Environment Canada has issued a freezing rain warning for Wednesday that covers the Guelph area and Waterloo region.
The agency said freezing rain is expected to move over southwestern Ontario, starting in the morning.
The system could persist much of the day before ending later at night.
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The morning commute will likely be affected and the weather office said untreated sidewalks and roads are likely to become icy.
The weather office is urging drivers to adjust to the changing road conditions and residents are being warned that ice build-up may cause tree branches to break off.