As a powerful storm moved up the East Coast on Friday, the National Weather Service issued several blizzard warnings, predicted blizzard conditions and even warned that parts of New England could experience a “historical blizzard.”
That led some people to wonder: What makes a storm a blizzard, anyway?
The storm, which has already produced as much as 18 inches on some parts of Long Island, is expected to dump upward of two feet of snow on some parts of the East Coast this weekend. But the National Weather Service’s definition of a blizzard doesn’t require heavy snow — or, for that matter, any particular temperature.
It defines a blizzard by three criteria: blowing or falling snow, winds of at least 35 miles per hour, and visibility of a quarter-mile or less for at least three hours.
“Whether or not the snow falls during the time of the blizzard, dangerous conditions can result,” a Weather Service Twitter account said on Friday. (On Saturday, the agency confirmed “that blizzard criteria was met this morning” in Suffolk County, N.Y., and New London County, Conn.)
In order to form, blizzards need cold air to make snow, and moisture to form clouds and precipitation. The moist air needs to rise over very cold air, making clouds and snow.
Officials have also described this weekend’s storm as a “nor’easter.” That term usually describes a weather system in which winds just off the East Coast collide with surface winds from the Northeast and Mid-Atlantic States amid areas of low pressure.
