What is a multi-vortex tornado? Why the EF3 storm that hit New Orleans area is unusual
A rare weather event happened Tuesday evening: two confirmed tornadoes touched down in the New Orleans area Tuesday, part of a storm system that moved from Texas and continued across the southeast, bringing with it possible risks of tornadoes, hail and flooding.
Though both twisters caused damage to some extent, one had peak winds of 160 mph and lifted homes, flipped cars and even took a life during its 11-mile journey from Jefferson Parish to New Orleans East.
The tornado, which left the town of Arabi in shambles, was classified as an EF3 and considered “strong” by meteorologists. As multiple photos and videos of the massive twister were shared on social media Tuesday evening, the storm was also described as a multi-vortex tornado.
What exactly is a multi-vortex tornado, and how common are they? WWNO spoke with a climatologist, who said they’re just as scary as they sound.
What exactly is a multi-vortex tornado?
Two things are needed for a tornado to form, according to Jill Trepanier, who works as an LSU climatologist and associate professor in the department of Geography and Anthropology
A friction-induced environment that forces air to flow in multiple directions must pair with a really strong thunderstorm, she said.
“If you have those two conditions, existing at one time, plus all of the additional moisture and heat that's required, there's a good chance you're making a tornado,” Trepanier said.
A multi-vortex tornado is a tornado that contains several vortexes revolving around inside of the main vortex. Those types of tornadoes cause the damage seen in St. Bernard Parish, where swaths of extreme damage were right next to minor damage.
Trepanier also said with the Louisiana coast going from open ocean to swamp land to landscape, these different environments have different amounts of expected friction that lends itself to the creation of this type of tornado.
“You go from a flat surface to a bumpy surface to an even bumpier surface to create this difference in drag that can lead to the creation of multiple tornadoes within a tornado,” Trepanier said.
When was the last time a tornado of this strength occurred?
Since records started in 1950, only one other EF3 has been recorded in the New Orleans area, according to National Weather Service New Orleans. That happened on Feb. 7, 2017, with a path length of 10.1 miles.
No deaths were reported from that tornado, but there were 33 recorded injuries.
Tuesday's EF-3 tornado had an est. peak wind of 160 mph, making it the strongest tornado to impact Orleans/Jefferson/St. Bernard Parishes on record. It's also only the second F-/EF-3 or higher tornado. A small section of New Orleans East were impacted by both EF-3 tornadoes. pic.twitter.com/IlEFLjLHGq— NWS New Orleans (@NWSNewOrleans) March 25, 2022
Is it rare to have two confirmed tornadoes happen in such close proximity in this area?
According to Trepanier, it is unusual to have two confirmed tornadoes occur in such close proximity here in New Orleans — this scenario would be more common in areas like the Great Plains, also known as Tornado Alley.
Trepanier said that it was unusual to see the cold front coming through to maintain the level of power needed to develop two tornadoes.
“I think what is kind of unique about this scenario is normally you don't have this strong of a cold front that persists as it moves over the open water. It'll start to grab a lot of heat, and it'll start to kind of transition into something else,” Trepanier said. “But to get two of them right along that coastal interface, at such a high strength, is relatively unprecedented.”
Trepanier also said that usually there's not enough strength between the two different air masses, the cold in the north and the warm in the south, to create really impressive tornadoes, such as a multi-vortex twister. If Louisiana gets a tornado, it typically occurs during early spring, but are minor, with EF0 or EF1 categorizations like the second confirmed tornado Tuesday that touched down near Lacombe.
How has this weather system been able to maintain so much destructive power?
Earlier, we saw the destruction that the weather system brought through Texas and later in Mississippi. There was a huge push from the polar jet stream from the far north into the south during a time when there was a lot of moisture available in our area.
Trepanier said that while Texas is overall a drier landscape, as the system moves closer to the Gulf, more moisture gets pulled from the Gulf of Mexico, amplifying its ability to make clouds and maintain its power.
“It just grabbed all of what it needed from the environment to make these really impressive, big thundering clouds, which then led to some of that spin, which pushed into the formation of tornadoes,” Trepanier said.
Trepanier said that tornado research is still relatively young, with about 30-40 years of good data.
But that research suggests that around the United States, we might not see more tornadoes, but we could experience more extreme twisters.
She doesn't know whether or not these events will happen more frequently in the future, but urges people to be mindful that these events can occur in our area.
“I definitely think it's something that is worth paying attention to. I don't know that I would say we're going to get more, but we are definitely not out of the woods of not receiving them,” Trepanier said.
Trepanier also focused on the lack of measures in place for people in Louisiana to be ready for tornadoes, such as operational sirens and better alert systems.
“Louisiana is very used to heavy rain. We're very used to hurricanes, as sad as that is,” Trepanier said. “But we're not used to tornadoes. And we don't even have very good warning mechanisms at play for tornadoes.”