Thunder Bay Weather: Morning Fog, Sunshine and a Mild Friday Ahead
THUNDER BAY – WEATHER DESK – Wednesday, September 23, 2026 – Thunder Bay begins Wednesday with clear, cool conditions and patches of fog. Sunshine will lift the temperature to 17 C this afternoon. Thursday will bring a mix of sun and cloud before a warmer Friday reaches 20 C.
It is a chilly start to the morning with temperatures above zero in the city but the potential for frost in parts of the city are possible.
Drivers should allow for locally reduced visibility during the morning commute today and again early Thursday. On Western Lake Superior, no marine warning is in effect, but south winds will increase to 15 knots Thursday evening.
Current Conditions and Weather Alerts
At 5:00 a.m. EDT, Thunder Bay Airport reported clear skies and a temperature of 1.9 C. Humidity was 100 per cent, the wind was southwest at 8 km/h and visibility was 24 kilometres. Barometric pressure was 103.4 kPa and rising.
Frost advisories were in effect farther east along the North Shore, including the Nipigon-Rossport and Marathon-Schreiber areas. Anyone travelling east on Highway 11 or Highway 17 should check current alerts and Ontario 511 before departure.
Wednesday, September 23: Fog Clears to Sunshine
Fog patches will dissipate this morning, leaving mainly sunny skies. The high will reach 17 C. The UV index will be 5, or moderate.
Tonight will begin clear, with some cloud developing during the evening. Fog patches will form after midnight. The low will be 5 C.
Thursday, September 24: Sun and Cloud
Thursday will bring a mix of sun and cloud after morning fog patches dissipate. The high will be 16 C, with a moderate UV index of 5.
Thursday night will be cloudy with a 30 per cent chance of showers and a low of 11 C.
Friday, September 25: Clearing and Warmer
Cloud will clear Friday, allowing the temperature to climb to 20 C. Friday night will be clear with a low of 10 C.
Three-Day Thunder Bay Forecast at a Glance
| Day | Forecast | High | Night |
|---|---|---|---|
| Wednesday, Sept. 23 | Mainly sunny after morning fog dissipates | 17 C | Clear, then partly cloudy with fog after midnight; low 5 C |
| Thursday, Sept. 24 | Mix of sun and cloud after morning fog dissipates | 16 C | Cloudy with a 30 per cent chance of showers; low 11 C |
| Friday, Sept. 25 | Clearing | 20 C | Clear; low 10 C |
Air Quality: Low Risk
Environment and Climate Change Canada forecasts a maximum Air Quality Health Index of 2, or low risk, for Wednesday, Wednesday night, Thursday and Thursday night.
At this level, the general population can continue normal outdoor activities. People who are unusually sensitive to air pollution should continue to follow their usual health plan and pay attention to symptoms.
Travel and Outdoor Conditions
Fog is the main local travel concern. Visibility was good at Thunder Bay Airport at 5:00 a.m., but fog can be uneven and may be thicker in low-lying areas, near waterways and outside the city. Drivers should use low-beam headlights, slow down when visibility drops and leave extra following distance.
Fog will redevelop after midnight and may affect the early Thursday commute. A 30 per cent chance of showers Thursday night could leave some roads wet. The three-day city forecast does not indicate heavy precipitation or strong winds, and it does not list any significant wind gusts.
Travellers heading east should note that frost advisories were posted Wednesday morning for several North Shore districts. Frost may be present on vehicles, docks and other exposed surfaces even when major highways remain clear.
Western Lake Superior Marine Forecast
Marine warnings: No marine warning was in effect for Lake Superior in the 3:00 a.m. EDT bulletin issued Wednesday, September 23.
Wednesday: Southeast wind 10 knots.
Tonight: The wind will veer to south 10 knots near midnight.
Thursday: South wind 10 knots will back to southeast 10 knots in the afternoon, then increase to south 15 knots Thursday evening.
Waves: Offshore Lake Superior waves will remain 0.5 metres or less through Wednesday, Wednesday night and Thursday.
Weather and visibility: The Lake Superior marine bulletin does not forecast showers, fog or another specific visibility restriction during this period. Nearshore and harbour visibility can still differ from the open-lake forecast, especially where fog develops over land and protected water.
Extended wind outlook: South wind 15 knots will diminish to light Friday morning. Light winds are forecast Saturday. South wind 15 knots is expected Sunday before diminishing to light.
Thunder Bay Harbour and the Open Lake Are Different
The Environment and Climate Change Canada wind and wave forecast describes offshore Lake Superior. Thunder Bay Harbour is partly protected by the breakwater, islands and shoreline, so water inside the harbour may be calmer than conditions farther offshore.
That protection is not complete. Harbour entrances and exposed shorelines can become choppy, and local winds can differ because of shoreline effects. Conditions seen at a sheltered marina should not be used as the only guide for a trip onto the open lake.
Waves of 0.5 metres or less and winds of 10 knots generally represent modest conditions for many powered vessels. The increase to 15 knots Thursday evening could be less comfortable for canoes, kayaks, paddleboards and smaller fishing boats, particularly on exposed routes. No dangerous storm conditions are indicated, but Lake Superior’s cold water means that even a minor capsize can become serious quickly.
Safety Guidance for Boaters
- Wear an approved personal flotation device at all times on the water.
- Check the latest marine forecast and local harbour observations immediately before departure.
- Carry reliable communications and leave a float plan with someone on shore.
- Dress for the water temperature, not only the afternoon air temperature.
- Small-craft operators should consider the Thursday evening wind increase when planning their return.
- Do not assume calm water at a marina means the open lake is equally calm.
Summary
Thunder Bay’s September 23-25 forecast brings morning fog, sunshine and a high of 20 C Friday. Western Lake Superior winds increase to 15 knots Thursday evening.
Sources Checked
- Environment and Climate Change Canada – Thunder Bay forecast and observations, observation at 5:00 a.m. and forecast issued at 5:30 a.m. EDT on September 23, 2026.
- Environment and Climate Change Canada – weather alerts, checked shortly after 6:00 a.m. EDT on September 23, 2026.
- Environment and Climate Change Canada – Thunder Bay AQHI, forecast issued at 6:00 a.m. EDT on September 23, 2026.
- Environment and Climate Change Canada – Great Lakes marine forecast, issued at 3:00 a.m. EDT on September 23, 2026.
- Environment and Climate Change Canada – Great Lakes wave forecast, issued at 3:00 a.m. EDT on September 23, 2026.
- Environment and Climate Change Canada – extended Great Lakes marine forecast, issued at 3:00 a.m. EDT on September 23, 2026.
