NASHVILLE, Tenn. − A fierce storm system that killed six people, including a 2-year-old boy in Middle Tennessee, was rolling east Sunday and threatening a swath of the nation from Maryland to Florida and across the Central Gulf Coast with severe thunderstorms, heavy rain, and even snow.

Dozens of people were injured, cars flipped on I-65, trees buckled, and roofs were blown off buildings as shoppers hunkered down in store basements Saturday in Tennessee for what the National Weather Service preliminarily determined was a string of tornadoes.

The "dynamic" system was bringing thunderstorms to much of the East Coast and and possibly heavy snow in the Appalachians and interior Northeast on Sunday and Monday, the National Weather Service said in an advisory.

Winds could gust to 50 mph around New York City and Boston, and higher gusts of 60-70 mph are possible on Long Island and along the southern coast of Massachusetts, AccuWeather warned. Travel on roads and on airlines could be difficult through Sunday night and into Monday morning, forecaster said.

The good news: Conditions should begin to improve Monday night into Tuesday morning, the weather service said.

The sun was already out Sunday in Tennessee as residents picked through the rubble of scores of flattened homes and businesses.

“We’re focused on taking care of people today and powering through heartbreak into resilience," Nashville Mayor Freddie O'Connell told USA TODAY on Sunday. "Today’s beautiful sunshine will become a dangerous cold snap tonight, so we’re working on safely restoring power and getting information out about shelter options.”

About 36,000 Tennessee homes and businesses were without power Sunday; another 8,000 outages were reported in Alabama.

The brutal storm system comes exactly two years after a system that ripped through Tennessee, Kentucky, Mississippi, Missouri and Illinois killed more than 80 people, the majority in Kentucky. And in March 2020, 25 people died and hundreds were injured after more than a half-dozen tornadoes struck Middle Tennessee, one within a few miles from where fatalities were reported Saturday.

At least six dead, 23 injured:Nashville area ravaged by tornadoes

Storm system may be the deadliest on record for December in region

The severe weather outbreak on Saturday may be the deadliest December on record for Middle Tennessee's tornado disasters, according to the Nashville Weather Service. The region previously recorded a total of eight tornado deaths, spanning decades of tornado incidents, in December.

The Tennessee Emergency Management Agency confirmed a "preliminary reporting" of 13 tornadoes across the state. The National Weather Service said an estimated nine counties were impacted by tornado damage and counties affected by severe weather damage were "likely double" that.

Numerous weather alerts were issued for the region, including 34 storm warnings — with 20 of those being tornado warnings. The weather service had issued a "tornado emergency" for parts of the region for the first time in over a decade as the storms swept through, according to meteorologist Sam Shamburger.

Storms flatten homes in Tennessee

The Metro Nashville Police Department confirmed there had been three fatalities − Joseph Dalton, 37; Floridema Gabriel Perez, 31; and her son, Anthony Elmer Mendez, 2. First responders were involved in scores of search and rescue missions and responded to dozens of vehicle crashes and other incidents involving property damage and injuries. The collapse of a roof in a church north of downtown sent 13 people to hospitals, according to Nashville emergency officials.

The Montgomery County Mayor's Office also confirmed three people died in Clarksville, about 45 miles northwest of downtown Nashville. Montgomery County officials said about 60 people were being treated at medical facilities for injuries, nine of them sent to a Nashville hospital in critical condition.

In a social media post, O'Connell urged residents to be extremely careful because of so many downed power lines across the city.

Lyanne Garay was at her mother’s home in suburban Madison, 10 miles north of Nashville, with her four children when they heard tornado sirens blare. Hours later she returned to her own home nearby to find her fence toppled and part of her roof torn off. She saw other homes in her neighborhood with far more damage.

“Compared to everybody, we’re fine, but it’s still a shock that we don’t have any place to go or anything to do and our house has been water damaged,” she said. “We always hear the alarms and everything but never experienced something like that." 

'Sad day for our community':At least 6 dead as tornadoes rampage through Middle Tennessee

Tornado in Clarksville 'devastating and tragic'

A tornado slammed Clarksville, 50 miles northwest of Nashville, at about 1:30 p.m. Saturday, prompting Shanika Washington to take her children, ages 5 and 10, to a windowless bathroom in the basement of her townhouse. She tried to shield them with her own body for 20 frightening minutes.

“The back door absolutely did fly open, and you just heard a bunch of wind,” she said. “I could tell that we were dead smack in the middle of a storm.”

Up to 100 military families from Fort Campbell in Clarksville were displaced, the Tennessean reported, adding that almost 80 people in the region have been hospitalized.

A shelter set up at Northeast High drew an outpouring of support and donations from churches, restaurants, businesses and community members. The Clarksville-Montgomery County School System announced schools would be closed Monday and Tuesday as the cleanup continues.

"Our hearts are heavy as we learn of the loss of lives and critical injuries," the district said in the announcement on its homepage. "Many families have completely lost their homes and others are doing what they can to make repairs. This was a devastating and tragic weather event in our community."

Mayor, governor warn and mourn

"Tonight, Nashville joins other communities across Middle Tennessee grieving loss of life from deadly tornadoes," O'Connell posted on X. "As we continue to take stock of the devastation, please keep our neighbors in your thoughts and prayers. Be safe and look after one another."

Gov. Bill Lee, who issued a Level-3 state of emergency, and his wife posted similar sentiments: "Maria & I are praying for all Tennesseans who have been impacted by the tornadoes that swept through the state ... We mourn the lives lost & ask that everyone continue to follow guidance from local & state officials."

Contributing: The Tennessean; The Associated Press