Environment Canada is warning that Toronto could see 10 centimetres of snow by Saturday, with up to 15 centimetres falling in areas outside the city.

The statement says a system moving up from the United States will reach southwestern Ontario on Friday night before moving over the Greater Toronto Area.

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A trace of snow was enough to slow northbound traffic on Highway 427 at Burnhamthorpe Road on Friday. About 10 centimetres is expected to fall in Toronto on Saturday, with higher accumulations outside the city core. (Evan Mitsui/CBC)

Many areas could see 10 to 15 centimetres, which would make it the first significant snowfall for Windsor, Kitchener-Waterloo, Hamilton and Toronto, which have so far seen only lake-effect snow over the past few weeks.

CBC meteorologist Ross Hull said the snow may make for tricky driving conditions.

"In general, we're talking five to 15 centimetres of snow," he said. "That snow will be blowing around at times with some strong winds so driving conditions will be poor at times on Saturday."

Environment Canada also issued a snow squall alert on Friday morning for Barrie, Orillia and areas near the Bruce Peninsula.  

The statement warns of low visibility and snowfall amounts reaching 60 centimetres by Saturday morning.

School buses in Simcoe county were cancelled Friday morning for the north and west zones.