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000
FXUS64 KBRO 171808 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
108 PM CDT FRI MAY 17 2013

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

&&

.AVIATION...BREEZY SOUTHERLY WINDS AND VFR CONDITIONS WILL
CONTINUE THROUGH EARLY THIS EVENING. LATEST GFS/NAM POINT SOUNDINGS
INDICATE THAT THE LOW LEVEL INVERSION WILL REFORM AGAIN LATE
TONIGHT RESULTING IN MVFR CEILINGS DEVELOPING AFTER 4Z SATURDAY.
PATCHY LOW STRATUS FROM 06Z TO 12Z SATURDAY MAY REDUCE CEILINGS BRIEFLY
TO IFR LEVELS BUT WILL NOT MENTION AT THIS TIME DUE TO LOW
CONFIDENCE AND A BRIEF DURATION. WILL LEAN TOWARDS PERSISTENCE OF
THE PREVIOUS 24 SURFACE OBSERVATIONS FOR THIS TAF CYCLE. MVFR
CEILINGS OVERNIGHT WITH VFR CONDITIONS DEVELOPING AFTER 14Z SATURDAY AS
CLOUDS ERODE AWAY AROUND MID MORNING ON SATURDAY. MODERATE SOUTH
TO SOUTHEAST WINDS WILL BECOME BREEZY BY LATE SATURDAY MORNING.

&&

.PREV DISCUSSION... /ISSUED 619 AM CDT FRI MAY 17 2013/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...IR SATL IMAGERY SHOWS RAGGED LOW LEVEL SC DECKS
PERSISTING MAINLY EAST OF HIGHWAY 281. THE LATEST NAM FORECAST
SOUNDINGS FROM THE LOWER RGV INDICATE THAT A FAIRLY MOIST LOW LEVEL
INVERSION WILL PERSIST ON THROUGH THE EARLY MORNING HOURS LIKELY
MAINTAINING IFR CEILINGS THROUGH THE FIRST PORTION OF THE TAF
PERIOD. AFTER SUNRISE THE DAYTIME HEATING AND INCREASING LOW LEVEL
MIXING WILL ERODE AWAY THE CEILINGS ALLOWING VFR CONDITIONS TO
PREVAIL. THE NIGHTTIME LOW LEVEL INVERSION WILL THEN REFORM AGAIN
LATE FRI NIGHT POSSIBLY ALLOWING SOME MORE PATCHY LOW SC FROM 06 TO
12Z SAT. THE PRELIMINARY WIND DATA FROM THE 12Z BRO SOUNDING
REPORTS ONLY AROUND 35 KNOTS AT 2500 FT WHICH SHOWS THAT THE KBRO
VWP IS OVERESTIMATING THE STRENGTH OF THE LLJ OVER THE REGION.

PREV DISCUSSION... /ISSUED 352 AM CDT FRI MAY 17 2013/

SHORT TERM /TODAY THROUGH SATURDAY/...MID LEVEL RIDGING WILL BUILD
OVER THE SOUTH CENTRAL PLAINS STATES TODAY INTO TONIGHT AS A LARGE
500 MB TROUGH AXIS DIGS ACROSS ROCKIES. THIS RIDGING WILL ERODE AWAY
ON SATURDAY AS THE ROCKIES TROUGH AXIS PUSHES FURTHER EAST AND
CLOSES OFF OVER THE THE CENTRAL AND UPPER MIDWEST. 1000-500 MB
THICKNESSES WILL REMAIN PRETTY ELEVATED THROUGHOUT TODAY AND
TOMORROW UNDER THE INFLUENCE OF THE RIDGING WHICH WILL MAINTAIN
ABOVE NORMAL HIGH TEMPS ACROSS ALL OF DEEP SOUTH TX. RH VALUES OVER
DEEP SOUTH TX REMAIN VERY LIMITED THROUGHOUT THE SHORT TERM PERIOD
DUE TO THE RIDGING AND THIS WILL IN TURN LIKELY RESULT IN AN
INCREASED IMPACT ON DAYTIME TEMPS FROM THE DIURNAL HEATING TODAY AND
TOMORROW.

THE MAV/MET AND ECMWF TEMP GUIDANCE ARE IN PRETTY GOOD AGREEMENT
THROUGHOUT THE SHORT TERM AND WILL GO CLOSE TO A BLEND OF THESE
THREE MODELS FOR HIGH AND LOW TEMPS.

HEAT INDICES WILL BE ON THE INCREASE TODAY AND SAT DUE TO THE
COMBINATION OF THE ABOVE NORMAL TEMPS AND THE ELEVATED GULF
DEWPOINTS WITH THE HIGHEST HEAT INDICES LOCATED OVER THE FAR WEST
COUNTIES. THE ESTIMATED HEAT INDEX READINGS OUT WEST DO NOT APPEAR
WARM ENOUGH FOR A HEAT ADVISORY AT THIS TIME. HOWEVER WILL HIGHLIGHT
THESE ELEVATED VALUES IN THE UPCOMING HWO PRODUCT.

AS THE 500 MB TROUGH AXIS PUSHES EAST THE SURFACE PGF WILL REMAIN
FAIRLY STRONG ACROSS DEEP SOUTH TX AS A SURFACE LOW PRESSURE SYSTEM
DEVELOPS AND MOVES ACROSS THE MIDWEST. AT THIS TIME DO NOT BELIEVE
THAT THE PGF WILL BE STRONG ENOUGH TO WARRENT A WIND ADVISORY.
HOWEVER BREEZY TO WINDY CONDITIONS WILL PREVAIL MAINLY DURING THE
LATE MORNING AND AFTERNOON HOURS.

LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
STRONG CONVERGENCE ALOFT AND LARGE SCALE SUBSIDENCE MARK MUCH OF THE
LONG TERM PORTION OF THE FORECAST. A POLAR JET TROUGH DIGGING INTO
THE CENTRAL PLAINS AND A WEST SOUTHWESTERLY SUBTROPICAL JET WILL
KEEP SURFACE/THERMAL TROUGHING IN PLACE IN THE LEE OF THE SIERRA
MADRE MOUNTAINS AND OVER THE CENTRAL PLAINS LEADING TO A BREEZY TO
WINDY NIGHT SATURDAY NIGHT INTO SUNDAY. WIND SPEEDS WILL LIKELY STAY
UP THROUGH MONDAY BEFORE STAIR STEPPING DOWNWARD A BIT ON TUESDAY.
TEMPERATURES WILL REMAIN VERY WARM THROUGH THE WEEKEND AND THE EARLY
PART OF THE WORK WEEK. WITH ENSEMBLE AND DETERMINISTIC GUIDANCE
STILL FAIRLY CLOSELY CLUSTERED MADE LITTLE CHANGE TO THE INHERITED
FORECAST. SUNDAYS WINDS MAY BE A LITTLE MORE DUE SOUTHERLY LEADING
TO WARMER CONDITIONS ALONG THE IMMEDIATE COAST BUT HIGHS RANGING
FROM NEAR 90 ALONG HIGHWAY 77 TO AROUND 100 IN ZAPATA COUNTY WITH
LOWS IN THE LOW TO MID 70S IS PRETTY HIGH CONFIDENCE WITH OVERALL
COLUMN THICKNESSES AND 1000-700MB TEMPERATURES HOLDING PRETTY
STEADY. DRIER AIR MIXING DOWN WILL LOWER AFTERNOON HUMIDITY BUT PEAK
HEAT INDEX VALUES 100 TO 105 APPEAR LIKELY THROUGH TUESDAY.

THE INITIAL PLAINS/GREAT LAKES TROUGHINESS EJECTS NORTHEASTWARD LATE
TUESDAY INTO WEDNESDAY WITH A DEEPER/STRONGER TROUGH MOVING INTO THE
WESTERN CONUS ON WEDNESDAY. ECMWF/GFS BOTH BRING IN MORE LOW LEVEL
MOISTURE WITH AT LEAST SOME LAYER WARM ADVECTION IN THE 850MB REGION
AND SUGGEST SOME SFC BASED INSTABILITY. HOWEVER AT LEAST IN THE
CURRENT RUNS...THE SYNOPTIC PATTERN IS PRETTY UNFAVORABLE FOR
DEVELOPMENT WITH THE LARGE SCALE FORCING TOO FAR AWAY TO
SIGNIFICANTLY ALTER OUR AIRMASS AND THE LAYER OF LOW MOISTURE VERY
THIN...LIKELY THIN ENOUGH TO SUBSTANTIALLY MIX DURING THE AFTERNOON
AND STABILIZE THE BOUNDARY LAYER. FOR THE FORECAST DID NUDGE CLOUD
COVER IN A NOD TO A LITTLE MORE MOISTURE AND KEPT MAX TEMPS A DEGREE
OR TWO LOWER BUT RAIN CHANCES APPEAR QUITE A BIT TOO LOW TO INCLUDE
IN THE FORECAST THIS RUN.

MARINE...TODAY THROUGH SATURDAY...CURRENTLY BUOY020 REPORTS SSE
WINDS 15G20KTS WITH SEAS AROUND 4.3 FEET. WILL ALLOW THE SCA FOR THE
GULF WATERS TO CONTINUE THROUGH 14Z THIS MORNING. THE PGF APPEARS TO
BE STRONG ENOUGH TO WARRENT AN SCA FOR THE LAGUNA MADRE AS THE
LATEST KBRO VWP SHOWS A PRETTY DECENT LLJ OVER THE LOWER TX
COASTLINE WITH A S WIND INDICATES AROUND 50 KNOTS. THE COOLER GULF
WATER TEMPS WILL LIKELY LIMIT THE DOWNWARD MIXING OF THE JET FURTHER
EAST AND WILL NOT EXTEND THE SCA FOR THE GULF AFTER 14Z.

THE FAIRLY STRONG PGF TOMORROW MAY REQUIRE ADDITIONAL SCAS FOR
EITHER THE BAY OR GULF WATERS.

SATURDAY NIGHT THROUGH WEDNESDAY...
SMALL CRAFT ADVISORIES MAY BE NEEDED SATURDAY NIGHT ON THE GULF OF
MEXICO AND SUNDAY ON THE LAGUNA MADRE. WINDS ARE EXPECTED TO BE
SLIGHTLY LOWER MONDAY THROUGH WEDNESDAY WITH CONDITIONS LIKELY NEAR
EXERCISE CAUTION LEVELS ON THE LAGUNA IN THE AFTERNOON AND ON THE
OPEN GULF DURING THE NIGHT. SEAS SHOULD BE PREDOMINANTLY MODERATE
POSSIBLY BECOMING BRIEFLY ROUGH DURING STRONGER WINDS IN THE
OVERNIGHT HOURS.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  87  75  89  76 /   0   0   0   0
BROWNSVILLE          92  74  92  76 /   0   0   0   0
HARLINGEN            95  74  96  76 /   0   0   0   0
MCALLEN              98  74  97  76 /   0   0   0   0
RIO GRANDE CITY     101  74 100  76 /   0   0   0   0
SOUTH PADRE ISLAND   83  76  82  77 /   0   0   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY FOR WINDS UNTIL 7 PM CDT THIS EVENING FOR
     GMZ130-132-135.

&&

$$

THIS PRODUCT IS ALSO AVAILABLE ON THE WEB AT:
HTTP://WEATHER.GOV/RGV

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