MESOSCALE PRECIPITATION DISCUSSION 0656
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
330 AM EST WED NOV 18 2015
 
AREAS AFFECTED...SOUTHEAST LA, EASTERN MS, & WESTERN AL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180829Z - 181429Z
 
SUMMARY...A BAND OF HEAVY RAINFALL CONTINUES MARCHING THROUGH
LA/MS.  HOURLY RAIN RATES UP TO 2" COULD CAUSE FLASH FLOODING,
PARTICULARLY IN URBAN AREAS.

DISCUSSION...A LONG-LIVED RAIN BAND CONTINUES MOVING EASTWARD INTO
THE CENTRAL GULF COAST AND SOUTHEASTERN STATES AT NEAR 15 KTS. 
SOME RECENT BROADENING HAS BEEN SEEN AS NEW CONVECTION MOVES INTO
SOUTH-CENTRAL LA FROM THE GULF OF MEXICO.  CONVECTION REMAINS
FOCUSED NEAR AND BEHIND A COLD FRONT, WHICH CONTINUES TO BE FED BY
40-65 KTS OF SOUTHERLY 850 HPA INFLOW.  INSTABILITY IS SLOWLY
DECREASING INLAND, WITH THE AREA OF 500-2000 J/KG MUCAPE CONFINED
TO SOUTHEAST LA, SOUTHERNMOST MS, AND THE SOUTHERN TIP OF AL. 
PRECIPITABLE WATER VALUES OF 1.75-2.25" INHABIT THE AREA PER
RECENT GPS INFORMATION.  HOURLY RAIN RATES CONTINUE TO PULSE
UPWARD INTO THE 1.5-2.5" RANGE FROM TIME TO TIME, MAINLY DUE TO
CELL TRAINING.  SITES NEAR BATON ROUGE AND LAFAYETTE LA HAVE
MEASURED ~1.5" OF RAIN IN AN HOUR OVERNIGHT.  OCCASIONAL CELL
MERGERS ARE SEEN ACROSS SOUTHERN LA WHICH BRIEFLY ENHANCE RAIN
RATES.

THE CAM GUIDANCE INDICATES THAT 3-5" OF RAINFALL IS POSSIBLE
LOCALLY, MAINLY SOUTH OF THE TN BORDER, THROUGH 15Z.  THE 00Z SSEO
NEIGHBORHOOD PROBABILITIES OF EXCEEDING THE THREE HOUR FLASH FLOOD
GUIDANCE SHOW AREAS OF 50+% EXCEEDANCE THROUGH 12Z.  THE GUIDANCE
HAS SHOWN A SLOW BIAS WITH THIS BAND'S MOVEMENT, AND USING THE
RAP'S BOUNDARY LAYER MOISTURE CONVERGENCE HAS BEEN COMPENSATING
FOR THIS ISSUE OVERNIGHT.  THIS RAINFALL COULD FALL QUICKLY, AS
HOURLY RATES UP TO 2" REMAIN POSSIBLE.  SOME SLIGHT SLOWING TO THE
BAND REMAINS POSSIBLE AS THE PARENT LOW ESCAPES QUICKLY TO THE
NORTH INTO/THROUGH MN THIS MORNING.  FLASH FLOOD GUIDANCE VALUES
SLOWLY INCREASE AHEAD OF THE BAND, SO CONTINUE TO USE POSSIBLE
WORDING.  THE GREATEST THREAT OF FLASH FLOODING REMAINS IN URBAN
AREAS.

ROTH

ATTN...WFO...BMX...HUN...JAN...LCH...LIX...MEG...MOB...

ATTN...RFC...LMRFC...SERFC...

LAT...LON   34878778 34798668 33438696 32108747 30348813 
            29088895 28978905 28868918 28848978 29068996 
            28919089 28979133 29479200 29619230 30169214 
            31039160 32269051 34468850