MESOSCALE PRECIPITATION DISCUSSION 0886
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
115 PM EDT SAT OCT 14 2017

AREAS AFFECTED...NORTHERN IL...NORTHERN IND...SOUTHWEST MI

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

VALID 141715Z - 142200Z

SUMMARY...PERSISTENT TRAINING OF MODERATE SHOWERS WITH EMBEDDED
CONVECTION TO CONTINUE THROUGH EARLY AFTERNOON ADDING TO 2-3"
TOTALS ALREADY OBSERVED KEEPING FLASH FLOODING POSSIBLE.

DISCUSSION...GOES-E WV LOOP SHOWS A SUBTLE FLAT SHORTWAVE ALONG
THE SUBTROPICAL STREAM GRADIENT ACROSS S CENTRAL IA ATTM...WITH
LOCALIZED DOWNSTREAM S/W RIDGING/DIFFLUENCE OF THE UPPER LEVEL
FLOW PATTERN PROVIDING MODEST UL DIVERGENCE/MID-LEVEL DPVA FOR
BROADER SCALE ASCENT.  16Z MESO ANALYSIS DEPICTS A WEAK 1015MB LOW
STARK COUNTY IL WHICH APPEARS TO BE THE NOSE OF INCREASING SWLY
LOW LEVEL JET (FROM 20KTS AT 850 TO 30-35KTS) PER VWP NETWORK AND
RAP ANALYSIS FIELDS.  CLEARING SKIES/DIFFERENTIAL HEATING HAS
INTENSIFIED THE BOUNDARY ACROSS N IL WITH TEMPS INTO THE UPPER 70S
AND MID 60S TDS...ALLOWING FOR INSTABILITY TO REACH CAPPED
500-1000 MLCAPE ATTM.  THOUGH WITH STRENGTHENED ASCENT AND LOW
LEVEL MOISTURE CONVERGENCE...TCU ARE BUBBLING ACROSS NW IL TOWARD
SOUTHERN CHICAGO.  THIS CONVECTIVE DEVELOPMENT WILL CONTINUE TO
ENHANCE AND GIVEN MEAN FLOW REMAINS FAIRLY UNIDIRECTIONAL FOR THE
NEXT FEW HOURS...TRAINING OF CONVECTION REMAINS LIKELY PERHAPS
ALIGNING WITH SWATH OF 2-3.5" TOTALS FROM N LA SALLE COUNTY TO
COOK COUNTY AND EXTENDING ACROSS S LAKE MI TO SW MI.

MOISTURE FLUX FROM THE STRENGTHENING LLJ IS EXPECTED TO ENHANCE
TPWS TO NEAR 2" AND SUPPORT RATES AOA 2-2.5"/HR.  THOUGH WITH
CONTINUED CELL MOTIONS REMAINING AT 45-50KTS HOURLY TOTALS OF
1.5-2"/HR ARE POSSIBLE BUT REQUIRE THE TRAINING NATURE OF
INDIVIDUAL CELLS TO ACCOMPLISH THESE TOTALS.  THE HIGH RATES/WET
GROUNDS AND AN ADDITIONAL 2-4" TOTALS ACROSS N IL TO SW MI THROUGH
22Z WILL CONTINUE TO POSE AT LEAST LONGER DURATION/INUNDATION
FLOODING WITH POSSIBLE FLASHY CONDITIONS ESPECIALLY IN THE
CHICAGOLAND URBAN CORRIDOR.  THIS FOLLOWS BEST WITH LAST FEW RUNS
OF THE HRRR/HRRRV3 WITHIN THE HI-RES GUIDANCE SUITE REGARDING
HANDLING THE CURRENT EVOLUTION. 

GALLINA

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

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

LAT...LON   42738499 42338456 41658541 41158742 40649031
            41269046 42288941 42438754 42608617