MESOSCALE PRECIPITATION DISCUSSION 0100
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1043 AM EDT SAT APR 14 2018

AREAS AFFECTED...SERN LA INTO SRN MS....ERN MS/CNTRL AL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 141442Z - 142040Z

SUMMARY...PERIODS OF TRAINING HEAVY RAINFALL EXTENDING FROM SERN
LA INTO MS AND AL MAY CAUSE FLASH FLOODING OVER THE NEXT SEVERAL
HOURS DESPITE AN OVERALL FORWARD MOTION TO THE CURRENT CONVECTIVE
LINE. LOCAL 3-5 INCH RAINFALL THROUGH 21Z CAN BE EXPECTED WHERE
LOCAL STALLING OF THE LINE OCCURS.

DISCUSSION...14Z REGIONAL RADAR IMAGERY SHOWED A SQUALL LINE
EXTENDING SSW FROM CNTRL MS INTO SERN LA...JUST WEST OF LAKE
PONTCHARTRAIN. OBSERVED RAINFALL RATES FROM LOCAL REPORTING SITES
HAVE GENERALLY BEEN 1-2 IN/HR OVER LA INTO MS. 12Z RAOBS...BLENDED
TPW IMAGERY AND RAP ANALYSES SHOWED THE HIGHEST MOISTURE...ROUGHLY
1.5 TO 2.1 INCH PRECIPITABLE WATER VALUES...EXTENDING FROM LA INTO
THE WRN GULF.

WHILE THIS LINE HAS BEEN STEADILY MOVING TOWARD THE EAST...AND
FLASH FLOOD GUIDANCE IS 2.5 TO 4+ INCHES IN 3 HOURS ACROSS THE
REGION...HIGHER TO THE SOUTH...THERE IS THE POTENTIAL FOR
MESOSCALE WAVES TO FORM ALONG THE LEADING EDGE OF HEAVY RAINFALL
ALLOWING FOR PERIODS OF TRAINING. THIS IS EXPECTED TO OCCUR AS
MID-UPPER LEVEL FLOW BECOMES ORIENTED IN A MORE SOUTH TO NORTH
DIRECTION IN ADVANCE OF A SHORTWAVE TROUGH PIVOTING NEAR THE TX
BIG BEND REGION...TO THE SOUTH OF A CLOSED LOW OVER THE CNTRL
PLAINS. FLOW ALOFT IS ALREADY DIFFLUENT...BUT STRENGTHENING OF THE
UPPER LOW IS EXPECTED AS THE SHORTWAVE TROUGH NEARS THROUGH
21Z...INCREASING EVACUATION ALOFT. WHILE THE GREATEST ML CAPE
VALUES ARE FORECAST TO REMAIN SOUTH OF I-20...SUFFICIENT
INSTABILITY IS FORECAST ACROSS NRN AL WHERE LOCAL STALLING OF THE
LINE HAS RECENTLY DEVELOPED ALONG THE OUTFLOW BOUNDARY TO HELP
SUPPORT 1-1.5 IN/HR RAIN RATES AND TRAINING.

FARTHER SOUTH...RAINFALL RATES OF 1.5 TO 2.5 IN/HR ARE FORECAST
WITH LOCALIZED TOTALS OF 3-5 INCHES POSSIBLE THROUGH ~21Z WHICH
MAY CAUSE FLASH FLOODING IN A COUPLE OF LOCATIONS.

OTTO

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

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

LAT...LON   34858687 34788615 34338591 33818583 33118610
            31718695 30218848 29598963 29349068 29699120
            30289072 30939034 31958981 33538916 33968872
            34528771