Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 220602 AAC
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
102 AM CDT FRI MAY 22 2015

.DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.
&&

.AVIATION...SATELLITE IMAGES AND SURFACE OBSERVATIONS INDICATE A
MIX OF LOW TO HIGH LEVEL CLOUDS ACROSS THE CWA LATE TONIGHT.
CEILINGS WERE NEAR 400FT AT KBKS TO NEAR 3600FT AT KT65.
VISIBILITIES WERE NEAR 5SM WITH FOG AT KBKS AND KEBG. EXPECT MVFR
TO IFR CONDITIONS TO DEVELOP ACROSS PORTIONS OF THE CWA THE REST
OF TONIGHT THROUGH EARLY FRI MORNING AS LOW TO MID LEVEL MOISTURE
CONTINUES TO POOL ACROSS THE NORTHERN RANCHLANDS WHERE A WEAK
STATIONARY FRONTAL BOUNDARY WAS DRAPED. THIS BOUNDARY WILL BE A
FOCUS FOR LOW LEVEL CONVERGENCE FRIDAY AND SHOWERS WILL LIKELY
DEVELOP THROUGH FRI MORNING AND THUNDERSTORMS WILL LIKELY DEVELOP
FRI AFTERNOON AS DIURNAL HEATING PROVIDES INSTABILITY ACROSS THE
AREA.
&&

.PREV DISCUSSION... /ISSUED 947 PM CDT THU MAY 21 2015/
DISCUSSION...CURRENT WATER VAPOR IMAGERY SHOWS THE NEXT SHORTWAVE
TROUGH MOVING ACROSS NORTHERN MEXICO/TEXAS BIG BEND REGION THIS
EVENING. STORMS ARE FORMING OVER COAHUILA STATE IN MEXICO PER
LATEST SATELLITE AND DEL RIO /DFX/ RADAR. MODELS CONTINUE TO
INDICATE THAT THIS CONVECTION WILL MOVE EAST AND SOUTHEAST
OVERNIGHT. IF THIS CONVECTION HOLDS TOGETHER...IT SHOULD REACH THE
WESTERN PORTIONS OF DEEP SOUTH AS EARLY AS 2AM. THE LATEST HRRR
SHOWS THAT THE LEADING EDGE OF THE WEAKENING COMPLEX MAKING IT TO
ZAPATA COUNTY JUST BEFORE DAWN. THE CONVECTION THEN MOVES EASTWARD
ACROSS THE AREA BUT WEAKENS AS IT HEADS INTO THE MIDDLE AND
EASTERN SECTIONS FRIDAY MORNING. DOPPLER RADAR RAINFALL ESTIMATES
OF 1-3 INCHES HAS FALLEN TODAY ACROSS ZAPATA...STARR...AND JIM
HOGG COUNTIES...ALONG WITH ABUNDANT RAINFALL FROM THE PAST SEVERAL
WEEKS...HAVE DECIDED TO EXTEND THE PREVIOUS FLASH FLOOD WATCH
THROUGH NOON FRIDAY. ALSO HAVE INCREASED POPS ACROSS THE AREA
TONIGHT AND FRIDAY AND UPDATED THE QPF/WEATHER GRIDS. NO OTHER
CHANGES NEEDED AT THIS TIME.

PREV DISCUSSION... /ISSUED 656 PM CDT THU MAY 21 2015/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...SURFACE OBSERVATIONS AND SATELLITE IMAGERY INDICATES A
FEW LOW LEVEL CLOUDS WITH DENSE CIRRUS OVERHEAD FROM CONVECTION
EARLIER TODAY. LIGHT AND VARIABLE WINDS WILL BECOME SOUTHEAST
LATER THIS EVENING. VFR CONDITIONS EXPECTED TONIGHT WITH BRIEF
PERIODS OF MVFR CEILINGS POSSIBLE. SHORT TERM MODELS SHOW ANOTHER
ROUND OF CONVECTION DEVELOPING ACROSS THE HIGHER TERRAIN OF MEXICO
AND MOVING TOWARDS DEEP SOUTH TEXAS OVERNIGHT...APPROACHING THE
TERMINALS AROUND AFTER DAWN. WILL MENTION VCTS FOR MFE/HRL AT 9Z
AND 10Z FOR BRO. MVFR CEILINGS WILL BE POSSIBLE IN AND AROUND ANY
CONVECTION.

PREV DISCUSSION... /ISSUED 328 PM CDT THU MAY 21 2015/

ABBREVIATED FORECAST DISCUSSION DUE TO ONGOING SEVERE WEATHER...

SHORT TERM /NOW THROUGH FRIDAY NIGHT/...CONTINUING TO TRACK MORNING
MCS AS A BULK OF THE HEAVIER ACTIVITY IS NOW INTO NORTHERN MEXICO.
THERE WERE A FEW REPORTS OF FLASH FLOODING AND SEVERE WEATHER. THE
ATMOSPHERE IS WORKED OVER AND AM EXPECTING A CONTINUED DOWNWARD
TREND IN ACTIVITY THROUGH THE REST OF THE AFTERNOON. TRENDED HIGH
TEMPERATURES DOWNWARD THROUGH THE REST OF THE AFTERNOON. MAYBE HAVE
ALREADY REACHED OUR HIGHS TODAY IN THE MIDDLE AND LOWER VALLEY
BUT MAY GET AN HOUR OR TWO HEATING OUT WEST TO PUSH TEMPERATURES
INTO THE LOWER 80S.

MODELS FORECASTING A STRONGER SHORTWAVE TROUGH MOVING ACROSS
NORTHERN MEXICO THIS EVENING WITH STORMS FORMING ACROSS THE SIERRA
MADRES AND MOVING EASTWARD TOWARD DEEP SOUTH TEXAS. IT APPEARS
ANOTHER COMPLEX OF STORMS OR MCS WILL ENTER OUR WESTERN SECTIONS
OVERNIGHT THEN MOVE EASTWARD ACROSS THE AREA BUT WEAKEN AS IT HEADS
INTO THE MIDDLE AND EASTERN SECTIONS FRIDAY MORNING.

DOPPLER RADAR RAINFALL ESTIMATES OF 1-3 INCHES HAS FALLEN TODAY
ACROSS ZAPATA...STARR...AND JIM HOGG COUNTIES. COUPLED THAT WITH 5-
10 INCHES THAT HAS FALLEN ACROSS THE MID VALLEY AND CORRESPONDING
RANCHLANDS OVER THE PAST SEVERAL WEEKS AND THE AREA WEST OF THE
COASTAL COUNTIES IS RIPE FOR FLASH FLOODING TO OCCUR. THEREFORE WILL
CONTINUE THE FLASH FLOOD WATCH THROUGH TONIGHT AND WILL LET NEXT
SHIFT MAKE THE CALL ON EXTENDING INTO FRIDAY.

LONG TERM /SATURDAY THROUGH THURSDAY/...A FAIRLY SLOW MOVING DEEP
500 MB TROUGH WILL DIG ACROSS THE SOUTHWESTERN AND SOUTH CENTRAL
STATES THIS WEEKEND INTO EARLY NEXT WEEK AND WILL FINALLY CLEAR
TX LATE TUES/EARLY WED. SINCE THIS TROUGH AXIS DIGS PRETTY FAR
SOUTHWARDS THROUGH EARLY NEXT WEEK EXPECT THE POTENTIAL FOR
ISOLD/SCT CONV TO PERSIST AT LEAST THROUGH MON AND TUES OF NEXT
WEEK WITH LOWER POPS PREVAILING ON AND AFTER WED AS DRIER AIR
FILTERS INTO THE REGION IN THE WAKE OF THE 500 MB TROUGH. THE MAIN
ISSUE CONCERNS THE TIMING OF THE PASSAGE OF THE TROUGH AXIS AND
THE OVERALL MOISTURE ADVECTION AHEAD OF THIS FEATURE. THE ECMWF IS
GOING WITH A WETTER SOLUTION VERSUS THE GFS WHICH DRIES OUT THE
ATMS QUICKER. FOR NOW WILL LEAN TOWARDS THE WETTER ECMWF SOLUTION
AS THE GFS MEX GUIDANCE FOR THE LOWER RGV MAY BE A BIT UNDERDONE.
MAX AND MIN TEMPS WILL BE A BLEND OF THE GFS AND ECWMF GUIDANCE
WITH A BIT OF A BIAS TOWARDS THE COOLER ECMWF NUMBERS EARLIER IN
THE LONGER RANGE PERIOD.

MARINE /NOW THROUGH FRIDAY NIGHT...THE MODERATE ONSHORE FLOW WILL
PREVAIL THROUGH THE SHORT TERM AS A WEAK FRONTAL WAVE MOVES SOUTH
AND STALLS OVER SOUTH CENTRAL TEXAS. SEAS WILL REMAIN NO MORE THAN 3
FEET OVER THE OFFSHORE WATERS. A FEW ISOLATED SHOWERS WILL DEVELOP
NEAR THE COAST DUE TO THE INSTABILITY IN THE AREA ASSOCIATED WITH
THE FRONTAL BOUNDARY. SMALL CRAFT MAY NEED TO EXERCISE CAUTION
ACROSS THE GULF WATERS FRIDAY NIGHT AS WINDS LOOK TO INCREASE TO 16-
18 KNOTS.

SATURDAY THROUGH THURSDAY...SURFACE RIDGING OVER THE WESTERN GULF
OF MEX WILL MAINTAIN A MODERATE TO STRONG SE FLOW THROUGHOUT THE
BULK OF THE CWF PERIOD. THIS WILL LIKELY MAINTAIN THE BAY AND GULF
WATERS CLOSE TO SCEC/SCA CRITERIA AT LEAST THROUGH MON. LOWER
WINDS AND SEAS WILL THEN PREVAIL FOR TUES THROUGH THURS ALLOWING
FOR A LITTLE BETTER BOATING CONDITIONS.
&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH UNTIL NOON CDT TODAY FOR TXZ248>250-252-253.

GM...NONE.
&&

$$

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