MESOSCALE PRECIPITATION DISCUSSION 0475
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 PM EDT MON JUL 18 2016
 
AREAS AFFECTED...SOUTHERN ILLINOIS AND CENTRAL/SOUTHERN INDIANA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 181730Z - 182200Z
 
SUMMARY...SHOWERS AND THUNDERSTORMS ARE INCREASING IN ASSOCIATION
WITH THE INTERSECTION OF TWO OUTFLOW BOUNDARIES FROM EARLIER
CONVECTION. HIGHLY MOIST AND UNSTABLE (ALBEIT RELATIVELY MODEST)
INFLOW INTO THE DEVELOPING CONVECTION SHOULD SUPPORT HEAVY
RAINFALL RATES. 1 TO 3 INCHES OF RAIN ARE POSSIBLE THROUGH 22Z.  

DISCUSSION...CONVECTION FROM EARLIER THIS MORNING ACROSS A COUPLE
AREAS PUT DOWN OUTFLOW BOUNDARIES THAT ARE INTERSECTING ACROSS
EAST CENTRAL IL. A HIGHLY MOIST (PWATS OF JUST SHY OF 2.0 INCHES)
AND UNSTABLE (MLCAPE OF 2000-3000 J/KG) AIR MASS IS IN PLACE IN
THE INFLOW REGION ACROSS CENTRAL/SOUTHERN IL. THIS AIR IS BEING
TRANSPORTED INTO THE REGION OF OUTFLOW BOUNDARY INTERSECTION BY
RELATIVELY MODEST 10-20 KT WEST-NORTHWESTERLY LOW-LEVEL FLOW.
GIVEN THE ORIENTATION OF THE LOW-LEVEL FLOW WITH THE SURFACE
OUTFLOW BOUNDARIES, THERE IS THE POTENTIAL FOR CONVECTION TO
PERSIST/REDEVELOP OVER THE SAME AREAS FOR A PERIOD OF TIME.
ADDITIONALLY, CONVECTION THAT HAS ALREADY DEVELOPED IS MOVING EAST
TOWARD AN AREA OF REDUCED FLASH FLOOD GUIDANCE IN CENTRAL INDIANA
ASSOCIATED WITH EARLIER HEAVY RAINS. WHILE THIS CONVECTION IS
MOVING INTO AN AREA OF LESS INSTABILITY, THE INFLOW APPEARS TO BE
SUFFICIENT TO MAINTAIN CONVECTION AS IT MOVES EAST INTO THE LESS
UNSTABLE AIR.

HI-RES CAMS DO NOT SHOW GOOD CONSENSUS WITH RESPECT TO THE
EVOLUTION OF CONVECTION IN THIS AREA. THE HRRR-PARALLEL SEEMS TO
HAVE THE BEST GRASP ON THE CURRENT CONVECTION BASED ON ITS
SIMULATED REFLECTIVITY, AND THIS MODEL MOVES THE CONVECTION
EAST-SOUTHEAST INTO INDIANA OVER THE NEXT FEW HOURS, GRADUALLY
WEAKENING IT ON THE NORTHERN SIDE. ADDITIONAL CONVECTION IS
POSSIBLE FARTHER WEST AS THE OUTFLOW BOUNDARIES CONTINUE TO
INTERSECT EACH OTHER, AND THE HIGHLY MOIST AND UNSTABLE AIR MASS
IN THIS AREA WOULD SUPPORT HEAVY RAINFALL RATES. TRENDS IN CURRENT
RADAR PRECIP ESTIMATES AS WELL AS LIMITED HI-RES MODEL DATA
SHOWING THE CONVECTION INDICATE THAT 1 TO 3 INCHES OF RAIN ARE
POSSIBLE THROUGH 22Z. FLASH FLOODING IS POSSIBLE. 

RYAN

ATTN...WFO...ILX...IND...LMK...LSX...PAH...

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

LAT...LON   39818633 39288578 38568581 38108597 37698655 
            37518746 37798850 38378958 38648984 38978937 
            39138845 39598761 39798713