How Schools Decide Snow Days: Factors, Timeline and What Snow Day Odds Mean

Every snowy evening, millions of students type "snow day calculator" into a search box. It is one of the most searched winter phrases in the United States, with an estimated 368,000 searches a month. But how do schools actually decide to close, and how do snow day calculators work? This part of our Winter Weather Guide 2026–27 explains the real factors superintendents weigh, the early-morning timeline, why ice and cold close more schools than people expect, how much snow it takes in different parts of the country, why some districts no longer have traditional snow days, and an honest look at what a snow day predictor can and cannot tell you, including the 77.today snow day calculator.

Who decides whether school is closed?

In most U.S. districts, the superintendent makes the call, usually after consulting transportation staff, facilities crews, local emergency management and the National Weather Service forecast. In a few places the decision sits elsewhere: in Washington, D.C., for example, the mayor decides for public schools and weighs temperature, wind chill, snow and ice, road conditions, the availability of public transportation and how the forecast will change through the day, according to WJLA's survey of Washington-area districts.

The same report shows how similar the process is across districts. Fairfax County Public Schools says it uses insights from emergency management agencies and the NWS. Montgomery County Public Schools in Maryland evaluates safety, the forecast and traffic, consults the NWS and county leaders, and tries to decide by 7 p.m. the night before or by 4:30 a.m. that morning. Prince George's County sends transportation supervisors to survey roads, driveways and sidewalks. Prince William County staff inspect roads, sidewalks, parking lots and bus lanes.

The factors behind a snow day

A Montgomery County spokesperson summed it up for WJLA: safety comes first, and "our ability to transport students, our staff's ability to get to work, and school campus conditions after a weather event are all factors," adding that conditions can vary significantly across a county, so one area may look clear while another is hazardous.

The early-morning timeline

When a storm is certain, many districts announce a closing the evening before so parents can plan. When it is uncertain, the decision waits for the latest overnight forecast and for staff who drive the roads before dawn. A typical uncertain-storm morning looks like this:

1. Evening: the district reviews the NWS forecast and any winter storm watches or warnings; if confidence is high, it announces early.
2. Around 3 to 4 a.m.: transportation and facilities staff check roads, bus lots and campuses. In cold districts, crews start bus engines early; one Minnesota district says its transportation team begins preparing buses as early as 4 a.m. so engines start and heaters work.
3. By about 4:30 to 5:30 a.m.: the superintendent decides between opening on time, a delay (often two hours), early dismissal or a full closing. Fairfax County and Montgomery County both cite 4:30 a.m. as their morning deadline.
4. Shortly after: the decision goes out by text, email, app, website and local media.

That timeline explains a common frustration: snow that starts at 9 a.m. rarely produces a snow day, because the decision was already made. It is also why districts sometimes dismiss early when a storm arrives during the school day.

How much snow does it take to close school?

"How many inches of snow for a snow day?" has no national answer, for the same reason the NWS has no national snowfall number for a winter storm warning: it depends on what an area is equipped for. A city with few plows and little salt can shut down for an inch or two or a glaze of ice, while districts in the snow belt routinely open with several inches on the ground because crews plow through the night.

Our own snow day calculator encodes this with three broad bands, which are 77.today's estimates rather than any official standard: in the South, about 1.5 inches of snow or a glaze of ice gives roughly an even chance of a closing; in a middle band from Virginia to Missouri, the Ohio Valley and the Pacific Northwest, about 4 inches; and in the snow belt from Minnesota to Maine, about 6.5 inches, or wind chills around −25°F. Mountain and rural districts with long bus routes often close earlier than city districts in the same state.

Ice and cold: the snow days without much snow

Ice is the most underrated cause of school closings. A thin layer of freezing rain makes roads more dangerous for buses than several inches of snow, which is why ice storms close schools across the South and Mid-Atlantic. Our part on freezing rain vs. sleet explains why.

Cold alone can close schools too. A Monticello, Minnesota, school district guide notes that a "snow day" can happen without a trace of snow in the air, because cold temperatures can be as hazardous as snow; its guidelines are based on how long it takes exposed skin to develop frostbite at a given wind chill on the NWS chart. Another Minnesota district, NRHEG, likewise bases cold-weather closings on the NWS wind chill forecast. Children wait at bus stops and walk to school in the coldest hours of the day, so districts watch NWS Extreme Cold Warnings and wind chill values closely. Criteria are local: what closes schools in Minneapolis is very different from what closes them in Atlanta.

How snow day calculators work

The best known is SnowDayCalculator.com, created by David Sukhin. WBUR reported in 2015 that Sukhin began it as a "pet project" in sixth grade, launched the online tool as a 16-year-old high school junior, and was then a computer science and business student at MIT. Its algorithm uses the user's ZIP code, the type of school (public, private and so on) and other factors such as snow removal and the school's previous snow days. Ahead of the January 2015 blizzard, 305,000 people used it in one day. The site itself says its predictions improve as users report what actually happened at their schools.

Most snow day predictors follow the same basic recipe:

1. Get the forecast for your location: snow, ice, temperature and wind for the night and early morning.
2. Compare it with local tolerance: how much it usually takes to close schools in your region.
3. Adjust for other signals: the type of school, the number of snow days already used, user reports or past closings.
4. Convert the result into a percentage.

The 77.today calculator is transparent about its inputs. It reads the National Weather Service gridded forecast for your ZIP code, adds up snow and ice expected between 6 p.m. and 8 a.m., checks the coldest wind chill between 5 and 8 a.m., and compares those numbers with the regional bands described above. Ice counts more than snow: it treats about 0.15 inch of ice like a closing-level snowfall. The percentage is our estimate from the forecast and local snow tolerance; only your school district decides, and the tool is not affiliated with any school or district.

How accurate are snow day calculators?

Snow day calculators are only as accurate as two things: the weather forecast and the predictability of your district. Forecasts for the next night are usually much better than forecasts several days out, but the exact timing of a storm and the changeover between snow, sleet and freezing rain are hard. Districts also weigh things no forecast can see, such as which bus routes climb hills, whether road crews can finish by 6 a.m., whether a school lost power, and how many make-up days remain on the calendar.

Some tools advertise near-perfect accuracy. Treat that with caution: a claim like "100 percent accurate in many locations" cannot be checked from the outside, and a predictor that only reports a few schools' results can look better than it is. Use calculators as a fun, forecast-based guide, check again late in the evening and early in the morning, and trust only your district's official announcement.

Why some districts no longer have snow days

Remote learning changed the snow day. New York City public schools stopped having traditional snow days in 2020, according to Chalkbeat, because schools can offer virtual instruction and need to fit 180 days into a crowded calendar; in January 2026 the chancellor confirmed the city would pivot to remote learning if a winter storm hit. Other districts keep traditional snow days built into the calendar and add make-up days at the end of the year if they run out.

State rules vary. New York's education department, for example, says schools are not required to provide remote instruction on emergency closure days, but its rules give districts permanent flexibility to do so. Check your district's inclement weather page at the start of the season to learn whether a storm means a day off, a two-hour delay or a day of logging in from the kitchen table.

Snow day odds this winter

NOAA's official outlook for December 2026 through February 2027, released October 15, favors a warmer-than-average winter across the northern U.S. and a wetter South and East Coast because of a very strong El Niño. That does not translate into a snow day count: NOAA does not forecast seasonal snowfall, and a single cold storm in the South can close more schools than a mild month up north. Read the full winter forecast 2026–27 for details.

The night before a possible snow day, check the NWS forecast and alerts, try the snow day calculator for your ZIP code, and make sure your family's winter storm preparedness basics are covered in case the storm brings power outages instead of a fun day off. Return to the Winter Weather Guide hub for every part of the series.

Cover image: A school bus on a snowy road. Photo by Coastline09 via Wikimedia Commons, CC BY-SA 4.0.