A severe thunderstorm watch has been issued by Environment Canada for Barrie, Collingwood, Hillsdale, Midland, Coldwater, Orr Lake, Orillia, Lagoon City and Washago.
According to the alert, conditions are favourable for the development of dangerous thunderstorms that may cause wind gusts of up to 90 km/h and torrential rain.
These storms will likely develop Monday afternoon and evening, Environment Canada says.
Strong wind gusts can damage buildings, bring down trees and blow large vehicles off the road, Environment Canada adds, and heavy rains can cause flash floods and water pooling over roads.
Severe thunderstorm watches are issued when atmospheric conditions are favourable for the development of thunderstorms that could produce large hail, damaging winds or torrential rain.
The Office of the Fire Marshal and Emergency Management recommends taking cover immediately if threatening weather approaches.