MESOSCALE PRECIPITATION DISCUSSION 0671
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
545 AM EDT SAT AUG 12 2017

AREAS AFFECTED...CENTRAL/EASTERN NC...SOUTH-CENTRAL/SOUTHEAST VA

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

VALID 120940Z - 121430Z

SUMMARY...SLOW-MOVING AND LOCALLY TRAINING BANDS OF HEAVY SHOWERS
AND THUNDERSTORMS WILL BE LIKELY OVER THE NEXT SEVERAL HOURS. SOME
FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE LATEST RADAR IMAGERY HAS BEEN SHOWING SOME
GRADUAL INCREASE IN COVERAGE OF HEAVY SHOWERS AND THUNDERSTORMS
OVER PORTIONS OF CENTRAL NC NEAR THE RALEIGH AREA...AND EXTENDING
NORTH UP INTO PARTS OF SOUTHERN VA. NON-OPERATIONAL GOES-16 10.3
MICRON/IR IMAGERY HAS BEEN SHOWING SOME ADDITIONAL COOLING OF THE
CONVECTIVE TOPS OVER THE LAST 30 MINUTES AND SUGGESTIVE OF
STRONGER FORCING OVER THE REGION.

THE CONVECTION IS GENERALLY DEVELOPING WITHIN A VERY MOIST AND
MODESTLY UNSTABLE ENVIRONMENT...AND WITH CONFLUENT LOW LEVEL FLOW
ASSOCIATED WITH A BROAD TROUGH OF LOW PRESSURE OVER THE SOUTHERN
MID-ATLANTIC REGION. MEANWHILE...THE UPPER LEVEL FLOW IS ALSO
BROADLY DIFFLUENT WHICH HAS HELPED FACILITATE SOME DEEPER LAYER
ASCENT.

SEVERAL RUNS OF THE HRRR AND ESPECIALLY THE HRRRX GUIDANCE HAVE
BEEN DEPICTING SOME LOCALLY VERY HEAVY RAINFALL TOTALS EARLY THIS
MORNING ACROSS PARTS OF MAINLY NORTHERN NC AND INTO AREAS OF
SOUTHERN AND SOUTHEAST VA. THE HRRRX GUIDANCE IS PROBABLY
OVERDONE...BUT WITH PWATS NEAR 2.25 INCHES...AND THE COOLING
CONVECTIVE TOPS...THE RAINFALL RATES ARE LIKELY TO BE QUITE
INTENSE AND MAY REACH 2.5 INCHES/HR.

BROADLY CYCLONIC FLOW AND SOMEWHAT MORE FOCUSED MOISTURE TRANSPORT
FROM THE SOUTH IS EXPECTED THROUGH MID MORNING...AND GIVEN THE
PROXIMITY OF AN INSTABILITY GRADIENT ALONG WITH AN APPROACHING
UPPER TROUGH OVER THE OH VALLEY...THE THREAT OF MULTIPLE
SLOW-MOVING CLUSTERS OF CONVECTION WILL CONTINUE. SOME EPISODIC
TRAINING OF CELLS WILL BE POSSIBLE AS WELL WHICH COULD ENHANCE
RAINFALL AMOUNTS.

EXPECT THROUGH MID TO LATE MORNING AS MUCH AS 2 TO 4 INCHES OF
RAIN...WITH SOME ISOLATED AMOUNTS TO NEAR 5 INCHES WHERE TRAINING
OF CELLS OCCUR. SOME FLASH FLOODING IS POSSIBLE AND ESPECIALLY IN
THE VICINITY OF ANY URBANIZED AREAS.

ORRISON

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

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

LAT...LON   37617728 37427684 36997665 36267688 34867771
            34137840 34287920 34857935 35717919 36757865
            37407800