Thunder Bay reaches 19°C Wednesday and Thursday before a cooler Friday. Western Lake Superior waves subside Wednesday
THUNDER BAY — WEATHER — Wednesday, September 16, 2026 — Thunder Bay will enjoy a mild mix of sun and cloud Wednesday before showers become possible overnight.
Thursday remains mild, but northwest winds will increase and could gust to 40 km/h. Friday will be cooler and cloudy.
Western Lake Superior’s earlier strong-wind warning has ended. Open-lake waves will continue subsiding Wednesday morning, creating improving conditions through the middle of the day.
Current Conditions in Thunder Bay
At 6:00 a.m. EDT, Environment Canada reported:
- Temperature: 5.9°C
- Humidity: 100%
- Dew point: 5.9°C
- Wind: West at 7 km/h
- Pressure: 102.7 kPa
No public weather alerts were in effect for the City of Thunder Bay early Wednesday.
Wednesday, September 16
Expect a mixture of sun and cloud with a daytime high of 19°C. The UV index will reach 4, or moderate.
Clouds will increase early this evening. There will be a 40% chance of showers late this evening and overnight, with a low of 8°C.
Wednesday offers the best opportunity for outdoor work, walking and yard projects. A light jacket will be useful during the cool morning, but conditions will become comfortable by the afternoon.
Thursday, September 17
Thursday will be mainly cloudy with a 30% chance of showers during the morning.
Northwest winds will increase to 20 km/h near noon, with gusts reaching 40 km/h. The daytime high will be 19°C, while the UV index will be 3, or moderate.
Skies will clear Thursday night as the temperature falls to 5°C.
People working outdoors should secure lightweight materials, signs and tarps before the wind increases. Drivers should also expect crosswinds on exposed sections of Highway 11/17 and Highway 61.
Friday, September 18
Friday will be cloudy and cooler, with a high of 16°C.
Skies will clear Friday night as the temperature falls to 6°C.
Friday should remain suitable for outdoor activities, but the cloudy sky and cooler temperature will make a jacket useful throughout the day.
Three-Day Thunder Bay Forecast
| Day | Conditions | High | Nighttime Conditions | Low |
|---|---|---|---|---|
| Wednesday | Mix of sun and cloud | 19°C | Cloudy with a 40% chance of showers | 8°C |
| Thursday | Mainly cloudy; 30% chance of morning showers; NW wind gusting to 40 km/h | 19°C | Clear | 5°C |
| Friday | Cloudy | 16°C | Clear | 6°C |
Western Lake Superior Marine Forecast
No marine warning is currently in effect for Western Lake Superior. Environment Canada ended the previous strong-wind warning at 5:39 a.m. EDT Wednesday.
Wednesday Marine Conditions
Northwest winds of 15 knots will diminish to light Wednesday morning. Winds will then become south at 10 knots during the evening.
Waves of 1 to 1.5 metres will subside to between 0.5 and one metre early Wednesday morning. Wave heights should fall to 0.5 metres or less around noon.
These improving conditions favour protected-water boating later in the morning and afternoon. However, residual waves may remain on exposed portions of the lake after winds decrease.
Wednesday Night and Thursday
South winds of 10 knots will turn southwest near midnight and then become west at 10 knots Thursday morning.
Winds will increase to north at 15 knots Thursday evening. Waves are forecast to build to between 0.5 and one metre Thursday evening.
No separate visibility restriction or significant marine-weather hazard was included in the morning bulletin.
Extended Marine Wind Outlook
| Day | Western Lake Superior Wind |
|---|---|
| Friday | Northeast 15 knots, diminishing to light during the afternoon |
| Saturday | Light winds |
| Sunday | Northeast 15 knots |
Thunder Bay Harbour Versus the Open Lake
Conditions inside Thunder Bay Harbour can be considerably calmer than conditions beyond the breakwall. Islands, the shoreline and the breakwater provide protection from some wind and wave directions.
Boaters should not assume that calm water at the marina or launch means the open lake will be equally calm. Wave heights in the marine forecast apply to the broader Western Lake Superior zone.
Anyone heading onto the lake should wear an approved personal flotation device, carry reliable communications equipment and check the latest forecast before leaving shore. Lake Superior water remains dangerously cold, making an unexpected fall into the water a serious emergency even when the air is mild.
Sources
- Environment Canada — Thunder Bay forecast and observations
- Environment Canada — Western Lake Superior marine forecast
- Environment Canada — Lake Superior marine warnings
Summary
Thunder Bay reaches 19°C Wednesday and Thursday before a cooler Friday. Western Lake Superior waves subside Wednesday, with no marine warning currently in effect.
Weather and marine conditions can change quickly. Forecast information was checked Wednesday morning, September 16, 2026. Boaters should refresh the marine forecast immediately before departure.
