Climate averages 1991–2020
Thunder Bay weather
by month.
See how the year changes. July (tied with August) has the highest average daily maximum; February has the lowest average monthly precipitation.
Long-term climate patterns, not a forecast for a particular trip.
Across the year Thunder Bay averages a daytime high of 7.2°C and a nighttime low of 0.5°C, with about 654 mm of precipitation on roughly 103 days. July (tied with August) is the warmest month (average high 22.3°C) and January the coolest (-9.6°C). September is the wettest month with 84 mm; February is the driest with 22 mm.
The annual picture
A year in Thunder Bay
Monthly precipitation
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Thunder Bay climate table
| Month | Average highHigh / low | Average low | Precipitation mm/month | Wet days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | -9.6°C-16.6°C | -16.6°C | 29 | 6.5 | 8.89 h |
| February | -8.0°C-15.0°C | -15.0°C | 22 | 4.9 | 10.210 h |
| March | -1.7°C-8.7°C | -8.7°C | 31 | 6.8 | 11.912 h |
| April | 5.1°C-2.2°C | -2.2°C | 54 | 8.3 | 13.614 h |
| May | 12.5°C4.2°C | 4.2°C | 66 | 10.1 | 15.215 h |
| June | 18.3°C10.7°C | 10.7°C | 65 | 10.5 | 16.016 h |
| July | 22.3°C15.3°C | 15.3°C | 76 | 10.6 | 15.716 h |
| August | 22.3°C15.6°C | 15.6°C | 67 | 9.1 | 14.314 h |
| September | 17.8°C11.7°C | 11.7°C | 84 | 10.5 | 12.613 h |
| October | 9.9°C4.8°C | 4.8°C | 72 | 10.4 | 10.911 h |
| November | 2.3°C-2.8°C | -2.8°C | 49 | 7.8 | 9.39 h |
| December | -4.8°C-11.3°C | -11.3°C | 38 | 7.4 | 8.48 h |
Precipitation (rain or snow, as water) is the average of the 30 separate monthly totals. A wet day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
Nearby cities
- DuluthUnited States · 278 kmHigh 8.9°C · Low 2.8°C · 896 mm precipitation a year
- Sault Ste. MarieCanada · 424 kmHigh 9.1°C · Low 1.9°C · 875 mm precipitation a year
- Green BayUnited States · 440 kmHigh 12.1°C · Low 3.7°C · 794 mm precipitation a year
- AppletonUnited States · 463 kmHigh 11.9°C · Low 3.5°C · 799 mm precipitation a year
- Brooklyn ParkUnited States · 481 kmHigh 12.0°C · Low 3.4°C · 825 mm precipitation a year
- Saint PaulUnited States · 482 kmHigh 12.2°C · Low 3.6°C · 831 mm precipitation a year
- MinneapolisUnited States · 487 kmHigh 12.1°C · Low 3.5°C · 825 mm precipitation a year
- Plymouth, United StatesUnited States · 493 kmHigh 11.9°C · Low 3.5°C · 819 mm precipitation a year
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsWhat do the high and low temperatures mean?
We average the daily maximum and daily minimum for each calendar month over 1991–2020. They are not record extremes, a forecast range or temperatures at a fixed time of day.
How is a rain day counted?
A local calendar day (standard time, UTC-5, no daylight saving) with at least 1 mm of total precipitation counts as one rain day. We count these for each year and month, then average across 30 years. The average does not predict which days will be wet.
Where do the numbers come from?
ERA5-Land (temperature) and ERA5 (precipitation) reanalysis from the Copernicus Climate Change Service, read from the Open-Meteo open-data archive. Temperature comes from the 0.1° model cell at 48.40°, -89.30° (4 km from the city centre), adjusted up by 0.2°C for the difference between the city's elevation (188 m) and the cell's (222 m). Rain comes from the 0.25° cell at 48.50°, -89.25°. These are model estimates, not weather-station readings; coast, hills and city streets can differ.
Does this page show sunshine, humidity or sea temperature?
No. The data used here contain air temperature and precipitation only. Daylight hours are calculated from the city's latitude (sunrise to sunset), not measured sunshine.