Flash Flood Guidance
Issued by NWS

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000
AWUS01 KWNH 260330
FFGMPD
TXZ000-260715-

MESOSCALE PRECIPITATION DISCUSSION 0706...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1130 PM EDT SUN SEP 25 2016

CORRECTED FOR TYPO IN LAST SENTENCE

AREAS AFFECTED...SOUTHERN TX

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

VALID 260315Z - 260715Z

SUMMARY...THUNDERSTORMS WITH HEAVY RAIN ARE MOVING SOUTHEAST
ACROSS SOUTHERN TX.  HOURLY RAIN RATES TO 3", WITH LOCAL AMOUNTS
IN THE 3-6" RANGE, COULD LEAD TO FLASH FLOODING.

DISCUSSION...SATELLITE IMAGERY SHOWS A PAIR OF SHORTWAVES IN THE
NEIGHBORHOOD OF THE CONVECTION, ONE ABOVE THE PERMIAN BASIN AND
ANOTHER MOVING BY CENTRAL MEXICO WHICH ARE ACTING TO ENCOURAGE
DIVERGENCE ALOFT.  SURFACE OBSERVATIONS AND RADAR IMAGERY REVEAL A
THERMAL/DEW POINT BOUNDARY EXTENDING FROM NORTH OF OSO BAY
SOUTHWEST INTO STARR COUNTY.  STORMS WITH CLOUD TOP TEMPERATURES
AROUND -80C HAVE BEEN SLIGHTLY ELEVATED OVER THE BOUNDARY DUE TO
CIN, DROPPING HOURLY RAIN TOTALS UP TO 3" PER RADAR ESTIMATES AS
THEY MOVE SOUTHEAST AT 10 KTS, NEAR THE MAGNITUDE OF THE UPWIND
CONVECTIVE PROPAGATION VECTORS.  RADAR IMAGERY REVEALS A FEW
MESOSCALE CIRCULATIONS NEAR THE BOUNDARY, WHICH LOCALLY HOLDS UP
THE SOUTHEAST MOTION FROM TIME TO TIME.  SCATTERED THUNDERSTORMS
NEAR THE MIDDLE TX COAST APPEAR TO BE SENDING OUTFLOW BOUNDARIES
INLAND BUT OTHERWISE SEEM TO BE STAYING GENERALLY OFFSHORE.
INFLOW AT 850 HPA IS 15-20 KTS FROM THE SOUTHEAST, EXCEEDING THE
850-400 HPA MEAN WIND.  PRECIPITABLE WATER VALUES OF 2-2.2" LIE
ACROSS THE REGION PER GPS VALUES, AND WET BULB ZERO HEIGHTS EXCEED
13,000 FEET.

AS THE THUNDERSTORM AREA APPROACHES THE COAST FROM THE NORTHWEST,
IT WILL ENTER AN ENVIRONMENT WITH INCREASING DEW POINTS AND
DECREASING CIN.  IT IS POSSIBLE THAT THUNDERSTORMS MAY REFORM
FARTHER SOUTHEAST CLOSER TO THE BOUNDARY WHEN THIS OCCURS.  AN
OUTFLOW BOUNDARY COLLISION OVER THE NEXT COUPLE HOURS COULD LEAD
TO NEW DEVELOPMENT CLOSER TO CORPUS CHRISTI.  THE MESOSCALE
GUIDANCE IS WELL TOO FAR TO THE WEST AND NORTHWEST WITH THIS
ACTIVITY, WITH ONLY THE 01Z HRRR AND 01Z RAP CLOSEST TO (BUT
LIKELY NORTHWEST OF) THE MOST PROBABLE SOLUTION.  HOURLY RAIN
RATES UP TO 3" AND LOCAL AMOUNTS OF 3-6" ARE EXPECTED (THE SIGNAL
IN THE MESOSCALE GUIDANCE), WHICH COULD LEAD TO/CONTINUE FLASH
FLOODING.  AFTER 07Z, LOWERING AMOUNTS OF INFLOW COULD LEAD TO A
DEGENERATION OF THE CONVECTIVE AREA`S ORGANIZATION.

ROTH

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

ATTN...WFO...BRO...CRP...

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

LAT...LON   28319811 27949758 27399762 26219820 26109838
            26209876 26509926 27349899 27959872


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