MESOSCALE PRECIPITATION DISCUSSION 0499
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 AM EDT FRI SEP 18 2015
 
AREAS AFFECTED...N ILLINOIS...N INDIANA...SW MICHIGAN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180800Z - 181200Z
 
SUMMARY...GENERAL DOWNWARD TREND OF CONVECTION WITH SOME EMBEDDED
STRONG CLUSTERS REMAINING A FLASH FLOOD THREAT FOR THE REMAINDER
OF THE EARLY MORNING HOURS.

DISCUSSION...RADAR AND IR LOOP SHOWS A GENERAL DOWNWARD TREND WITH
CONVECTIVE CORES ALONG A OUTFLOW REINFORCED WEAK E-W FRONTAL
BOUNDARY ACROSS NORTHERN IL ACROSS S LAKE MICHIGAN INTO SW MI.
THOUGH MUCH OF THE INSTABILITIES HAVE BEEN EXHAUSTED AS RAP
ANALYSIS MUCAPES HAVE REDUCED TO THE 750 J/KG RANGE AND FALLING
AND THE LOW LEVEL JET IS GENERALLY VEERING PARALLEL TO THE E-W
FRONTAL ZONE AS THE SYNOPTIC WAVE SHIFTS NORTHEAST OVER LAKE
MICHIGAN...SOME ISOLATED MAXIMIZED POCKETS OF MOISTURE CONVERGENCE
NEAR THE WEAK SURFACE LOW/TRIPLE POINT INTERSECTION WITH ADVANCING
COLD FRONT AND ALONG THE NOSE OF THE SLOWLY WEAKENING LLJ
NEAR/CHICAGO CONTINUE TO INITIATE DEEP CORES WITH IR TOPS COOLING
TO -60 TO -65C INCLUDING A -69C IN BUREAU COUNTY IN W IL.  IN
THESE STRONGER CELLS... EFFICIENT RAIN PROCESSES WILL CONTINUE
GIVEN AOA 2" TPW...WITH RATES IN EXCESS OF 2"/HR. 

THE SLACKING LOW LEVEL FLOW AND CELLS TRACKING ALONG THE
NORTHEASTERN PERIPHERY OF NARROW RIDGING ALOFT...UPWIND
PROPAGATION VECTORS HAVE REDUCED TO NEAR ZERO OR EVEN NOW OUT OF
THE NORTHEAST TO ALLOW FOR A SHORT PERIOD OF POTENTIAL UPSTREAM
REDEVELOPMENT IF IT CAN BE MANAGED MAINLY OVER COLD POOLS AND WITH
THE MAIN WAVE EXITING AND DRIER AIR ADVECTING IN ALOFT...THE
POTENTIAL FOR THESE COLD POOLS AND OUTFLOWS INCREASES ALLOWING FOR
THE  POTENTIAL FOR SOME REMAINING TRAINING FOR INCREASED TOTALS IN
THE 1-3" RANGE OVER THE NEXT 3-4 HOURS...MAINLY OVER N IL NEAREST
THE TRIPLE POINT WHERE ISENTROPIC ASCENT AND CONVERGENCE WILL BE
MAXIMIZED.  

GALLINA

ATTN...WFO...DVN...GRR...ILX...IWX...LOT...

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

LAT...LON   42268599 41828563 41508580 40898612 40658729 
            40518786 40408873 40688972 40859005 41459001 
            41898951 42068902 42268658