MESOSCALE PRECIPITATION DISCUSSION 0159
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT MAY 30 2015
 
AREAS AFFECTED...SRN/CNTRL ILLINOIS INTO CNTRL/NRN INDIANA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 301859Z - 310059Z
 
SUMMARY...FLASH FLOODING WILL BE POSSIBLE THROUGH THE REST OF THE
AFTERNOON INTO THE EARLY EVENING FROM SRN/CNTRL ILLINOIS INTO
PORTIONS OF W-CNTRL INDIANA. THE THREAT IS GREATEST ACROSS WRN
PORTIONS OF THE THREAT AREA WHERE FLASH FLOOD GUIDANCE VALUES OF
1.5 TO 2.5 INCHES IN 3 HOURS COULD BE MET.

DISCUSSION...AT 18Z...WATER VAPOR IMAGERY DEPICTED A WELL DEFINED
MCV OVER THE ERN MISSOURI/ARKANSAS BORDER WITH A BAND OF MID-UPPER
LEVEL MOISTURE OVER THE MISSISSIPPI/ALABAMA BORDER EXTENDING NWD
AND WRAPPING INTO THE NRN SIDE OF THE CIRCULATION CENTER. AT THE
SURFACE...AN AXIS OF CONVERGENCE...ORIENTED FROM SW TO
NE...EXTENDED FROM NEAR STL TO DNV TO GUS...OUT AHEAD OF A
PROGRESSIVE COLD FRONT. THIS AXIS OF CONVERGENCE HAS BEEN A FOCUS
FOR CONVECTION OVER THE PAST FEW HOURS WHERE THE SPC MESOANALYSIS
INDICATES ROUGHLY 1000 J/KG OF ML CAPE IS PRESENT GIVEN GREATER
INSOLATION FROM EARLIER THIS AFTERNOON.

AS THE MCV CONTINUES NNEWD OVER THE NEXT 6 HOURS...A ZONE OF
STRONGER 850-700 MB FLOW...ROUGHLY 30-35 KTS...IS EXPECTED TO
ACCOMPANY THE LOW LEVEL CIRCULATION INTO THE THREAT AREA WHICH
WILL BE ROUGHLY PARALLEL TO OBSERVED/FORECAST MEAN STORM MOTIONS.
IN ADDITION...ENHANCED UPPER DIFFLUENCE IS FORECAST TO ACCOMPANY
THE LIFTING MCV THROUGH THE REMAINDER OF THE AFTERNOON INTO THE
EARLY EVENING. DESPITE A RAINFALL DEFICIT ACROSS ILLINOIS/INDIANA
OVER THE PAST 7-14 DAYS...FLASH FLOOD GUIDANCE IS LOWER ACROSS THE
WRN PORTION OF THE THREAT AREA WHERE 3 HOURLY RATES OF 1.5 TO 2
INCHES ARE POSSIBLE AS THE CONVERGENCE AXIS SLOWLY PIVOTS NWWD. 

RECENT 12Z HI-RES MODEL GUIDANCE DOES NOT DEPICT WIDESPREAD
EXCEEDANCE OF 3 HR FLASH FLOOD GUIDANCE...BUT THE THREAT AREA
APPEARS TO BE A FOCUS FOR LOCALLY HEAVY RAIN THROUGH 01Z WITH
POSSIBLE TRAINING LEADING TO A SOMEWHAT LOW END FLASH FLOOD THREAT.

OTTO

ATTN...WFO...ILX...IND...IWX...LOT...LSX...PAH...

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

LAT...LON   41338625 41118574 40718580 40198644 39098779 
            38308832 37948872 37878926 38718999 39638978 
            40178920 40798829 41198744