Mist clung to downtown New Orleans on Wednesday morning, December 18, as the National Weather Service (NWS) issued a dense fog advisory.Footage posted online shows the Louisiana city covered in fog as the day began.The NWS urged commuters to exercise caution when traveling.On Tuesday, dense fog caused a pileup of cars on the Lake Pontchartrain Causeway, injuring dozens of people. Credit: @davidnola via Storyful