And yet the city’s public schools — the nation’s largest system — were closed for a snow day.

How did that happen?

Why did Mayor de Blasio call a snow day?

Timing. He had to make a decision Sunday evening, when the forecast looked ominous. The weather changed overnight, but by that point, it was too late to adjust the plan.

The call to close schools is made early, “with as much time as possible for parents to plan,” the mayor’s spokesman said. Then there are all the school buses to think about.

As my colleagues Eliza Shapiro and Michael Gold wrote, buses leave depots before dawn and could interfere with the nearly 1,600 snow plows combing the streets.

How many snow days have there been in New York City?

Seven since 2014, compared with 11 from 1978 to 2013, according to The City’s Alyssa Katz.