MESOSCALE PRECIPITATION DISCUSSION 0568...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 AM EDT FRI OCT 09 2015
 
AREAS AFFECTED...SOUTH-CENTRAL TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 090556Z - 091156Z
 
SUMMARY...THE LEADING EDGE OF A THUNDERSTORM COMPLEX WITH HEAVY
RAINFALL IS SLOWLY MIGRATING INTO SOUTH-CENTRAL TX.  WITH HOURLY
RAIN RATES UP TO 3", FLASH FLOODING IS CONSIDERED POSSIBLE.

DISCUSSION...A MATURE THUNDERSTORM COMPLEX LIES SOUTH AND EAST OF
DEL RIO TX, IN AN ANAFRONTAL FASHION BEHIND A WEAK MESOSCALE
FRONTAL WAVE AND ITS SLOW MOVING COLD POOL/FRONT.  THUNDERSTORMS
FROM NORTHEAST MEXICO ARE ATTEMPTING TO TRAIN ALONG ITS
TRAILING/SOUTHWEST SIDE.  ITS LEADING EDGE HAS BEEN MOVING EAST AT
10-15 KTS, WITH ITS CONVECTIVE TAIL SHOWING SLOWER PROGRESSION
NEAR THE RIO GRANDE CLOSER TO 10 KTS.  DUAL POL ESTIMATES NEAR/
NORTHEAST OF EAGLE PASS INDICATE THAT 9-10" HAS FALLEN.  HOWEVER,
GROUND TRUTH REPORTED BY THE EWX/SAN ANTONIO FORECAST OFFICE
INDICATES THAT THE DUAL POL ESTIMATES ARE ~30% TOO HIGH.  INFLOW
AT 850 HPA IS 20-30 KTS PER VAD WIND PROFILES, WHICH IS ADVECTING
IN MUCAPES IN THE 1000-2000 J/KG RANGE PER RECENT SPC MESOANALYSES
(WHICH HAVE REMAINED UNCHANGED SINCE 00Z).  PRECIPITABLE WATER
VALUES OF 1.75-2" LIE ACROSS THE AREA PER GPS VALUES, 1.5-2 SIGMAS
ABOVE THE MEAN FOR EARLY OCTOBER.  STORM-BASED INFLOW (35-40 KTS)
SIGNIFICANTLY EXCEEDS THE MEAN 850-400 HPA WIND (10-15 KTS), WHICH
HAS LED TO HIGH RAINFALL EFFICIENCY GIVEN THE AVAILABLE MOISTURE.

THE CAM GUIDANCE IS UNIFIED IN THE IDEA THAT THIS THUNDERSTORM
AREA SHOULD REMAIN STATIONARY/DRIFT SLIGHTLY EASTWARD FOR THE REST
OF THE NIGHT.  HOWEVER, MOST OF GUIDANCE INITIALIZED THE STORM
COMPLEX 40+ MILES TOO FAR WEST TO NORTHWEST, WHICH HAD LED TO
UNREALISTIC SOLUTIONS, WITH THE 00Z NAM CONEST THE FARTHEST
AFIELD.  GIVEN THE LONGER TERM MOTION TO THE EAST AT 10-15 KTS,
BEING DRIVEN BY THE INSTABILITY AHEAD OF THE RAIN BAND WITH SOME
CONTRIBUTION BY THE 850-400 HPA MEAN FLOW WHICH HAS A SLIGHT
EASTERLY COMPONENT, HAVE USED THIS AS A PROXY FOR FUTURE MOTION. 
IT IS POSSIBLE THAT WITH SLIGHTLY DECREASING 850 HPA INFLOW AFTER
07Z THAT THE COMPLEX COULD PICK UP THE PACE SLIGHTLY TO THE EAST
AND SOUTHEAST.  THE 18Z SSEO NEIGHBORHOOD PROBABILITIES SUGGEST
THAT THE PEAK OF THE EVENT IS NEAR, WITH 50+% PROBABILITIES OF
EXCEEDING THREE HOUR FLASH FLOOD GUIDANCE VALUES IN THE 06-08Z
WINDOW BEFORE SLOWLY FADING THEREAFTER.  PEAK HOURLY RAIN RATES OF
3" REMAIN POSSIBLE, WITH LOCAL AMOUNTS OF 5-7" INDICATED BY MOST
OF THE CAM GUIDANCE, IN THE NEIGHBORHOOD OF A 75 YEAR RECURRENCE
INTERVAL.  FLASH FLOODING IS POSSIBLE WITHIN A REGION THAT HAS
BEEN QUITE DRY FOR THE PAST THREE MONTHS (PER SOUTHERN REGION
PRECIPITATION ESTIMATES).  

ROTH

ATTN...WFO...CRP...EWX...MAF...

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

LAT...LON   30210163 30200026 30209856 29849767 28329861 
            27439941 27609968 27960007 28720068 29650156 
            29600145 30060177