Louisiana super fog is wreaking havoc, causing delay highway wrecks

Parts of Interstate 10 in southeast Louisiana were closed Wednesday because of “super fog” — a mix of dense fog and smoke. It comes after a deadly super fog accident Tuesday as well as one last month, when a 158-vehicle crash killed seven people and injured dozens.

On Wednesday morning, the National Weather Service issued dense-fog advisories for southeast Louisiana, including around New Orleans, cautioning that visibility could drop below 100 feet. On X, formerly Twitter, the Weather Service wrote that super fog was affecting the Causeway along Lake Pontchartrain as well as eastern Orleans Parish and making travel “very hazardous.”

The advisories were allowed to expire at 10 a.m. in most areas as sunshine helped to dissolve the fog, and the New Orleans Police Department said all road closures had been lifted.

How does super fog form?

Super fog can form suddenly and reduce visibility below 10 feet. Sometimes it forms on days that otherwise feature little to no fog, catching motorists off guard and leading to chain-reaction crashes.

‘Super fog’ caused a deadly vehicle pileup in Louisiana. What is it?

In the case this week, the fire responsible for the super fog in Louisiana is the New Orleans East wildfire, which is burning in marshy areas and has grown to 200 acres. More super fog is possible Thursday, but the potential for light rain will lower the risk after that.

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Tuesday’s super fog caused crashes involving 11 vehicles, left one person dead and shut down I-10 for hours. The areas most affected were between Irish Bayou and Michoud Boulevard.

Research suggests super fog forms during the smoldering phase of brushfires or wildfires as diminishing heat helps release water vapor stored in burning organic materials. Cool air outside the burn zone acts to chill fire-heated water vapor, transforming the gas into thick condensate, which clouds the air.

That’s exactly what is happening with the New Orleans East wildfire, which could burn for months.

Here are some pictures Chase Ward shared with @WWLTV this morning. This was on I10 where that super fog, fog and smoke from a wild fire in the area, dropped visibility to zero. pic.twitter.com/mBkpjUmwvD

New Orleans CBS affiliate WWL (Channel 4) reported that, on Tuesday, fire officials had eight pumps blasting thousands of gallons of water per minute onto the fire. Each pump can move about 3,000 gallons of water per minute. Their goal is to saturate the soil. Unfortunately, that also leads to even more hot vapor, which can support the formation of super fog.

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In addition, the burning of live and dead fuels adds condensation nuclei — tiny specks that act as “seeds” for water vapor to condense onto — to the air. That results in more fog droplets. It is estimated that during a super fog event, every cubic meter of air contains about 5 grams of moisture — the weight of two pennies.

Fires are burning in Louisiana as it grapples with the worst drought in the country; more than two-thirds of the state is dealing with a top-tier “exceptional” drought — the worst category — according to the federal drought monitor.

Past super fog incidents

It’s not the first time the area has been plagued by super fog. In December 2011, a marsh fire in New Orleans triggered an accident that caused two deaths and 61 injuries.

Here’s a look at several damaging and/or deadly super fog events that have occurred across the country:

• In January 2008, super fog from a nearby prescribed burn caused a 70-car pileup on Interstate 4 near Gainesville, Fla. Five people died and 38 were injured.
• In June 2008, super fog occurred on U.S. 17 in North Carolina between Dixon and Verona, causing an accident. A volunteer firefighter and a sheriff’s deputy responding to the accident were struck by a truck and died.
• In March 2012, a super fog event occurred between Supply and Bolton, N.C., along State Highway 211. The culprit was a prescribed burn. While a vehicular accident resulted, there were no injuries.
• In January 2012, 10 people were killed in 20 crashes on both the northbound and southbound sides of Interstate 75 in Gainesville. Super fog formed because of smoke from a wildfire on the Paynes Prairie. Seven tractor-trailers and 12 cars were involved.
• In October 2016, super fog caused a multivehicle crash along Interstate 40 in Arizona near the town of Parks.
• In November 2016, super fog caused an accident near Slade, Ky.

Jason Samenow contributed to this report.

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