MESOSCALE PRECIPITATION DISCUSSION 0200
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
718 AM EDT TUE AUG 06 2013
 
AREAS AFFECTED...SOUTHEAST MO...WESTERN KY...NORTHEAST
AR...WESTERN TN...SOUTHERN IL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 061117Z - 061402Z
 
SUMMARY...A SLOWLY WEAKENING MESOSCALE CONVECTIVE SYSTEM -- MCS --
IS EXPECTED TO MOVE INTO THE MID-MISSISSIPPI VALLEY BEFORE
DISSIPATING AROUND 14Z.  RAINFALL RATES OF 1-2" PER HOUR COULD
CAUSE REGIONAL FLASH FLOODING.

DISCUSSION...AN MCS MOVING THROUGH PORTIONS OF SOUTHERN AND
CENTRAL MO IS BEING DRIVEN BY UPPER DIVERGENCE NEAR THE SOUTHERN
EDGE OF THE WESTERLIES.  MUCAPE VALUES STARTING OFF NEAR 2000 J/KG
-- PER THE 00Z ARW GUIDANCE -- ARE BEING FED OVER A FRONTAL
ZONE/POSSIBLE MESOSCALE BAROCLINIC BOUNDARY DOWN ACROSS NORTHWEST
AR WHICH SHOWS ASSOCIATED SURFACE FRONTOGENESIS.  CIN IS FORCING
CONVECTION TO BE ELEVATED IN NATURE TO ITS NORTHEAST.  LOW-LEVEL
INFLOW AT THE 700 HPA AND 850 HPA LEVELS IS AROUND 35-40 KNOTS
FROM THE WEST-SOUTHWEST, WITH ITS INTENSITY EXPECTED TO CONTINUE
THROUGH THE REMAINDER OF THE MORNING.  HOWEVER, MUCAPE VALUES
SLOWLY BECOME EXHAUSTED WITH TIME, WITH THE 00Z ARW BRINGING
VALUES BELOW 1000 J/KG BY 14Z, WHICH IS ALSO WHEN THE 06Z HRRR
DECREASES RAINFALL INTENSITY.  PRECIPITABLE WATER VALUES OF 2-2.25
INCHES ARE HELPING TO DRIVE THE PRECIPITATION EFFICIENCY, WITH
ASSOCIATED RAINFALL RATES CURRENTLY IN THE 1-2" PER HOUR RANGE. 
FLASH FLOOD GUIDANCE VALUES ARE NEAR TWO INCHES IN THREE HOURS,
WHICH COULD BE EXCEEDED REGIONALLY WHERE CELLS TRAIN FOR OVER AN
HOUR. THE MOVEMENT OF THE COMPLEX IS EXPECTED TO BE SOUTH OF EAST
OVER THE NEXT FEW HOURS, PER 06Z GFS-BASED CORFIDI VECTORS AND THE
850-400 HPA MEAN FLOW ACROSS THE REGION. 

MCS ARE KNOWN TO SLOWLY WEAKEN WITH TIME.  AFTER COORDINATION WITH
SAB (WHICH INDICATED THE ACTIVITY SHOULD STICK AROUND ANOTHER HOUR
OR TWO), USING THE LATEST GUIDANCE (WHICH INDICATES 14Z), AND THE
USUAL 15Z WEAKENING OF MCS WITHIN HIGH PW ENVIRONMENTS, USED THE
COMPROMISE 14Z AS A VALID TIME.

ROTH

ATTN...WFO...PAH...MEG...LSX...LZK...SGF...EAX...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...

LAT...LON   39229123 39359223 39159305 38569283 37549231 36619220
            36059215 35719118 35818976 36608889 37838929 38739017
            39229123