After a mild December, the first winter storm is starting to hit much of Ontario tonight, as an intense low-pressure weather system from Texas is rolling in toward the lower Great Lakes.

The storm is bringing snow, freezing rain and later, rain to the region. The rain/snow mix will likely make for a difficult Tuesday commute for some drivers.

Ice will mainly impact southern Ontario overnight & tmrw am. But some mixing possible for the Ottawa valley <a href="https://twitter.com/hashtag/onstorm?src=hash">#onstorm</a> <a href="https://t.co/FxLKll2S13">pic.twitter.com/FxLKll2S13</a> —@JWagstaffe

Towns and cities across the region started seeing snowfall late Monday afternoon, with blowing snow starting in Toronto, Hamilton and Kitchener.

Freezing rain started in London around 6 p.m., and freezing rain warnings are in effect for Windsor, Niagara and Hamilton.

Snow has already started coming down in much of southern Ontario, as seen here from the road near Kitchener at about 5 p.m. (Mark Robinson/Twitter)

Sault Ste. Marie is expected to be hit hard with upwards of 35 centimetres of snow Monday night.

Environment Canada is warning of snowfall this evening for the Toronto area, which is expected to become heavy quickly. Accumulations of five to 10 centimetres are likely before the snow changes to ice pellets just after midnight.

A changeover to rain is expected by Tuesday morning, with a risk of freezing rain overnight.

First <a href="https://twitter.com/hashtag/onstorm?src=hash">#onstorm</a> of the season. Grimsby. <a href="https://t.co/1v6FAVrKXa">pic.twitter.com/1v6FAVrKXa</a> —@kylebrobertson

Environment Canada meteorologist Steve Knott said the snow will likely arrive in the Toronto area sometime after 7 p.m. ET this evening before turning to a mix of rain and ice pellets by midnight.

"When the snow starts it could be fairly intense," said Knott. "I think that's going to be the greatest risk to motorists."

Low visibility caused by blowing snow might also pose a problem for drivers, with winds of up to 80 kilometres an hour forecast for some areas of the province.

'If you don't have to drive, don't'

Toronto police Const. Scott Mills said police generally see hundreds of collisions during the first winter storm of the season.

Whiteouts near Tavistock <a href="https://twitter.com/hashtag/onstorm?src=hash">#onstorm</a> <a href="https://twitter.com/hashtag/onsnow?src=hash">#onsnow</a> <a href="https://t.co/JpJLKo2KaJ">pic.twitter.com/JpJLKo2KaJ</a> —@205mph

"If you don't have to drive, don't," he told CBC News.

In areas closer to Lake Ontario, the precipitation is more likely to fall as rain. Environment Canada is calling for accumulations of three to four centimetres of snow for areas near the lake. Areas farther inland are more likely to see snow.

Toronto Hydro is calling in extra crews and extra staff in their control room to handle calls.

Winter storm warning for Ottawa

​Other parts of Ontario will also see some combination of snow, rain or freezing rain overnight Monday and into Tuesday. A winter storm warning is in place for the Ottawa region, where five to 10 centimetres of snow is expected tonight with accumulations reaching up to 25 centimetres by Tuesday.

The Sudbury area has been told to expect 20 to 35 centimetres of snow beginning tonight.

"Visibility will be suddenly reduced to near zero at times in heavy snow and blowing snow," Environment Canada said on its website. Sidewalk snowplows stand at the ready in Toronto. The city could see up to 10 centimetres of snow starting Monday evening before it turns to rain or freezing rain overnight. (CBC)

Winter storm warnings are also in place for Sault Ste. Marie, Manitoulin, Blind River, Killarney, North Bay, and West Nipissing.

Special weather statements have been issued for Barrie and Kingston.

Environment Canada says it is closely monitoring the winter storm as it develops. Warnings may be issued if snowfall exceeds current expectations.

Travel Alert – Dec 28-29: Toronto, Montreal & Ottawa. Details, Flight Status & rebook online. Change fees waived: <a href="https://t.co/j6Q9rcq8zw">https://t.co/j6Q9rcq8zw</a>. —@AirCanada

Air Canada issued a weather alert for today and tomorrow, warning that flights operating from Toronto's Pearson airport could be cancelled or delayed. Travellers are asked to check their flight status online before heading to the airport. Passengers whose flights are affected by the weather can rebook flights today or tomorrow without a penalty.