The atmosphere was in turmoil before sunrise one day last week, and more than 58 million people were at risk.
A tornado threat was stalking the Texas and Oklahoma panhandles, and the Dallas-Fort Worth metroplex. Damaging winds were a danger along the entire length of Interstate 70 in Missouri. A possibility of quarter-size hail lurked as far north as Minnesota and Wisconsin.
The following day would bring even more menaces in more places. By the weekend, at least five people would be dead as storms raged, trees splintered and homes and businesses were destroyed.
But before the funnel clouds and cracks of thunder struck, a handful of government meteorologists huddled at the Storm Prediction Center, just south of Oklahoma City, to divine the future. Inside a quiet second-floor room, they studied dozens of computer monitors, drew maps with lime-green Sharpies and colored pencils and looked for the atmospheric ingredients that could turn clouds into killers.