December is one of the cooler months of the year in San Mateo, with average highs near 13.4°C and lows around 8.7°C (mean 11.1°C). It is a relatively wet time of year, averaging 102 mm of rainfall and 82% relative humidity across the period.
December is one of the cooler months of the year in San Mateo. Across 45 years of records, the warmest December in San Mateo was 2014 — when the month averaged 13.4°C — while the coldest was 1990 at 9.1°C. Typical December days reach 13.4°C with nights near 8.7°C. The long-term trend is warming, about 0.2°C per decade.
December is a relatively wet time of year in San Mateo, averaging 102 mm of rainfall. The wettest December on record was 2022 with 257 mm, while the driest were 1989 and 2017 at 4 mm.
Relative humidity in San Mateo during December averages 82%. The most humid December was 2001 at 88%, and the least humid was 2013 at 70%.
December receives about 2.2 kWh/m²/day of solar energy in San Mateo. The sunniest Decembers were 1990 and 2013 at 2.7 kWh/m²/day, and the cloudiest was 2010 at 1.7.
Average wind speed in San Mateo during December is 3.8 m/s. The windiest December was 1987 at 5.2 m/s, while the calmest was 1986 at 2.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.0°C | 10.7°C | 10.9°C | 11.4°C | 11.5°C | +0.5°C |
| Avg High | 13.5°C | 13.3°C | 13.1°C | 13.6°C | 13.9°C | +0.4°C |
| Avg Low | 8.6°C | 8.1°C | 8.7°C | 9.2°C | 9.2°C | +0.6°C |
| Avg Rain | 77 mm | 80 mm | 133 mm | 96 mm | 134 mm | +57 mm |
December temperatures in San Mateo have risen by about 0.7°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -0.3°C (1990) to a record high of 20.5°C (2021).
Rainfall in December is a relatively wet time of year, averaging 102 mm, with a wettest year of 257 mm.
A quieter season to visit San Mateo
If your dates are flexible, the more temperate months of September and August tend to be the most comfortable for visiting San Mateo. That said, December — with days averaging 13.4°C and nights around 8.7°C (mean 11.1°C) and higher rainfall (102 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 | 13.9°C | 11.6°C | 9.2°C | 16.2°C | 6.2°C | 89 mm | 88% | 3.7 m/s | — |
| 2024 | 14.8°C | 12.4°C | 10.0°C | 18.0°C | 6.4°C | 114 mm | 87% | 3.2 m/s | 2.2 |
| 2023 | 15.2°C | 12.9°C | 10.7°C | 18.3°C | 6.9°C | 102 mm | 86% | 3.2 m/s | 2 |
| 2022 🌧️ | 12.6°C | 10.4°C | 8.2°C | 15.2°C | 4.9°C | 257 mm | 86% | 3.3 m/s | 2.1 |
| 2021 | 12.7°C | 10.7°C | 8.8°C | 20.5°C | 5.2°C | 200 mm | 87% | 4 m/s | 2 |
| 2020 | 14.0°C | 11.3°C | 8.5°C | 18.4°C | 5.2°C | 39 mm | 83% | 3.2 m/s | 2.5 |
| 2019 | 13.9°C | 12.1°C | 10.4°C | 15.9°C | 7.1°C | 124 mm | 88% | 3.8 m/s | 1.8 |
| 2018 | 14.4°C | 12.2°C | 10.0°C | 16.1°C | 6.7°C | 57 mm | 82% | 3.6 m/s | 2.2 |
| 2017 | 14.7°C | 11.6°C | 8.6°C | 17.6°C | 6.4°C | 4 mm | 72% | 3.2 m/s | 2.6 |
| 2016 | 12.7°C | 10.5°C | 8.3°C | 15.4°C | 4.4°C | 98 mm | 83% | 4 m/s | 2.3 |
| 2015 | 13.2°C | 11.4°C | 9.6°C | 16.3°C | 5.6°C | 100 mm | 79% | 3.9 m/s | 2.2 |
| 2014 🔥 | 15.1°C | 13.4°C | 11.7°C | 18.0°C | 5.7°C | 246 mm | 85% | 4 m/s | 1.9 |
| 2013 | 13.5°C | 10.3°C | 7.1°C | 17.2°C | 2.3°C | 12 mm | 70% | 3.2 m/s | 2.7 |
| 2012 | 12.8°C | 11.1°C | 9.4°C | 16.8°C | 5.5°C | 153 mm | 81% | 4.1 m/s | 2.1 |
| 2011 | 13.2°C | 10.3°C | 7.4°C | 17.3°C | 4.3°C | 5 mm | 74% | 2.8 m/s | 2.6 |
| 2010 | 12.9°C | 11.2°C | 9.4°C | 16.1°C | 5.8°C | 162 mm | 87% | 3.6 m/s | 1.7 |
| 2009 | 11.9°C | 9.7°C | 7.6°C | 14.7°C | 3.4°C | 73 mm | 84% | 3.4 m/s | 2 |
| 2008 | 12.1°C | 9.8°C | 7.6°C | 16.3°C | 3.6°C | 56 mm | 81% | 3.7 m/s | 2.2 |
| 2007 | 12.2°C | 9.8°C | 7.5°C | 15.6°C | 4.6°C | 70 mm | 81% | 4.1 m/s | 2.3 |
| 2006 | 13.5°C | 10.8°C | 8.1°C | 17.1°C | 3.1°C | 93 mm | 77% | 3.8 m/s | 2.2 |
| 2005 | 13.8°C | 11.7°C | 9.7°C | 17.6°C | 5.5°C | 222 mm | 85% | 4.1 m/s | 1.8 |
| 2004 | 13.7°C | 11.1°C | 8.5°C | 16.0°C | 5.1°C | 167 mm | 83% | 3.7 m/s | 2.3 |
| 2003 | 13.4°C | 11.5°C | 9.7°C | 15.8°C | 6.3°C | 170 mm | 85% | 4 m/s | 1.9 |
| 2002 | 13.9°C | 12.2°C | 10.5°C | 16.4°C | 5.9°C | 257 mm | 85% | 4.5 m/s | 1.9 |
| 2001 | 12.4°C | 10.8°C | 9.2°C | 14.6°C | 5.4°C | 202 mm | 88% | 4.4 m/s | 1.8 |
| 2000 | 14.0°C | 11.2°C | 8.4°C | 16.0°C | 5.3°C | 17 mm | 81% | 2.9 m/s | 2.3 |
| 1999 | 14.1°C | 10.8°C | 7.6°C | 18.2°C | 5.6°C | 10 mm | 80% | 3.4 m/s | 2.6 |
| 1998 | 11.7°C | 9.3°C | 6.8°C | 17.9°C | 1.0°C | 29 mm | 80% | 3.7 m/s | 2.4 |
| 1997 | 14.3°C | 11.6°C | 9.0°C | 16.4°C | 5.4°C | 84 mm | 77% | 4.6 m/s | 2.4 |
| 1996 | 13.7°C | 11.8°C | 9.8°C | 16.2°C | 6.5°C | 181 mm | 87% | 4.5 m/s | 1.9 |
| 1995 | 14.3°C | 12.1°C | 9.9°C | 16.5°C | 6.3°C | 147 mm | 87% | 3.5 m/s | 2 |
| 1994 | 12.0°C | 9.8°C | 7.6°C | 15.0°C | 3.8°C | 73 mm | 83% | 3.3 m/s | 2.2 |
| 1993 | 13.7°C | 11.0°C | 8.3°C | 16.7°C | 3.6°C | 53 mm | 80% | 3.8 m/s | 2.3 |
| 1992 | 13.1°C | 10.7°C | 8.3°C | 15.2°C | 4.5°C | 125 mm | 79% | 4.8 m/s | 2.1 |
| 1991 | 13.9°C | 10.9°C | 8.0°C | 15.9°C | 5.0°C | 60 mm | 78% | 3.5 m/s | 2.3 |
| 1990 ❄️ | 12.2°C | 9.1°C | 5.9°C | 19.3°C | -0.3°C | 42 mm | 72% | 3.9 m/s | 2.7 |
| 1989 | 15.2°C | 11.8°C | 8.5°C | 17.7°C | 5.1°C | 4 mm | 75% | 2.9 m/s | 2.6 |
| 1988 | 13.3°C | 10.6°C | 7.9°C | 19.2°C | 3.0°C | 78 mm | 76% | 3.8 m/s | 2.2 |
| 1987 | 12.6°C | 10.6°C | 8.6°C | 16.0°C | 3.8°C | 96 mm | 77% | 5.2 m/s | 2 |
| 1986 | 14.7°C | 11.8°C | 8.9°C | 18.5°C | 5.9°C | 35 mm | 76% | 2.7 m/s | 2.2 |
| 1985 | 13.0°C | 10.0°C | 7.0°C | 15.7°C | 2.4°C | 56 mm | 82% | 3.5 m/s | 2.3 |
| 1984 | 12.4°C | 10.0°C | 7.7°C | 16.5°C | 4.7°C | 52 mm | 81% | 4 m/s | 2.3 |
| 1983 | 13.2°C | 11.7°C | 10.3°C | 15.3°C | 6.5°C | 166 mm | 87% | 4.5 m/s | — |
| 1982 | 13.2°C | 10.8°C | 8.5°C | 15.1°C | 3.3°C | 88 mm | 79% | 4.3 m/s | — |
| 1981 | 13.9°C | 12.0°C | 10.1°C | 17.1°C | 7.9°C | 114 mm | 87% | 3.9 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 13.4°C with lows near 8.7°C (mean 11.1°C), based on 45 years of NASA POWER data.
December averages 102 mm of rainfall in San Mateo, a relatively wet time of year. The wettest on record was 257 mm in 2022.
The hottest December reached 20.5°C in 2021. The coldest dipped to -0.3°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 0.7°C. Daytime highs moved from 13.1°C to 13.8°C and overnight lows from 8.7°C to 9.4°C over the same span.
December is one of the cooler months of the year in San Mateo and a relatively wet time of year, so plan for around 13.4°C daytime highs and 8.7°C at night.
Not quite — December is the 2nd coolest month in San Mateo, averaging 11.1°C.
For December in San Mateo, pack light layers you can adjust through the day, with typical highs of 13.4°C and lows of 8.7°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 82% — quite humid.
Average wind speed in December is 3.8 m/s. The windiest December on record averaged 5.2 m/s (1987).
The wettest December on record was 2022 with 257 mm. On average, December sees 102 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 Mateo 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.
