Thunder Bay weather forecast for August 11-15, 2026. Warm temperatures reach 26°C Tuesday, with showersTHUNDER BAY – WEATHER – Thunder Bay is starting Tuesday under mostly cloudy skies, with a warm and somewhat humid day ahead. Today’s Weather OverviewCurrent ConditionsAt 7:00 AM EDT Tuesday, August 11, Thunder Bay Airport was reporting mostly cloudy skies and a temperature of 13.8°C. Thunder Bay will see a mix of sun and cloud today, along with a 30 per cent chance of showers this afternoon. Thunder Bay Weather TrendThe overall pattern from August 11 through August 15 is one of alternating summer warmth and cooler, unsettled periods.