Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 181127
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
527 AM CST THU DEC 18 2014

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

&&

.AVIATION...STATIONARY BOUNDARY DRAPED NORTH OF THE VALLEY ACROSS
JIM HOGG AND STARR COUNTIES AND WILL STAY NORTH OF THE TERMINALS
TODAY. ISOLATED SHOWERS AND THUNDERSTORMS MAY DEVELOP LATER TODAY
AS WEAK INSTABILITY DEVELOPS SOUTH OF THE FRONT BUT CONFIDENCE NOT
GREAT AT THIS TIME SO HAVE JUST VCSH TODAY FOR THE SITES. CONDS
SHOULD BE VFR TODAY BUT BRIEF MVFR IN SHRA/TSRA CANNOT BE RULED
OUT. PREDOMINATE MVFR RETURNS THIS EVENING AFTER SUNSET.

&&

.PREV DISCUSSION... /ISSUED 332 AM CST THU DEC 18 2014/

SHORT TERM /NOW THROUGH FRIDAY/...STATIONARY BOUNDARY LIES ACROSS
SOUTHERN TEXAS THEN SOUTHWESTWARD TO A WEAK LOW PRESSURE AREA IN JIM
HOGG/ZAPATA COUNTY THEN BACK WESTWARD INTO NORTHERN MEXICO. WINDS
NORTH AND WEST OF THIS BOUNDARY ARE NORTH TO NORTHWESTERLY AND WINDS
IN THE VALLEY ARE FROM THE SOUTH. UPPER TROUGH IS LOCATED ACROSS THE
INTERMOUNTAIN WEST DOWN TO THE DESERT SOUTHWEST WITH HEIGHT FALLS
OUT AHEAD OF IT AND PLENTY OF MID/UPPER LEVEL MOISTURE IN THE FORM
OF CLOUDS ACROSS THE AREA STREAMING IN FROM THE PACIFIC. LOWS
TONIGHT ARE ON TRACK...AROUND 70 IN THE VALLEY AND AROUND 60 NORTH
OF THE BOUNDARY.

PRECIPITATION CHANCES WILL INCREASE TODAY AS THE UPPER TROUGH EDGES
CLOSER PLACING THE AREA IN INCREASING DIFFLUENCE ALOFT AND UPPER JET
DYNAMICS MOVE CLOSER TO THE AREA. LOW LEVEL CONVERGENCE WILL BE IN
PLAY TODAY DUE TO THE MEANDERING FRONT DRAPED IN THE WESTERN THIRD
OF THE AREA. WEAK INSTABILITY WILL ALSO BE PRESENT LEADING TO
CHANCES FOR THUNDERSTORMS TODAY WITH THE BETTER CHANCES ACROSS THE
NORTH AND WEST LATER TODAY AND TONIGHT. A FEW STRONGER STORMS
POSSIBLE AS WELL AND SPC HAS ISSUED A MARGINAL RISK FOR SEVERE FOR
OUR FAR WESTERN SECTIONS FOR LATER TODAY AND TONIGHT. HIGH
TEMPERATURES WILL ALSO BE A CHALLENGE WITH COOLER TEMPERATURES NORTH
OF THE BOUNDARY OF MID/UPPER 60S AND UPPER 70S SOUTH AND EAST OF THE
BOUNDARY EAST OF HWY 281.

SURFACE LOW PRESSURE WILL DEEPEN SLIGHTLY FRIDAY ACROSS DEEP SOUTH
TEXAS AS THE UPPER TOUGH GETS CLOSER THEN LIFT INTO NORTHERN TEXAS.
A SECOND COLD FRONT MOVING SOUTHWARD THROUGH TEXAS WILL LINK UP WITH
THE STATIONARY BOUNDARY AND SURFACE LOW PRESSURE AND SWEEP THROUGH
OUR AREA FRIDAY AND MOVE OFFSHORE THE LOWER VALLEY BY EARLY FRIDAY
EVENING. WEAK INSTABILITY WILL REMAIN AHEAD OF THE FRONT SO WILL
KEEP MENTION OF THUNDERSTORMS GOING UNTIL THE FRONT SWEEPS THROUGH.
BETTER CHANCES FOR PRECIPITATION WILL BE IN THE RANCH LANDS AS BETTER
DYNAMICS WILL BE JUST NORTH OF THE AREA. EXPECT NORTHWESTERLY WINDS
BEHIND THE FRONT AND A SLOW DECREASE TO THE CLOUDS.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...DRIER AIR MOVING INTO
THE AREA BEHIND A COLD FRONT PASSAGE ON FRIDAY WILL ALLOW OVERNIGHT
TEMPERATURES TO DECREASE FRIDAY NIGHT...LANDING MUCH CLOSER TO
NORMAL WITH SOME MID TO UPPER 40S ACROSS THE NORTHERN RANCH LANDS
AND BRUSH COUNTRY. NORMAL HIGH TEMPERATURES SATURDAY IN THE MID 60S
WILL SEEM COOL. HIGH PRES WILL SPREAD OVER THE AREA IN THE WAKE OF
THE FRONT WITH NEAR NORMAL TEMPERATURES SUNDAY AND ABOVE NRML TEMPS
MONDAY AND TUESDAY WITH A WARMING TREND UNDERWAY.

ANOTHER LOW LATITUDE MID LEVEL TROUGH WILL TRACK INTO WEST TEXAS
SATURDAY NIGHT. THE LIFT WILL INCREASE MOISTURE OVER THE AREA ON
SUNDAY AS SURFACE WINDS REMAIN NORTHEAST. SCATTERED CONVECTION WILL
BE POSSIBLE SUNDAY...PARTICULARLY ACROSS EASTERN SECTIONS.

AT THIS POINT THE ECMWF AND THE GFS DIVERGE IN SOME RESPECTS. THE
ECMWF DIGS A DEEPER TROUGH INTO THE UPPER MIDWEST SUNDAY NIGHT. THE
RESULT WILL BE PRESSURE FALLS SOUTH OVER THE HIGH PLAINS WHICH ARE
NOT SEEN BY THE GFS. WINDS ARE THUS PROGGED TO BECOME SOUTHEAST BY
THE ECMWF SOONER THAN THE GFS...ENDING THE DRY AIR INFLUX AND
INSTEAD INCREASING MOISTURE. IT LOOKS LIKE THE TWO MODELS COME BACK
TOGETHER SOMEWHAT LATE MONDAY HOWEVER...BUT IT IS AN INTERESTING
ANOMALY. THE GFS BRINGS THE NEXT FRONT THROUGH THE AREA TUESDAY
AFTERNOON...BY THAT TIME DEVELOPING A STRONGER STORM SYSTEM OVER THE
UPPER MIDWEST. THE ECMWF IS WEAKER WITH INCOMING DRY AIR TUESDAY...
BUT THE NET RESULT SEEMS SIMILAR...WITH STRONG UPSTREAM RIDGING
BUILDING OVER THE WESTERN UNITED STATES AND A TUESDAY OVERNIGHT
TEMPERATURE DROP TO NEAR NORMAL. HIGH TEMPS WEDNESDAY WILL BE NEAR
NORMAL...WITH THE REST OF THE WEEK EXHIBITING DRY WEATHER AND A WEAK
WARMING TREND.

MARINE...
NOW THROUGH FRIDAY...SEAS WERE NEAR 4 FEET WITH SOUTHEAST WINDS
NEAR 9 KNOTS AT BUOY020 EARLY THIS MORNING. LIGHT TO MODERATE
SOUTH TO SOUTHEAST WINDS WILL PREVAIL ACROSS THE COASTAL WATERS
TODAY AS A WARM FRONT WILL BE LOCATED ACROSS THE MIDDLE TEXAS
COAST. WINDS WILL INCREASE SLIGHTLY THURS NIGHT AS LOW PRESSURE
ACROSS THE WESTERN PORTIONS OF THE RGV ALLOWS THE PRESSURE
GRADIENT TO INCREASE SLIGHTLY ACROSS THE LOWER TEXAS COAST. A COLD
FRONT WILL MOVE THROUGH THE COASTAL WATERS FRIDAY AFTERNOON WITH
WINDS BECOMING OFFSHORE.

FRIDAY NIGHT THROUGH MONDAY...THE MAIN IMPACT PERIOD WILL BE FRIDAY
NIGHT INTO SATURDAY MORNING AS NORTH WINDS INCREASE BEHIND A FRONT
TO AROUND 20 KNOTS AND SEAS BUILD TO BETWEEN 5 AND 7 FEET. A FEW
HOURS OF LOW END SMALL CRAFT ADVISORY CONDITIONS MAY DEVELOP AROUND
MIDNIGHT BUT BY MID SATURDAY MORNING CONDITIONS WILL BE IMPROVING.

SCATTERED SHOWERS WILL DEVELOP FRIDAY WITH THE FRONT...MOVING
OFFSHORE FRIDAY NIGHT...BUT IT LOOKS LIKE MOST OF THE ENERGY WILL BE
FARTHER TO THE NORTH. MODERATE TO BREEZY NORTH WINDS AND HIGHER SEAS
WILL SET UP BEHIND THE FRONT FRIDAY NIGHT THROUGH EARLY SATURDAY. A
FEW HOURS OF LOW END SMALL CRAFT ADVISORY CONDITIONS MAY DEVELOP.
HIGH PRESSURE WILL SPREAD OVER THE AREA SATURDAY WITH MODERATE NORTH
WINDS SHIFTING TO NORTHEAST WHILE SEAS REMAIN MODERATE THOUGH SLOWLY
DECREASING. WINDS WILL REMAIN OUT OF THE NORTHEAST SATURDAY NIGHT
WITH HIGH PRESSURE OVER THE NORTHWEST GULF...WHILE A MID LEVEL
SHORTWAVE TROUGH APPROACHES ON A LOW LATITUDE TRAJECTORY...SWINGING
OVER WEST TEXAS SATURDAY NIGHT. THE TROUGH WILL RESULT IN UNSETTLED
MARINE WX SATURDAY NIGHT THROUGH SUNDAY WHEN DRIER AIR OF SIMILAR
PRESSURE WILL DISPLACE THE PREVIOUS AIR MASS. THE ECMWF IS MORE
AGGRESSIVE IN CHANGING WINDS TO SOUTHEAST SUNDAY NIGHT AS IT DEEPENS
LOW PRESSURE OVER THE TEXAS PANHANDLE...WHILE THE GFS WAITS UNTIL
MONDAY.

&&

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

$$

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