Environment Canada is advising of the potential for thunderstorms Friday afternoon and evening.
The weather agency posted a severe thunderstorm watch for Sarnia-Lambton just before 1pm, and a warning was issued for Sarnia, Petrolia and Western Lambton County just after 3pm.
Scattered and slow-moving thunderstorms with heavy rain and strong wind gusts developed over portions of southwestern Ontario.
An inch of rain (25 mm) fell in just one hour in Sarnia from about 2:15pm to 3:15pm.
The warning for Sarnia-Lambton was ended at about 3:45pm but the watch remained in effect.
Meteorologists were tracking a line of thunderstorms that could dump as much as 50 mm (2 inches) to 70 mm of rain in an hour.
Motorists are advised to watch for ponding on roads and potential flash flooding in some areas.