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 major winter storm is set to spread heavy snow and damaging ice across a large portion of the United States over the coming days. Dangerously cold temperatures will only worsen the storm and increase its danger.

What to Know Preliminary forecasts show 8-12 inches of snow can be expected for much of the tri-state area, including New York City, the Hudson Valley, nearly all of New Jersey and into Connecticut; areas along the coast may see slightly lower totals,

A 13 Weather Impact Alert has been issued for Sunday night through Tuesday morning for the bitter cold, coupled with several inches of snowfall.