A blizzard, as defined by the National Weather Service, is a winter storm with large amounts of snow or blowing snow, winds in excess of 35 mph and visibilities of less than a quarter-mile for an extended period, at least three hours.
When these conditions are expected, the agency will issue a "blizzard watch" or "blizzard warning."
"In the watch phase, we believe those conditions are favorable to occur," said Brian Ciemnecki, a meteorologist with the National Weather Service in Upton.
The difference between the two is the time element, Ciemnecki said. When conditions are 36 hours to 48 hours from happening, a watch is issued. "When we believe the conditions are within 24 to 36 hours, then we would issue a warning," he said.
Based on the time element, Long Island is under a "blizzard watch" through Sunday morning. Snowfall accumulations of 6 to 12 inches with wind gusts of up to 50 mph are possible.
The potential for cold, snowy weather is based on a low-pressure system over the northern Gulf Coast that will track to near Cape Hatteras, N.C., Saturday morning, then deepen as it tracks to the northeast over the Atlantic on Saturday night.
The intense low will produce a swath of heavy snowfall, as well as a corridor of high winds. As of late Friday morning, the exact track of the system is still uncertain. A difference of only 100 miles will have a significant impact on the weather across the region, the National Weather Service said.
Ciemnecki said if the low-pressure system tracks south, snow totals could be much lower. If the low pressure moves slightly north, then there could be as much precipitation - rain not snow - and warmer temperatures.