August 13, 2026: Thunder Bay Weather – Warm Sunshine Through Friday as Lake Superior Stays Mostly Calm
THUNDER BAY – WEATHER – Thunder Bay is heading into a pleasant stretch of mid-August weather from Thursday through Saturday, with daytime temperatures staying in the low to mid-20s. Thursday and Friday will offer the warmest and sunniest conditions, while Saturday brings a little more cloud and a cooler high of 23°C.
For boaters, anglers and sailors, Western Lake Superior is relatively calm Thursday and Friday, with light winds and waves below half a metre. There is, however, a risk of thunderstorms over the western lake Thursday afternoon and evening, along with patches of fog. Winds begin to increase from the southeast Saturday afternoon.
Today’s Weather Overview – Thursday, August 13
Current Conditions
Thunder Bay Airport was reporting mainly sunny skies and 11.9°C at 7:00 AM EDT Thursday. Humidity was at 100 per cent, with a dew point of 11.9°C. Winds were light from the west-southwest at 6 km/h.
Barometric pressure was 101.4 kPa and rising, while visibility was a very good 32 kilometres.
Fog patches around the area will dissipate this morning, leaving sunny skies before a mix of sun and cloud develops this afternoon.
The high will reach 25°C, although the humidex will make it feel closer to 30. The UV index is forecast at 7, or high.
Tonight will clear, with an overnight low of 12°C.
Friday, August 14
Friday is shaping up to be another excellent summer day in Thunder Bay.
Expect mainly sunny skies and a high of 25°C. The humidex will be 27, while the UV index again reaches 7, or high.
Cloudy periods develop Friday night as temperatures fall to 11°C.
For people planning an afternoon at the waterfront, hiking, camping or other outdoor activities, Friday currently offers the best combination of sunshine and warm temperatures in this three-day forecast.
Saturday, August 15
Saturday will be slightly cooler but remains favourable for outdoor plans.
Environment Canada is forecasting a mix of sun and cloud with a high of 23°C.
Saturday night marks the beginning of a wetter pattern, with cloudy skies and a 40 per cent chance of showers. The overnight low will be 15°C.
Western Lake Superior Marine Forecast
Thursday, August 13
Environment Canada’s Western Lake Superior marine forecast, issued at 6:10 AM EDT Thursday, calls for light winds throughout today and tonight. Waves are forecast to remain below 0.5 metres.
The main concern for boaters is the weather rather than wave height. Scattered showers are expected this afternoon and evening with a risk of thunderstorms, and fog patches are also forecast over the lake.
That means conditions around Thunder Bay itself may be sunny while parts of the broader Western Lake Superior marine district experience showers or thunderstorms.
There were no marine watches or warnings in effect when Environment Canada issued the morning forecast.
Friday, August 14
Friday remains relatively quiet on Western Lake Superior.
Winds are forecast to stay light, with waves less than 0.5 metres through Friday.
Those conditions look favourable from a wind-and-wave standpoint, but mariners should continue checking updated forecasts before leaving harbour because fog and localized summer weather can change visibility quickly.
Saturday, August 15
The extended marine forecast calls for light winds Saturday morning, becoming southeast at 15 knots during the afternoon.
That developing southeast wind will be the main marine trend to watch Saturday, particularly for smaller recreational craft and anyone planning a longer trip away from sheltered waters.
Environment Canada had not yet provided a Saturday wave-height forecast in the morning marine bulletin, so boaters should check the next forecast rather than assuming Friday’s sub-half-metre waves will continue.
Lake Superior Boating Outlook
Thursday: Light winds and waves below 0.5 metres, but scattered afternoon and evening showers, fog patches and a thunderstorm risk could create rapidly changing conditions.
Friday: Light winds and waves below 0.5 metres make this the more favourable marine day based on the morning forecast.
Saturday: Conditions begin to change as southeast winds increase to 15 knots during the afternoon.
Remember that Lake Superior can produce conditions quite different from those experienced within the protected waters of Thunder Bay Harbour. Check the latest marine forecast before departure.
Wardrobe Recommendations
Thursday and Friday are good days for summer clothing, with afternoon temperatures reaching 25°C. Sunscreen, sunglasses and a hat are recommended because the UV index will be high.
A sweater or light jacket will still be useful after sunset, with overnight lows of 12°C Thursday and 11°C Friday.
For Saturday, comfortable summer clothing remains suitable during the day, but anyone expecting to be outdoors into Saturday night should have a light rain jacket available as the chance of showers increases.
Boaters should have appropriate waterproof gear onboard even during otherwise pleasant weather, particularly Thursday because of the offshore shower and thunderstorm risk.
Weather Trivia
Thunder Bay’s forecast normal for this point in August is a daytime maximum of 24°C and an overnight minimum of 10°C. That puts Thursday and Friday’s forecast highs of 25°C just slightly above the seasonal normal.
Sunrise in Thunder Bay on Thursday is at 6:48 AM EDT, with sunset at 9:15 PM EDT, still providing more than 14 hours of daylight for mid-August outdoor activities.
Forecast information is based on Environment and Climate Change Canada’s Thunder Bay public forecast issued at 5:30 AM EDT and Western Lake Superior marine forecasts issued between 3:00 AM and 6:11 AM EDT on Thursday, August 13, 2026. Marine forecasts can change quickly, and mariners should check the latest Environment Canada forecast and warnings before departure.
META Description
Thunder Bay weather forecast for August 13-15, 2026, including Western Lake Superior marine weather. Sunshine and highs near 25°C continue through Friday, with light lake winds before southeast winds increase Saturday.
