Thunder Bay Weather Forecast – Crisp Start, Sunshine Building, and a Gorgeous Week Unfolds
A Serene Morning by a Still Lake
Thunder Bay, ON – Tuesday, May 27, 2025: It’s a postcard-perfect morning along Lake Superior. The water is nearly glass smooth, the air is crisp, and the sky is mostly clear — a peaceful start to the day in Northwestern Ontario. As of 7:00 AM at Thunder Bay Airport, the temperature is a cool 3.4°C, with 100% humidity and no difference between temperature and dew point, which means a hint of ground-level moisture or fog may still be hanging around in sheltered spots.
Winds are light out of the west at 5 km/h, and visibility is excellent at 32 km — a clear indicator that the sunshine is already beginning to burn off the early chill. Pressure sits high and rising at 102.8 kPa, promising stable, calm weather as we head into a warming day.
Sunshine and Warming Temperatures Today
As the sun rises higher, so will the temperature. Today’s forecast brings mainly sunny skies, with conditions staying dry and pleasant. The high will reach around 20°C, providing a stunning contrast to the chilly morning start. Expect a moderate UV index of 6, so while it might not feel hot, sun protection is still important for those out for long periods.
By mid-morning, jackets will come off and sunglasses will go on — a classic spring turnaround for the Lakehead.
Clear Skies Tonight
Tonight, skies will remain clear, and while it will cool off again, the overnight low will settle around +5°C, a bit milder than this morning’s brisk wake-up. A calm evening is in store, perfect for a lakeside stroll or firing up the backyard grill.
Midweek Outlook: Warmer and Staying Dry
Looking ahead, Wednesday will bring a mix of sun and cloud with a high of 22°C, and no real threat of rain. Thursday and Friday look even better, with sunny skies and highs in the 24–26°C range, and nighttime lows comfortably between 10°C and 13°C. If you’ve been waiting to get the garden in or plan some time by the lake, this is the stretch you’ve been hoping for.
What to Wear?
It’s all about layers today. A toque and warm jacket are still in order early this morning, especially with Lake Superior’s cool influence, but you’ll be switching to short sleeves by this afternoon. Sunglasses and sunscreen will come in handy from mid-morning onward.
Historic Temperatures for May 27
Thunder Bay has experienced a record high of 30.5°C and a record low of -3.0°C on this date. With today starting near the freezing mark and ending around 20°C, it’s a classic local swing — and a reminder that here, spring likes to take its time warming up.
Thunder Bay Weather Trivia
Did you know that Lake Superior holds 10% of the world’s surface freshwater? With a surface area larger than some countries, its moderating effect on Thunder Bay’s climate is profound — keeping things cool in the spring and delaying summer heat, but also blessing the region with stunningly calm, clear mornings like this one.
