Thunder Bay climate
Thunder Bay (Ontario, Canada) has a warm-summer humid continental climate (Köppen Dfb). The average temperature over the year is 4 °C40 °F, and about 632 mm25 in of precipitation falls in an average year.
Temperature by month
Precipitation by month
Thunder Bay climate table
| Month | High °C°F | Low °C°F | Mean °C°F | Precip. mmin | Frost days |
|---|---|---|---|---|---|
| Jan | −817 | −171 | −139 | 261.0 | 31 |
| Feb | −719 | −163 | −1211 | 200.8 | 28 |
| Mar | 133 | −916 | −425 | 301.2 | 30 |
| Apr | 948 | −229 | 438 | 552.2 | 24 |
| May | 1660 | 439 | 1050 | 722.8 | 6 |
| Jun | 2170 | 1049 | 1559 | 863.4 | 0 |
| Jul | 2576 | 1356 | 1966 | 753.0 | 0 |
| Aug | 2475 | 1356 | 1966 | 592.3 | 0 |
| Sep | 1967 | 948 | 1458 | 702.8 | 0 |
| Oct | 1051 | 337 | 644 | 662.6 | 12 |
| Nov | 337 | −424 | −131 | 401.6 | 25 |
| Dec | −523 | −1210 | −916 | 331.3 | 31 |
| Year | 2576 | −171 | 440 | 63225 | 186 |
“Year” row: highest monthly high, lowest monthly low, annual mean and annual total. Frost days are for the whole grid cell.
| Month | Humid. | Cloud | Solar | Daylight |
|---|---|---|---|---|
| Jan | 97% | 70% | 1.1 | 8:44 |
| Feb | 96% | 67% | 2.0 | 10:07 |
| Mar | 85% | 67% | 3.2 | 11:45 |
| Apr | 72% | 69% | 4.7 | 13:36 |
| May | 72% | 73% | 5.4 | 15:12 |
| Jun | 75% | 70% | 5.9 | 16:05 |
| Jul | 75% | 65% | 5.9 | 15:43 |
| Aug | 74% | 64% | 5.0 | 14:19 |
| Sep | 78% | 65% | 3.6 | 12:30 |
| Oct | 80% | 73% | 2.1 | 10:43 |
| Nov | 84% | 78% | 1.2 | 9:08 |
| Dec | 93% | 74% | 0.9 | 8:20 |
Humid. = average relative humidity at 2 m; cloud = average cloud amount; solar = average daily solar energy reaching the ground in kWh/m² (all-sky); daylight in hours:minutes, calculated for the 15th of each month.
What the climate of Thunder Bay is like
The warmest month is July, with an average high of 25 °C76 °F and a low of 13 °C56 °F. The coldest is January, when highs average −8 °C17 °F and lows −17 °C1 °F. The climate is extremely continental — the average temperature swings by 31.5 °C56.7 °F between the coldest and the warmest month.
Annual precipitation is moderate at about 632 mm25 in. The wettest three-month stretch is May–July, which brings 37% of the annual total. Months with less than 20 mm0.8 in on average: February. The wettest month is June (86 mm3.4 in), the driest is February (20 mm0.8 in).
Relative humidity ranges from 72% in May to 97% in January. The clearest skies (lowest average cloud amount, 64%) are typical of August. Average wind speed near the ground ranges from 2 km/h (1 mph) in June to 5 km/h (3 mph) in February. Daylight lasts from about 8.3 hours in December to 16.1 hours in June.
A lasting snow cover is typical in November–April, when the average snow depth in the reanalysis exceeds 10 cm (deepest in January, about 20 cm).
Best time to visit Thunder Bay
Based on these averages, the most comfortable months for sightseeing and outdoor activities are June–September: average highs of 19 °C67 °F to 25 °C76 °F with 59 mm2.3 in to 86 mm3.4 in of precipitation per month.
The most challenging month is January, which is cold, with average highs of −8 °C17 °F.
Comfort score: months are ranked by how close they come to an average high of 21–28 °C (70–82 °F), lows above 5 °C (41 °F), little precipitation and moderate humidity. The best-ranked months of each place are recommended, even where none meets all of these. These are general rules of thumb applied to long-term averages.
What to pack for Thunder Bay
- Winter (December–February) — highs −817 to −5 °C23 °F, lows −171 to −12 °C10 °F, about 26 mm1.0 in of precipitation a month. Pack heavy insulated clothing, thermal base layers, a warm hat, mittens and insulated boots.
- Spring (March–May) — highs 133 to 16 °C60 °F, lows −916 to 4 °C39 °F, about 52 mm2.1 in of precipitation a month. Pack a warm coat, layers and closed shoes, an extra layer for the cooler mornings and evenings and shoes with good grip, as frost is common.
- Summer (June–August) — highs 2170 to 25 °C76 °F, lows 1049 to 13 °C56 °F, about 73 mm2.9 in of precipitation a month. Pack light layers — T-shirts plus a light sweater or jacket and an extra layer for the cooler mornings and evenings.
- Autumn (September–November) — highs 337 to 19 °C67 °F, lows −424 to 9 °C48 °F, about 59 mm2.3 in of precipitation a month. Pack a warm coat, layers and closed shoes.
How Thunder Bay compares
Of the 40 places in Canada covered by World Climates, Thunder Bay is the 35th warmest by annual mean temperature and the 30th wettest by annual precipitation. See all of them on the Canada climate page.
Places in other countries with the most similar temperature and rainfall pattern: Vladimir (Russia, Dfb), Murom (Russia, Dfb) and Saransk (Russia, Dfb).
Nearby places
- Green Bay 440 km · 8 °C46 °F · 878 mm35 in
- Minneapolis 487 km · 7 °C45 °F · 839 mm33 in
- Rochester 544 km · 7 °C45 °F · 886 mm35 in
- Fargo 589 km · 6 °C43 °F · 608 mm24 in
- Madison 590 km · 8 °C47 °F · 970 mm38 in
- Winnipeg 598 km · 3 °C38 °F · 573 mm23 in
- Milwaukee 603 km · 9 °C48 °F · 945 mm37 in
- Greater Sudbury 656 km · 4 °C40 °F · 817 mm32 in
Frequently asked questions
What is the warmest month in Thunder Bay?
July is the warmest month in Thunder Bay, with an average high of 25 °C (76 °F) and an average low of 13 °C (56 °F).
What is the coldest month in Thunder Bay?
January is the coldest month, with an average high of -8 °C (17 °F) and an average low of -17 °C (1 °F).
When does it rain the most in Thunder Bay?
June is the wettest month with about 86 mm (3.4 in) of precipitation; February is the driest with about 20 mm (0.8 in).
What is the best time to visit Thunder Bay?
Judging by long-term averages, the most comfortable months are June–September.
About this data
All figures are 25-year averages (January 2001 – December 2025) from the NASA POWER project. Temperature, humidity, wind and precipitation come from the MERRA-2 reanalysis (precipitation is the bias-corrected MERRA-2 product), cloud and solar values from CERES satellite data. They describe a grid cell of roughly 50–70 km, not a single weather station, so they can differ from airport records — most of all on coasts, in mountains and for rainfall. Average highs and lows are the monthly mean temperature plus/minus half of the average daily temperature range. Counts of rainy days are not part of this dataset.
The grid cell’s average elevation is 360 m, while Thunder Bay lies at about 188 m. Temperatures on this page were therefore adjusted by +1.1 °C2 °F using the standard lapse rate of 6.5 °C per 1,000 m.