MESOSCALE PRECIPITATION DISCUSSION 0139
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
757 PM EDT SUN APR 23 2017

AREAS AFFECTED...CENTRAL/WESTERN SC...WESTERN NC...FAR NORTHEAST
TN...SOUTHWEST VA

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

VALID 232357Z - 240557Z

SUMMARY...HEAVY TO EXCESSIVE RAINFALL IS EXPECTED THROUGH THIS
EVENING ACROSS THE SC/NC PIEDMONT AND INTO THE SOUTHERN
APPALACHIANS AS FAR NORTH AS SOUTHWEST VA. STRONGER EMBEDDED
THUNDERSTORMS OVER NC/SC WILL ENHANCE FLASH FLOODING POTENTIAL.

DISCUSSION...THE LATEST EXPERIMENTAL GOES-16 WV/IR SATELLITE
IMAGERY SHOWS A DEEP LAYER LOW PRESSURE SYSTEM SLOWLY CROSSING THE
TN VALLEY AND MUCH OF THE SOUTHEAST U.S. WHICH IS HELPING TO
ADVANCE A CONVECTIVELY ACTIVE COLD FRONT ACROSS THE SOUTHEAST
COASTAL PLAIN. A RATHER DEEP SURGE OF SUBTROPICAL MOISTURE
CONTINUES TO LIFT NORTH AROUND THE EAST SIDE OF THE CLOSED LOW
WHICH COUPLED WITH STRONG LARGE SCALE ISENTROPIC LIFT...UPPER
LEVEL DIFFLUENCE AND OROGRAPHIC FORCING IS RESULTING IN WIDESPREAD
MODERATE TO HEAVY RAIN UP ACROSS THE SC/NC PIEDMONT AND INTO THE
SOUTHERN APPALACHIANS. FARTHER SOUTH AND CLOSER TO A STRONG
QUASI-STATIONARY FRONT ACROSS FAR EASTERN GA AND SOUTHERN
SC...THERE IS SUFFICIENT INSTABILITY FOR NUMEROUS THUNDERSTORMS
AND LOCALLY VERY HEAVY RAINFALL RATES OF UP 2 INCHES/HR.

RECENT RUNS OF THE HRRR/HRRRX SHOW A PERSISTENCE OF CONVECTION
THROUGH THE EVENING HOURS ACROSS ESPECIALLY CENTRAL SC AND PARTS
OF THE SC/NC PIEDMONT WHERE A NOSE OF ELEVATED INSTABILITY AND
HIGHER PWATS NEAR 1.5 INCHES WILL BE MAINTAINED BY DEEPER LAYER
S/SE FLOW OVERRUNNING THE AFOREMENTIONED STATIONARY FRONT. A
GRADUAL UPTICK IN LARGER SCALE ASCENT AHEAD OF THE UPPER LOW IS
EXPECTED TOO AS MODEST 250 MB  RIGHT-ENTRANCE REGION JET DYNAMICS
SET UP OVER THIS REGION THROUGH THE EVENING. MEANWHILE...FARTHER
NORTH...STRONG ISENTROPIC LIFT AND OROGRAPHIC FORCING WILL
MAINTAIN A LARGE AREA OF MODERATE TO HEAVY RAIN ACROSS THE
SOUTHERN APPALACHIANS AND ADJACENT PIEDMONT. MANY AREAS INCLUDING
THE FAR WESTERN CAROLINAS...EASTERN TN AND SOUTHWEST VA HAVE
ALREADY SEEN AS MUCH AS 3 TO 5 INCHES OF RAIN WITH THIS EVENT.

OVER THE PIEDMONT REGION AND EAST-FACING SLOPES OF THE SOUTHERN
APPALACHIANS...EXPECT ANOTHER 1 TO 3 INCHES OF RAIN TO BE POSSIBLE
THROUGH 06Z. MEANWHILE FARTHER SOUTH AND CLOSER TO THE STATIONARY
FRONT OVER SC...THE ELEVATED INSTABILITY AXIS SHOULD PROMOTE
HEAVIER RAINFALL RATES AND POTENTIAL FOR CELL-MERGERS AND SOME
SMALL SCALE CELL-TRAINING. THE HRRR/HRRRX GUIDANCE SUGGESTS AS
MUCH AS 3 TO 5 INCHES OF RAIN MAY FALL AT LEAST LOCALLY THROUGH
06Z...WITH THE GREATEST POTENTIAL FOCUSED OVER CENTRAL/NORTHERN SC.

THE ADDITIONAL HEAVY RAIN FALL WILL ELEVATE THE THREAT OF FLASH
FLOODING INCLUDING MUDSLIDES AND DEBRIS FLOWS OVER THE HIGHER
TERRAIN GIVEN THE WET ANTECEDENT CONDITIONS. FARTHER SOUTH...AND
GENERALLY OVER CENTRAL/NORTHERN SC...THE HEAVIER RAINFALL RATES
WHICH MAY REACH 2 INCHES/HR WILL ALSO FOSTER ENHANCED FLASH FLOOD
POTENTIAL. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...CAE...CHS...GSP...ILM...MRX...RAH...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   37408103 37318025 36937993 36428000 35768019
            34948004 34478007 33918019 33288052 33198102
            33308171 33778227 34398273 34908286 35638284
            36208263 36788212 37158161