Cold Day Calculator

Worked examples

Wind chill -38 °F in Minneapolis

Air -18 °F, wind 15 mph, wind chill -38 °F at 7 am, Extreme Cold Warning active → about 90 %. Minnesota districts cancel around -35 °F and most have a written policy saying so.

Wind chill -20 °F in Chicago

Air -5 °F, wind 12 mph, wind chill -20 °F → about 25 %. Chicago Public Schools have cancelled at -30 °F and stayed open at -20 °F; expect delays in the suburbs rather than closures.

5 °F in Atlanta

Air 5 °F, calm → under 10 %. Cold alone rarely closes southern schools; add a glaze of ice from the day before and the snow day calculator takes over.

How it is calculated

The lowest forecast wind chill between 5 am and 9 am sets the score: below -15 °F adds a little, below -25 °F a lot, below -35 °F almost everything. An Extreme Cold Warning or Wind Chill Warning adds on top, an advisory adds less. Snow and ice in the same window are scored by the snow day model, so a cold snap behind a storm shows the combined chance.

Questions people ask

At what wind chill do schools close?

Most northern districts publish a line: commonly -25 °F to -35 °F wind chill at the time buses run. Some use air temperature (-20 °F is a frequent cut-off). Southern districts rarely have a written cold policy and close for ice instead.

Does the calculator use wind chill or air temperature?

Wind chill (the forecast's apparent temperature), read between 5 am and 9 am. That is when children are at bus stops and when district policies are written for.

What is an Extreme Cold Warning?

The National Weather Service's warning for dangerously cold air and wind chills, which replaced the Wind Chill Warning in most offices in 2024. Either one, when active for your coordinates, adds to the score and appears in the reasons.

Do cold days count as snow days for the school calendar?

Usually yes: a cold-weather closure uses one of the district's built-in emergency days, and many districts now switch to an e-learning day instead of closing outright.

Why is my chance low when it is -10 °F outside?

-10 °F air with little wind is a normal January morning in the Upper Midwest and schools stay open. The score moves when the wind chill, not the air temperature, drops past about -25 °F, or when a warning is issued.