Montreal has been hit with its first big snowstorm, with 15 centimetres expected by the end of Monday.

Heavy, blowing snow started falling at 7 a.m. ET and forced at least one major highway southeast of Montreal to close temporarily.

Meteorologist René Héroux of Environment Canada said the blast of winter weather puts an end to the unusually warm weather in Quebec this year.

'…people have to be careful and always remember that snow means slow.'-Maria Soteriades of the Transport Ministry

"It's quite a change," he told CBC News Online. "I would say now this really mild weather is behind us."

Environment Canada says temperatures Monday will hover around –8 C, with winds blowing at 30 km/h. By Tuesday, the snow should have eased off, but temperatures are expected to plummet to –18 C.

By Wednesday, they will hit –24 C.

Snowy slippery conditions sent about 20 cars and trucks rolling off a two-kilometre stretch of Highway 20, near St-Hyacinthe, on Monday afternoon.

Provincial police closed the westbound lanes in the early afternoon. They were reopened by 3:30 p.m. ET.

No one was injured.

Police and officials from Transport Quebec were urging motorists to be careful.

"Roads are not closed … we have a snowstorm, and people have to be careful and always remember that snow means slow," said Maria Soteriades of the Transport Ministry.

Flights delayed, cancelled

While drivers struggled on snow-covered roads, passengers were coping with delayed and cancelled flights at Pierre Elliott Trudeau airport.

Jacqueline Richard, a spokeswoman for the airport, said the problem isn't the snow in Montreal, but freezing rain that attacked Ontario and other regions.

"The conditions are not so bad here in Montreal; our runways have been kept clear," she told CBC News.

"But it seems that the problems are flights coming in from Toronto, New York, Chicago and so on. There's a lot of freezing rain which makes it difficult."

Toronto's Pearson airport cancelled more than 100 inbound and outgoing flights because of a backlog of planes being deiced.

Richard advised travellers to check with their airlines before arriving at the airport.