More than 850,000 customers in the US, as far west as New Mexico, were without electricity and over 10,000 flights were cancelled on Sunday during a monster winter storm that paralysed eastern and southern states with heavy snow and ice.

As snow, freezing rain and dangerously frigid temperatures swept into the eastern two-thirds of the nation on Sunday, the number of power outages continued to rise. As of 10:47am EST (8:47pm PKT) on Sunday, more than 850,000 US customers were without electricity, according to PowerOutage.us, with at least 290,000 in Tennessee and over 100,000 each in Mississippi, Texas and Louisiana. Other states affected included Kentucky, Georgia, Virginia and Alabama.

More than 10,200 US flights scheduled for Sunday were cancelled, according to flight tracking website FlightAware. Over 4,000 flights were cancelled on Saturday.

Washington, DC’s Ronald Reagan National Airport said airlines had cancelled all flights at the airport on Sunday.

Delta Air Lines on Sunday said that it intended to operate on a reduced schedule “subject to real-time frozen precipitation and afternoon storm conditions.”

The airline had adjusted its schedule on Saturday, with additional cancellations in the morning for Atlanta and along the East Coast, including in Boston and New York City, and said it would move experts from cold-weather hubs to support de-icing and baggage teams at several southern airports.

The National Weather Service’s latest forecast for Sunday through Monday morning calls for heavy snow from the Ohio Valley to the Northeast, including up to 18 inches in New England. Much of the Southeast and parts of the Mid-Atlantic are expected to get rain and freezing rain.

Forecasters predicted “bitterly cold temperatures and dangerously cold wind chills” from the southern plains to the Northeast in the wake of the storm, bringing “prolonged hazardous travel and infrastructure impacts.”

Federal, State govts declare emergencies

Calling the storms “historic,” President Donald Trump on Saturday approved federal emergency disaster declarations in South Carolina, Virginia, Tennessee, Georgia, North Carolina, Maryland, Arkansas, Kentucky, Louisiana, Mississippi, Indiana, and West Virginia.

“We will continue to monitor and stay in touch with all States in the path of this storm. Stay Safe, and Stay Warm,” Trump wrote in a post on Truth Social.

Seventeen states and the District of Columbia have declared weather emergencies, the Department of Homeland Security said.

DHS Secretary Kristi Noem, at a news conference on Saturday, warned Americans to take precautions.

“It’s going to be very, very cold,” Noem said. “So we’d encourage everybody to stock up on fuel, stock up on food, and we will get through this together.”

The Department of Energy on Saturday issued an emergency order authorising the Electric Reliability Council of Texas to deploy backup generation resources at data centres and other major facilities, aiming to limit blackouts in the state.

On Sunday, the DOE issued an emergency order to authorise grid operator PJM Interconnection to run “specified resources” in the mid-Atlantic region, regardless of limits due to state laws or environmental permits.

US electric grid operators on Saturday stepped up precautions to avoid rotating blackouts.

Dominion Energy, whose Virginia operations include the largest collection of data centres in the world, said if its ice forecast held, the winter event could be among the largest to affect the company.