A cold and clear Tuesday morning will give way to sunshine, while Western Lake Superior remains below marine warning criteria with offshore waves near 0.5 metres.
THUNDER BAY – WEATHER DESK – Tuesday, September 22, 2026 – Thunder Bay begins Tuesday at the freezing mark under clear skies. Patchy fog may form in some areas before sunrise, but it should lift during the morning as sunshine takes over.
Wednesday will remain sunny and slightly warmer. Clouds will increase Thursday, although the daytime forecast remains dry. Western Lake Superior will see generally modest winds and low offshore waves through Wednesday.
It is not as chilly as the thermometer would make you think. You still need a jacket and light gloves might be a good idea too.
Current Conditions and Weather Alerts
At 3:00 a.m. EDT, Thunder Bay Airport reported clear skies and a temperature of 0.3°C. The west-southwest wind was 8 km/h, humidity was 99 per cent and visibility was 24 kilometres. Atmospheric pressure was 103.2 kPa and rising.
Tuesday, September 22: Fog Patches Give Way to Sunshine
Tuesday will be sunny after any early fog patches dissipate. The daytime high will reach 17°C.
Tuesday night will be clear with a low near 3°C. Rural and low-lying locations outside the warmer parts of the city may become colder. Gardeners should consider protecting sensitive plants.
Wednesday, September 23: Sunny and Mild
Wednesday will be sunny with a high of 18°C. That is slightly above the late-September normal daytime high of 16°C.
Wednesday night will remain clear with a low near 6°C.
Thursday, September 24: Clouds Increase
Thursday will begin with some sunshine before cloud cover increases. The high will reach 19°C.
Thursday night will be cloudy with a 30 per cent chance of showers and a low near 11°C. Residents planning late-evening outdoor activities should check the updated forecast before leaving.
Three-Day Thunder Bay Forecast at a Glance
| Day | Daytime Conditions | High | Night |
|---|---|---|---|
| Tuesday, Sept. 22 | Sunny after morning fog patches dissipate | 17°C | Clear; low 3°C |
| Wednesday, Sept. 23 | Sunny | 18°C | Clear; low 6°C |
| Thursday, Sept. 24 | Increasing cloudiness | 19°C | Cloudy; 30% chance of showers; low 11°C |
Air Quality: Low Risk
Thunder Bay’s Air Quality Health Index was forecast to reach a maximum of 2, or low risk, Tuesday, Tuesday night and Wednesday.
At this level, the general population can enjoy normal outdoor activities. People with heart or lung conditions should continue following their regular medical advice and watch for unexpected symptoms.
Travel and Outdoor Conditions
Early fog patches may reduce visibility over short distances, particularly near low-lying areas, waterways and rural roads. Drivers should use low-beam headlights and leave additional following distance if they encounter fog.
Temperatures close to freezing may leave frost on vehicles, grass, wooden steps and exposed docks. Bridges and shaded rural surfaces should be approached with care before sunrise, although no widespread freezing condition is forecast.
Tuesday and Wednesday should otherwise provide good conditions for road travel, construction and outdoor work. Thursday will remain mild, but increasing cloud will signal the approach of less settled weather Thursday night.
Western Lake Superior Marine Forecast
Marine warnings: No marine watch or warning was in effect for Lake Superior when the 3:00 a.m. EDT bulletin was issued Tuesday.
Tuesday: Offshore wind east at 10 knots will veer to southeast 10 knots near noon, then back to northeast 10 knots early in the evening.
Tuesday night and Wednesday: The wind will increase to east 15 knots near midnight, then diminish to southeast 10 knots Wednesday morning.
Waves: Offshore Lake Superior waves are forecast near 0.5 metres through Tuesday, Tuesday night and Wednesday. Environment Canada notes that nearshore waves can vary because of shoreline effects.
Weather and visibility: The marine bulletin does not specify showers, thunderstorms or fog for Lake Superior during this period. However, boaters should still watch for localized fog near shore during the cold early-morning hours.
Extended wind outlook: South wind 15 knots is forecast Thursday. On Friday, south wind 15 knots will diminish to light. Light winds are forecast Saturday.
Thunder Bay Harbour and the Open Lake Can Be Different
The official marine wind and wave forecasts describe offshore Lake Superior. Thunder Bay Harbour, the breakwall and protected bays may be calmer than the open lake. Conditions near harbour entrances and exposed shorelines can still become choppy when winds change direction.
A forecast wave height of 0.5 metres is not severe, but it can still be uncomfortable for people in canoes, kayaks, paddleboards and smaller open boats. Cold water is the larger risk. An unexpected capsize can quickly lead to cold-water shock, even when the air is mild and no warning is in effect.
Safety Guidance for Recreational Boaters
- Wear an approved personal flotation device at all times;
- Check the latest marine forecast immediately before departure;
- Carry reliable communications and tell someone your planned route;
- Dress for the water temperature, not only the afternoon air temperature;
- Use caution around harbour entrances and exposed points; and
- Do not assume calm water at a marina represents conditions farther offshore.
Sources Checked
- Environment Canada Thunder Bay forecast and airport observation;
- Environment Canada Thunder Bay weather alerts;
- Environment Canada Thunder Bay AQHI forecast;
- Environment Canada Great Lakes marine wind forecast;
- Environment Canada Great Lakes wave forecast; and
- Environment Canada extended marine wind forecast.
