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A major winter storm is set to take aim at a wide swath of Southern Ontario on Wednesday, bringing the threat of significant freezing rain in some regions and heavy snow in others.

The most hazardous conditions are expected to occur right at the height of the morning commute. That timing alone makes school bus cancellations and potentially even school closures highly likely in the hardest hit areas.

The highest confidence for bus cancellations is focused across Southwestern Ontario, particularly west of the Golden Horseshoe, where the most strongly worded alerts are currently in place from Environment Canada.

An orange-level freezing rain warning has been issued for this region, highlighting dangerous travel conditions and the potential for prolonged power outages. Freezing rain of this magnitude almost always leads to widespread cancellations, especially across rural routes where untreated roads can quickly become impassable.

Because of this, we have assigned a 90 percent chance of a snow day to all regions covered by the Bluewater District School Board, most areas within the Avon Maitland District School Board with the exception of southern Huron County, all of the Upper Grand District School Board, and the Waterloo Region District School Board. In these areas, it would be surprising to see buses operate given the expected severity of the icing.

The next tier carries a 75 percent chance of cancellations. This includes southern Huron County under the Avon Maitland District School Board, Oxford County under the Thames Valley District School Board, the Hamilton-Wentworth District School Board, northern Halton under the Halton District School Board, North Peel Region under the Peel District School Board, all regions within the Simcoe County District School Board, Kawartha Lakes under the Trillium Lakelands District School Board, Peterborough and Northumberland counties under the Kawartha Pine Ridge District School Board, and Central Hastings, Belleville and Prince Edward County under Tri-Board Student Transportation Services.

These areas either have a history of not being proactive with cancellations, as is often the case with urban boards in the Golden Horseshoe and Simcoe County, or they sit just outside the most intense freezing rain zone, where conditions could still be severe enough to justify cancellations. However, there remains enough uncertainty regarding whether it will reach the threshold for cancellations to keep them from being put in the 90% zone.

The forecast becomes more complicated across the core of the Greater Toronto Area. In our toss-up category, with a 50 percent chance, we have included the York Region District School Board, North Durham under the Durham District School Board, the Toronto District School Board, southern Peel Region under the Peel District School Board, and southern Halton under the Halton District School Board.

We believe that conditions will likely deteriorate enough to warrant cancellations in at least some of these areas. However, these boards cover more urban routes and have a higher threshold for cancellation decisions. The Toronto District School Board, in particular, tends to cancel only during the most extreme events due to its limited reliance on bused students. This makes proactive decisions less certain, even if conditions are forecasted to be hazardous.

Farther south, we have also assigned a 50 percent chance to the District School Board of Niagara, the Grand Erie District School Board, and London and Middlesex County under the Thames Valley District School Board. In these areas, less freezing rain is expected overall, and temperatures may rise above freezing during the morning. Whether cancellations occur here will depend heavily on actual surface conditions at decision time.

In Central Ontario, the toss-up zone also includes southern Muskoka and Haliburton under the Trillium Lakelands District School Board, as well as North Hastings, and North, Central and South Lennox and Addington under Tri-Board Student Transportation Services. These areas sit on the edge of the heavier snowfall zone associated with the storm. Some are currently under snowfall warnings calling for 10 to 15 cm. However, with totals not expected to be extreme and with TLDSB’s stricter approach to snow days this season, it remains uncertain whether thresholds will be met.

A slight 25 percent chance has been assigned to Chatham-Kent and Lambton County under the Lambton Kent District School Board, Elgin County under the Thames Valley District School Board, North Muskoka under the Trillium Lakelands District School Board, Parry Sound and East Parry Sound under the Near North District School Board, the remaining Tri-Board regions, and the Madawaska region under the Renfrew County District School Board.

We are leaning toward a regular school day in most of these areas. However, surprises are still possible, particularly in parts of Central Ontario if school boards opt for system-wide cancellations rather than region-by-region decisions. With no major winter weather warnings currently in effect for many of these regions, confidence in cancellations remains limited.

We have also included a slight chance for areas covered by the Rainbow District School Board, primarily due to Manitoulin Island being under a snowfall warning. Sudbury itself carries a lower probability and is expected to see a normal school day.

Elsewhere across Southern Ontario, the chance of school bus cancellations drops to low or very low. This includes Deep Southwestern Ontario, where precipitation is expected to fall mainly as rain, and the Ottawa Valley, which is forecast to avoid the worst of this storm altogether.

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.