Thunder Bay’s September 25-27 forecast brings a mild Friday, evening and morning fog risk, Saturday clearing and a 30 per cent chance of showers Sunday

THUNDER BAY – WEATHER DESK – Friday, September 25, 2026 – Thunder Bay will see a mild but changeable three-day stretch. Friday starts cloudy with a chance of early showers, Saturday brings clearing after morning fog, and Sunday offers a mix of sun and cloud with another chance of showers.

Environment and Climate Change Canada (ECCC) reported cloudy skies and 12 C at Thunder Bay Airport at 5:07 a.m. Friday. The southwest wind was 5 km/h, humidity was 100 per cent and visibility was 24 kilometres.

Weather Alerts and Current Conditions

No ECCC weather warning, watch or advisory was listed for Thunder Bay when this report was prepared. Alerts can change quickly, especially when fog develops overnight. Check the ECCC public alerts page before travelling or beginning outdoor work.

Friday, September 25: Cloudy and Mild

Cloudy skies and a 30 per cent chance of showers are expected early Friday. The high will reach 21 C, with a Humidex of 25. The UV index will be 3, or moderate.

Friday night will be partly cloudy. Fog patches are expected to develop during the evening, with a low near 10 C.

Saturday, September 26: Fog Early, Then Clearing

Saturday will begin mainly cloudy, with fog patches dissipating during the morning. Skies should clear near noon. The high will be 18 C, with a moderate UV index of 5.

Saturday night will have cloudy periods and a low near 9 C.

Sunday, September 27: Sun, Cloud and a Shower Risk

Sunday will bring a mix of sun and cloud with a 30 per cent chance of showers. The high will be 18 C. Sunday night will remain partly cloudy with a 30 per cent chance of showers and a low near 8 C.

Three-Day Forecast at a Glance

Wind, Travel and Outdoor Conditions

The latest public ECCC city forecast does not provide sustained wind speeds or gust forecasts for Friday through Sunday. The latest airport observation showed a southwest wind at 5 km/h. Editors should check the hourly forecast before publication if wind-sensitive travel, construction or outdoor events are planned.

Fog is the main travel concern. Patches may reduce visibility Friday night and early Saturday, particularly near the airport, rural roads, bridges and low-lying areas. Drivers should slow down, use low-beam headlights and leave extra following distance. Wet pavement is possible with Friday morning or Sunday showers, but the forecast shows no snow or freezing rain threat.

Outdoor workers should carry rain protection, use layers during the cool mornings and secure light equipment if winds increase. Anyone planning a hike, hunt or camping trip should prepare for damp conditions and reduced visibility near dawn.

Air Quality: Low Risk

The latest ECCC Air Quality Health Index forecast lists a maximum of 2, or low risk, for Friday, Friday night, Saturday and Saturday night. At this level, the general population can continue normal outdoor activities. People with heart or lung conditions should follow their health plan and monitor symptoms.

The AQHI page notes that real-time readings can be inaccurate for publication. The forecast should be refreshed before this article is posted, and Sunday conditions should be checked when the next bulletin is available.

Western Lake Superior Marine Forecast

Warnings: The 3:00 a.m. Friday ECCC marine bulletin did not include a strong wind warning for Western Lake Superior. A strong wind warning was listed for Eastern Lake Ontario, not Lake Superior.

Winds: Western Lake Superior winds are forecast from the south at 10 knots, becoming light early Friday morning, then becoming southeast at 10 knots Saturday morning. These are offshore winds. ECCC warns that nearshore winds can vary considerably because of shoreline effects.

Waves: The current ECCC bulletin does not provide a wave-height value for Western Lake Superior. Boaters should not treat the missing number as a guarantee of calm water. Check the next marine bulletin and local observations before leaving harbour.

Weather and visibility: The bulletin does not list a specific fog or visibility restriction for Western Lake Superior. ECCC defines fog in its marine products as visibility of less than one mile. Conditions can change quickly, especially near shore and in the harbour entrance.

Extended wind outlook: The bulletin checked covers Friday, Friday night and Saturday only. It does not provide a Sunday or Monday wind outlook. The next scheduled ECCC marine forecast was set for 10:30 a.m. Friday. Editors and boaters should use that update for the extended outlook.

Thunder Bay Harbour Is Different from the Open Lake

Thunder Bay Harbour is sheltered by shoreline and harbour structures, so it may look calmer than the open lake. However, wind can funnel through entrances and along exposed shorelines. A calm marina does not prove that conditions are safe beyond the breakwater.

South winds near 10 knots are not a severe-wind forecast, but cold Lake Superior water leaves little margin for error. Small craft, canoes, kayaks and paddleboards should stay close to shore, wear approved personal flotation devices, carry reliable communication equipment and leave enough time to return before conditions change. Check the forecast immediately before departure and tell someone the planned route.

Sources Checked

• Environment and Climate Change Canada Thunder Bay forecast and airport observation, issued 5:30 a.m. EDT Friday, September 25, 2026.
• ECCC public weather alerts, checked Friday morning.
• ECCC Thunder Bay Air Quality Health Index, issued 6:00 a.m. EDT Friday, September 25, 2026.
• ECCC Great Lakes marine bulletin FQCN13 CWTO 250700, issued 3:00 a.m. EDT Friday, September 25, 2026.