The combination of marsh fire smoke and moisture in the air created what a meteorologist called a “perfect storm.” Low visibility contributed to the traffic accidents.
A dense “super fog” hovered over New Orleans on Monday, shrouding the area in an impenetrable mist that led to traffic pileups involving dozens of vehicles and leaving at least seven people dead, the authorities said.
At least 158 vehicles were involved in a series of crashes, which began just before 9 a.m. on Interstate 55 northwest of New Orleans, the Louisiana State Police said, noting that fog had been a “contributing factor.” An additional 25 people were injured, some of them critically, the police said.
After the accidents, which involved vehicles in both the north- and southbound lanes, some of the vehicles caught fire, according to the police. A tanker truck carrying “hazardous liquid” was being removed, the police said, adding that it was possible that “additional fatalities could be located.” The State Police urged anyone with a missing family member to contact the agency.
Aerial images posted to the State Police’s Facebook page show several pileups on Interstate 55, including some cars and trucks that appeared to be charred.
The thick fog came from a combination of moisture in the air and smoke from sporadic marsh fires across the Mississippi River Valley toward Baton Rouge, La., said Tyler Stanfield, a meteorologist for the National Weather Service in New Orleans.
“It was the perfect storm,” Mr. Stanfield said.
While super fog is uncommon, it’s not an unheard-of phenomenon. New Orleans typically experiences super fog twice a year. It is usually fueled by marsh fires, which have become more frequent in the area this year because of drier conditions, Mr. Stanfield said.
The fog began to set in around 3 a.m. on Monday and became dense around sunrise, he said. Visibility for drivers was as low as one-eighth of a mile.
The State Police closed parts of Interstates 10, 55 and 310 on Monday morning and warned that, because of the heavy fog, “drivers should avoid the area if possible and use alternate routes.” Interstates 10 and 310 South later reopened, but portions of Interstate 55 remained closed on Monday evening.
By the afternoon most of the fog had cleared, with the last of it lingering in the suburbs west of New Orleans, Mr. Stanfield said.