Thunder Bay – Weather – A crisp and almost autumnal morning greets Thunder Bay today, with temperatures hovering at 6°C and humidity near saturation. While the skies are mostly cloudy for now, conditions will brighten as the day progresses—before a potential shift tonight brings showers or even a thunderstorm. It’s a week of contrasts: calm mornings, windy afternoons, and fluctuating skies.

Monday’s Weather Overview

Current Conditions

At 7:00 AM EDT from Thunder Bay Airport, conditions are mostly cloudy with a cool temperature of 6.0°C. The dew point is nearly identical at 5.9°C, meaning the humidity is extremely high at 99%—a sign of lingering overnight moisture and possible morning fog in low-lying areas.

Winds are light, blowing from the north-northwest at 4 km/h, but barometric pressure is at 102.1 kPa and falling, suggesting a weather system is approaching. Visibility remains excellent at 24 km.

As the morning progresses, expect sunny conditions to return, gradually giving way to a mix of sun and cloud this afternoon. Winds will shift to the south at 20 km/h, gusting up to 40 km/h later this morning. The high will reach 18°C, with a moderate UV index of 5.

Tonight, cloud cover increases significantly with a 60% chance of showers or thunderstorms, especially after dark. The overnight low will be 12°C.

Weather Forecast

Expected Conditions

The weather remains unsettled into Tuesday, before settling midweek with milder, drier conditions.

• Tuesday, September 9:
  Expect cloudy skies with a 60% chance of showers or thunderstorms in the morning, before clearing to a mix of sun and cloud by the afternoon. The high reaches 20°C, with a UV index of 5 (moderate).
  Night: Skies will have cloudy periods, with a low of 10°C.

• Wednesday, September 10:
  A mix of sun and cloud continues, with stable conditions and a high of 20°C.
  Night: Continued cloudy periods, with another low of 10°C.

Wardrobe Recommendations

With wide-ranging temperatures and changing conditions, layering is key this week in Thunder Bay:

• Morning: A warm jacket, hoodie, or fleece is a must for the early chill.

• Afternoon: Swap layers for lighter wear as temperatures rise to the high teens or 20°C by midweek.

• Evening: Keep an umbrella or rain jacket handy tonight and Tuesday morning due to possible rain or thunderstorms.

• Wind Protection: A windbreaker may be helpful today as gusts increase from the south.

Weather Trivia

Did you know?
Thunder Bay’s September weather is known for dramatic transitions. The city’s proximity to Lake Superior often results in “lake effect moderation,” meaning warmer lakes can delay the onset of consistent fall chill. But when cold air meets lake warmth, fog, wind shifts, and sudden thunderstorms—like what’s possible tonight—can all occur in the same 24-hour period!