Flash floods occur when excessive water rapidly fills dry creeks or riverbeds. A creek only six inches deep in mountainous areas can swell to a 10-foot deep raging river in less than an hour by a thunderstorm packing intense rainfall. Moreover, flash flood waters can travel at fast speeds with tremendous force, sweeping up debris, moving large boulders and uprooting trees.
The National Weather Service offers the following flash flood warning signs and suggestions, particularly for activities along streams and rivers.
—When thunderstorms are in the area, stay alert for rapidly changing conditions. You may notice the stream start to rise quickly and become muddy.
—Trust your ears. The sound of roaring sound upstream may be a flood wave moving rapidly toward your location. Head immediately for higher ground.
—Do not camp or park along streams or washes, particularly during threatening conditions.
—When hiking in a canyon or near a streambed, climb up from the flash flood. Do not try to outrun it. A flash flood moves much faster than most people.
—Be especially cautious at night. Flood dangers are much more difficult to see in the dark.