MESOSCALE PRECIPITATION DISCUSSION 0618
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 AM EDT THU AUG 03 2017

AREAS AFFECTED...UPPER TX & LA COASTAL REGION

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 030623Z - 031223Z

SUMMARY...THUNDERSTORMS ARE BEGINNING TO BUILD NEAR THE COASTLINE
IN THE VICINITY OF THE TX/LA BORDER.  HOURLY RAIN RATES TO 3",
WITH LOCAL AMOUNTS TO 6", ARE EXPECTED.

DISCUSSION...A SURFACE BOUNDARY IS NOTED IN THE THERMAL FIELD JUST
OFFSHORE THE REGION, WITH A WEAK WAVE SOUTH OF GALVESTON ISLAND. 
ALOFT, A SHORTWAVE IS NOTED ON WATER VAPOR IMAGERY FROM WESTERN AR
WEST-SOUTHWEST INTO NORTHEAST TX WHICH IS AIDING DIVERGENCE ALOFT.
 PRECIPITABLE WATER VALUES OF 2.1-2.3" LIE ACROSS THE REGION PER
RECENT GPS DATA.  MU CAPE VALUES NEAR THE COAST AND JUST OFFSHORE
ARE IN THE 2000-3000 J/KG RANGE.  THE WINDS AT 850 HPA ARE
CYCLONIC OUT OF THE SOUTHEAST AT 15 KTS ON REGIONAL VAD WIND
PROFILES, NEAR THE MAGNITUDE OF THE 850-400 HPA MEAN WIND. 

RAP GUIDANCE OVERNIGHT HAS BEEN INDICATING AN INCREASE IN THE 850
HPA WIND WITH TIME, THOUGH THE MAGNITUDE HAS BEEN SLOWLY LOWERING
OVER THE PAST SEVERAL RUNS, NOW ADVERTISED TO BE PEAK IN THE 20-25
KTS, JUST IN EXCESS OF THE MEAN 850-400 HPA WIND.  VEERING WINDS
WITH TIME IMPLY FORWARD PROPAGATION AND/OR EXTENSION TO THE EAST
WITH TIME, WHICH IS ALSO HINTED AT IN THE 18Z SSEO NEIGHBORHOOD
PROBABILITIES, WHICH INDICATE THE PEAK OF THE HEAVY RAINFALL
OCCURRING IN THE 07-11Z/2 AM-6 AM CDT TIME FRAME.  HOURLY RAIN
RATES UP TO 3" WITH LOCAL AMOUNTS TO 6" ARE EXPECTED THROUGH 12Z.

ROTH

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

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

LAT...LON   30589042 30228905 29938876 29138889 28918943
            29128978 28939024 28989105 29339172 29489283
            29629322 29409397 29169470 29699476 30519281