Last week I devoted several Franklin Facts to lightning, which all thunderstorms have. But lightning is not the thunderstormsís greatest killer - flash flooding is. And so today I'd like to say a little about this often under-respected thunderstorm hazard.

In our area, most flash flooding results from slow-moving or stationary thunderstorms, or from a line of thunderstorms that moves parallel to itself, so that thunderstorm after thunderstorm passes over the same area like railroad cars on a track. Whatever the cause, the adjective "flash" implies a rapid rise of streams, creeks, and small rivers in a matter of a few hours, perhaps even minutes. Water is deceptively heavy, and people often underestimate the power of moving water. A cubic yard of water weighs 1600 pounds, and relatively shallow slow-moving water that barely covers the hubcaps of a car can still carry a person away. And it only takes about two feet of water, moving at a seeming crawl of five to ten miles per hour, to carry most vehicles away.

The best advice in flash flooding - never drive or walk through flooded roadways, especially at night. You may have no idea how deep the water is, and the road may be washed out beneath the water.