Winter has arrived in the Greater Toronto Area.

The season doesn’t officially start until Dec. 21. But up to 25 centimetres of snow are expected this weekend in parts of the region and temperatures will hover below – 20 with the wind chill.

A winter storm warning was issued for Oakville, Burlington, Hamilton. Environment Canada also issued a snowfall warning for Toronto, Mississauga and the Niagara area.

CityNews meteorologist Natasha Ramsahai said by the evening the downtown core had already seen between 10 to 20 centimetres of snow, with as much as 10 more centimetres possible by the morning.

“The snow is continuing right through the evening hours. It’s going to be heavy at times,” she explained. “We’re not going to start to see the snow taper to flurries until the wee hours of the morning…About the time we wake up on Sunday this snowstorm will be over.”

Toronto’s director of transportation services Peter Noehammer told 680News about 200 salt trucks have been deployed and 600 plows started moving at 2:30 p.m. on expressways and arterial roads.

Noehammer says once the main roads have been cleared plows will begin work on residential streets.

“We’ll hit the local streets after the snow’s done in the overnight and we’ll be plowing the local and residential streets,” he explained.

While crews work around the clock, Noehammer reminds residents to do their part to help keep the streets safe and clear.

“If you are shovelling your driveway, probably tomorrow, don’t put the snow back out onto the roadway,” he said. “That just causes it to be unsafe again and does carry a fine so our bylaw officers are instructed to look out for those things – especially from commercial parking lots.”

Meanwhile, dozens of flights through Toronto Pearson and Montreal-Trudeau airports have been delayed or cancelled.

Ontario Provincial Police are cautioning motorists to take care on highways, posting on Twitter — “IF YOU SEE SNOW, GO SLOW!”

Police also say there have been numerous accidents including a 20-car pileup on the Queen Elizabeth Highway in Mississauga.

Drivers should prepare for poor road conditions tonight and into tomorrow morning.

With files from The Canadian Press