Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 260834
AFDBRO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
334 AM CDT TUE AUG 26 2014

.SHORT TERM /NOW THROUGH WEDNESDAY/...
SOUTH TEXAS REMAINS SITUATED UNDER RELATIVELY DRY MID AND LOWER
LAYER AIR WITH THE THERMODYNAMIC SITUATION LITTLE CHANGED FROM THE
PAST FEW DAYS. THE LEADING EDGE OF ENHANCED 300MB FLOW AND AN
UPPER LEVEL LOW IS MOVING INTO SOUTHEASTERN TEXAS THIS MORNING AND
ON THE EAST SIDE OF THIS SYSTEM RESTS AIR THAT HAS MUCH RICHER AND
DEEPER MOISTURE. VERY WEAK SURFACE RIDGING IS SITUATED JUST OFF
THE CENTRAL TEXAS COAST AND WINDS ARE LIGHT TO CALM ACROSS MOST OF
THE AREA.

TODAY...THE UPPER AND MID LEVEL DISTURBANCE WILL CONTINUE TO WORK
IN THIS GENERAL DIRECTION. NAM/GFS/ECMWF PROJECTIONS KEEP THE BEST
MID LEVEL DCVA/LIFT TO THE NORTH OF THE CWA BUT THERE APPEARS TO
BE JUST ENOUGH RIPPLE IN THE WESTERN JET MAXIMUM TO CREATE A
SLIGHT UPTICK IN VORTICITY AND SOME MID LEVEL HEIGHT FALLS OVER
THE NORTHEASTERN QUARTER OF THE AREA. MOISTURE DEPTH/RICHNESS
STARTS OFF MARGINAL BUT IMPROVES OVER THE NORTHERN HALF OF THE CWA
BY LATE AFTERNOON. LIGHT WINDS WILL ALLOW A STRONG SEA BREEZE FRONT
TO SET UP AND ALSO HELP THE SEA BREEZE MODERATE HIGH TEMPERATURES A
BIT WORKING IN CONCERT WITH LIGHT NORTHEASTERLY SYNOPTIC FLOW.
CARRIED A 20 PCT CHANCE OF SEA BREEZE SHOWERS OVER MOST OF THE
VALLEY LOCATIONS AND THEN A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS FROM ABOUT RAYMONDVILLE NORTH WORKING INLAND ALONG
THE SEA BREEZE.

TONIGHT...LOWER LEVEL MOISTURE INCREASES MARKEDLY THROUGH THE
OVERNIGHT HOURS WITH 850-700MB RELATIVE HUMIDITY VALUES AVERAGING
AROUND 70 PCT ACROSS THE AREA. KEPT A SLIGHT CHANCE OF SHOWERS
BEFORE MIDNIGHT OVER ZAPATA COUNTY WHERE SOME UPSLOPE GENERATED
CONVECTION MAY LINGER AND THEN BEGAN TO INCREASE POPS FROM EAST TO
WEST AFTER MIDNIGHT AS THE CORE OF THE UPPER LOW PASSES OVERHEAD.
KEPT A 20 POP FROM 281 EASTWARD AND A 30 POP OVER THE WATER BUT
COULD SEE THAT BEING A LITTLE TOO CONSERVATIVE. ONLY REAL LIMITING
FACTOR IS A LACK OF LOW LEVEL CONVERGENCE AND HEATING IN THE
OVERNIGHT HOURS.

WEDNESDAY...DEEP AND RICH LOW LEVEL AND COLUMN MOISTURE WILL BE
IN PLACE AT THE START OF THE DAY WEDNESDAY AS THE UPPER LOW MOVES
JUST TO THE EAST OF THE AREA. FAIR MID LEVEL DIVERGENCE/DCVA WILL
BE PRESENT AND WEAK NORTHEASTERLY LOW LEVEL WINDS ARE EXPECTED
AMID A LITTLE MORE CLOUD COVER THAN WE HAVE SEEN LATELY. THIS
SHOULD SET THE TABLE FOR ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE AREA TO BE FURTHER ENHANCED BY THE
AFTERNOON SEA BREEZE FRONT. WENT WITH 20 TO 30 PCT MORNING
CHANCES...HIGHER CLOSE TO THE COAST...EXPANDING WESTWARD TO A PEAK
OF 40 PCT ALONG THE 77/281 CORRIDOR SHAVED JUST SLIGHTLY TO 30 TO
35 PCT AT THE RIVER. EXPECTING SCATTERED TO LOCALLY NUMEROUS
SHOWERS AND STORMS OVER THE OFFSHORE COASTAL WATERS AND JUST A
LITTLE LESS COVERAGE RIGHT AT PADRE ISLAND AND THE IMMEDIATE
NEAR SHORE ZONES OVER COOLER WATER. PREFER THE GFS/ECMWF DEPICTION
OF A 300/850MB LOW WITH INDIVIDUAL LOCAL ENHANCEMENTS TO LOW LEVEL
CONVERGENCE AND DAYTIME HEATING DRIVEN CONVECTION. THE NAM12 AND
HIRES WRF/NMM APPEARS TO OVERDO A CONVECTIVELY DRIVEN SURFACE
CIRCULATION...A KNOWN NAM12 ISSUE AND PAINTS TOO MUCH PRECIP OVER
THE AREA ALTHOUGH THE THERMODYNAMIC SETUP/MODEL SOUNDINGS LOOK
CLOSE TO THE GFS AND APPEAR FAIRLY REASONABLE THE SURFACE WINDS
ARE NOT. DISCOUNTED MET MOS AS A RESULT AS WELL BUT DID GO HIGHER
THAN ECS/MAV CONSENSUS GIVEN THE COMBINATION OF DEEP AND RICH
MOISTURE A STRONG SEA BREEZE REGIME...AND EXTRA MID LEVEL ASCENT.
/68-JGG/

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A 593 DAM HGT RIDGE WILL SNAKE LIKE THE LETTER S...ARCING ACROSS
NORTHWEST MEXICO AND THEN NORTHEAST ACROSS TEXAS AND FINALLY SOUTH
TOWARD FLORIDA. A SLIGHT WEAKNESS ALOFT WILL EMERGE OUT OF THE SHORT
TERM PERIOD OVER THE NORTHWEST GULF...RATHER CLOSE TO THE CWA...IF
NOT RIGHT OVER THE LOWER TEXAS COAST. CHANCE POPS WILL BE DEPICTED
OVER THE MARINE AREAS WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WITH
ONLY SLIGHTLY LESSER NUMBERS FADING TO THE WEST OVER THE CWA. THE
CONCURRENT APPROACH OF A MID LEVEL TROUGH MOVING OUT OF THE CENTRAL
ROCKIES WILL HELP MERGE THE WEAKNESS INTO THE BASE OF THE TROUGH
THURSDAY NIGHT INTO FRIDAY...WITH UNSETTLED WEATHER MOVING OVER THE
CWA. WHILE THE LIFTING OF THE MID LEVEL TROUGH OVER EAST TEXAS THIS
WEEKEND WILL NOT SPELL THE IMMEDIATE END OF POPS OVER THE MID AND
UPPER VALLEY...THEY WILL DECREASE THROUGH THE WEEKEND AS TROPICAL
MOISTURE BRINGS ENHANCED CONVECTION BACK TO THE MARINE AREAS. THIS
WILL PROVE TO BE A POWERFUL EFFECT...SINCE DESPITE A REESTABLISHMENT
OF THE MID LEVEL RIDGE ACROSS THE AREA...LOW END CHANCES OF SHOWERS
WILL REMAIN IN THE FAR LONG TERM SUNDAY AND MONDAY...ALBEIT SILENT.
THE ECMWF SOLUTION IS SLIGHTLY PREFERRED IN THIS CYCLE...CLUSTERING
WELL WITH THE GEM...WHILE THE GFS...THOUGH NOT TOO TERRIBLE...IS A
LITTLE SHALLOWER AND FASTER WITH THE PLAINS TROUGH AND DEVELOPS SOME
FEEDBACK ISSUES LATE IN THE RUN.

CHALLENGES FOR THIS FORECAST CENTERED AROUND POPS...WHICH MAY HAVE
BEEN SLIGHTLY INCREASED IN NUMBER BUT NOT CATEGORY. HIGH TEMPS WERE
SHAVED A DEGREE OR TWO LWR DUE TO ENHANCED UPPER CLOUDINESS EXPECTED
WITH THE OVERHEAD WEAKNESS...THOUGH THEY WILL REMAIN ABOVE NORMAL...
RANGING FROM THE MID 90S NEAR THE COAST TO A FEW DEGREES ABOVE THE
CENTURY MARK TO THE WEST. LOW TEMPERATURES WILL BE MAINLY IN THE MID
TO UPPER 70S. HEAT INDEX VALUES WILL FOCUS AROUND 105 DEGREES EACH
AFTERNOON...PLUS OR MINUS A COUPLE OF DEGREES. THE REMAINDER OF THE
INHERITED FORECAST CARRIED OVER QUITE WELL. LIGHT TO MDT SOUTHEAST
WINDS SHOULD PREVAIL THROUGH THE FORECAST. THE BEST SHOT OF RAIN FOR
THE CWA LOOKS LIKE IT WILL BE THURSDAY THROUGH FRIDAY AS THE WEAK
NESS MOVES OVERHEAD...SUPPORTED BY PWAT VALUES OF ABOVE TWO INCHES.
THIS COULD RESULT IN CONVECTION PRODUCING LOCALLY HEAVY RAINFALL...
AND THE DIFFERENCE BETWEEN A COUPLE OF TENTHS OF AN INCH OF RAIN AND
A HALF INCH OR MORE. STAY TUNED.

&&

.MARINE...
NOW THROUGH WEDNESDAY...LIGHT EAST TO NORTHEASTERLY PREVAILING WINDS
ARE FORECAST THROUGH WEDNESDAY. SEAS SHOULD REMAIN LOW. HOWEVER AN
INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY IS FORECAST STARTING
TONIGHT THROUGH WEDNESDAY WITH ACTIVITY LIKELY PEAKING DURING THE
DAY ON WEDNESDAY.

WEDNESDAY NIGHT THROUGH SATURDAY...MID LEVEL RIDGING ALONG THE
TROPIC OF CANCER WILL EXHIBIT A WEAKNESS OVER TEXAS INITIALLY...
WITH A VERY WEAK LOW OVER THE LOWER TEXAS COAST WEDNESDAY NIGHT.
THE FEATURE WILL HOWEVER...WHEN COUPLED WITH DEEPER MOISTURE...KEEP
A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE MARINE FORECAST THROUGH
FRIDAY. AT THAT POINT A MID LEVEL TROUGH AXIS WILL SWING ACROSS THE
NORTHERN HALF OF TEXAS...PICKING UP THE WEAKNESS AS IT GOES. RIDGING
WILL THEN FILL IN ACROSS THE AREA ONCE AGAIN BY THE END OF THE LONG
TERM. EXPECT A LIGHT TO MDT SOUTHEAST WIND...INCREASING SOMEWHAT
OVER THE WEEKEND AS LOWER PRESSURE DEVELOPS OVER THE PLAINS...WITH
LOW SEAS OF 2 TO 4 FEET BECOMING MDT...3 TO 5 OR 4 TO 6 FEET...OVER
THE WEEKEND. EXERCISE CAUTION CONDITIONS MAY BE POSSIBLE SATURDAY
INTO SUNDAY AS A RESULT.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  93  79  93  79 /  10  20  30  30
BROWNSVILLE          96  78  95  77 /  20  20  40  20
HARLINGEN            97  78  96  75 /  20  20  40  20
MCALLEN             100  79  99  78 /  10  20  30  20
RIO GRANDE CITY     101  78 100  79 /  10  10  30  20
SOUTH PADRE ISLAND   90  80  89  78 /  10  30  30  30

&&

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

$$

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