Flash Flood Guidance
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000
AWUS01 KWNH 301357
FFGMPD
LAZ000-TXZ000-301800-

MESOSCALE PRECIPITATION DISCUSSION 0155
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
956 AM EDT SAT APR 30 2016

AREAS AFFECTED...UPPER TX COAST...SOUTHERN LA

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

VALID 301355Z - 301800Z

SUMMARY...HEAVY CONVECTIVE RAINS WILL BE FOCUSING ACROSS THE FAR
UPPER TX COAST AND INTO SOUTHERN LA THROUGH EARLY AFTERNOON.

DISCUSSION...VERY DIFFLUENT FLOW ALOFT WHICH IS BEING FACILITATED
BY THE ARRIVAL OF A SHORTWAVE IMPULSE ACROSS EASTERN TX THIS
MORNING WILL CONTINUE TO HELP SUSTAIN AN AREA OF HEAVY SHOWERS AND
THUNDERSTORMS FROM THE UPPER TX COAST EASTWARD INTO SOUTHERN LA.
CLOUD TOP TEMPERATURES HAVE WARMED SOMEWHAT OVER THE LAST
HOUR...BUT CONFLUENT SOUTHERLY 850 MB FLOW OF 30 TO 40 KTS AIMED
INTO SOUTHERN LA IS EXPECTED TO CONTINUE TO TRANSPORT A RELATIVELY
MOIST AND UNSTABLE AIRMASS IN OFF THE GULF OF MEXICO.

BLENDED-TPW DATA ALONG GPS-DERIVED PWATS DO SHOW A SOMEWHAT DRIER
AIRMASS DOWNSTREAM ACROSS SOUTHEAST LA BUT THIS RELATIVELY DRIER
AIR SHOULD TEND TO FOCUS FARTHER EAST WITH TIME AND AWAY FROM THE
APPROACHING ACTIVITY FROM THE WEST. THE CONVECTION IS EMBEDDED
GENERALLY WITHIN AN AXIS OF 1.5 TO 1.7 INCH PWATS...AND BEING
AIDED BY A NOSE OF MLCAPE VALUES OF 1000 TO 2000 J/KG.

THE RAP GUIDANCE DOES NOT SUGGEST MUCH CHANGE IN THE THERMODYNAMIC
ENVIRONMENT OVER THE NEXT COUPLE OF HOURS...AND CONSIDERING THE
LARGER SCALE SHORTWAVE DYNAMICS APPROACHING FROM THE WEST ALONG
WITH A LARGER SCALE SPLIT UPPER JET PATTERN...THE CURRENT ACTIVITY
SHOULD TEND TO BE STEADY-STATE WHILE SHIFTING GRADUALLY EAST.

RAINFALL RATES OF 1.5 TO 2 INCHES/HR ARE LIKELY ACROSS THE FAR
UPPER TX COAST AND INTO SOUTHERN LA AND THERE IS SUFFICIENT W/E
ORIENTATION OF THE CONVECTION FOR THERE TO BE AT LEAST SOME
PERIODIC TRAINING POTENTIAL. THE 00Z WRF-ARW APPEARS TO HAVE THE
BEST HANDLE ON THE CURRENT ACTIVITY...AND SUGGESTS RAINFALL
AMOUNTS THROUGH 18Z OF 2 TO 4 INCHES...WITH ISOLATED HEAVIER
AMOUNTS. THIS MAY RESULT IN AT LEAST SOME RUNOFF/FLASH FLOOD
PROBLEMS...PARTICULARLY IN VICINITY OF URBANIZED AREAS.

ORRISON

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

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

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

LAT...LON   30899300 30779180 30489094 30019066 29409099
            29439173 29499266 29689343 29649394 29719431
            29919468 30139472 30519464 30849398


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