MESOSCALE PRECIPITATION DISCUSSION 0158
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
508 AM EDT SUN MAY 01 2016
 
AREAS AFFECTED...FAR SE TX...SW LA...CENTRAL LA...SW MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 010908Z - 011438Z
 
SUMMARY...MODELS SIGNAL LOCALLY VERY HEAVY RAINFALL THIS MORNING.
GREATEST CONFIDENCE LIES IN CENTRAL LA TO SOUTHWEST MS...THOUGH A
SECOND MAXIMUM MAY OCCUR NEAR THE TX/LA COAST. FLASH FLOODING
LIKELY.

DISCUSSION...MODELS HAVE SIGNALED VERY HEAVY RAIN...EVEN IN THE
WAKE OF EXTENSIVE OVERTURNING THAT OCCURRED SATURDAY.
OBSERVATIONAL TRENDS LEND INCREASING CONFIDENCE THAT A FLASH FLOOD
THREAT WILL DEVELOP THIS MORNING. SURFACE TO 850 MB FLOW WAS
FAIRLY WEAK...BUT WARM ADVECTION ALONG THE NORTH SIDE OF A PW
MAXIMUM OVER THE GULF...HAD YIELDED SCATTERED CONVECTIVE
INITIATION OVER TX/LA BY 09Z. FLOW IN THE VERY LOW LEVELS IS
FORECAST TO REMAIN TAME...BUT GEFS ANOMALIES DO INDICATE RATHER
ANOMALOUS SOUTHERLY 700 MB FLOW CENTERING ON LOUISIANA THIS
MORNING...WITH RAP FORECAST SOUNDING INDICATING STRONG WARM
ADVECTION ROUGHLY IN THE 800-600 MB LAYER. PRECIPITABLE WATER WAS
RISING TOWARD 1.7 TO 1.9 INCHES WITH MODERATE MIXED LAYER CAPE
WELL OVER 1000 J/KG. THIS ENVIRONMENT WILL FAVOR VERY EFFICIENT
RAINFALL...SUPPORTING THE NOTION IN THE HI-RES MODELS THAT SPOT
AMOUNTS OF 4 OR MORE INCHES ARE LIKELY TO OCCUR...AND ISOLATED
EXTREME TOTALS ABOVE 7 INCHES ARE POSSIBLE.

THE MAIN UNCERTAINTY IS WHERE THE EVENT WILL FOCUS. ONLY ABOUT
HALF OF THE GUIDANCE GENERATES INTENSE RAIN FROM THE EAST SIDE OF
HOUSTON INTO SW LA...WHERE ORGANIZATION WILL BE MORE DEPENDENT ON
ESTABLISHING A COLD POOL. A LITTLE GREATER CONFIDENCE EXISTS FROM
CENTRAL LA TO SW MS...WHERE THE RAP HAS COME INTO SYNC WITH GLOBAL
GUIDANCE IN PREDICTING A PERSISTENT AXIS OF 250 MB DIVERGENCE AND
ASSOCIATED DEEP LAYER LIFT. THE HRRR ALSO SHIFTED ITS HEAVY RAIN
SIGNAL INTO THIS REGION. AT 09Z...HOWEVER...RADAR TRENDS SUGGESTED
THAT A COLD POOL MAY INDEED BECOME ESTABLISHED BACK OVER
TX/LA...SUCH THAT A PRONOUNCED FLASH FLOOD THREAT EXISTS
THROUGHOUT THE MPD AREA. FFG WILL QUICKLY BE EXCEEDED ALONG THE
TX/LA COAST...WHERE ANTECEDENT CONDITIONS ARE THE WETTEST.

BURKE

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

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

LAT...LON   32798930 31488963 30589060 29959223 29629379 
            29499495 29789521 30709470 31759347 32539173