MESOSCALE PRECIPITATION DISCUSSION 0347
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
322 AM EDT MON JUL 13 2015
 
AREAS AFFECTED...SOUTHEAST WISCONSIN...NORTHERN AND EASTERN
ILLINOIS...NORTHWEST INDIANA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 130721Z - 131321Z
 
SUMMARY...COMBINATION OF SLOW MOVING ELEVATED CONVECTION AHEAD OF
QUICK BURST OF HEAVY RAIN ASSOCIATED WITH SQUALL LINE TO INCREASE
FLASH FLOOD THREAT.    

DISCUSSION...STRONG UPPER LEVEL JET IS ROUNDING THE TOP OF SW TO
NE RIDGE ACROSS IOWA ALLOWING FOR INCREASED LEFT EXIT REGION
DIVERGENCE FOR ENHANCED UVVS ACROSS SW WISCONSIN AT THIS TIME
SHIFTING SOUTH SLOWLY.  AN EMBEDDED SHORT WAVE SWINGING OUT OF IA
TO DEEPEN AND TAKE OVER AS MCV CENTER.  THIS STRENGTHENS LOW LEVEL
WESTERLY LOW LEVEL FLOW AS SEEN IN  VWP TO OVER 30 KTS IN 85H-7H
INCREASING DEEP LAYERED MOISTURE CONVERGENCE ALONG NORTH SOUTH
FRONTAL BOUNDARY EXTENDING FROM SQUALL LINE NEAR EAU SOUTHWEST
WISCONSIN INTO CENTRAL ILLINOIS.  MUCAPES OF 2500-3000 J/KG WILL
SUPPORT STRONG UPDRAFTS THAT DEVELOP IN THE PRE-SQUALL LINE
ENVIRONMENT.  AMPLE TOTAL PWATS OVER 2" LIKELY MAKE FOR HIGHLY
EFFICIENT RAINFALL PRODUCERS WITH RATES IN EXCESS OF 1.5"/HR. 
THESE CELLS ALONE MAY LEAD TO SOME ISOLATED FLASH FLOODING
PARTICULARLY IF THEY SITUATE OVER URBAN CENTERS OR ACROSS THE
SATURATED SOILS OF NORTHERN ILLINOIS WHERE 1 HR FLASH FLOOD
GUIDANCE VALUES ARE IN THE 1-1.5" RANGE.  MORE LIKELY...THE FLASH
FLOOD THREAT IS ASSOCIATED WITH THESE PRE-SQUALL LINE TOTALS TO BE
COMPOUNDED WITH THE QUICK BURST OF 1-1.5" IN LESS THAN AN HOUR
FROM THE APPROACHING SQUALL LINE.  THE INTERFACE BETWEEN THE
SQUALL LINE AND FRONTAL SHOWERS WILL HAVE  THE HIGHEST POTENTIAL
FOR MERGERS INCREASING RATES/TOTALS OVER A SMALL LOCALIZED AREA. 

HI-RES GUIDANCE HAS BEEN A BIT MORE SCATTERED ESPECIALLY GIVEN THE
POOR PERFORMANCE OF THE MORE RELIABLE/RAPIDLY REFRESHING
HRRR...THOUGH RECENT RUN IS BECOMING IN BETTER AGREEMENT SHOWING
THE AXIS OF INCREASED TOTALS FROM SOUTHEAST WISCONSIN ACROSS
CHICAGOLAND INTO NORTHWEST INDIANA --- IN LINE WITH THE WRF-ARW
AND WRF-NMMB.  SWATH OF HIGHER TOTALS MAY HAVE A STRONG EASTERN
GRADIENT TO TOTALS GIVEN LACK OF INSTABILITY AS SEEN BY GOES
SOUNDER CAPE LOOP GOING TO ZERO ACROSS MICHIGAN AND CENTRAL AND
NORTHEAST INDIANA.

GALLINA

ATTN...WFO...ARX...DVN...ILX...IND...IWX...LOT...MKX...

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

LAT...LON   43778961 43358814 41998757 41008653 40208691 
            39938755 40158858 41418997 42579056 43219050