As a large winter storm tumbles toward southern Ontario, OPP are warning motorists to use extra caution on the roads.

“Poor driving conditions added to the Christmas season’s higher than usual traffic volume of shoppers and families leaving the cities to spend time at the cottage, could greatly increase the incidence for motor vehicle collisions,” provincial police said in a statement Thursday afternoon.

Just one day before the official start of winter, a large storm is set to bring a mixed bag of weather to a wide swath of Ontario.

In a special weather statement, Environment Canada said the storm is expected to bring rain and snow to parts of the province Thursday and Friday.

For Toronto, the low-pressure system will likely bring a mix of rain and wet snow, in addition to strong winds and a high of 6 C, the national weather agency said.

In the GTA, up to two centimetres of snow is possible Friday, but the bulk of the storm's precipitation will be rain as the temperature hovers above the freezing mark.

Peter Noehammer, the City of Toronto’s director of transportation services, said the city’s fleet of salters are prepared for the storm and will be dispatched if the roads and sidewalks get slippery.

Heavy snow expected north of GTA

Further north and to the northeast of the GTA, people are bracing for heavy snow.

Ahead of the storm, a snowfall warning has been issued from Bayfield Inlet to Cornwall, including Ottawa, because the region may be blanketed by about 15 centimetres of snow by Friday night.

A winter storm warning was issued for Sault Ste. Marie, Manitoulin Island, Sudbury and North Bay.

South and west of a line roughly from Muskoka to Brockville, mostly rain is expected, although it may start briefly as freezing rain or snow, Environment Canada said.

The rain will likely change back to or become mixed with snow Friday, but significant accumulations are not expected, according to the special weather statement.

“The exceptions may be the traditional snow belt areas to the southeast of Lake Huron and Georgian Bay, where heavier snow and possibly snow squalls could develop Friday night and into Saturday,” Environment Canada said.

To the north and east of the Muskoka-to-Brockville boundary, precipitation is expected to be mostly snow, although it may be mixed with rain or brief freezing rain.

Because the storm is expected to bring a messy mix of weather, motorists are being told to prepare for hazardous conditions on the roads, including poor visibility and snow-packed sections.

Environment Canada said driving conditions are expected to deteriorate Thursday, especially over northern sections where more snow is expected.

That prompted OPP to warn motorists Thursday to drive more slowly than usual, ensure that lights are on in dark conditions and to leave more room between vehicles. They also advised drivers to leave more time to get to their destinations and to avoid going out unless necessary.

People who are scheduled to fly are asked to check their flight status before heading to the airport, in case of weather-related cancellations or delays.

Same system wreaks havoc in U.S.

The Colorado low was the first major snowstorm to hit the U.S. Midwest, where it closed schools, created dangerous driving conditions and delayed flights ahead of the busiest holiday season.

Forecasters warned that heavy snowfall coupled with strong winds would create blizzard conditions from Kansas to Wisconsin.

Nebraska's largest school district cancelled classes because of heavy snow, and so did many districts across Iowa, where drivers were told to stay off the roads because of whiteout conditions.

South of the border, the heaviest snow was expected across a swath extending from northwest Missouri into Milwaukee, Chicago and Michigan.

With files from The Associated Press

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