Warm Midweek Sunshine Before Cooler, Cloudier Days Return
THUNDER BAY – WEATHER – The city is waking up in a fog—literally. Fog patches are lingering across Thunder Bay this morning, but don’t let the hazy start fool you. Sunshine is on the way, and with it comes a warm and humid afternoon. But enjoy it while you can, because cooler, cloudier conditions are lining up just beyond the horizon.
Foggy Morning Gives Way to Late-Summer Warmth
At 7:00 AM EDT, Thunder Bay Airport reported fog patches, with a temperature of 14.8°C. The dew point is also 14.8°C, which means the air is completely saturated—100% humidity. Visibility remains fair at 11 km, and light southwest winds at 8 km/h are barely stirring the heavy morning air. The barometric pressure is 101.7 kPa and falling, suggesting changes are in the works.
This morning’s fog will dissipate by mid-morning, giving way to sunshine and then a mix of sun and cloud around noon. The high will climb to a pleasant 25°C, with the humidex pushing it to 30°C—a surprise splash of summer for mid-September. The UV index is moderate at 5, so if you’re spending time outdoors today, don’t forget the sunscreen.
Tonight: Calm and Clear
Tonight, expect partly cloudy skies, with a mild low of 13°C. It’ll be a comfortable evening—ideal for a walk, patio dinner, or a late catch-up around the fire pit before temperatures start to dip.
Thursday: Shift to Cooler, Cloudier Conditions
Thursday, September 18, starts off cloudy, with skies clearing to a mix of sun and cloud in the afternoon. Winds will blow from the northeast at 20 km/h, becoming light later in the day. It will be noticeably cooler than today, with a high of 20°C. The UV index will slip slightly to 4, still moderate.
Thursday night brings cloudy skies and a 30% chance of showers, with temperatures dipping to a chillier low of 8°C—our first real brush with autumn evenings.
Friday and Saturday: More Fall-Like Feel
Friday, September 19, looks to stay cloudy with a 30% chance of showers, and a high of just 16°C. Fall jackets will be back in style.
Friday night stays cloudy with a low of 6°C, and Saturday, September 20, features a mix of sun and cloud and a repeat high of 16°C. Saturday night will remain cool and partly cloudy, with a low of 7°C.
What to Wear?
Today is all about layers—start with a sweater for the foggy morning, but prepare to shed it by lunch. With the humidex hitting 30°C, lightweight and breathable clothing will keep you comfortable. By Friday, though, it’s time to pull out those cozy fall layers, especially for the cooler mornings and evenings.
Weather Trivia: Fog’s Lake Superior Signature
Thunder Bay’s fog patches are most common during seasonal transitions—especially near large bodies of water like Lake Superior. As warm, humid air moves over the cooling land and water overnight, fog forms quickly and can linger through the morning hours. It’s nature’s quiet little alarm clock (albeit not the most visible one).
