December is one of the cooler months of the year in Helena, with average highs near -2.2°C and lows around -11.8°C (mean -7°C). It is about average for rainfall, averaging 33 mm of rainfall and 88% relative humidity across the period.
December is one of the cooler months of the year in Helena. Across 45 years of records, the warmest December in Helena was 2025 — when the month averaged -1.4°C — while the coldest was 1983 at -15.4°C. Typical December days reach -2.2°C with nights near -11.8°C. The long-term trend is warming, about 0.8°C per decade.
December is about average for rainfall in Helena, averaging 33 mm of rainfall. The wettest December on record was 1996 with 84 mm, while the driest was 1986 at 11 mm.
Relative humidity in Helena during December averages 88%. The most humid December was 2010 at 96%, and the least humid was 1990 at 80%.
December receives about 1.2 kWh/m²/day of solar energy in Helena. The sunniest Decembers were 2020, 2022 and 2023, among others at 1.3 kWh/m²/day, and the cloudiest were 2008, 2016 and 2021, among others at 1.
Average wind speed in Helena during December is 1.4 m/s. The windiest December was 1990 at 1.9 m/s, while the calmest was 2023 at 1.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | -8.3°C | -7.3°C | -7.1°C | -7.4°C | -3.9°C | +4.4°C |
| Avg High | -3.3°C | -2.4°C | -2.3°C | -2.7°C | 0.6°C | +3.9°C |
| Avg Low | -13.3°C | -12.2°C | -12.0°C | -12.2°C | -8.4°C | +4.9°C |
| Avg Rain | 28 mm | 34 mm | 31 mm | 41 mm | 31 mm | +3 mm |
December temperatures in Helena have risen by about 5.8°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -43.1°C (1983) to a record high of 12.4°C (2021).
Rainfall in December is about average for rainfall, averaging 33 mm, with a wettest year of 84 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 Helena
If your dates are flexible, the more temperate months of July and August tend to be the most comfortable for visiting Helena. That said, December — with days averaging -2.2°C and nights around -11.8°C (mean -7°C) and moderate rainfall (33 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 🔥 | 2.6°C | -1.4°C | -5.4°C | 7.9°C | -16.1°C | 66 mm | 85% | 1.6 m/s | — |
| 2024 | 2.5°C | -1.7°C | -6.0°C | 6.8°C | -11.6°C | 26 mm | 82% | 1.3 m/s | 1.1 |
| 2023 | 2.2°C | -2.3°C | -6.8°C | 8.4°C | -14.3°C | 12 mm | 86% | 1.1 m/s | 1.3 |
| 2022 | -3.4°C | -8.6°C | -13.8°C | 3.0°C | -36.3°C | 32 mm | 90% | 1.3 m/s | 1.3 |
| 2021 | -1.4°C | -5.8°C | -10.2°C | 12.4°C | -22.7°C | 36 mm | 82% | 1.6 m/s | 1 |
| 2020 | 1.0°C | -3.7°C | -8.4°C | 6.4°C | -13.1°C | 15 mm | 83% | 1.4 m/s | 1.3 |
| 2019 | 0.4°C | -4.3°C | -8.9°C | 5.9°C | -17.2°C | 16 mm | 87% | 1.3 m/s | 1.2 |
| 2018 | -1.9°C | -6.6°C | -11.4°C | 3.5°C | -24.7°C | 28 mm | 87% | 1.4 m/s | 1.2 |
| 2017 | -2.8°C | -7.9°C | -12.9°C | 3.7°C | -26.3°C | 62 mm | 89% | 1.3 m/s | 1.1 |
| 2016 | -6.9°C | -12.0°C | -17.1°C | 1.5°C | -34.5°C | 46 mm | 93% | 1.5 m/s | 1 |
| 2015 | -2.5°C | -7.1°C | -11.6°C | 7.2°C | -23.2°C | 51 mm | 92% | 1.3 m/s | 1.1 |
| 2014 | -1.2°C | -5.8°C | -10.4°C | 7.0°C | -28.0°C | 47 mm | 93% | 1.3 m/s | 1.2 |
| 2013 | -5.0°C | -9.2°C | -13.3°C | 2.9°C | -26.5°C | 44 mm | 89% | 1.6 m/s | 1.1 |
| 2012 | -2.2°C | -6.7°C | -11.3°C | 7.8°C | -18.1°C | 36 mm | 86% | 1.5 m/s | 1.1 |
| 2011 | -1.3°C | -6.3°C | -11.3°C | 3.6°C | -19.9°C | 33 mm | 89% | 1.5 m/s | 1.3 |
| 2010 | -3.6°C | -8.6°C | -13.5°C | 1.3°C | -24.8°C | 49 mm | 96% | 1.2 m/s | 1.3 |
| 2009 | -6.6°C | -11.3°C | -16.0°C | 0.9°C | -25.0°C | 41 mm | 91% | 1.3 m/s | 1.3 |
| 2008 | -5.7°C | -10.6°C | -15.6°C | 5.3°C | -29.1°C | 58 mm | 89% | 1.6 m/s | 1 |
| 2007 | -3.1°C | -7.7°C | -12.4°C | 4.1°C | -17.8°C | 32 mm | 87% | 1.6 m/s | 1.1 |
| 2006 | -1.0°C | -5.8°C | -10.5°C | 3.0°C | -18.3°C | 24 mm | 88% | 1.4 m/s | 1.2 |
| 2005 | -3.9°C | -8.8°C | -13.6°C | 4.4°C | -28.0°C | 35 mm | 95% | 1.3 m/s | 1.3 |
| 2004 | 0.3°C | -4.4°C | -9.0°C | 6.8°C | -21.5°C | 25 mm | 86% | 1.5 m/s | 1.1 |
| 2003 | -0.2°C | -4.9°C | -9.7°C | 6.9°C | -20.8°C | 37 mm | 87% | 1.3 m/s | 1.2 |
| 2002 | 1.2°C | -3.7°C | -8.6°C | 6.0°C | -15.6°C | 17 mm | 84% | 1.2 m/s | 1.1 |
| 2001 | -1.9°C | -6.8°C | -11.7°C | 2.2°C | -16.5°C | 20 mm | 85% | 1.4 m/s | 1.2 |
| 2000 | -2.4°C | -7.5°C | -12.5°C | 4.3°C | -20.3°C | 21 mm | 88% | 1.2 m/s | 1.2 |
| 1999 | 0.2°C | -4.2°C | -8.6°C | 3.6°C | -12.8°C | 30 mm | 83% | 1.6 m/s | 1.1 |
| 1998 | -3.5°C | -7.7°C | -12.0°C | 4.1°C | -27.8°C | 44 mm | 86% | 1.7 m/s | 1 |
| 1997 | -1.0°C | -5.7°C | -10.3°C | 3.6°C | -14.5°C | 15 mm | 87% | 1.5 m/s | 1.3 |
| 1996 🌧️ | -4.6°C | -9.5°C | -14.5°C | 1.3°C | -30.0°C | 84 mm | 96% | 1.4 m/s | 1.2 |
| 1995 | -0.8°C | -5.9°C | -11.0°C | 3.8°C | -23.8°C | 36 mm | 86% | 1.3 m/s | 1.3 |
| 1994 | -1.7°C | -6.5°C | -11.3°C | 3.6°C | -18.4°C | 23 mm | 87% | 1.3 m/s | 1.2 |
| 1993 | -1.0°C | -5.3°C | -9.6°C | 4.8°C | -14.4°C | 20 mm | 85% | 1.5 m/s | 1.2 |
| 1992 | -4.0°C | -9.1°C | -14.3°C | 2.6°C | -24.5°C | 30 mm | 84% | 1.5 m/s | 1.3 |
| 1991 | -1.6°C | -7.4°C | -13.2°C | 1.4°C | -21.2°C | 27 mm | 95% | 1.4 m/s | 1.3 |
| 1990 | -6.4°C | -11.6°C | -16.8°C | 6.0°C | -32.6°C | 30 mm | 80% | 1.9 m/s | 1.2 |
| 1989 | -2.1°C | -6.6°C | -11.2°C | 6.2°C | -24.0°C | 36 mm | 89% | 1.4 m/s | 1 |
| 1988 | -1.9°C | -6.7°C | -11.4°C | 3.8°C | -22.6°C | 23 mm | 85% | 1.4 m/s | 1.2 |
| 1987 | -1.8°C | -6.1°C | -10.4°C | 7.7°C | -17.7°C | 28 mm | 82% | 1.5 m/s | 1.2 |
| 1986 | -1.0°C | -6.2°C | -11.5°C | 3.1°C | -17.5°C | 11 mm | 86% | 1.2 m/s | 1.3 |
| 1985 | -3.4°C | -8.8°C | -14.2°C | 0.5°C | -25.8°C | 14 mm | 96% | 1.3 m/s | 1.3 |
| 1984 | -4.5°C | -10.1°C | -15.7°C | 2.4°C | -23.8°C | 32 mm | 90% | 1.4 m/s | 1.3 |
| 1983 ❄️ | -9.5°C | -15.4°C | -21.2°C | 1.2°C | -43.1°C | 32 mm | 95% | 1.2 m/s | — |
| 1982 | -3.5°C | -8.1°C | -12.7°C | 2.8°C | -21.8°C | 45 mm | 92% | 1.4 m/s | — |
| 1981 | -2.2°C | -6.6°C | -11.0°C | 3.8°C | -17.5°C | 31 mm | 87% | 1.5 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around -2.2°C with lows near -11.8°C (mean -7°C), based on 45 years of NASA POWER data.
December averages 33 mm of rainfall in Helena, about average for rainfall. The wettest on record was 84 mm in 1996.
The hottest December reached 12.4°C in 2021. The coldest dipped to -43.1°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 5.8°C. Daytime highs moved from -4.6°C to 0.5°C and overnight lows from -15°C to -8.4°C over the same span.
December is one of the cooler months of the year in Helena and about average for rainfall, so plan for around -2.2°C daytime highs and -11.8°C at night.
Not quite — December is the 2nd coolest month in Helena, averaging -7°C.
For December in Helena, pack warm layers and a jacket for chilly mornings, with typical highs of -2.2°C and lows of -11.8°C.
Relative humidity in December averages 88% — quite humid.
Average wind speed in December is 1.4 m/s. The windiest December on record averaged 1.9 m/s (1990).
The wettest December on record was 1996 with 84 mm. On average, December sees 33 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 Helena 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.
