Climate averages 1991–2020
Thunder Bay weather
in August.
A warm, moderately wet month: one of the warmest and the 9th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
August is a warm month in Thunder Bay: daytime highs average 22.3°C and nights cool to about 15.6°C. By daytime temperature it is one of the warmest months of the year.
Expect about 67 mm of rain on roughly 9 days, which makes August a moderately wet month (the 9th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 14 h 20 min on an average August day.
The nearest other city in this atlas is Duluth (278 km away). In August its highs average 23.6°C, 1.3°C warmer than Thunder Bay, with 102 mm of rain.
Among the 86 cities listed in Canada, Thunder Bay ranks joint 70th of 86 for the warmest August highs and joint 25th of 86 for the driest August (rainfall, lowest first). The mean August high of those 86 cities is 23.8°C; Thunder Bay is 1.5°C cooler than that mean.
From August to September, average highs fall by 4.5°C to 17.8°C, and monthly rainfall rises from 67 mm to 84 mm.
The annual picture
August in context
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, selected | 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
August in nearby cities
- Duluth in AugustUnited States · 278 kmHigh 23.6°C · Low 17.8°C · 102 mm rain
- Sault Ste. Marie in AugustCanada · 424 kmHigh 22.8°C · Low 15.5°C · 95 mm rain
- Green Bay in AugustUnited States · 440 kmHigh 25.6°C · Low 17.3°C · 87 mm rain
- Appleton in AugustUnited States · 463 kmHigh 25.3°C · Low 17.1°C · 85 mm rain
- Brooklyn Park in AugustUnited States · 481 kmHigh 26.0°C · Low 17.5°C · 98 mm rain
- Saint Paul in AugustUnited States · 482 kmHigh 26.1°C · Low 17.6°C · 98 mm rain
- Minneapolis in AugustUnited States · 487 kmHigh 26.2°C · Low 17.6°C · 98 mm rain
- Plymouth, United States in AugustUnited States · 493 kmHigh 25.9°C · Low 17.5°C · 99 mm rain
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 limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Thunder Bay) is explained once on the Thunder Bay year overview and on the Sources, method and limits page.