From CBC news:

A major snowstorm pummelling southern Ontario and parts of the U.S. is forcing school and other closures as well as flight delays and cancellations, and has prompted warnings of hazardous driving conditions.

Between 15 and 25 centimetres of snow are expected to fall across southern Ontario, which is also slugging through strong and gusty northeasterly winds.

"This potentially could become an historic storm not only for the city of Toronto but for places south of the border," said CBC meteorologist Johanna Wagstaffe Friday morning.

It's expected the storm will deliver the Greater Toronto Area's most significant snowfall in five years. CBC meteorologist Claire Martin said the last time Toronto experienced similar snow accumulations was Feb. 6, 2008, when 30.4 cm hit the city.

The same weather system is also poised to dump up to 60 cm of snow across the northeastern United States.

Environment Canada is warning commuters of hazardous travelling conditions due to near-zero visibility, and heavy and blowing snow.

The heaviest snowfall is expected to hit during the morning rush hour along the Highway 401 corridor from London, Ont., across the Waterloo region and into the Greater Toronto Area.

Parts of southern Quebec can also expect to see snow as the system moves east toward the Maritimes.

Thousands of international flights have been cancelled in anticipation of the storm.

Thirty per cent of flights at Toronto Pearson Airport had already been cancelled late Thursday night. WestJet pre-emptively cancelled 40 flights Thursday and Friday to avoid a backlog in its schedule as the storm intensifies.

Travellers at airports across Canada are being advised to call airlines ahead of time to check if flights have been cancelled or delayed. Ontario Provincial Police are warning people to drive carefully as travelling conditions worsen throughout the morning.

In the U.S., New York's LaGuardia, Newark's Liberty, Boston's Logan and Chicago's O’Hare among the most affected airports.