Winter storm updates: Dozens dead across US in wake of massive snowfall, deep freeze

American Airlines said this was the most disruptive storm in the airline's 100-year history. American has canceled more than 9,000 flights and expects impacts to be felt for two more days.

American said 25% of its Tuesday flights are canceled. Across the U.S., more than 2,000 flights are canceled on Tuesday, with Dallas, Boston and New York hit the hardest.

Over 11,000 flights were canceled on Sunday, marking the highest day for cancellations since the pandemic, according to Cirium data.

-ABC News’ Sam Sweeney

More than 500,000 customers are still without power, with the worst outages in Tennessee, Mississippi and Louisiana.

Public schools in Nashville, Tennessee, will remain closed Wednesday and Thursday as the city grapples with massive power outages, officials said.

Nashville Electric Service has restored power to about 100,000 customers, but another 135,000 customers remained without electricity Tuesday morning, officials said.

More than 400 people stayed warming centers Monday night, including at the Fairgrounds Nashville, officials said.

The medical examiner is investigating two possible storm-related deaths in Nashville, officials said. In one incident, a 90-year-old woman at an assisted living facility fell inside her apartment during a power outage, and in the second incident, a woman died after sliding down a hill.

-ABC News’ Jason Volack

Three brothers -- ages 6, 8 and 9 -- died after falling through an icy pond in Fannin County, Texas, north of Dallas, on Monday, according to the Texas Game Wardens.

The 8-year-old and 9-year-old were pulled from the pond by a neighbor and first responders and they were rushed to a hospital where they died, officials said.

"The 6-year-old did not resurface but was later recovered by Texas Game Wardens after an extensive search of the pond," the officials said, adding, "Our thoughts and prayers are with the family and all affected by this tragic incident."