National Weather Service map showing regional snowfall totals for March...

National Weather Service map showing regional snowfall totals for March 13, 2018. Credit: Twitter / National Weather Service NY

What a difference a couple of heavy snow bands make.

A look at the National Weather Service’s snow map for the nor’easter that barreled through Tuesday shows considerable variation in snowfall amounts on Long Island, with some areas buried and others not too far away barely worth an Instagram photo.

Take Plainview and Old Bethpage, for instance — both in the same school district. By 11 a.m., a trained weather spotter reported 11 inches of snow in Plainview. Close to four hours later, Old Bethpage had seen just 5.5 inches.

And just 3 inches were reported in Farmingdale, neighbor of Old Bethpage to the south.

Heavy bands can be a trademark of such quickly intensifying storms, with the weather community, this time, especially impressed, including on Twitter.

Bands, ordinarily, are “not as large and not as long lasting,” said Tim Morrin, a National Weather Service meteorologist in Upton, who expects considerable research to be conducted on the length and duration of the two that hit Long Island.

One was over the Twin Forks — where 18 inches of snow was reported in the Hamptons — the other in the vicinity of a section of western Suffolk and a snippet of Nassau.

Morrin estimated that the band over central Long Island spent a couple of hours there — dropping snow at rates of 2 to 4 inches an hour — stretching anywhere from 180 to 250 miles and starting well to the south of the Island and continuing to the border of Massachusetts.

That explains a significant shift in snowfall amounts, from the likes of 10 inches for Centereach, 9.6 for South Huntington, 11 for Plainview and Dix Hills, to the band-free areas of Riverhead, registering just 5.5 inches, Shoreham’s 4 inches and Ridge’s 3 inches. Snowfall in Bay Shore and Massapequa Park was a hair more than 3 inches.

“I’ve lived here 44 years and never saw such a discrepancy,” Richard Siegelman, a retired elementary school teacher in Plainview, said in an email to Newsday.

He was surprised to hear 11 inches of snow reported in his community, while he estimated 4, maybe 5 inches fell in his yard.

Told of the heavy snow bands, he compared the scenario to a tornado — a narrow strip of destruction, with houses on either side untouched.

“Everything has an edge or outer limit,” Siegelman, 74, said later in a telephone interview.

Contributing to the significant drop-off, Morrin said, was the phenomenon of sinking air, which sets up on the periphery of such bands and results in “a corridor of little or no snow.”

In a nutshell, the scenario can be viewed through the range of colors on the weather service’s snowfall map, indicating the reach of those bands into Connecticut. The East End of the Island saw 18.3 inches reported in Southampton, 10.3 inches in East Hampton, and 12.5 inches in Orient.

Those and other such unofficial measurements are taken in the field by volunteer spotters and other observers who get training from the weather service, weather service employees, Federal Aviation Administration observers at area airports, volunteers with the Community Collaborative Rain, Hail and Snow Network, and broadcast meteorologists, with News 12 Long Island’s Rich Hoffman weighing in on this storm’s snowfall from Woodbury.

Members of the public also submit observations, with the weather service providing tips for correctly measuring snowfall.