The season's first big snowfall has already hit the American Rockies and the plains, and it's now headed toward to the Great Lakes.
The temperature will drop to 3 this afternoon in Niagara.
Environment Canada has issued a special weather statement for areas north and west.
Places like London, Woodstock, Barrie, Collingwood and Orillia will see lake effect snow tonight with snowfall amounts of 5 to 10 centimetres.
Local amounts near 15 centimetres are possible by Sunday evening.
Meantime, authorities report hundreds of crashes in Minnesota as a snowstorm sweeps across the state.
The Minnesota State Patrol reports 340 crashes, including 37 with injuries, and more than 550 spinouts statewide since Thursday night. At least one person died on icy roads