Officials urge Americans to stay indoors as a historic winter storm creates "catastrophic" ice conditions and triggers the largest weather alert ever.

A massive winter storm headed towards the northeast United States on Sunday after sweeping across much of the country, threatening tens of millions of Americans with blackouts, transportation chaos and bone-chilling cold.

Roughly a million power outages were reported on Jan. 25 as a massive winter storm raged across the country, bringing "catastrophic" ice accumulation that downed power lines and created treacherous road conditions.

There have been flight cancellations and delays since Friday at Fresno Yosemite International, according to the airport spokesperson.

More than 11,000 US flights scheduled for Sunday were cancelled by major carriers, according to an industry tracking service FlightAware.com. Ronald Reagan National Airport, located in northern Virginia just across the Potomac River from Washington, was effectively closed altogether.

More than 200 million people are under winter storm threats as officials brace for power outages and travel difficulties.

A winter storm affecting the southern U.S. is causing flight delays and cancellations at Des Moines Airport, impacting travelers.

A fierce winter storm was cutting a massive swath through much of the United States, impacting millions.