December is one of the cooler months of the year in Boise, with average highs near 2.4°C and lows around -5.2°C (mean -1.4°C). It is a relatively wet time of year, averaging 62 mm of rainfall and 79% relative humidity across the period.
December is one of the cooler months of the year in Boise. Across 45 years of records, the warmest December in Boise was 2025 — when the month averaged 4.2°C — while the coldest was 1985 at -6.2°C. Typical December days reach 2.4°C with nights near -5.2°C. The long-term trend is warming, about 0.7°C per decade.
December is a relatively wet time of year in Boise, averaging 62 mm of rainfall. The wettest December on record was 1996 with 158 mm, while the driest was 1989 at 5 mm.
Relative humidity in Boise during December averages 79%. The most humid December was 1985 at 92%, and the least humid was 1990 at 68%.
December receives about 1.4 kWh/m²/day of solar energy in Boise. The sunniest December was 2011 at 1.9 kWh/m²/day, and the cloudiest was 2015 at 1.1.
Average wind speed in Boise during December is 2.1 m/s. The windiest Decembers were 2010, 2012 and 2014 at 2.6 m/s, while the calmest was 1985 at 1.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | -2.7°C | -1.8°C | -0.9°C | -1.3°C | 0.5°C | +3.2°C |
| Avg High | 1.2°C | 1.9°C | 2.8°C | 2.5°C | 4.3°C | +3.1°C |
| Avg Low | -6.5°C | -5.6°C | -4.6°C | -5.1°C | -3.3°C | +3.2°C |
| Avg Rain | 50 mm | 55 mm | 65 mm | 65 mm | 80 mm | +30 mm |
December temperatures in Boise have risen by about 4.5°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -26°C (1990) to a record high of 15.6°C (2021).
Rainfall in December is a relatively wet time of year, averaging 62 mm, with a wettest year of 158 mm.
A quieter season to visit Boise
If your dates are flexible, the more temperate months of August and July tend to be the most comfortable for visiting Boise. That said, December — with days averaging 2.4°C and nights around -5.2°C (mean -1.4°C) and moderate rainfall (62 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 🔥 | 8.3°C | 4.2°C | 0.1°C | 15.6°C | -5.1°C | 108 mm | 76% | 2.1 m/s | — |
| 2024 | 5.1°C | 1.8°C | -1.6°C | 9.8°C | -5.2°C | 104 mm | 79% | 1.9 m/s | 1.3 |
| 2023 | 4.8°C | 1.4°C | -1.9°C | 13.0°C | -6.1°C | 63 mm | 82% | 1.8 m/s | 1.3 |
| 2022 | 0.4°C | -3.5°C | -7.4°C | 7.9°C | -17.2°C | 88 mm | 87% | 2.2 m/s | 1.3 |
| 2021 | 3.7°C | -0.3°C | -4.3°C | 15.6°C | -17.8°C | 83 mm | 78% | 2.1 m/s | 1.2 |
| 2020 | 3.3°C | -0.7°C | -4.7°C | 11.1°C | -7.9°C | 35 mm | 74% | 1.9 m/s | 1.6 |
| 2019 | 4.1°C | 0.7°C | -2.7°C | 12.0°C | -8.6°C | 53 mm | 77% | 2.1 m/s | 1.2 |
| 2018 | 2.2°C | -1.8°C | -5.9°C | 8.0°C | -13.7°C | 63 mm | 80% | 2.2 m/s | 1.4 |
| 2017 | 1.5°C | -2.0°C | -5.6°C | 8.3°C | -11.5°C | 30 mm | 80% | 1.6 m/s | 1.3 |
| 2016 | -1.0°C | -5.5°C | -10.0°C | 5.8°C | -20.8°C | 100 mm | 84% | 2.1 m/s | 1.4 |
| 2015 | 1.3°C | -2.4°C | -6.1°C | 11.1°C | -16.9°C | 117 mm | 86% | 2.4 m/s | 1.1 |
| 2014 | 5.8°C | 1.9°C | -2.0°C | 14.6°C | -13.4°C | 93 mm | 79% | 2.6 m/s | 1.2 |
| 2013 | 1.5°C | -2.5°C | -6.5°C | 7.9°C | -16.0°C | 22 mm | 74% | 1.8 m/s | 1.5 |
| 2012 | 3.1°C | -0.3°C | -3.8°C | 12.7°C | -10.9°C | 60 mm | 75% | 2.6 m/s | 1.4 |
| 2011 | 3.4°C | -0.8°C | -4.9°C | 9.4°C | -8.5°C | 24 mm | 69% | 1.7 m/s | 1.9 |
| 2010 | 2.8°C | -0.6°C | -3.9°C | 9.5°C | -17.2°C | 92 mm | 85% | 2.6 m/s | 1.3 |
| 2009 | 0.2°C | -3.7°C | -7.6°C | 5.1°C | -15.0°C | 53 mm | 76% | 2 m/s | 1.6 |
| 2008 | 2.2°C | -1.7°C | -5.5°C | 11.8°C | -13.4°C | 70 mm | 74% | 2.4 m/s | 1.4 |
| 2007 | 1.8°C | -1.8°C | -5.3°C | 10.0°C | -12.6°C | 54 mm | 80% | 2 m/s | 1.3 |
| 2006 | 2.7°C | -0.9°C | -4.5°C | 8.3°C | -9.2°C | 64 mm | 77% | 2.1 m/s | 1.6 |
| 2005 | 1.3°C | -2.2°C | -5.8°C | 8.4°C | -13.9°C | 122 mm | 83% | 2.1 m/s | 1.3 |
| 2004 | 5.1°C | 1.1°C | -2.9°C | 10.3°C | -7.8°C | 44 mm | 79% | 2 m/s | 1.4 |
| 2003 | 4.8°C | 1.1°C | -2.5°C | 13.6°C | -12.6°C | 80 mm | 77% | 2.5 m/s | 1.3 |
| 2002 | 5.5°C | 1.9°C | -1.6°C | 11.8°C | -6.0°C | 77 mm | 76% | 2.3 m/s | 1.3 |
| 2001 | 1.6°C | -2.1°C | -5.9°C | 4.8°C | -13.3°C | 56 mm | 83% | 2.4 m/s | 1.3 |
| 2000 | 2.4°C | -1.2°C | -4.8°C | 6.2°C | -8.1°C | 28 mm | 80% | 1.7 m/s | 1.4 |
| 1999 | 3.0°C | -0.7°C | -4.3°C | 6.2°C | -8.5°C | 38 mm | 77% | 1.9 m/s | 1.4 |
| 1998 | 1.1°C | -2.0°C | -5.1°C | 10.3°C | -17.7°C | 56 mm | 75% | 2.2 m/s | 1.3 |
| 1997 | 2.4°C | -1.4°C | -5.2°C | 7.0°C | -11.5°C | 24 mm | 75% | 2 m/s | 1.6 |
| 1996 🌧️ | 2.5°C | -0.5°C | -3.5°C | 9.3°C | -10.1°C | 158 mm | 83% | 2.5 m/s | 1.3 |
| 1995 | 3.4°C | -0.4°C | -4.2°C | 13.1°C | -10.3°C | 84 mm | 81% | 2.1 m/s | 1.3 |
| 1994 | 1.3°C | -2.5°C | -6.3°C | 6.2°C | -14.5°C | 54 mm | 85% | 1.9 m/s | 1.4 |
| 1993 | 2.8°C | -0.9°C | -4.5°C | 6.9°C | -9.6°C | 29 mm | 75% | 2.3 m/s | 1.4 |
| 1992 | 0.2°C | -4.0°C | -8.2°C | 3.7°C | -15.5°C | 56 mm | 85% | 2.5 m/s | 1.3 |
| 1991 | 3.9°C | -0.2°C | -4.3°C | 7.5°C | -7.9°C | 21 mm | 77% | 2.3 m/s | 1.5 |
| 1990 | -1.2°C | -5.7°C | -10.2°C | 10.4°C | -26.0°C | 25 mm | 68% | 2.4 m/s | 1.6 |
| 1989 | 4.0°C | 0.0°C | -3.9°C | 8.2°C | -8.4°C | 5 mm | 74% | 1.6 m/s | 1.6 |
| 1988 | 0.6°C | -3.4°C | -7.5°C | 6.4°C | -18.5°C | 38 mm | 82% | 1.8 m/s | 1.4 |
| 1987 | 3.0°C | -1.1°C | -5.1°C | 12.8°C | -13.7°C | 43 mm | 76% | 2.5 m/s | 1.4 |
| 1986 | 3.6°C | -0.4°C | -4.4°C | 7.9°C | -8.8°C | 10 mm | 71% | 1.7 m/s | 1.3 |
| 1985 ❄️ | -2.4°C | -6.2°C | -10.0°C | 2.7°C | -16.7°C | 34 mm | 92% | 1.4 m/s | 1.7 |
| 1984 | -0.3°C | -4.9°C | -9.4°C | 3.9°C | -15.3°C | 33 mm | 84% | 2.1 m/s | 1.6 |
| 1983 | -2.1°C | -5.4°C | -8.7°C | 4.5°C | -20.9°C | 109 mm | 90% | 2.1 m/s | — |
| 1982 | 1.0°C | -2.6°C | -6.1°C | 6.8°C | -13.9°C | 78 mm | 86% | 2.4 m/s | — |
| 1981 | 3.7°C | 0.1°C | -3.5°C | 12.1°C | -13.4°C | 99 mm | 83% | 2.5 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 2.4°C with lows near -5.2°C (mean -1.4°C), based on 45 years of NASA POWER data.
December averages 62 mm of rainfall in Boise, a relatively wet time of year. The wettest on record was 158 mm in 1996.
The hottest December reached 15.6°C in 2021. The coldest dipped to -26°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 4.5°C. Daytime highs moved from 0°C to 4.5°C and overnight lows from -7.5°C to -3°C over the same span.
December is one of the cooler months of the year in Boise and a relatively wet time of year, so plan for around 2.4°C daytime highs and -5.2°C at night.
Not quite — December is the 2nd coolest month in Boise, averaging -1.4°C.
For December in Boise, pack warm layers and a jacket for chilly mornings, with typical highs of 2.4°C and lows of -5.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 79% — quite humid.
Average wind speed in December is 2.1 m/s. The windiest December on record averaged 2.6 m/s (2010).
The wettest December on record was 1996 with 158 mm. On average, December sees 62 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 Boise 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.
