MESOSCALE PRECIPITATION DISCUSSION 0555
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 AM EDT SAT AUG 13 2016
 
AREAS AFFECTED...SOUTHWESTERN TO SOUTHERN LA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 130603Z - 131103Z
 
SUMMARY...THUNDERSTORMS CONTINUE TO FLARE UP ON THE NORTH SIDE OF
THE CIRCULATION OVER SOUTHERN LA. THE THERMODYNAMIC AND KINEMATIC
ENVIRONMENT REMAIN FAVORABLE FOR HEAVY RAINFALL WITH FLASH
FLOODING LIKELY IN AREAS WITH SATURATED SOILS.

DISCUSSION...THE PARENT MID-LEVEL CIRCULATION HAS NOT MOVED
SIGNIFICANTLY IN THE PAST 24 HOURS WITH THE CENTER IN THE VICINITY
OF LAKE PONTCHARTRAIN. POSITIVE VORTICITY ADVECTION WITHIN THE
CYCLONIC CIRCULATION CONTINUE TO DRIVE UPWARD VERTICAL MOTIONS IN
THE PRESENCE OF VERY CONFLUENT LOW-LEVEL FLOW. 00Z SOUNDINGS FROM
LCH/LIX INDICATE TROPICAL MOISTURE REMAINS IN PLACE WITH PWATS
NEARING 2.50 INCHES. THIS IS ACTUALLY ABOUT 0.25 INCHES LOWER THAN
THE PREVIOUS NIGHT OVER LIX. FURTHER...WET-BULB ZERO HEIGHTS ARE
RATHER HIGH...ON THE ORDER OF 15 TO 16 KFT SUGGESTING WARM RAIN
PROCESSES WILL DOMINATE. WHILE THE INSTABILITY HAS WANED AS
INDICATED BY THE WARMING TOPS...LOCAL ADVECTION CONTINUES TO
ADVANCE HIGHER CAPE AIR INTO THE AFFECTED REGION. THIS SHOULD HELP
BOLSTER THE CONVECTIVE POTENTIAL OVERNIGHT ACROSS MUCH OF SOUTHERN
LA. 

EVALUATING SOME OF THE RECENT CAMS...THE 00Z HRW-ARW/HRW-NMM-B AS
WELL AS THE LATEST HRRR/HRRR-PARALLEL HAVE A DECENT HANDLE ON THE
SITUATION. MEANWHILE...THE 00Z NAM CONUS NEST/NSSL-WRF WERE
DISPLACED EASTWARD WHICH DID NOT LOOK AS REASONABLE BASED ON
RECENT RADAR/SATELLITE TRENDS. THE GUIDANCE SUPPORT 6-HOUR
RAINFALL TOTALS IN THE 3 TO 5 INCH RANGE WHICH LOOKS REASONABLE
CONSIDERING THE ENVIRONMENT IN PLACE. OF COURSE THE HIGHEST FLASH
FLOOD RISK WILL BE AREAS WHICH HAVE BEEN IMPACTED BY RECENT HEAVY
RAINFALL WHERE 1 HOUR FFG VALUES ARE AROUND 0.25 INCHES. AS
SUCH...WILL MAINTAIN THE FLASH FLOODING LIKELY DESIGNATION. 


RUBIN-OSTER

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

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

LAT...LON   31219208 31149136 30789074 29589050 28979089 
            29199194 29159272 29569319 30359308 31009264