Snow day calculators: how they work and why they exist
Every winter night, students and parents type a ZIP code and hope. Here is what is actually behind the number.
By Petar M., editor · Updated October 18, 2026 · How we research
In this guide (6)
Why people use them
A snow day changes a family's whole day: childcare, work, homework, sleep. The official decision usually comes early in the morning, so people want a good guess the night before. A calculator turns the weather forecast into that guess.
Three kinds of calculator
| Kind | How it works | Weak spot |
|---|---|---|
| Form-based | You enter snow, temperature and school details; a formula turns them into a percentage. | Only as good as what you type in. |
| Forecast-based | Pulls a weather forecast for your location and applies fixed rules. | The same inch of snow means very different things in different places. |
| Forecast + local normals | Compares the forecast with what is normal for your area, plus timing, ice, cold and warnings. This is what this site does. | Still can't see roads, budgets or the superintendent's calendar. |
What any calculator can know
- The forecast: how much snow and ice, when, and how cold at bus time.
- Official weather warnings for your county.
- What is normal for your area, from decades of climate data.
- School calendars in general: weekends and the major holidays.
What no calculator can know
- How well your roads were plowed overnight.
- How many snow days your district has left, or whether it will use a remote day.
- Power outages, staffing, or a building problem.
- The judgment call itself.
Why accuracy claims deserve suspicion
There is no public national record of school closures, so a calculator can only measure accuracy by collecting outcomes itself. We publish ours from parent reports, once there are enough, on theaccuracy page. Until then we make no accuracy claim.
How this calculator is different
- No forms: one ZIP code, and your school district from public NCES data.
- Public data only: National Weather Service forecasts and NOAA climate normals.
- Closure and delay chances shown separately, with the reasons.
- An open method: how it works.
Check your district
See tomorrow's chance of a closure or delay for your ZIP code. Open the calculator, or find your state or city.
Sources
- National Weather Service, National Digital Forecast Database
- NOAA NCEI, U.S. Climate Normals 1991–2020
- NCES, EDGE school district geographic relationship files