How the Snow Day Calculator Works
No black box. Here is the exact formula behind every score β so you can judge it for yourself.
The formula in 30 seconds
Expected snowfall in the next 24 hours sets a base score. Then three adjustments are added for extreme cold, high wind, and snow during the 4β7 AM commute window. The result is capped at 95% β a forecast is never certain.
Step 1 β base score from snowfall
We take the maximum expected snowfall (cm) in the next 24 hours:
- 0 cm β 5%
- 2 cm β 25%
- 5 cm β 50%
- 10 cm β 75%
- 15 cm or more β 90%
- Values between these points are interpolated (e.g. 7.5 cm β 62%).
Step 2 β adjustments
- Overnight low below β10Β°C: +5% (extreme cold alone can close schools)
- Wind over 40 km/h: +10% (blowing snow, wind chill, drifting)
- Snow falling between 4β7 AM local time: +10% (hits buses and the morning commute)
Step 3 β verdict bands
- Below 20% β Unlikely
- 20β50% β Possible
- 50β75% β Likely
- 75% and above β Very likely
Where the data comes from
Your ZIP or postal code is converted to coordinates with a free geocoding service, then we fetch hourly forecast data (temperature, snowfall, wind speed) from Open-Meteo, a free weather API. Results are cached for one hour, because forecasts update hourly.
What the score deliberately ignores
Honesty matters more than a bigger number. The score does not know your district's plowing capacity, bus fleet, or past closure habits β and those decide real closures. That is why every result is labelled an estimate, and why you should always confirm with your district.