BARRIE, ONT. -- The first day of December left many across south-central Ontario digging out Tuesday morning as the season's first multi-day snowfall blanketed the region.

The winter storm began on Monday with heavy rainfall that turned to wet snow later in the afternoon and evening.

Environment Canada issued a snowfall warning for southern Ontario, suggesting 10 to 15 centimetres more of the white stuff throughout the day into Wednesday for Simcoe County, Dufferin-Innisfil and Grey Bruce.

Traditional snowbelt areas around Georgian Bay and southeast of Lake Huron could see snowfall totals doubled.

Collingwood, The Blue Mountains and surrounding areas could see over 50 centimetres of the white stuff over the next 24 to 48 hours.

Give yourself extra time for the morning commute Wednesday if you're heading out. Road conditions could prove to be dicey with snow squalls and lake effect snow.

The snow is expected to continue overnight Wednesday but should start to ease off into Thursday with highs hitting around 4C.

The heavy accumulation of snow forced plenty of school bus cancellations across the region and the closure of all Simcoe Muskoka Catholic schools for the first time ever on Tuesday.

"We wouldn't be able to maintain cohorts," said Simcoe Muskoka Catholic school board spokesperson Pauline Stevenson. "We collapse classes, and when you collapse a class, you would have to mix cohorts, and we can't be doing that in this environment."