MESOSCALE PRECIPITATION DISCUSSION 0186
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
926 PM EDT WED MAY 03 2017

AREAS AFFECTED...FAR SOUTHEAST AND SOUTHERN LA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 040130Z - 040730Z

SUMMARY...CONVECTION TRAINING AHEAD OF A COLD FRONT IN A HIGH
MOISTURE ENVIRONMENT IS EXPECTED TO PRODUCE FLASH FLOODING AS THE
FRONT CROSSES SOUTHERN LA INTO THE EARLY MORNING HOURS.

DISCUSSION...EXPERIMENTAL GOES-16 IR IMAGERY SHOWED A BLOSSOMING
AREA OF COOLING CLOUD TOPS WITH CONVECTION EXTENDING FROM CENTRAL
LA INTO FAR EASTERN TX. THE CONVECTION WAS
DEVELOPING/STRENGTHENING IN AN AXIS OF 1500-2500 J/KG OF SBCAPE
(PER THE 00Z LCH SOUNDING) POKING NORTHEAST FROM CENTRAL TX INTO
FAR SOUTHWEST LA. REGIONAL VWP ACROSS SOUTHEAST TX AND SOUTHWEST
LA SHOWED A 35 TO 45 KNOT LOW LEVEL SOUTHWEST FLOW...WHICH
CONTINUES TO TRANSPORTS 1.75/2.00 INCH PRECIPITABLE WATER AIR
(WITH 1.94 INCH PWAT VALUES ON THE 00Z LCH SOUNDING) AHEAD OF THE
COLD FRONT TRACKING SLOWLY SOUTHEAST ACROSS EAST TX AND FAR
NORTHWEST LA.

THE 00Z LCH SOUNDING SHOWED A MOIST COLUMN THROUGH 700
MB...SUGGESTING THAT THE HAIL THREAT LAS LESSENED ACROSS SOUTHERN
LA. THE KPOE RADAR SHOWED HOURLY RAINFALL RATES NEAR 1.75
INCHES...AND BASED ON MESONET REPORTS...THIS MAY BE JUST A BIT ON
THE HIGH SIDE. THE REGIONAL VWP SHOWED STRONG VEERING IN THE LOW
LEVELS...SUGGESTING THAT THE CONVECTION AHEAD OF THE FRONT WILL
CONTINUE TO ORGANIZE AS IT MOVES SLOWLY SOUTHEAST.

THROUGH ABOUT 06Z...THE 300 MB FLOW BECOMES INCREASINGLY DIFFLUENT
AHEAD OF LONG WAVE TROUGH CROSSING THE SOUTHERN PLAINS SHOULD ALSO
ALLOW CONVECTION TO DEEPEN. EARLY IN THE PERIOD...THE MID LEVEL
FLOW BECOMES BETTER ALIGNED WITH THE CONVECTION... PROMOTING
TRAINING ACROSS PORTIONS OF SOUTHWEST LA. AFTER THE SHORT WAVE
APPROACHES...THE CONVECTION SHOULD BEGIN TO ACCELERATE TO THE
SOUTHEAST...REACHING SOUTHEAST LA BY THE END 0730Z OR SO.

THE TRAINING SHOULD RESULT IN AREAS OF 2.00 TO 4.00 INCHES OF
RAINFALL ALONG AND AHEAD OF THE SLOW MOVING FRONT (WITH THE 00Z
HRRR INDICATING THE POTENTIAL FOR LOCAL 6.00 INCH AMOUNTS ACROSS
SOUTH CENTRAL LA). GIVEN THE RAINFALL RATES OCCURRING WITH THE
CONVECTION...THESE VALUES SEEM PLAUSIBLE. THE MOST RECENT HRRR
SOIL SATURATION PRODUCE SHOWED A LARGE AREA OF GREATER THAN 95
PERCENT SATURATION STRETCHING FROM FAR EASTERN TX INTO SOUTHWEST
MS. THE ADDITIONAL RAINFALL AMOUNTS OVER SATURATED SOILS COULD
RESULT IN LOCALLY LIFE THREATENING FLOODING.

THE THREAT FOR FLASH FLOODING MAY PERSIST PAST 0730Z...SO
ADDITIONAL MPD MESSAGES COULD BE REQUIRED.

HAYES

ATTN...WFO...HGX...JAN...LCH...LIX...

ATTN...RFC...LMRFC...WGRFC...

LAT...LON   31239188 30909105 29298948 29069056 29489341
            29969450 30639476 31109370