A rainfall warning is in effect for parts of central Ontario in and around the Barrie, Midland, Orillia and Bracebridge areas Wednesday.
Environment Canada said heavy rain is expected, with amounts reaching nearly 50 millimetres in some areas.
The alert is also in effect for areas in and around Parry Sound, Owen Sound, Blue Mountain, Hanover and parts of Bruce County.
The national weather agency said several areas are experiencing thunderstorms.
“A Colorado low is expected to bring rain, at times heavy, and thunderstorms to the area,” Environment Canada said in a statement.
Precipitation is expected to begin as freezing rain or ice pellets for areas east of Georgian Bay before changing to rain later Wednesday morning.
Environment Canada said the heaviest rain is expected Wednesday morning through the afternoon.