December is one of the cooler months of the year in Flagstaff, with average highs near 7.1°C and lows around -4.2°C (mean 1.4°C). It is about average for rainfall, averaging 44 mm of rainfall and 63% relative humidity across the period.
December is one of the cooler months of the year in Flagstaff. Across 45 years of records, the warmest December in Flagstaff was 2025 — when the month averaged 6.4°C — while the coldest was 1990 at -2.4°C. Typical December days reach 7.1°C with nights near -4.2°C. The long-term trend is warming, about 0.6°C per decade.
December is about average for rainfall in Flagstaff, averaging 44 mm of rainfall. The wettest December on record was 1992 with 127 mm, while the driest were 2017 and 2024 at 0 mm.
Relative humidity in Flagstaff during December averages 63%. The most humid December was 1984 at 83%, and the least humid was 2017 at 38%.
December receives about 2.8 kWh/m²/day of solar energy in Flagstaff. The sunniest Decembers were 2017 and 2024 at 3.2 kWh/m²/day, and the cloudiest were 1984, 2010 and 2014 at 2.4.
Average wind speed in Flagstaff during December is 2.1 m/s. The windiest Decembers were 1983 and 2021 at 2.9 m/s, while the calmest was 1986 at 1.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 1.1°C | 0.5°C | 1.0°C | 1.7°C | 3.8°C | +2.7°C |
| Avg High | 6.7°C | 6.1°C | 6.6°C | 7.2°C | 9.7°C | +3°C |
| Avg Low | -4.5°C | -5.2°C | -4.7°C | -3.8°C | -2.1°C | +2.4°C |
| Avg Rain | 49 mm | 41 mm | 47 mm | 51 mm | 25 mm | -24 mm |
December temperatures in Flagstaff have risen by about 2.7°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -25.3°C (1990) to a record high of 19.9°C (2025).
Rainfall in December is about average for rainfall, averaging 44 mm, with a wettest year of 127 mm.
A quieter season to visit Flagstaff
If your dates are flexible, the more temperate months of June and August tend to be the most comfortable for visiting Flagstaff. That said, December — with days averaging 7.1°C and nights around -4.2°C (mean 1.4°C) and moderate rainfall (44 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 🔥 | 12.8°C | 6.4°C | -0.1°C | 19.9°C | -6.2°C | 14 mm | 55% | 2 m/s | — |
| 2024 | 12.9°C | 5.5°C | -1.9°C | 18.8°C | -6.3°C | 0 mm | 46% | 1.8 m/s | 3.2 |
| 2023 | 9.5°C | 3.6°C | -2.3°C | 18.1°C | -6.6°C | 13 mm | 55% | 1.7 m/s | 2.9 |
| 2022 | 7.4°C | 2.4°C | -2.5°C | 12.9°C | -10.6°C | 43 mm | 69% | 2.4 m/s | 2.7 |
| 2021 | 9.2°C | 3.9°C | -1.4°C | 17.0°C | -8.2°C | 74 mm | 61% | 2.9 m/s | 2.7 |
| 2020 | 6.3°C | 1.0°C | -4.3°C | 15.6°C | -8.5°C | 5 mm | 48% | 2.1 m/s | 3 |
| 2019 | 5.7°C | 0.7°C | -4.3°C | 15.6°C | -15.0°C | 67 mm | 70% | 2 m/s | 2.5 |
| 2018 | 7.5°C | 1.8°C | -3.9°C | 13.4°C | -10.5°C | 19 mm | 60% | 1.9 m/s | 2.8 |
| 2017 | 10.6°C | 4.3°C | -2.0°C | 18.2°C | -7.0°C | 0 mm | 38% | 2 m/s | 3.2 |
| 2016 | 8.2°C | 2.7°C | -2.7°C | 16.0°C | -12.2°C | 113 mm | 69% | 2.5 m/s | 2.9 |
| 2015 | 5.7°C | 0.3°C | -5.0°C | 18.3°C | -11.6°C | 25 mm | 63% | 2.4 m/s | 2.9 |
| 2014 | 8.7°C | 3.2°C | -2.3°C | 17.0°C | -8.1°C | 56 mm | 68% | 2 m/s | 2.4 |
| 2013 | 5.3°C | -0.2°C | -5.7°C | 15.1°C | -15.9°C | 32 mm | 63% | 2.1 m/s | 3 |
| 2012 | 6.7°C | 1.2°C | -4.4°C | 19.3°C | -12.0°C | 53 mm | 64% | 2.4 m/s | 2.8 |
| 2011 | 4.8°C | -0.5°C | -5.9°C | 15.9°C | -13.5°C | 50 mm | 68% | 1.7 m/s | 2.8 |
| 2010 | 9.2°C | 3.5°C | -2.2°C | 19.4°C | -20.8°C | 92 mm | 68% | 2.6 m/s | 2.4 |
| 2009 | 3.4°C | -1.8°C | -7.0°C | 12.4°C | -16.0°C | 74 mm | 68% | 2.3 m/s | 2.8 |
| 2008 | 5.6°C | 0.5°C | -4.7°C | 17.5°C | -13.7°C | 100 mm | 67% | 2.7 m/s | 2.7 |
| 2007 | 4.5°C | -0.9°C | -6.2°C | 17.6°C | -11.9°C | 102 mm | 66% | 2.5 m/s | 2.7 |
| 2006 | 6.4°C | 0.7°C | -4.9°C | 14.4°C | -11.7°C | 25 mm | 62% | 2 m/s | 2.9 |
| 2005 | 8.3°C | 2.2°C | -3.9°C | 15.9°C | -9.5°C | 0 mm | 50% | 2 m/s | 3 |
| 2004 | 7.6°C | 1.9°C | -3.8°C | 17.2°C | -11.5°C | 83 mm | 67% | 2.1 m/s | 2.7 |
| 2003 | 8.1°C | 2.2°C | -3.8°C | 18.4°C | -10.2°C | 22 mm | 53% | 2.4 m/s | 3 |
| 2002 | 7.1°C | 1.5°C | -4.1°C | 13.5°C | -9.5°C | 27 mm | 64% | 1.9 m/s | 2.7 |
| 2001 | 6.1°C | 0.3°C | -5.4°C | 14.1°C | -12.6°C | 34 mm | 60% | 2.1 m/s | 2.8 |
| 2000 | 9.3°C | 3.1°C | -3.1°C | 15.6°C | -6.7°C | 7 mm | 54% | 1.9 m/s | 3.1 |
| 1999 | 6.6°C | 0.7°C | -5.3°C | 14.0°C | -10.9°C | 2 mm | 52% | 2.1 m/s | 3.1 |
| 1998 | 6.6°C | 1.0°C | -4.6°C | 16.1°C | -12.0°C | 13 mm | 63% | 2.4 m/s | 3 |
| 1997 | 4.5°C | -0.9°C | -6.2°C | 12.1°C | -14.0°C | 54 mm | 68% | 2.2 m/s | 2.8 |
| 1996 | 8.2°C | 2.4°C | -3.5°C | 17.3°C | -13.0°C | 13 mm | 56% | 2.7 m/s | 2.9 |
| 1995 | 8.8°C | 2.9°C | -3.1°C | 17.6°C | -9.1°C | 11 mm | 59% | 1.8 m/s | 2.8 |
| 1994 | 6.6°C | 1.4°C | -3.9°C | 12.8°C | -10.8°C | 51 mm | 69% | 1.8 m/s | 2.7 |
| 1993 | 6.0°C | 0.2°C | -5.6°C | 14.2°C | -11.8°C | 17 mm | 62% | 2.1 m/s | 3 |
| 1992 🌧️ | 3.5°C | -1.7°C | -6.9°C | 10.3°C | -13.3°C | 127 mm | 80% | 2.3 m/s | 2.5 |
| 1991 | 6.2°C | 1.0°C | -4.3°C | 12.5°C | -15.0°C | 74 mm | 78% | 1.6 m/s | 2.6 |
| 1990 ❄️ | 3.5°C | -2.4°C | -8.3°C | 13.7°C | -25.3°C | 51 mm | 64% | 2.5 m/s | 3 |
| 1989 | 7.9°C | 1.8°C | -4.3°C | 15.0°C | -8.2°C | 20 mm | 50% | 1.8 m/s | 3.1 |
| 1988 | 5.6°C | -0.3°C | -6.1°C | 13.2°C | -15.2°C | 30 mm | 64% | 2.2 m/s | 2.8 |
| 1987 | 5.1°C | -0.7°C | -6.4°C | 16.5°C | -14.8°C | 56 mm | 72% | 2 m/s | 2.7 |
| 1986 | 5.9°C | 0.7°C | -4.4°C | 14.0°C | -10.7°C | 45 mm | 71% | 1.5 m/s | 2.5 |
| 1985 | 7.0°C | 1.3°C | -4.5°C | 13.1°C | -11.4°C | 9 mm | 65% | 1.7 m/s | 3 |
| 1984 | 5.3°C | 0.5°C | -4.3°C | 10.3°C | -11.7°C | 124 mm | 83% | 2 m/s | 2.4 |
| 1983 | 7.7°C | 2.5°C | -2.7°C | 14.7°C | -8.4°C | 66 mm | 72% | 2.9 m/s | — |
| 1982 | 5.4°C | 0.0°C | -5.4°C | 14.3°C | -13.1°C | 85 mm | 73% | 2.3 m/s | — |
| 1981 | 10.5°C | 4.2°C | -2.2°C | 19.3°C | -7.8°C | 9 mm | 58% | 2 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 7.1°C with lows near -4.2°C (mean 1.4°C), based on 45 years of NASA POWER data.
December averages 44 mm of rainfall in Flagstaff, about average for rainfall. The wettest on record was 127 mm in 1992.
The hottest December reached 19.9°C in 2025. The coldest dipped to -25.3°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 2.7°C. Daytime highs moved from 7.2°C to 10.4°C and overnight lows from -3.8°C to -1.6°C over the same span.
December is one of the cooler months of the year in Flagstaff and about average for rainfall, so plan for around 7.1°C daytime highs and -4.2°C at night.
Not quite — December is the 2nd coolest month in Flagstaff, averaging 1.4°C.
For December in Flagstaff, pack warm layers and a jacket for chilly mornings, with typical highs of 7.1°C and lows of -4.2°C.
Relative humidity in December averages 63% — moderately humid.
Average wind speed in December is 2.1 m/s. The windiest December on record averaged 2.9 m/s (1983).
The wettest December on record was 1992 with 127 mm. On average, December sees 44 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 Flagstaff 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.
