Snow Day Calculator
Snow day calculator works out Snow-day chance and Closure hazard index (0-100) from Forecast snowfall, Local NWS Winter Storm Warning snow criterion and Forecast freezing-rain accretion. The default figures on this page give snow-day chance of 60 %; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Snow: 6 in against a local warning criterion of 6 in = 1x, capped at 2x; 45 x 1 = 45 points.
- Ice: 0 in against the 0.25 in Ice Storm Warning criterion = 0x, capped at 1.5x; 40 x 0 = 0 points.
- Timing: accumulation starts 02:00 - overnight - roads are snow-covered before the morning run; +15 points.
- Wind chill: WC = 35.74 + 0.6215(28) - 35.75(1.44544) + 0.4275(28)(1.44544) = 18.77 F; against a -25 F closure threshold that is 25 x min((-25 - 18.77) / 10, 1) clamped at 0 = 0 points.
- Index = 45 + 0 + 15 + 0 = 60, clamped to 0-100 = 60.
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
What the snow day calculator calculates
Scores the chance of a snow-day school closure from a forecast you supply - snowfall against the local NWS warning criterion, ice accretion, NWS wind chill and the timing of the storm.
How to use this snow day calculator
Enter Forecast snowfall, Local NWS Winter Storm Warning snow criterion, Forecast freezing-rain accretion and Air temperature at the morning decision. Snow-day chance updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Snow-day chance, Closure hazard index (0-100) and Verdict.
The method follows NOAA National Weather Service, Winter Weather Warnings, Watches and Advisories, NOAA National Weather Service, Wind Chill Temperature Index (November 2001) and NOAA National Weather Service API Web Service.
Eight inches overnight where the warning criterion is six example
With Forecast snowfall: 8, Local NWS Winter Storm Warning snow criterion: 6, Forecast freezing-rain accretion: 0, Air temperature at the morning decision: 28, the calculator returns Closure hazard index (0-100): 75, Points from snowfall: 60, Points from storm timing: 15. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Snow-day chance, Closure hazard index (0-100) and Verdict. The inputs you can vary are Forecast snowfall, Local NWS Winter Storm Warning snow criterion, Forecast freezing-rain accretion, Air temperature at the morning decision, Wind speed and Wind chill at which the district closes for cold.
Understanding Snow-day chance, Closure hazard index (0-100) and Verdict
This is an indicator built from a stated point scale, not a validated forecast of any district’s decision. Closures are announced by the school district and hazardous-weather information comes from the National Weather Service; check both.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What information do I need for the snow day calculator?
You need Forecast snowfall, Local NWS Winter Storm Warning snow criterion, Forecast freezing-rain accretion, Air temperature at the morning decision, Wind speed, Wind chill at which the district closes for cold, When the accumulation starts and The day would otherwise be a school day. The page opens with default figures that give snow-day chance of 60 %, so you can see the scale before entering your own.
What does this snow day calculator show?
It shows Snow-day chance, Closure hazard index (0-100), Verdict, Wind chill, Points from snowfall, Points from ice, Points from storm timing and Points from cold, with the working and any warnings for your entries.
Can I check how the snow day calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.