MESOSCALE PRECIPITATION DISCUSSION 0414
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
331 PM EDT FRI JUL 06 2018

AREAS AFFECTED...SRN VA...NC...UPSTATE SC

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

VALID 061930Z - 070100Z

SUMMARY...STORMS WERE BECOMING MORE NUMEROUS AND CONCENTRATED IN
CENTRAL NORTH CAROLINA AND ADJACENT AREAS THIS AFTERNOON. THESE
STORMS WERE MOVING SLOWLY AND MAY PRODUCE RAIN RATES UP TO 2-3
IN/HR IN SOME LOCATIONS...WHICH COULD LEAD TO FLASH FLOODING.

DISCUSSION...RAP MODEL ANALYSIS SHOWED (AND 12Z RAOBS IMPLIED) A
COL AND GENERAL WEAKNESS IN THE MID-LEVEL FLOW CENTERED ON NORTH
CAROLINA. THIS WAS INDEED WHERE LATEST RADAR TRENDS SHOWED THE
SLOWEST AVERAGE STORM MOTIONS AND TRENDS FOR STALLING AND
BACKBUILDING CLUSTERS OF STORMS... PARTICULARLY FROM GREENSBORO NC
EAST TO JUST NORTH OF THE TRIANGLE REGION. EVEN THE NORTHERN END
OF A FAIRLY PROGRESSIVE LINE OF THUNDERSTORMS BEGAN TO STALL IN
ROCKINGHAM AND GUILFORD COUNTIES AS IT APPROACHED THAT WEAKNESS IN
THE MID-LEVEL FLOW. CONVECTION WAS GENERALLY BECOMING MORE
CONCENTRATED IN THIS COL...AND IN A COINCIDENT PLUME OF HIGH
PRECIPITABLE WATER VALUES (BETWEEN 1.8 AND 2.1 INCHES). VALUES
THIS HIGH SHOULD ENABLE EFFICIENT RAINFALL PRODUCTION... AND WITH
MODERATE TO STRONG INSTABILITY REGIONWIDE 2-3 IN/HR RAIN RATES
SHOULD BE ACHIEVABLE. THEREFORE... FLASH FLOODING DOES APPEAR
POSSIBLE ACROSS THE REGION THIS AFTERNOON. GIVEN THE INCREASING
CONCENTRATION OF CONVECTION AND SLOWING STORM MOTIONS... PARTS OF
THE REGION WERE UPGRADED TO A SLIGHT RISK ON THE DAY 1 EXCESSIVE
RAINFALL OUTLOOK.

WITH THE SYNOPTIC COLD FRONT WELL TO THE NORTH... THERE IS A LACK
OF A STRONG LOW-LEVEL FOCUS TO LOCK CONVECTION INTO A SPECIFIC
LOCATION FOR AN EXTENDED PERIOD OF TIME. LOW-LEVEL FLOW IS ALSO
RATHER WEAK... SO STORMS SHOULD HAVE A TENDENCY TO DRIFT AND
INDIVIDUAL UPDRAFTS MAY NOT BE ABLE TO LAST FOR EXTENDED PERIODS
OF TIME. NEVERTHELESS... WITH THE SLOW STORM MOTIONS AND ABUNDANT
LOW-MID LEVEL MOISTURE... LOCALLY HEAVY RAINFALL APPEARS VERY
LIKELY AND THIS MAY PRODUCE LOCALIZED FLASH FLOODING AS WELL...
PARTICULARLY IF THE 2-3 IN/HR RATES CAN ALIGN WITH SOME OF THE
URBANIZED AREAS IN THE REGION.

LAMERS

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

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

LAT...LON   37737635 37247533 36577557 36017689 34877999
            34768187 35628187 36298043 37137925 37637805