Water School

The National Weather Service classifies a flash flood as an overflow of water onto normally dry land caused by heavy or excessive rainfall in a short period of time, generally less than 6 hours.

Flash floods are usually characterized by raging torrents after heavy rains that rip through river beds, urban streets, or mountain canyons sweeping everything before them. They can occur within minutes or a few hours of excessive rainfall. They can also occur even if no rain has fallen, for instance after a levee or dam has failed, or after a sudden release of water by a debris or ice jam.