December is one of the cooler months of the year in Thunder Bay, with average highs near -6.6°C and lows around -14.3°C (mean -10.4°C). It is one of the drier months, averaging 31 mm of rainfall and 93% relative humidity across the period.
December is one of the cooler months of the year in Thunder Bay. Across 45 years of records, the warmest December in Thunder Bay was 2023 — when the month averaged -2.8°C — while the coldest was 1983 at -19°C. Typical December days reach -6.6°C with nights near -14.3°C. The long-term trend is warming, about 0.9°C per decade.
December is one of the drier months in Thunder Bay, averaging 31 mm of rainfall. The wettest December on record was 1984 with 73 mm, while the driest were 1986, 1987 and 1994 at 12 mm.
Relative humidity in Thunder Bay during December averages 93%. The most humid December was 1985 at 100%, and the least humid was 2023 at 86%.
December receives about 0.9 kWh/m²/day of solar energy in Thunder Bay. The sunniest Decembers were 2002, 2008 and 2010, among others at 1 kWh/m²/day, and the cloudiest were 1999 and 2022 at 0.7.
Average wind speed in Thunder Bay during December is 1.3 m/s. The windiest Decembers were 2016 and 2025 at 1.5 m/s, while the calmest was 1994 at 1.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | -12.6°C | -10.0°C | -10.5°C | -10.1°C | -8.2°C | +4.4°C |
| Avg High | -8.7°C | -6.0°C | -6.7°C | -6.4°C | -4.4°C | +4.3°C |
| Avg Low | -16.6°C | -14.0°C | -14.3°C | -13.7°C | -12.0°C | +4.6°C |
| Avg Rain | 32 mm | 25 mm | 37 mm | 29 mm | 34 mm | +2 mm |
December temperatures in Thunder Bay have risen by about 5.6°C between 1981–1985 and 2021–2025.
December has ranged from a record low of -35.5°C (1983) to a record high of 6.8°C (2023).
Rainfall in December is one of the drier months, averaging 31 mm, with a wettest year of 73 mm.
A quieter season to visit Thunder Bay
If your dates are flexible, the more temperate months of August and July tend to be the most comfortable for visiting Thunder Bay. That said, December — with days averaging -6.6°C and nights around -14.3°C (mean -10.4°C) and moderate rainfall (31 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 | -7.2°C | -12.0°C | -16.9°C | 2.2°C | -23.4°C | 26 mm | 91% | 1.5 m/s | — |
| 2024 | -4.4°C | -7.8°C | -11.1°C | 2.8°C | -26.2°C | 34 mm | 92% | 1.3 m/s | 0.9 |
| 2023 🔥 | 0.1°C | -2.8°C | -5.7°C | 6.8°C | -14.1°C | 31 mm | 86% | 1.2 m/s | 0.8 |
| 2022 | -6.2°C | -9.7°C | -13.3°C | 0.8°C | -22.2°C | 33 mm | 95% | 1.4 m/s | 0.7 |
| 2021 | -4.3°C | -8.5°C | -12.6°C | 3.4°C | -21.1°C | 49 mm | 90% | 1.3 m/s | 0.9 |
| 2020 | -4.5°C | -8.4°C | -12.4°C | 4.2°C | -25.3°C | 29 mm | 91% | 1.2 m/s | 0.9 |
| 2019 | -6.2°C | -10.1°C | -14.1°C | 0.7°C | -27.5°C | 34 mm | 95% | 1.3 m/s | 0.9 |
| 2018 | -4.3°C | -8.2°C | -12.1°C | 2.6°C | -26.2°C | 22 mm | 93% | 1.2 m/s | 0.9 |
| 2017 | -9.6°C | -13.4°C | -17.2°C | 4.7°C | -30.5°C | 27 mm | 93% | 1.3 m/s | 0.9 |
| 2016 | -6.6°C | -10.0°C | -13.4°C | 1.6°C | -27.5°C | 28 mm | 92% | 1.5 m/s | 0.8 |
| 2015 | -2.6°C | -5.6°C | -8.7°C | 4.6°C | -21.5°C | 51 mm | 95% | 1.3 m/s | 0.8 |
| 2014 | -5.1°C | -8.8°C | -12.5°C | 1.5°C | -27.6°C | 26 mm | 95% | 1.2 m/s | 0.9 |
| 2013 | -12.7°C | -16.9°C | -21.0°C | 0.2°C | -35.0°C | 37 mm | 97% | 1.3 m/s | 0.9 |
| 2012 | -4.8°C | -8.1°C | -11.5°C | 5.2°C | -20.3°C | 20 mm | 88% | 1.2 m/s | 0.8 |
| 2011 | -3.7°C | -7.5°C | -11.3°C | 1.6°C | -20.3°C | 21 mm | 87% | 1.3 m/s | 0.8 |
| 2010 | -8.3°C | -12.0°C | -15.7°C | 0.7°C | -28.0°C | 29 mm | 98% | 1.3 m/s | 1 |
| 2009 | -7.6°C | -10.7°C | -13.9°C | -0.3°C | -21.8°C | 31 mm | 88% | 1.3 m/s | 0.9 |
| 2008 | -10.3°C | -14.6°C | -18.8°C | 0.6°C | -29.4°C | 35 mm | 95% | 1.4 m/s | 1 |
| 2007 | -7.6°C | -11.8°C | -15.9°C | 1.1°C | -24.9°C | 42 mm | 99% | 1.3 m/s | 0.8 |
| 2006 | -3.0°C | -6.5°C | -10.1°C | 1.8°C | -17.6°C | 40 mm | 93% | 1.2 m/s | 0.9 |
| 2005 | -6.4°C | -10.0°C | -13.6°C | 0.1°C | -21.3°C | 34 mm | 97% | 1.2 m/s | 0.8 |
| 2004 | -7.1°C | -12.2°C | -17.3°C | 1.7°C | -32.2°C | 63 mm | 94% | 1.4 m/s | 0.8 |
| 2003 | -3.9°C | -8.0°C | -12.0°C | 2.5°C | -20.2°C | 26 mm | 96% | 1.3 m/s | 0.9 |
| 2002 | -4.4°C | -8.0°C | -11.5°C | 3.0°C | -20.3°C | 26 mm | 91% | 1.3 m/s | 1 |
| 2001 | -3.6°C | -7.0°C | -10.5°C | 3.7°C | -17.6°C | 35 mm | 93% | 1.4 m/s | 0.9 |
| 2000 | -12.7°C | -16.3°C | -19.9°C | -0.5°C | -27.2°C | 42 mm | 94% | 1.3 m/s | 1 |
| 1999 | -4.0°C | -7.7°C | -11.5°C | 3.4°C | -22.2°C | 21 mm | 88% | 1.3 m/s | 0.7 |
| 1998 | -5.5°C | -8.9°C | -12.3°C | 4.4°C | -28.0°C | 31 mm | 89% | 1.4 m/s | 0.8 |
| 1997 | -2.4°C | -6.0°C | -9.5°C | 3.4°C | -24.8°C | 13 mm | 89% | 1.2 m/s | 0.9 |
| 1996 | -8.7°C | -12.8°C | -16.9°C | 0.4°C | -30.8°C | 31 mm | 98% | 1.2 m/s | 0.9 |
| 1995 | -9.0°C | -13.5°C | -18.0°C | 0.2°C | -29.3°C | 27 mm | 99% | 1.4 m/s | 0.9 |
| 1994 | -2.2°C | -5.9°C | -9.6°C | 3.0°C | -20.6°C | 12 mm | 90% | 1.1 m/s | 0.8 |
| 1993 | -6.6°C | -10.6°C | -14.6°C | 1.5°C | -33.9°C | 16 mm | 95% | 1.2 m/s | 0.8 |
| 1992 | -6.4°C | -10.0°C | -13.5°C | 1.5°C | -23.8°C | 34 mm | 92% | 1.3 m/s | 0.8 |
| 1991 | -6.4°C | -10.8°C | -15.2°C | 0.1°C | -26.6°C | 29 mm | 98% | 1.2 m/s | 0.8 |
| 1990 | -9.1°C | -13.8°C | -18.6°C | 1.1°C | -33.4°C | 41 mm | 98% | 1.3 m/s | 0.8 |
| 1989 | -12.3°C | -16.7°C | -21.1°C | -1.0°C | -29.9°C | 24 mm | 94% | 1.3 m/s | 0.9 |
| 1988 | -8.3°C | -12.7°C | -17.1°C | 1.5°C | -32.4°C | 34 mm | 93% | 1.4 m/s | 0.8 |
| 1987 | -3.9°C | -7.3°C | -10.7°C | 1.7°C | -19.5°C | 12 mm | 90% | 1.2 m/s | 0.8 |
| 1986 | -4.5°C | -8.3°C | -12.1°C | 0.7°C | -25.0°C | 12 mm | 94% | 1.3 m/s | 0.8 |
| 1985 | -13.2°C | -16.7°C | -20.2°C | -5.0°C | -28.8°C | 17 mm | 100% | 1.4 m/s | 0.9 |
| 1984 🌧️ | -8.3°C | -12.8°C | -17.2°C | 3.4°C | -32.8°C | 73 mm | 94% | 1.4 m/s | 0.8 |
| 1983 ❄️ | -14.5°C | -19.0°C | -23.5°C | -2.7°C | -35.5°C | 41 mm | 100% | 1.4 m/s | — |
| 1982 | -5.4°C | -9.0°C | -12.5°C | 5.1°C | -28.3°C | 43 mm | 90% | 1.3 m/s | — |
| 1981 | -7.6°C | -11.3°C | -14.9°C | 0.5°C | -24.6°C | 30 mm | 96% | 1.2 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around -6.6°C with lows near -14.3°C (mean -10.4°C), based on 45 years of NASA POWER data.
December averages 31 mm of rainfall in Thunder Bay, one of the drier months. The wettest on record was 73 mm in 1984.
The hottest December reached 6.8°C in 2023. The coldest dipped to -35.5°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 5.6°C. Daytime highs moved from -9.8°C to -4.4°C and overnight lows from -17.7°C to -11.9°C over the same span.
December is one of the cooler months of the year in Thunder Bay and one of the drier months, so plan for around -6.6°C daytime highs and -14.3°C at night.
Not quite — December is the 3rd coolest month in Thunder Bay, averaging -10.4°C.
For December in Thunder Bay, pack warm layers and a jacket for chilly mornings, with typical highs of -6.6°C and lows of -14.3°C.
Relative humidity in December averages 93% — quite humid.
Average wind speed in December is 1.3 m/s. The windiest December on record averaged 1.5 m/s (2016).
The wettest December on record was 1984 with 73 mm. On average, December sees 31 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 Thunder Bay 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.
