Climate Insights for Thunder Bay

The climate in Thunder Bay is cool. The average annual temperature is 3°C and approximately 749mm of precipitation falls per year. Thunder Bay receives a notable amount of rainfall throughout the year, including during its driest month. Thunder Bay is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: July, August, June. The coldest months are February, January, December, when temperatures can drop to -14°C. Thunder Bay experiences heavy snowfall, typically from January through December.

Thunder Bay has a wide annual temperature range, spanning 36°C from the coldest to warmest months. July is the warmest month, though highs remain moderate at 22°C with a mean of 18°C. The coldest month is February, when overnight lows fall to -14°C and the daily average is -11°C. Daily temperature variation is modest, with an average difference of 7°C between highs and lows. The sharpest temperature change occurs between October and November, with a 7°C shift in average temperatures.

Thunder Bay is a relatively dry area, receiving approximately 749mm of precipitation annually, which averages out to around 62mm per month. The wettest month is September, averaging 106mm of rainfall. October and July also tend to see above-average precipitation. The driest month is March, with just 32mm. That's 74mm less than September, the wettest month. Precipitation varies noticeably between seasons, with the second half (July to December) of the year generally seeing more rainfall. Thunder Bay receives heavy snowfall, accumulating around 223cm annually from January through December. The snowiest month is December, with approximately 47cm. Winter travel should account for significant snow cover.

Thunder Bay is relatively calm, with an average annual wind speed of 4km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is November, averaging 5km/h, though still comfortable for most outdoor activities. The calmest conditions occur in June, with average winds dropping to 3km/h, making it an ideal period for wind-sensitive activities. There is moderate seasonal variation in wind speed, with a 2km/h gap between the calmest and windiest months.

It is currently summer in Thunder Bay, which began on June 21, 2026. Thunder Bay is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in July at around 22°C, while the coldest stretch bottoms out in February near -14°C. Autumn is next, beginning on September 23, 2026 — 93 days from now.

The best time to visit Thunder Bay is during July and August, when the weather is most comfortable for travellers. During these months, average temperatures hover around 17°C with modest rainfall averaging 76mm per month. By contrast, February can be quite cold with temperatures dropping to -14°C. Despite being the best months overall, some rain is still likely — pack a waterproof layer and plan a mix of indoor and outdoor activities.

The table below shows monthly climate averages for Thunder Bay based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Snow is measured in centimetres (cm) and reflects average monthly snowfall accumulation. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.