September 29, 2025: Thunder Bay Weather Outlook

Thunder Bay – Weather – Thunder Bay starts the day with clear skies and cool conditions, typical of late September. A calm breeze, dry air, and rising pressure signal that today will bring another gorgeous autumn day, with highs reaching 23°C and plenty of sunshine.

Cooler air moves in Tuesday with gusty east winds, and a few chances for showers arrive by Thursday — but for now, the city remains in the midst of a dry and mild early fall stretch.

Current Conditions

• Observed at: Thunder Bay Airport

• Time: 7:00 AM EDT

• Temperature: 7.3°C

• Dew Point: 6.1°C

• Humidity: 92%

• Wind: North at 2 km/h (very light)

• Visibility: 24 km

• Pressure: 102.0 kPa (rising)

• Condition: Clear

Forecast Overview

Monday, September 29:

• Sunny skies all day.

• Light winds becoming easterly by evening.

• High: 23°C

• UV Index: 5 (moderate) — sunscreen recommended if you’ll be outside midday.

Tonight:

• Clear early, becoming partly cloudy later in the evening.

• Winds becoming east at 20 km/h late.

• Low: 9°C

Tuesday, September 30:

• Mainly sunny, with clouds increasing later.

• Winds east at 20 km/h, gusting to 40 km/h.

• High: 18°C — a cooler day with breezy conditions.

• UV Index: 5 (moderate)

• Night: Cloudy periods, low of 12°C.

Wednesday, October 1:

• Cloudy skies throughout the day.

• High: 20°C

• Night: Cloudy periods, low near 12°C

Thursday, October 2:

• A mix of sun and cloud with a 30% chance of showers.

• High: 24°C

• Night: Cloudy periods with a 30% chance of showers.

• Low: 10°C

Wardrobe Recommendations

• Mornings:

  • Dress in layers. A warm jacket or sweater is ideal in the early chill.

• Afternoons:

  • Light layers or long sleeves will be comfortable, especially today and Thursday when highs reach into the 20s.

• Evenings:

  • Bring a jacket or light fleece as temperatures drop into single digits.

• Tuesday:

  • A windbreaker is a good idea due to gusty easterly winds.

Weather Trivia

Did you know?
Thunder Bay’s average high for late September is about 15°C, meaning today’s forecast high of 23°C is nearly 8 degrees above normal. While frost is common this time of year, 2025 is delivering an extended warm stretch, thanks to a strong high-pressure ridge over northwestern Ontario. This system is also helping block rain systems, keeping skies mostly dry into early October.

Enjoy the sunshine while it lasts — and keep an eye on the wind as we head into Tuesday! For continued updates, stay with the NetNewsLedger Weather Desk.