Parts of southern Ontario could receive snowfall between 20 to 40 centimetres or more by Sunday, Environment Canada warns. 

Lake effect snow from Lake Huron and Georgian Bay is expected to become heavier throughout Saturday, the weather agency said in an alert Saturday morning. 

The following areas are under a snow squall warning: Newmarket, Georgina, northern York Region, Barrie, Collingwood, Hillsdale, Uxbridge, Beaverton, northern Durham Region and Orillia. 

More than 40 centimetres of snow is possible if snow squalls stay in one area, Environment Canada said. 

Heavy and blowing snow may suddenly reduce visibility to near zero. People are advised to consider postponing non-essential travel until the weather improves. 

Snow squalls should become less intense on Sunday, Environment Canada said. 

To the north, Bracebridge and Gravenhurst are also under snow squall warnings, with 15 to 25 centimetres of snow or more expected to begin falling Saturday afternoon.

While Toronto is not under a weather warning, the city opened its warming centres on Friday as temperatures were expected to drop below -5 C.

Temperatures fell to -4 C overnight, according to data recorded at Toronto Pearson International Airport. 

The city is forecast to see a high of -2 C on Saturday, with temperatures expected to feel like -13 C because of windchill. 

Earlier this week, Environment Canada warned snow squalls could dump up to 60 centimetres of snow in some areas north of the GTA.