Snow Day Calculator: Your Snow Day Percent for Tomorrow

Type your ZIP code to get the snow day percent for the next school morning, worked out from the National Weather Service forecast for your area, with every point in the number shown.

How your snow day percent is worked out

The calculator starts with the National Weather Service (NWS) forecast for the roughly 2.5 km square of map your ZIP code sits in. NWS calls that square a grid cell. From that forecast it reads five things a school district cares about on a winter night: how much snow falls between the evening and the morning bus run, how much falls during the school day, whether any freezing rain leaves ice, how cold the wind chill gets while kids wait for buses, and which winter alert NWS has issued.

Each of those turns into points. The points add up, and a smooth curve turns the total into a percent. Forty points is a coin flip; about 58 points is a 90% chance. We never show 0% or 100%, because no forecast is that certain and districts sometimes surprise everyone. Results stay between 5% and 95%.

Here's a real one. The NWS forecast for Utqiagvik (Barrow), Alaska, ZIP 99723, saved November 9, 2026 at 1:10 PM AKST, called for 1.52 in of snow between 6 pm and 7 am before Wednesday, November 11, 2026, plus 0.55 in that afternoon, under a Winter Weather Advisory. The receipt for that morning looked like this:

The snow was worth 13.9 points rather than more because Utqiagvik averages 45.8 in of snow a year, so its scale is ×0.78. A town that rarely sees snow would score the same inches higher. That morning came out at a 10% closure chance but a 70% chance of a 2-hour delay: an inch or two before the buses is classic delay weather. The full method lists every weight.

Why 3 inches closes school in some towns and not others

Three inches of snow shuts down a city that sees it once a winter. It's a normal Tuesday in Buffalo. Districts in snowy places own more plows and salt, bus drivers are used to it, and families expect school to go on. So the same forecast should mean different odds in different places.

The calculator handles this with your local normal snowfall: the 1991-2020 average annual snowfall at the nearest weather station that has one, published by NOAA's National Centers for Environmental Information (NCEI). Your result card names the station and says how far away it is. Snow in a place with a low normal counts for more; snow in a place with a high normal counts for less. Our guide on how much snow it takes goes through real numbers by region.

Timing matters more than totals

Four inches that fall from midnight to 6 am are a very different problem from four inches that start at noon. Many districts make the call early in the morning, before the buses roll. Snow that's still falling then, or that has left ice on untreated side streets, is what closes schools.

That's why the calculator splits the snow by time. Snow from 6 pm the evening before through 7 am gets full weight. Snow in the afternoon before counts half, since crews have time to clear it. Snow during the school day counts for much less toward a closure; it's more likely to mean an early dismissal. Open "Why?" on any result to see an hour-by-hour bar of when the snow is forecast to fall.

Snow day, delay, or cold day?

A district has more choices than open or closed. A light overnight snow or a glaze of ice often brings a 2-hour delay, which gives crews daylight and time to treat roads. That's why your result shows a separate delay percent: it's the chance of a late start on a morning school doesn't close.

Some districts in the northern Plains and Midwest also close for extreme cold, even with no snow at all, because waiting at a bus stop in a dangerous wind chill is the risk. The card flags cold-day risk from the lowest wind chill forecast between 6 and 9 am. A full delay calculator and a cold day calculator are on the way.

What the percent means (and doesn't)

The snow day percent is not the "chance of snow" in a weather app. That number is the NWS probability of precipitation, which NWS defines as the chance that a given point gets at least 0.01 in of precipitation. A 40% chance of snow can mean a dusting or nothing.

Our percent is our estimate of how likely a closure is, given the whole forecast. It can't see everything a superintendent weighs: how many drivers called in, whether a bus contractor is short-staffed, how many snow days are already used, or what neighboring districts decide. The optional adjusters let you nudge the number if you know your district closes easily or rarely.

Questions