Forty years later, the numbers still boggle the mind.
Nearly 150 tornadoes struck in 13 states over an 18-hour period in 1974, spanning April 3 and 4, from Canada to the Deep South. There were at least 15 tornadoes on the ground at the same time.
Several of the tornadoes from what became known as the Super Outbreak were among the most severe ever recorded, according to an assessment conducted by the National Oceanic and Atmospheric Administration. The outbreak killed 330 people, injured more than 6,000 and caused more than $1 billion in damage.
On average, there are about seven violent tornadoes – those measuring EF-4 or EF-5 on the Enhanced Fujita Scale of tornado strength, with winds of at least 207 mph – in any given year. But the Super Outbreak had 30 tornadoes measuring EF-4 or stronger in a single day.
“The outbreak was the benchmark by which all other outbreaks are judged,” Greg Forbes, the severe weather expert for the Weather Channel, told a crowd of hundreds of people last month at ChaserCon, the national stormchasers convention in Denver.
Forbes was studying under Ted Fujita at the University of Chicago at the time and became part of the team that conducted a damage survey of the outbreak.
In retrospect, the outbreak wasn’t just a dark day for the cities struck by tornadoes; officials say it was the catalyst for sweeping changes in warning technology and understanding how tornadoes work.
“The outbreak was very, very significant,” said Les Lemon, who was working at the National Severe Storms Laboratory at the time of the outbreak and was part of the team that surveyed more than 2,500 miles of tornado paths. “It certainly increased the awareness of tornadic storms.”
The National Oceanic and Atmospheric Administration survey of the outbreak and the effectiveness of the tornado warnings pointed out numerous shortcomings in technology that hampered meteorologists and those trying to warn the public.
“One thing they were critical of was radar technology and how limited it was,” said Don Burgess, a young researcher who was working for the NSSL in Oklahoma at the time of the outbreak.
He was already working on research for what would become Doppler radar.
The outbreak “gave us another bump to continue that research,” Burgess said.
It took nearly 20 years for Doppler radar systems to start being installed in National Weather Service branches around the nation, but weather officials say the upgrade is difficult to overstate.
Going from the radar used during the Super Outbreak to Doppler was “like going from the Stone Age to the Space Age,” Lemon said.
The National Severe Storms Forecast Center in Kansas City used a bank of teletype machines to transmit weather alerts all over the country in the mid-1970s, Lemon said, but the machines were overwhelmed by all the watches and warnings being issued on April 3 and 4. They typed 55 words per minute, weather officials said.
“If you’ve got 15 tornadoes at once, the teletype writers couldn’t keep up,” Forbes told the crowd at ChaserCon.
The teletype machines fell more than an hour behind, in part because watches and warnings weren’t given priority over routine messages. More than two dozen warnings didn’t reach their destinations until after the warnings had expired, according to the national survey of the outbreak.
Faster teletype machines capable of filtering non-essential messages were developed in the wake of the outbreak, weather officials said.
“As a result of the service assessment, Kansas became the first state to get a ‘high-speed’ weather wire,” said Mike Smith, a Wichita-based senior vice president for AccuWeather.
The wire could transmit 300 words per minute and would give priority to tornado warnings. Now, satellite uplinks make communications almost instantaneous, said Brian Smith, warning coordination meteorologist for the National Weather Service branch in Omaha.
Spotter networks became common in Kansas after the Udall tornado of 1955, but they were scattered elsewhere in the country. The Super Outbreak changed that, Brian Smith said.
He was a high school student in 1974 and was a spotter for his hometown 35 miles west of Chicago on April 3. He saw a couple of squall lines that day, he said, but no tornado.
Weather radios were something found only in a few big cities prior to 1974, he said. They were in great demand after the Super Outbreak.
Schools in Tornado Alley routinely practiced tornado safety drills, Brian Smith said, but not elsewhere. The damage survey in 1974 revealed that schools in Xenia, Ohio, had never conducted tornado safety drills.
The tornado that hit Xenia on April 3 killed 32 people on its 32-mile path and damaged or destroyed about half the structures in the town of 27,000 people. Among the buildings hit were seven of Xenia’s 12 schools, though classes had been let out for the day an hour before the tornado struck.
“Now there’s a big emphasis on safety in our schools,” Brian Smith said.
Severe weather safety education was emphasized in areas outside of Tornado Alley after the outbreak, he said.
“Local communities really got into purchasing more outdoor warning sirens,” he said.
The federal government expanded its radar network after the outbreak, adding supplemental radar to fill in gaps, Brian Smith said. That supplemental radar was important, he said, because “it took a long time to finally get the Doppler radar into the field.”
Federal funding before the outbreak had dwindled to almost nothing, prompting Forbes to ponder a career change.
“But for the Super Outbreak of ’74, I might have become a hurricane expert rather than a tornado expert,” he said.
Assessing damage from the air – using Cessna airplanes because their high wings above the fuselage allowed the surveyors unobstructed views of the ground – researchers were stunned by what they saw:
• Physical confirmation of suction vortices inside large tornadoes, inside which the worst damage occurs.
• “Families” of tornadoes produced by the same thunderstorm.
• One tornado path after another, adding up to more than 2,000 miles.
“There were so many of them,” Lemon said. “That was shocking.”
He had been doing tornado damage surveys for at least five years, and “I’d never seen anything like that,” he said.
A multiple-vortex tornado was captured on film during the outbreak, adding visual confirmation to what the damage paths indicated, researchers said.
“Dr. Fujita got very excited about those,” Lemon said. “That added another detail” to understanding what tornadoes can do.
“It really opened up a lot of the the work on the suction vortices,” he said.
Before the outbreak, Forbes said, multiple vortices within large tornadoes was more a theory than a fact.
Worried about the dangers large tornadoes pose to nuclear power plants, the Nuclear Regulatory Commission funded a great deal of research into tornado strength, Brian Smith said. Fujita had been using the scale to measure tornado strength for a few years prior to the outbreak, but it became accepted as the standard gauge following the outbreak. It has since been embraced by mainstream culture.
As the decades passed, weather officials wondered whether there would ever be an event to rival the Super Outbreak of 1974. They got their answer in 2011, when more than 200 tornadoes touched down over a four-day period in late April in the Deep South. More than 315 people were killed.
A month later, an EF-5 tornado killed more than 160 people in Joplin, Mo. It was the highest death toll from a single tornado in more than half a century. Those tornadoes sent a sobering message, weather researchers said.
“Despite all of our new, much-improved warnings and our much-improved ability to detect tornadoes,” Forbes said, “if the most violent of tornadoes hits a highly populated area, we can still have death rates just as bad as we had back in the stone ages prior to the Super Outbreak.”
That’s what makes awareness and preparation so important, weather officials said.