Snow Day Calculator: Will School Be Closed Tomorrow?

A snow day comes down to a handful of numbers: how much snow falls overnight, whether there is ice, how cold the morning is, and how much snow your district is used to handling. The calculator gets the first three from the National Weather Service and asks you about the rest.

How the estimate works

For each of the next three school days (weekends skipped), the calculator reads the NWS forecast grid for your location and adds up:

• Overnight snow, 6 p.m. the evening before to 7 a.m. — the snow that is on the roads when buses roll.
• 24-hour snow, 6 p.m. to 6 p.m. Snow during the school day counts half.
• Ice accumulation from freezing rain, 6 p.m. to 7 a.m.
• Lowest wind chill (or temperature) between 5 and 8 a.m.

Each hazard gets its own closure odds. Snow uses s^3.2 ÷ (s^3.2 + T^3.2), so odds stay low until the snow nears your area’s threshold T, then rise fast. Snow that falls mostly between midnight and 6 a.m. counts 25% more. Ice uses the same shape with an exponent of 3. Cold uses a logistic curve centered on a local wind chill. The three odds are combined as independent chances, then shifted on the log-odds scale by your adjustments: private school −0.3, college −1.5, cautious district +0.6, tough −0.6, big city −0.5, rural +0.4, and −0.1 to −0.6 as snow days get used up. A delayed start is estimated by running the same model at roughly half the thresholds.

Your state sets the tolerance automatically when we have its largest-city snowfall normal; you can change it if your town is snowier or milder than that city.

How much snow does it take to close school?

The model’s closure odds for a public school in an average suburban district, with no ice, cold or timing boost:

Worked example. Columbus, Ohio is a regular-snow area (28.2 inches a year). The forecast shows 6 inches overnight, most of it between midnight and 6 a.m., plus another inch after 7 a.m. Effective snow = (6 + 0.5 × 1) × 1.25 = 8.1 inches, so snow odds = 8.1^3.2 ÷ (8.1^3.2 + 6^3.2) ≈ 73%. Add 0.1 inch of ice and the combined chance rises to about 83%.

The steep curve reflects the evidence: in Massachusetts, each day with 10 or more inches produced about 0.51 additional closings, while a day with 4 to 10 inches produced only 0.04 (Goodman, 2015). Moderate snow mostly causes absences, not closures.

How districts decide

In most states the superintendent makes the call after checking the forecast and talking with neighboring districts and local officials. The timing is remarkably consistent:

• Montgomery County, Md.: evening decisions by 7 p.m.; an NWS update by 4:30 a.m.; morning decisions announced by 5 a.m.
• The same district in 2018: transportation staff checked roads from about 3 a.m., and a recommendation went to the superintendent around 4:15 a.m.
• Denver: decision usually around 5 a.m., weighing timing, accumulation, ice and temperature.
• Des Moines area: typically by 5:30 a.m., no later than 7 a.m. Boise: by about 5:30 a.m. Mountain time.

That is why the calculator focuses on the overnight window: snow that is still coming down at 4–6 a.m. is what decision-makers see.

Why ice and timing matter

A Cleveland meteorologist’s rule of thumb (WEWS) puts 8 or more inches within 12 hours as a strong signal, a quarter to half an inch of freezing rain overnight as a serious problem, and heavy snow between midnight and 6 a.m. as the strongest timing signal. Boston closed its schools in January 2022 for a forecast of several inches because snow was expected to fall at about an inch an hour between 5 and 8 a.m. — right during the commute.

Logistics matter too. Rural districts with long bus routes tend to close more readily than cities, and big-city districts are often the last to close.

Cold days

In the Upper Midwest, cold closes schools more often than snow. Published triggers cluster around −25°F air temperature or −35°F wind chill at 6–6:30 a.m. (St. Paul, Burnsville-Eagan-Savage, Minneapolis). Madison, Wis., lowered its threshold to −25°F wind chill in 2016; northern Minnesota districts such as Bemidji wait for −40°F, and Grand Rapids ISD 318 uses −50°F. Our research on snow day thresholds lists every district we could source.

Regional differences

The crowdsourced map behind several rows was built from hundreds of reader responses and NOAA snowfall data; its creator warned that elevation, wind chill and big-city plow fleets make any single number approximate.

What is the chance of a snow delay instead of a closure?

A delayed start is the most common result of light or moderate snow, and the snow day calculator estimates it separately. It runs the same snow curve at 45% of your area’s threshold, then takes the gap between those “any disruption” odds and the full closure odds (times 0.9) as the delay chance. The result: delay odds peak just below the snow amount that closes school, then fall as a closure becomes the more likely outcome.

Closure vs. delayed-start odds by overnight snow (public suburban district, average style, no ice, cold or pre-dawn boost)

How to read it. In a regular-snow state such as Ohio, 4 inches overnight gives only a 21% closure chance but a 51% delay chance, so a late start is the likeliest single outcome. The same 4 inches in an occasional-snow area (3 to 15 inches a year) flips the picture: 82% closure, 15% delay. Ice changes this fast, because the delay model uses half the ice threshold.

If your district runs late starts often, compare its actual triggers with our list of how much snow closes school in each state, or open a preset like the Michigan snow day predictor. A late start still shortens the evening, so the homework planner helps you move due dates around.

Remote learning is replacing some snow days

New York City stopped calling traditional snow days in 2020 and moves classes online instead; the state Board of Regents formally allowed remote instruction in place of closures in 2022. The first big remote snow day, in February 2024, ran into widespread login failures, but the policy still stood in January 2026. Elsewhere, Minnesota allows up to 5 e-learning days a year, Pennsylvania up to 5 flexible instructional days, and Ohio lets schools make up as much as three days’ worth of hours online. By 2022–23, more than three-quarters of the 35 snowiest states had policies to curb closures, up from half in 2018–19.

Snow day calculator by state

Preset versions with state rules, cold-day policies and school-year minimums: Michigan, Ohio, New York, Pennsylvania, New Jersey, Massachusetts, Minnesota, Wisconsin, Illinois, Indiana, Connecticut and Maine.