A storm system moving north from the U.S. is expected to cause severe weather conditions Friday across southern Ontario, before heading east across Quebec to Atlantic Canada.

"The commute to work tomorrow right across southern Ontario will be messy," said CBC meteorologist Johanna Wagstaffe.

The worst hit areas will be between Windsor, Ont., and the Niagara Peninsula along the shores of Lake Erie, with snowfall predicted to start between 1 a.m. and 3 a.m. Friday. The region between Hamilton and Niagara could get 20 centimetres or more of snow. Windsor will see up to 15 cm, Toronto seven to 12 cm, Ottawa five to 10 cm, and Montreal 10 to 15 cm, said CBC meteorologist Natasha Ramsahai.

It is expected to be windy, with winds gusting up to 70 km/h, so blowing snow could reduce visibility.

Environment Canada has issued winter storm watches for communities along Lake Erie and parts of Lake Ontario as well as Kingston, Brockville and Cornwall. There is no weather warning in effect for Toronto.

CBC Ottawa's weather specialist Ian Black said weather won't be nice Friday, but the capital city will likely dodge a major snowfall because it will be on the northern edge of the storm.

Light snowfall is expected to begin around 7 a.m., and conditions will deteriorate as the day goes on, with the heaviest snowfall expected between noon and 3 p.m.

The snow is expected to taper off across southern Ontario later Friday afternoon.

Environment Canada has issued a winter storm warning for Montreal, central Quebec and Quebec City.   Light snow started falling on the region Thursday afternoon and snow is expected to get heavier late Friday morning, with wind gusts up to 80 km/h. But the temperature will be mild, with a high of –4. The storm is expected to pass through Quebec by the end of Friday.

The system will then head east to the Maritimes bringing heavy snow to New Brunswick and heavy rain to parts of Nova Scotia and Prince Edward Island. Weather warnings have been issued in all three provinces.

As much as 30 millimetres of rain is expected to fall by Saturday morning in Kings County, P.E.I., and Prince County could see as much as 30 centimetres of snow, according to Environment Canada. Queens County is expected to get significant snowfall and freezing rain is predicted for Friday night.

Strong northerly winds will cause blowing snow and reduced visibility across the Island on Saturday.

The system will continue to strengthen as it moves over Newfoundland bringing heavy rain, heavy snow and strong winds on Saturday.

"They will see the messiest conditions out of all the provinces," said Ramsahai.

Cold in the West

Looking west, it's going to be chilly on the Prairies and in British Columbia with overnight lows expected to hit –27 C in Cranbrook, B.C., and –30 C in Lethbridge, Alta.

Some regions may approach record lows, according to Environment Canada.

Temperatures across B.C. are running 10 to 15 degrees below seasonal. It will remain cold Thursday night along B.C.'s coast as far south as Whistler, where the overnight temperature is expected to feel like –20 C to –25 C with the wind chill.

But things should start to warm up on Saturday, said Wagstaffe.