MESOSCALE PRECIPITATION DISCUSSION 0096
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 AM EDT SUN MAR 27 2016
 
AREAS AFFECTED...SOUTHEAST LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 271250Z - 271650Z
 
SUMMARY...VERY HEAVY SHOWERS AND THUNDERSTORMS WITH RAINFALL RATES
OF 2 TO 3 INCHES/HR IS EXPECTED TO CAUSE SOME RUNOFF PROBLEMS AND
POSSIBLE FLASH FLOODING.

DISCUSSION...IR SATELLITE IMAGERY SHOWS INCREASINGLY COLD
CONVECTIVE TOPS OVER SOUTH-CENTRAL LA IN ASSOCIATION WITH A RATHER
WELL-DEFINED SUBTROPICAL SHORTWAVE TROUGH CROSSING THE WESTERN
GULF COAST...AND A RELATED VORT CENTER MOVING INTO SOUTHWEST LA.
AN 0814Z RGB AQUA-MODIS PASS SHOWED THIS FEATURE FAIRLY WELL AND
IT HAS GOOD DEFINITION IN CONVENTIONAL WV IMAGERY AS WELL.

THE CONVECTION HAS BEEN GRADUALLY GETTING BETTER ORGANIZED WITH
NOT ONLY THE APPROACH OF THE SHORTWAVE DYNAMICS...BUT ALSO WITH
EXCELLENT JET SUPPORT...AS THE ACTIVITY IS CONCENTRATING WITHIN
THE RIGHT-ENTRANCE REGION OF A 110-130 KT 250 MB JET STREAK RIDING
UP INTO THE TN VALLEY AHEAD OF THE SHORTWAVE.

INSTABILITY IS QUITE MODEST OVER SOUTHEAST LA RIGHT NOW...WITH THE
BULK OF THE INSTABILITY POOLED OFFSHORE AND TENDING TO BE
INTERCEPTED BY A CONVECTIVELY REINFORCED OUTFLOW BOUNDARY/WEAK
FRONT OVER THE NORTHERN GULF OF MEXICO. NEVERTHELESS...THE AIRMASS
OVER SOUTHEAST LA IS VERY MOIST...WITH BLENDED-TPW AND GPS VALUES
BETWEEN 1.8 AND 2 INCHES OVER SOUTHEAST LA AND JUST OFFSHORE.
DESPITE THE WEAK INSTABILITY PROFILES...THE STRONGER JET-ENHANCED
ASCENT THROUGH THE COLUMN IS COMPENSATING TO SUSTAIN AND EVEN
ENHANCE THE CONVECTION OVER THE SOUTH-CENTRAL PORTION OF THE STATE.

OVER THE NEXT FEW HOURS...RECENT RUNS OF THE HRRR AND THE NAMRR
SUGGEST THE STRONGER CONVECTIVE CLUSTERS FROM KBTR DOWN TO KPTN
AND THE ADJACENT COAST WILL ORGANIZE A BIT MORE AND ADVANCE
GENERALLY TO THE EAST WITH THE MEAN LAYER FLOW...AND GENERALLY
TAKING ON THE CHARACTER OF AN MCS. THE LATEST VAD WIND PROFILER
FROM TMSY SHOWS S/SW 850 MB FLOW OF 30 KTS...AND THIS WILL BE ABLE
TO HELP CONTINUE TRANSPORTING SUBTROPICAL MOISTURE AND SOME
INSTABILITY INTO THE MORE ORGANIZED AXIS OF CONVECTION.

RAINFALL RATES ARE EXPECTED TO BE VERY HIGH GIVEN THE PWAT
ENVIRONMENT AND COLD CONVECTIVE TOPS...INCLUDING A LIKELIHOOD OF A
FEW OVERSHOOTING TOPS. EXPECT RATES OF 2 TO 3 INCHES/HR...AND WITH
RELATIVELY SLOW CELL MOTION...SOME VERY HEAVY TOTALS OF 3 TO 5
INCHES WILL BE POSSIBLE OVER ONLY A COUPLE OF HOURS. THE MAIN
CONCERN WILL BE EXCESSIVE SHORT-TERM RUNOFF PROBLEMS AND POSSIBLE
FLASH FLOODING GIVEN THE RATES...AND ALSO URBAN FLOODING CONCERNS.

ORRISON

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

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

LAT...LON   30869029 30568975 29968934 29228940 28998983 
            28979065 29309131 29539183 30149165 30839104