A severe thunderstorm watch has been issued for St. Catharines, Grimsby and Northern Niagara Region.
Environment Canada says the conditions are favourable for the development of severe thunderstorms that may be capable of producing strong wind gusts, large hail and heavy rain.
A few thunderstorms may hit severe thunderstorm warning criteria this afternoon or early this evening.
The main threats are heavy downpours and wind gusts to 90 kilometres per hour.