A slow-moving low pressure system could bring heavy and freezing rain to the City of Toronto and much of southern Ontario overnight.
Environment Canada issued the special weather statement for areas including Toronto, Oxford, Niagara, Hamilton, Halton and York shortly before 8 p.m. Monday night.
The agency said 20 to 40 millimetres of rain are expected into Tuesday.
Brief periods of freezing rain are also possible, with rain potentially changing to wet snow by Wednesday morning.
Environment Canada is urging motorists to drive with caution as heavy rain will reduce visibility and create possibly hazardous winter driving conditions.
Freezing rain warning
A winter storm warning upgraded to a freezing rain warning Monday afternoon remains in effect for the Parry Sound and Huntsville areas in central Ontario.
Environment Canada said a significant amount of freezing rain is expected to enter the region tonight and Tuesday.
The weather agency said significant ice may accumulate due to the freezing rain and will likely become mixed with ice pellets at times.
Environment Canada said the precipitation will continue until Tuesday night, and include snow.
