THUNDER BAY – WEATHER – Thunder Bay wakes up under gray skies, misty air, and persistent drizzle this Sunday morning.

With saturated air, low visibility, and light rainfall, today starts off feeling more like early October than late September. That said, this moisture-laden pattern will soon break, with a welcome return of sunshine and clearer skies midweek.

Today’s Weather Overview

Current Conditions

As of 8:00 AM EDT from Thunder Bay Airport, it’s 15°C with light drizzle falling steadily. The temperature and dew point are both at 14.5°C, indicating 100% humidity—meaning the air is fully saturated, and fog or mist may persist in areas.

Winds are blowing from the east at 10 km/h, and visibility is reduced to 5 km due to the drizzle and fog.
Barometric pressure is 101.4 kPa and falling, hinting that this unsettled pattern will continue today and into Monday before improving.

Extended Thunder Bay Weather Forecast

Sunday, September 21:

• Light drizzle through the morning, tapering to cloudy periods by the afternoon.

• Some fog patches may linger into late morning.

• High near 19°C, with humid, damp conditions continuing.

• Winds east at 10–15 km/h.

• UV index: 2 (low) due to thick cloud cover.

Tonight:

• Cloudy skies persist.

• A 30% chance of showers or drizzle overnight.

• Fog patches likely redevelop near midnight.

• Low of 14°C.

Monday, September 22:

• Cloudy with a 30% chance of drizzle in the morning.

• 30% chance of showers by the afternoon.

• Risk of a thunderstorm late in the day.

• Winds shifting to the southwest, increasing to 20 km/h.

• High of 21°C, with humidex near 25.

• UV index: 3 (moderate).

Monday Night:

• Skies clear overnight, with fog patches possible.

• Low of 11°C.

Tuesday, September 23:

• Sunny and clear, a welcome change!

• High of 22°C.

• Night: Clear, with a low of 12°C.

Wednesday, September 24:

• Continued sunshine, with a warm high of 23°C.

• Night: Clear skies, low around 11°C.

Thursday, September 25:

• A mix of sun and cloud.

• High of 23°C, continuing the stretch of pleasant early fall weather.

• Night: Partly cloudy, low near 10°C.

Wardrobe Recommendations

With cool drizzle, humidity, and fog giving way to sun later in the week, your wardrobe should adapt to shifting conditions:

• Today & Monday:

  • A water-resistant jacket or raincoat is essential.

  • Consider waterproof shoes and a hat with a brim to manage drizzle and fog.

  • Light but long-sleeved layers will keep you comfortable in the humidity.

• Tuesday to Thursday:

  • Embrace lighter clothing during the day—short sleeves or breathable tops.

  • Mornings and evenings will be cool, so have a sweater or light jacket on hand.

Weather Trivia

Did you know?
Thunder Bay’s lake-effect fog and drizzle events are common in late September due to warm Lake Superior waters meeting cool overnight air. This results in near-saturation humidity, as we’re seeing today. Interestingly, Thunder Bay averages more fog in September than in May, and these foggy conditions often linger into the morning, especially after clear nights or light overnight rainfall.

Stick with the NetNewsLedger Weather Desk for the latest updates—brighter skies are on the way!