Environment Canada has issued a special weather statement for much of southwestern Ontario.
Grey-Bruce, Huron-Perth, London-Middlesex, Oxford, Elgin, Sarnia-Lambton, Windsor-Essex, and Chatham-Kent could see at least 30 to 50 mm of rain from Saturday afternoon into the evening.
"Rainfall warnings for greater than 50 mm within 24 hours may be required at a later time," the weather agency warned.
There's also a risk of thunderstorms during this time.