Western Lake Superior remains below strong-wind-warning criteria, although northeast winds will build waves overnight before calmer conditions return Friday afternoon
THUNDER BAY — WEATHER DESK — Thursday, September 17, 2026 — Thunder Bay begins Thursday under mostly cloudy skies, with a few showers possible during the morning. A northwest wind will develop and gust to 40 km/h before easing this evening.
Friday will be cooler and mainly sunny, while Saturday brings sunshine and a modest rebound in temperature. Residents in frost-prone locations should be ready for temperatures close to freezing tonight and again Friday night.
Current Conditions and Weather Alerts
At 6:00 a.m. EDT, the Thunder Bay Airport reported mostly cloudy skies and a temperature of 10.5°C. The south-southwest wind was 5 km/h, humidity was 93 per cent and visibility was 24 kilometres.
No Environment and Climate Change Canada weather warning, watch or advisory was in effect for Thunder Bay when this report was prepared early Thursday.
Alerts can change quickly; check the official ECCC alert page before travel or outdoor work.
Thursday, September 17: Cloudy Start, Then Clearing
Expect mainly cloudy skies with a 30 per cent chance of showers this morning. The wind will become northwest at 20 km/h, gusting to 40. The daytime high will reach 19°C. The UV index will be 4, or moderate.
Skies will clear tonight. The northwest wind of 20 km/h, gusting to 40, will become light during the evening. The low will fall to 2°C, with a risk of frost.
Friday, September 18: Mainly Sunny and Cooler
Friday will be mainly sunny with a high of 14°C. The UV index will be 5, or moderate. Friday night will be clear with a low near 1°C.
Gardeners should protect sensitive plants. Patchy frost may also form in rural and low-lying areas outside the warmer parts of the city.
Saturday, September 19: Sunshine and a Milder Afternoon
Saturday will be sunny with a high near 18°C. Saturday night will remain clear with a low of 6°C.
Three-Day Thunder Bay Forecast at a Glance
| Day | Conditions | High | Night |
|---|---|---|---|
| Thursday, Sept. 17 | Mainly cloudy; 30% chance of morning showers; northwest 20 km/h, gusting to 40 | 19°C | Clear; wind becoming light; low 2°C with frost risk |
| Friday, Sept. 18 | Mainly sunny | 14°C | Clear; low 1°C |
| Saturday, Sept. 19 | Sunny | 18°C | Clear; low 6°C |
Air Quality: Low Risk
Thunder Bay’s Air Quality Health Index was 1, or low risk, at 6:00 a.m. EDT. The forecast maximum is 2, also low risk, for Thursday, Thursday night and Friday.
At this level, the general population can continue normal outdoor activities. People with heart or breathing conditions should still follow their usual medical advice and monitor any symptoms.
Travel and Outdoor Conditions
A passing morning shower may leave short stretches of wet pavement. Northwest gusts to 40 km/h could also move unsecured items and produce crosswinds on exposed roads. No major precipitation, snow or freezing-rain threat is indicated in the three-day forecast.
Drivers should watch for reduced traction from wet leaves. Late tonight and early Friday, patchy frost could make exposed decks, docks, bridges and rural road surfaces locally slippery.
Western Lake Superior Marine Forecast
Marine warnings: No watches or warnings were in effect for Western Lake Superior in the 3:00 a.m. EDT marine forecast issued September 17.
Thursday: Southwest wind 10 knots will veer to west 10 knots this morning and north 10 knots early this evening. Scattered showers will end this morning.
Tonight and Friday: The wind will increase to northeast 15 knots near midnight, then turn east at 15 knots Friday morning. It will ease to southeast 10 knots near noon Friday.
Waves: Open-lake waves of 0.5 metres or less will build to 0.5 to 1 metre overnight. They are expected to subside to 0.5 metres or less Friday afternoon.
Weather and visibility: Scattered showers will end Thursday morning. The marine forecast does not call for fog or another specific visibility restriction during this period.
Extended wind outlook: Light winds are forecast Saturday. Northeast wind 15 knots is expected Sunday. On Monday, east wind 15 knots is forecast to diminish to light.
Thunder Bay Harbour Is Not the Open Lake
The Western Lake Superior forecast describes offshore conditions. Thunder Bay Harbour and protected bays may be calmer because of the breakwall, islands and shoreline. However, local wind direction and channel effects can still create choppy water near harbour entrances and exposed shorelines.
Conditions seen from a marina or sheltered launch do not necessarily represent conditions beyond the harbour. The overnight rise to 0.5-to-1-metre waves could be uncomfortable or difficult for small boats, canoes, kayaks and paddleboards, even though no strong wind warning is in effect.
Safety Guidance for Boaters
- Wear an approved personal flotation device; Lake Superior water remains cold even on mild days.
- Check the latest marine forecast and local observations immediately before departure.
- Carry reliable communications and tell someone your route and expected return time.
- Small-craft operators should consider returning before northeast winds and waves increase tonight.
- Do not use sheltered harbour conditions as the only guide for an open-lake trip.
