NOAA National Weather Service Weather Forecast Office

Flash Flood Safety

There are several kinds of floods.  The "traditional" flood results from days of heavy rain and/or melting snow, with rivers gradually rising and going over their banks.  These can usually be predicted with considerable accuracy, providing adequate warnings that result in saving lives and reducing loss of property. 

Flash floods are a different matter.  They usually result from rapidly changing weather situations, such as the sudden development of an intense local storm over the drainage basin of a small stream or river.  Rivers can rise way above flood stage in a matter of hours if not minutes.  However, not all flash floods are caused directly by heavy rain.  Ice and log jams can suddenly let loose huge torrents of water.  Natural or constructed dams can collapse due to earthquakes or mudslides. 

Why do so many people die in flash floods?  Aside from the factor of surprise (many people are caught sleeping), people just don't appreciate the power of moving water.  Even six inches of fast-moving flood water can knock you off your feet.  Most automobiles will float and can be swept away in only two feet of water.  Never try to walk, swim, or drive through the swift currents of a flash flood.  Nearly half of all U.S. flash flood fatalities are auto related. Never attempt to drive over a flooded road.  The depth of water is not always obvious. Also, the road bed may have been washed out under water.  Dry creek beds can go from dusty bone dry to a ten-foot-deep torrent of water within a minute as the thunderstorm rains drain down from surrounding higher terrain.

Many vehicle-related fatalities are preventable, but too many people continue to drive around the barriers that warn you the road is flooded.  Whether you are driving or walking, if you come to a flooded road, Turn Around Don't Drown� You will not know the depth of the water nor will you know the condition of the road under the water.  Click the TADD barricade image at left to visit the Turn Around Don't Drown homepage.

In recent memory, one of most devastating flash floods to affect western and central Wyoming occurred in Kaycee on August 27, 2002.  This flash flood was caused by thunderstorm rainfall of 6+ inches near this small town in Johnson County, Wyoming.  To increase warning reception a NOAA Weather Radio was installed near Kaycee to commemorate the one year anniversary.

Flood and Flash Flood Terminology:

• FLASH FLOOD OR FLOOD WATCH:  Flash flooding or flooding is possible within the designated WATCH area--Be alert to signs of flash flooding and be ready to evacuate on a moment's notice.

• FLASH FLOOD OR FLOOD WARNING:  Flash flooding or flooding has been reported or is imminent, act quickly to save yourself.  You may have only SECONDS!

• URBAN AND SMALL STREAM FLOOD ADVISORY:   Flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.  The Flood Statement will be used to issue this advisory.

• FLASH FLOOD OR FLOOD STATEMENT:   Follow-up information regarding a flash flood/flood event.

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