September 23, 2025: Thunder Bay’s Detailed Weather Forecast

THUNDER BAY – WEATHER – It’s a fog-filled morning in Thunder Bay, with near-zero visibility in many areas and 100% humidity wrapping the region in moisture. But don’t worry—the sun is on the way.

Once the fog lifts, a beautiful stretch of sunny, late-September warmth takes hold, lasting through Thursday. Showers could return by Friday night, but until then, it’s a golden opportunity to enjoy fall at its finest.

Today’s Weather Overview

Current Conditions

As of 7:09 AM EDT at Thunder Bay Airport, the temperature is 10.4°C, with the dew point matching at 10.4°C, producing 100% relative humidity—a classic recipe for thick fog.

Winds are light from the west-northwest at 4 km/h, and visibility is reduced to just 0.6 km.
Barometric pressure is 101.6 kPa and rising, indicating stable weather conditions once the fog dissipates.

Forecast for Tuesday:

• Dense fog patches will dissipate by mid-morning, revealing a mix of sun and cloud.

• High of 22°C, with a humidex of 27°C—it’ll feel warm for late September.

• UV index 5 (moderate)—apply sunscreen if you’ll be out midday.

Tonight:

• Clear skies overnight.

• Fog patches likely developing after midnight.

• Low of 9°C.

The Rest of the Week’s Forecast

Expected Conditions

• Wednesday, September 24:

  • Sunny all day after morning fog patches clear.

  • High of 22°C, feeling like 27°C with the humidex.

  • UV index: 5 (moderate).

  • Night: Clear skies, with a low of 9°C.

• Thursday, September 25:

  • Another sunny and pleasant day, with a high of 23°C.

  • Night: Clear skies, and a chillier low of 7°C.

• Friday, September 26:

  • A slightly cooler day, but still sunny, with a high of 18°C.

  • Night: Cloudy periods, and a 60% chance of showers developing overnight.

  • Low of 9°C.

Wardrobe Recommendations

The next few days will feature cool, foggy mornings and warm, sunny afternoons, so layering is the key to comfort:

• Mornings (Tuesday–Thursday):

  • Start with a light jacket or sweater, especially when fog and dampness are present.

  • If you’re driving, allow extra time for reduced visibility early in the day.

• Afternoons:

  • Temperatures will feel like summer, so switch to short sleeves or light, breathable clothing.

• Evenings:

  • After sunset, temperatures drop quickly—bring a jacket or fleece if you’re outdoors.

Weather Trivia

Did you know?
Thunder Bay often sees its longest-lasting fog in late September, especially when clear nights are followed by calm winds—like we’ve had over the past couple of days. This is a perfect setup for radiation fog, where the ground cools quickly overnight and condenses the moist air just above it. That’s why the airport is frequently socked in during early fall mornings!

Enjoy the sunshine and warm afternoons while they last—a cool-down and showers arrive Friday night. Stay with the NetNewsLedger Weather Desk for daily updates.