MESOSCALE PRECIPITATION DISCUSSION 0350
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
809 PM EDT TUE JUN 20 2017

AREAS AFFECTED...SOUTHEAST LA...COASTAL MS & AL

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

VALID 210010Z - 210600Z

SUMMARY...NORTHERN OUTER BAND OF TS CINDY PRODUCING HEAVY RAINFALL
CAPABLE OF FLASH FLOODING.

DISCUSSION...EXPERIMENTAL GOES-16 VISIBLE/EIR IMAGERY CONTINUES TO
DEPICT CONVECTION ALONG THE NORTHERN/NORTHEASTERN CONVERGENCE BAND
EXTENDING FROM SOUTH OF TERREBONNE BAY THROUGH THE MS RIVER DELTA
TOWARD THE CHANDELEUR ISLANDS.  STRONG SURFACE AND LOW LEVEL
MOISTURE CONFLUENCE OF ELY 45-50KTS AND SELY FLOW AS WELL AS SOME
ADDITIONAL ENELY FLOW OFF THE LAND WITH TDS IN THE LOW TO MID-70S
HAS SATURATED THE LOWER PROFILE SUPPORTING TPW NEAR 2.7"
SUGGESTING RAIN RATES OF 3"/HR ARE LIKELY  WITH THIS CONVECTION. 
GIVEN THE LOW LEVEL CENTER AS BEEN VERY SLOW TO MOVE WITH ONLY A
MINOR JOG NNW OVER THE LAST HOUR OR SO...THE FORWARD ADVANCEMENT
OF THE CONVERGENCE BAND IS ALSO NEAR ZERO...SUPPORTING COMPOUNDING
TOTALS WITH THE POTENTIAL OF 6"+ LEADING TO FLASH FLOODING
CONCERNS.  DUE TO MASS PILING FROM EASTERLY WINDS...RIVER OUTLETS
WILL LIKELY BE EFFECTIVELY BLOCKED ALLOWING FOR UPSTREAM FLOW TO
BACK UP QUICKER THAN NORMAL.

FURTHER NORTH AND EAST...BAND WILL SLOWLY LIFT NORTHWARD TOWARD
THE MS/AL COASTLINE OVER THE NEXT HOUR OR SO.  RAP ANALYSIS SHOWS
AREA CONTINUES TO BE SOCKED IN WITH LIMITED INSTABILITY AVAILABLE
FOR SIGNIFICANT VERTICAL GROWTH OVER THE LAST FEW HOURS...LIMITING
TO SHOWERS OF .15-.25"/HR.  RAP/HRRR FORECASTS SUGGEST INSTABILITY
WILL BE INCREASING SUPPORTING FURTHER CONVECTIVE DEVELOPMENT THAT
IS LIKELY TO BE SHALLOW INITIALLY BUT LIKELY HIGHLY EFFICIENT
EVENTUALLY REACH RATES UP TO 2"/HR. STRONG SELY FLOW BEHIND THE
BOUNDARY WILL ALSO SUPPORT UPSTREAM PROPAGATION VECTORS ALLOWING
FOR SOME BACK-BUILDING.

SOME HI-RES GUIDANCE (HRRR/HRRRX) CONTINUES TO SUGGEST A STRONG
NNW TO SSE BAND OF CONVECTION ALONG CONFLUENCE OF SLY AND SELY LOW
LEVEL STREAMS WAS TO HAVE FORMED AND FORECAST TO TRACK THROUGH THE
CHANDELEUR ISLANDS TOWARD THE MS COAST.  THIS HAS NOT MANIFESTED
LIKELY DUE TO SLIGHT INCREASED SWLY MID-LEVEL FLOW AND ASSOCIATED
DRYING (SEEN IN GOES-16 7.3/6.9 WV CHANNELS)...PRESSING THE WARM
CONVEYOR BELT FURTHER EAST IS LIKELY DELAYED A FEW HOURS...PERHAPS
RAMPING UP TOWARD DIURNAL MAXIMA IN THE LATE OVERNIGHT HOURS. 
WILL CONTINUE TO MONITOR THIS EVOLUTION.  

GALLINA

ATTN...WFO...JAN...LCH...LIX...MOB...

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

LAT...LON   31088921 30988778 30438748 30208761 30148824
            29848861 29398882 29048895 28918929 29088983
            28979005 28949047 29109122 29609135 30149092
            30789003