The supercell was pushing in fast from the west. Wind gusts were approaching a hurricane-like 100 mph. The hilly landscape and limited highway network were not making things easy.
“This is not a scientific term, but it was a mean-looking storm,” said Adam Houston, an atmospheric scientist who helped track that supercell through the Black Hills of western South Dakota in June.
As the storm roared toward the small city of Belle Fourche, the researchers found themselves out of position. They raced through the town to catch up, dodging 1-inch hailstones and collecting a trove of hard-earned data.
“Our ears popped, which means that the pressure was dropping very quickly,” said Houston, a professor at the University of Nebraska-Lincoln and one of the principal investigators on a team of scientists who traveled across the Great Plains this spring to learn more about which storms produce tornadoes and which ones do not.
Tornadoes can form and dissipate rapidly, making them difficult to predict and sometimes impossible to avoid. Hundreds of tornadoes touch down across the country in a typical year, killing dozens of people while destroying homes, tearing up roads and flattening town squares. The most fearsome tornadoes, like the one that hit Joplin, Missouri, in 2011, can have far higher death tolls and can turn large sections of cities into rubble piles.
By chasing storms across the country’s midsection, covering more than 9,000 miles across 11 states, the researchers hoped to gather data that would reveal secrets of tornado formation and eventually improve forecasters’ ability to warn people about coming storms. The project, known as TORUS, short for Targeted Observation by Radars and UAS of Supercells, deployed dozens of university and government scientists, who used highly sensitive instruments to measure structures within supercells, the storm systems that produce many of the most severe tornadoes.
“When you get to the tornado formation itself and why that’s happening and what actually governs it, we’ve been pretty stuck for, actually, I would say about 20 years,” said Erik Rasmussen, a research scientist at the National Oceanic and Atmospheric Administration who helped lead the project with Houston and others. He attributed that lull in discoveries to limitations in computer modeling and the difficulty of collecting good data on real-world tornadoes.
Forecasting tornadoes is a mixture of art and science. Decades of research have allowed meteorologists to warn when there is a risk of severe weather, to pinpoint which storms have the potential to spawn tornadoes and to quickly identify them and issue warnings when those tornadoes emerge. But for all those advances, much remains unknown.
The TORUS researchers were especially focused on air rotations near the ground that can resemble rolling pins. Those distinct rotations have been suggested as a potential determining factor in whether storms will spawn tornadoes. Rasmussen said researchers were hypothesizing “that one of these rolling-pin-type rotations has to form in the right spot, so that it actually finds its way into the strong updraft and can get turned upward into a tornado.”
When the convoy of professors, students and federal scientists set out in late May to begin tracking supercells, they roamed across the Plains, a tornado-prone region that is popular among researchers because of its robust network of rural roads, necessary to get close to the storms, and its relative dearth of large hills, which can block views and hamstring their equipment. Even so, finding the right place to gather data was a perpetual challenge.
On one sunny day in the hills of northern Nebraska, Thea Sandmael set up her team’s radar truck at a promising site, only to see an approaching storm start to dissipate. But what was looking like a wasted effort quickly became a close call.
“We saw this wall cloud kind of moving in, and then it started to produce a funnel, and at that point it was kind of headed towards us,” said Sandmael, a research meteorologist at the University of Oklahoma. “So that was the point where we were like, ‘oh, we’ve got to get out of here.’”
After long days spent driving or waiting in gas-station parking lots for supercells to form, the team would gather at night in small-town hotels to review the latest forecasts. College students and early-career meteorologists mingled with some of the country’s most prominent names in tornado forecasting, sharing dinner and examining data together.
“To kind of get all that knowledge that they’ve created just through their own experiences is really cool, because it’s not necessarily stuff that you learn in classes,” said Morgan Schneider, a doctoral student at the University of Oklahoma who hopes to pursue a career in research meteorology.
By the end of their trip, the TORUS team had collected data from 16 supercells. Analyzing that data — which will be combined with data collected during a 2019 trip and other past research efforts — will probably take years.
The researchers eventually hope to help improve the country’s tornado warning system, a vital but imperfect effort dating back to the 1940s that alerts people when a severe storm could soon hit. With some storms, by the time the system issues a warning, a tornado is already bearing down and residents have only a brief window of time to prepare. On other occasions when all signals point to a possible disaster, forecasters issue urgent calls to take shelter just before the threat fizzles.
“There have been environments where everything seems to be in place, and yet a tornado doesn’t form,” Houston said. “So what is that piece that we’re missing? What is that thing that short-circuits the process?”
One afternoon while the team was stationed in the Nebraska Panhandle, a supercell began to form nearby. The teams raced to their positions. Schneider led a truck full of fellow graduate students whose job was to release weather balloons into the thick of the storm. As their target became clear, they crossed the state line into Colorado and looked for their chance.
“We found this perfect north-south road,” Schneider said. “The precipitation was kind of off to our right, the circulation off to our left, which is exactly where we want to be.”
After a successful balloon launch, they dropped back and saw a series of “gustnadoes” — small whirlwinds that form in thunderstorms — as well as hail so plentiful that it was piled along the side of the road. Other researchers who drove through a nearby town found fallen tree limbs and evidence that a small tornado had touched down.
The day was a reminder, Schneider said, of why their work is so important.