How Schools Decide to Call a Snow Day

A snow day rarely comes down to a single number on a forecast. It’s a judgment call, usually made by a superintendent or a small transportation team, late at night or before dawn. Understanding what they’re weighing is the key to reading the snow day odds on our predictor sensibly.

Who makes the call, and when

Most districts decide between 4:00 and 6:00 a.m., after road crews and transportation directors have driven the actual bus routes. Some make a “call it the night before” decision when a storm is obvious. That timing is why our model leans so heavily on the overnight-into-morning window (roughly 10 p.m. to 7 a.m.) rather than total storm snowfall — a foot of snow that arrives at noon doesn’t cancel school the way three inches at 5 a.m. does.

The factors that actually matter

Snowfall during the commute. Accumulation between about 2 and 6 a.m. is the single biggest driver. Plows and salt trucks can stay ahead of slow, early snow but not a fast pre-dawn burst.
Ice. Freezing rain and sleet close schools far more reliably than snow. An untreated glaze on bus routes and sidewalks is dangerous at any depth.
Bus routes and rural roads. Districts with long, hilly, or unplowed rural routes cancel more readily than compact urban ones. That’s why our predictor lets you pick a district type.
Wind chill. In the Upper Midwest and Plains, dangerously cold mornings (often −20 °F wind chill or colder) close schools even with no fresh snow — kids wait for buses outside.
Wind and visibility. Blowing and drifting snow can re-cover a cleared road and make travel hazardous.
What’s already on the ground. A storm on top of an existing snowpack, or a second storm in a week, raises the odds.

Why two districts make different calls

Neighboring towns frequently disagree, and that’s normal. A district’s snow-removal budget, the age of its bus fleet, how walkable its schools are, and even how many days it has already used all push the decision. A region that sees snow constantly (New England, the Upper Midwest) tolerates far more before closing than one where snow is rare (the South or Pacific lowlands), where a single inch can shut everything down.

How to use the prediction

Treat the percentage as a well-informed estimate of how this specific forecast usually plays out — not a promise. When the odds are high, it’s worth checking your district’s website, app, or local news the night before and again early in the morning. When they’re borderline, watch for a 2-hour delay, which is exactly what districts reach for when conditions are bad but not bad enough to cancel.

Curious how the number is built? Read the full methodology, or check tomorrow’s odds for your town.