MESOSCALE PRECIPITATION DISCUSSION 0271
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1128 PM EDT SAT OCT 05 2013
 
AREAS AFFECTED...PORTIONS OF THE MS AND OH RIVER VALLEYS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 060328Z - 060728Z
 
SUMMARY...MULTIPLE WAVES OF THUNDERSTORMS ARE TRAINING OVER
INCREASINGLY SATURATED GROUND ACROSS PORTIONS OF THE MS AND OH
RIVER VALLEYS.  REGIONAL FLASH FLOODING IS CONSIDERED POSSIBLE IN
THIS REGION THROUGH 07Z.

DISCUSSION...A BROAD, BROKEN ARC OF THUNDERSTORMS STRETCHES FROM
NORTHERN LA UP THE MS RIVER VALLEY TO PADUCAH, KY AND THEN
EAST-NORTHEAST TOWARDS CINCINNATI OH.  THE BAND APPEARS TO BE
FOCUSING NEAR A LONG PRE-FRONTAL TROUGH, WITH NEW ACTIVITY
OCCASIONALLY DEVELOPING ALONG THE UPSTREAM COLD FRONT, WITH NEW
CONVECTION MOVING INTO THE REGION FROM TIME TO TIME.  PRECIPITABLE
WATER VALUES ARE IN THE RANGE OF 1.75-2 INCHES, WHICH ARE BETWEEN
THE 90TH AND 95TH PERCENTILES FOR EARLY OCTOBER, WHICH IS LEADING
TO EFFICIENT RAINFALL RATES IN THE STRONGER CELLS OF 1-2" PER HOUR
PER RADAR ESTIMATES.  LOW-LEVEL INFLOW OF 35-40 KNOTS IS GENTLY
CONVERGENT INTO THE BOUNDARY.  WHEN COMBINED WITH CAPE VALUES OF
1000-1500 J/KG, THE ENVIRONMENT FAVORS WET MACROBURST MULTICELLS. 
THE 850-400 HPA MEAN FLOW IS PARALLEL TO THE FRONTAL ZONE,
IMPLYING THAT CELL TRAINING IS POSSIBLE.  DIVERGENCE ALOFT IS
BEING CAUSED BY A DEEP CYCLONE NEAR THE SD/NE/IA BORDER JUNCTION. 
FLASH FLOOD GUIDANCE VALUES ACROSS THE REGION HAVE LOWERED SINCE
EARLY THIS AFTERNOON DUE TO THE ONGOING HEAVY RAINFALL, LYING
ROUGHLY NEAR 2.5 INCHES/3 HOURS, WITH SMALL POCKETS OF LOWER
GUIDANCE NEAR THE CONFLUENCE OF THE OH/MS RIVERS, ACROSS SOUTHEAST
AR, AND ALONG PORTIONS OF THE OH RIVER VALLEY.

THE GUIDANCE INDICATES THAT A SLOW EASTWARD PROGRESSION IS
EXPECTED OVERNIGHT.  THE MESOSCALE GUIDANCE IS UNANIMOUS IN
PRODUCING HEAVY RAINS ACROSS THE REGION DURING THE 03Z-09Z TIME
FRAME, ON THE ORDER OF 2-5 INCHES.  DUE TO SLIGHTLY STRENGTHENING
LOW-LEVEL INFLOW, CORFIDI VECTORS ARE RELATIVELY LIGHT OVER THE
NEXT SEVERAL HOURS.  SINCE THE ARCING BAND OF THUNDERSTORMS IS
BROKEN/SEGMENTED, BELIEVE REGIONAL FLASH FLOODING IS POSSIBLE --
RATHER THAN LIKELY -- ACROSS THIS AREA.  THE 12Z ARW INDICATES
EXISTING CAPE VALUES BECOME EXHAUSTED AROUND 07Z, SIMILAR TO THE
ENVIRONMENT SEEN ACROSS THE REGION OVER THE PAST FEW NIGHTS.  DUE
TO THIS, USED A VALID TIME NEAR 07Z.

ROTH

ATTN...WFO...JKL...ILN...LMK...OHX...IND...PAH...MEG...JAN...
LZK...SHV...

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

LAT...LON   36718798 35078926 32539086 32089240 32909262 36239050
            38298821 39188463 38178371 36718798