5°C | 132 mm | 77% | 1.6 m/s | 2.1 |
| 2005 🌧️ | 12.9°C | 9.0°C | 5.0°C | 20.1°C | -1.3°C | 392 mm | 86% | 1.8 m/s | 1.7 |
| 2004 | 13.4°C | 8.8°C | 4.3°C | 16.7°C | -0.5°C | 233 mm | 83% | 1.6 m/s | 2.1 |
| 2003 | 11.6°C | 8.0°C | 4.4°C | 17.6°C | -1.1°C | 259 mm | 90% | 1.5 m/s | 1.7 |
| 2002 | 12.6°C | 8.9°C | 5.2°C | 18.2°C | 0.6°C | 363 mm | 87% | 1.9 m/s | 1.7 |
| 2001 | 11.2°C | 7.9°C | 4.6°C | 16.0°C | -0.4°C | 254 mm | 91% | 1.7 m/s | 1.7 |
| 2000 | 14.6°C | 9.2°C | 3.8°C | 18.7°C | 1.0°C | 23 mm | 75% | 1.4 m/s | 2.1 |
| 1999 | 15.4°C | 9.2°C | 3.0°C | 19.7°C | 0.2°C | 12 mm | 71% | 1.6 m/s | 2.5 |
| 1998 | 11.6°C | 6.6°C | 1.6°C | 19.4°C | -5.4°C | 36 mm | 79% | 1.5 m/s | 2.3 |
| 1997 | 12.1°C | 7.4°C | 2.7°C | 16.8°C | -2.4°C | 75 mm | 81% | 1.8 m/s | 2.2 |
| 1996 | 13.3°C | 9.6°C | 5.9°C | 17.2°C | -0.6°C | 316 mm | 87% | 2 m/s | 1.7 |
| 1995 | 13.8°C | 9.6°C | 5.4°C | 19.7°C | -0.2°C | 251 mm | 86% | 1.6 m/s | 1.8 |
| 1994 | 11.0°C | 6.6°C | 2.2°C | 15.5°C | -2.0°C | 109 mm | 86% | 1.2 m/s | 1.9 |
| 1993 | 12.8°C | 7.8°C | 2.8°C | 19.2°C | -2.0°C | 100 mm | 82% | 1.6 m/s | 2.1 |
| 1992 | 11.3°C | 6.8°C | 2.3°C | 14.8°C | -2.5°C | 254 mm | 84% | 2 m/s | 1.9 |
| 1991 | 14.4°C | 9.0°C | 3.5°C | 18.2°C | 0.2°C | 93 mm | 70% | 1.7 m/s | 2.2 |
| 1990 | 12.6°C | 6.5°C | 0.5°C | 21.0°C | -6.1°C | 34 mm | 62% | 1.5 m/s | 2.6 |
| 1989 | 16.3°C | 10.1°C | 3.8°C | 22.1°C | -0.1°C | 2 mm | 68% | 1.4 m/s | 2.6 |
| 1988 | 13.0°C | 8.0°C | 3.0°C | 21.9°C | -3.6°C | 102 mm | 77% | 1.8 m/s | 2.2 |
| 1987 | 10.7°C | 6.9°C | 3.1°C | 17.7°C | -2.9°C | 178 mm | 83% | 2.1 m/s | 1.9 |
| 1986 | 14.9°C | 9.2°C | 3.5°C | 20.6°C | 0.1°C | 57 mm | 72% | 1.2 m/s | 2 |
| 1985 | 12.5°C | 7.4°C | 2.4°C | 15.8°C | -3.6°C | 79 mm | 83% | 1.6 m/s | 2.2 |
| 1984 ❄️ | 11.2°C | 6.4°C | 1.7°C | 16.1°C | -1.3°C | 53 mm | 85% | 1.5 m/s | 2.2 |
| 1983 | 11.9°C | 8.5°C | 5.1°C | 17.0°C | 0.0°C | 281 mm | 93% | 1.6 m/s | — |
| 1982 | 11.9°C | 7.4°C | 3.0°C | 17.5°C | -2.5°C | 113 mm | 84% | 1.7 m/s | — |
| 1981 | 13.2°C | 9.4°C | 5.5°C | 17.2°C | 1.5°C | 222 mm | 89% | 1.5 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 12.9°C with lows near 3.6°C (mean 8.3°C), based on 45 years of NASA POWER data.
December averages 145 mm of rainfall in Santa Rosa, a relatively wet time of year. The wettest on record was 392 mm in 2005.
The hottest December reached 22.1°C in 1989. The coldest dipped to -6.1°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 1.3°C. Daytime highs moved from 12.1°C to 13.4°C and overnight lows from 3.5°C to 4.7°C over the same span.
December is one of the cooler months of the year in Santa Rosa and a relatively wet time of year, so plan for around 12.9°C daytime highs and 3.6°C at night.
Not quite — December is the 2nd coolest month in Santa Rosa, averaging 8.3°C.
For December in Santa Rosa, pack warm layers and a jacket for chilly mornings, with typical highs of 12.9°C and lows of 3.6°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 81% — quite humid.
Average wind speed in December is 1.6 m/s. The windiest December on record averaged 2.1 m/s (1987).
The wettest December on record was 2005 with 392 mm. On average, December sees 145 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 Santa Rosa 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.
