A snow day is the most random of childhood holidays, bestowed from above, with no way to plan for it other than having your sled on standby.

For many parts of the country, this has been an unusually mild winter, and snow days have been rare. But on Wednesday, families in Chicago, Detroit and places across the Midwest were checking to learn if the 2 to 8 inches of snow in the forecast would close their schools.

Children protest that a single snowflake is reason enough to cancel class. Parents insist they never got this many days off when they were young. And school administrators remind everyone that a snow day can cause disruptions that they are loath to unleash.

Here’s a look at what has changed over time, from the frequency of snow days, to the effects of climate change.

The trends

There is no single database that records the number of snow days in the United States. If you swear that kids were tougher in your day and you had to walk to school through 3-foot snowdrifts, uphill, both ways, we cannot prove you wrong. But let’s take a look at some examples from around the country:

• Loudoun County, Va., averaged four snow days a school year in the 1970s, three in the ’80s, 5 ½ in the ’90s and 2000s, and seven in the 2010s. That is a gently upward trend.

• In Des Moines, Iowa, records beginning in 1972-73 indicate there were only four snow days in the remainder of the 1970s. The district averaged just one canceled day each year in the ’80s, slightly higher at 1 ½ days in the ’90s, and then up to about two a year in the 2000s. But in the 2010s, the average dipped to roughly 1.3 a year.

• Mayor Bill de Blasio of New York was criticized last March for having called seven snow days in his first five years in office. Between 1978 and 2013, school was canceled only 11 times.

Location, location

From Hancock, Mich., where there is snow on the ground nearly 200 days a year but schoolchildren rarely get a wintry day off, to tropical Miami, where a “hurricane day” is more likely, one thing is clear to students: Life is not fair. If you live in the snowier parts of the country, your state’s transportation department probably has the road-clearing drill down pat.

“We don’t call off school for snow when we get 6 inches,” said Steve Patchin, the schools superintendent in Hancock, in Michigan’s Upper Peninsula. “Sometimes not even for 12 inches.” As a consolation, the elementary school has its own sledding hill.

By contrast, in January 2019, Atlanta’s public schools and those in nine surrounding districts were shut down when just a couple of inches of snow were forecast. The January storm fizzled, and far more time was lost at the beginning of that school year to another storm — Hurricane Irma.

According to data from Clear Roads, a private group that collects information on winter preparedness, the state has fewer than 400 snowplows.

Minnesota has more than double that number. Pennsylvania and Maryland each have approximately 2,700 plows, but Wisconsin tops them all with more than 3,050 plows.

Is climate change a factor?

Knowing that the planet is warming, you might expect fewer snowstorms. The National Climate Assessment tells us that the North American snow season is shrinking and that snow is gradually being shouldered out by rainfall. But Barbara Mayes Boustead, an author of the National Climate Assessment’s chapters on the Midwest and Northern Great Plains, said “There are still swings up and down.” And because climate change is putting more moisture into the air, the snowfalls that do come can be extremely heavy. So climate change doesn’t mean that snow days are going away.