Thunder Bay starts Saturday with a cool, fresh morning near 12°C, a reminder that Lake Superior is still helping moderate temperatures while much of the broader region deals with heat alerts and more intense summer conditions. The city will warm up nicely today, but the lake influence should keep Saturday more comfortable than areas farther inland.
The weekend still turns hotter by Sunday, with temperatures climbing into the low 30s and humidex values reaching the mid-30s.
Today’s Weather Overview
Current Conditions
At 7:00 AM EDT, Thunder Bay reported a temperature of 11.8°C. The dew point was 10.5°C, with humidity at 92 percent, giving the morning a cool and slightly damp feel.
Winds were light from the northwest at 4 km/h, and the barometric pressure was 101.7 kPa.
Today’s forecast calls for sunny skies this morning, then a mix of sun and cloud with a 30 percent chance of showers late this afternoon. The high will reach 26°C, with a humidex of 28. The UV index is 8, or very high.
Weekend Forecast
Expected Conditions
Tonight: Thunder Bay will see partly cloudy skies with a 30 percent chance of showers early this evening. The overnight low will fall to 11°C, offering another relatively comfortable night compared with hotter inland communities.
Sunday, July 12: Heat builds into the city with a mix of sun and cloud and a 30 percent chance of showers late in the morning and early afternoon. There is also a risk of a thunderstorm. The high will reach 32°C, with a humidex of 36. The UV index remains 8, or very high.
Sunday Night: Cloudy periods are expected with a 30 percent chance of showers and a much warmer low of 18°C.
Monday, July 13: The hot pattern continues with sunny skies and a high of 32°C. Monday night will be clear and warm, with a low of 18°C.
Lake Superior’s Cooling Role
While inland areas of Northwestern Ontario can heat up quickly during July heat events, Thunder Bay often gets some relief from nearby Lake Superior. Cooler lake air can keep mornings fresher and may soften the daytime heat near the shoreline.
That said, by Sunday and Monday, even Thunder Bay will feel the heat, especially away from the lake and in areas with limited shade or airflow.
Wardrobe Recommendations
For Saturday morning, a light sweater or jacket may be useful, especially near the waterfront. By afternoon, light summer clothing will be comfortable.
For Sunday and Monday, dress for heat. Choose lightweight, light-coloured, loose-fitting clothing, wear sunscreen, sunglasses, and a hat, and drink water often. With the UV index at 8, sun protection is important even during mixed cloud conditions.
Keep a compact umbrella or light rain jacket nearby for late-day shower chances today and the shower or thunderstorm risk on Sunday.
Weather Trivia
Lake Superior is the largest freshwater lake in the world by surface area, and its cool water can strongly influence Thunder Bay’s weather. In summer, that often means cooler mornings near the lake, even when inland communities are dealing with much hotter conditions.
Overview: Thunder Bay weekend weather for July 11–13, 2026: Lake Superior offers some relief from regional heat alerts, with 12°C early Saturday, a high of 26°C today, then hotter Sunday and Monday near 32°C.
