Flash Flood Guidance
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000
AWUS01 KWNH 211556
FFGMPD
LAZ000-TXZ000-212145-

MESOSCALE PRECIPITATION DISCUSSION 0017
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EDT SAT MAR 21 2015

AREAS AFFECTED...TEXAS COASTAL PLAINS INTO SWRN LOUISIANA

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

VALID 211554Z - 212145Z

SUMMARY...RAINFALL RATES OF 1-2 IN/HR WITH PERIODIC TRAINING WILL
SLOWLY MOVE UP THE TEXAS COAST AND INTO SWRN LOUISIANA THROUGH
21Z. THIS WILL LIKELY CAUSE ADDITIONAL FLASH FLOODING DESPITE THE
HEAVIEST RAINFALL FROM OVERNIGHT BEING NORTHWEST OF THE
HIGHLIGHTED AREA.

DISCUSSION...WATER VAPOR IMAGERY SHOWED A WELL DEFINED LOBE OF
VORTICITY APPROACHING THE BIG BEND REGION OF TEXAS WITH PLENTIFUL
MID-UPPER LEVEL MOISTURE STREAMING NNEWD AHEAD OF THIS FEATURE
ACROSS THE ERN HALF OF TEXAS INTO THE LOWER MISSISSIPPI VALLEY.
MOISTURE ANALYSIS FROM THE 12Z MORNING RAOB CONFIRMS ANOMALOUS
PRECIPITABLE WATER VALUES WITH +2 TO +3 STANDARDIZED ANOMALIES
CONTAINING NEAR OR RECORD BREAKING VALUES ACROSS SOUTH TEXAS.
CONVECTIVE CELLS ARE MOVING ROUGHLY NEWD AT 20-25 KTS WITH 700 MB
WINDS PARALLELING THESE MOTIONS ALLOWING PERIODS OF TRAINING
ACTIVITY.

AS A LARGE UPPER LOW OVER NWRN MEXICO CONTINUES TO EJECT EWD
THROUGH THE AFTERNOON...LOW LEVEL MOISTURE SURROUNDING A SLOW
MOVING SURFACE FRONT WILL CONTINUE TO ADVECT NEWD...WITH FLOW
PARALLEL TO THE BOUNDARY...WITH WEAK ELEVATED INSTABILITY
IMPINGING UPON THE TEXAS AND SOUTHWESTERN LOUISIANA COASTS. THE
FRONT MAY EVEN RETREAT A BIT AS A WEAK SURFACE LOW MOVES NORTH
FROM SOUTH TEXAS. FLASH FLOOD GUIDANCE IS GENERALLY 2.5 TO 4
INCHES IN 3 HOURS ACROSS THE THREAT AREA WHICH IS EXPECTED TO BE
MET OR EXCEEDED IN A FEW LOCATIONS THROUGH 21Z. DESPITE HI-RES
MODELS GENERALLY STRUGGLING WITH TODAYS EARLY MORNING RAINS...THE
12Z NAM CONEST AND RECENT RUNS OF THE ESRL EXPERIMENTAL HRRR SEEM
TO BE DOING THE BEST THROUGH 15Z.

OTTO

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

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

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

LAT...LON   31209267 30509214 29449256 29289371 28789513
            27639650 27079746 27079778 27439810 27959811
            28949743 30069592 31089458


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