Ricky Carioti/The Washington Post via Getty Images
Shown is the storm shelter that Gary and Ferrell Mitchusson used to ride out a massive tornado on May 21, 2013 in Moore, Ok. Their home was completely destroyed in the massive tornado.
Deadly tornadoes have lashed the United States for centuries. Most of the worst occurred before modern warning systems existed, although one occurred almost exactly two years before the deadly twister that struck Oklahoma on May 20.
The deadliest tornado in U.S. history, the Tri-State Tornado of March 18, 1925, ravaged 219 continuous miles of Missouri, Illinois and Indiana. Nearly 700 people lost their lives in that single tornado, according to NOAA. However the twister was not officially classified by NOAA as an EF5 -- the most damaging type -- because of a lack of data, nor were there official records of wind speeds.
On May 22, 2011, the deadliest tornado yet recorded by the new Enhanced Fulita Scale struck Joplin and killed 158 Americans, making it the seventh deadliest in U.S. history. Winds exceeded 200 miles per hour as the EF5 tornado demolished a path that was 22.1 miles long and up to 1 mile wide.
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The second deadliest tornado in U.S. history whipped along the Mississippi River on May 2, 1840, ending 317 lives, according to NOAA’s Storm Prediction Center. The tornado killed hundreds on boats and barges on the river until striking Natchez, where the storm killed dozens more. Like all tornadoes from before 1950, NOAA lacks sufficient data to classify the Natchez tornado as F5 or EF5.
St. Louis, Mo.
St. Louis suffered a tornado’s wrath on May 27, 1896, when at least 255 people died. A study published in Weather and Forecasting estimated that the tornado cost $2.2-$2.9 billion in 1997 dollars when adjusted for inflation and wealth increases, making it the costliest tornado in American history. The death toll made it the third deadliest.
On April 5, 1936, the fourth deadliest tornado in U.S. history struck Tupelo, Miss., and killed 216. A total of 436 people died in the outbreak of 17 tornadoes that included the Tupelo twister. Tetsuya Fujita of the University of Chicago and Tom Grazulis, head of the Tornado Project, retroactively rated the Tupelo tornado as an F5 on the scale invented by Fujita.
The same storm system that lashed Mississippi in 1936 continued on to Georgia where it unleashed the fifth deadliest tornado in U.S. history and killed 203 people in Gainesville. Fujita and Grazulis rated this tornado an F4, meaning winds reached 207-260 miles per hour.
Oklahoma is no stranger to tornadoes. The sixth deadliest on record struck on April 9, 1947. The storm nearly destroyed the towns of Higgins and Glazier. In Woodward, Okla., 100 city blocks were destroyed and 107 lives lost, according to the Tornado Project. A total of 181 people died in the tornado.
The largest outbreak of F5 super-tornadoes occurred April 3-4, 1974. Seven F5 tornadoes struck in a single 24-hour period. In total, 147 tornadoes whirled through the central portion of the United States on that day.
On May 22, 2004, the largest tornado ever recorded hit Hallum, Neb. The twister stretched nearly 2 1/2 miles across. No one died in the massive twister.
Groups of tornadoes or outbreaks can cause as much or more damage than a single giant storm. The “Dixie Outbreak” of April 27, 2011, killed 316 people according to NOAA’s Storm Prediction Center. More Americans died in tornadoes that day than any other in this century.
How do you protect yourself from a tornado that reaches 2 miles wide with wind gusts above 200 miles per hour?
When the winds blow that hard, there's little you can do to save your house. But when it comes to protecting yourself and your family, the safest bet is to buy a storm shelter, according to engineering professor Larry Tanner of Texas Tech University's Wind Science and Engineering Research Center.
These structures are usually installed inside or nearby a home and made of reinforced concrete, or even of plywood and steel.
Some scientists are looking into structures built of carbon fiber, or underground "subscrapers," that could easily survive extreme weather disasters. But these constructs are still in the experimental stage and are used mostly at military bases and other high-security facilities.
The typical Midwestern family home depends on simpler architectural standbys. Since the 1980s, building codes in the American Midwest require that a house be able to withstand wind gusts up to 90 miles an hour. A standard stick frame house with wooden trusses and support rafters should be able to survive up to 100 miles per hour, if made properly. (Video: Storms that Spawned Deadly Oklahoma Tornadoes Seen from Space)
For additional strength, you can reinforce the joints and connections in your house with metal clips, called "wind clips" or "hurricane clips." These might raise your house's durability another 5 or 10 miles per hour.
But what's that to a tornado like the monstrosity that ripped through Moore, Okla., leveling whole city blocks and killing what's believed to be at least 24 people?
The use of wind clips would likely have narrowed the swath of destruction that the tornado cut into Oklahoma City's suburbs, but they wouldn't have saved the houses directly in the tornado's path, Tanner said.
The clips do nothing to address a house's key structural weakness: doors and windows. Contrary to popular belief, opening your window during a tornado or hurricane is not a good idea. The myth is that if a house's entrances are all sealed, the difference in barometric pressure within and outside of the house could damage it. But it's not the change in barometric pressure you have to worry about — it's wind pressure. If wind starts to blow into your house — either because you’ve opened a window or door or because a piece of debris smashed it open — the combined pressure from both sides can cause the walls to blow out and the roof to blow off.
The basement is relatively safer than the rest of the house, but the wind forces that blew off the roof could also blow off the first floor — in other words, the basement's ceiling — exposing anyone taking shelter down there to flying debris, Tanner said.
"TV news meteorologists say that the only place is below ground [in a tornado] … that is false, truly false," said Tanner.
The safest place to be in a tornado is in an above-ground storm shelter, said Tanner. These structures are usually made of reinforced concrete, but sometimes are made of plywood and steel. (See also: Futuristic Materials Could Build Tornado-Proof Homes)
At Texas Tech University and the National Storm Shelter Association, Tanner helps test and rate storm shelters. A full list of NSSA-approved engineering firms can be found on the organization's website.
The testing process involves using a wind cannon to blast 2-by-4-inch wooden planks at the shelters at up to 100 miles per hour.
The Federal Emergency Management Agency (FEMA) offers small subsidies for these shelters, which can be installed in a backyard or patio or even inside the residence as a sort of safe room.
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