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Flash floods occur suddenly, usually within 6 hours of the rain event, and result from heavy localized rainfall or levee failures. Flash floods can begin before the rain stops. Water level on small streams may rise quickly in heavy rainstorms, especially near the headwaters of river basins. Heavy rains can also cause flash flooding in areas where the floodplain has been urbanized.
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A flood is the inundation of a normally dry area caused by an increased water level in an established watercourse, such as a river, stream, or drainage ditch, or ponding of water at or near the point where the rain fell. Flooding can occur anytime during the year. However, many occur seasonally after winter snow melts or heavy spring rains.
Ice jams and dam failures can also cause both flooding and flash flooding.
Many people are killed by flash floods when driving or walking on roads and bridges that are covered by water. In fact, flash floods are the number one weather-related killer in the United States. Even 6 inches of fast-moving flood water can knock you off your feet, and a depth of only 2 feet of water will float many of today's automobiles. If you are in a car and water starts rising, get out and move to higher ground.
A flash flood or flood warning indicates that flash flooding or flooding is already occurring or imminent within the designated warning area - take necessary precautions at once. When a flash flood or flood warning is issued for your area, act quickly! Get out of areas subject to flooding and avoid areas where flooding has already occurred.
A flash flood or flood statement is used for follow-up information regarding a flash flood or flood event.