Tornado Alley, USA

New map defines nation's twister risk

Residents of Pontotoc County, Okla., take note: You’re sitting smack dab at the center of a meteorological bull’s-eye. Once every 4,000 years or so, a tornado strong enough to rip the roof off a house will sweep across the very spot in southeastern Oklahoma that you call home. That doesn’t sound very frequent, does it? Truth be told, it isn’t.