MESOSCALE PRECIPITATION DISCUSSION 0031
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
510 PM EDT WED APR 08 2015
 
AREAS AFFECTED...FAR EASTERN IL...CENTRAL IN...SOUTHWEST OH 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 082109Z - 090030Z
 
SUMMARY...POCKETS OF SLOW-MOVING SHOWERS AND THUNDERSTORMS
EXPECTED OVER THE NEXT COUPLE OF HOURS WITH LOCALLY INTENSE
RAINFALL RATES. SOME FLASH FLOODING IS POSSIBLE GIVEN RECENT HEAVY
RAINS.

DISCUSSION...SHOWERS AND THUNDERSTORMS ARE EXPANDING IN COVERAGE
OVER PORTIONS OF CENTRAL AND SOUTHERN IN ASSOCIATION WITH A WEAK
SURFACE WAVE THAT IS ADVANCING EAST OUT OF EASTERN IL. A WARM
FRONT DOWNSTREAM FROM THIS WAVE IS VERY SLOWLY LIFTING NORTH AND
ALLOWING A DEEPER POOL OF MOISTURE AND INSTABILITY TO ADVANCE
NORTHEAST OUT OF THE LOWER OH AND MID MS VALLEYS.

OVERWHELMING THE BEST INSTABILITY IS FOCUSED ALONG AN OUTFLOW
BOUNDARY FARTHER SOUTH AND CLOSER TO THE OH RIVER...BUT SUFFICIENT
DIURNAL HEATING HAS ENSUED THIS AFTERNOON FOR CONVECTION TO
INITIATE WITHIN THE WARM SECTOR AHEAD OF THE WEAK SURFACE WAVE.
CONVECTION IS RATHER ORGANIZED OWING TO RATHER ROBUST BULK SHEAR
PROFILES...BUT THE CONVECTION IS TENDING TO MOVE RATHER SLOWLY AND
THERE HAVE BEEN MULTIPLE CELL-MERGERS AND OVERSHOOTING TOPS NOTED
OVER THE LAST HOUR OR SO. THIS IS LEADING TO THE EVOLUTION OF
SOMEWHAT LARGER SCALE CLUSTERS OF CONVECTION THAT WILL FAVOR
INTENSE RAINFALL RATES INTO THE EVENING HOURS. THIS WILL
ESPECIALLY BE THE CASE WHERE OVERSHOOTING TOPS AND CELL-MERGERS
OCCUR.

THE LATEST HIRES MODELS ARE DOING A TERRIBLE JOB HANDING THE
ACTIVITY OVER CENTRAL IN...AS THE GUIDANCE STRONGLY FAVORS MUCH
MORE CONVECTION NEAR THE OUTFLOW BOUNDARY FARTHER SOUTH.
NEVERTHELESS...CONVECTIVE TRENDS AND SURFACE OBSERVATIONS FAVOR
THE ACTIVITY FARTHER NORTH LINGERING OVER THE NEXT FEW HOURS AT
LEAST UNTIL ABOUT 00Z. GIVEN RECENT HEAVY RAINS FOR PORTIONS OF
THE THREAT AREA...ADDITIONAL HEAVY CONVECTIVE RAINS WILL FOSTER
THE POTENTIAL FOR FLASH FLOODING. 

ORRISON

ATTN...WFO...ILN...ILX...IND...IWX...JKL...

ATTN...RFC...NCRFC...OHRFC...

LAT...LON   40608507 40368398 39838309 39038293 38578315 
            38498360 38888428 39118516 39258591 39338734 
            39358815 39588831 40088738 40548615