Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 231747 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1147 AM CST TUE DEC 23 2014

.DISCUSSION...COLD FRONT IS MOVING THROUGH THE NORTHWEST
RANCHLANDS WITH A SURFACE TROUGH PASSING EAST OFF THE COAST
EARLIER THIS MORNING. NORTHWEST WINDS TO CONTINUE TO INCREASE
THROUGH THE AFTERNOON AND INTO THE EVENING HOURS AS THE PRESSURE
GRADIENT BECOMES STRONGER. A JET MAX MOVES OVER DEEP SOUTH TEXAS
BETWEEN 4 PM AND MIDNIGHT AND SOME OF THE HIGHEST GUSTS COULD BE
REALIZED AT THAT TIME. SKIES TO CONTINUE TO CLEAR WITH SOME PATCHY
LOWER CLOUDS THROUGH THE MID AFTERNOON HOURS.

&&

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

&&

.AVIATION...COLD FRONT MOVING THROUGH THE REGION WITH STRONG
NORTHWEST FLOW INCREASING THROUGH AT LEAST 03Z WEDNESDAY. GUSTS OF
30 TO 40 KNOTS ARE POSSIBLE BETWEEN 21 AND 06Z AND MAY EVEN LAST
THROUGH THE NIGHT AS STRONG MID TO UPPER JET PASSES OVERHEAD. LOW
CLOUDS ARE BREAKING UP HOWEVER SATELLITE LOOPS INDICATE PATCHES OF
IFR TO MVFR LINGERING BEHIND THE FRONT. BELIEVE THE INCREASE IN
WINDS AND SOME COOLER AIR MOVING INTO THE AREA WILL ALLOW FOR THE
IFR CONDITIONS TO DISSIPATE WITH MVFR TO MAINLY VFR THROUGH THE
LATTER HALF OF THE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 517 AM CST TUE DEC 23 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...IFR/LIFR CONDITIONS EXPECTED THROUGH EARLY MORNING
WITH LOW CIGS IN THE RGV METRO AREAS AND DENSE FOG IN THE OUTLYING
RANCHLANDS. MODERATE SOUTHEAST WINDS AND SLOW IMPROVEMENT TO VFR
IS EXPECTED BY LATE MORNING. A STRONG FRONT ARRIVES LATE THIS
MORNING/THIS AFTERNOON. BEHIND THE FRONT STRONG GUSTY WINDS ARE
FORECAST FOR SEVERAL HOURS WITH GUSTS OF 33 TO 38 KNOTS LASTING
INTO THE EARLY EVENING. THE FRONT WILL CLEAR OUT LOW MOISTURE
HOWEVER AND PREVAILING VFR CONDITIONS ARE EXPECTED AMID THE GUSTY
WINDS. LOWER WIND SPEEDS ARE FORECAST IN THE OVERNIGHT HOURS BUT
PREVAILING WINDS WILL VERY LIKELY REMAIN AT OR ABOVE 15 KNOTS. /68-JGG/

PREV DISCUSSION... /ISSUED 420 AM CST TUE DEC 23 2014/

SHORT TERM /NOW THROUGH WEDNESDAY...

IMPACTS...AREAS OF DENSE FOG THIS MORNING...STRONG WINDS TODAY/THIS
EVENING.

RELEVANT FEATURES...
A 160-180KT NORTHWESTERLY 250MB SPEED MAXIMUM IS REACHING THE BASE
OF A LARGE UPPER TROUGH CURRENTLY STRETCHING FROM WEST CENTRAL
MEXICO...TO THE BIG BEND REGION AND INTO THE NORTHERN PLAINS. 80 TO
100 KNOT SOUTHWESTERLY WINDS ASSOCIATED WITH THE SUBTROPICAL JET ARE
LOCATED TO THE EAST OF THIS TROUGH AXIS AND THOSE SPEEDS ARE
EXPECTED TO INCREASE AS THE FIRST JET MAXIMUM SENDS THE LARGER
TROUGH EASTWARD. THOSE TWO FEATURES ARE EXPECTED TO PHASE PRODUCING
RELATIVELY STRONG DIVERGENCE OVER THE WESTERN GULF OF MEXICO LATER
TODAY LEADING TO SURFACE CYCLOGENESIS AND FURTHER FALLING PRESSURES.
AT THE SURFACE LOW PRESSURE TROUGHING IS ALREADY DEVELOPING OVER
DEEP SOUTH TEXAS CENTERED IN THE LEE OF THE SIERRA MADRE MOUNTAINS
WITH SURFACE SEA LEVEL PRESSURES BETWEEN 1000 AND 1002MB. THE BROAD
SURFACE TROUGHING IS LEADING TO VERY LIGHT WINDS AT THE SURFACE
WHICH IS HELPING DENSE FOG FORM ACROSS THE NORTHWESTERN HALF OF THE
CWA. CLODUS ASSOCIATED WITH THE LEADING SPEED MAX HAVE KEPT FOG
FORMATION AT BAY IN THE RGV METRO AREAS BUT SATELLITE TRENDS SUGGEST
THAT WILL LIKELY NOT REMAIN THE CASE THROUGH SUNRISE AND MAY NEED A
DENSE FOG ADVISORY FOR ALL OR PART OF THE RGV LATER THIS AM.

TODAY...
IMPACTS...STRONG WINDS...GUSTING UP TO 50 MPH WITH LOCALLY HIGHER
GUSTS POSSIBLE. MINOR TIDAL OVERWASH/SEICHING IN THE LAGUNA MADRE.

AS THE MAIN LARGE SHORTWAVE TROUGH MOVES EASTWARD IT INFLUENCES A
STRONG COLD FRONT...FURTHER ENHANCED BY INCREASED MID LEVEL
CONVERGENCE AND SURFACE LOW PRESSURE DEVELOPMENT OVER THE PLAINS.
THIS FRONT IS STILL SCHEDULED TO MOVE INTO THE CWA BY 10 TO 11
AM...AND SWEEP ACROSS THE ENTIRE AREA BY 1 TO 2 PM. VERY STRONG
WINDS ARE FORECAST WITH THE PASSAGE OF THIS FRONT AND FOR SEVERAL
HOURS BEHIND IT. SURFACE PRESSURES INCREASE ABOUT 10MB IN 3 TO 6
HOURS IN HIGH RESOLUTION GUIDANCE AND NAM/GFS/ECMWF ALL SHOW 45 TO
50KTS NORTHWEST FLOW IN THE 850/925MB LAYER BY EARLY THIS EVENING.
TOTAL PRESSURE INCREASES ARE APPROACHING 20MB IN 12 HOURS. MOS
GUIDANCE DOES NOT SHOW WINDS THIS STRONG BUT THIS IS BELIEVED TO BE
A FUNCTION OF THE RELATIVE RARITY OF WIDESPREAD WINDS THIS STRONG IN
THE STATISTICAL DATABASE. RAW MODEL OUTPUT ALSO SEEMS A LITTLE TOO
CONSERVATIVE GIVEN THE STRENGTH OF THE PRESSURE GRADIENT AND THE
DEGREE OF MIXING INVOLVED AND IS TRENDING UPWARD BUT THE OFFICIAL
FORECAST IS PRETTY CLOSE TO RAW 00Z NAM/GFS OUTPUT WITH SUSTAINED WINDS
FOR SEVERAL HOURS AT 25 TO 35 MPH WITH GUSTS TO 45 TO 50 MPH. THIS
IS STRONGER THAN THE AVERAGE STRONG COLD FRONT FOR THIS AREA. HIGH
RESOLUTION GUIDANCE DEVLOPS STRONGER WINDS JUST OFF THE SURFACE IN A
CORE OVER STARR/HIDALGO/CAMERON COUNTIES WHICH INCREASES CONFIDENCE
THAT ADVISORY LEVEL WINDS WILL PERSIST AFTER SUNSET AND IF ALL
CONDITIONS COME TOGETHER JUST RIGHT MAY APPROACH HIGH WIND WARNING
LEVELS IN THE 5 TO 7 PM WINDOW. A WIND ADVISORY HAS BEEN ISSUED FOR
ALL COUNTIES WITH ITS EFFECTIVE TIME STARTING AND ENDING EARLIER IN
THE NORTHERN COUNTIES AND LASTING THROUGH MID EVENING IN THE RGV
METRO AREAS. PRECIPITATION CHANCES STILL LOOK QUITE LOW GIVEN THE
VERY SHARP FRONTAL SLOPE...RAPID FORWARD PROGRESS...AND RELATIVELY
DRY ANTECEDENT COLUMN.

SIMLIAR WIND PATTERS DO NOT TYPICALLY CAUSE SIGNIFCIANT COASTAL
FLOODING ISSUES AS THEY WILL BE RUNNING PARALLEL TO THE ISLAND...BUT
MINOR SEICHING IN THE LAGUNA MADRE AND WATER LEVELS RISING UP TO THE
DUNE LEVEL...CAUSING ISSUES WITH DRIVING ON THE BEACH APPEAR
POSSIBLE AND WILL ISSUE A COASTAL FLOOD STATEMENT TO ADDRESS THIS.

TONIGHT...
IMPACTS...STRONG WINDS EARLY.

WIND SPEEDS WILL STAY HIGH THROUGH THE OVERNIGHT GRADUALLY
DECREASING AS THE EVENING PROGRESSES. THE STEADY WINDS WILL KEEP
TEMEPRATURES A LITTLE MILD DESPITE THE ONGOING COLD ADVECTION. SKIES
SHOULD BE MOSTLY CLEAR.

WEDNESDAY...
IMPACTS...NOTICEABLY COOLER...CHILLY FEELING WITH THE WIND.

PERSISTENT NORTHWEST BREEZES CONTINUE WEDNESDAY WITH
TEMPERATURES FAILING TO REACH INTO THE MIDDLE 60S AREA WIDE. SKIES
SHOULD BE MOSTLY SUNNY WITH A FEW MID LEVEL CLOUDS POSSIBLY FORMING
THROUGH THE DAY. /68-JGG/

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...THE MAJOR 500 MB
TROUGH AXIS WILL CLEAR THROUGH THE SOUTH CENTRAL PLAINS REGION WED
NIGHT AND THURS WITH A SECOND TROUGH AXIS DIGGING MORE SLOWLY INTO
THE DESERT SW BY FRI AND SAT WITH THE TROUGH DIGGING INTO TX ON
SUN PUSHING ANOTHER COLD FRONT THROUGH THE REGION SAT NIGHT
BRINGING ANOTHER SHOT OF COOLER AIR. AFTER THE PASSAGE OF THE
FIRST 500 MB TROUGH AXIS THE FAIRLY COLD TEMPS EARLY THURS MORNING
WILL GIVE WAY TO WAA THROUGHOUT THURS/FRI AND SAT AS THE SURFACE
RIDGING SLIDES EAST ALLOWING FOR A RETURN OF WARMER AIR FROM THE
SOUTH. THE MAIN SUPPLY OF COLDER AIR WITH BOTH OF THESE TROUGH
AXES WILL LIKELY REMAIN SHUNTED EAST OF THE REGION DUE TO THE
FAIRLY PROGRESSIVE NATURE OF THE 500 MB FLOW PATTERN. SO AT THIS
POINT THE FREEZING TEMP POTENTIAL APPEARS PRETTY MININAL FOR THE
AREA THROUGH MON.

OVERALL MOISTURE LEVELS WILL REMAIN PRETTY LIMITED IN THE WAKE OF
THE FIRST 500 MB TROUGH AXIS PASSAGE BUT WILL START TO REBOUND
SOMEWHAT AHEAD OF THE 2ND 500 MB TROUGH THIS WEEKEND. SO WILL
MAINTAIN SOME 20 TO 30 % POPS AT THE END OF THE FORECAST PERIOD.

THE ECMWF AND GFS ARE IS PRETTY DECENT AGREEMENT IN THE HANDLING
OF THE LONGER TERM FEATURES WITH THE MODEL DERIVED TEMPS AND POPS
GENERALLY STAYING IN THE BALLPARK. RUN TO RUN CONSISTENCY WITH THE
GFS MEX MOS IS PRETTY STABLE SO OVERALL CONFIDENCE IN THE LONGER
TERM FORECAST WORDING IS ABOVE AVERAGE.

MARINE...
NOW THROUGH WEDNESDAY...
GALE WARNINGS HAVE BEEN ISSUED FOR ALL LOWER TEXAS COASTAL WATERS.
VERY STRONG NORTHWEST WINDS ARE FORECAST WITH FREQUENT WIND GUSTS
WELL OVER GALE FORCE...APPROACHING STORM FORCE ON THE OFFSHORE
WATERS LATE THIS AFTERNOON AND THIS EVENING. EXTREMELY ROUGH SEAS
ARE FORECAST WITH WAVE HEIGHTS APPROACHING 12 FEET OR HIGHER BY
SUNSET INTO EARLY TONIGHT. GALE FORCE WIND GUSTS WILL LIKELY
CONTINUE MOST OF THE OVERNIGHT WITH STRONG WINDS AND VERY ROUGH SEAS
PERSISTING THROUGH WEDNESDAY. SMALL CRAFT ADVISORIES WILL BE ISSUED
AFTER THE TIME OF THE GALE WARNING LIKELY THROUGH ALL OF WEDNESDAY.

WEDNESDAY NIGHT THROUGH SATURDAY...THE PGF INTO WED EVENING WILL
REMAIN STRONG ENOUGH TO MAINTAIN SOME SCA CONDITIONS EARLY IN THE
EVENING. THE SURFACE FLOW WILL THEN WEAKEN SOME AND SHIFT AROUND
TO A MORE SOUTHERLY DIRECTION ON THURS AS THE SURFACE RIDGE SHIFTS
EAST. THE PGF WILL THEN STRENGTHEN ONCE AGAIN THURS NIGHT INTO FRI
AS A SURFACE LOW DEVELOPS OVER THE CENTRAL PLAINS STATES WHICH
WILL INTERACT WITH THE SURFACE RIDGE TO THE EAST POSSIBLY
REQUIRING ANOTHER ROUND OF SCAS FOR THE GULF WATERS THURS NIGHT.
THE NEXT COLD FRONT WILL THEN PUSH TOWARDS THE LOWER TX COASTLINE
LATE SAT WHICH WILL LIKELY RESULT IN ANOTHER ROUND OF POTENTIAL
SCEC/SCA CONDITIONS SATURDAY NIGHT.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  78  48  61  45 /  10  10   0   0
BROWNSVILLE          78  47  62  43 /  10  10   0   0
HARLINGEN            78  45  62  41 /  10   0   0   0
MCALLEN              77  48  63  41 /   0   0   0   0
RIO GRANDE CITY      75  46  63  39 /   0   0   0   0
SOUTH PADRE ISLAND   77  51  62  51 /  10  10   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR TXZ248>251.

     WIND ADVISORY FROM 3 PM THIS AFTERNOON TO 10 PM CST THIS EVENING
     FOR TXZ252>257.

GM...GALE WARNING UNTIL 6 AM CST WEDNESDAY FOR GMZ130-132-135-150-155-
     170-175.

&&

$$

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