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

In Nashville, Tennessee, the Monroe Carell Jr. Children's Hospital at Vanderbilt has treated 46 children for carbon monoxide exposure since Sunday, hospital officials said.

The cases come as many families try to heat their homes during power outages caused by downed powerlines and fallen trees.

Carbon monoxide is an odorless gas and carbon monoxide poisoning can be fatal. Symptoms of carbon monoxide poisoning include dizziness, headaches, nausea and confusion.

To avoid carbon monoxide poisoning, never use generators or grills near open windows or vents, and make sure your battery-powered carbon monoxide detectors are working.

-ABC News’ Jason Volack

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