MESOSCALE PRECIPITATION DISCUSSION 0095
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
336 AM EDT SUN MAR 27 2016
 
AREAS AFFECTED...S LOUISIANA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 270735Z - 271235Z
 
SUMMARY...FRACTURED CONVECTION CAPABLE OF RATES TO 1.5"/HR WITH
POSSIBILITY OF TRAINING COULD LEAD TO ISOLATED FLASH FLOODING. 

DISCUSSION...ENVIRONMENT ELEMENTS SUPPORTIVE FOR POTENTIAL FLASH
FLOODING PARTICULARLY IF RAIN FALLS WITHIN TRIBUTARIES THAT FEED
INTO CURRENTLY SWOLLEN MAIN STEM RIVERS. CURRENTLY THOUGH THE
ELEMENTS ARE NOT FOCUSED LEADING TO A FRACTURED NATURE TO THE
CONVECTION JUST OFF SHORE OF S LA. 

WV/IR LOOP INDICATES A FLATTENING SHORTWAVE IN THE SUBTROPICAL
STREAM NEAR S TX ATTM WITH AN ASSOCIATED NARROW 3H 120KT SPEED MAX
ACROSS THE TX COAST INTO CENTRAL LA...HOWEVER FLOW IS ALSO
DIFFLUENT IN THE REGION TO SUPPORT SOME BROAD SCALE ASCENT... AT
5H THOUGH DUAL JET STRUCTURE IS A BIT MORE SUPPORTIVE OF DEEPER
ASCENT WITHIN THIS LEVEL ALLOWING FOR MODERATELY DEEP CONVECTION
TO -60C TOPS...AS JET STREAK MOVES PAST BY MIDDAY...UPPER LEVEL
ENVIRONMENT WILL BE MUCH MORE SUPPORTIVE.  

NEARER THE SURFACE...A WEAK SURFACE TROF/OLD FRONTAL BOUNDARY
EXISTS WITH STRONG 20-30KT SELY SURFACE FLOW NEARING THE COAST
WITH HIGH MOISTURE CONTENT WITH TDS IN THE 70S...AND WITH 7H SWLY
FLOW TAPPING SUBTROPICAL PACIFIC MOISTURE LEADING A STRONG TPW
GRADIENT ACROSS S LA WITH 1.75-2.0" SOUTH OF I-10.  ALSO GIVEN THE
FLOW IS HIGHLY VEERED SOUTH OF LA...LOW LEVEL MASS CONVERGENCE IS
AIDING CONVECTIVE DEVELOPMENT EVEN IF IT IS NOT PARTICULARLY
FOCUSED THROUGH A DEEPER DEPTH.  GIVEN ALL CONDITIONS OF DEEP
MOISTURE BUT WEAK FLUX...MODERATE UPPER LEVEL
EVACUATION/OUTFLOW...CELLS SHOULD BE CAPABLE OF 1.5-1.75"/HR
RATES.  MEAN CLOUD BARRING FLOW IS ALSO GENERALLY PARALLEL TO THE
SURFACE TROF AND LOW LEVEL CONVERGENCE AXES...THIS MAY SUPPORT
SOME TRAINING.  ONCE ASHORE CONVECTION WILL BE GENERALLY STARVED
AS INSTABILITY RAPIDLY DIMINISHES BELOW 500 J/KG MUCAPE
SO...THREAT WOULD BE LIMITED TO BAYOUS FROM MARSH ISLAND TO NEW
ORLEANS AND SOUTHWARD THROUGH THE EARLY MORNING HOURS.  THIS
RAINFALL WILL ALSO SERVE TO SET THE STAGE FOR BETTER INSTABILITY
AND MUCH HIGHER FOCUSED FORCING BY EARLY MORNING MIDDAY...AS SSEO
NHOOD PROBABILITIES OF FFG EXCEEDANCE START INDICATING POTENTIALS
TOWARD 25 PERCENT (GIVEN FFG OVER 3") AFTER 15Z.   

GALLINA

ATTN...WFO...LCH...LIX...

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

LAT...LON   30248956 30138890 29848877 29138897 28908931 
            29028980 29009044 29069107 29319158 29479189 
            29539187 29699193 30109153 30229046