The area, south of the city of Toronto near the U.S. border, rarely sees tornadoes. However, strong winds up to 100 kilometers per hour (62 mph) and ping pong ball-sized hail are expected Tuesday. Severe rain is also expected in Toronto and Hamilton.
Four people were struck by lightning while playing golf Monday in Stouffville, near Toronto. Each person was hospitalized, one in critical condition, police said.
Environment Canada, the federal agency that includes the nation's weather service, issued tornado warnings and advice regarding tornado precautions Tuesday afternoon, adding, "The main threats will be torrential downpours, damaging winds and large hail."
The tornadoes killed two people, including a child, in Nebraska Monday.
In July 2013, severe thunderstorms in the area left 50,000 people, mostly in Toronto, without power. In a two-hour span, 126 millimeters (five inches) of rain fell on the city.