MESOSCALE PRECIPITATION DISCUSSION 0627
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 AM EDT SAT OCT 31 2015
 
AREAS AFFECTED...FAR SERN TEXAS INTO WRN LOUISIANA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 310631Z - 311231Z
 
SUMMARY...RAINFALL RATES OF 3-4 INCHES IN 3 HOURS ARE EXPECTED TO
BEGIN BY ABOUT 09Z FROM SERN TEXAS INTO SWRN LOUISIANA. POSSIBLE
FLASH FLOODING WILL ACCOMPANY THESE RAINS ESPECIALLY IN AND AROUND
URBAN CORRIDORS FROM HOUSTON TO LAKE CHARLES.

DISCUSSION...RADAR IMAGERY OVER THE PAST FEW HOURS HAS SHOWN AN
EXPANDING AREA OF CONVECTION CLIMBING THE MID TO UPPER TEXAS
COAST...LOCATED AT THE LEADING EDGE OF DEEPER INSTABILITY FOUND
ALONG A LIFTING WARM FRONT. THE VAD WIND PROFILE AT KLCH SHOWED
850 MB WINDS FROM THE SOUTH NEAR 50 KTS AT 06Z...REPRESENTING THE
STRONGEST CORE OF LOW LEVEL WINDS WITHIN AN AXIS EXTENDING FROM
THE WRN GULF OF MEXICO INTO MISSOURI...OUT AHEAD OF AN APPROACHING
UPPER TROUGH MOVING INTO WEST TEXAS.

AS DEEPENING LOW LEVEL MOISTURE CONTINUES TO ADVECT NWD WITH THE
LOW LEVEL JET AIMED ALONG THE SABINE RIVER...INSTABILITY IS
FORECAST TO INCREASE ACROSS THE SRN TEXAS/LOUISIANA BORDER BETWEEN
250 AND 750 J/KG BY 10-12Z...HELPING TO SUPPORT POTENTIALLY VERY
HEAVY RAINFALL RATES. PRECIPITABLE WATER VALUES...VIA RECENT GPS
NETWORK LOCATIONS...SHOWED VALUES OF 2.2 TO 2.4 INCHES WEST OF
GALVESTON BAY AT 06Z...SUPPORTING A DEEP WARM LAYER AND WARM RAIN
PROCESSES. LARGELY UNIDIRECTIONAL FLOW FROM THE SSW-SW WILL ALLOW
FOR TRAINING CELLS WITH 3 HOURLY RATES OF 3-4 INCHES. GIVEN HEAVY
RAINFALL LAST WEEKEND ACROSS PARTS OF EAST TEXAS AND POORER URBAN
RUNOFF ACROSS CITIES ALONG I-10...FLASH FLOODING WILL BE POSSIBLE. 

MODELS BEST SUPPORTING THIS IDEA INCLUDE THE LAST SEVERAL RUNS OF
THE HRRR ENDING WITH THE 05Z RUN AND TONED DOWN QPF FROM THE 00Z
HRW-ARW.

OTTO

ATTN...WFO...HGX...LCH...SHV...

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

LAT...LON   31909322 31819232 30959224 29899303 29439416 
            28739539 28799596 29259615 29829595 30569506 
            31429424