Environment Canada has forecast snowfall with total amounts of 15 to 25 cm overnight.
Two rounds of precipitation are expected Monday into Tuesday morning across portions of southern Ontario, said the advisory.
The first one is expected to begin overnight or early Monday morning with 5 cm of snow expected by afternoon. Potentially higher amounts of up to 10 cm may occur near Lake Erie.
The precipitation may diminish during the afternoon, but another round of even heavier snow is expected to move in Monday evening and persist until Tuesday morning. An additional 10 to 20 cm is likely.
Prepare for quickly changing and deteriorating travel conditions. Visibility may be suddenly reduced at times in heavy snow. Surfaces such as highways, roads, walkways and parking lots may become difficult to navigate due to accumulating snow, said the advisory.