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As expected, snow squall activity has been hammering the traditional snowbelt regions around Lake Huron and Georgian Bay throughout the day on Monday. This has already led to widespread school bus cancellations and even a handful of school closures in the hardest hit areas. With this lake effect activity expected to persist into Tuesday, it is becoming increasingly clear that some students will be waking up to their second snow day of the week.

Overnight, attention will turn to a particularly intense snow squall that is forecast to stretch across the Bruce Peninsula and then push southeast of Georgian Bay. This includes parts of Simcoe County, southern Muskoka, the Kawartha Lakes region and potentially as far east as Peterborough. At the same time, additional lake effect activity off Lake Huron is expected to continue impacting Huron and Perth counties, keeping snowfall rates elevated through the night and into Tuesday morning.

In addition to the snow, very cold Arctic air will remain firmly in place. Wind chills overnight into Tuesday morning are expected to drop sharply, with parts of Northern and Central Ontario potentially seeing wind chills as low as minus 35 to minus 40. In a few of the more northern and rural school boards, this may be cold enough to raise concerns about cold-related cancellations on top of the ongoing snow squall impacts.

The strongest confidence for a snow day on Tuesday lies across all regions covered by the Bluewater District School Board, the Simcoe West and Simcoe North weather zones under the Simcoe County District School Board, and the northern Kawartha Lakes region within the Trillium Lakelands District School Board.

These areas sit directly within the core of the most persistent snow squall activity and are very likely to see dangerous travel conditions during the morning bus run. As a result, we have assigned these regions a 90 percent chance of a snow day, with school closures even being a possibility in some communities.

A second tier of regions carries a strong likelihood, with a 75 percent chance of bus cancellations. This includes northern portions of Huron and Perth counties under the Avon Maitland District School Board, Dufferin County within the Upper Grand District School Board, the Simcoe Central weather zone, South Kawartha Lakes and South Muskoka under the Trillium Lakelands District School Board, and the Parry Sound region within the Near North District School Board. In these areas, we are leaning toward cancellations, but confidence is slightly lower than in the core snowbelt due to some uncertainty in squall placement and intensity.

In the toss-up category, where outcomes could genuinely go either way, we have included southern Huron and southern Perth counties under the Avon Maitland District School Board, Wellington County for the Upper Grand District School Board, the Simcoe South weather zone, Georgina within the York Region District School Board, the northern portion of the Durham District School Board, North Muskoka under the Trillium Lakelands District School Board, East Parry Sound within the Near North District School Board, Peterborough County under the Kawartha Pine Ridge District School Board, and Prince Edward County within Tri-Board Student Transportation Services. These areas are either positioned just outside the most intense squall bands or are covered by school boards that typically maintain a higher threshold for cancellations.

A slight chance, around 25 percent, has been assigned to a number of additional regions. This includes the Waterloo Region District School Board, Guelph within the Upper Grand District School Board, the southern York Region District School Board weather zone, Haliburton under the Trillium Lakelands District School Board, Northumberland County within the Kawartha Pine Ridge District School Board, and Belleville, South Lennox and Addington, and Kingston under Tri-Board Student Transportation Services.

We have also included a slight chance for North Bay within the Near North District School Board and areas covered by the Rainbow District School Board. In these northern regions, the concern shifts more toward extreme cold, though confidence is lower on whether temperatures will reach the threshold required for cold-related cancellations.

For the rest of Southern Ontario, the risk of a snow day on Tuesday drops to low or very low. This includes most urban school boards across the Golden Horseshoe, the London area, Deep Southwestern Ontario and the Ottawa Valley. These regions are not expected to see significant impacts from the lake effect snow, and travel conditions should remain manageable enough for buses to operate as normal.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures.

It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.