The national weather service warned of significant snowfall across most of Ontario with total amounts of 15 to 20 cm expected on Wednesday.
Areas impacted included Toronto, Mississauga, Brampton, Hamilton, Burlington, Oakville, Halton Hills, Milton, Vaughan, Richmond Hill, Pickering and Oshawa.
Environment Canada says rapidly accumulating snow will make travel difficult, cause visibilty issues and isolated power outages are also possible.
A Texas low tracking northeastward is expected to bring snow to the area late Wednesday morning until midnight and possibly into early Thursday morning, the weather service said in its advisory.
Drivers are urged to be prepared for quickly changing and deteriorating travel conditions where visibility may be suddenly reduced in heavy snow.