MESOSCALE PRECIPITATION DISCUSSION 0682
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EDT SUN AUG 13 2017

AREAS AFFECTED...SOUTHEAST NC...EASTERN SC

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

VALID 131810Z - 140000Z

SUMMARY...MERGING CONVECTIVE LINES POSE LOCALIZED FLOODING CONCERN
ESPECIALLY IN AREAS THAT HAVE NEARLY SATURATED SOILS.

DISCUSSION...WV LOOP SHOWS FAIRLY FLAT WSW-ENE FLOW WITH A 50KT 3H
JET STREAK ENTRANCE OVER THE OUTER BANKS OF NC...BUT ALSO A TIGHT
GRADIENT WITH THE SUBTROPICAL RIDGE LINE THAT EXTENDS ACROSS GA
COAST TOWARD BERMUDA.  THIS COMBINATION PROVIDES AN IDEAL SETUP
FOR GOOD OUTFLOW CHANNEL FOR ANY CONVECTION THAT WERE TO DEVELOP.

AT THE SURFACE A FEW BOUNDARIES LINGER TO HELP FOCUS AND CORRAL
ANY CONVECTION THAT DOES DEVELOP.   A SURFACE FRONT EXTENDS FROM
MQI TO DPL TO MEB TO CAE. VISIBLE IMAGERY ALSO SHOWS A W-E
ORIENTED BOUNDARY THAT APPEARS TO BE A MANIFESTATION OF THE 850MB
FRONT ACROSS CENTRAL NC INTERSECTING THE FRONT NEAR MQI THAT IS
SLOWLY DROPPING SOUTH. LASTLY IS SEA-BREEZE BOUNDARY THAT IS
ALREADY STARTING TO ACTIVATE WITH SOME OUTFLOW PRESSING ASHORE.  
BETWEEN THESE BOUNDARIES IN THE COASTAL PLAIN WARM SECTOR HAS
BECOME SUFFICIENTLY UNSTABLE WITH MLCAPES TO 2500 J/KG AND FAIRLY
MOIST PROFILES (PARTICULARLY IN THE BOUNDARY LAYER/LOWEST 250MB)
WITH TOTAL PWS OVR 2 TO 2.25" AVAILABLE. 

CURRENTLY STRONG MST CONVERGENCE NEAR WEAK SURFACE REFLECTION NEAR
CAE HAS STARTED THE CONVECTIVE DEVELOPMENT ALONG THE
FRONT...THOUGH TCU AND NASCENT ECHOS ON RADAR EXTEND FURTHER UP
THE CHAIN.  CELLS WILL BE CAPABLE OF 2-2.5"/HR RATES THOUGH SHOULD
START OFF TO BE OUTFLOW DOMINANT GIVEN MODEST DRY AIR IN
MID-LEVELS BUT WITH WEAK FLOW THERE SHOULD BE POCKETS OF 2-2.5"
TOTALS WITH THE INITIAL BOUTS.  AS THE OUTFLOWS SEEK INSTABILITY
OVER THE SE NC/E SC COASTAL PLAIN...THERE SHOULD BE
COLLISION/MERGERS WITH TIME LIKELY TO START FURTHER NORTH AND
UNZIP SOUTHWESTWARD INTO NE SC TOWARD EVENING (GIVEN WEAK/SW
ORIENTED CORFIDI VECTORS).  THIS PROCESS SHOULD KEEP FOCUS FOR A
SLIGHTLY LONGER DURATION (PARTICULARY GIVEN BETTER/STRONGER
OUTFLOW FURTHER NORTH IN SE NC) LEADING TO THE POTENTIAL FOR 2-4"
RAINFALLS.

WHILE NORMALLY NOT TOO MUCH OF AN ISSUE...MUCH OF THE AREA HAS
RECEIVED 300-600% OF NORMAL PER AHPS ANALYSIS OVER THE LAST 7 DAYS
(WITH EXCEPTION OF COLUMBIA, SC TO LUMBERTON, NC ZONE) LEADING TO
SATURATED SOILS AND LEADING TO THE POTENTIAL FOR FLOODING AND
POSSIBLE FLASH FLOODING CONDITIONS THROUGH THE EVENING.  WORSE
CASE SCENARIOS ARE PAINTED BY 12Z ARW/NMMB THOUGH BOTH APPEAR A
SHADE TOO FAR NORTH GIVEN CURRENT OBSERVATION BUT THE
AXIS/ORIENTATION LOOK REASONABLE.    

GALLINA

ATTN...WFO...CAE...CHS...ILM...MHX...RAH...

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

LAT...LON   35617678 35377595 34697645 34447731 33997780
            33707825 33227905 33037956 33148012 33678086
            34258095 34638059 34947973 35127902 35337804