Toronto and a large swath of southern Ontario is being warned to expect freezing rain and snow flurries overnight as a low pressure system pushes a weather disturbance into the area.

Environment Canada said in a special weather statement that a system developing over Colorado will gradually approach Ontario through the day on Tuesday.

Snow is expected to fall over southwestern Ontario beginning shortly after midnight on Wednesday, with the likelihood of changing to freezing rain later that morning.

The snow will spread across much of south central Ontario during the day.

Environment Canada says between two and four centimetres will fall in short bursts in Toronto and give way to patchy drizzle and scattered showers by Wednesday afternoon.

"The odd thunderstorm is also possible over Southwestern Ontario and from Southern Lake Huron to the Niagara Peninsula where very mild air will skirt the region," Environment Canada said in the statement.

Between five and 10 centimetres of snow is to be expected in eastern Ontario by Wednesday night, continuing into Thursday morning.