A powerful storm system, spawning multiple tornadoes, has tragically claimed four lives across the Southern United States. The severe weather has caused widespread damage, prompting emergency responses and leaving millions under threat.

The fatalities include an 18-year-old in Mississippi, killed when a tree fell on her home, and another resident in the same state. A death was also reported in Texas, with a fourth victim succumbing to a fallen tree in North Carolina.

Preliminary reports indicate that Saturday's storms produced 37 tornadoes across Texas, Louisiana, Mississippi, and Georgia. These twisters resulted in significant structural damage in various affected areas.

The National Weather Service has begun assessing the strength of the tornadoes, categorizing some as high as EF-3, with wind speeds reaching at least 136 mph. These assessments reveal the intensity of the storms, with one tornado in Texas traveling nine miles and causing substantial damage.

A significant portion of the damage has been concentrated in Texas, particularly in Montgomery and Chambers counties. An elementary school in Brazoria County also sustained major damage.

Emergency response teams are on the ground and working to support affected communities. Texas state agencies have deployed over 300 responders and 180 assets, including search and rescue personnel, to aid the state's storm response.

The storm system continued to move eastward Sunday, placing more than 20 million people across the eastern Gulf Coast and the Carolinas at risk of extreme weather. Cities such as Jacksonville, Florida; Charlotte and Raleigh, North Carolina; and Atlanta were all within the forecast risk zone.

While tornado watches expired on Sunday evening, the aftermath of the storm has left thousands without power. Over 140,000 utility customers across several states, including Mississippi, West Virginia, Ohio, Pennsylvania, and Texas, experienced outages due to the storm system.

The system is a result of cold air colliding with unusually warm December temperatures, causing unstable weather conditions. Despite the severe storms, temperatures in parts of Texas could climb back up to the 90s this week, while the Southeast could experience highs in the 70s.

The weather has impacted air travel as well, causing over 9,500 flights to be delayed, with nearly 500 canceled across the U.S. Major airports, such as those in Houston, Charlotte, and Miami, have been significantly affected by the weather-related disruptions.

Mirna Alsharif, Christine Rapp, and Dennis Romero contributed to this report.