A severe thunderstorm watch and rainfall warning have been issued for the region.
Environment Canada says conditions are favourable for the development of severe thunderstorms that may be capable of producing strong wind gusts, large hail, and heavy rain.
A line of dangerous thunderstorms is forecast to move into Ontario early this evening, persist through the evening hours and weaken overnight. The main threats are damaging wind gusts up to 110 km/h, dime to ping pong ball sized hail, and heavy downpours.
The weather agency adds that another round of precipitation is expected to move in from Minnesota this evening and will likely persist through Tuesday. Rainfall amounts remain fairly uncertain but an additional 20 to 40 mm appears possible, with locally higher amounts in areas that receive thunderstorms.