MESOSCALE PRECIPITATION DISCUSSION 0615
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
500 PM EDT SUN OCT 25 2015
 
AREAS AFFECTED...SOUTHERN LA/SOUTHERN MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 252100Z - 260200Z
 
SUMMARY...EFFICIENT WARM RAIN PROCESSES WILL CONTINUE TO PRODUCE A
HEAVY RAIN THREAT OVER PORTIONS OF THE CENTRAL GULF STATES. FLASH
FLOODING IS POSSIBLE IN LOCATIONS WHERE SOILS ARE SATURATED. 
 
DISCUSSION...A LARGE AREA OF MODERATE TO HEAVY RAINFALL ACROSS
MUCH OF LA AND SOUTHERN MS IS DRIVEN MAINLY BY A 30 TO 40 KNOT LOW
LEVEL SOUTHEAST INFLOW PUMPING 2.00 TO 2.25 INCH PRECIPITABLE
WATER AIR (WHICH IS BETWEEN TWO AND THREE STANDARD DEVIATIONS
ABOVE THE MEAN) OVER A STATIONARY FRONT STRETCHED ACROSS SOUTHEAST
LA. INSTABILITY IS MEAGER ACROSS SOUTHERN LA AND SOUTHWEST MS
(WITH MUCAPE VALUES GENERALLY BELOW 500 J/KG)...WITH THE BEST
INSTABILITY REMAINING OFF THE SOUTHEAST LA COAST.

RAINFALL RATES (BASED ON THE KLIX RADAR AND MRMS PRECIPITATION
RATE PRODUCT) ARE GENERALLY 1.25 INCHES OR LESS. GIVEN THE
EFFICIENT WARM RAIN PROCESSES IN PLACE (WITH A SATURATED COLUMN
THROUGH AT LEAST 400 MB) THESE PLATFORMS COULD BE UNDERESTIMATING
HOURLY RAINFALL RATES...DESPITE THE LACK OF DEEP INSTABILITY. 

ALMOST ALL OF THE HIGH RESOLUTION GUIDANCE (INCLUDING THE 18Z
RAP/HRRR) HAS BEEN SLOW WITH THE PROGRESSION OF THE BEST LIFT
AHEAD OF A MID LEVEL DRY SLOT ENTERING SOUTHWEST LA. BASED ON
THIS...IT APPEARS AS THOUGH THE BEST THREAT FOR HEAVY RAINFALL
SHOULD LIE ACROSS SOUTHEAST LA AND A PORTION SOUTHERN MS INTO THE
EARLY EVENING HOURS. 

THERE IS A FAIRLY STRONG SIGNAL IN THE HIGH RESOLUTION GUIDANCE
FOR LOCAL 3-4 INCH RAINFALL AMOUNTS...WHICH ARE EXPECTED MAINLY
ACROSS SOUTHEAST LA AND SOUTHWEST MS. WHILE INSTABILITY SHOULD BE
LIMITED INTO THE EARLY EVENING...THE HIGH MOISTURE CONTENT OF THE
AIR...AUGMENTED BY LARGE SCALE SYNOPTIC SCALE LIFT (DUE TO
PERSISTENT MID/UPPER LEVEL DIFFLUENCE)...COULD SUPPORT LOCAL 3+
INCH RAINFALL AMOUNTS. 

THREE HOUR FLASH FLOOD VALUES ARE LOWERING ACROSS LA (AS LOW AS
1.00 TO 1.50 INCH PORTIONS OF SOUTH CENTRAL AND SOUTHEAST LA)...SO
LOCAL FLASH FLOODING ISSUES ARE POSSIBLE.

HAYES

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

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

LAT...LON   32509042 32028918 30798851 29188856 28989069 
            28989073 29059102 29289122 29519170 29669224 
            29759250 29759250 29639254 29729322 29989375 
            30399371 30919348 31089348 31269325 31409287 
            31519243 31679210 31819182 31829169