A rainfall warning has been issued for Niagara with up to 45 mm on the way.
Environment Canada says rain at times heavy is expected, and the frozen ground has a reduced ability to absorb the rainfall.
Rain is expected to start late tonight and continue into tomorrow.
"Rain is forecast to begin tonight over southwestern Ontario and then spread northeastward early Tuesday. The rain will continue for several hours before tapering to showers from west to east Tuesday afternoon."
Localized flooding in low-lying areas is possible. Keep children and pets away from creeks and river banks.