MESOSCALE PRECIPITATION DISCUSSION 0308
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 AM EDT FRI AUG 22 2014
 
AREAS AFFECTED...NORTHERN IL...CENTRAL AND NORTHERN IN...WESTERN
OH 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 220630Z - 221200Z
 
SUMMARY...NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED OVER THE
NEXT SEVERAL HOURS WITH CELL-MERGERS AND SOME TRAINING EXPECTED.

DISCUSSION...THE LATEST IR SAT IMAGERY SHOWS A RAPIDLY EXPANDING
AREA OF COLD-TOPPED CONVECTION OVER NERN IL AND INTO NWRN IN. THE
ACTIVITY IS DEVELOPING JUST EAST OF THE CREST OF A LARGE SCALE
RIDGE AXIS FOCUSED OVER THE MID MS VLY AND APPEARS IN PART TO BE
GETTING ORGANIZED WITH THE AID OF A WEAK SHORTWAVE IMPULSE AND
ASSOCD JET STREAK TRAVERSING WI AND NRN IL ATTM.

THERE HAD BEEN A BIT OF A MID LVL CAPPING INVERSION THAT WAS
PREVENTING CONVECTION THROUGH MUCH OF THE EVENING...BUT THE LATEST
RAP ANALYSIS CONFIRMS THAT MUCH OF THAT HAS ERODED AND SO
CONVECTION IS EXPECTED TO CONTINUE TO EXPAND AND ORGANIZE THE NEXT
FEW HOURS OVER NERN IL AND ESP DOWNWIND INTO CNTRL/NRN IN AND WRN
OH THROUGH THE EARLY MORNING HOURS. THE LOW LVL JET IS NOT
PARTICULARLY STRONG...ON THE ORDER OF 30 KTS...BUT SUFFICIENT
FORCING ALOFT WILL COMPENSATE AND THERE IS SUFFICIENT ELEVATED
INSTABILITY AND DEEP MOISTURE FOR THE CONVECTION TO BE INTENSE
FROM A RAINFALL PERSPECTIVE.

THE LATEST HI-RES MODELS INCLUDING THE 00Z NAM-CONEST...00Z
ARW...AND 00Z NMMB ALL SHOW SIGNALS FOR VERY HVY RAINFALL THROUGH
THE REMAINDER OF THE NIGHT. THERE IS DISAGREEMENT ON THE PLACEMENT
OF HEAVIEST AMTS...BUT A COMMON OVERLAP IS NRN IN AND ALONG THE
IN/OH BORDER WHERE ALL THREE MODELS SUGGEST RAINFALL POTENTIAL
EXCEEDING 5 INCHES THROUGH 12Z.

THE ENVIRONMENT IS CONDUCIVE FOR CELL-MERGERS AND TRAINING THROUGH
THE NIGHT AND SO THESE RAINFALL AMTS ARE NOT UNREALISTIC. GIVEN
PWATS AOA 2 INCHES...THERE WILL BE A NOTABLE FLASH FLOOD THREAT
AND ESP WHERE HVY RAINS HAD OCCURRED EARLIER. WILL CONTINUE TO
MONITOR.

ORRISON

ATTN...WFO...CLE...ILN...IWX...IND...LOT...ILX...DVN...

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

LAT...LON   39728563 40328685 40668836 40768998 41259018 41828957
            42108874 42158791 41978672 41468496 40808369 40088306
            39318348 39288455 39728563