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A Flash Flood Warning (SAME code: FFW) is issued by the United States National Weather Service 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.[not in citation given]
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. Flash floods can also occur because of a dam or levee failure, 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:
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), which indicates a severe flooding situation in densely populated areas, similar to the procedure for declaring a tornado emergency.
An example of a flash flood warning in Tennessee.
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Flash Flood Warning MNC115-WIC013-031-192330- /O.NEW.KDLH.FF.W.0012.180618T2329Z-180619T2330Z/ /00000.U.DM.000000T0000Z.000000T0000Z.000000T0000Z.OO/ BULLETIN - EAS ACTIVATION REQUESTED Flash Flood Warning National Weather Service Duluth MN 629 PM CDT MON JUN 18 2018 The National Weather Service in Duluth MN has issued a * Flash Flood Warning for... A Dam Failure in... East central Pine County in east central Minnesota... Southwestern Douglas County in northwestern Wisconsin... North central Burnett County in northwestern Wisconsin... * Until 630 PM CDT Tuesday * At 629 PM CDT, local law enforcement reported the Radigan Flowage Dam west of Dairyland has failed, causing flash flooding downstream on the Tamarack River south of the Dam as it flows towards the Saint Croix River. * Locations impacted include... Town Rd T west of Dairyland. Swedish Highway at the Tamarack River. Highway T west of Cozy Corner. Markville Road east of Markville. PRECAUTIONARY/PREPAREDNESS ACTIONS... Turn around, don`t drown when encountering flooded roads. Most flood deaths occur in vehicles. Move to higher ground now. Act quickly to protect your life. Please report flooding to your local law enforcement agency when you can do so safely. && LAT...LON 4623 9218 4616 9226 4611 9228 4607 9229 4605 9234 4612 9234 4617 9230 4622 9225 $$ LE
An example of a flash flood emergency in Tennessee.
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FLASH FLOOD WARNING KSC091-209-MOC047-095-270645- /O.NEW.KEAX.FF.W.0043.160827T0247Z-160827T0645Z/ /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/ BULLETIN - EAS ACTIVATION REQUESTED FLASH FLOOD WARNING NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 947 PM CDT FRI AUG 26 2016 ...FLASH FLOOD EMERGENCY FOR THE IMMEDIATE DOWNTOWN KANSAS CITY AREA!... THE NATIONAL WEATHER SERVICE IN PLEASANT HILL HAS ISSUED A * FLASH FLOOD WARNING FOR... EASTERN WYANDOTTE COUNTY IN NORTHEASTERN KANSAS... NORTHEASTERN JOHNSON COUNTY IN EAST CENTRAL KANSAS... NORTHWESTERN JACKSON COUNTY IN WEST CENTRAL MISSOURI... SOUTHWESTERN CLAY COUNTY IN WEST CENTRAL MISSOURI... * UNTIL 145 AM CDT * AT 943 PM CDT...DOPPLER RADAR INDICATED HEAVY RAIN ACROSS THE WARNED AREA. LIFE THREATENING FLASH FLOODING IS ALREADY OCCURRING! THIS IS A FLASH FLOOD EMERGENCY FOR THE KANSAS CITY METRO...PARTICULARLY THE DOWNTOWN KANSAS CITY AREA! THIS IS A PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW! * SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE... KANSAS CITY...OVERLAND PARK...INDEPENDENCE...SHAWNEE...LENEXA... LEAWOOD...RAYTOWN...LIBERTY...GLADSTONE...PRAIRIE VILLAGE... MERRIAM...MISSION...EDWARDSVILLE...NORTH KANSAS CITY...FAIRWAY... MISSION HILLS...SUGAR CREEK...RIVERSIDE...WESTWOOD AND CLAYCOMO. PRECAUTIONARY/PREPAREDNESS ACTIONS... MOVE TO HIGHER GROUND NOW. THIS IS AN EXTREMELY DANGEROUS AND LIFE-THREATENING SITUATION. DO NOT ATTEMPT TO TRAVEL UNLESS YOU ARE FLEEING AN AREA SUBJECT TO FLOODING OR UNDER AN EVACUATION ORDER. BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE DANGERS OF FLOODING. A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING. IF YOU ARE IN THE WARNED AREA MOVE TO HIGHER GROUND IMMEDIATELY. RESIDENTS LIVING ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE PRECAUTIONS TO PROTECT LIFE AND PROPERTY. && LAT...LON 3917 9466 3915 9466 3916 9460 3919 9460 3927 9435 3907 9428 3892 9477 3912 9481 $$ GITRO
This particular Flash Flood Emergency also includes the enhanced wording "Particularly Dangerous Situation".
Flash Flood Statement National Weather Service Chicago/Romeoville Il 827 PM CDT MON JUN 18 2018 ILC007-201-190515- /O.CON.KLOT.FF.W.0005.000000T0000Z-180619T0515Z/ /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/ Winnebago IL-Boone IL- 827 PM CDT MON JUN 18 2018 ...THIS IS A FLASH FLOOD EMERGENCY FOR THE CITY OF ROCKFORD... ...THE FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1215 AM CDT FOR WINNEBAGO AND BOONE COUNTIES... At 821 PM CDT, Doppler radar indicated heavy rain across the warned area. Flash flooding is ongoing and could become worse as heavy rainfall continues to fall over the area this evening. There have been numerous reports of people stranded in their cars as well as reports of flooding in Mercy Hospital leading to evacuations. With rainfall amounts of over 3 inches already fallen and additional rainfall amounts expected through the evening conditions are not likely to improve quickly. This is a FLASH FLOOD EMERGENCY for The city of Rockford. This is a PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW! Some locations that will experience flooding include... Rockford, Belvidere, Loves Park, Machesney Park, Rockford Airport, Roscoe, Poplar Grove, Cherry Valley, Winnebago, Pecatonica, Capron, Timberlane, Caledonia and New Millford. PRECAUTIONARY/PREPAREDNESS ACTIONS... Move to higher ground now. This is an extremely dangerous and life-threatening situation. Do not attempt to travel unless you are fleeing an area subject to flooding or under an evacuation order. Turn around, don`t drown when encountering flooded roads. Most flood deaths occur in vehicles. && LAT...LON 4241 8871 4216 8871 4215 8916 4221 8917 4220 8940 4241 8939 $$ BIRK