Severe thunderstorms are in the forecast Thursday evening.
Just before 3 p.m., Environment Canada issued a severe thunderstorm watch for a large area including Sarnia-Lambton, London-Middlesex, Huron County, and Perth County.
A watch was put into effect for Windsor-Essex and Chatham-Kent at around 4:45 p.m.
The national weather agency said the main threats are wind gusts up to 110 kilometres per hour, torrential rainfall with amounts possibly in excess of 50 millimetres, and nickel sized hail.
It said utility outages and significant damage to property, buildings and trees is possible.
If threatening weather approaches, take cover in a basement or interior room.
If outside, protect yourself from flying debris and hail.
Emergency Management Ontario recommends that you take cover immediately if threatening weather approaches.
Heavy rain can cause flash flooding and significant reductions to visibility.
Strong wind gusts can damage trees, buildings and overturn vehicles.
All thunderstorm watches and warnings ended overnight.