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Monthly climate in Thunder Bay, Canada

Last updated: July 31, 2025

Under the Köppen–Geiger climate classification Thunder Bay features a humid continental climate (Dfb). Temperatures typically range between -13 °C (9 °F) and 19 °C (66 °F) through the year, but rarely can drop to -36 °C (-33 °F) or can rise to as high as 31 °C (89 °F). The average annual precipitation amounts to about 715 mm (28.2 inches) and receives 103 rainy days on the 1 mm (0.04 inches) threshold annually. Thunder Bay enjoys an average of 2892 hours of sunshine throughout the year, and daylight varies from 8 hours 20 minutes to 16 hours 2 minutes per day.

Monthly average temperatures in Thunder Bay, Canada

The warmest months in Thunder Bay are June, July and August, with daily mean temperatures ranging from 14 to 19 °C (58 - 66 °F) throughout the day. The coldest temperatures usually occur in January, February and December, when daily mean temperatures range from -13 to -9 °C (9 - 16 °F) throughout the day. On average each year, Thunder Bay experiences 14 days above 25 °C (77.0 °F) and 170 days below 0 °C (32.0 °F).

Monthly average temperatures with daily means, minimums and maximums for period, average high and low temperatures in Thunder Bay. Generated using Copernicus Climate Change Service information. Data for period from January 2017 to June 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Maximum3°C
(37°F)		10°C
(49°F)		10°C
(51°F)		20°C
(68°F)		24°C
(76°F)		28°C
(83°F)		31°C
(89°F)		29°C
(84°F)		25°C
(78°F)		19°C
(67°F)		16°C
(62°F)		8°C
(47°F)
Mean maximum0°C
(33°F)		3°C
(38°F)		9°C
(48°F)		14°C
(58°F)		21°C
(69°F)		25°C
(77°F)		29°C
(85°F)		27°C
(81°F)		24°C
(75°F)		18°C
(64°F)		8°C
(47°F)		4°C
(40°F)
Average high-8°C
(17°F)		-8°C
(18°F)		-0°C
(32°F)		5°C
(42°F)		13°C
(56°F)		19°C
(67°F)		23°C
(74°F)		21°C
(71°F)		17°C
(62°F)		9°C
(48°F)		0°C
(33°F)		-5°C
(23°F)
Daily mean-13°C
(9°F)		-13°C
(9°F)		-5°C
(23°F)		1°C
(33°F)		8°C
(47°F)		14°C
(58°F)		19°C
(66°F)		17°C
(63°F)		13°C
(55°F)		6°C
(43°F)		-3°C
(27°F)		-9°C
(16°F)
Average low-17°C
(2°F)		-18°C
(0°F)		-10°C
(14°F)		-4°C
(26°F)		3°C
(39°F)		10°C
(50°F)		14°C
(58°F)		13°C
(56°F)		9°C
(49°F)		3°C
(38°F)		-6°C
(22°F)		-13°C
(9°F)
Mean minimum-30°C
(-22°F)		-31°C
(-24°F)		-22°C
(-7°F)		-12°C
(10°F)		-3°C
(26°F)		5°C
(41°F)		10°C
(50°F)		8°C
(47°F)		2°C
(36°F)		-4°C
(25°F)		-16°C
(3°F)		-26°C
(-15°F)
Minimum-36°C
(-33°F)		-35°C
(-30°F)		-26°C
(-14°F)		-18°C
(1°F)		-5°C
(23°F)		1°C
(35°F)		9°C
(48°F)		6°C
(44°F)		-1°C
(31°F)		-7°C
(20°F)		-20°C
(-4°F)		-32°C
(-26°F)

Compare climate in Thunder Bay with other places

Compare temperature, precipitation, sunshine, UV index in Thunder Bay, Canada with other places around the world.

Monthly average precipitation in Thunder Bay, Canada

Thunder Bay usually has the most precipitation in July, September and October, with an average of 11 rainy days and 89 mm (3.5 inches) of precipitation per month. The driest months in Thunder Bay are January, February and March. On average, 32 mm (1.3 inches) of precipitation falls during these months.

Monthly average precipitation and precipitation days in Thunder Bay. Generated using Copernicus Climate Change Service information. Data for period from January 2017 to January 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Average precipitation mm (inches)30 (1.2)35 (1.4)31 (1.2)58 (2.3)52 (2.0)58 (2.3)82 (3.2)77 (3.0)98 (3.9)87 (3.4)51 (2.0)55 (2.2)
Average precipitation days (≥ 1 mm)6659911109131177

Monthly sunshine hours in Thunder Bay, Canada

The sunniest months in Thunder Bay are June, July and August, when the sun shines an average of 11 hours 9 minutes a day. Least sunny months in Thunder Bay: January, November and December receive an average of 4 hours 17 minutes of sunshine daily.

Mean monthly sunshine duration, average sunshine hours per day and mean daily daylight hours in Thunder Bay. Generated using Copernicus Atmosphere Monitoring Service information. Data for period from January 2017 to January 2022.
 JanFebMarAprMayJunJulAugSepOctNovDec
Mean monthly sunshine hours115195259259316346362316256183134144
Mean daily daylight hours8h 47m10h 12m11h 56m13h 43m15h 15m16h 2m15h 36m14h 14m12h 31m10h 44m9h 10m8h 20m

Solar UV radiation in Thunder Bay, Canada

Thunder Bay experiences the highest level of ultraviolet (UV) radiation in May, June and August, when the maximum UV index can reach values of 8 - 9, which corresponds to the Very High category of sun exposure. January, November and December are in the Low exposure category. In these months, the maximum values of the UV index do not exceed 2. For more detailed information, check out our hourly Thunder Bay UV Index data.

Average daily maximum UV levels by month for Thunder Bay. Generated using Copernicus Atmosphere Monitoring Service information. Data for period from January 2022 to January 2023.
 JanFebMarAprMayJunJulAugSepOctNovDec
UV Index (month maximum)235789887421