Flash flood warning
A flash flood warning (SAME code: FFW) is issued when a flash flood is imminent or occurring in the warned area. A flash flood is a sudden, violent flood after a heavy rain, or occasionally after a dam break. Rainfall intensity and duration, topography, soil conditions, and ground cover contribute to flash flooding.
Most flash floods occur when there is a heavy amount of precipitation falling in an area and that water is then channeled through streams or narrow gullies. Flash floods may take minutes or hours to develop. It is possible to experience a flash flood without witnessing any rain. In this case, there would be heavy rain in areas upstream of the warned location.[1][not in citation given]
Contents
Flash flood alerts
There are two types of alerts for flash floods which are issued by the National Weather Service. One is a flash flood watch, which means that conditions are favorable for flash flooding, and the other is a flash flood warning, meaning that a flash flood is occurring or one will occur imminently and is usually issued when there are strong weather radar echoes for an area that is prone to flash flooding.[2] Flash floods can also occur because of a dam or levee failure,[3] or because of a sudden release of water held by an ice jam.
Residents are usually urged to do the following when flash flooding is imminent:[4]
- Be aware of any signs of heavy rain
- Move to higher ground if rapidly rising water is seen or heard
- Not attempt to cross the flowing water
In addition, some NWS Weather Forecast Offices have instituted an enhanced flash flood warning, referred to as a flash flood emergency (or as termed by the Albany, New York office as a flash flood warning emergency[5]), which indicates a severe flooding situation in densely populated areas, similar to the procedure for declaring a tornado emergency.
Example of a flash flood warning and emergency
Warning
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FLASH FLOOD WARNING KSC003-302230- BULLETIN - EAS ACTIVATION REQUESTED FLASH FLOOD WARNING NATIONAL WEATHER SERVICE TOPEKA KS 1129 AM CDT SAT JUN 30 2007 THE NATIONAL WEATHER SERVICE IN TOPEKA HAS ISSUED A * FLASH FLOOD WARNING FOR... ANDERSON COUNTY IN EAST CENTRAL KANSAS... * UNTIL 530 PM CDT SATURDAY * AT 1129 AM CDT...THE PUBLIC REPORTED WATER FLOWING OVER A COUPLE OF PAVED ROADS NEAR WESTPHALIA. ANDERSON COUNTY EMERGENCY MANAGEMENT ALSO INDICATED THAT SEVERAL PAVED ROADS HAD WATER RISING AND APPROACHING ROADWAYS. DOPPLER RADAR INDICATED THAT ANOTHER BAND OF HEAVY RAINFALL WAS DEVELOPING AND TRAINING OVER ANDERSON COUNTY PRODUCING RAINFALL RATES UP TO ONE INCH PER HOUR. ENHANCED RAINFALL RATES WILL LIKELY BE ENOUGH TO BRING WATER OVER SEVERAL PAVED ROADS IN THE COUNTY * LOCATIONS IMPACTED INCLUDE... HARRIS... GREELEY... GARNETT... WESTPHALIA... RUNOFF FROM THIS STORM WILL CAUSE FLASH FLOODING OF CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. ADDITIONALLY ROADS AND FARMLANDS ALONG THE BANKS OF CREEKS AND STREAMS AND LOW LYING AREAS ARE SUBJECT TO FLASH FLOODING. A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING. IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY. RESIDENTS ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE PRECAUTIONS TO PROTECT LIFE AND PROPERTY. TO REPORT FLOODING...HAVE THE NEAREST LAW ENFORCEMENT AGENCY RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST OFFICE IN TOPEKA. STAY TUNED TO NOAA WEATHER RADIO OR LOCAL MEDIA OUTLETS FOR THE LATEST INFORMATION CONCERNING THE SEVERE WEATHER. LAT...LON 3803 9551 3803 9507 3839 9506 3838 9550 $$
Emergency
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FLASH FLOOD STATEMENT NATIONAL WEATHER SERVICE TOPEKA KS 210 PM CDT SAT JUN 30 2007 KSC003-302230- ANDERSON- 210 PM CDT SAT JUN 30 2007 ...A FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 530 PM CDT FOR ANDERSON COUNTY... .A FLASH FLOOD EMERGENCY FOR ANDERSON COUNTY... AT 200 PM CDT...TRAINED WEATHER SPOTTERS AND PUBLIC REPORTED WIDESPREAD FLOODING OVER ANDERSON COUNTY. KNOWN WATER RESCUES ARE ONGOING WEST OF GARNETT. EMERGENCY CREWS ARE UNABLE TO FIND A ROUTE FROM WESTPHALIA TO GARNETT. NUMEROUS PAVED AND GRAVEL ROADS HAVE BEEN REPORTED TO BE UNDER WATER ACROSS THE COUNTY....SEVERAL AREAS 1 TO 2 FEET DEEP. MEASURED STORM TOTAL PRECIPITATION AMOUNTS RANGE FROM 14 TO 16 INCHES OF RAINFALL DURING THE PAST THREE DAYS. WITH ONGOING RAINFALL AMOUNTS ON THE ORDER OF 1 TO 2 INCHES PER HOUR...ANY ADDITIONAL RAINFALL WILL CONTINUE TO AGGRAVATE THE FLOODING SITUATION. LOCATIONS IMPACTED INCLUDE... WESTPHALIA...COLONY...HARRIS...GREELEY AND GARNETT. RUNOFF FROM THIS STORM WILL CAUSE FLASH FLOODING OF CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. ADDITIONALLY ROADS AND FARMLANDS ALONG THE BANKS OF CREEKS AND STREAMS AND LOW LYING AREAS ARE LIKELY TO CONTINUE OR QUICKLY BEGIN TO FLASH FLOOD. DO NOT DRIVE INTO AREAS WHERE THE WATER COVERS THE ROAD. A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING. IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY. RESIDENTS ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE PRECAUTIONS TO PROTECT LIFE AND PROPERTY. LAT...LON 3803 9551 3803 9507 3839 9506 3838 9550 $$ BLAIR / CAVANAUGH
See also
Severe weather terminology (United States)
References
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