Nearly half of the U.S. population was under a winter storm watch or warning Friday as a major system moved from the Rockies through the Ohio and Tennessee River valleys.The system is forecast to start in the plains, then trudge east and into the South, and eventually move into the Mid-Atlantic and Northeast. Millions could see a foot or more of snow by Sunday.Others may face ice accumulation topping a half-inch, which could cripple travel and knock out power.Heavy snow, intense sleet and freezing rain are likely to blanket more than half of the country by Monday.RELATED STORY | Winter storm travel insurance: What's covered and what's not?While the Upper Midwest will be spared the heaviest snow, the region will not escape extreme cold. The wind chill dropped to minus 45 Friday morning in Minneapolis and minus 38 in Milwaukee.The National Weather Service is spreading the word about the danger of ice, predicting widespread tree damage and prolonged power outages from snapped utlity lines, especially in the South in states like Texas, where just five years ago a storm took out much of its power grid.CNN reports FEMA is pausing the planned firings of hundreds of disaster workers ahead of the winter weather, avoiding more cuts for now to an agency already down two thousand employees since President Donald Trump took office.Now the agency says it's actively working with states to prepare.Travel waiversNearly all major U.S. airlines have announced travel waivers for passengers flying this weekend. The waivers allow travelers to rebook without paying a change fee.In most cases, passengers who rebook within a few days can also avoid fare differences if they stay in the same class of service. Those rebooking for later in the year, however, may be subject to a fare difference.Waiver details by airline: Delta Air Lines: Waivers apply for flights to or from Southern airports from Jan. 2325 and for Northeast and Mid-Atlantic airports from Jan. 2426. Travelers flying through the South can rebook without a fare difference if they travel by Jan. 28; the deadline is Jan. 29 for the Northeast and Mid-Atlantic. American Airlines: Waivers apply for Southern airports from Jan. 2326 and for Northeast and Mid-Atlantic airports from Jan. 2427. Passengers can fly without a fare difference until Jan. 29 for Southern routes and Jan. 30 for Northeast and Mid-Atlantic routes. Southwest Airlines: Waivers apply for flights booked Jan. 2326. Passengers have two weeks from their original travel date to rebook without paying a fare difference. Southwest says customers whose flights are canceled or significantly delayed may be eligible for a refund. United Airlines: Waivers apply for flights to or from Southern airports from Jan. 2325 and for Northeast and Mid-Atlantic airports from Jan. 2426. The rebooking deadlines are Jan. 28 for the South and Jan. 29 for the Northeast and Mid-Atlantic.Other airlines have announced similar policies.As of Friday evening there had been more than 600 cancellations and ore than 4,100 delays at U.S. airports, according to FlightAware. ...read more read less