A Tornado Watch has been issued for the Kenora, Grassy Narrows, Whitedog, Sioux Narrows-Nestor Falls and Morson areas.
Environment Canada says conditions are favourable for the development of possible tornadoes, up to 120 km/h winds, nickel to golf ball-sized hail and heavy downpours, as early as this afternoon into tonight.
Residents are warned to seek shelter immediately if threatening weather approaches. Environment Canada says this is a dangerous and potentially life-threatening situation.
In the event of a tornado, residents should go indoors to a room on the lowest floor, away from outside walls and windows, leave any vehicles, trailers, tents or other temporary shelters and move to a strong building if you can, and to lie low and protect your head from debris as a last resort.
A Severe Thunderstorm Watch is in effect for the Dryden, Ignace, Vermilion Bay and English River areas.