CSI Tornado: Decoding – and chasing – supercells with the experts
CSI Tornado: Chasing supercells, interviewing a homeowner sucked off his front porch in an Oklahoma tornado outbreak, and examining the path of a destructive funnel, an expert expedition shows how science is close to decoding the way a tornado works.
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Typically, a damage survey is a race against time. Residents aim to put their lives back together as quickly as possible.Skip to next paragraph
"You have to work hard and fast to get the information before it's gone," observes Tanya Brown, who does post-storm surveys as a research engineer with the Insurance Institute for Business and Home Safety.
When LaDue pulled in to Woodward about noon the day after the tornado, police officers, firefighters, and other first responders had already been working nearly 12 hours.
LaDue's first step was to map the tornado's path. In Woodward, the damaged area was small enough to map by driving through neighborhoods until he ran out of visible damage.
Two areas drew particular attention: a trailer park, where the tornado pulverized several mobile homes; and a neighborhood a mile away, where the Lord home once stood.
His main task was to determine the tornado's intensity and wind speeds – estimated from the damage it inflicted. The tools: a tape measure, a camera, and a smart phone with software that contains a rogue's gallery of damage images that would help LaDue and Mr. Smith classify the twister on the EF scale.
During the May 24, 2011, outbreak over western and central Oklahoma, one twister picked up a Chevy Avalanche and carried it half a mile. "It was unrecognizable, a foot-wide piece of metal wrapped around a tree," says Smith, LaDue's NWS colleague. "Right in the core of what we believe was an EF5 tornado, an oil rig was pulled out of the ground – despite some 3 million pounds of force holding that heavy steel mechanism in the ground – and heavily damaged."
Damage indicators on the EF scale crib sheet don't include 1,500-ton oil rigs, Smith quips. Damaged and displaced vehicles are far more common, but aren't covered either. Despite hints from other damage indicators about a twister's intensity, its vehicular mayhem "really makes you scratch your head and wonder: Gosh, what kind of force, what kind of wind, and what kind of motion does it take to carry a giant pickup truck a half mile," shredding it in the process?
The neighborhood LaDue is surveying is a mix of homes built in the 1950s and – like the Lords' – homes built as recently as the '90s. As he works his way through the neighborhood, he stops to speak with residents for information on a damaged home's pedigree.
The need to work hard and fast doesn't trump compassion, however, or an ability to be amazed, even touched, at how residents spontaneously rally to help their neighbors or by remarkable stories of endurance and survival.
The tornado hit around 12:19 a.m. and by 1, more than 100 volunteers were combing the stricken area to look for survivors and begin to help them clean up.
"It's one of those small, Mayberry towns. Everybody knows everybody, and everybody lends a hand," says Chad Lord, above the buzz of chain saws and rumble of front-end loaders.
Early in the survey, LaDue works through the older part of the neighborhood, getting owners' permission to take photos and make measurements when he sees something that may have contributed to the severity of the damage. At one of the postwar-construction homes, he kneels to examine the rim of a foundation exposed when the tornado blew an exterior wall in. He hunts for signs of anchor bolts, and finds none. Exposed framing on interior walls reveals 1-by-3-inch wall studs, in contrast to the 2-by-4s used today.
Garages seem to be a weak link. Many homes have two-car garages with a single metal door with no braces on the back. On the periphery of the tornado's path, one house is intact, but its garage door is buckled inward. The garage doors of a house that was closer to the tornado blew in completely, which peeled the roof off.