Thunder Bay – Weather – After a night of the city living up to its name, Thunder Bay, the streets and sidewalks are slowly drying.
Fortunately the weather held off for Harbourfest!
Thunder Bay begins this Friday morning under thick mist, with visibility reduced to just over a kilometre. Conditions will improve through the morning, but a gusty, unsettled day lies ahead with showers and possible thunderstorms. The weekend stays cooler, cloudy, and damp.
Today’s Weather Overview
Current Conditions
At Thunder Bay Airport (7:00 AM EDT): Mist, 15.1°C, dew point the same at 15.1°C, humidity 100%, light W wind 3 km/h, visibility 1.2 km, pressure 101.4 kPa and falling.
-
Friday (Today): Mainly cloudy with a 40% chance of showers early this morning and again this afternoon, with a risk of a thunderstorm. Winds becoming W 20 km/h gusting 40 early afternoon. High 22°C, humidex 28. UV index 8 (Very High).
-
Tonight: Partly cloudy, 60% chance of showers, with risk of a thunderstorm early this evening. Low near 11°C.
Tomorrow’s Forecast
Expected Conditions (next three days)
-
Saturday, Aug 23: A mix of sun and cloud with a 60% chance of showers, plus a risk of an afternoon thunderstorm. Wind NW 20 km/h by late morning. High ~19°C. UV index 6 (High).
-
Saturday Night: Cloudy with a 60% chance of showers. Low ~11°C.
-
-
Sunday, Aug 24: Cloudy with a 40% chance of showers. High ~16°C.
-
Sunday Night: Cloudy with a 30% chance of showers. Low ~9°C.
-
-
Monday, Aug 25 (outlook): Partly sunny, drier, with a high near 20°C.
Wardrobe Recommendations
-
Friday: A light waterproof jacket or umbrella is advised; humidex will make it feel warmer than the air temperature.
-
Saturday: A layered outfit—sweater or fleece under a rain shell—will keep you dry and comfortable.
-
Sunday: Cooler with showers likely—fall-like attire (long sleeves, pants, light jacket).
-
Evenings: Lows around 9–11°C mean a hoodie or fleece is ideal for outdoor plans.
Weather Trivia
Why does mist form so often in Thunder Bay?
The city’s location in the Kaministiquia River Valley, adjacent to Lake Superior, creates a natural trap for moisture. On calm summer mornings when temperatures dip to the dew point, water vapor condenses near the surface, forming mist or fog. This is especially common in August when warm, moist air lingers but nights grow longer and cooler.
