September 6-8, 2026: Thunder Bay Forecast — Sunny Sunday Gives Way to a Wet Labour Day and Showery Tuesday
THUNDER BAY – WEATHER – Sunday, September 6, 2026 – Thunder Bay gets one more pleasant late-summer day Sunday before conditions become increasingly unsettled for Labour Day Monday and Tuesday.
Environment Canada is forecasting a sunny 23°C Sunday, followed by clouds, showers and a thunderstorm risk overnight. Labour Day Monday cools to 21°C with a 40 percent chance of showers and possible thunderstorms, while rain becomes more persistent Monday night. Tuesday remains wet, with showers and a high of 23°C.
Today’s Weather Overview
Current Conditions
Early Sunday morning, Thunder Bay was sitting near 11°C under mostly sunny skies, setting up a pleasant start to the final Sunday of the Labour Day weekend.
Conditions will warm quickly through the morning and afternoon, with temperatures reaching the low 20s.
Sunday, September 6 — Best Weather of the Three Days
Environment Canada forecasts sunny skies for Thunder Bay today.
The high reaches 23°C, with a humidex of 28. The UV index reaches 6, or high.
This makes Sunday the strongest outdoor-weather day of the three-day forecast.
Anyone spending extended time outside should still use sunscreen and sunglasses, particularly through the midday and afternoon hours.
Sunday Night
Conditions begin changing tonight.
Skies will be clear this evening before becoming partly cloudy, with a 30 percent chance of showers overnight.
There is also a risk of a thunderstorm overnight.
The temperature falls to 14°C.
People camping or spending the evening outdoors should keep rain gear nearby despite the clear start to the night.
Labour Day Monday, September 7 — Cloudier and Unsettled
Labour Day Monday will be considerably less settled.
Environment Canada forecasts cloudy skies with a 40 percent chance of showers. A thunderstorm is also possible.
The afternoon high reaches 21°C.
Monday will still be mild enough for outdoor activities, but anyone heading to the Hymers Fall Fair, hiking, camping or travelling around the district should be prepared for passing showers.
Monday Night
The weather becomes wetter Monday night.
Environment Canada is forecasting rain, with an overnight low near 15°C.
Roads may become wet for people returning home after the Labour Day weekend, especially if rainfall becomes steady.
Tuesday, September 8 — Showers Continue
Tuesday keeps the unsettled pattern in place.
Environment Canada forecasts showers with a high of 23°C.
Tuesday night brings cloudy periods with a 30 percent chance of showers and a low near 13°C.
Despite the rain, temperatures remain several degrees above Thunder Bay’s typical early-September daytime high.
Three-Day Weather Trend
The overall pattern is straightforward:
Sunday: Sunny, warm and the best outdoor day, with a high of 23°C.
Labour Day Monday: Cloudier and cooler at 21°C, with showers and a thunderstorm risk.
Tuesday: Mild at 23°C but wet, with showers continuing.
Thunder Bay’s seasonal normal high for early September is approximately 20°C, with a normal overnight low near 7°C.
That means all three daytime highs remain near or above normal despite the increasing rainfall.
Travel and Outdoor Outlook
Sunday offers the most favourable conditions for hiking, cycling, fishing, backyard gatherings and waterfront activities.
Anyone travelling Monday should prepare for occasional reductions in visibility during heavier showers or thunderstorms.
Conditions may become wetter Monday night into Tuesday, so drivers using Highways 11/17, 61, 102 and 130 should allow extra travel time if rainfall becomes persistent.
For hikers and campers, waterproof footwear becomes more useful Monday and Tuesday as trails may become muddy.
Wardrobe Recommendations
Sunday is a light-clothing day. A T-shirt and lighter pants or shorts will be comfortable through the afternoon, while sunscreen and sunglasses are recommended with a high UV index.
Keep a light jacket available for Sunday evening as temperatures fall into the teens.
For Labour Day Monday, add a water-resistant jacket or umbrella.
Tuesday calls for a waterproof outer layer and footwear that can handle wet sidewalks, parking lots and trails.
Weather Trivia
Early September often produces some of Thunder Bay’s widest day-to-day weather contrasts.
The city can still experience afternoon temperatures well into the 20s, while the longer September nights allow temperatures to cool rapidly once skies clear.
Thunder Bay’s normal high at this time of year is about 20°C, making Sunday’s 23°C forecast roughly three degrees warmer than normal.
Source: Environment and Climate Change Canada Thunder Bay forecast issued at 5:30 a.m. EDT Sunday, September 6, 2026. Forecast details can change as the Labour Day weather system approaches.
