Flash Flood Guidance
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000
AWUS01 KWNH 302107
FFGMPD
VAZ000-NCZ000-302335-

MESOSCALE PRECIPITATION DISCUSSION 0716
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
505 PM EDT FRI SEP 30 2016

AREAS AFFECTED...SRN VA...NRN NC

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

VALID 302105Z - 302335Z

SUMMARY...ESTABLISHED COLD POOLS WILL FOCUS A FLASH FLOOD THREAT
FOR A COUPLE OF HOURS UNTIL LARGE SCALE ASCENT SUBSIDES.

DISCUSSION...AT 21Z CONVECTION HAD EVOLVED OUT OF A PURELY
SUPERCELLULAR PHASE AND INTO A MIXED MODE INCLUDING LINE SEGMENTS.
COMBINED COLD POOLS WERE PROMOTING UPSCALE GROWTH...BOTH OVER
SOUTHWEST AND SOUTHEAST VA...WITH COLD POOLS LIKELY EXTENDING INTO
NORTH CAROLINA. ESTABLISHMENT OF THESE CONVECTIVE OUTFLOWS WILL
MORE READILY PROMOTE CELL REGENERATION AND TRAINING IN A FEW LOCAL
AREAS...AS HAD ALREADY OCCURRED SOUTH OF RICHMOND. SYNOPTIC ASCENT
WILL LIFT AND EXPAND NORTHWARD...BUT CONVECTION MAY TRY TO
PROPAGATE BACK SOUTHWARD INTO THE INSTABILITY GRADIENT AND LOW
LEVEL INFLOW...RESULTING IN A RELATIVELY NARROW ZONE WHERE FLASH
FLOODING IS POSSIBLE THROUGH 2330Z.

RECENT HRRR RUNS HAD A DECENT HANDLE ON THE LOCATION OF THIS
ZONE...INDICATING A FEW SMALL SCALE SOUTH TO NORTH ORIENTED SWATHS
OF HEAVIER RAIN. PRECIPITABLE WATER VALUES INCREASE EASTWARD
ACROSS THE REGION...WITH VALUES CLIMBING FROM 1.2 INCHES IN
SOUTHWEST VA TO 1.8 INCHES IN SOUTHEAST VA AND EASTERN NC. WITH
CELL MERGERS OCCURRING ALONG THE ESTABLISHED COLD
POOLS...RADAR-BASED RAIN RATES IN EXCESS OF 2 INCHES PER HOUR FROM
KAKQ LOOK REALISTIC. RAP MASS FIELDS SUGGEST THAT SYNOPTIC SUPPORT
FOR THE EVENT WILL DIMINISH AS A JET STREAK ROTATES UP INTO THE
OHIO VALLEY AND WELL AWAY FROM THE INSTABILITY GRADIENT BY 00Z.
MODERATE LOW LEVEL INFLOW COULD...HOWEVER...SUPPORT SHALLOW
CONVECTION TO COMPOUND THE RAINFALL TOTALS EVEN AS THE MORE ROBUST
CONVECTION SUBSIDES.

BURKE

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

ATTN...WFO...AKQ...LWX...RAH...RNK...

ATTN...RFC...MARFC...SERFC...

LAT...LON   37947955 37827662 37037612 36707689 36437804
            36277921 36547979 37077995


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