December is one of the cooler months of the year in San Bernardino, with average highs near 17.4°C and lows around 5.1°C (mean 11.3°C). It is a relatively wet time of year, averaging 54 mm of rainfall and 54% relative humidity across the period.
December is one of the cooler months of the year in San Bernardino. Across 45 years of records, the warmest December in San Bernardino was 2025 — when the month averaged 15.7°C — while the coldest was 1987 at 7.7°C. Typical December days reach 17.4°C with nights near 5.1°C. The long-term trend is warming, about 0.6°C per decade.
December is a relatively wet time of year in San Bernardino, averaging 54 mm of rainfall. The wettest December on record was 2010 with 268 mm, while the driest was 2017 at 0 mm.
Relative humidity in San Bernardino during December averages 54%. The most humid December was 1983 at 68%, and the least humid was 2017 at 25%.
December receives about 2.9 kWh/m²/day of solar energy in San Bernardino. The sunniest December was 2017 at 3.3 kWh/m²/day, and the cloudiest were 1984 and 2019 at 2.5.
Average wind speed in San Bernardino during December is 1.9 m/s. The windiest December was 1997 at 2.5 m/s, while the calmest were 2023 and 2024 at 1.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 10.6°C | 10.6°C | 11.0°C | 11.6°C | 13.4°C | +2.8°C |
| Avg High | 16.7°C | 16.8°C | 17.1°C | 17.6°C | 19.4°C | +2.7°C |
| Avg Low | 4.4°C | 4.3°C | 4.9°C | 5.5°C | 7.3°C | +2.9°C |
| Avg Rain | 53 mm | 44 mm | 43 mm | 70 mm | 63 mm | +10 mm |
December temperatures in San Bernardino have risen by about 2.7°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -6.1°C (1990) to a record high of 28.7°C (2025).
Rainfall in December is a relatively wet time of year, averaging 54 mm, with a wettest year of 268 mm.
A quieter season to visit San Bernardino
If your dates are flexible, the more temperate months of June and October tend to be the most comfortable for visiting San Bernardino. That said, December — with days averaging 17.4°C and nights around 5.1°C (mean 11.3°C) and moderate rainfall (54 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 🔥 | 21.8°C | 15.7°C | 9.5°C | 28.7°C | 3.1°C | 95 mm | 53% | 1.6 m/s | — |
| 2024 | 22.0°C | 15.3°C | 8.5°C | 26.4°C | 3.8°C | 0 mm | 43% | 1.4 m/s | 3 |
| 2023 | 20.0°C | 14.0°C | 7.9°C | 26.0°C | 3.4°C | 34 mm | 55% | 1.4 m/s | 2.8 |
| 2022 | 16.6°C | 11.2°C | 5.8°C | 26.2°C | 0.1°C | 67 mm | 66% | 1.5 m/s | 2.7 |
| 2021 | 16.3°C | 11.1°C | 6.0°C | 28.4°C | -0.6°C | 155 mm | 64% | 1.8 m/s | 2.8 |
| 2020 | 19.5°C | 12.8°C | 6.1°C | 25.9°C | 0.9°C | 29 mm | 40% | 2 m/s | 3 |
| 2019 | 15.7°C | 10.6°C | 5.6°C | 23.2°C | -1.1°C | 94 mm | 65% | 1.8 m/s | 2.5 |
| 2018 | 17.9°C | 12.0°C | 6.0°C | 24.8°C | -0.7°C | 48 mm | 56% | 1.5 m/s | 3 |
| 2017 | 22.0°C | 14.9°C | 7.9°C | 27.9°C | 0.9°C | 0 mm | 25% | 2 m/s | 3.3 |
| 2016 | 17.0°C | 11.2°C | 5.4°C | 24.0°C | -1.5°C | 108 mm | 61% | 2 m/s | 2.9 |
| 2015 | 17.1°C | 10.5°C | 3.9°C | 28.3°C | -1.4°C | 24 mm | 49% | 1.8 m/s | 3.1 |
| 2014 | 17.3°C | 12.1°C | 6.8°C | 26.2°C | -0.5°C | 89 mm | 65% | 1.6 m/s | 2.7 |
| 2013 | 18.6°C | 11.5°C | 4.5°C | 25.0°C | -2.4°C | 9 mm | 45% | 1.9 m/s | 3.2 |
| 2012 | 16.1°C | 10.5°C | 4.9°C | 24.5°C | -1.5°C | 48 mm | 64% | 1.6 m/s | 2.9 |
| 2011 | 17.0°C | 10.4°C | 3.8°C | 25.6°C | -1.0°C | 12 mm | 45% | 1.8 m/s | 3.2 |
| 2010 🌧️ | 17.3°C | 12.0°C | 6.6°C | 27.5°C | -2.0°C | 268 mm | 67% | 1.9 m/s | 2.6 |
| 2009 | 15.8°C | 10.0°C | 4.3°C | 23.4°C | -2.1°C | 77 mm | 59% | 1.8 m/s | 2.9 |
| 2008 | 15.7°C | 9.8°C | 3.9°C | 27.5°C | -2.8°C | 82 mm | 62% | 1.8 m/s | 2.8 |
| 2007 | 15.5°C | 9.4°C | 3.4°C | 26.1°C | -1.3°C | 40 mm | 57% | 2.1 m/s | 3.1 |
| 2006 | 18.6°C | 11.6°C | 4.6°C | 25.7°C | -0.6°C | 16 mm | 43% | 2 m/s | 3.2 |
| 2005 | 19.2°C | 12.8°C | 6.5°C | 26.9°C | 2.7°C | 9 mm | 52% | 1.6 m/s | 2.8 |
| 2004 | 17.1°C | 11.2°C | 5.3°C | 26.7°C | -0.9°C | 96 mm | 61% | 2.2 m/s | 3 |
| 2003 | 17.0°C | 10.8°C | 4.7°C | 24.6°C | -2.0°C | 32 mm | 55% | 1.7 m/s | 2.8 |
| 2002 | 16.1°C | 10.4°C | 4.6°C | 21.4°C | -0.3°C | 56 mm | 63% | 1.6 m/s | 3 |
| 2001 | 16.0°C | 10.0°C | 4.1°C | 22.4°C | -0.6°C | 25 mm | 57% | 1.7 m/s | 2.9 |
| 2000 | 20.3°C | 13.7°C | 7.1°C | 25.2°C | 3.3°C | 1 mm | 42% | 1.7 m/s | 3 |
| 1999 | 19.0°C | 11.9°C | 4.9°C | 25.2°C | 1.1°C | 13 mm | 38% | 2.2 m/s | 3.2 |
| 1998 | 17.2°C | 10.5°C | 3.8°C | 25.6°C | -2.4°C | 17 mm | 46% | 2.2 m/s | 3.2 |
| 1997 | 15.6°C | 9.7°C | 3.8°C | 24.2°C | -1.0°C | 69 mm | 52% | 2.5 m/s | 3.1 |
| 1996 | 16.8°C | 11.2°C | 5.6°C | 22.4°C | 1.6°C | 84 mm | 63% | 2.4 m/s | 2.7 |
| 1995 | 19.0°C | 12.5°C | 5.9°C | 26.7°C | 0.6°C | 24 mm | 56% | 1.7 m/s | 2.8 |
| 1994 | 16.5°C | 10.5°C | 4.5°C | 23.2°C | -0.5°C | 29 mm | 59% | 1.7 m/s | 2.8 |
| 1993 | 17.5°C | 10.8°C | 4.1°C | 23.3°C | -0.2°C | 22 mm | 49% | 2.1 m/s | 3.1 |
| 1992 | 14.2°C | 8.6°C | 3.0°C | 21.5°C | -2.2°C | 121 mm | 62% | 2.2 m/s | 2.9 |
| 1991 | 16.8°C | 11.0°C | 5.1°C | 22.0°C | 0.4°C | 55 mm | 52% | 2.1 m/s | 3 |
| 1990 | 15.5°C | 8.8°C | 2.0°C | 24.0°C | -6.1°C | 4 mm | 39% | 2.2 m/s | 2.9 |
| 1989 | 19.9°C | 12.7°C | 5.4°C | 27.5°C | 0.8°C | 3 mm | 33% | 2.1 m/s | 3.1 |
| 1988 | 15.4°C | 9.5°C | 3.5°C | 26.2°C | -3.7°C | 86 mm | 55% | 2.2 m/s | 2.6 |
| 1987 ❄️ | 13.3°C | 7.7°C | 2.2°C | 25.1°C | -4.6°C | 58 mm | 61% | 2.2 m/s | 2.6 |
| 1986 | 17.8°C | 11.4°C | 5.0°C | 24.8°C | 0.9°C | 25 mm | 49% | 1.7 m/s | 2.7 |
| 1985 | 17.5°C | 11.2°C | 5.0°C | 23.1°C | -1.8°C | 18 mm | 54% | 2 m/s | 3 |
| 1984 | 14.5°C | 8.9°C | 3.2°C | 19.6°C | -1.8°C | 147 mm | 66% | 2.3 m/s | 2.5 |
| 1983 | 16.2°C | 10.5°C | 4.7°C | 23.2°C | 0.0°C | 78 mm | 68% | 1.8 m/s | — |
| 1982 | 15.9°C | 9.9°C | 3.9°C | 22.2°C | -1.5°C | 51 mm | 57% | 2.4 m/s | — |
| 1981 | 20.0°C | 13.3°C | 6.6°C | 25.0°C | 1.4°C | 15 mm | 50% | 1.8 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 17.4°C with lows near 5.1°C (mean 11.3°C), based on 45 years of NASA POWER data.
December averages 54 mm of rainfall in San Bernardino, a relatively wet time of year. The wettest on record was 268 mm in 2010.
The hottest December reached 28.7°C in 2025. 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 2.7°C. Daytime highs moved from 16.8°C to 19.3°C and overnight lows from 4.7°C to 7.5°C over the same span.
December is one of the cooler months of the year in San Bernardino and a relatively wet time of year, so plan for around 17.4°C daytime highs and 5.1°C at night.
Not quite — December is the 2nd coolest month in San Bernardino, averaging 11.3°C.
For December in San Bernardino, pack warm layers and a jacket for chilly mornings, with typical highs of 17.4°C and lows of 5.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 54% — relatively dry.
Average wind speed in December is 1.9 m/s. The windiest December on record averaged 2.5 m/s (1997).
The wettest December on record was 2010 with 268 mm. On average, December sees 54 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 San Bernardino 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.
