Mississippi is still reeling from the deadly tornado that struck and killed at least 25 people on March 24.
The violent storm was particularly destructive to the small city of Rolling Fork and neighboring areas, leaving torn-up buildings and demolished vehicles in its wake.
The twister formed from a supercell storm—the least common type of thunderstorm, but one that is capable of producing severe weather, including violent tornadoes.
Storm-prediction officials had issued warnings on the storm for several days. The first tornado warning was issued just before 8 p.m. Central time on March 24. As the tornado started approaching Rolling Fork, the National Weather Service (NWS) issued an extremely rare tornado emergency, warning of a life-threatening situation.
Warnings were issued 11 minutes before the tornado struck the small city.
While that doesn’t seem like a lot of time, it is the standard range for predicting a tornado.
Forecasters can predict storms capable of producing tornadoes in advance, and weather-forecasting systems are the most advanced they have ever been
But tornadoes can form within just a few minutes, and it remains extremely difficult to predict when and where they will happen.
So why are these destructive systems so difficult to predict, even with the advancement of weather-forecasting systems?
Dr. Jana Houser, an associate professor of meteorology at Ohio State University and atmospheric scientist specializing in the study of supercells and tornadoes, told Newsweek that there are essentially two levels to forecasting tornadoes.
“The first level, so to speak, is when we are investigating environments that are potentially favorable for tornadoes. We are quite good at this actually! We have learned, over the past several decades, what environmental parameter space is required for most tornadoes to form,” Houser said. “This allows us to identify and characterize environments several days into the future where tornadoes might be possible. The second level is a bit more complicated.”
This is when storms start to form, and scientists begin trying to determine whether a tornado is going to happen or not.
“Scientists still don’t quite understand all of the nuances in figuring this out and differentiating between storms that are occurring in essentially the exact same environment but one produces a tornado and another neighboring storm does not, even when they’re separated by distances that are relatively small,” Houser said. “So it’s the part of looking at a storm and figuring out if it’s going to produce a tornado in the next 15 minutes that really is challenging!”
A 2010 study published in the Journal of the American Meteorological Society found that, during a five-year period, some 26 percent of all tornadoes to occur in the U.S. were not forewarned by the NWS.
However, most of these unwarned tornadoes were weak. The study also found that 11 percent of all tornadoes that caused fatality occurred from non-warned tornadoes.
There are also a lot of false alarms with tornadoes.
“What operation weather forecasters do is they take the environmental conditions into consideration while looking for cues in ongoing storms, mostly using radar data,” Houser said. “If they see rotation starting to develop in a storm, and that storm is in an environment that is particularly favorable for tornado formation, they will often issue a warning. The challenge is we don’t know with strong confidence whether or not that storm will actually produce a tornado. This is why there ends up being a lot of false alarms. Many storms which are warned, do not end up actually producing tornadoes.”
In many cases, the predictions have been accurate and correct. One example is was the tornado that hit Western Kentucky on December 10, 2021. The tornado caused at least 57 fatalities.
In this case, forecasters predicted the tornado would hit Mayfield—one of the towns most severally damaged by the tornado—at 9.30 p.m. This is exactly the time the tornado ended up hitting.
This shows the vast improvement of technology in recent years.
Before the emergence of certain forecasting technologies in the late 1980s, federal data showed that scientists were able to issue warnings for just over half of 88 severe tornadoes, as reported by the New York Times. Nowadays, 97 percent of the time, tornado warnings are issued before they hit.
But sadly, warnings do not prevent them from being deadly.
How dangerous are tornadoes?
As sadly seen in Mississippi, tornadoes can be deadly. According to data from the NWS, in an average year there are 80 deaths and 1,500 injuries caused by tornadoes in the U.S.
With the case of Mississippi, it turned out the conditions were perfect for the tornado to last a long time, allowing it to cause more destruction.
“The conditions were just perfect for the storm to last a very long time, and that is usually not common,” Lance Perrilloux, a meteorologist with the NWS in Jackson, Mississippi told the BBC. “It caused that tornado to just wreak havoc for a long distance.”
Although this particular tornado was more destructive than most, any tornado is a hazard.
“Tornadoes are so dangerous because the wind speeds within them can be incredibly high. The fastest observed winds in the world have been associated with tornadoes,” Houser said. “The average tornado has wind speeds on the order of 100 to 120 mph. The most violent and strongest tornadoes can have winds that exceed 300 mph.”
Subsequently, when these wind speeds hit structures, it causes them to rip apart. The winds then cause debris to fly through the air.
“That debris creates an additional threat to other buildings around because then you have projectile objects that crash into buildings, stores, bridges, etc,” Houser said. “In fact, most of the deaths that occur associated with tornadoes are as a result of blunt force trauma to the head associated with flying debris.”
How do tornadoes form?
Any kind of severe thunderstorm has the potential to produce a tornado, but most form from a supercell storm. However, these storms are quite rare.
Supercell storms are violent storms that last for a long time, circulating from above. In these storms, the circulation aloft grows in an upwards direction through the storm, and then also downward, towards the floor.
Most supercell storms cause violent weather, but only around 30 percent actually result in tornadoes, the NWS reported.
“Tornadoes form in a pretty complicated manner. Tornado formation requires moderately strong rotation to be present at the ground before the tornado itself ever forms. The source of this rotation is not entirely clear, nor is it necessarily the same for every single tornado,” Houser said.
“But we believe, most of the time, it gets there from the forward (or northeastern) part of the storm, where downward-moving rain and cooled air meets warmer, more buoyant air from the environment. This boundary creates horizontal spin like a bike tire, and that spin gets transported around the backside of the storm, where it encounters a downward-moving zone of air called the rear flank downdraft.
“That downward-moving air now pushes this rotating air to the ground and simultaneously acts to reorient it from spinning like a bicycle tire to spinning like a top. When this area of rotation becomes collocated underneath the strong upward-directed air, moving into the storm’s updraft, the rotation is concentrated and stretched upward in a manner consistent with an ice skater, pulling in her arms. The rotation then quickly intensifies and moves upward with time forming a tornado.”
Why are there so many tornadoes in the U.S.?
Tornadoes happen in many countries across the world.
However, they are most common in the U.S. On average, the U.S. receives 1200 tornadoes per year. Why is this?
“The reason why they are so prolific here and not in other places fundamentally has to do with the geography of the U.S. The environmental ingredients needed to form a tornado include, warm and moist surface, air, cold air above that warm surface air, some sort of atmospheric feature to get air, moving upward, and a strong change in wind, speed, and direction with height. The central and southern portion of the U.S. is perfectly positioned for this match-up of conditions.
“The Gulf of Mexico, for example, provides a moisture source. And the Rocky Mountains act as a natural wall that inhibits jet streams.
“This acts to transport warm, moist air toward the north, across the central plains and southern portion of the United States. Furthermore, we frequently have cold air aloft that pledges south word with the large-scale jetstream pattern,” Houser said.
“This occurs in what we referred to as atmospheric troughs. The troughs are home to both cold air and strong winds. Because we have the large, relatively cold landmass of Canada to our north, all of the ingredients can really come together across the central and southeastern U.S.”
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about tornadoes? Let us know via [email protected].
The post Why Tornadoes Are So Difficult to Predict appeared first on Newsweek.