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.

Heavy snow, ice and brutal cold are expected to make this winter storm a potentially life-threatening weather event, stretching across two-thirds of the U.S.

The impending winter storm is set to begin across the south-central U.S. on Friday.

Several emergency declarations have already been issued as a massive winter storm barrels toward more than 35 states, putting more than 200 million people in its path and threatening “considerable disruption” to New York with up to a foot of snow.

A winter storm with “the potential to be historic” is eyeing a large strip of the U.S. and it appears Illinois and the Chicago area could now be a part of its path. While confidence surrounding the snowy and icy system’s track and intensity remain uncertain,

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.

Large parts of the eastern and central United States are expected to see heavy snow. But south of the snow line, forecasters are warning that the storm could deliver dangerously icy conditions. Exactly where that snow vs. ice line will fall was still uncertain on Wednesday.

The National Weather Service has issued a winter storm watch for much of central and south Indiana beginning on Saturday, Jan. 24. For the state's southern counties, that advisory has been upgraded to a winter storm warning.