Cold days
Wind Chill Calculator: the NWS formula, and cold school closures
Calculate wind chill from the air temperature and wind with the National Weather Service formula, in °F or °C, and see how cold alone affects the chance of a school closure.
Wind chill: -13 °F (-25 °C)
Air temperature 5 °F, wind 15 mph. The NWS formula applies at 50 °F or colder with wind above 3 mph.
Closure outlook from cold alone
Closure risk is low and delay risk is low.
Why
- Snow: little or none is expected in the hours that matter.
- Cold: a wind chill near -13 °F is cold for this area, with risk to students waiting at bus stops.
This is a rough estimate from a simple rule-of-thumb model, not a prediction and not a school decision. The scores are not probabilities and have not been tested against real closures. Districts set their own rules, so confirm with your district.
| Wind | 40° | 30° | 20° | 10° | 0° | -10° | -20° | -30° | -40° |
|---|---|---|---|---|---|---|---|---|---|
| 5 mph | 36 | 25 | 13 | 1 | -11 | -22 | -34 | -46 | -57 |
| 10 mph | 34 | 21 | 9 | -4 | -16 | -28 | -41 | -53 | -66 |
| 15 mph | 32 | 19 | 6 | -7 | -19 | -32 | -45 | -58 | -71 |
| 20 mph | 30 | 17 | 4 | -9 | -22 | -35 | -48 | -61 | -74 |
| 25 mph | 29 | 16 | 3 | -11 | -24 | -37 | -51 | -64 | -78 |
| 30 mph | 28 | 15 | 1 | -12 | -26 | -39 | -53 | -67 | -80 |
| 35 mph | 28 | 14 | 0 | -14 | -27 | -41 | -55 | -69 | -82 |
| 40 mph | 27 | 13 | -1 | -15 | -29 | -43 | -57 | -71 | -84 |
Checking a ZIP code converts it to approximate coordinates in your browser, using a table on this site, and sends those rounded coordinates to the National Weather Service for its forecast. Nothing you enter is stored, and there is no account. This is an independent estimate from a simple model, not a prediction and not an official decision. It is not affiliated with any school or district. Confirm closures and delays with your district.
How to use the wind chill calculator
Enter the air temperature and the wind speed, choose your units, and the calculator shows the wind chill in °F and °C. It also shows how a closure and a delay look from the cold alone, for your area’s snow setting. The table below the calculator lists wind chills for common combinations.
The formula
The calculator uses the National Weather Service formula: wind chill (°F) = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16, where T is the air temperature in °F and V is the wind speed in mph. The National Weather Service says wind chill temperature is only defined for temperatures at or below 50 °F and wind speeds above 3 mph. Outside that range the calculator shows the air temperature.
For example, 0 °F air with a 15 mph wind gives a wind chill of about −19 °F. The National Weather Service says exposed skin can freeze in 30 minutes at that wind chill.
Cold school closures vary by district
There is no common wind chill at which schools close. St. Paul Public Schools told MPR News it has no magic number and uses a wind chill chart to estimate how fast frostbite could set in. In that same 2014 story the Atwater-Cosmos-Grove City district started school two hours late at a wind chill of −30. Districts weigh bus stop waits, whether buses will start, winter clothing and road conditions.
National Weather Service cold alerts are also set locally. Omaha lists an Extreme Cold Warning for wind chill or temperatures of minus 30 °F or colder; Raleigh uses 0 to −5 °F apparent temperature. The calculator’s cold steps are our assumptions, not district rules.
Common questions
Is wind chill the same as the air temperature?
No. Wind chill describes how cold exposed skin feels with the wind, and it does not change the actual temperature of objects such as car engines or pipes.
Why does the calculator show the air temperature below 3 mph?
The National Weather Service formula is defined only for winds above 3 mph and temperatures at or below 50 °F.
At what wind chill do schools close?
It varies. Districts have no common number, and the same wind chill can close school in one district and not in another.
Sources and further reading
- National Weather Service: Wind chill chart and formula
- National Weather Service: Cold watch, warning and advisory products revised (October 2024)
- National Weather Service Omaha: Winter products and criteria
- National Weather Service Raleigh: Weather criteria (winter storm, advisory and extreme cold)
- MPR News (2014): When temps plummet, how do school districts decide when to close?
The studio notebook
A useful place to begin.
Clear steps, considered details, and ideas you can put to use.
How much snow closes schools? It depends where you live
There is no national number. Here is why the same snowfall closes schools in one place and not another, and how the calculator’s snow-tolerance setting reflects that.
How school districts decide on snow days, and when you hear
Who makes the call, how early it happens, how families are notified, and what a two-hour delay changes, using published policies from real districts.
Snow days vs remote learning days: what changes for families
Some states let districts hold school online instead of closing. How a remote day works, what limits apply, and how to read a closure announcement.
Extreme cold and wind chill: when cold alone closes schools
How wind chill is calculated, what the National Weather Service cold alerts mean, and why there is no single wind chill at which schools close.
How the Snow Day Calculator works, and what it cannot know
The forecast source, the scoring rules and their limits, written out so you can judge the result for yourself.
The night before a possible snow day: a parent’s checklist
What to check in the forecast, which alerts matter, and how to be ready for a delay, a closure or a remote day.