‘Super Fog’ Blankets New Orleans, Causing Pileups

A dense “super fog” hovered over New Orleans on Monday, shrouding the area in an impenetrable mist that prompted the authorities to close sections of three major interstate highways.

WVUE-TV, the local Fox affiliate, reported that two people were killed when the fog set off more than two dozen crashes on Interstate 55 northwest of New Orleans, citing information from the sheriff’s office in St. John the Baptist Parish.

The sheriff’s office referred queries about the accidents to the Louisiana State Police, which declined to comment when reached on Monday afternoon. The State Police posted aerial images of several pileups on Interstate 55 on Facebook.

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. Monday and became dense around sunrise, he said. Visibility for drivers was down to as low as one-eighth of a mile.

The State Police closed parts of Interstates 10, 5 and 310 on Monday morning and warned that, because of the heavy fog, “drivers should avoid the area if possible and use alternate routes.” Interstate 10 reopened at 2:30 p.m. local time, but portions of Interstates 55 and 310 remained closed later on Monday afternoon.

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.