May 23, 2013

The Moore Tornadoes: Lessons Learned

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Seven students died when a tornado struck Plaza Towers Elementary School in Moore.

Clifton Adcock/Oklahoma Watch

Seven students died when a tornado struck Plaza Towers Elementary School in Moore.

Oklahoma Watch invited Nancy Mathis, a Tahlequah native and author of a book on the deadly 1999 Moore tornado, to offer thoughts about the twister of May 20. Mathis’ 2007 book, “Storm Warning: The Story of a Killer Tornado,” explored the causes and effects of the 1999 tornado, plus the science behind tornado forecasting and protection.

May 3, 1999, might have passed as an unremarkable spring day in Tornado Alley, with a few run-of-the-mill thunderstorms at first. But, as Oklahomans know, the unusual did happen.

“May 3” is shorthand for a tragic event and needs no explanation when mentioned in Oklahoma: An F5 tornado plowed through the city with devastating violence, claiming dozens of lives. Now we have May 20 and another massive tornado, with obliterated schools, fallen children and the lessons of May 3 to be learned again.

Even the questions are the same, especially: What more can we do to protect ourselves?

Few states are as prone to violent tornadoes as Oklahoma, especially central Oklahoma. Blame it on location. There is the confluence of cold air off the Rockies and warm, moist air from the Gulf of Mexico, plus a jet stream riling the atmosphere. The invisible boundary separating the warm and cool air is called the dry line, and it’s here where severe weather often begins, especially supercell thunderstorms that produce the most violent twisters.

Researchers have calculated that on any given day in May, you have a 10 percent chance of seeing a tornado just south of Oklahoma City.

On May 3, 1999, the national Storm Prediction Center issued only a slight chance for severe weather. But thin, cooling cirrus clouds began to part and the sun warmed the ground, which sent more warm air aloft. Such subtleties make forecasting an art.

Meteorologists began to upgrade their forecasts. In contrast, on May 20, 2013, it was well known that conditions signaled a major event. The day before, a twister had struck Shawnee.

In 1999, the first few flaring storms near the Red River died quickly. Near Lawton, a supercell thunderstorm organized into a familiar anvil shape, caused by rising clouds flattening against the troposphere, and at 4:45 p.m. began spinning up twisters.

It was the ninth tornado created that made the record books. A9, as it was initially labeled by the National Weather Service, arose over Chickasha and tracked northward along I-44. The National Weather Service in Norman, which already had issued a tornado warning, issued a higher-level “tornado emergency,” the first ever, hoping that people would take shelter.

A mile-wide mass of dirt, rain, wind and debris crossed into Bridge Creek west of Newcastle, where it shredded a mobile home community. Turning east, the twister crossed I-35 and entered Moore. It leveled one neighborhood after another, destroying 600 homes. It creased the parking lot at Crossroads Mall and cut through Del City and Midwest City before losing steam.

A mobile Doppler radar clocked the wind speeds at 300 miles per hour, the most powerful tornado ever recorded. It was the first to cause more than $1 billion in damages.

That one tornado alone was historic. But with an atmosphere packed with convective energy, one super-cell after another also appeared, producing 71 tornadoes in Oklahoma.

The Bridge Creek-Moore twister killed 36 people. Yet it could have been much worse. The tornado was on the ground for more than 35 miles, allowing time for warnings to be widely broadcast. The early-evening time meant children already were home from school.

Every major tornado prompts a lessons-learned assessment. The first from 1999 was the danger of taking shelter under highway overpasses. Three of the 36 people killed by A9 were ripped away from those spots. Overpasses serve to tunnel tornado winds, making them faster and deadlier.

The second was the need for shelter. Like on May 20, broadcasters warned people to seek shelter in underground or above-ground safe rooms. Traditional precautions, like huddling in a bathroom or closet, were useless against a powerful EF4 or EF5. Mobile homes and cars are the most dangerous places to be.

Many people had nowhere to go. After May 3, Oklahoma created a rebate program for people who built shelters, and hundreds of people took advantage. Perhaps that saved lives on May 20 this year.

Then there were issues over shelters at public venues. Meteorologists have long feared that a violent tornado would hit a sporting event, a shopping mall or a school. On May 20, the fear became real. The destruction of Plaza Towers Elementary School, where seven children died, is prompting calls for more safe rooms.

After May 3, Bridge Creek Public Schools, southwest of Oklahoma City, expanded its elementary school and all new rooms were reinforced as safe rooms. Kelly Elementary in Moore, also destroyed on May 3, was rebuilt to include safe rooms.

Another lesson from May 3 stemmed from a Texas Tech University study that attracted little interest from state officials. Housing construction was of such poor quality that some homes were destroyed, not by the tornado itself but by the less-powerful force of inflow, the ground-level winds pulled into the base of a tornado.

Hurricane straps that secure rafters and anchor bolts that secure the frame can make a difference, especially against less powerful tornadoes. But they also add to home costs.

Construction quality is one reason the Fujita Scale was reassessed after May 3. The Fujita Scale imperfectly measured tornado wind speed based on damage. Damage surveyors had long suspected it took a lot less wind speed to wipe a home off its foundation, and construction quality varies. After 1999, experts created the Enhanced Fujita scale, or EF scale, which significantly lowered the wind speeds attributed to violent tornadoes and took into account construction quality.

Perhaps the biggest problem is one that forecasters and lawmakers can’t fix: public inaction. As KFOR meteorologist Mike Morgan implored viewers on May 20, “You cannot delay. You can’t think. You can’t delay. You’ve got to act … You’ve got to act to save your life and your loved ones’ lives.”

On May 22, 2011, an EF5 rammed through Joplin, Mo. More than 150 people died, more than half in their homes. It was the first twister to claim more than 100 lives since a 1953 tornado in Flint, Mich. That twister pre-dated the use of radar and tornado forecasting.

Scientists still do not exactly know how tornadoes form or why one thunderstorm will produce a tornado and another will not. Weather forecasters are approaching the limits of their prediction capabilities.

But even the most accurate forecasts are useless without people taking, and demanding, action.

The views of guest authors do not necessarily reflect those of Oklahoma Watch.