There is no single number that answers what temperature do schools have to close at, because no federal law and almost no state law sets one. The decision belongs to your local superintendent, who weighs wind chill or heat index against building conditions, bus reliability, and road safety. A wind chill around −20°F or a heat index above 95°F will put most districts into a serious conversation about closing, but neither figure is a legal trigger.
Why No Fixed Temperature Exists
OSHA, the federal agency that handles workplace safety, has never set a binding minimum or maximum temperature for any workplace, schools included.1Occupational Safety and Health Administration. What Can I Do if My Indoor Workplace Is Too Hot or Cold? No other federal agency fills that gap for school buildings. Most states have not written hard cutoffs into law either. At least one state now requires schools to take action when indoor temperatures hit 82°F and to relocate students and staff from spaces that reach 88°F, but that kind of enforceable rule is still unusual.
What exists in most places are informal district policies. Many districts treat sustained wind chills in the −20°F to −30°F range as a closure trigger, and many treat a heat index above 95°F the same way. These are guidelines. The superintendent uses them as a starting point and then looks at everything else going on.
How Cold Is Too Cold
Air temperature by itself matters less than wind chill, which reflects how fast exposed skin loses heat when wind and cold combine. The National Weather Service wind chill chart shows exposed skin can freeze in about 30 minutes at a wind chill of −19°F, 10 minutes near −35°F, and as little as 5 minutes below −48°F.2National Weather Service. Wind Chill Temperature Index That math is especially important for children waiting at bus stops.
Buses themselves are often the deciding factor. Diesel fuel starts to gel at roughly 10°F to 15°F below zero, thickening until it can no longer flow through fuel lines. When a district runs hundreds of diesel buses, even a small failure rate strands kids in dangerous cold. Ice and compacted snow on roads make the problem worse.
Indoor conditions matter too. Most local property maintenance codes require schools to keep indoor temperatures at a minimum of around 65°F. A boiler failure or power outage during a deep freeze can force a closure even when the outdoor forecast is manageable, because the buildings simply cannot be kept warm enough to use.
How Hot Is Too Hot
Heat closures hinge on the heat index, which combines air temperature and humidity to reflect what the air actually feels like. Humidity is the critical variable because it prevents sweat from evaporating, which is how the body cools itself. An air temperature of 90°F with 70% humidity produces a heat index well above 100°F and poses real health risks, especially for younger children, who regulate body temperature less efficiently than adults.
Whether a district closes often comes down to air conditioning. Research has estimated that close to 40% of public schools nationwide may lack full air conditioning. In those buildings, indoor temperatures can match or exceed outdoor heat, and a 95°F classroom is not a place anyone can learn or work safely. Some districts close only the schools without adequate cooling and keep the air-conditioned buildings open. Others shut everything if enough buildings are affected. Bus air conditioning counts too: a 45-minute ride in a hot bus can be as dangerous as a hot classroom.
Some students face elevated risk at lower thresholds. Children with asthma, seizure disorders, or endocrine conditions may be entitled to accommodations under Section 504 of the Rehabilitation Act, which can include staying indoors during outdoor activities on hot days. A student body with a significant number of documented heat-sensitive conditions adds urgency to the closure decision.
When Air Quality Changes the Call
Heat waves often bring poor air quality. Hot, stagnant air traps ground-level ozone, and during wildfire season it carries smoke particulates that can trigger respiratory distress in children. EPA guidance for schools recommends progressively restricting outdoor activity as Air Quality Index readings climb, starting with more frequent breaks at the “Unhealthy for Sensitive Groups” level and moving to no outdoor activity at the worst readings.3Environmental Protection Agency (EPA). Air Quality and Outdoor Activity Guidance for Schools Districts may close entirely when ventilation systems cannot adequately filter incoming air. Air quality alone rarely closes schools, but combined with heat it is often the factor that pushes a superintendent from a modified schedule to a cancellation.
Sports and Practice Have Separate Rules
School can stay open while outdoor practices and games are canceled. Most state high school athletic associations use the Wet Bulb Globe Temperature, which factors in temperature, humidity, wind, and sun exposure, rather than the simpler heat index. WBGT readings are typically taken hourly, starting 30 minutes before an event, and all outdoor activity must stop above a set threshold, commonly in the low-to-mid 90s on the WBGT scale.
In cold weather, guidance from the NFHS Sports Medicine Handbook recommends increased monitoring once wind chill drops below −18°F and suggests postponing or canceling events at that level. State associations set their own cutoffs. The practical result is that your child’s school may be open while the afternoon football practice is called off. Coaches can generally cancel on their own, but the formal thresholds come from the state association.
Who Makes the Decision
The superintendent of the district typically has the final say on weather closures. A governor or public health agency declaring a state of emergency can override that authority, but under normal conditions the call is the superintendent’s. The decision usually draws on input from the district’s transportation director (who checks road conditions and whether buses will start), the facilities manager (who reports on heating and cooling across buildings), National Weather Service meteorologists, and local emergency management.
What Happens to the Missed Day
Closures do not simply erase an instructional day. About 31 states plus the District of Columbia require at least 180 school days per year, and districts that fall short risk losing state funding. Before COVID-19, the only option was make-up days, usually by extending the school year into June or converting scheduled holidays into school days.
As of the 2025–26 school year, roughly 23 states allow remote learning days to count toward instructional time, though most cap the number somewhere between three and ten days. Four states plus the District of Columbia still prohibit counting remote learning days entirely, which means every closure must be made up. The rest fall in between, often leaving the decision to individual districts or requiring state approval. Where remote days are allowed, students generally have to complete assigned work for the day to count toward attendance.
When closures outrun a district’s buffer of snow days and allowable remote days, the district either adds days to the calendar or applies to the state for a waiver. Waivers usually require the district to show it tried to reschedule missed time first. A brutal winter or an extended heat wave can push the last day of school into late June or even July.
How You Find Out
Most districts use mass notification platforms that push voice calls, text messages, emails, and social media posts at the same time, often within minutes of the superintendent’s decision. If you have not opted into your district’s notification system or confirmed your contact information is current, do that before winter. Districts also post closures on their websites and social accounts and relay them to local television and radio.
Announcements usually come early in the morning, often by 5:00 or 6:00 a.m., though some districts call it the night before when forecasts are clear. A two-hour delay is a common middle option that lets roads improve or temperatures rise without burning an instructional day.
Meals When School Is Closed
For families whose children rely on free or reduced-price school meals, a closure creates an immediate food concern. USDA guidance allows schools participating in the National School Lunch Program and other child nutrition programs to serve meals during unanticipated closures through various program flexibilities.4Food and Nutrition Service (U.S. Department of Agriculture). Meal Service During Unanticipated School Closures Whether a district activates that option depends on the length of the closure and local logistics. Extended closures often bring grab-and-go distribution at designated sites. A single snow day usually does not. If your family depends on school meals, ask your district about its emergency meal plan before severe weather season.