A blast of winter across southern Ontario caused travel havoc in Toronto, with more than half of all flights cancelled at Pearson Airport and 'treacherous' driving conditions due to snowy roads.

GO Transit suspended service on its Barrie line late Friday afternoon after a train struck an abandoned vehicle near York University.

And Toronto police closed the intersection of Leslie Street and Finch Avenue East after three TTC buses and a number of other vehicles found it impossible to climb the hill. The road will be closed until plows can clear the way.

Most of southern Ontario remains under a snowfall warning with the weather causing widespread school closures, flight cancellations and poor visibility for drivers.

More than 20 centimetres of snow had fallen in the Greater Toronto Area by Friday evening, according to the CBC Weather Centre.

Anger at the airport

More than 800 flights were cancelled at Toronto Pearson International Airport — more than half of all incoming and outgoing flights on Friday.

Billy Bishop airport, in downtown Toronto, was also reporting cancellations.

At Pearson, by mid-evening, there was growing anger among the thousands of passengers who were stranded.

Some said they sat on flights for hours only to be taken off and told to re-book.

All hotels in vicinity of airport are swamped — with most airlines still directing passengers to find a hotel.

Many people are furious at Air Canada. They say the airline is telling passengers to call its 1-800 number to re-book flights, but the lines are jammed.

CAA gets 4,000 calls

Roads in and around Toronto were snow-covered and slippery across the city.

By about Friday afternoon, the southern Ontario branch of the Canadian Automobile Association received more than 4,000 calls for service since midnight. In the Greater Toronto Area, the wait time for a tow truck was between 75 minutes and two hours, it said on Twitter.

"We are on track to double the number of calls on an average winter day," the association said.

By 8:30 a.m., the OPP had responded to 625 calls since midnight — 350 of which were collisions.

Sgt. Dave Woodford said traffic Friday morning was moving at 20 km/h on Highway 400 as drivers contended with blowing snow and near-zero visibility.

“Conditions are treacherous right now," said Woodford. “People think because they have snow tires or four-wheel drive, nothing can happen to them. If you have to be out, slow down. If you don’t have to be out anywhere, don’t go on the roads.”

OPP tells drivers to stay off highways

On Friday afternoon, OPP warned drivers to stay off of the highways in the Greater Toronto Area for the next few hours so crews "can get caught up clearing the snow."

OPP said the snowplows were out in force, but were overwhelmed with the number of calls.

A man walks along the street carrying his shovel during a snow storm in Toronto on Friday. (Frank Gunn/Canadian Press)

"We must restrict travel on the highways so the snow removal can be done properly," OPP said in a statement.

City crews had dispatched about 600 plows to the city's main routes but they were struggling to keep up with the fast-falling snow.

“You can forget about seeing the markings on the roads, they’re covered in snow," reported CBC’s Trevor Dunn on Friday morning. "If you accelerate too fast, you’ll start to fish tail quite easily.”

“The Gardiner Expressway is moving very slowly, but that’s a good thing because it’s covered in snow.”

GO Transit said it was operating on a disrupted storm schedule, with trains running between 10 to 20 minutes late. They’ve posted updated information here.

Extreme weather alert

The city also wasted no time issuing an extreme weather alert, asking homeless people who normally stay outside to seek shelter.

Most City of Toronto offices and services were operating as usual, such as indoor arenas, child care centres and ski and snowboard programs. However, some outdoor artificial rinks may close due to the heavy snowfall, the city said in a statement.

Toronto has not seen a snowfall exceeding 15 centimetres since Dec. 19, 2008, said Environment Canada senior climatologist David Phillips, adding the precipitation from the current system represents nearly half the total snowfall for all of last year.

With the forecast calling for snow to continue falling throughout the day, the outbound commute is expected to be difficult as well.

The storm was caused when two weather systems, a Texas low and an Alberta clipper, merged. The storm brought winter conditions not only to the GTA, but to much of southern Ontario and the northern U.S.

"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.

However, things will be quite different come Monday, when much of the weather will turn to a slushy mess.

Monday forecasts for much of Ontario are calling for rain and above-zero temperatures, including:

• Toronto daytime highs that are expected to hit 7 C.
• Windsor experiencing above-zero temperatures
• Ottawa expecting a mix of snow and rain.

With files from the CBC's Ivy Cuervo