A Special Weather Statement has been issued by Environment Canada warning of a significant amount of rain in Windsor-Essex and Chatham-Kent.
15-25 mm, or up to 1-inch, is expected to fall starting Monday night into Tuesday.
"There are thunderstorms in the forecast and that will come on Tuesday morning when people are heading back to work and heading back to school, so something to be mindful of," says Environment Canada meteorologist Gerald Cheng. "We've been dealing with wintery weather for quite some time and now we have the milder air coming into southwestern Ontario and temperatures are going to be very mild, 10 degrees for the forecast high for Windsor for Tuesday so that is quite something. That's eight degrees above normal."
He says the system is affecting all of southern Ontario and northeastern Ontario.
"For southwestern Ontario, we are mainly dealing with rain" he says. "This is a system that's going to bring some milder temperatures back into the area.
The weather agency says the frozen ground has a reduced ability to absorb the rainfall which may lead to flooding.
There's also a risk of light freezing rain in portions of southwestern Ontario Monday evening.
— with files from AM800's Rob Hindi