May 1889: After a deluge of rainfall—nearly a foot in less than twenty-four hours—swelled the Little Conemaugh River, panicked engineers watched helplessly as swiftly rising waters threatened to breach the South Fork Dam in central Pennsylvania. Though they telegraphed neighboring towns on this last morning in May, warning of the impending danger, residents used to false alarms remained in their homes. At 3:10 p.m., the dam gave way, releasing twenty million tons of water. Gathering speed as it flowed southwest, the deluge wiped out entire towns in its path and picked up debris—trees, houses, animals—before reaching Johnstown, fourteen miles downstream. Travelling forty miles an hour, with swells as high as 60 feet, the deadly floodwaters razed the mill town—home to 20,000 people—in minutes. The Great Flood, as it would come to be called, today remains the deadliest in U.S. history, killing more than 2,200 people and causing $17 million in damage. Al Roker tells the riveting story of