JOPLIN, Mo. — Disaster officials estimate the killer tornado that tore through here two weeks ago caused as much as $3 billion in damage.
They said the twister destroyed or seriously damaged 18,000 vehicles, 8,000 housing units, 400 business buildings, several schools, two fire stations and a hospital.
With winds ranging beyond 200 mph, the twister cut a six-mile long, half-mile wide swath through the city's south side.
At least 141 people died, making it the deadliest U.S. tornado since 181 deaths in Woodward, Okla., in 1947.
The experts said the tornado's overall path was 13.8 miles long, but built up intensity and ferocity as it approached, then ripped through Joplin, a city of 50,000 in southwest Missouri, at dinner time on May 22.
"It remained on the ground the entire length of Joplin," said Steve Runnels, National Weather Service meteorologist. "That led to it being more destructive."
A tornado research team from Iowa State University, in Joplin within hours of the twister, said it gained in intensity from an EF-3 (130-165 mph winds) to an EF-4 (165-190 mph) to the ultimate EF-5 (more than 200 mph)as it crossed the city.
Researcher Partha Sarkar said an EF-5 tornado is so rare that only 56 of them have been recorded in the U. S. since the Weather Service began keeping records in 1950.
Oddly, he said, there have been four EF-5 tornadoes this year.
Sarkar said an EF-5 tornado is "born at 65,000 feet" from the clash of cool air from the north, warm and humid air from the Gulf of Mexico, and dry air from the west. This year, he said, there has been unusual drought conditions in the west and warmer-than-normal water in the Gulf.
The Weather Service's Runnels said a likely major factor in this year's record outbreak of tornadoes across the south and midwest is La Nina, the lower-than-normal sea surface temperature of the Pacific Ocean that, in turn, affects the jet stream of air moving across the country.
He said La Nina years are typically above average for tornadoes, especially violent ones.
Joplin's tornado was so ferocious that it shifted St. John's Medical Center hospital from its foundation, flattened steel structures, tossed cars several feet in the air, and ripped concrete parking lot stops from their rebar pins.
Sarkar said the Iowa State University research team aims to learn valuable lessons from the destruction caused by the Joplin tornado, and come up with ways to improve chances of suviving such storms.
He said the team found evidence of shoddy construction of homes and businesses, and few safe rooms within the structures in the path of the tornado.
According to the local assessor's office, only 18 to 20 percent of the buildings in Joplin have basements or storm cellars even though the city is in so-called tornado alley.
Sarkar said the usual objection to requiring safety features in buildings is the additional cost.
"But then," he asked, "why put an air bag in a car?"
The Iowa State researchers said homes in tornado alley can be made more resistant to violent winds through building codes that require hardened walls, safe rooms, and simple hurricane straps that reinforce rafters to wall studs.
Even then, said the Weather Service's Runnels, there is "some degree of luck" to surviving an EF-5 tornado like the one that struck Joplin.
He said warning people of approaching tornadoes is still helpful, but only if they hear and heed the sirens.
Two warnings were sounded in Joplin, one nearly a half-hour before the tornado struck, and the other 20 minutes in advance. Many of the people who died were found in their cars or trucks.
The federal Storm Prediction Center also issued a tornado watch for the Joplin area four hours in advance of the twister's arrival.
In short, said Iowa State's Sarkar, Joplin and other cities and towns in tornado alley need tougher construction codes so homes, schools and businesses can withstand violent twisters.
"Schools, hospitals, other essential structures -- we dcannot afford to lose them," he said. "These are places people go to for help."
Details for this story were provided by the Joplin, Mo., Globe.