MESOSCALE PRECIPITATION DISCUSSION 0482
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1050 PM EDT THU JUL 21 2016
 
AREAS AFFECTED...SOUTHWEST WI...NORTHWEST IL...EASTERN IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 220250Z - 220700Z
 
SUMMARY...STRONG THUNDERSTORMS WITH HEAVY RAIN WILL FOCUS OVER
PORTIONS OF EASTERN IA AND NORTHWEST IL OVER THE NEXT FEW HOURS.
FLASH FLOODING WILL BE POSSIBLE.

DISCUSSION...A STRONG MCS IS ONGOING OVER SOUTHWEST WI AND
NORTHERN IL...WITH A WELL-DEFINED BOWING CONVECTIVE LINE SEEN
ADVANCING SOUTHWARD INTO A VERY UNSTABLE AIRMASS POOLED FROM
CENTRAL AND EASTERN IA OVER INTO CENTRAL AND NORTHERN IL. .
SURFACE OBSERVATIONS SHOW A WELL-DEFINED CONVECTIVELY INDUCED COLD
POOL CENTERED OVER SOUTHERN WI WHICH IS HELPING THE FORWARD
PROPAGATION OF THE CONVECTION. HOWEVER...THE NORTHWEST FLANK OF
THE MCS INVOLVING SOUTHWEST WI IS TENDING TO HANG UP AND
BACKBUILD/TRAIN OVER THE SAME AREA...WITH A VERY MOIST/UNSTABLE
LOW LEVEL FETCH EMANATING FROM EASTERN IA AND INTERCEPTING THE
CONVECTION.

OVER THE NEXT FEW HOURS...CONVECTION WITH VERY HEAVY RAINFALL
RATES ARE EXPECTED TO GRADUALLY FOCUS OVER FAR EASTERN IA AND
CONTINUE TO IMPACT NORTHWEST IL. PWATS AS PER GPS DATA ARE SEEN TO
BE AROUND 2.0 TO 2.1 INCHES...AND SURFACE DEWPOINTS OVER CENTRAL
AND EASTERN IA ARE GENERALLY NEAR 80F. THIS VERY MOIST AIRMASS IS
HELPING TO CONTRIBUTE TO MLCAPE VALUES OF 4000 TO 5000 J/KG OVER
CENTRAL AND EASTERN IA WHICH REFLECTS AN EXTREMELY UNSTABLE
AIRMASS.

RAINFALL RATES APPROACHING 3 INCHES/HR ARE ANTICIPATED GIVEN THE
DEEP MOISTURE AND HIGHLY EFFICIENT VERTICAL PROFILE. THE
BACKBUILDING AND/OR TRAINING NATURE OF THE CONVECTION IS EXPECTED
TO RESULT IN RAINFALL TOTALS OF AS MUCH AS 4 TO 6 INCHES WITHIN
THE THREAT AREA OVER THE NEXT FEW HOURS. THIS IS EXPECTED TO
ELEVATE THE THREAT FOR FLASH FLOODING. THE CONVECTION FARTHER EAST
BOWING TOWARD CENTRAL IL IS LIKELY TO BE PROGRESSIVE ENOUGH TO
LIMIT THE FLASH FLOOD POTENTIAL THERE...SO THE THREAT IS MAINLY
GOING TO BE CONFINED TO FAR EASTERN IA AND NORTHWEST IL.

ORRISON

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

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

LAT...LON   43369101 43099046 42578984 42048947 41448936 
            41058954 40799010 40909055 41409125 41979166 
            42809204 43349162