Some of the storms are generating winds of up to 90 kilometres an hour, as well as large hail and "torrential downpours," Environment Canada said late Sunday night.
The agency's weather office said the winds are strong enough to be damaging, and recommended people take cover immediately if a threatening storm system approaches.
Thunder Bay was still under a severe thunderstorm watch, with the possibility of more than 50 millimetres of rain in under an hour. "An isolated tornado is also possible," Environment Canada said.
Severe thunderstorm warnings — a notch above a watch — are in place for several areas:
- Ear Falls – Perrault Falls – Western Lac Seul
- Sioux Lookout – Eastern Lac Seul
- Savant Lake - Sturgeon Lake
- Sioux Narrows – Nestor Falls – Morson
- Dryden – Vermilion Bay
- Fort Frances – Emo – Rainy River
The severe thunderstorm warnings for Red Lake – Woodland Caribou Park and Kenora – Grassy Narrows – Whitedog have been downgraded to watches.
For Dryden and Vermilion Bay, the federal weather agency issued a strong caution, saying "persons in or near this area should be on the lookout for adverse weather conditions and take necessary safety precautions."
In all areas, Environment Canada warned that severe thunderstorms can sometimes produce tornadoes.