A dust blanket that blew in Friday from the Great Plains to shroud the Tennessee Valley had unraveled by Friday night.
The cloud, which thickened over the day, originated in Nebraska, Kansas and Oklahoma after strong windstorms stirred up dust and carried it east, according to the Chattanooga-Hamilton County Air Pollution Control Bureau.
"We have seen it like this before, but it usually comes from wildfires," said bureau spokeswoman Amber Boles.
Air quality levels remained safe in the Chattanooga area during the day, though the bureau kept a close watch on them, she said.
"If those levels become unhealthy, we will notify the public," Noles said.
At the Chattanooga Airport, spokeswoman Christina Siebold reported no problems from the haze.
"Visibility was still seven miles, which would not dictate any changes [in service]," she said.
The plume dissipated Friday night, said National Weather Service at Morristown meteorologist Andrew Pritchett, because the atmosphere stabilized after sunset.
"The plume is very large -- it's hundreds of miles long -- and it's just kind of this dust that has hung over and stayed aloft in the atmosphere," he said. "When we lose heating after sunset, the atmosphere stabilizes a little bit, and the dust falls back out. There might be a fine film of dust on people's cars."
Seeing an event of this magnitude is uncommon in the Tennessee Valley, he said.
"That's not to say it's never happened," Pritchett said, "but it's certainly not something we see every day. It's a rare event."
In extreme cases, thick dust can block the sun and actually create lower temperatures on the ground, he said, but Friday's dust was not thick enough to significantly change the weather.
The haze over Chattanooga started with a massive dust storm swirling reddish-brown clouds over the Plains on Thursday. The near-blackout conditions caused by the storm triggered a multivehicle accident along a major interstate Thursday, forcing police to shut down part of the road.
In a scene reminiscent of the Dust Bowl days, choking dust suspended on strong wind gusts shrouded Interstate 35, which links Dallas and Oklahoma City to Kansas City, Mo. Video from television station helicopters showed the four-lane highway virtually disappearing into billowing dust on the harsh landscape near Blackwell, Okla., plus dozens of vehicles scattered in the median and on the shoulders.
"I've never seen anything like this," said Jodi Palmer, a dispatcher with the Kay County (Okla.) Sheriff's Office. "In this area alone, the dirt is blowing because we've been in a drought."
The highway patrol said the dust storm caused a multicar accident, and local police said nearly three dozen cars and tractor-trailers were involved. The stretch of closed roadway reopened Thursday evening after crews cleaned up debris and waited for winds to die down.
Staff writers Shelly Bradbury and Mike Pare and The Associated Press contributed to this story.