MEGA DISASTERS: Tornado Alley Twister

What would happen if the most intense tornado ever measured struck Dallas, Texas? With winds clocking 318 miles per hour, the monster twister would carve a path through the city up to a mile wide.

It happened once before, just 200 miles to the north in Oklahoma City. There, in May 1999, a "Mega Tornado" scoured the earth for 85 minutes along a 38-mile path - 43 people died and property damage was enormous.

It became history's first billion-dollar tornado. But in more densely developed Dallas, the scenario would be far worse: as many as 1,000 dead...and five-billion dollars in damage.