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.

The storm began to lash the central and southern parts of the country with snow on Saturday and the Northeast on Sunday. Meteorologists said to expect heavy snow, sleet and freezi

The U.S. National Weather Service warned of an unusually expansive and long-duration winter storm that will bring widespread, heavy ice accumulation in the southeast U.S. and cited "crippling to locally catastrophic impacts.