Snow Day
Guide
How much snow does it take for a snow day?
For most boards in Ontario, Quebec, the Maritimes and the US Northeast, about 12 centimetres overnight is a coin flip, and 20 or more is close to certain. Rural boards and bus consortia cancel nearer to 8. Big-city boards and the Prairies rarely cancel below 18. But the total matters less than the timing: 8 centimetres falling during the 5 to 8 AM bus run cancels buses more often than 15 that ended at midnight.
Why timing beats totals
Boards decide between 4:30 and 6 AM. By then, snow that fell before midnight has been plowed on the main roads and the route supervisors have driven it. Snow still falling at 6 AM, at two centimetres an hour, is on the road during loading, the plows are losing ground, and visibility is poor. That is the storm that cancels.
The rough thresholds
| Board style | Coin-flip amount | Examples |
|---|---|---|
| Cancels easily | About 4 cm | Mid-Atlantic and southern US districts |
| Cancels sometimes | About 8 cm | Rural Ontario and Quebec consortia, New England towns |
| Typical | About 12 cm | Most of Ontario, Quebec, the Maritimes, the US Northeast |
| Rarely cancels | About 18 cm | Toronto, Montreal, Buffalo, the Prairies, lake-effect country |
These are the four tolerance settings in Snow Day. Pick the one that matches your board and the app moves its whole curve to match.
What else cancels buses
- Freezing rain. Even a couple of hours during the bus run is close to an automatic cancellation in southern Ontario and the Northeast.
- A flash freeze. Rain or melt in the evening, then a hard freeze before dawn. No snow, all ice.
- Blowing snow. Gusts over 40 km/h with loose snow on open rural roads drops visibility below what a bus driver will accept.
- Extreme cold. Many Prairie and northwestern Ontario boards cancel buses at a wind chill of −40 or −45.
- A storm arriving mid-morning. If the buses can't get children home at 3 PM, they don't go out at 7.
Why the forecast total is often too low
Weather models report snow at a fixed ten-to-seven water-to-snow ratio. Cold air makes fluffier snow: at −12 °C the real ratio is closer to 16:1, so a forecast of "12 cm" can mean 20 on the driveway. Snow Day corrects for this; most calculators don't.