As a dangerously cold weather front plunges into the U.S., tens of millions across much of the country can expect heavy snow, sleet and freezing rain.
The storm system hit the northern Plains with subzero temperatures. It's now on its way to the Mississippi Valley, and expected to reach the Northeast and the Ohio Valley by Sunday.
Texas and other Southern states could experience dangerously low temperatures as soon as Saturday.
The Winter Storm Severity Index from the National Oceanic and Atmospheric Administration’s Weather Prediction Center forecasts how dangerous conditions will become for travel and key infrastructure.
NBC News is tracking the center’s data on the interactive map below, which shows the storm forecast for the next 72 hours. It will be updated with the latest data every two hours.
The Weather Prediction Center uses forecasts of various factors, including the amount of snow expected, projected accumulation of ice and the likelihood of blowing snow, to help predict how bad it will get in certain places.
For this storm, the National Weather Service predicts hazardous travel conditions, prolonged power outages and falling trees because of snow and ice in Southern states. Northern states can expect snow-covered roads and subzero temperatures.
