Tornadoes ripped through four states Wednesday, killing at least two, as a cold front clashed with warm air, producing unusual weather patterns over a large part of the country. The Weather Channel's Julie Martin reports.

Updated at 9 p.m. ET: Severe thunderstorms continued to threaten Wednesday night along a multi-state line stretching from the Southeast to as far north as the nation's capital, according to The Weather Channel.

The National Weather Service issued tornado watches across large swaths of Georgia, as well as parts of Maryland, Virginia, the District of Columbia, the Carolinas and northwest Florida, through Wednesday night. The Weather Channel warned of thunderstorms with spotty, damaging gusts and low chance of tornado in northeastern Florida and on the east side of the Florida panhandle.

Thirteen tornadoes were confirmed to have blown through the South on Tuesday and Wednesday, according to The Weather Channel -- they touched down in Missouri, Oklahoma, Arkansas, Mississippi and Illinois on Tuesday and Indiana, Tennessee and Georgia on Wednesday.

Earlier Wednesday, a violent tornado that ripped through Adairsville, Ga., killed at least one person, overturned cars, littered Interstate 75 with debris and forced officials to shut down a 10-mile stretch of the road, officials said.

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Numerous buildings in nearby Bartow, Ga., some with people inside, were also damaged in the powerful storm, and police have received multiple calls of injuries and trauma, the Atlanta Journal-Constitution reported.

A man was killed in the state when the tornado hit his mobile home, Bartow County officials said.

Eight people went to the hospital with injuries following the storm, officials at Gordon Hospital in Calhoun, Ga., said. The storm also left at least 12,400 without power statewide, utilities providers said.

That twister was only one of a handful that touched down in the South and the Midwest Wednesday, as storms throughout the region caused widespread power outages, structural damages and were blamed for another death in the region.

The National Weather Service also confirmed another twister touched down in Sardis, Miss., heavily damaging homes in Solsberry, Ind.

Earlier, a 47-year-old man in Nashville, Tenn., was killed when a tree fell on a shed he was in, according to local fire department officials.

Amateur video taken from inside a Food Lion store captures a tornado as it tears through Adairsville, Georgia. NBCNews.com's Dara Brown reports.

Meanwhile, in Monticello, Ark., a woman was struck by lightning late Tuesday but only had minor injuries, according to police, and a 32-year-old woman and a 7-year-old boy were treated for minor injuries in Marion County, Ky., the emergency management division reported.

Packing quarter-size hail and powerful winds, the storms also knocked out power to thousands of people throughout the region early Wednesday.

In Memphis, Tenn., more than 13,000 customers lost power as high winds tore down power lines and at least two tornado warnings were issued in the area, but later expired, according to the National Weather Service.

And more than 7,300 Nashville customers were without power, according to Nashville Electric. Utilities reported another 8,000 outages in Arkansas, 7,000 in Mississippi, and nearly 12,000 in Indiana.

In Arlington, Tenn., downed power lines sparked a fast-spreading grass fire that caused the evacuation of a small mental-health facility, Arlington Fire Department Lt. Chad Wiseman said.

"The wind was pushing everything really fast," Wiseman said, adding that gusts reached 50 mph as the fire was burning. "The wind feeds everything. The wind will turn a little grass fire into something that was shooting 15- or 20-foot flames in the air. It looked pretty scary."

The fire was brought under control within an hour, officials said.

A number of factors have helped build the storm system, according to meteorologists. Unseasonably warm, wet air has been pushed up from the Gulf of Mexico by southerly winds, and that is being met by cold air coming in from the Plains via Canada, The Weather Channel’s Chad Burke said, adding that the cold air is being driven eastward by unusually high winds.

"It's not a normal pattern for this time of year," said Burke. "The warm air has changed the dynamic. On the back end of the storm, you have high temperatures in the 50s and 60s in places like Chicago. By tomorrow night, they'll be at 11 (degrees)."

NBC staff writers Vignesh Ramachandran and Isolde Raftery contributed reporting.