December is one of the cooler months of the year in Idaho Falls, with average highs near -1.8°C and lows around -11°C (mean -6.4°C). It is a relatively wet time of year, averaging 55 mm of rainfall and 86% relative humidity across the period.
December is one of the cooler months of the year in Idaho Falls. Across 45 years of records, the warmest December in Idaho Falls was 2025 — when the month averaged -0.1°C — while the coldest was 1990 at -11.3°C. Typical December days reach -1.8°C with nights near -11°C. The long-term trend is warming, about 0.8°C per decade.
December is a relatively wet time of year in Idaho Falls, averaging 55 mm of rainfall. The wettest December on record was 1996 with 151 mm, while the driest was 1986 at 7 mm.
Relative humidity in Idaho Falls during December averages 86%. The most humid December was 1985 at 95%, and the least humid was 1986 at 77%.
December receives about 1.4 kWh/m²/day of solar energy in Idaho Falls. The sunniest December was 2011 at 1.9 kWh/m²/day, and the cloudiest was 2021 at 1.
Average wind speed in Idaho Falls during December is 2.6 m/s. The windiest December was 1996 at 3.8 m/s, while the calmest was 1986 at 1.6 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | -7.6°C | -7.1°C | -6.2°C | -6.5°C | -3.7°C | +3.9°C |
| Avg High | -2.8°C | -2.5°C | -1.7°C | -1.9°C | 0.6°C | +3.4°C |
| Avg Low | -12.4°C | -11.6°C | -10.7°C | -11.2°C | -8.0°C | +4.4°C |
| Avg Rain | 41 mm | 53 mm | 58 mm | 61 mm | 64 mm | +24 mm |
December temperatures in Idaho Falls have risen by about 5°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -33.1°C (1990) to a record high of 11°C (1995).
Rainfall in December is a relatively wet time of year, averaging 55 mm, with a wettest year of 151 mm.
Daytime highs and overnight lows have shifted differently — highs rose about 0.7°C per decade while lows rose 0.9°C per decade, narrowing the gap between day and night.
A quieter season to visit Idaho Falls
If your dates are flexible, the more temperate months of July and August tend to be the most comfortable for visiting Idaho Falls. That said, December — with days averaging -1.8°C and nights around -11°C (mean -6.4°C) and moderate rainfall (55 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 🔥 | 3.8°C | -0.1°C | -4.0°C | 10.3°C | -13.1°C | 113 mm | 80% | 3.6 m/s | — |
| 2024 | 1.9°C | -2.1°C | -6.0°C | 5.9°C | -14.5°C | 68 mm | 82% | 2.5 m/s | 1.5 |
| 2023 | 0.9°C | -3.4°C | -7.7°C | 6.1°C | -14.7°C | 48 mm | 86% | 2.1 m/s | 1.6 |
| 2022 | -3.1°C | -8.0°C | -12.9°C | 2.2°C | -32.1°C | 61 mm | 93% | 2.7 m/s | 1.6 |
| 2021 | 0.2°C | -3.8°C | -7.9°C | 10.1°C | -18.5°C | 66 mm | 81% | 3.7 m/s | 1 |
| 2020 | 0.1°C | -4.6°C | -9.3°C | 5.8°C | -16.1°C | 31 mm | 79% | 2.3 m/s | 1.6 |
| 2019 | -1.8°C | -6.3°C | -10.7°C | 3.1°C | -20.2°C | 44 mm | 90% | 2.3 m/s | 1.2 |
| 2018 | -2.8°C | -8.0°C | -13.3°C | 1.3°C | -21.9°C | 41 mm | 91% | 2.4 m/s | 1.3 |
| 2017 | -1.3°C | -5.8°C | -10.3°C | 4.6°C | -22.9°C | 45 mm | 84% | 2.3 m/s | 1.4 |
| 2016 | -5.2°C | -10.7°C | -16.2°C | 0.8°C | -29.0°C | 115 mm | 93% | 2.6 m/s | 1.3 |
| 2015 | -2.1°C | -6.2°C | -10.4°C | 9.5°C | -23.1°C | 68 mm | 89% | 2.9 m/s | 1.4 |
| 2014 | 0.8°C | -3.6°C | -8.0°C | 10.2°C | -30.7°C | 66 mm | 87% | 2.6 m/s | 1.4 |
| 2013 | -2.7°C | -7.2°C | -11.7°C | 3.7°C | -20.5°C | 38 mm | 80% | 2.9 m/s | 1.5 |
| 2012 | -1.4°C | -5.8°C | -10.3°C | 8.8°C | -19.8°C | 77 mm | 85% | 3.1 m/s | 1.2 |
| 2011 | -1.0°C | -5.7°C | -10.4°C | 7.4°C | -15.8°C | 27 mm | 81% | 2.3 m/s | 1.9 |
| 2010 | -1.6°C | -6.2°C | -10.8°C | 1.3°C | -27.2°C | 83 mm | 94% | 2.5 m/s | 1.2 |
| 2009 | -3.7°C | -8.3°C | -12.9°C | 1.7°C | -20.2°C | 30 mm | 81% | 2.4 m/s | 1.4 |
| 2008 | -2.0°C | -6.7°C | -11.4°C | 6.3°C | -22.4°C | 75 mm | 80% | 3.2 m/s | 1.2 |
| 2007 | -3.0°C | -7.1°C | -11.3°C | 4.0°C | -19.9°C | 56 mm | 86% | 2.7 m/s | 1.1 |
| 2006 | -0.9°C | -5.5°C | -10.0°C | 5.7°C | -18.8°C | 56 mm | 82% | 2.4 m/s | 1.6 |
| 2005 | -3.3°C | -7.8°C | -12.4°C | 3.5°C | -29.1°C | 91 mm | 93% | 2.5 m/s | 1.5 |
| 2004 | 0.2°C | -3.9°C | -8.1°C | 5.0°C | -20.8°C | 50 mm | 85% | 2.6 m/s | 1.4 |
| 2003 | 0.2°C | -4.2°C | -8.6°C | 5.1°C | -22.5°C | 77 mm | 86% | 2.8 m/s | 1.3 |
| 2002 | 1.3°C | -2.9°C | -7.0°C | 7.5°C | -16.5°C | 47 mm | 83% | 2.6 m/s | 1.2 |
| 2001 | -4.1°C | -9.0°C | -13.9°C | 1.1°C | -19.6°C | 63 mm | 95% | 2.4 m/s | 1.4 |
| 2000 | -1.3°C | -6.3°C | -11.3°C | 3.3°C | -18.1°C | 35 mm | 86% | 2.2 m/s | 1.4 |
| 1999 | -1.2°C | -5.8°C | -10.4°C | 2.9°C | -16.5°C | 40 mm | 85% | 2.3 m/s | 1.4 |
| 1998 | -2.0°C | -5.7°C | -9.5°C | 7.3°C | -25.8°C | 37 mm | 81% | 2.8 m/s | 1.1 |
| 1997 | -1.9°C | -6.6°C | -11.2°C | 3.4°C | -18.9°C | 28 mm | 85% | 2.1 m/s | 1.6 |
| 1996 🌧️ | -2.8°C | -6.5°C | -10.1°C | 2.3°C | -27.5°C | 151 mm | 94% | 3.8 m/s | 1.1 |
| 1995 | -0.3°C | -4.7°C | -9.0°C | 11.0°C | -15.1°C | 60 mm | 84% | 2.5 m/s | 1.5 |
| 1994 | -2.6°C | -6.6°C | -10.6°C | 2.4°C | -23.9°C | 52 mm | 92% | 2.3 m/s | 1.5 |
| 1993 | -1.8°C | -6.6°C | -11.4°C | 4.1°C | -18.5°C | 28 mm | 86% | 2.5 m/s | 1.4 |
| 1992 | -4.9°C | -9.7°C | -14.6°C | 1.0°C | -26.3°C | 68 mm | 94% | 3 m/s | 1.3 |
| 1991 | -1.8°C | -7.3°C | -12.7°C | 2.1°C | -25.0°C | 20 mm | 89% | 2.2 m/s | 1.6 |
| 1990 ❄️ | -6.2°C | -11.3°C | -16.3°C | 7.0°C | -33.1°C | 42 mm | 81% | 2.7 m/s | 1.6 |
| 1989 | -0.9°C | -5.8°C | -10.8°C | 2.9°C | -21.1°C | 13 mm | 82% | 2.1 m/s | 1.4 |
| 1988 | -4.3°C | -9.3°C | -14.2°C | 0.7°C | -26.4°C | 42 mm | 91% | 2.2 m/s | 1.3 |
| 1987 | -1.4°C | -5.8°C | -10.2°C | 8.5°C | -23.6°C | 42 mm | 80% | 2.8 m/s | 1.3 |
| 1986 | 0.3°C | -4.6°C | -9.6°C | 5.6°C | -16.2°C | 7 mm | 77% | 1.6 m/s | 1.5 |
| 1985 | -5.1°C | -9.9°C | -14.7°C | 1.4°C | -26.4°C | 30 mm | 95% | 1.7 m/s | 1.5 |
| 1984 | -3.8°C | -9.3°C | -14.8°C | 2.1°C | -23.2°C | 31 mm | 89% | 2.7 m/s | 1.7 |
| 1983 | -5.6°C | -10.4°C | -15.2°C | 1.3°C | -29.2°C | 73 mm | 95% | 2.2 m/s | — |
| 1982 | -3.4°C | -8.0°C | -12.6°C | 1.6°C | -25.6°C | 57 mm | 92% | 2.7 m/s | — |
| 1981 | -0.6°C | -5.1°C | -9.7°C | 8.8°C | -22.2°C | 70 mm | 87% | 2.9 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around -1.8°C with lows near -11°C (mean -6.4°C), based on 45 years of NASA POWER data.
December averages 55 mm of rainfall in Idaho Falls, a relatively wet time of year. The wettest on record was 151 mm in 1996.
The hottest December reached 11°C in 1995. The coldest dipped to -33.1°C in 1990.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 5°C. Daytime highs moved from -3.7°C to 0.7°C and overnight lows from -13.4°C to -7.7°C over the same span.
December is one of the cooler months of the year in Idaho Falls and a relatively wet time of year, so plan for around -1.8°C daytime highs and -11°C at night.
Not quite — December is the 2nd coolest month in Idaho Falls, averaging -6.4°C.
For December in Idaho Falls, pack warm layers and a jacket for chilly mornings, with typical highs of -1.8°C and lows of -11°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 86% — quite humid.
Average wind speed in December is 2.6 m/s. The windiest December on record averaged 3.8 m/s (1996).
The wettest December on record was 1996 with 151 mm. On average, December sees 55 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 Idaho Falls 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.
