A twist on tornadoes
If regions east of the Mississippi are the dartboard of the future, ‘the bull’s-eye is Chicago,’ says extreme-weather expert at NIU
On a Sunday in late June, Tom Shaw and his relatives gathered at his sister’s South Bend home for a poolside birthday celebration for his 8-year-old nephew. The family was forced inside as the sunny weather ceded to heavy bursts of rain followed by a spooky calm.
Then the clouds above South Bend began to rotate.
“I looked out, and the clouds directly above us are real low and you can see them starting to spin,” said Shaw, 39. “I had a real bad feeling.”
Moments later, a tornado as
wide as two football fields touched down a mile north of the home, and Shaw swiftly ordered family members to head for the basement. The twister blazed a 2-mile trail through the city’s south side, downing power lines, uprooting trees and pulverizing an empty day care facility, leaving behind a jumble of wooden beams, roof shingles and children’s toys.
Only a month earlier, a flurry of thunderstorms in late May unleashed at least 23 weak tornadoes across Illinois over a two-week period. On Memorial Day, darkened clouds began to swirl over Romeoville, and a tornado packing 85 mph winds briefly spun through a subdivision and due north of Lewis University Airport before dissipating.
In a study published last year, Northern Illinois University assistant professor Victor Gensini examined nearly four decades worth of tornado reports across the U.S. While he found the overall number of significant tornadoes has remained relatively flat nationwide, the Midwest and the Southeast are
seeing more of them.
Although the states that make up the Plains — Texas, Oklahoma and Kansas, often referred to as Tornado Alley — still see the lion’s share of significant touchdowns, data shows the region has experienced fewer cyclones between 1979 and 2017. Meanwhile, the Midwest and Southeast are seeing more significant tornadoes — those carrying 86-plus-mph winds — marking an intriguing but poorly understood eastward trend.
Illinois has also seen about 100 more tornadoes per decade, according to Gensini, a number that includes weaker tornadoes that fall below the 86-mph bar.
If this progression continues, experts say, it could foreshadow more costly disasters and perhaps higher death tolls as tornadoes become more frequent near broadening suburbs and already densely populated city centers like Chicago, which has largely been spared from calamity in recent memory. Elsewhere, small and midsize cities, like Jefferson City, Mo., and Dayton, Ohio, are still recovering from the devastating effects of tornado strikes.
“East of the Mississippi River, the population density across the United States greatly increases,” Gensini said. “If you have more tornadoes in that area, you are throwing more darts on the dartboard, and you’re eventually going to hit the bull’s-eye.
“If you look at the three largest cities in the United States — New York, LA and Chicago — out of those three, which has the highest probability of having a tornado strike? The answer is Chicago. Certainly there are other cities that have greater chance of getting a tornado: Oklahoma City, Wichita, Omaha. But those cities don’t even have close to the population that Chicago has. In other words, the bull’s-eye is Chicago …”
“If you have more energy (moisture and instability) in the wintertime, does this mean that we’re going to start seeing more in the cooler months? We don’t know. These are all potential theories.” — Patrick Marsh, National Weather Service meteorologist, speaking of tornadoes
Urban sprawl increases risk
This May, the United States saw 555 preliminary tornado reports, the most on record for the month of May. The count will be finalized later in the year.
Over the years, scientific research has suggested a warming atmosphere has contributed to torrential rainfall, overwhelming flooding, crippling drought, uncontrollable wildfires and intensifying hurricanes. But how climate change might affect tornado activity in the United States remains a question.
Any rise in Midwest tornado activity will be exacerbated by urban and suburban sprawl. The growth of housing and commercial development amplifies the risk and exposure of a tornado strike, according to Stephen Strader, assistant professor of geography and the environment at Villanova University. So, although the central Plains see the most tornadoes strikes, the Midwest stands to lose the most.
Researchers are studying how “the environment is changing, but we also have to consider how society is changing,” Strader said. “That’s going on at the same time. The same tornadoes going through a cornfield in 1930s and ’40s, now they’re going through the hearts of subdivisions.”
Since 1980, the U.S. has endured 246 weather and climate disasters in which damages have exceeded $1 billion, according to the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. These events have collectively cost $1.6 trillion. And disaster costs are accelerating over time, according to Strader.
“Billion-dollar disasters are more frequent because we have more stuff,” Strader said.
A prime example is the deadly tornado with 200-plus-mph winds that tore through Chicago’s western suburbs in 1990. On Aug. 28, 1990, the twister rumbled through Plainfield on its way toward Joliet, killing 29 people and injuring 350. In its path, the tornado left Plainfield High School destroyed, St. Mary Immaculate Church and rectory flattened, and 470 homes razed.
At that time, the population of Plainfield was around 4,500, and it had 1,700 housing units, according to census data. Today, the village has an estimated 44,000 residents and 12,700 housing units.
Cropping up in bunches
It’s unclear whether this upward trend in Midwestern tornadoes and decline in Tornado Alley is a natural occurrence or could be driven by climate change. However, Gensini said the findings are consistent with what scientists would expect as temperatures continue to rise.
“We would expect the southern Plains — Texas and Oklahoma — to begin to dry out in the next 30 to 50 years, become a more arid climate,” Gensini said. “And along with that, the storm track would shift eastward. There are some hypotheses we have, but we’re not able to say for certain what’s driving that trend. It’s very possible in the next 40 years that the trend will reverse itself.”
Scientists are noticing that more tornadoes are cropping up in bunches, with fewer overall days with twisters but larger outbreaks on days they do occur.
That certainly was the case in late May, when there were 13 straight days with eight or more tornadoes, according to the National Weather Service’s Storm Prediction Center.
“Tornadoes require big, explosive thunderstorms,” said Patrick Marsh, a weather service meteorologist in Norman, Oklahoma. “It removes quite a bit of energy out of the atmosphere, and you have to replenish that. So if you have two or three days with decently big tornado activity, the atmosphere has to take a break and reload before it can do it again. We didn’t see that this time. The atmosphere was able to continue to produce these thunderstorms day after day after day.”
Difficult to track
The key ingredients for tornado creation are moisture, wind shear, upward lift and atmospheric instability resulting from a rising warm air mass trapped underneath a cold air mass. Together, they compel the base of a thunderstorm to swirl and extend downward into a funnel cloud.
A warming atmosphere could mean more moisture and instability, resulting in more energy for tornado formation. But some research also suggests that wind shear, the change in speed and direction with elevation, could decline.
Scientists are unsure how these potential changes could pan out. Though peak tornado activity occurs in May and June, tornadoes have been observed in every month of the year. However, there is concern that climate change could alter tornado season, especially in the winter months when wind is plentiful as the polar jet stream dips into the Midwest.
“If you have more energy (moisture and instability) in the wintertime, does this mean that we’re going to start seeing more in the cooler months? We don’t know. These are all potential theories,” Marsh said.
On Dec. 1, all of those factors came together. One week after a blizzard dumped more than a foot of snow on parts of the state, temperatures spiked into the 60s, and the dew point rivaled a summer afternoon near Chicago’s lakefront. Severe storms spawned 29 tornadoes across the state, the largest December outbreak since 1957. A tornado carrying winds up to 155 mph rumbled through the heart of Taylorville, razing nearly three dozen homes and damaging hundreds of others.
The main obstacle to unraveling tornado trends remains the reliability of long-term data.
Whereas scientists can more easily track large weather events, like drought, flooding, hurricanes and wildfires, tornadoes are difficult to track because of their relatively small size and short manifestation. Even the largest tornadoes are less than 3 miles wide, and the longest-lasting cyclone was about 3½ hours, a blip in time and space compared with hurricanes that can last several days and are typically 300 miles wide.
Despite improvements in technology, tornado records rely on witnesses and weather spotters to confirm a touchdown, since weather radar can only detect rotation in storm clouds and when debris is whipped up.
And tornado spotting can be challenging.
Even though tornadoes are the most violent atmospheric storms on Earth, they can be difficult to observe. Because wind is invisible, it may be hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris. In some instances, this funnel can be shrouded by downpours of rain.
The same traits that make tornadoes hard to spot also make them extremely dangerous.
For Shaw, the South Bend resident, the tornado materialized without warning. He remembers only faintly hearing tornado sirens in the distance around the time the twister touched down. After driving by the wreckage and downed trees, he said it’s a wonder no one was hurt or killed, especially considering how fast the tornado moved through.
“I’ve lived here for 40 years and always been told growing up that South Bend won’t get hit, because we’re in a valley here. But it’s obvious to see it definitely can.”