"Ice accumulations of this magnitude combined with gusty northeast winds ... may result in widespread power outages due to fallen tree limbs and power lines", the agency said.
The National Weather Service used an Ice Storm Waring for Erie, Niagara, Orleans, Genesee, Monroe, Wyoming and Livingston counties from 2 p.m. Saturday through 2 p.m. Sunday.
Then, more rain is in the forecast, right into Monday. - Freezing rain should fairly quickly to finish near highway 401, but can last for several hours in regions located further North, especially on high ground.
That is expected to change to freezing rain by Sunday.
There is the potential for a significant ice storm in some areas with freezing rain amounts in excess of 20mm.
A Winter Weather Advisory has been issued for Barry, Calhoun, Jackson and Washtenaw Counties where up to two tenths of an inch of ice will be possible by Sunday morning.
Ice from freezing rain starts to form on a railing in Toronto on Saturday April 14, 2018.
Scattered rain showers mixed at times with freezing rain in the morning.
In the Toronto area, Environment Canada said an ice buildup of 10 to 20 millimetres are likely by late Sunday.
"We're ready to respond 24/7", Hydro One said in a tweet. By early Saturday afternoon, about 8,000 people were without power.
Residents from the GTA and beyond are sharing their photos and videos from across the region as the storm passes through their neighbourhoods.