Graphic for MPD #0779

MESOSCALE PRECIPITATION DISCUSSION 0779
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT FRI SEP 01 2017

AREAS AFFECTED...NC

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 011820Z - 020020Z

SUMMARY...SHOWERS AND THUNDERSTORMS WILL BE DEVELOPING AND
EXPANDING IN COVERAGE AND INTENSITY THIS AFTERNOON WITH HEAVY
RAINFALL RATES THAT COULD APPROACH 3 INCHES/HR. SOME FLASH
FLOODING IS LIKELY.

DISCUSSION...A WELL-DEFINED SOUTHERLY FETCH OF INCREASINGLY
MOIST/UNSTABLE AIR IS SEEN ADVANCING NORTH ACROSS THE SOUTHEAST
COASTAL PLAIN EARLY THIS AFTERNOON AROUND THE FAR EASTERN FLANK OF
POST-TROPICAL HARVEY LOCATED OVER SOUTHERN KY. THIS AIRMASS IS
BEGINNING TO INTERACT WITH A WELL-DEFINED QUASI-STATIONARY FRONT
OVER SOUTHERN NC. IN FACT...THE LATEST NON-OPERATIONAL GOES-16
0.64 MICRON/VIS IMAGERY SHOWS AN INCREASINGLY AGITATED CU/TCU
FIELD ACROSS SOUTHERN NC AND SC RIGHT NOW LIFTING NORTH-NORTHEAST
TOWARD THE FRONT...AND THE INSTABILITY IS CONFIRMED BY THE LATEST
RAP ANALYSIS DEPICTING MLCAPE VALUES OF 1500 TO 2000 J/KG.

THE GREATER INSTABILITY IS ACTUALLY TENDING TO BE FOCUSED MORE
OVER SOUTH-CENTRAL AND SOUTHEAST NC WHERE THERE IS ACTUALLY
SOMEWHAT MORE CONFLUENT LOW LEVEL FLOW AND POOLING OF HIGHER
PWATS/INSTABILITY. PWATS ACROSS CENTRAL/SOUTHEAST NC ARE AROUND 2
TO 2.25 INCHES...AND THE 15Z CIRA-LPW DATA SHOWS A FAIRLY
CONCENTRATED POOL OF MOISTURE UP IN THE 500/300 MB LAYER WHICH
WILL CONTRIBUTE TO AN ENVIRONMENT CONDUCIVE FOR EFFICIENT RAINFALL
PROCESSES AND THUS HEAVIER RAINFALL RATES.

OVER THE NEXT FEW HOURS...CONVECTION WHICH HAS ALREADY BEGUN TO
INITIATE OVER CENTRAL/SOUTHERN NC AND DOWN THROUGH CENTRAL/WESTERN
SC SHOULD BECOME BETTER ORGANIZED AND EXPAND IN COVERAGE.
INCREASING MLCAPE VALUES TO NEAR 2500 J/KG ALONG WITH EFFECTIVE
BULK SHEAR VALUES OF OVER 50 KTS WILL BE SUPPORTIVE OF A HIGHLY
ORGANIZED CONVECTIVE CELL ENVIRONMENT WITH NUMEROUS MULTI-CELLS
AND SUPERCELLS THAT IN TIME WILL TEND TO LIKELY CONSOLIDATE/MERGE
FOR AN ENVIRONMENT CONDUCIVE FOR VERY HEAVY RAINFALL AND SOME
FLASH FLOODING.

FURTHER FACILITATING THE CONVECTIVE RAINFALL POTENTIAL IS ALSO THE
PROXIMITY OF FAVORABLE 250 MB RIGHT-ENTRANCE REGION JET DYNAMICS
AND ENHANCED SURFACE CONVERGENCE NEAR THE FRONT WHICH IS BEING
REINFORCED BY A NORTHEASTERLY LOW LEVEL SURGE ADVANCING DOWN THE
MID-ATLANTIC COAST.

THE LATEST HRRR/HRRRX GUIDANCE SUPPORTS RAINFALL AMOUNTS THROUGH
00Z OF AS MUCH AS 4 TO 6 INCHES WITH ISOLATED HEAVIER AMOUNTS
POSSIBLE. THE HEAVIEST THREAT AREA WILL BE CENTRAL AND EASTERN
NC...INCLUDING THE RALEIGH-DURHAM METROPOLITAN AREA. SOME FLASH
FLOODING IS LIKELY GIVEN THESE EXPECTED RAINFALL TOTALS...WHICH
SHOULD BE FACILITATED BY RAINFALL RATES AS HIGH AS 3 INCHES/HR.
WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...AKQ...GSP...ILM...MHX...RAH...RNK...

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

LAT...LON   36568021 36527853 36237679 35677645 35157654
            34747702 34487797 34497872 34817941 34998053
            35308128 35558141 35888140 36418107


Last Updated: 221 PM EDT FRI SEP 01 2017