Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 242229 AAA
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
529 PM CDT FRI APR 24 2015

.DISCUSSION...CONTINUING TO MONITOR SVR WX THREAT CLOSELY THIS
EVENING. 22Z MODIFIED LAPS/RAP SOUNDINGS YIELD EXTREME INSTABILITY
WITH EVEN 100MB MLCAPE VALUES OF 3000 TO 3500 J/KG WITH SURFACE
DEWPOINTS IN THE UPPER 80S. DEEP LAYER SHEAR IS ALSO FAVORABLE
WITH LOW LAYER SHEAR THAT IS WEAK...BUT VEERS WITH HEIGHT. A
STURDY CAP REMAINS IN PLACE OVER THE AREA...REINFORCED BY STRONG
SOUTHWESTERLY WINDS ALOFT...BUT SHOULD BE THIN ENOUGH TO ALLOW FOR
CONVECTION IF SOME MID LEVEL ASCENT CAN GET GOING. AN AREA OF
FAVORABLE SPEED SHEAR IS APPROACHING FROM MEXICO AT THE SOUTH END
OF A BROADER JET MAX THAT IS FOCUSED OVER TEXAS...AND THAT MAY BE
SUFFICIENT TO INITIATE MORE CONVECTION IN THE IMMEDIATE LEE OF THE
SIERRA MADRE MOUNTAINS THIS AFTERNOON. HRRR/RAP/NAM SUPPORT
SCATTERED CELLS UPSCALING INTO AN MCS/LEWP OVER THE NEXT FEW HOURS
AND MOVING ACROSS THE AREA. THE END OF DAYTIME HEATING SHOULD
LIMIT THE SEVERE WEATHER RISK EASTWARD SOMEWHAT BUT IT IS
DIFFICULT TO ESTIMATE IF IT WILL BE QUICK ENOUGH TO EXCLUDE SOME
OR ALL OF THE RGV METRO AREAS IF CONVECTION INITIATES. IR/RADAR/LIGHTNING
TRENDS IN THE AREA ARE UP...BUT YET TO BE EXPLOSIVE. SPC SWOMCD
PROVIDES FURTHER DETAIL ON OUR NEAR TERM CONVECTIVE SITUATION.

UPDATED GRIDS TO INCLUDE SEVERE WORDING OVER A LARGER PORTION OF
THE AREA AND WILL BE BEEFING UP THE HWO SLIGHTLY IN THE NEXT FEW
MINUTES. /68-JGG/

&&

.PREV DISCUSSION... /ISSUED 255 PM CDT FRI APR 24 2015/

SHORT TERM /NOW THROUGH SATURDAY NIGHT/...H5 TROUGH PROGRESSING
NEWD THROUGH NM CURRENTLY...WITH STRONG MIDLEVEL FLOW WRAPPING
AROUND IT OVERHEAD. INSTABILITY ALOFT IS PEAKING THIS EVENING...
WITH DECENT CAPE VALUES STILL FORECAST ESPECIALLY OUT WEST.
MRNG BRO SOUNDING STILL SHOWED SIGNIFICANT CAPPING INVERSION...
BUT MORE REPRESENTATIVE INLAND SOUNDING FROM DRT SHOWED MINIMAL
CAP AND LOWER CONVECTIVE TEMPERATURE. GOOD CU BUBBLING NOTED TO
THE SOUTHWEST IN MAIN THREAT AREA...SO GOOD CHANCES FOR TSTMS
STILL REMAINS IN THE FORECAST FOR THIS EVENING...ESPECIALLY WEST
OF US281. MOST MODELS LOOK TO BE STARTING THE CONVECTION AS
CELLULAR BEFORE MORPHING INTO A BROKEN SQUALL LINE AS IT CROSSES
SOUTH TEXAS. MOST MODELS DO HAVE EVERYTHING THROUGH THE VALLEY BY
JUST AFTER MIDNIGHT...SO HAVE FOCUSED BIGGEST THREATS DURING THE
SUNSET TO MIDNIGHT. SATURDAY WILL BE THE BRIEF STABILIZATION
BEHIND THE OVERNIGHT THUNDERSTORMS...SO DAYTIME CONVECTION WILL BE
LOWER. TEMPERATURES WILL BE SIMILAR TO TODAY...WITH HIGHS A FEW
DEGREES EITHER SIDE OF 90 AND TD VALUES AROUND 75. THIS EQUATES TO
HEAT INDEX VALUES OF 100 TO 105 IN THE AFTERNOON. THUNDERSTORM
CHANCES SATURDAY WILL HINGE ON THE ABILITY OF THE DRYLINE TO PUSH
EASTWARD INTO THE WESTERN VALLEY IN THE EVENING. THIS SCENARIO
LOOKING MORE UNLIKELY WITH STEERING FLOW STILL FROM THE SW...SO
RAIN CHANCES REMAIN LOW SATURDAY INTO SATURDAY NIGHT.

LONG TERM /SUNDAY THROUGH THURSDAY/...A FLAT PRESSURE FIELD WITH
LIGHT SOUTH WINDS AND CONTINUED MOIST LOW LEVEL AIR WILL GREET
RESIDENTS SUNDAY MORNING. THERE MAY BE A FEW LINGERING SHOWERS FROM
SATURDAY NIGHT STILL MOVING INTO OR OVER THE MID AND UPPER VALLEY. A
MID LEVEL SHORT WAVE WILL BE OVER THE FOUR CORNERS AND MOVING EAST
TOWARD NORTH TEXAS. SUNDAY HIGH TEMPS WILL HIT THE LOWER 90S ACROSS
MUCH OF THE AREA EXCEPT FOR THE IMMEDIATE COAST. A PUSH OF DRIER AIR
WILL ENTER THE UPPER VALLEY BY AFTERNOON BUT WILL MOST LIKELY NOT
MAKE IT TO THE COAST...WHICH WILL REMAIN ENSCONCED WITH HIGHER DEW
POINT AIR. A FEW SHOWERS OR THUNDERSTORMS MAY POP UP ALONG THE
BOUNDARY OVER THE HILL COUNTRY AND EXTEND SOUTH THROUGH THE COASTAL
BEND AND RIO GRANDE PLAINS...AS CYCLOGENESIS OCCURS OVER NORTH
CENTRAL TEXAS...AND ESPECIALLY AS MID LEVEL ENERGY MAY BE PRESENT...
WITH CONVECTION TOUCHING THE NORTH AND NORTHEAST PARTS OF THE CWA
LATER ON SUNDAY. LOW TEMPS WILL BE IN THE 70S ONCE MORE SUNDAY NIGHT
AS SOME CONVECTION HANGS ON TO THE NORTH.

AT THIS POINT...MONDAY THROUGH MID WEEK...THE FORECAST BECOMES A
LITTLE MORE COMPLEX...WITH DETAILS MORE DIFFICULT TO SUSS OUT. AT
FIRST LOOK...THE LONG RANGE MODELS ARE NOT TOO DIFFERENT AND A
CONSENSUS SHOULD BE ACCEPTABLE. A WEAK INITIAL FRONT WILL PUSH INTO
THE RIO GRANDE PLAINS AND EVEN THE UPPER VALLEY EARLY MON MORNING.
HIGH TEMPS WILL BE MILDER...IN THE MID 80S. SOME CONVECTION MAY
CONTINUE ACROSS THE NORTH AND THEN NORTHEAST THROUGH THE DAY AS THE
FRONT PULLS TO THE NORTHEAST. SOME CLEARING AND DRIER AIR MONDAY
NIGHT WILL LEAD TO OVERNIGHT LOWS IN THE 60S AND 70S.

THE MAIN SECONDARY FRONT WILL ARRIVE TUESDAY MORNING...BUT THE
EXTREME LOWER VALLEY MAY NOT CLEAR COMPLETELY UNTIL LATER IN THE
DAY. NORTH WINDS WILL INCREASE TO MODERATE OR BREEZY DURING THE DAY
WITH HIGHS AROUND 80. DID LEAN MORE TOWARD THE ECMWF ON WINDS FOR
THE DAY AS IT WAS A LITTLE STRONGER THAN THE GFS AND DIDN`T WANT TO
COME UP SHORT AT THIS POINT. THE H5 PATTERN WILL SLOWLY VEER AS THE
UPPER TROUGH EJECT  OVER OKLAHOMA AND UPSTREAM RIDGING BEGINS TO
PLAY A BIGGER ROLE. NIGHT TIME LOWS WILL DECREASE FURTHER TO THE
UPPER 50S AND LOWER 60S.

HIGH PRESSURE WILL SETTLE OVER NORTH TEXAS ON WEDNESDAY WITH FINE
WEATHER CONDITIONS. MILDER TEMPS AND SUNNIER SKIES WILL PREVAIL
THROUGH THURSDAY.

MARINE...
NOW THROUGH SATURDAY NIGHT...WINDS HAVE VARIED CONSIDERABLY
ACROSS THE GULF WATERS...WITH 15G20KTS ALONG TEH COAST...WHILE
BEYOND 30NM WINDS ARE ONLY AROUND 5KTS. WINDS SHOULD EVEN OUT
OVERNIGHT...AROUND 10KTS ALL LOCATIONS. SEAS WILL REMAIN RIGHT
AROUND 3 FT TONIGHT...WITH A SLIGHT INCREASE TO NEAR 4 FEET LATE
TOMORROW. NOT EXPECTING ANY AADVISORIES THROUGH THE NEXT 36
HOURS. A SQUALL LINE IS EXPECTED TO REACH THE GULF WATERS LATER
TONIGHT... WHICH WOULD BRING DOWNPOURS...VARIABLY GUSTY WINDS AND
FREQUENT LIGHTNING AS IT PASSES.

SUNDAY THROUGH TUESDAY...A WEAK PRESSURE GRADIENT OVER THE NORTHWEST
GULF WILL RESULT IN LIGHT SOUTHEAST WINDS AND LOW SEAS INITIALLY.
WINDS WILL INCREASE TO MODERATE SUNDAY AS A SURFACE TROUGH DEVELOPS
NEAR THE BIG BEND...TIGHTENING THE GRADIENT. AS THE TROUGH SHIFTS
TOWARD THE COAST SUNDAY NIGHT...WINDS WILL AGAIN DECREASE. LIGHT
WINDS WILL BECOME VARIABLE AS HIGH PRESSURE APPROACHES FROM UPSTREAM
MONDAY AND MONDAY NIGHT. NORTH WINDS WILL INCREASE AFTER A FRONTAL
PASSAGE TUESDAY MORNING...BECOMING MODERATE AND THEN STRONG BY TUE
AFTERNOON...WHEN SMALL CRAFT ADVISORY CONDITIONS WILL DEVELOP. A FEW
SHOWERS WILL BE POSSIBLE TUE DURING THE DAY. WAVE HEIGHTS WILL THEN
BUILD TOWARD SEVEN FT TUESDAY NIGHT. CONDITIONS WILL SLOWLY IMPROVE
ON WEDNESDAY AS HIGH PRESSURE BEHIND THE FRONT SPREADS OVER THE
AREA.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  77  86  77  84 /  50  20  10  10
BROWNSVILLE          78  88  77  88 /  50  20  10  10
HARLINGEN            77  90  77  91 /  50  20  10  10
MCALLEN              76  93  77  95 /  50  20  10  10
RIO GRANDE CITY      75  92  76  97 /  60  20  10  10
SOUTH PADRE ISLAND   77  84  77  79 /  40  20  10  10

&&

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

$$

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