MESOSCALE PRECIPITATION DISCUSSION 0325
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
440 AM EDT TUE JUN 19 2018

AREAS AFFECTED...SOUTH-CENTRAL TO SOUTHEAST TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 190840Z - 191440Z

SUMMARY...CONCENTRATED AREAS OF VERY HEAVY SHOWERS AND
THUNDERSTORMS WILL CONTINUE THROUGH THE MID MORNING HOURS WITH
FLASH FLOODING LIKELY.

DISCUSSION...GOES-16 10.3 MICRON/IR SATELLITE IMAGERY SHOWS
MULTIPLE CLUSTERS OF VERY COLD CONVECTIVE TOPS ACROSS
SOUTH-CENTRAL TX IN ASSOCIATION WITH VERY HEAVY SHOWERS AND
THUNDERSTORMS ORGANIZING NEAR AND JUST EAST OF THE RELATIVELY
COMPACT MID LEVEL LOW CENTER. IN FACT...THE CONVECTION IS IN THE
PROCESS OF BECOMING HIGHLY CONCENTRATED ACROSS REFUGIO AND GOLIAD
COUNTIES TO THE NORTH-NORTHEAST OF CORPUS CHRISTI WITH EVIDENCE OF
AN MCV SHOWING UP IN AREA DUAL-POL RADAR IMAGERY.
MEANWHILE...FARTHER NORTHEAST UP ALONG THE MIDDLE AND UPPER TX
COAST...THERE ARE MULTIPLE BANDS OF SOMEWHAT WARMER TOPPED
CONVECTION ADVANCING NORTHWEST IN OFF THE GULF OF MEXICO.

THE LARGER SCALE SET-UP ACROSS THE REGION REMAINS GENERALLY THE
SAME AS A FEW HOURS AGO...EXCEPT THE MID LEVEL LOW CENTER
CONTINUES TO TIGHTEN UP WITH STRONGER MID LEVEL FORCING AND ALSO
MORE PRONOUNCED LOW LEVEL BANDING ASSOCIATED WITH CONVERGENT FLOW
IN OFF THE WESTERN GULF OF MEXICO WHERE THE AIRMASS IS VERY MOIST
AND UNSTABLE. IN FACT...A WELL-DEFINED INSTABILITY GRADIENT IS
NOTED RIGHT ALONG THE IMMEDIATE TX COASTLINE WITH OFFSHORE MUCAPE
VALUES OF 2000+ J/KG.

PWATS REMAIN VERY HIGH AND GENERALLY BETWEEN 2.3 AND 2.5 INCHES
BASED ON HOURLY GPS-DERIVED DATA WHICH AGAIN WILL MAINTAIN HIGHLY
EFFICIENT RAINFALL PROCESSES FOR ENHANCED RAINFALL RATES AND
ESPECIALLY WITH THE CONCENTRATION OF MOISTURE SEEN IN THE 500/300
MB LAYER AS PER THE CIRA-LPW DATA. EXPECT RAINFALL RATES OF AS
MUCH AS 3 INCHES/HR LOCALLY AND ESPECIALLY WITH THE CONVECTION
TIED IN CLOSE TO THE MID LEVEL LOW CENTER THIS MORNING.

THE HRRR/HRRRX GUIDANCE SUPPORTS ADDITIONAL RAINFALL AMOUNTS OF 4
TO 6 INCHES ACROSS PORTIONS OF SOUTH-CENTRAL TX...WITH LESSER
AMOUNTS OF AS MUCH AS 3 TO 5 INCHES FARTHER UP THE COAST TOWARD
THE HOUSTON/GALVESTON METROPOLITAN AREA. GIVEN THESE AMOUNTS AND
SOME OF THE EARLIER HEAVY RAINS...FLASH FLOODING IS LIKELY.

ORRISON

ATTN...WFO...BRO...CRP...EWX...HGX...LCH...

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

LAT...LON   30589443 30389399 29829386 29559405 29409431
            29199476 28809566 28229655 27759716 27259753
            26759805 26919862 27699881 28309866 28869831
            29599746 30219638 30549526