From a Cloudy Start to Sunny Highs: Thunder Bay Gears Up for a Golden Week

THUNDER BAY – WEATHER REPORT – A calm, cool Sunday morning in Thunder Bay is setting the stage for a beautiful transition into warm, sunny weather this week. While not as hot as neighbouring regions under heat warnings, Thunder Bay is enjoying a more measured step into spring warmth—with 25°C on tap for Tuesday and overnight lows staying comfortably cool.

A Gentle Rise in Temperature with Mostly Sunny Skies Ahead

As of 6:00 AM EDT, conditions at Thunder Bay Airport are mostly cloudy, and the temperature sits at a crisp 6.0°C. Humidity is measured at 54%, and the dew point is a chilly -2.5°C, with light southeasterly winds at 11 km/h. The barometric pressure is currently 102.3 kPa, though falling, suggesting an evolving weather pattern.

The forecast for today calls for showers tapering off this morning, followed by a mix of sun and cloud and a 30 percent chance of lingering showers into the afternoon. Winds will shift south and increase to 20 km/h, gusting to 40, then swing around to the east at 30 km/h. The high for today is expected to reach 19°C, with a UV index of 7, meaning sun protection is still a must—even if clouds are hanging around.

Tonight, skies will clear, and east winds will taper off to calm conditions. Expect a refreshing low of 6°C—ideal for sleeping with the windows open and letting in some fresh northern air.

Looking ahead to Monday, Thunder Bay gets its dose of May magic with full sun and a high of 23°C. The UV index climbs to 8, so consider sunscreen a wardrobe essential. Monday night remains clear with a low of 8°C.

Tuesday is even warmer, with sunshine pushing the high to a delightful 25°C—perfect weather for a walk along the waterfront or a lunch break outdoors. The night stays clear with another low of 8°C.

Wednesday will bring a mix of sun and cloud and a 30 percent chance of showers. Highs will reach 23°C, followed by cloudy periods overnight and another 30 percent chance of showers. Low: 7°C.

By Thursday, more clouds move in with a 30 percent chance of showers during the day and a high of 18°C. Showers become more likely overnight, with a low of 9°C.

Dress for the Shift: Layers Are Your Friend

With cool mornings and sunny, warmer afternoons, dressing in layers is the name of the game. Mornings call for a jacket, but by lunch, it’s T-shirt weather. Sunglasses and sunscreen will be essential early this week, and if you’re heading out in the evening, a light sweater or windbreaker will still be a smart addition.

May 11 Historical Weather Snapshot

On this day, Thunder Bay’s record high reached 27.8°C, while the record low plunged to a chilly -5.6°C. Today’s expected high of 19°C sits comfortably between the extremes, making for a classic Northwestern Ontario spring day.

Thunder Bay Weather Trivia

Did you know? Thunder Bay’s position on Lake Superior means it often warms up slower than its inland neighbours in spring—but when the winds shift just right, the city can heat up quickly. Those big lake breezes? Nature’s air conditioning… until they’re not!