A Killer F5 Tornado Rips Through Dallas County -- How Ready Are We for this Nightmare Scenario?

Tim Marshall and his wife, Kay, were bickering like seagulls when the cow dung flew inside their pickup's passenger-side window and splattered across his face. "Put the vehicle in drive," Marshall said in a hectoring tone that any spouse would find annoying. "No. No. No. We are fine. We...are...fine."

About a half-mile away, a wedge-shaped tornado was heading straight at them, cutting across a field peppered with some low-slung farm and industrial buildings that were about to be blasted into oblivion. To Marshall, who's been keen on weather since his boyhood, this was no time to flee, even if the chunky black twister, a rare and violent F5, was bearing down on him and his wife, whom he recruited "as sort of a last resort" to be his storm-chasing driver.

In the video footage the Irving engineer captured from that spot—an overpass on Interstate 44 just north of Newcastle, Oklahoma—the tornado hangs perilously from a shroud of black clouds, rotating and churning in debris-laden shades of black and gray.

As it rips through electrical transformers, the flashes and explosions can be seen getting sucked back into the vortex. Dirt and tree limbs wake out from the bottom of the funnel, hinting at its destructive power, while at a bit more distance from the cylinder an intense wind known as the rear flank downdraft is hurling lighter objects across the sky, including the shower of cow dung that found Marshall's face.

"It's actually shaking the ground, like in Jurassic Park," Marshall explains later, referring to the rings in the puddle signaling T. rex's arrival in the movie. As far as tornadoes go, this one also tops the food chain, and it has burned the date May 3, 1999, into the memories of many Oklahomans.

The twister, one of the best-recorded in history, was on the ground for 37 miles, nearly all of it in open country, but in its track lay the tiny farm town of Bridge Creek and three Oklahoma City suburbs. Along that path, it killed 36 people, injured 295 and turned whole neighborhoods to rubble. In all it destroyed 1,780 homes and did $963 million in property damage, making it the costliest tornado on record. Its winds were clocked at 301 mph, the highest wind speed ever recorded by a mobile Doppler radar (with a margin of error of 20 mph). In Bridge Creek, where it grew a beastly mile wide, it tossed about a dozen cars a quarter-mile. A canceled check from an aircraft parts business near its starting point turned up 65 miles away, on the other side of Oklahoma City. It had just a minor tear in one corner.

Statistically, Dallas-Fort Worth is only slightly less vulnerable than central Oklahoma to a violent tornado, an EF4 or EF5, and federal weather researchers have said repeatedly the region is an overdue target for a major strike. (The Enhanced Fujita scale, like the F-scale damage-intensity measurements it replaced in 2007, infers wind speeds from damage to buildings, trees and other objects. EF4 winds begin at 166 mph and are capable of leveling well-constructed houses. While about 2 percent of all tornadoes are rated EF4 or EF5, they account for 65 percent of tornado deaths.) Dallas is well within the southern Great Plains' "Tornado Alley," an area with a distinct tornado season from April through June. Conditions are right this time of year for dry air from the north and west to clash with warm, moist air from the Gulf of Mexico, setting up the unstable conditions that lead to the formation of supercell thunderstorms that spawn twisters.

Yet Dallas' vulnerability has inspired less than full preparation by disaster response officials and prompted few homeowners or builders to construct storm shelters above or below ground.

"A level-5 tornado hitting inside the city limits is too big to plan for," says city of Dallas emergency management director Kenny Shaw. "It would be a mass casualty event requiring outside resources on a large scale. We are not sitting around trying to figure out what to do in these worst-case scenarios. We'd have a response, we have response planning, but it would not run smoothly by any means."

One of the city's chief partners in emergency response, the Dallas Area Chapter of the American Red Cross, committed itself this winter to provide mass care in the event of just such a tornado strike. The nonprofit agency aims to build the capacity to provide food and emergency housing to 40,000 people, the number it estimates would be left without homes in the event of a major tornado. The $50 million project, dubbed "Protect the Metroplex," uses the 1999 Moore, Oklahoma, tornado as its model threat. Steve Vetrano, the organization's chief operating officer, says the Red Cross hopes to complete the project by September 2011, the chapter's 100th anniversary. To do so, it needs to train 11,000 more volunteers than the 3,000 it currently has on its roster, acquire 37,500 cots above the 2,500 now in its warehouses, and conduct a massive planning effort to identify schools, churches and other buildings that could serve as temporary shelters.