MESOSCALE PRECIPITATION DISCUSSION 0168
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
725 PM EDT SUN JUL 21 2013
 
AREAS AFFECTED...SOUTHEAST IL...SOUTHWEST IN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 212324Z - 220324Z
 
SUMMARY...A LINE OF CONVECTION MOVING IN FROM WESTERN KENTUCKY AND
SOUTHERNMOST ILLINOIS COMBINED WITH CURRENT THUNDERSTORM ACTIVITY
ACROSS A SATURATED AREA OF SOUTHEAST IL AND SOUTHWEST IN COULD
LEAD TO FLASH FLOODING OVER THE NEXT FOUR HOURS.

DISCUSSION...A LINE OF SCATTERED TO NUMEROUS THUNDERSTORMS IS
MOVING INTO SOUTHERN ILLINOIS FROM SOUTHEAST MO AND WESTERN KY. 
THIS ACTIVITY FORMED ALONG A SURFACE TROUGH WITH POOLED
PRECIPITABLE WATER VALUES ABOVE TWO INCHES, WITH THUNDERSTORMS
ENHANCING THE LOW-LEVEL CONVERGENCE DUE TO THEIR ASSOCIATED
OUTFLOW BOUNDARIES.  THE LATEST GUIDANCE FROM SAB AND RADAR TRENDS
SUGGEST THAT THE INVADING THUNDERSTORMS SHOULD MOVE OVER AREAS
SATURATED BY HEAVY RAINFALL THIS TIME YESTERDAY DURING THE NEXT
FOUR HOURS. 

WHILE CAPE VALUES ABOVE 1000 J/KG HAVE BEEN THE DRIVING FORCE
BEHIND THIS CONVECTION, AN APPROACHING SHORTWAVE MOVING IN FROM
MISSOURI COULD SUSTAIN THE ACTIVITY FOR A COUPLE HOURS PAST SUNSET
BY AIDING UPPER LEVEL DIVERGENCE.  THE HISTORY OF THE LINE
INDICATES THAT RAINFALL RATES/AMOUNTS SHOULD APPROACH FLASH FLOOD
GUIDANCE IN THE AREA, WHICH IS NEAR 1.5 INCHES IN THREE HOURS.  A
QUICK 1-2 OF RAINFALL COULD LEAD TO FLASH FLOODING IN THIS REGION.

ROTH

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

ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   38218701 37468824 37768950 38908901 39458783 39298694
            38218701