Environment Canada has issued a severe thunderstorm watch for Georgian Bay northeast to the Ottawa River on Thursday afternoon.
It includes the risk of a tornado, large hail and heavy rain.
Forecasters say the storm could hit the area, which includes western Renfrew County and Algonquin Park, in the afternoon or early evening.
“Despite it being early Autumn, a tornado or two cannot be ruled out,” said Environment Canada when issuing the watch around 12:10 p.m.
Between 30 to 50 millimetres of rain could fall.
A tornado watch is issued when there’s a storm approaching with conditions that could produce a tornado. A warning goes out either when a tornado sighting has been reported or when there’s sufficient evidence to suggest a tornado is on the way.
When a tornado forms, people are advised to stay away from exterior walls and windows, ideally going to a basement or the ground floor. They should also get out of vehicles.