Environment Canada issued another special weather statement for Sarnia-Lambton, London-Middlesex and Huron-Perth late Monday afternoon.
The national weather agency says a few evening thunderstorms could pack wind gusts to 70 km/h, heavy downpours, frequent lightning and small hail.
Motorists were being told to be prepared for sudden low visibility in downpours resulting in difficult driving conditions.
The thunderstorms were expected to weaken into isolated showers later Monday evening.