As of noon ET., 245 arrival and 263 departure flights have been cancelled due to the weather. Officials say further delays are expected throughout the day.
WATCH: Winter storm over southern Ontario hits Niagara region hardest. Mark Carcasole reports.
The cancellations are primarily due to blizzard-like conditions in the U.S. east coast which have forced school closures and weather warnings.
Travellers are being reminded to check their flight status before arriving at the airport.
Environment Canada issued a special weather statement for the GTA with 5 to 10 centimetres of snow to fall by Tuesday evening.
WATCH: Snowstorm doesn’t stop tourists from sightseeing in Niagara Falls.
However, the bulk of the snow is staying south and well to the west of Toronto with the Hamilton, Oakville and Niagara Region. They are expected to receive about 20 to 30 centimetres of snow accumulation.
“For the most part the snowfall amounts were less than originally anticipated,” Environment Canada meteorologist Mark Schuster said.
“Most of southern Ontario was on the northwestern edge of this weather system. Originally we were saying 10 to 15 centimetres of snow across many areas, and it looks like it’s been a little bit less than that.”
Officials are telling motorists to slow down and to adjust their driving to the changing weather conditions.
WATCH: GTA motorists capture conditions on snowy roads, highways
A number of road collisions have been reported overnight and early Tuesday morning including a tractor-trailer rollover on eastbound Highway 401 near Milton.
Environment Canada said the snow will taper off to scattered flurries Tuesday night as the winter storm moves away to the northeast.
The temperature will reach -11C this evening with more seasonal weather expected for the end of the week.
All classes and activities planned for Brock University’s main campus, as well as those at the Marilyn I. Walker School of Fine and Performing Arts and the Hamilton campus are cancelled Tuesday.
The buildings are closed for the day and only essential services, such as dining for students in residences, are available.
McMaster University is also closed on Tuesday. The closure also applies to classes and other activities scheduled for Tuesday evening.
Mohawk College and Sheridan College are also closed for the day.
-With a file from The Canadian Press
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