Thunder Bay weather forecast for August 11-15, 2026. Warm temperatures reach 26°C Tuesday, with showers
THUNDER BAY – WEATHER – Thunder Bay is starting Tuesday under mostly cloudy skies, with a warm and somewhat humid day ahead. Temperatures will climb well into the mid-20s today before a cooler, more unsettled pattern arrives Wednesday.
The best stretch of weather this week appears to be Thursday and Friday, when sunshine returns and daytime highs settle into the low 20s. By Saturday, another chance of showers moves back into the forecast.
Today’s Weather Overview
Current Conditions
At 7:00 AM EDT Tuesday, August 11, Thunder Bay Airport was reporting mostly cloudy skies and a temperature of 13.8°C.
Humidity is high at 91 per cent, with a dew point of 12.4°C, making the morning feel damp and cool. Winds are light from the northwest at 5 km/h.
Barometric pressure is 101.4 kPa and falling, while visibility remains excellent at 32 kilometres.
Despite the cloudy start, temperatures are expected to rise quickly through the morning and afternoon.
Thunder Bay will see a mix of sun and cloud today, along with a 30 per cent chance of showers this afternoon.
The high will reach 26°C, with a humidex of 29. The UV index will be 7, or high, so sunscreen, sunglasses and a hat are recommended if you are spending extended time outdoors.
Tonight will be partly cloudy with a 30 per cent chance of showers early this evening. The overnight low will fall to 12°C.
Wednesday, August 12
Showers and Thunderstorm Risk
Wednesday will be noticeably cooler and more unsettled.
Environment Canada is calling for mainly cloudy skies, with a 40 per cent chance of showers beginning late in the morning and continuing through the afternoon.
There will also be a risk of a thunderstorm during the afternoon.
The daytime high will reach 21°C, with a UV index of 6, or high.
Wednesday night will bring cloudy periods and a 30 per cent chance of showers, with a low of 11°C.
Anyone planning outdoor work, travel or recreation should keep an eye on changing weather conditions Wednesday afternoon, particularly if thunderstorms begin to develop.
Thursday, August 13
Thursday brings an improvement in the weather.
Expect a mix of sun and cloud with a daytime high of 22°C.
Skies will clear Thursday night as temperatures fall to 10°C.
For outdoor activities, Thursday should offer one of the more comfortable days of the forecast period, with seasonal temperatures and no precipitation currently indicated.
Friday, August 14
Friday is shaping up to be the best weather day of the week.
Thunder Bay can expect sunny skies and a high of 23°C.
Friday night will feature some cloudy periods, with the temperature dropping sharply to 8°C.
That overnight temperature is slightly cooler than Thunder Bay’s normal minimum of about 10°C for this time of August.
Saturday, August 15
Saturday brings another change.
A mix of sun and cloud is forecast, along with a 30 per cent chance of showers.
The daytime high will reach 22°C.
Saturday night will remain partly unsettled, with cloudy periods and a 30 per cent chance of showers. The overnight low will be 12°C.
Wardrobe Recommendations
Tuesday will be warm enough for shorts, T-shirts and other summer clothing, although carrying a lightweight rain jacket or umbrella would be a good idea because of the afternoon shower risk.
Wednesday will feel cooler, especially under cloudy skies. A light jacket or sweater may be useful during the morning and evening.
Thursday and Friday should be comfortable for most outdoor activities, but overnight temperatures of 10°C Thursday and 8°C Friday mean campers and anyone spending time outdoors after sunset should have warmer layers available.
With UV levels rated high Tuesday and Wednesday, sunscreen, sunglasses and a hat remain important even when skies are partly cloudy.
Thunder Bay Weather Trend
The overall pattern from August 11 through August 15 is one of alternating summer warmth and cooler, unsettled periods.
Tuesday will be the warmest day, reaching 26°C, before temperatures dip to 21°C Wednesday.
Conditions improve Thursday and Friday, with highs of 22°C and 23°C, before another chance of showers arrives Saturday.
Thunder Bay’s normal temperatures for this period are approximately 24°C for the daytime high and 10°C overnight, putting most of this week’s forecast relatively close to seasonal values.
Sunrise Tuesday is at 6:45 AM EDT, while sunset is at 9:19 PM EDT, providing more than 14 hours of daylight.
Weather Trivia
Thunder Bay’s location at the western end of Lake Superior can have a significant influence on local temperatures.
During summer, Lake Superior often moderates temperatures near the waterfront. On some days, neighbourhoods close to the lake can be several degrees cooler than inland areas, particularly when winds blow off the water.
That lake influence is one reason temperatures around Thunder Bay can vary considerably over relatively short distances.
Forecast information is based on Environment and Climate Change Canada observations and the forecast issued at 5:30 AM EDT on Tuesday, August 11, 2026. Weather conditions and thunderstorm risks can change quickly, so residents should monitor updated forecasts and alerts throughout the day.
