As millions of Americans hunker down for the winter storm, 19 states and Washington, D.C., have declared states of emergency.

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 ...

Forecasters say over half the U.S. population could be affected by snow, ice or bitter cold as a winter storm sweeps across the county.

Track the winter storm as it's forecasted to bring heavy snow and extremely cold weather to the U.S., reaching millions from the southern U.S. to the Northeast.