MESOSCALE PRECIPITATION DISCUSSION 0398...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
818 AM EDT WED JUL 04 2018

CORRECTION TO HOURLY RAIN TOTALS TO CONFORM WITH GRAPHIC

AREAS AFFECTED...SOUTHEAST TX & SOUTHWEST LA

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

VALID 041214Z - 041814Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE INCREASING IN COVERAGE
ACROSS FAR SOUTHEAST TX.  HOURLY RAIN TOTALS TO 3" WITH LOCAL
AMOUNTS OF 6"+ ARE EXPECTED.

DISCUSSION...SURFACE OBSERVATIONS REVEAL AN AREA OF LOW PRESSURE
NORTHWEST OF GALVESTON TX.  SHOWERS AND THUNDERSTORMS HAVE BEEN
BROADENING NEAR AND TO ITS EAST WITHIN AN AREA OF CONVERGENT 850
HPA FLOW, WHICH HAS ALSO LED TO AN EXPANSION OF 500-1000 ML/MU
CAPE IN SOUTHEAST TX, DESPITE RECENT RAP GUIDANCE INDICATING
TRENDS TO THE CONTRARY.  RADAR IMAGERY SHOWS WHAT APPEARS TO BE
THE MAIN 850 HPA WIND CIRCULATION NEAR LUFKIN.  PRECIPITABLE WATER
VALUES ARE 2-2.5" PER RECENT GPS DATA.  WHILE INFLOW AT 850 HPA IS
CYCLONIC OUT OF THE SOUTH AT 15-25 KTS PER VAD WIND PROFILES,
THERE IS AN EXPANSIVE AREA 30 KT EFFECTIVE BULK SHEAR TO ITS WEST
WITHIN AN AREA OF BETTER INSTABILITY FROM ARANSAS PASS TX
NORTHWARD.  THE MEAN 850-400 HPA WIND IS LESS THAN 10 KTS, WHICH
HAS LED TO RELATIVELY STATIONARY HEAVY RAIN CORES THUS FAR.

THE MESOSCALE GUIDANCE HAS A STRONG SIGNAL FOR 6-9" OF RAIN
THROUGH 18Z.  THE GUIDANCE TRACKS THE LOW TOWARDS AUSTIN OVER THE
NEXT SIX HOURS, AND ISSUES ARE EXPECTED NEAR AND SOUTH AND
SOUTHWEST OF THE 850 HPA CIRCULATION CENTER.  THE MAIN THREATS
FROM A HEAVY RAIN PERSPECTIVE ARE MINIMAL CELL MOVEMENT AND THE
POSSIBILITY OF TRAINING, CURVED CONVECTIVE BANDS.  GIVEN THE
AVAILABLE MOISTURE AND INSTABILITY, HOURLY RAIN TOTALS TO 3" ARE
EXPECTED.  THIS WOULD ESPECIALLY PROBLEMATIC WITHIN URBAN AREAS. 

ROTH

ATTN...WFO...CRP...EWX...FWD...HGX...LCH...SHV...

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

LAT...LON   31139475 30889334 30089267 29409267 29619355
            29329477 28369634 29099730 30309760 31029678