Thunder Bay and the area experiences a humid continental climate (Köppen climate classification Dfb) that is influenced by Lake Superior, with especially noticeable effects in the city's north end. This results in cooler summer temperatures and warmer winter temperatures for an area extending inland as far as 16 km. The average daily temperatures range from 17.6 °C in July to −14.8 °C in January. The average daily high in July is 24.2 °C and the average daily high in January is −8.6 °C. On 10 January 1982, the local temperature in Thunder Bay dropped to −36 °C, with a wind speed of 54 km/h for a wind chill temperature that dipped to −58 °C. As a result, it holds Ontario's record for coldest day with wind chill.
The city is quite sunny, with an average of 2167.7 hours of bright sunshine each year, ranging from 283.4 hours in July to 88.8 hours in November, sunnier than any city in Canada located to the east of it
