Thunder Bay Weather October 18–20: Mild Sunshine Before a Freezing Monday Night
THUNDER BAY – WEATHER – Mainly sunny skies and a high of 18°C will make Sunday a mild autumn day in Thunder Bay. Sunshine continues into the workweek, but Monday night brings a sharp temperature drop to −4°C.
Forecast for Sunday, October 18, through Tuesday, October 20, 2026, based on Environment Canada’s 5:30 a.m. EDT Sunday bulletins.
Current conditions
At 7:00 a.m. EDT, Thunder Bay Airport reported mainly clear skies and 3.4°C. Winds were west-southwest at 8 km/h, humidity was 79 per cent, and barometric pressure was 101.3 kPa and falling. Visibility was 24 kilometres.
Thunder Bay’s three-day forecast
| Day | Conditions | High | Following overnight |
|---|---|---|---|
| Sunday, October 18 | Mainly sunny; southwest winds becoming 20 km/h, gusting to 40 late morning | 18°C | Clear, 3°C |
| Monday, October 19 | Sunny | 15°C | Clear, −4°C |
| Tuesday, October 20 | Sunny | 14°C | Clear, 5°C |
The UV index is 3, or moderate, Sunday and Monday. No precipitation is forecast during this three-day period.
Kakabeka Falls: Breezy Sunday, cold Monday night
Kakabeka Falls will be mainly sunny Sunday, reaching 18°C, with west winds increasing to 30 km/h gusting to 50. Winds ease Sunday evening under clear skies, with a low of 3°C.
Monday stays sunny with a high of 15°C, followed by a clear night and a low of −3°C. Tuesday brings more sunshine, a high of 13°C, and an overnight low of 3°C.
Nipigon and Red Rock: Sunshine with stronger south winds
Both communities will have mainly sunny skies Sunday and highs of 15°C. South winds of 30 km/h gusting to 50 turn west at 20 km/h during the evening. Clear skies follow, with lows of 4°C.
Monday is sunny with highs of 14°C. Northwest winds of 20 km/h become light during the afternoon, and overnight temperatures fall to 0°C.
Tuesday remains sunny with highs of 14°C, followed by clear skies and lows of 8°C.
What to wear and plan for
Wear layers for cool mornings and warmer afternoons. A wind-resistant jacket will be useful Sunday, particularly around Kakabeka Falls, Nipigon and Red Rock.
Before Monday night, bring temperature-sensitive plants indoors and allow time to clear possible windshield frost Tuesday morning. Keep a warmer jacket and gloves handy for early departures.
Weather trivia
Thunder Bay’s listed normal high for this forecast period is 9°C. Sunday’s predicted 18°C is nine degrees above that benchmark—despite the freezing night expected just a day later.
