A winter storm watch has been issued for Toronto and southern Ontario as a major weather system moving into the region could drop as much as 30 centimetres of snow.

As much as 50 centimetres of snow could fall over the Niagara Peninsula and in parts of eastern Ontario by the time the weekend is over, Environment Canada said.

"A winter storm is currently brewing over Texas with the potential to bring significant snow to most of southern Ontario," the weather service stated on its website Thursday afternoon.

"It appears that the snow will come in two doses. The first shot will begin as early as Friday afternoon for southwestern Ontario and Friday evening in eastern Ontario.

"The heaviest snowfall is then expected in the second shot beginning later Saturday."

Environment Canada said the storm is expected to last between 36 and 48 hours.

The storm could bring wind gusts of 60 km/h, which would create whiteouts and treacherous driving conditions. Environment Canada is warning travellers to be prepared to change their plans.

Total snowfall amounts will depend on the track of this system, Environment Canada said. There is still some uncertainty as to the exact path of the storm.