December is one of the cooler months of the year in San Tan Valley, with average highs near 18.1°C and lows around 4.6°C (mean 11.4°C). It is about average for rainfall, averaging 37 mm of rainfall and 48% relative humidity across the period.
December is one of the cooler months of the year in San Tan Valley. Across 45 years of records, the warmest December in San Tan Valley was 2025 — when the month averaged 16°C — while the coldest was 1987 at 8.8°C. Typical December days reach 18.1°C with nights near 4.6°C. The long-term trend is warming, about 0.7°C per decade.
December is about average for rainfall in San Tan Valley, averaging 37 mm of rainfall. The wettest December on record was 1984 with 127 mm, while the driest was 2024 at 0 mm.
Relative humidity in San Tan Valley during December averages 48%. The most humid December was 1984 at 68%, and the least humid was 2005 at 27%.
December receives about 3.1 kWh/m²/day of solar energy in San Tan Valley. The sunniest Decembers were 1985 and 1999 at 3.4 kWh/m²/day, and the cloudiest was 1984 at 2.5.
Average wind speed in San Tan Valley during December is 2.3 m/s. The windiest December was 1988 at 2.9 m/s, while the calmest was 2014 at 1.8 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 | 10.8°C | 11.7°C | 13.7°C | +3.1°C |
| Avg High | 17.3°C | 17.4°C | 17.7°C | 18.2°C | 20.5°C | +3.2°C |
| Avg Low | 3.9°C | 3.8°C | 3.8°C | 5.3°C | 6.8°C | +2.9°C |
| Avg Rain | 45 mm | 46 mm | 29 mm | 34 mm | 28 mm | -16 mm |
December temperatures in San Tan Valley have risen by about 3.2°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -8.6°C (1990) to a record high of 28.7°C (2025).
Rainfall in December is about average for rainfall, averaging 37 mm, with a wettest year of 127 mm.
A quieter season to visit San Tan Valley
If your dates are flexible, the more temperate months of October and May tend to be the most comfortable for visiting San Tan Valley. That said, December — with days averaging 18.1°C and nights around 4.6°C (mean 11.4°C) and moderate rainfall (37 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 🔥 | 23.2°C | 16.0°C | 8.9°C | 28.7°C | 3.4°C | 2 mm | 44% | 2.1 m/s | — |
| 2024 | 23.2°C | 15.6°C | 8.0°C | 28.1°C | 2.8°C | 0 mm | 28% | 2.1 m/s | 3.3 |
| 2023 | 20.4°C | 13.6°C | 6.8°C | 26.8°C | 0.6°C | 31 mm | 40% | 2.3 m/s | 3.1 |
| 2022 | 17.5°C | 11.5°C | 5.4°C | 23.5°C | -1.1°C | 66 mm | 57% | 1.9 m/s | 2.8 |
| 2021 | 19.7°C | 13.6°C | 7.4°C | 28.4°C | -0.1°C | 61 mm | 50% | 2 m/s | 2.9 |
| 2020 | 18.8°C | 11.6°C | 4.3°C | 26.1°C | -0.9°C | 10 mm | 32% | 2.4 m/s | 3.3 |
| 2019 | 17.1°C | 11.0°C | 5.0°C | 22.9°C | -3.2°C | 46 mm | 58% | 2.3 m/s | 2.7 |
| 2018 | 18.0°C | 11.5°C | 5.1°C | 24.3°C | -2.7°C | 22 mm | 49% | 2.1 m/s | 2.9 |
| 2017 | 21.5°C | 14.6°C | 7.7°C | 27.1°C | 0.2°C | 4 mm | 28% | 2.2 m/s | 3.2 |
| 2016 | 19.3°C | 13.1°C | 6.9°C | 25.9°C | -0.1°C | 42 mm | 50% | 2.3 m/s | 2.9 |
| 2015 | 16.8°C | 10.1°C | 3.4°C | 25.0°C | -1.5°C | 11 mm | 45% | 2.2 m/s | 3 |
| 2014 | 17.7°C | 11.8°C | 6.0°C | 24.9°C | -1.7°C | 53 mm | 55% | 1.8 m/s | 2.8 |
| 2013 | 17.9°C | 10.9°C | 4.0°C | 26.0°C | -1.8°C | 14 mm | 47% | 2.5 m/s | 3.3 |
| 2012 | 17.6°C | 11.4°C | 5.2°C | 27.5°C | -1.0°C | 49 mm | 45% | 2.1 m/s | 3.1 |
| 2011 | 15.8°C | 9.3°C | 2.8°C | 25.5°C | -3.3°C | 54 mm | 55% | 2.3 m/s | 2.9 |
| 2010 | 20.5°C | 13.6°C | 6.7°C | 27.7°C | -4.0°C | 47 mm | 43% | 2.4 m/s | 2.8 |
| 2009 | 15.9°C | 9.5°C | 3.0°C | 22.2°C | -2.2°C | 34 mm | 48% | 2.3 m/s | 3 |
| 2008 | 17.3°C | 10.8°C | 4.3°C | 24.9°C | -2.8°C | 60 mm | 54% | 2.4 m/s | 2.8 |
| 2007 | 15.4°C | 8.9°C | 2.5°C | 25.6°C | -3.8°C | 61 mm | 53% | 2.2 m/s | 3.2 |
| 2006 | 17.9°C | 10.7°C | 3.4°C | 24.9°C | -3.0°C | 9 mm | 41% | 2.4 m/s | 3.2 |
| 2005 | 20.3°C | 12.9°C | 5.5°C | 25.9°C | -0.4°C | 1 mm | 27% | 2 m/s | 3.2 |
| 2004 | 18.1°C | 11.1°C | 4.1°C | 26.2°C | -2.6°C | 52 mm | 50% | 2.6 m/s | 3.1 |
| 2003 | 18.7°C | 11.4°C | 4.2°C | 27.6°C | -4.6°C | 15 mm | 40% | 2.7 m/s | 3.3 |
| 2002 | 16.9°C | 10.4°C | 3.9°C | 22.7°C | -1.3°C | 23 mm | 52% | 2 m/s | 3 |
| 2001 | 17.0°C | 9.8°C | 2.6°C | 24.7°C | -2.5°C | 30 mm | 47% | 2.2 m/s | 3.1 |
| 2000 | 19.7°C | 12.2°C | 4.8°C | 23.4°C | -0.1°C | 2 mm | 47% | 2.4 m/s | 3.3 |
| 1999 | 18.8°C | 11.3°C | 3.8°C | 25.2°C | -0.6°C | 1 mm | 28% | 2.7 m/s | 3.4 |
| 1998 | 17.9°C | 10.7°C | 3.5°C | 24.5°C | -3.8°C | 12 mm | 49% | 2.4 m/s | 3.2 |
| 1997 | 15.4°C | 8.9°C | 2.4°C | 21.0°C | -3.3°C | 66 mm | 56% | 2.4 m/s | 3.1 |
| 1996 | 19.4°C | 12.0°C | 4.6°C | 25.9°C | -3.4°C | 1 mm | 39% | 2.4 m/s | 3.3 |
| 1995 | 19.3°C | 12.3°C | 5.3°C | 25.7°C | 0.4°C | 6 mm | 40% | 2.1 m/s | 3.1 |
| 1994 | 17.1°C | 10.7°C | 4.4°C | 22.8°C | -1.6°C | 81 mm | 59% | 2.5 m/s | 2.9 |
| 1993 | 18.2°C | 10.8°C | 3.4°C | 24.2°C | -2.8°C | 10 mm | 47% | 2.5 m/s | 3.3 |
| 1992 | 15.5°C | 9.3°C | 3.2°C | 21.6°C | -3.1°C | 125 mm | 63% | 2.2 m/s | 2.8 |
| 1991 | 16.8°C | 11.0°C | 5.1°C | 22.9°C | -2.4°C | 65 mm | 63% | 2.7 m/s | 2.8 |
| 1990 | 15.7°C | 9.0°C | 2.2°C | 24.1°C | -8.6°C | 95 mm | 54% | 2.8 m/s | 3 |
| 1989 | 18.8°C | 11.5°C | 4.2°C | 25.6°C | -1.8°C | 17 mm | 36% | 2.6 m/s | 3.3 |
| 1988 | 16.9°C | 10.1°C | 3.3°C | 23.4°C | -4.0°C | 10 mm | 47% | 2.9 m/s | 3.2 |
| 1987 ❄️ | 15.3°C | 8.8°C | 2.3°C | 25.2°C | -5.4°C | 53 mm | 54% | 2.2 m/s | 2.9 |
| 1986 | 16.9°C | 10.5°C | 4.0°C | 23.9°C | -2.0°C | 62 mm | 59% | 2.3 m/s | 2.9 |
| 1985 | 18.6°C | 11.3°C | 4.0°C | 23.5°C | -3.6°C | 18 mm | 51% | 2.4 m/s | 3.4 |
| 1984 🌧️ | 15.9°C | 10.3°C | 4.8°C | 23.4°C | -1.5°C | 127 mm | 68% | 2.4 m/s | 2.5 |
| 1983 | 16.7°C | 10.3°C | 4.0°C | 22.8°C | -0.9°C | 59 mm | 67% | 2.4 m/s | — |
| 1982 | 16.1°C | 9.6°C | 3.2°C | 23.7°C | -2.0°C | 56 mm | 60% | 2.8 m/s | — |
| 1981 | 20.8°C | 13.2°C | 5.7°C | 27.3°C | -0.8°C | 2 mm | 44% | 2.2 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 18.1°C with lows near 4.6°C (mean 11.4°C), based on 45 years of NASA POWER data.
December averages 37 mm of rainfall in San Tan Valley, about average for rainfall. The wettest on record was 127 mm in 1984.
The hottest December reached 28.7°C in 2025. The coldest dipped to -8.6°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 3.2°C. Daytime highs moved from 17.6°C to 20.8°C and overnight lows from 4.3°C to 7.3°C over the same span.
December is one of the cooler months of the year in San Tan Valley and about average for rainfall, so plan for around 18.1°C daytime highs and 4.6°C at night.
Not quite — December is the 2nd coolest month in San Tan Valley, averaging 11.4°C.
For December in San Tan Valley, pack warm layers and a jacket for chilly mornings, with typical highs of 18.1°C and lows of 4.6°C.
Relative humidity in December averages 48% — relatively dry.
Average wind speed in December is 2.3 m/s. The windiest December on record averaged 2.9 m/s (1988).
The wettest December on record was 1984 with 127 mm. On average, December sees 37 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 Tan Valley 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.
