Thunder Bay weather for September 1-3, 2026: Dense morning fog gives way to 25°C and west winds gusting to 50 km/h Tuesday
THUNDER BAY – WEATHER – Tuesday, September 1, 2026 – September opens in Thunder Bay with dense fog early this morning, but conditions will improve quickly as the fog burns off and a strengthening west wind takes over.
Thunder Bay is headed for a warm 25°C this afternoon, with west winds gusting to 50 km/h. Wednesday and Thursday remain mild, with highs in the low to mid-20s and generally dry conditions.
On Western Lake Superior, conditions are considerably quieter than during Monday’s unsettled weather. Southwest winds increase to 15 knots this afternoon before turning west, while waves build temporarily to between 0.5 and 1 metre. Winds and waves then decrease overnight, with relatively favourable marine conditions expected Wednesday and Thursday.
Today’s Weather Overview
Current Conditions
At 6:00 AM EDT, Thunder Bay Airport was reporting fog and 17.1°C.
Humidity was 100 percent, with a dew point of 17.1°C. Barometric pressure was 101.1 kPa and falling.
Winds were light from the north at 4 km/h, but visibility was reduced to only 400 metres.
Drivers should allow extra stopping distance through the early morning, particularly in low-lying areas and along highways where fog may be locally thicker.
Environment Canada expects the fog patches to dissipate this morning.
Tuesday, September 1
Thunder Bay will see a mix of sun and cloud once the morning fog clears.
The biggest weather factor today will be the wind. West winds develop late this morning at 30 km/h with gusts to 50 km/h.
The afternoon high reaches 25°C, with a humidex of 30. The UV index is 6, or high.
Tuesday Night
Tonight will be partly cloudy with a 30 percent chance of showers this evening and after midnight.
West winds of 20 km/h gusting to 40 become light this evening.
The overnight low falls to 12°C.
Wednesday, September 2
Wednesday looks like the most comfortable city-weather day of the three-day forecast.
Expect a mix of sun and cloud, with a high of 24°C and a humidex of 30.
The UV index again reaches 6, or high.
Wednesday night will be clear, with a low of 12°C.
Thursday, September 3
Thursday remains mild with a mix of sun and cloud and a high of 23°C.
Cloudy periods develop Thursday night with another overnight low near 12°C.
Temperatures throughout the three-day period will be above Thunder Bay’s September 1 seasonal normal maximum of about 20°C.
Lake Superior West Marine Forecast
No Marine Warnings in Effect
Environment Canada reported no watches or warnings in effect for Western Lake Superior with the marine forecast issued at 3:00 AM EDT Tuesday.
That is an important improvement from the stronger-wind conditions that affected the lake earlier in the week.
Tuesday Marine Conditions
Western Lake Superior starts Tuesday with southwest winds at 10 knots.
Winds increase to southwest 15 knots near noon, then veer to west 15 knots early this evening.
Near midnight, winds diminish to northwest 10 knots.
For comparison:
- 10 knots is approximately 19 km/h
- 15 knots is approximately 28 km/h
Waves
Waves are 0.5 metres or less this morning.
They build to 0.5 to 1 metre this afternoon as southwest winds strengthen, before subsiding again to 0.5 metres or less overnight.
For small boats and paddlers, the afternoon will therefore be somewhat rougher than the morning or overnight period.
Fog and Showers
Scattered showers are forecast to end early this morning.
Fog patches are expected to dissipate near noon.
Visibility will be the primary early-morning marine concern. Mariners should not assume visibility over the lake will improve at exactly the same time as conditions at Thunder Bay Airport.
Wednesday Marine Outlook
Northwest winds near 10 knots early Wednesday become variable at 10 knots near noon.
Waves are forecast to remain 0.5 metres or less after subsiding overnight.
If the forecast holds, Wednesday should provide one of the better recreational boating windows of the three-day period, particularly after the morning.
Thursday Marine Outlook
Environment Canada’s extended forecast calls for light winds Thursday on Western Lake Superior.
Light winds are also expected Friday and Saturday in the current extended outlook.
Specific Thursday wave heights are not yet included in the extended forecast, so boaters should check the updated marine bulletin before departure rather than assuming flat water from the light-wind forecast alone.
Boating Outlook
Tuesday morning: Generally light winds and low waves, but fog may sharply reduce visibility.
Tuesday afternoon: Southwest winds increase to 15 knots and waves build as high as one metre. Conditions remain manageable for many vessels but become less comfortable for small craft and paddlers.
Wednesday: Improving marine conditions, with variable winds near 10 knots and waves around half a metre or less.
Thursday: Currently looks favourable, with light winds expected.
Even on quieter days, Lake Superior can change quickly. Mariners should check Environment Canada’s newest marine forecast immediately before leaving shore.
Wardrobe Recommendations
Tuesday will be warm but windy. Light summer clothing will be comfortable during the afternoon, but a wind-resistant outer layer will be helpful with gusts reaching 50 km/h.
Sunglasses, sunscreen and a hat are recommended with the UV index reaching the high category.
A light jacket or hoodie will be useful Tuesday night as temperatures fall to 12°C.
Wednesday and Thursday remain warm enough for lighter daytime clothing, but evenings continue to cool into the low teens.
Anyone heading onto Lake Superior should carry an additional warm, wind-resistant layer. Air temperatures over open water can feel significantly cooler than conditions inland.
Weather Trivia
September 1 marks the beginning of meteorological autumn, but Thunder Bay’s weather is starting the month on a decidedly summer-like note.
Environment Canada lists Thunder Bay’s normal September 1 high at approximately 20°C and the normal low near 7°C. Tuesday’s forecast high of 25°C is about five degrees warmer than normal, while Wednesday’s 24°C and Thursday’s 23°C also remain above seasonal values.
Thunder Bay’s sunrise Tuesday is at 7:14 AM EDT, with sunset at 8:39 PM EDT.
Sources: Environment and Climate Change Canada Thunder Bay observations and public forecast issued 5:30 AM EDT Tuesday, September 1, 2026, and Western Lake Superior marine forecast issued 3:00 AM EDT Tuesday.
Overview
Thunder Bay weather for September 1-3, 2026: Dense morning fog gives way to 25°C and west winds gusting to 50 km/h Tuesday, followed by warm weather Wednesday and Thursday. Western Lake Superior waves build to one metre Tuesday before calmer conditions return.
