When Fog Met Fire: The Deadly Superfog of New Orleans and What We Learned

From late summer 2023 into early fall, a combination of prolonged extreme heat and minimal rainfall produced an unprecedented drought across southeast Louisiana. The severe drought heightened the risk for rapidly-developing wildfires and slow-burning marsh fires t. Fog events frequently occur in the fall and winter across the region due to the abundant moisture and cooler air masses moving over the warmer waters of tidal lakes, nearshore sounds, and wetlands. The ongoing fires, fueled by the persistent drought, created a favorable setup for superfog events as the climatological fog season began. Superfog occurs when smoke and moisture from burning organic matter combine with fog, resulting in areas of extremely low visibility.

On the morning of 23 October 2023, a light southeasterly wind carried smoke from a marsh fire located just east of New Orleans over Lake Pontchartrain and Lake Maurepas. As fog developed over these lakes, smoke particles from the marsh fire mixed with the fog, producing superfog that reduced visibility to near zero during the morning commute. This dangerous scenario resulted in a one-mile long, 150-car pileup on Interstate 55 that caused eight fatalities and 63 injuries.

This tragic event significantly changed the operational approach of local meteorologists from the National Weather Service (NWS). Heightened safety concerns and media attention led partners to be more proactive in closing major interstates, government buildings, and schools on days when superfog was forecast. Operational forecasters utilized advanced fire detection tools to track active fires in near real-time and target threat areas for superfog formation downwind of the smoke sources. Data from the Fire Information for Resource Management System (FIRMS), incorporating a variety of satellites, including VIIRS, MODIS, and GOES-16, enabled forecasters to detect not only large, intense hot spots, but smoldering marsh fires like the one that contributed to the 23 October superfog event. This dataset was also used to help diagnose the analysis quality of High Resolution Rapid Refresh (HRRR) smoke dispersion model runs, allowing forecasters to make informed decisions on whether or not to incorporate HRRR forecasts into IDSS briefings.

As a result of these adaptations, efforts were made to reduce the impact of subsequent superfog events on the community, and the NWS received positive feedback from partners. Additionally, focused outreach was conducted to improve the public's understanding of superfog, clarifying both what it is and what it isn’t, as well as highlighting the associated threats. This outreach further enhanced the community's ability to respond effectively to such events. Targeted IDSS threat-based briefings and graphics to local core partners each day when superfog potential was identified. This information was used by EMs and DOT to close fog-prone bridges and overpasses in order to mitigate the risk of another pileup. This presentation will share the lessons learned and the best practices adopted following this deadly superfog event, with the goal of providing insights that can enhance future risk mitigation strategies in similar situations.