MESOSCALE PRECIPITATION DISCUSSION 0419
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
716 AM EDT SUN JUL 08 2018

AREAS AFFECTED...UPPER TX AND LA COASTAL PLAIN

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

VALID 081116Z - 081616Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE SLOWLY INCREASING IN
COVERAGE.  HOURLY RAIN TOTALS TO 2.5" WITH LOCAL AMOUNTS TO 4" ARE
POSSIBLE WITHIN THE PULSE CONVECTION.

DISCUSSION...AN UPPER LOW WITH A TRAILING UPPER TROUGH/SHORTWAVE
EXTEND FROM EASTERN AR SOUTHWEST THROUGH NORTHERN LA INTO EASTERN
TX PER GOES-16 WATER VAPOR IMAGERY.  SINCE 08Z, ML CAPE IN THE
REGION HAS BEEN COMING UP UNDER ITS BASE NEAR AND SOUTH OF I-10
PER SPC MESOANALYSES NEAR AND SOUTH OF A SURFACE
TROUGH/CONVERGENCE ZONE, WITH AN UPTICK IN EFFECTIVE BULK SHEAR
OFFSHORE.  PRECIPITABLE WATER VALUES OF 2.1-2.3" EXIST HERE PER
GPS DATA.  INFLOW IS WEAK BUT CONVERGENT OUT OF THE SOUTHWEST AT
5-10 KTS PER VAD WIND PROFILES.

WHILE CONVECTION IN SOUTHEAST LA SHOULD PEAK WITHIN THE NEXT
COUPLE HOURS, BOTH THE 06Z GFS-BASED GALVEZ-DAVISON INDEX AND 06Z
HREF PROBABILITIES OF 1"+ IN AN HOUR IMPLY/ADVERTISE A FURTHER
INCREASE IN CELL COVERAGE THROUGH ROUGHLY 16Z FOR SOUTHWEST LA AND
SOUTHEAST TX.  AFTER THAT TIME, SEA BREEZE CIRCULATIONS ARE
EXPECTED TO TAKE OVER WHICH WOULD SPREAD THE THUNDERSTORM ACTIVITY
MORE INLAND.  BELIEVE THE 06Z CANADIAN REGIONAL MODEL, 00Z NMMB,
00Z NSSL WRF, AND 06Z NAM CONEST HAVE A BETTER GRASP OF WHAT IS
EXPECTED OVER THE NEXT SEVERAL HOURS.  TWO WEEK PRECIPITATION
ANOMALIES ARE POSITIVE IN PATCHES NEAR THE LA COAST, WITH AREAS OF
SOUTHEAST TX 200-400% OF NORMAL.  WITHIN THIS ENVIRONMENT, MOSTLY
PULSE CONVECTION SHOULD LEAD TO HOURLY PRECIPITATION TOTALS TO
2.5" WITH LOCAL AMOUNTS TO 4".  THIS RAINFALL WOULD BE MOST
PROBLEMATIC IN URBAN AREAS.

ROTH

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

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

LAT...LON   30469032 30158935 30118893 30008874 29668889
            29458911 29088893 28888942 29168963 29078997
            28999080 29039108 29449201 29469244 29679354
            29429437 28939496 28929534 29289549 29579588
            29839593 30149578 30459560 30229535 30209395
            30319324 30419199