Environment Canada has issued a rainfall warning for Waterloo Region and Wellington County, with 25 to 50 millimetres of rain expected by Friday.
The agency expects an intense weather system will bring rising temperatures, significant precipitation and strong winds to Southern Ontario.
The rain is expected to reach southwestern Ontario by midday Thursday. Freezing rain and ice pellets are also possible as the snow transitions to rain, Environment Canada said.
Thunderstorms are also a possibility in these areas. Significant snow melt due to the rising temperatures is also a concern.