Thunder Bay weather for August 18, 2026: Partly cloudy skies give way to a sunny morning, then a 30 percent chance of afternoon showers with west winds gusting to 50 km/h and a high of 23°C. Cooler, mainly sunny weather follows Wednesday
Thunder Bay is starting Tuesday with partly cloudy skies and mild temperatures, but the wind will become the main weather story as the day progresses. Sunshine dominates the morning before clouds increase, bringing a 30 percent chance of afternoon showers. West winds will strengthen to 30 km/h with gusts to 50 km/h, making for a breezy day across the city and along exposed areas near Lake Superior.
Temperatures will reach the seasonal normal of 23°C this afternoon. A cooler night follows, and Wednesday promises plenty of sunshine before a somewhat cooler mix of sun and cloud Thursday.
Today’s Weather Overview
Current Conditions
At 7:00 AM EDT Tuesday, Thunder Bay Airport was reporting partly cloudy skies and 14.5°C. Humidity was 87 percent, with a dew point of 12.4°C. Barometric pressure was 101.0 kPa and rising, while winds were from the west-northwest at 13 km/h. Visibility was a very good 32 kilometres.
The early clouds will give way to sunshine this morning, followed by a mix of sun and cloud later today. Environment Canada is forecasting a 30 percent chance of showers this afternoon. West winds increase to 30 km/h gusting to 50 km/h. The daytime high reaches 23°C, with a humidex of 25. The UV index is 5, or moderate.
Those stronger winds will be especially noticeable for people spending time along the waterfront, on open stretches of road or on area lakes. Boaters should factor the gusty conditions into Tuesday plans.
Tonight — Cooler With a Few Showers Possible
Tuesday evening will be partly cloudy with a 30 percent chance of showers during the evening and after midnight. Northwest winds of 20 km/h gusting to 40 will become light during the evening.
Temperatures fall sharply after sunset, reaching an overnight low of 9°C. That will make Wednesday morning considerably cooler than Tuesday afternoon.
Tomorrow’s Forecast
Wednesday, August 19
Wednesday will start sunny, with a mix of sun and cloud developing around noon. West winds increase to 20 km/h late in the morning. The daytime high reaches 21°C, with the UV index climbing to 6, or high.
Wednesday night will be clear and chilly, with a low of only 8°C.
For outdoor activities, Wednesday currently looks like the best combination of dry weather and sunshine in the immediate forecast, although the morning will have a distinctly cool late-summer feel.
Thursday, August 20
Thursday brings a mix of sun and cloud with a high of 20°C. There is no daytime precipitation mentioned in Environment Canada’s current forecast.
Clouds increase Thursday night, when there will be a 30 percent chance of showers. The overnight low rises to 13°C, making Thursday night considerably milder than Wednesday night.
Friday, August 21
Friday becomes more unsettled. Environment Canada is calling for cloudy skies with a 40 percent chance of showersand a high of 20°C. Friday night remains cloudy with another 40 percent chance of showers and a low of 12°C.
Wardrobe Recommendations
Tuesday calls for layers and wind protection. A light shirt will be comfortable during the afternoon high near 23°C, but a light windbreaker or jacket will be useful with west winds gusting to 50 km/h. Keep a compact umbrella or light rain shell nearby because an afternoon shower remains possible.
The temperature falls to 9°C tonight and only 8°C Wednesday night, so anyone heading out early in the morning or spending the evening outdoors will want a hoodie, fleece or light jacket. Wednesday’s high UV index also makes sunglasses, sunscreen and a hat worthwhile for extended outdoor activities.
Weather Trivia
Environment Canada’s climate information puts Thunder Bay’s normal temperature for August 18 at a high of 23°C and a low of 10°C. That means Tuesday’s forecast high of 23°C is right on the seasonal normal, while tonight’s expected 9°C low is just slightly cooler than average.
Thunder Bay still has more than 14 hours of daylight at this point in August. Sunrise Tuesday was at 6:55 AM EDT, with sunset at 9:06 PM EDT.
Source: Environment and Climate Change Canada observations from Thunder Bay Airport at 7:00 AM EDT and the public forecast issued at 7:10 AM EDT Tuesday, August 18, 2026.
