Last week, Mayor de Blasio and Schools Chancellor Farina decided to keep schools open on Thursday during a Nor'easter that dumped 12.5 inches of snow on the city. Parents, teachers, the teachers' union, principals, elected officials, famous people and conservatives were up in arms about the move. But a detailed analysis of data from the Department of Education and National Weather Service shows that despite dozens of storms since 1978, there have only been 11 snow days in NYC since the department started keeping track. In fact, there have been many years with multiple storms producing more than 6" of snow that generated no snow days at all. So the de Blasio administration's decision to keep the schools open seems to be in keeping with the last four decades of NYC tradition. Here are the facts:

Here are some charts looking at the number of snow days charted against the number of 6"+ storms and 12"+ storms. Note all the years with multiple storms that produced no snow days at all. A lot of this is timing. There were no snow days between 1983 and 1995, despite a number of storms. Some big storms have occurred during weekends; for example, a February 11-12, 1983 snow storm with 17.6 inches happened on Friday and Saturday. Other storms, like the February 17, 2003 President's Day snow storm (19.8 inches) and Boxing Day Blizzard of 2010 (20 inches), happened during school breaks. (Note: The Department of Education's data on snow days only goes back to 1978.)

However, there were a number of big storms on school days: During one week in February 1994, there were two storms that combined for 21.8 inches.

Here's a look at the snow day by mayoral administration; keep in mind that Koch served for three terms, Dinkins one, Giuliani two, Bloomberg three, and de Blasio is just 1.5 months into his term:

Finally, here's a look at the cumulative snowfall from the ten worst winters—as we said, this winter has been historically, unusually terrible (or awesome, depending on how much you enjoy swimming in curbside slush lagoons). In fact, we're just a storm or two away from the worst winter on record since 1869:

And here are all the snow days that NYC public schools have had since 1978:

February 6, 1978: About 8-12 inches of snow fell in NYC during this blizzard, which started on a Sunday, February 5, 1978. Between February 5 and February 7, 17.7 inches fell.

April 7, 1982: A "rare April blizzard" came on Sunday, April 6—9.6 inches.

January 8 and 9, 1996: Two snow days! The blizzard hit on Sunday, January 7, 1996, dumping 20 inches onto the region.

March 5, 2001: Even though there wasn't much snow, Schools Chancellor Harold Levy called a snow day on the day before (a Sunday) so parents could make childcare arrangements because the forecasts seemed very severe. (According to NWS, this storm doesn't even measure for being in the 6"+ storm club.)

January 28, 2004: A snow day was called the day before, and 10.3 inches fell. One person said, "I think we wimped out."

March 2, 2009: Eight inches of snow and there was a snow day.

February 10, 2010: The Department of Education cancelled school the day before 10 inches fell.

February 26, 2010: School was closed after the DOE said school would be open. Mayor Bloomberg, when the decision was to keep schools open, said, "My hope is that the snow will stay to the north and west of us and we'll just have rain, our kids need another school day ... We will cancel school only if it really would be dangerous to get the kids into school and get them home."

January 27, 2011: This was the only snow day that School Chancellor Cathie Black called—19 inches fell between January 26 and 27. (Bloomberg was previously slammed for not calling a snow day on January 12.)

January 3, 2014: This was Mayor de Blasio's third day in office, and Dante de Blasio's friends were lobbying him to lobby his dad to make the call. The snow day was announced a little before 5 a.m. Dante still had to shovel his front walk. Snowfall total was 6.4 inches.

Of course, February 13, 2014 will go down in history as the snow day that never was. Only time will tell if de Blasio's decision on that day that will cost him a second term. Suburban parents, though, admire de Blasio's grit.

Addendum for statistics nerds: you can find our raw data and charts here.