MESOSCALE PRECIPITATION DISCUSSION 0125
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
746 PM EDT SUN APR 17 2016
 
AREAS AFFECTED...CNTRL TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 172345Z - 180545Z
 
SUMMARY...VERY HEAVY RAIN IS EXPECTED NORTH OF AN OUTFLOW BOUNDARY
LOCATED ACROSS CNTRL TEXAS WITH HOURLY RATES OF 2+ IN/HR THROUGH
05Z. ALSO WATCHING POTENTIAL FOR THE DEVELOPMENT OF AN AXIS OF
FLASH FLOODING RAIN ALONG THE CNTRL TEXAS COAST BY 03Z.

DISCUSSION...23Z OBSERVATIONS PLACED A QUASI-STATIONARY OUTFLOW
BOUNDARY ACROSS CNTRL TEXAS...SW TO NE...FROM NEAR HDO TO AUS TO
JDD. A WWD SURGING OUTFLOW LOCATED SOUTH OF THIS BOUNDARY WAS
OBSERVED TO INTERSECT THE NEARLY STATIONARY OUTFLOW BOUNDARY JUST
WEST OF HDO. LOW LEVEL FLOW CONTINUES TO OVERRUN THE
QUASI-STATIONARY BOUNDARY PRODUCING FLASH FLOODING RAINFALL OVER
WILLIAMSON...BELL...FALLS AND MILAM COUNTIES. 850 MB VAD WIND
PLOTS SHOWED 30-40 KTS FROM THE SOUTHEAST AND GPS PRECIPITABLE
WATER VALUES WERE BETWEEN 1.6 - 1.8 INCHES ACROSS A BROAD SWATCH
OF CNTRL-ERN TEXAS. WHILE INSTABILITY HAS LIKELY WANED SOMEWHAT
COMPARED TO EARLIER IN THE DAY AS SURFACE TEMPERATURES BEGIN TO
COOL...ANYWHERE FROM 500-1500 J/KG ML CAPE REMAINS ALONG I-10
BETWEEN SAN ANTONIO AND HOUSTON.

RAP/GFS FORECASTS HAVE BEEN CONSISTENT IN SHOWING AN UPTICK IN LOW
LEVEL WIND/MOISTURE TRANSPORT ACROSS THE CNTRL TEXAS COAST INTO
AND OVER THE QUASI-STATIONARY OUTFLOW BOUNDARY IN CNTRL TEXAS.
GIVEN INSTABILITY AND UPPER DIFFLUENCE IS EXPECTED TO LINGER INTO
THE EARLY OVERNIGHT HOURS...CONTINUED TRAINING OF HEAVY RAIN IS
EXPECTED IN THE VICINITY OF I-35 IN CNTRL TEXAS WITH ADDITIONAL
RAINFALL TOTALS OF 3-5 INCHES POSSIBLE. 

ALSO OF NOTE...THE 22Z HRRR HAS INTRODUCED AN AXIS OF VERY HEAVY
RAIN...WHICH MAY BE IN THE BEGINNING STAGES...BETWEEN GALVESTON
AND MATAGORDA BAY...AS A ZONE OF GREATER LOW LEVEL FLOW/TOTAL
PRECIPITABLE WATER OVERRUNS RELATIVELY COOLER AIR LOCATED IN THE
W-CNTRL GULF AT THE BASE OF SURFACE RIDGING. CONFIDENCE IN FLASH
FLOODING IS LOWER ACROSS THE COASTAL PLAIN...AND HIGHER IN THE
VICINITY OF THE OUTFLOW BOUNDARY IN CNTRL TEXAS.

OTTO

ATTN...WFO...CRP...EWX...FWD...HGX...SJT...

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

LAT...LON   32989609 32819597 32329573 32009567 31269558 
            30309555 29479524 28959557 28649627 28739674 
            28929777 28889924 29079955 29529975 30259944 
            30919883 31499793 32249723 32709671 32949629