MESOSCALE PRECIPITATION DISCUSSION 0334
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 AM EDT SAT AUG 30 2014
 
AREAS AFFECTED...WRN LA...CENTRAL LA...SE TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 301011Z - 301611Z
 
SUMMARY...A HEAVY RAIN EVENT WAS GRADUALLY MATURING AT 0945Z.
MODELS CONTINUE TO SHOW STRONG EVIDENCE OF EXPANSION AND
INTENSIFICATION THROUGH 15Z. MODERATE FORCING WITHIN AN UNUSUALLY
MOIST ENVIRONMENT MAY YIELD EXCESSIVE RAIN AND FLASH FLOODING.

DISCUSSION...THE RAPIDLY UPDATING MODELS CONTINUED WITH A
CONSISTENT OUTPUT OF MULTIPLE INCHES OF RAIN OVER A BROAD PART OF
SOUTHWEST LA AND ADJACENT SE TX THROUGH 15Z. CONSISTENCY OF THE
MODELED LOCATION OF THIS EVENT WAS EVIDENCED BY AN UNUSUALLY HEAVY
2-3 INCH SWATH FROM THE NEW EMC NCASE...A 15-MEMBER ENSEMBLE MEAN
CONSISTING OF MULTI-PHYSICS MEMBERS AND TIME LAGGED MEMBERS OF THE
HRRR...ARW...NMM...AND NAM CONUS NEST. NUMEROUS INDIVIDUAL HRRR
RUNS PREDICT SMALL SCALE LOCAL MAXIMA ABOVE 6 INCHES DURING THIS
SAME TIME.

THUS FAR DUAL-POL ESTIMATES HAVE REMAINED NEAR OR BELOW 2 INCHES
IN AN HOUR...BUT EXPECT CLOUD DEPTH TO INCREASE IF UPSCALE GROWTH
OCCURS AS PREDICTED...AT WHICH TIME WEAK COLD POOLS WILL ENHANCE
CONVERGENCE ALONG THE LEADING EDGE OF 35 KT NEAR-SURFACE INFLOW.
WITH PW VALUES ABOVE 2.25 INCHES...AND CORFIDI VECTORS CALLING FOR
ONLY 5 KT EASTWARD PROPAGATION OF A MATURE MCS...RAIN RATES AND
INSTANCES OF TRAINING ARE LIKELY TO INCREASE. THE RESULT...AS
SUGGESTED BY THE MODELS...COULD BE MULTIPLE INCHES OF RAIN IN A
SHORT TIME...CAPABLE OF EXCEEDING THE 3-4 INCH GRIDDED FLASH FLOOD
GUIDANCE IN THIS REGION.

BURKE

ATTN...WFO...JAN...LIX...LCH...SHV...HGX...

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

LAT...LON   32039235 31669164 31159149 30259177 29199249 28649354
            28989498 29619506 30789428 31909322 32039235