MESOSCALE PRECIPITATION DISCUSSION 0416
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM EDT SAT JUL 07 2018

AREAS AFFECTED...SERN TX...SRN LA...SRN MS...FAR SW AL

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

VALID 071830Z - 080030Z

SUMMARY...NUMEROUS THUNDERSTORMS WILL DEVELOP THIS AFTERNOON ALONG
THE WEST-CENTRAL GULF COAST AND MOVE SLOWLY ACROSS THE REGION.
RAIN RATES OF UP TO 2-3 IN/HR WILL BE POSSIBLE WHICH COULD LEAD TO
FLASH FLOODING.

DISCUSSION...GOES-16 DAY CONVECTION RGB IS SHOWING A BLOSSOMING OF
INCREASINGLY VIGOROUS CONVECTION IN THE VICINITY OF A DISSIPATING
STALLED FRONT ALONG THE GULF COAST. ADDITIONAL CONVECTION WAS
DEVELOPING ALONG SOME SEA BREEZE BOUNDARIES THAT WERE SLOWLY
ADVANCING INLAND. GOES-16 IR SATELLITE CHANNELS ALSO SHOW A
GENERAL COOLING OF THE CLOUD TOPS...AND REGIONAL RADARS HAVE SHOWN
A SIGNIFICANT EXPANSION IN THE COVERAGE OF CONVECTION OVER THE
PAST COUPLE HOURS (16-18Z). THIS TREND IS EXPECTED TO CONTINUE FOR
THE NEXT HOUR OR TWO WITH AN INCREASING TREND FOR CONSOLIDATION OF
CONVECTION INTO LARGER CLUSTERS...PARTICULARLY NEAR COLLISIONS IN
OUTFLOW BOUNDARIES...SEA BREEZES...AND THE STALLED FRONT. THIS
SHOULD LEAD TO A RELATIVELY HIGH COVERAGE OF RAIN IN THE NEXT SIX
HOURS...WITH POCKETS OF HEAVY RAINFALL IN EXCESS OF 2-3 INCHES.

THE ENVIRONMENT IN THE OUTLINED AREA IS VERY MOIST...WITH NUMEROUS
GPS-PW OBSERVATIONS IN THE 1.9 TO 2.1 INCH RANGE SUPPORTIVE OF
HEAVY RAIN RATES AND EFFICIENT RAINFALL PRODUCTION. THE DEEP LAYER
(0-6KM) MEAN WINDS WERE ONLY AROUND 5-10 KNOTS...INDICATING THE
POTENTIAL FOR VERY SLOW STORM MOTIONS. COLLIDING BOUNDARIES MAY
FURTHER INCREASE RESIDENCE TIME OF HEAVY RAIN IN CERTAIN
LOCATIONS. THESE TWO FACTORS SHOULD BE AMONG THE MOST FAVORABLE
FOR FLASH FLOOD POTENTIAL THIS AFTERNOON AND EARLY THIS EVENING
ACROSS THE REGION.

FLASH FLOOD GUIDANCE IS NOT ESPECIALLY LOW IN THE REGION...WITH
3-HR FFG AROUND 3-4 INCHES. RAINFALL APPROXIMATELY THAT HIGH IS
POSSIBLE GIVEN THE ENVIRONMENT AND STORM MOTIONS...BUT GIVEN THE
LACK OF STRONG LOW-LEVEL FOCUSING MECHANISMS...THE COVERAGE OF
SUCH RAINFALL MAY BE LIMITED IN AREAL EXTENT. THEREFORE...WHILE
FLASH FLOODING IS POSSIBLE IT SHOULD BE LOCALIZED. THE 12Z HREF
SHOWS THE HIGHEST MEAN QPF AND GREATEST PROBABILITIES OF FFG
EXCEEDANCE IN SOUTHWEST AND SOUTH-CENTRAL LOUISIANA. A DECREASING
TREND IN CONVECTIVE COVERAGE AND THE FLASH FLOOD THREAT IS
EXPECTED AROUND SUNSET.

LAMERS

ATTN...WFO...EWX...FWD...HGX...JAN...LCH...LIX...MOB...SHV...

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

LAT...LON   31659489 31289166 31538968 31318836 30538797
            30098891 29339003 29349200 29649335 29819454
            30079591 30089703 31149697