A developing low pressure area originating in Colorado is forecast to track across the central Great Lakes on Wednesday.
Precipitation is expected to arrive in the form of freezing rain towards dawn Wednesday over southwestern Ontario and spread northeastwards throughout the morning, the weather agency said.
It will likely persist for a few hours in some areas and may pose hazardous driving conditions Wednesday morning given the cold overnight temperatures just prior to the precipitation.
Also, it may fall somewhat heavily in some areas with two to five millimetres of ice accumulation possible.
Much milder air will change the freezing rain to rain from west to east during the day and should tapering off as the day progresses.
Freezing rain warnings will likely be issued later today as the path of the low pressure area becomes more clear, Environment Canada said.