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We’ve seen snow squalls developing off the southeastern shorelines of Lake Huron and Georgian Bay as of Sunday evening. These squalls are expected to continue through the night, and there is a good chance they will intensify as colder air pours in.

Accumulation from these squalls could reach 30 to 40cm in the hardest hit areas. With Environment Canada issuing snow squall warnings for several regions, it’s looking very likely that school buses will be kept off the roads on Monday, where conditions are at their worst.

The highest level of certainty for a snow day is southeast of Lake Huron. This is where the most intense squall activity is expected to set up and persist overnight. That includes the Exeter region of AMDSB and the Middlesex area of TVDSB. We’ve given both zones a 90 percent chance of a snow day on Monday based on the current setup.

Elsewhere in AMDSB and TVDSB, the chance of bus cancellations ranges from 50 to 75 percent. The closer a region is to the heart of the snow squalls, the higher the likelihood of cancellations. Farther out, confidence drops as it becomes less clear how far inland the heavier bands will reach.

We’ve also assigned a 50 percent chance to the Kincardine and Southampton regions under BWDSB. A weather advisory is currently in place there, but confidence is lower compared to areas southeast of Lake Huron. The snowfall might still fall short of what boards in that area need to see before pulling the plug on buses.

For the Georgian Bay snow squall, the highest risk sits in Simcoe’s west zone, including Collingwood. This area sits closest to the lake and is in the best position to see the most intense and consistent snowfall overnight. Simcoe’s Central and South zones, as well as Dufferin County, are sitting at a 50 percent chance. The main challenge here is determining whether the squall will stay strong enough as it pushes inland and exactly where that band decides to park itself.

York Region has been given a 25 percent chance, mainly for its northern sections, where some of the Georgian Bay activity could drift in. However, York tends to be more urban, and school boards in these areas are usually more cautious with cancellations, which lowers the confidence.

Much of the rest of Southern Ontario is sitting at a less than 10 percent chance of a snow day on Monday. These regions are simply too far from the lake effect zones to be significantly impacted by the squalls.

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.