Environment Canada issued the alert at 1:41 p.m. Saturday warning of freezing rain for Hamilton, Waterloo Region, Wellington County, Niagara Region, Brant County and Halton.
Freezing rain warnings are issued when rain falling in sub-zero temperatures creates ice build-up and icy surfaces. The freezing rain is expected to change to flurries early this afternoon over southwestern Ontario to the Golden Horseshoe later Sunday afternoon or early evening.
Freezing rain will persist for several hours before changing back to light snow Sunday afternoon.
Motorists should exercise caution, as road surfaces may become icy and slippery. Slow down and maintain a safe driving distance. "The freezing rain will then affect Quebec City in the evening and reach Chaleur Bay area overnight tonight", the agency says.
The latest bout of winter weather comes after Toronto received 6.8 centimetres of snow Friday afternoon, wreaking havoc with the afternoon commute.