In a warning issued Thursday night, the agency said a "major ice storm" was "likely" overnight for parts of Southern Ontario.
The icy mix “may fall heavy at times and be accompanied by a few rumbles of thunder,” the agency warned.
The weather could also trigger power outages overnight “from downed tree limbs and power lines due to significant ice accumulation combined with northeast winds gusting to 60 km/h,” Environment Canada said.
Toronto Hydro officials said they would be on alert for possible overnight trouble as a result of any icy accumulation.
“Sometimes the weight of it will cause wires to sag or cause them to fall, and that's obviously a public safety concern for us,” Christina Basil of Toronto Hydro told CBC News.
The result could well be headaches for many people as they begin the day on Friday.
“It’s going to be mess,” the CBC's Claire Martin said.
'Icy, slow, dangerous'
“It's going to be an icy, slow, dangerous morning commute for thousands right across southern and central Ontario,” Martin said.
“If you could draw a line from Sarnia to St. Catharines, everything north of that is looking at freezing rain,” she said.
On Thursday, icy, snowy, wet weather caused dozens of flights to be cancelled at Pearson, although airlines had warned customers to check the status of departures before proceeding to the airport.
Toronto even sent out salt trucks on Thursday, just over a week after its winter contracts expired.
Peter Noehammer, the city’s director of transportation services, said the trucks had already gone out on the roads twice by the late morning.
Salt trucks — in April
"To augment our own 40 to 50 salt trucks and operators, we called back some of our contractors whose term ended at the end of March, the first week of April," he told CBC News.
"So we’ve got actually a fair number of trucks at our disposal today, upwards of about 140, 150 trucks."
Noehammer said the city would continue to salt the roads as necessary to make them safe for drivers.
Follow live updates on the weather from the Claire Martin below: