May is one of the warmer months of the year in Thunder Bay, with average highs near 15.1°C and lows around 3.3°C (mean 9.2°C). It is a relatively wet time of year, averaging 68 mm of rainfall and 71% relative humidity across the period.
May is one of the warmer months of the year in Thunder Bay. Across 45 years of records, the warmest May in Thunder Bay was 2018 — when the month averaged 11.7°C — while the coldest was 1997 at 6.2°C. Typical May days reach 15.1°C with nights near 3.3°C. The long-term May temperature trend is broadly flat.
May is a relatively wet time of year in Thunder Bay, averaging 68 mm of rainfall. The wettest May on record was 2012 with 128 mm, while the driest was 2025 at 33 mm.
Relative humidity in Thunder Bay during May averages 71%. The most humid May was 2001 at 79%, and the least humid was 1998 at 63%.
May receives about 5.5 kWh/m²/day of solar energy in Thunder Bay. The sunniest May was 1998 at 6.5 kWh/m²/day, and the cloudiest was 1993 at 4.6.
Average wind speed in Thunder Bay during May is 0.6 m/s. The windiest Mays were 2008, 2009 and 2013, among others at 0.7 m/s, while the calmest were 1985, 2014 and 2018 at 0.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 9.6°C | 9.2°C | 8.5°C | 9.3°C | 9.7°C | +0.1°C |
| Avg High | 15.6°C | 15.2°C | 14.2°C | 15.2°C | 15.7°C | +0.1°C |
| Avg Low | 3.6°C | 3.2°C | 2.9°C | 3.4°C | 3.6°C | 0°C |
| Avg Rain | 75 mm | 58 mm | 81 mm | 68 mm | 55 mm | -19 mm |
May temperatures in Thunder Bay have risen by about 1°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -5.5°C (2020) to a record high of 30.6°C (1986).
Rainfall in May is a relatively wet time of year, averaging 68 mm, with a wettest year of 128 mm.
A good time to visit Thunder Bay
May is a good time to visit Thunder Bay, with days averaging 15.1°C and nights around 3.3°C (mean 9.2°C, warmer than Thunder Bay's yearly average) and moderate rainfall. August and July are marginally more temperate, but May still suits most travellers.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 16.4°C | 9.9°C | 3.4°C | 25.4°C | -3.4°C | 33 mm | 67% | 0.6 m/s | 6.2 |
| 2024 | 15.6°C | 9.8°C | 4.0°C | 20.8°C | 0.1°C | 89 mm | 72% | 0.6 m/s | 5.7 |
| 2023 | 16.2°C | 10.1°C | 4.0°C | 25.8°C | -3.0°C | 41 mm | 72% | 0.6 m/s | 5.7 |
| 2022 | 14.5°C | 9.0°C | 3.4°C | 23.6°C | -1.8°C | 94 mm | 76% | 0.6 m/s | 5 |
| 2021 | 16.2°C | 10.1°C | 4.0°C | 27.0°C | -2.1°C | 38 mm | 67% | 0.6 m/s | 5.7 |
| 2020 | 15.3°C | 9.0°C | 2.8°C | 25.4°C | -5.5°C | 37 mm | 67% | 0.6 m/s | 6.1 |
| 2019 | 12.7°C | 7.3°C | 1.9°C | 21.0°C | -3.2°C | 46 mm | 73% | 0.6 m/s | 5.1 |
| 2018 🔥 | 18.6°C | 11.7°C | 4.8°C | 25.9°C | -2.4°C | 42 mm | 68% | 0.5 m/s | 6.1 |
| 2017 | 13.2°C | 7.7°C | 2.2°C | 19.4°C | -3.6°C | 74 mm | 74% | 0.6 m/s | 5.1 |
| 2016 | 16.3°C | 10.0°C | 3.8°C | 26.8°C | -3.1°C | 60 mm | 70% | 0.6 m/s | 5.6 |
| 2015 | 14.7°C | 8.8°C | 2.9°C | 25.6°C | -1.8°C | 86 mm | 75% | 0.6 m/s | 5.5 |
| 2014 | 14.9°C | 9.3°C | 3.8°C | 27.2°C | -2.2°C | 50 mm | 74% | 0.5 m/s | 5.2 |
| 2013 | 13.4°C | 7.5°C | 1.7°C | 23.2°C | -3.4°C | 92 mm | 72% | 0.7 m/s | 5.2 |
| 2012 🌧️ | 16.2°C | 10.5°C | 4.9°C | 23.9°C | 0.9°C | 128 mm | 73% | 0.6 m/s | 4.8 |
| 2011 | 14.5°C | 8.9°C | 3.4°C | 22.1°C | -2.2°C | 56 mm | 73% | 0.6 m/s | 5.4 |
| 2010 | 17.1°C | 11.1°C | 5.1°C | 26.3°C | -3.7°C | 43 mm | 70% | 0.6 m/s | 5.9 |
| 2009 | 13.2°C | 7.5°C | 1.8°C | 21.7°C | -1.8°C | 62 mm | 72% | 0.7 m/s | 5.6 |
| 2008 | 12.5°C | 7.0°C | 1.5°C | 22.6°C | -4.3°C | 73 mm | 73% | 0.7 m/s | 5.3 |
| 2007 | 17.5°C | 11.3°C | 5.0°C | 28.2°C | -2.1°C | 74 mm | 67% | 0.6 m/s | 5.5 |
| 2006 | 15.4°C | 10.2°C | 5.1°C | 24.8°C | -0.6°C | 80 mm | 77% | 0.7 m/s | 5.1 |
| 2005 | 13.7°C | 8.4°C | 3.2°C | 23.3°C | -3.0°C | 111 mm | 77% | 0.6 m/s | 5.3 |
| 2004 | 12.0°C | 6.4°C | 0.9°C | 19.0°C | -4.0°C | 97 mm | 72% | 0.7 m/s | 5.1 |
| 2003 | 16.0°C | 9.9°C | 3.8°C | 25.0°C | -1.4°C | 75 mm | 67% | 0.6 m/s | 6 |
| 2002 | 12.4°C | 6.3°C | 0.3°C | 22.3°C | -3.5°C | 58 mm | 72% | 0.7 m/s | 5.8 |
| 2001 | 14.7°C | 9.3°C | 4.0°C | 22.2°C | -0.6°C | 97 mm | 79% | 0.6 m/s | 5.4 |
| 2000 | 14.8°C | 9.0°C | 3.3°C | 22.9°C | -1.5°C | 78 mm | 74% | 0.6 m/s | 5.3 |
| 1999 | 14.8°C | 9.3°C | 3.7°C | 28.1°C | -2.2°C | 109 mm | 75% | 0.7 m/s | 5.2 |
| 1998 | 18.1°C | 11.5°C | 4.9°C | 24.1°C | 0.5°C | 57 mm | 63% | 0.6 m/s | 6.5 |
| 1997 ❄️ | 11.8°C | 6.2°C | 0.5°C | 22.8°C | -2.3°C | 52 mm | 71% | 0.7 m/s | 5.5 |
| 1996 | 14.1°C | 7.8°C | 1.6°C | 21.1°C | -3.9°C | 45 mm | 66% | 0.6 m/s | 6.1 |
| 1995 | 15.0°C | 9.4°C | 3.9°C | 27.6°C | -1.6°C | 49 mm | 69% | 0.6 m/s | 4.9 |
| 1994 | 16.6°C | 10.0°C | 3.4°C | 27.3°C | -1.3°C | 59 mm | 67% | 0.6 m/s | 5.5 |
| 1993 | 14.2°C | 8.7°C | 3.2°C | 23.9°C | -0.3°C | 56 mm | 72% | 0.6 m/s | 4.6 |
| 1992 | 16.9°C | 10.2°C | 3.4°C | 26.3°C | -4.2°C | 40 mm | 70% | 0.6 m/s | 5.7 |
| 1991 | 17.0°C | 11.3°C | 5.5°C | 27.6°C | -2.4°C | 66 mm | 73% | 0.6 m/s | 5.4 |
| 1990 | 13.8°C | 8.0°C | 2.1°C | 24.0°C | -2.7°C | 49 mm | 68% | 0.6 m/s | 5.5 |
| 1989 | 16.6°C | 10.2°C | 3.8°C | 24.6°C | -4.7°C | 68 mm | 70% | 0.6 m/s | 5.7 |
| 1988 | 18.4°C | 11.3°C | 4.1°C | 28.8°C | -2.6°C | 51 mm | 66% | 0.6 m/s | 5.9 |
| 1987 | 16.1°C | 9.8°C | 3.5°C | 25.6°C | -3.7°C | 77 mm | 70% | 0.6 m/s | 5.4 |
| 1986 | 16.8°C | 11.0°C | 5.1°C | 30.6°C | -2.8°C | 60 mm | 74% | 0.6 m/s | 5.6 |
| 1985 | 15.1°C | 9.8°C | 4.4°C | 23.8°C | 0.3°C | 127 mm | 77% | 0.5 m/s | 5 |
| 1984 | 14.0°C | 8.0°C | 2.1°C | 22.9°C | -4.0°C | 77 mm | 73% | 0.6 m/s | 5.2 |
| 1983 | 12.5°C | 6.7°C | 1.0°C | 19.6°C | -5.2°C | 46 mm | 73% | 0.6 m/s | — |
| 1982 | 16.1°C | 10.6°C | 5.0°C | 24.3°C | -1.0°C | 100 mm | 77% | 0.6 m/s | — |
| 1981 | 15.2°C | 9.1°C | 3.1°C | 23.1°C | -4.0°C | 69 mm | 70% | 0.6 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 15.1°C with lows near 3.3°C (mean 9.2°C), based on 45 years of NASA POWER data.
May averages 68 mm of rainfall in Thunder Bay, a relatively wet time of year. The wettest on record was 128 mm in 2012.
The hottest May reached 30.6°C in 1986. The coldest dipped to -5.5°C in 2020.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 1°C. Daytime highs moved from 14.6°C to 15.8°C and overnight lows from 3.1°C to 3.8°C over the same span.
May is one of the warmer months of the year in Thunder Bay and a relatively wet time of year, so plan for around 15.1°C daytime highs and 3.3°C at night.
Not quite — May is the 8th coolest month in Thunder Bay, averaging 9.2°C.
For May in Thunder Bay, pack warm layers and a jacket for chilly mornings, with typical highs of 15.1°C and lows of 3.3°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 71% — moderately humid.
Average wind speed in May is 0.6 m/s. The windiest May on record averaged 0.7 m/s (1997).
The wettest May on record was 2012 with 128 mm. On average, May sees 68 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 May, 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 May specifically, along with year-by-year records and how the month has changed over the decades.
