MESOSCALE PRECIPITATION DISCUSSION 0534
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1127 AM EDT SAT JUL 22 2017

AREAS AFFECTED...PORTIONS OF OH, WV, AND WESTERN PA

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

VALID 221526Z - 222126Z

SUMMARY...THUNDERSTORMS ARE BEGINNING TO CONCENTRATE ACROSS
NORTHEAST OH AND REDEVELOP ACROSS PORTIONS OF SOUTHERN OH.  HOURLY
RAIN RATES UP TO 2.5" WITH LOCAL AMOUNTS TO 4" ARE POSSIBLE.

DISCUSSION...AN MCV FROM EARLIER CONVECTIVE ACTIVITY IS GAINING
CENTRAL CONVECTION ACROSS NORTHEAST OH, WHILE OTHER ACTIVITY
WITHIN ITS TAIL ACROSS SOUTH-CENTRAL OH HAS RECENTLY SHOWN SIGNS
OF REDEVELOPING.  RAIN RATES ARE CURRENTLY MODEST, IN THE 0.5-1"
AN HOUR RANGE.  PRECIPITABLE WATER VALUES ARE 1.75-2" IN THIS
AREA.  ML CAPE VALUES ARE CURRENTLY 250-1500 J/KG IN THIS REGION,
AND RISING.  SPC MESOANALYSES SHOW CIN BEGINNING TO ERODE NEAR THE
MCV.  INFLOW AT 850 HPA IS WESTERLY AT 25-35 KTS PER VAD WIND
PROFILES ACROSS SOUTHERN OH AND SOUTHWEST PA, NEAR THE MAGNITUDE
OF THE MEAN 850-400 HPA WIND.  EFFECTIVE BULK SHEAR IN THE REGION
IS 30-40 KTS.

RAP GUIDANCE SHOWS INSTABILITY SOUTH OF THE OUTFLOW
BOUNDARY/EFFECTIVE FRONT IN SOUTHERN OH/SOUTHERN WV BUILDING
WITHIN A CAPPED REGION ALOFT WHILE MOVING NORTHWARD TOWARDS
CENTRAL OH AND SOUTHWEST PA WITH TIME, CLOSER TO THE MAIN FRONTAL
BOUNDARY.  THE MCV ITSELF IS EXPECTED TO MOVE EAST-SOUTHEAST AT 25
KTS CLOSER TO THE FORECAST INSTABILITY TOWARDS CENTRAL PA WITH THE
BEST INFLOW AT 850 HPA REMAINING NEAR THE UPPER OH VALLEY OVER THE
NEXT SEVERAL HOURS.  DUE TO THE BULK SHEAR AND NEARLY
UNIDIRECTIONAL FLOW IN THE REGION, SHORT TRAINING CONVECTIVE BANDS
ARE THE MAIN HEAVY RAIN THREAT, WITH ANY DEVELOPING MESOCYCLONES
ADDING TO THE HEAVY RAIN RISK.  AVAILABLE MOISTURE AND INSTABILITY
SUPPORT HOURLY RAIN RATES UP TO 2.5".  THE MESOSCALE GUIDANCE
SHOWS A GOOD SIGNAL FOR 2.5-3.5" OVER THE NEXT SEVERAL HOURS --
BELIEVE THE CEILING IS CLOSER TO 4" SHOULD ANY CONVECTION TRAIN
FOR MORE THAN AN HOUR.  THIS DEGREE OF RAINFALL COULD LEAD TO
ISSUES IN RUGGED TERRAIN AND WHERE SOILS ARE PARTIALLY SATURATED.

ROTH

ATTN...WFO...CLE...CTP...ILN...LWX...PBZ...RLX...

ATTN...RFC...MARFC...OHRFC...

LAT...LON   41908116 41697864 40807738 39297840 38467957
            38838170 39968450 40308304