In Buffalo, where the average low temperature in January is 19 degrees, public schools are closing Friday, and Saturday programming is canceled. Why? It’s going to be cold. Very, very cold.

How cold is too cold to keep schools open? The question is being raised, at least in the Northeast, where a “bomb cyclone” is sending temperatures way below zero.

There are no national or professional standards for temperatures that adults can consult when considering whether to keep students indoors. School district officials — and sometimes principals — make their decisions on a case-by-case basis, usually assessing factors including temperature, wind chill and road conditions. Keith Marty, superintendent of the Parkway School District in Missouri, published a letter to parents on the system’s website on Wednesday saying in part:

Some of you have asked how we decide whether or not to close school due to cold temperature.  As the superintendent of a large school district, it is always challenging to balance my desire to have children in school and also my desire to keep them safe.

Location can affect closure decisions; children in Minnesota are accustomed to frigid winter temperatures, but kids in the South aren’t. Also at play are concerns about state student-attendance requirements and commuting (such as how long students have to wait outdoors for a bus, whether roads are passable by car and whether public transportation is working), as well as health dangers posed by the cold and the condition of many old or poorly maintained school buildings.

And many districts worry about students who receive most or all of their meals at school and who have working parents or guardians who can’t stay home with them. Matt Guilfoyle, spokesman for Fairfax County Public Schools in Virginia, said in an email on Thursday:

FCPS strongly believes students are better served, both academically and socially, by being in school. FCPS also considers the nearly 56,000 students who receive free and reduced-price meals each day at school…. If schools are open and a parent does not believe it is safe for his or her child, the parent should keep the child at home for an excused absence.

A few years ago, Chicago public schools closed when the National Weather Service said temperatures would feel, with wind chill, like 30 degrees below zero. But they opened the next day even though the temperature didn’t rise much. A Chicago lawyer named William Choslovsky wrote an opinion piece in the Chicago Tribune mocking the schools for closing when Milwaukee schools stayed open with frigid temperatures, saying,

Consider this the continued wussification of society. … Our kids can go to school. Considering that so few even walk anymore, what difference does the temperature make? That Jenny and Johnnie may actually stand at the bus stop shivering for all of 10 minutes? Who cares? Frankly, it’s good for the pups.

Still, sometimes, the temperatures demand school closure, at least in the eyes of school district officials. The Idaho Falls School District 91 has a Web page explaining when it closes schools, saying this about temperature:

In Idaho Falls School District 91, our students’ safety is our first priority. In the winter, it’s not unusual for temperatures in eastern Idaho to dip well below zero, and reach as low as 20 below with the wind chill factor. Occasionally, these cold temperatures and other severe weather conditions make it necessary to close schools for the safety of our students.

A wind chill of negative 25 degrees is the tipping point for closure in some districts; that’s what the Department of Public Health in Monroe County, N.Y.,  has urged school districts to stick to.

Buffalo officials decided to close schools for Friday, with the forecast calling for temperatures around zero degrees, with the wind chill making it feel more like 20 degrees below zero. And in Ohio, the Mason City Schools district has set specific temperature guidelines, published on its website:

Closing for Cold Weather
Mason City Schools will close on days when the temperature and/or wind chill are below -20ºF to -25ºF. Temperatures with wind chills in this range are considered dangerously cold if exposure is over 10-15 minutes. With students walking to school and waiting at bus stops, we consider this extreme cold a safety issue.
  • The National Weather Service issues a Wind Chill Warning when wind chills are -25 or colder.

  • The National Weather Service issues a Wind Chill Advisory when wind chills are -15 or colder.

In Baltimore, bad heating forced the closure of four city schools on Wednesday, with students complaining about the cold for weeks. That’s a problem that plagues a lot of older and/or poorly maintained schools around the country.

Frostbite, which causes permanent damage to tissue and can be fatal, occurs at different temperatures and wind speeds. This chart from the Weather Service can be found on a number of school district websites for principals to determine whether to allow students to participate in outdoor activities:

And the Weather Service offers this advice:

  • Wear layers of loose-fitting, lightweight, warm clothing. Trapped air between the layers will insulate you. Outer garments should be tightly woven, water repellent and hooded.

  • Wear a hat. Forty percent of your body heat can be lost from your head.

  • Wear mittens. Mittens, snug at the wrist, are better than gloves to keep your hands warm.

  • Try to stay dry and out of the wind.

  • Cover your mouth with a scarf to protect your lungs from extreme cold. This is especially important if you have a respiratory condition such as asthma.