Thunder Bay – Weather – Thunder Bay begins Friday under shallow fog and dense humidity, with a moisture-laden atmosphere and local smoke still lingering. As the fog lifts and the sun emerges, conditions will quickly shift to hot, hazy, and unstable, with a strong chance of showers or thunderstorms by this afternoon.

The humidex is expected to peak near 36°C—making today feel more like southern Ontario than the north shore of Lake Superior.

A heat warning is in effect for the city, so today take precautions to stay cool, stay hydrated and make sure your pets and livestock have plenty of water and shade.

Today’s Weather Overview

Current Conditions

As of 7:00 AM EDT at Thunder Bay Airport:

• Temperature: 15.5°C

• Humidity: 100%

• Dew Point: 15.5°C

• Wind: East-northeast at 4 km/h

• Pressure: 101.2 kPa, falling

• Visibility: 32 km (improving as fog dissipates)

• Condition: Shallow fog, high moisture

Today’s forecast features sun early, then shifting to a mix of sun and cloud by mid-morning. There is a 40% chance of showers and a risk of thunderstorms by this afternoon. Local smoke may reduce air quality, particularly early in the day.

Winds will pick up as follows:

• East 20 km/h this afternoon

• Turning southwest 20 km/h gusting to 40 km/h later in the day

• High: 28°C

• Humidex: 36°C – oppressive heat and humidity

• UV Index: 8 – very high, sunscreen is essential during clear periods

Tonight

• Mainly cloudy skies

• 40% chance of showers, increasing overnight

• Risk of thunderstorms this evening and into the early morning

• Showers could become heavy before dawn, with 10–20 mm of rain possible

• Winds shift to west 20 km/h before morning

• Overnight low: 19°C

Tomorrow’s Forecast

Expected Conditions

Saturday, August 9

• Showers ending late morning, followed by mainly cloudy skies

• Risk of a thunderstorm during the morning hours

• Rainfall totals of 15 to 25 mm expected in the early day

• Winds southwest at 20 km/h, becoming light late morning

• High: 25°C

• Humidex: 33°C

• UV Index: 7 or high

Saturday Night

• Cloudy periods with a 30% chance of showers

• Low: 15°C

Sunday, August 10

• Sunny and dry

• High: 26°C

• Night: Clear, low: 14°C

Wardrobe Recommendations

• Today: Wear light, moisture-wicking clothing to stay cool in the heat and humidity. Sunscreen, sunglasses, and a hat are essential for the strong UV index. Bring a light jacket or umbrella for sudden showers or storms.

• Tonight: With thunderstorms and heavy rain likely, have rain gear and closed shoes ready.

• Saturday: Rain gear is recommended in the morning, but dress in layers as skies begin to clear.

• Sunday: Perfect summer weather—light layers and sun protection will serve you well.

Weather Trivia

Did you know?
Thunder Bay holds the record for Ontario’s highest August humidex reading outside of the southern region—reaching 42.5°C in 2001. The city’s inland valley location allows heat to build up rapidly, especially when southerly winds push warm air over Lake Superior’s cooler surface.