Significant winter weather for a watch means 5 or more inches of snow and/or sleet within 12 hours, or 7 inches of snow/sleet within 24 hours, or ice accumulation that could cause damage to trees and powerlines, or life-threatening combinations of snow and/or ice with wind.

This index, from NOAA's National Weather Service, attempts to scale the impacts from winter weather, taking into account factors such as snowfall, accumulated snow on rooftops, ice accumulation, the potential for a flash freeze, and blowing snow. Not all factors are in play in a given winter storm.

A snow squall warning was released by the National Weather Service on Thursday at 1:16 p.m. in effect until 2:15 p.m. for Clinton, Essex and Franklin counties.

The major storm is set to hit starting on Jan. 23 and will stretch into the weekend, spreading snow and ice from the southern Plains to the Northeast.

The Philadelphia region could see up to 18 inches of snow, along with sleet and freezing rain. Here’s everything to know, including the latest forecast, weather advisories, travel impacts and more. City emergency and school closures: Philly will be under a snow emergency beginning at 9 p.