Flash Flood Guidance
Issued by NWS

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000
AWUS01 KWNH 230751
FFGMPD
SCZ000-FLZ000-GAZ000-ALZ000-MSZ000-231346-

MESOSCALE PRECIPITATION DISCUSSION 0264
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
350 AM EDT TUE MAY 23 2017

AREAS AFFECTED...PORTIONS OF THE SOUTHEAST

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 230746Z - 231346Z

SUMMARY...EMBEDDED CONVECTION WITHIN A BROAD RAIN SHIELD WILL
RESULT IN AN INCREASED THREAT FOR POCKETS OF FLASH FLOODING ACROSS
PORTIONS OF THE SOUTHEAST INTO THE MORNING HOURS.

DISCUSSION...AT 07Z AN AREA OF LOW PRESSURE WAS MOVING NORTHEAST
ACROSS LA INTO SOUTHERN MS. LOW LEVEL MOISTURE TRANSPORT IS
EXPECTED TO INCREASE THROUGH THE NIGHT AHEAD OF THIS LOW ACROSS
PORTIONS OF THE SOUTHEAST. MEANWHILE FLOW IN THE UPPER LEVELS WAS
BECOMING INCREASINGLY DIVERGENT ACROSS PORTIONS OF AL/MS/GA...WITH
THE REGION MOVING INTO THE LEFT EXIT REGION OF THE SUBTROPICAL JET
AND THE RIGHT ENTRANCE REGION OF A JET OVER THE TN VALLEY. THUS
FACTORS ARE IN PLACE FOR AN UPTICK IN CONVECTIVE COVERAGE AND
INTENSITY ACROSS PORTIONS OF THE SOUTHEAST OVER THE NEXT SEVERAL
HOURS.

COMPLICATING MATTERS IS A BROAD AREA OF STRATIFORM RAINFALL THAT
HAS DEVELOPED ACROSS THE REGION...LIKELY IMPACTING THE DEGREE OF
INSTABILITY PRESENT. HOWEVER SPC RAP ANALYSIS SUGGESTS THAT THE
REGION OF FAVORABLE UPPER AND LOWER LEVEL SUPPORT MENTIONED ABOVE
IS BEGINNING TO MOVE INTO A REGION OF ROUGHLY 1000 J/KG MUCAPE.
RADAR IMAGERY ALSO SUGGESTS A BIT OF AN UPTICK IN EMBEDDED
CONVECTION WITHIN THE BROAD STRATIFORM RAIN AREA. THUS THE
EXPECTATION IS THAT WE WILL CONTINUE TO SEE AN INCREASE IN
COVERAGE OF EMBEDDED CONVECTIVE CLUSTERS DEVELOP WITHIN THE BROAD
RAIN AREA AS WE HEAD THROUGH THE NIGHT.

WARM/MOIST PROFILES AND PWAT VALUES ABOVE 1.75" SUPPORT EFFICIENT
RAINFALL IN ANY EMBEDDED CONVECTION. RECENT RUNS OF THE HRRR AND
EXPERIMENTAL HRRR HAVE BEEN PRETTY CONSISTENT IN SHOWING SOME 2-4"
AMOUNTS ACROSS PORTIONS OF AL/GA OVER THE NEXT SEVERAL HOURS. HAVE
KEPT THE MPD AREA PRETTY BROAD...AS THERE IS NOT REALLY ANY FOCUS
MECHANISM TO HELP PIN DOWN WHERE THE HIGHEST FLASH FLOOD THREAT
EXISTS ACROSS AL/GA AND WESTERN SC. WOULD NOT EXPECT TO SEE
WIDESPREAD FLASH FLOOD GUIDANCE EXCEEDANCE...BUT THE SETUP DOES
SUPPORT THE POTENTIAL FOR LOCALIZED AREAS OF EXCEEDANCE INTO THE
MORNING HOURS.

CHENARD

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...BMX...CAE...CHS...FFC...GSP...JAN...JAX...LIX...
MOB...TAE...

ATTN...RFC...LMRFC...SERFC...

LAT...LON   34738230 33448205 32088211 31638271 31698390
            31558585 31148722 30318806 30458888 31788852
            32098839 32908756 33178666 33528532 34148412
            34528317



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