Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 152055
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
255 PM CST MON DEC 15 2014

.SHORT TERM /NOW THROUGH TUESDAY NIGHT/...MIDLEVEL TROUGH AND
SURFACE LOW WILL CONTINUE TO TREK NORTHEAST ACROSS IA TODAY AND
ACROSS THE GREAT LAKES REGION TUESDAY. ASSOCIATED COLD FRONT IS
CURRENTLY PUSHING SOUTH ACROSS CENTRAL TEXAS WITH DRIER AIR
FILTERING IN BEHIND IT...AS EVIDENCED BY A 30 DEGREE DEWPOINT
DIFFERENCE. THE COLD FRONT WILL PUSH ITS WAY INTO DEEP SOUTH TEXAS
LATE THIS EVENING AND THROUGH THE VALLEY EARLY TUESDAY MORNING. HAVE
MAINTAINED A SLIGHT CHANCE OF RAIN STARTING OUT ACROSS THE
RANCHLANDS AND SPREADING FURTHER SOUTH TO THE RIVER AS THE FRONT
PUSHES ACROSS THE CWA. 1000 TO 500 MB MOISTURE REMAINS LIMITED AHEAD
OF THE FRONT...WITH MOST OF THE MOISTURE IN THE LOWER LEVELS.
HOWEVER...THERE MAY BE ENOUGH CONVERGENCE ALONG THE FRONT TO GET A
FEW SHOWERS GOING. AHEAD OF THE FRONT FOG WILL BE THE CONCERN OF THE
NIGHT...AS LOW LEVEL MOISTURE POOLS AHEAD OF THE FRONT AND WINDS
BECOME LIGHT TO NEARLY CALM. CANNOT RULE OUT DENSE FOG
FORMING...ESPECIALLY ACROSS THE LOWER AND MID VALLEY.

MODELS CONTINUE TO SHOW ISENTROPIC LIFT DEVELOPING DURING THE DAY
TUESDAY AS THE FRONT REMAINS IN THE VICINITY. HAVE MAINTAINED A
SLIGHT CHANCE FOR LIGHT RAIN AND SHOWERS...PRIMARILY FOR THOSE AREAS
ALONG THE RIVER. MOISTURE INCREASES LATE TUESDAY INTO TUESDAY NIGHT
AS SW FLOW AT 700 MB BRINGS IN A SWATH OF MOISTURE AND SURFACE FLOW
RETURNS TO THE EAST AND SOUTHEAST. GREATER RAIN CHANCES SPREAD NORTH
DURING THE OVERNIGHT PERIOD.

STRONG CAA ADVECTION IS NOT EXPECTED WITH THE FRONT BUT COOLER
TEMPERATURES ARE EXPECTED TUESDAY AND TUESDAY NIGHT. TEMPERATURES
ACROSS THE RANCHLANDS WILL TOP OUT IN THE MID TO UPPER 60S WHILE
THOSE AREAS FURTHER SOUTH WILL SEE HIGHS IN THE LOWER 70S. LOWS
TUESDAY NIGHT WILL RANGE FROM THE MID TO UPPER 50S ACROSS THE
WESTERN BRUSH COUNTRY TO THE LOWER 60S ACROSS THE LOWER VALLEY AND
THE ALONG THE COAST.

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
SOUTHEASTERLY RETURN FLOW CRANKS UP IN EARNEST ON WEDNESDAY WITH
ANOTHER STRONG WESTERN CONUS TROUGH LEADING TO A PRETTY TIGHT LOW
LAYER GRADIENT BETWEEN WEST CENTRAL GULF RIDGING. WIND GUSTS WILL
PROBABLY PUSH 25 TO 35 MPH IN THE AFTERNOON ACROSS MOST OF THE AREA.
WEAK LOW LEVEL LIFT AND SOME RESIDUAL MOISTURE KEEP A SLIGHT CHANCE
OF SHOWERS AMID BROAD MID LEVEL ASCENT...BUT THOSE CHANCES TAPER OFF
IN THE VALLEY METRO AREAS THROUGH THE DAY AS DRIER AIR ADVECTS IN
FROM THE SOUTH. HIGHS IN THE LOW 70S WEST...MID TO UPPER 70S COASTAL
LOOK TO BE IN ORDER.

GULF RIDGING RETREATS EASTWARD ON THURSDAY AS THE LARGER SCALE
WESTERN US TROUGHING APPROACHES. THE LOW LEVEL PRESSURE GRADIENT
STEPS DOWNWARD JUST A BIT AND THUSLY CONTINUED A FORECAST OF WIND
SPEEDS ABOUT 5 TO 8 MPH WEAKER. RESIDUAL LOW LEVEL
MOISTURE/CLOUDINESS PERSIST BUT SHOULD BE MORE OF A PARTLY CLOUDY TO
PARTLY SUNNY APPROACH RATHER THAN FULL OVERCAST. CONTINUED TO WARM
TEMPERATURES 3 TO 4 DEGREES FROM WEDNESDAY.

FOR FRIDAY THE 12Z GFS HAS TRENDED CLOSER TO THE ECMWF REGARDING THE
SYNOPTIC SCALE DETAILS AS THAT WESTERN US TROUGH EJECTS EASTWARD
OVER TEXAS AND INTO THE SOUTHEASTERN US. REASONABLE ENOUGH AGREEMENT
ON A SURFACE TROUGH/LOW OVER THE NORTHWESTERN GULF SHIFTING EASTWARD
ALONG THE NORTHCENTRAL GULF COAST WHICH BRINGS A COLD FRONT THROUGH
DURING THE DAY ON FRIDAY. KEPT A 30 PCT RAIN CHANCE IN THE VALLEY
FRIDAY WITH 40 PCT ACROSS THE NORTHEASTERLY QUARTER OF THE CWA. BEST
MID LEVEL ASCENT WILL BE TO THE NORTHEAST BUT MIGHT SPARK A DEEPER
SHOWER OR THUNDERSTORM OR TWO AS THE BOUNDARY WORKS ACROSS THE
REGION. THE MAIN IMPACT FROM THIS SYSTEM THOUGH WILL PROBABLY BE
BRISK NORTHWEST WINDS OVER THE MARINE WATERS THAT WILL ROUGHEN SEAS.
A MODEST DROP IN TEMPERATURES IS ALSO FORECAST BEHIND THE FRONT WITH
HIGHS ON SATURDAY ABOUT 8 TO 10 DEGREES COOLER THAN TUESDAY. WITH A
SOURCE AIRMASS OF NEW MEXICO HOWEVER THIS FRONT WONT PUT US IN THE
ICEBOX BY ANY MEASURE. TOTAL PRECIPITATION AMOUNTS LOOK PRETTY LIGHT
TOO WITH ANY PRECIP THAT FALLS AS THE SYSTEM SWEEPS QUICKLY EASTWARD.

SATURDAY INTO THE BEGINNING OF NEXT WEEK ANOTHER FAIRLY FAST MOVING
TROUGH SWEEPS ACROSS THE AREA. THE PERSISTENT WEST SOUTHWESTERLY
FLOW ALOFT SUPPORTS SOME COASTAL TROUGHING WITH THE SUBTROPICAL AND
POLAR JETS COMBINING TO KEEP SOME LOW CLOUDS AND MOISTURE INTO THE
AREA THROUGH THE WEEKEND...WHICH THE GFS SHOWS WITH A FAIRLY STRONG
GRADIENT OF SUNNIER SKIES OVER THE RANCHLANDS AND CLOUDIER SKIES
ALONG THE COAST AND THE IMMEDIATE VALLEY. THE GFS ALSO DEPICTS
STRONGER NORTHEASTERLY WINDS FEEDING INTO A TROUGH AXIS OVER THE
WEST CENTRAL GULF STARTING SATURDAY NIGHT. THIS IS IN CONTRAST TO
THE ECMWF WHICH REGENERATES SOUTHEASTERLY RETURN FLOW IN ADVANCE OF
THE NEXT ADVANCING SYSTEM. PREFER THE GFS SOLUTION GIVEN THE
SYNOPTIC PICTURE WHICH KEEPS SOME FORM OF TROUGHINESS/CLOUD COVER
GENERATION IN THE AREA THROUGH THE WEEKEND ALTHOUGH EXPECT THERE
WILL BE SOME BREAKS...ESPECIALLY SATURDAY.

GFS/ECMWF DO AGREE ON BRINGING THE MAIN TROUGH AXIS THROUGH
MONDAY/MONDAY NIGHT. THE DIFFERENCE THOUGH IN SURFACE FLOW IMPACTS
SENSIBLE WEATHER WITH THE NORTHERLY COASTAL TROUGH PREVENTING MUCH
IN THE WAY OF SURFACE HEATING AND DEEP MOISTURE FOR SHOWERS/STORMS
WHERE THE ECMWFS STRONG RETURN FLOW HELPS PRODUCE HEAVIER RAIN AND
SHOWERS/STORMS ACROSS A LARGER AREA MONDAY AND MONDAY NIGHT. AGAIN
PREFER THE MORE SUBDUED GFS SOLUTION AS WE VERY FREQUENTLY SEE
PERSISTENT COASTAL TROUGHING IN MID/LATE DECEMBER IN THESE
PERSISTENT MODESTLY DIVERGENT/DIFFLUENT UPPER AIR REGIMES FORECAST
TO BE PRESENT THROUGH THE WEEKEND. THE GFS SOLUTION THOUGH DOES OPEN
THE WINDOW FOR A LITTLE MORE STRATIFORM PRECIP THAN CURRENTLY
INDICATED BUT THE DETAILS OF WHERE QUASI CONVECTIVE BANDING AND
OTHER FEATURES MIGHT SET UP ARE TOO FINE FOR A DAY 7 FORECAST SO
JUST CARRIED SOME CLOUD COVER AND A SLIGHT CHANCE OF SHOWERS FOR
NOW. HIGHS THROUGH THE WEEKEND RUN FROM ABOUT 67 TO 71. IF THE ECMWF
SOLUTION BEGINS TO LEAD THE CHARGE HOWEVER FAIRLY SIGNIFICANT
CHANGES TO FORECAST TEMPS AND PRECIP WILL LIKELY BE REQUIRED
ALTHOUGH AS MENTIONED BEFORE THE ECMWF APPEARS TO BE MOVING CLOSER
TO THE GFS FROM RUN TO RUN. /68-JGG/

&&

.MARINE...NOW THROUGH TUESDAY NIGHT...LIGHT TO MODERATE SOUTHEAST
WINDS WILL PREVAIL THROUGH THIS EVENING AND SEAS WILL CONTINUE TO
SUBSIDE TO AROUND 3 FEET. THE NEXT COLD FRONT WILL SLOWLY PUSH
ACROSS THE COASTAL WATERS TONIGHT WITH WINDS BECOMING NORTHEASTERLY
BY TUESDAY MORNING. WINDS WILL INCREASE AND SEAS WILL BUILD BACK TO
5 FEET DURING THE DAY TUESDAY RESULTING IN LIKELY SMALL CRAFT
EXERCISE CAUTION TO BORDERLINE SMALL CRAFT ADVISORY CONDITIONS.

WEDNESDAY THROUGH FRIDAY...
RELATIVELY STRONG SOUTHEAST BREEZES ARE FORECAST ON WEDNESDAY WHICH
MAY PUSH WIND SPEEDS CLOSE TO OR ABOVE EXERCISE CAUTION
LEVELS...PARTICULARLY ON THE OFFSHORE WATERS AND THE LAGUNA MADRE.
MORE MODEST WINDS ARE FORECAST ON THURSDAY BEFORE A FRONT ARRIVES
DURING THE DAY ON FRIDAY. WINDS BEHIND THE FRONT ARE CURRENTLY
FORECAST TO BE AT OR ABOVE SMALL CRAFT ADVISORY LEVELS WITH SEAS
BECOMING ROUGH.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  67  71  64  75 /  20  20  20  20
BROWNSVILLE          67  74  65  76 /  20  30  20  20
HARLINGEN            66  72  63  76 /  20  20  20  20
MCALLEN              66  71  63  76 /  20  20  20  20
RIO GRANDE CITY      65  70  59  72 /  20  20  20  20
SOUTH PADRE ISLAND   68  71  66  73 /  20  20  20  20

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

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