Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 220002
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
602 PM CST FRI NOV 21 2014

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

&&

.AVIATION...AN INCREASED IN LOW LEVEL CLOUDS WILL RETURN TONIGHT
WITH MVFR GIGS THROUGH SUNRISE. THE PRESSURE GRADIENT WILL
STRENGTHEN SATURDAY INCREASING THE SE WINDS THROUGH THE DAY WITH
GUSTS APPROACHING 30 TO 35 KNOTS BY 18Z AND PERSISTING THROUGH
LATE IN THE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 255 PM CST FRI NOV 21 2014/

SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...
IMPACTS...
WINDY SATURDAY...CONDITIONAL RISK FOR SEVERE STORMS SAT PM.

RELEVANT FEATURES...
A LARGE CLOSED UPPER LEVEL LOW IS CENTERED OVER THE NORTHERN GULF OF
MEXICO THIS AFTERNOON. BROAD 70 TO 90 KT SOUTHWESTERLY 250 MB FLOW IS
HELPING WORK WITH THIS TROUGH/LOW IN INCREASING THE LOW LAYER
PRESSURE GRADIENT ACROSS THE AREA. THIS IS RESULTING IN A BREEZY TO
WINDY DAY WITH 20 KT WINDS OVER THE GULF...PER BUOY AND ASCAT
OBSERVATION...AND 20 TO 25 MPH WINDS WITH GUSTS TO 35 MPH OVER LAND.
WEAK WARM ADVECTION WITHIN LOW LEVEL SOUTHEASTERLIES ARE ALSO
KEEPING A CLOUD LAYER AT AROUND 2000 TO 4000 FT WHICH IS SPARKING A
FEW SPRINKLES/SHOWERS. THIS SHOULD CONTINUE FOR MUCH OF THE REST OF
THE DAY.

TONIGHT...
850/925MB PRESSURE GRADIENT PEAKS LATE TONIGHT AS THE UPPER LOW
APPROACHES. NAM/GFS GUIDANCE SUPPORTS 35 TO 45 KNOT WINDS 3000 TO
5000 FT OFF THE SURFACE...WHICH TEND TO BE UNDERDONE IN STRONG UPPER
LEVEL STORM SYSTEMS LIKE THIS ONE. COOLER NIGHTTIME TEMPERATURES
WILL ALLOW FOR LOWER SURFACE WINDS...AROUND 15 MPH OR SO. WEAK WARM
ADVECTION IN THE LOW LEVELS WILL LEAD TO A CONTINUE CHANCE FOR
SHOWERS AREA WIDE WITH THE BEST CHANCE OVER THE GULF OF MEXICO.

SATURDAY...
WINDY AREA WIDE...SOME SEVERE THUNDERSTORM RISK IN RANCHLANDS.

CONFIDENCE IS HIGH IN STRONG SOUTHEASTERLY WINDS MOST OF THE DAY
SATURDAY. THE PEAK LOW LEVEL GRADIENT WILL SHIFT WEST TO EAST
THROUGH THE DAY. CURRENT FORECAST WIND SPEEDS ARE NEAR OR SLIGHTLY
ABOVE WIND ADVISORY CRITERIA IN THE HIGHWAY 77/281 CORRIDOR. GUSTS
OF 35 TO 40 MPH WILL BE LIKELY...ESPECIALLY BEFORE 3 TO 4 PM BEFORE
THE MAIN TROUGH GETS CLOSER AND THE GRADIENT WEAKENS. WEAK WARM
ADVECTION SHOULD KEEP AT LEAST SOME CLOUD COVER IN PLACE BUT
TEMPERATURES SHOULD STILL BE ABLE TO REACH INTO THE MID 80S.

LESS CERTAIN IS THE THUNDERSTORM RISK.  STRONG DOWN SLOPING
SOUTHWESTERLIES ARE EVIDENT IN THE 700MB LAYER THROUGH THE DAY. THIS
COMMONLY RESULTS IN A SIGNIFICANT WARMING AND DRYING IN THE
850/700MB LAYER OVER DEEP SOUTH TEXAS AS THESE WINDS COME DOWN OFF
THE SIERRA MADRE MOUNTAINS AND MEXICAN PLATEAU. 12Z GFS FORECAST SOUNDINGS
SHOW THIS DRYING FAIRLY WELL WHILE THE NAM ONLY BRINGS THE INFLUENCE
OF THIS LAYER TO ABOUT THE RIO GRANDE BEFORE THE SIGNAL DIMINISHES. FEEL
CONFIDENT THIS LAYER WILL WIN OUT DURING THE DAYTIME IN THE RGV
METRO AREAS AND KEPT THE FORECAST DRIER. THE LEFT FRONT QUADRANT OF
A JET MAXIMUM ARRIVING DURING THE DAY PROVIDES SOME DIVERGENCE OVER
THE NORTHERN COUNTIES...WHO WILL ALSO BE FURTHER FROM THE INFLUENCE
OF DOWNSLOPING...SO CARRIED HIGHER POPS IN NORTHERN JIM
HOGG/BROOKS/KENEDY COUNTIES WHERE STRONG DEEP LAYER SHEAR AND MODEST
INSTABILITY COULD PRODUCE SEVERE THUNDERSTORMS WITH DAMAGING WINDS
THE MAIN THREAT IN THE AFTERNOON.

SATURDAY NIGHT...
CONDITIONAL SEVERE WEATHER RISK AREA WIDE...BEST CHANCES REMAIN OVER
THE BRUSH COUNTRY.

THE MAIN UPPER LEVEL TROUGH PUSHES ACROSS SOUTH TEXAS SATURDAY
NIGHT. VERY STRONG LARGE SCALE ASCENT FROM THIS FEATURE SHOULD
ERADICATE ANY RESIDUAL CAPPING. THUNDERSTORMS APPEAR TO INITIATE
ALONG THE SIERRA MADRE MOUNTAINS AND MOVE INTO THE REGION WITH THE
TRAJECTORY SUPPORTING BETTER COVERAGE OVER THE HEBBRONVILLE AND
FALFURRIAS AREA. THE SURFACE FRONT/WIND SHIFT ASSOCIATED WITH THIS
FEATURE IS WEAK AND A STRONGER 850MB WESTERLY WIND SHIFT IS MARKED
BY MUCH DRYER AND WARMER AIR THAT WILL QUICKLY QUASH ANY SURFACE
BASED INSTABILITY. 0-6KM BULK SHEAR REMAINS HIGH THROUGH THE NIGHT
HOWEVER WITH VALUES FROM 35 TO 45 KNOTS WHICH WOULD BE SUFFICIENT
FOR LARGE SCALE STORM ORGANIZATION.

IN TERMS OF SEVERE THUNDERSTORMS...CONVECTION THAT INITIATES ON THE
SIERRA MADRE MOUNTAINS IN THE AFTERNOON AND MOVES INTO THE AREA IN
THE EARLY EVENING WOULD HAVE THE BEST CHANCE FOR SEVERE WEATHER
POTENTIAL. DURING THIS TIME A FAIR BALANCE OF AVAILABLE INSTABILITY
AND STRONG SHEAR COULD WORK WITH CONVERGENCE/COLD POOLS GENERATED BY
CONVECTION TO KEEP A RELATIVELY STRONG COMPLEX MOVING NORTHEASTWARD
ACROSS THE CWA. SHEAR REMAINS FAVORABLE ALL NIGHT BUT IT APPEARS THE
SURFACE TO 850MB TEMPERATURE AND MOISTURE PROFILES ARE GOING TO BE
SOMEWHAT  DISORGANIZED WITH STRONGLY ADVANCING WESTERLIES FROM 850MB
AIDING IN REDUCING SURFACE BASED INSTABILITY AS THE ACTUAL SURFACE
FRONT ARRIVES. THIS WOULD MEAN SOME OF THE LATER THUNDERSTORMS MAY
BE ROOTED ABOVE THE BOUNDARY LAYER WHICH WOULD GREATLY REDUCE THE
POTENTIAL FOR DAMAGING WIND. A BETTER CHANCE EXISTS OVER THE GULF
WATERS FOR STRONG/DAMAGING WIND WHERE LOW LEVEL MOISTURE WILL BE
MORE PLENTIFUL AND HIGHER TEMPERATURES WILL LINGER LONGER. IN ALL IT
APPEARS THE RISK FOR THUNDERSTORMS...AND SEVERE THUNDERSTORMS IS
HIGHER OVER THE NORTHERN COUNTIES OF THE CWA. /68-JGG/

LONG TERM /SUNDAY THROUGH FRIDAY/...MID LEVEL SHORT WAVE TROUGH
AXIS WILL BE EAST OF THE CWA SUNDAY MORNING...WITH DRY AIR TAKING
OVER. HIGH TEMPERATURES SUNDAY WILL PUSH INTO THE 80S...UP TO 10
DEGREES ABOVE NORMAL...UNDER MOSTLY SUNNY SKIES. LIGHT SOUTHWEST
WINDS WILL PROVIDE A WEAK DOWNSLOPING COMPONENT TO HELP PROP UP
TEMPS. ANOTHER MID LEVEL TROUGH WILL MOVE ACROSS THE SOUTHERN PLAINS
SUNDAY AS RIDGING AMPLIFIES OVER THE WESTERN UNITED STATES. CLEAR
SKIES SUNDAY NIGHT WILL HELP LOW TEMPS RADIATE DOWN CLOSER TO NORMAL
IN THE 50S TO LOWER 60S...ABOUT 5 DEGREES ABOVE NORMAL. A MARITIME
POLAR AIR MASS WILL PUSH INTO THE AREA MID MONDAY...AND WILL KEEP
HIGH TEMPERATURES IN THE MIDDLE 70S AND CLOSE TO NORMAL WITH A FEW
EXTRA CLOUDS IN THE AREA...BUT NOT MORE THAN PARTLY CLOUDY. WINDS
WILL SHIFT MORE DEFINITIVELY TO MODERATE NORTHWEST...THOUGH A BIT
STRONGER OVER THE WATER...RESULTING IN ISOLATED COASTAL SHOWERS FOR
A FEW HOURS MONDAY AFTERNOON. A COUPLE OF ADDITIONAL WEAK SHORT WAVE
TROUGHS MONDAY AND TUESDAY WILL MOVE OVER EAST TEXAS WITH LITTLE
IMPACT THIS FAR SOUTH. WILL SEE MOSTLY CLEAR SKIES AND COOLER TEMPS
BEGINNING MONDAY AND THROUGH THURSDAY AS MARITIME POLAR HIGH
PRESSURE CONTINUES TO MOVE IN FROM THE NORTHWEST. LOW TEMPERATURES
TUESDAY NIGHT AND WEDNESDAY NIGHT WILL DIP INTO THE 40S...BENEFITING
FROM CLEAR SKIES TO GET BELOW NORMAL. THURSDAY THROUGH FRIDAY WILL
BEGIN A TRANSITION TO A MORE ZONAL MID LEVEL PATTERN WITH HIGH
PRESSURE SHIFTING EAST AND WINDS VEERING TO SOUTHEAST WITH AN UPWARD
TREND IN DEW POINTS AND OVERNIGHT LOW TEMPERATURES. COASTAL SHOWERS
COULD DEVELOP ON FRIDAY WITH SUFFICIENT MOISTURE RETURN.

MARINE...
TODAY THROUGH SATURDAY NIGHT...SMALL CRAFT ADVISORIES REMAIN IN
EFFECT TODAY FOR ALL OF THE LOWER TEXAS COAST AND A SMALL CRAFT
ADVISORY REMAINS IN EFFECT THROUGH SATURDAY FOR THE GULF WATERS OF
THE LOWER TEXAS COAST DUE TO STRONG SOUTHEAST WINDS AND ROUGH
SEAS. A SMALL CRAFT ADVISORY WILL ALSO BE NEEDED DURING THE DAY ON
SATURDAY. SOUTHEAST WINDS WILL WEAKEN AND SHIFT TO THE WEST OR
SOUTHWEST DURING THE NIGHT SATURDAY. THESE WINDS SHOULD BE MORE
MODERATE...AND SEAS MAY FALL BELOW ADVISORY CONDITIONS SATURDAY
NIGHT.

SUNDAY THROUGH WEDNESDAY...LIGHT SOUTH TO SOUTHWEST WINDS SUNDAY
AND SUNDAY NIGHT WILL BECOME LIGHT TO MDT NORTH MONDAY MORNING AS
A MODIFIED MARITIME POLAR AIR MASS ARRIVES FROM UPSTREAM. A FEW
HOURS OF LOW END SMALL CRAFT ADVISORY CONDITIONS WILL BE POSSIBLE
MONDAY BEHIND THE WEAK COLD FRONT. REINFORCING HIGH PRESSURE WILL
ARRIVE ON TUESDAY WHICH WILL AGAIN PUSH NORTH WINDS TOWARD 20 KTS
AND LOW END SMALL CRAFT ADVISORY CONDITIONS...ALONG WITH SEAS
BUILDING TO SIX OR SEVEN FEET TUESDAY NIGHT. WEDNESDAY WILL BE A
TRANSITION DAY WITH WINDS VEERING TO SOUTHEAST AS THE UPSTREAM
RIDGING SHIFTS EAST...AND PUSHES HIGH PRESSURE AHEAD OF IT OUT
INTO THE MISSISSIPPI VALLEY.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 6 PM CST SATURDAY FOR GMZ150-155-170-
     175.

&&

$$

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