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

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."

As Washington, D.C., digs out from the snow, federal offices will remain closed on Tuesday, as well as the National Zoo and the Smithsonian museums.

Some 220 million Americans are on alert for extreme cold temperatures forecast to follow the weekend's record-breaking winter storm.

The extreme cold warnings and cold weather advisories stretch from Texas and Florida in the South to New York in the Northeast and Detroit in the Midwest.

Cold air is expected to produce another round of lake-effect snow on Tuesday for western Michigan and western New York -- an additional 8 to 16 inches of snow is possible in some areas.

Record low temperatures are possible in the South, where temperatures will feel as low as the 20s and 30s in Florida and the 20s along the Gulf Coast.

Wind chill is expected to drop into single digits on Tuesday in the Northeast, ahead of even lower temperatures later this week. Multiple days of below-zero wind chills are forecast for the Northeast from Wednesday into the weekend.

-ABC News' Melissa Griffin