MESOSCALE PRECIPITATION DISCUSSION 0715
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1140 PM EDT THU SEP 29 2016
 
AREAS AFFECTED...NORTHWEST NC...SOUTHWEST VA...SOUTHEAST WV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 300340Z - 300730Z
 
SUMMARY...ADDITIONAL TRAINING OF HEAVY SHOWERS AND THUNDERSTORMS
WILL CONTINUE OVER THE NEXT SEVERAL HOURS. FLASH FLOODING WILL
REMAIN POSSIBLE.

DISCUSSION...RADAR IMAGERY CONTINUES TO SHOW MULTIPLE BANDS OF
TRAINING SHOWERS AND THUNDERSTORMS DEVELOPING OVER PORTIONS OF
NORTHWEST NC...SOUTHWEST VA AND SOUTHEAST WV...WITH THE ACTIVITY
ADVANCING GENERALLY NORTH-NORTHWEST INTO THE SOUTHEAST FACING
SLOPES OF THE HIGHER TERRAIN ACROSS THIS REGION. OVER THE LAST TWO
HOURS THERE HAS BEEN SOME SUGGESTION OF A SLIGHT UPTICK IN
INTENSITY WHICH APPEARS TO BE MORE DIRECTLY TIED INTO IMPROVING
RIGHT-ENTRANCE REGION JET DYNAMICS AROUND THE EASTERN FLANK OF THE
UPPER LOW CENTER OVER CENTRAL KY.

INSTABILITY IS THE ONE MITIGATING FACTOR FOR MORE ORGANIZED
CONVECTION...BUT THERE IS A MODEST GRADIENT OF NOTE OVER NORTHWEST
NC AND SOUTHWEST VA WHICH HAS BEEN GENERALLY THE INITIATING POINT
FOR THE ACTIVITY THIS EVENING. HOWEVER...THERE IS LARGE SCALE
ASCENT ALONG WITH UPSLOPE EAST TO SOUTHEAST FLOW INTO THE TERRAIN.
THE PERSISTENCE OF THE BANDS OF CONVECTION AND ESPECIALLY WITH THE
FOCUS UP OVER THE OROGRAPHICALLY FAVORED TERRAIN IS EXPECTED TO
INCREASE THE FLASH FLOOD THREAT OVER THE NEXT COUPLE OF HOURS
BEYOND WHAT HAS ALREADY MATERIALIZED THIS EVENING.

THE 12Z NSSL-WRF SUGGESTS A NW/SE AXIS OF TRAINING CONVECTION WITH
ADDITIONAL AMOUNTS OF AS MUCH AS 2 TO 4 INCHES THROUGH 06Z...WITH
POSSIBLY MORE THEREAFTER. THE LATEST HRRR-TLE OUTPUT ALSO SUGGESTS
PERSISTENT ELEVATED PROBABILITIES FOR EXCEEDENCE OF 1 INCH OF
RAIN/HR THROUGH 06Z ALONG THE WV/VA BORDER EXTENDING FROM
NORTHWEST OF KROA UP TO NEAR KHSP AND OVER TO KLWB.

RAINFALL RATES HAVE ALREADY BEEN APPROACHING LOCALLY 1.5 INCHES/HR
BASED ON DUAL-POL ESTIMATES...AND THUS THE ADDITIONAL FOCUS OF
RAINS OVERNIGHT WILL CONTINUE TO FLASH FLOOD THREAT.

ORRISON

ATTN...WFO...GSP...LWX...RAH...RLX...RNK...

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

LAT...LON   38967962 38537951 38087947 37497945 36458004 
            35998071 36018119 36228147 36818161 37138149 
            37618111 38178066 38868040