Environment Canada has issued a tornado watch for parts of the Rainy River District, Dryden and Ignace areas.
It is tracking a slow moving system in Minnesota that could develop severe thunderstorms and tornadoes.
The storms could bring hail measuring from a quarter to ping pong balls in size, with wind gusts up to 60-70 mph.
There are reports of hail measuring one inch in diameter falling in areas of Minnesota where the storm has already passed.
The system is expected to reach northwestern Ontario this evening before moving away near midnight.
Environment Canada says the greatest threat could be in areas close to the Ontario-Minnesota border.
